This material is based on work supported by the
National Science Foundation under Grant Number 1104095
*Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.

Traditional “shop” classes have been designed and taught to teach students the basic competencies and skills needed to gain entry-level employment. They have focused on teaching a concept and then having students practice the skills related to that concept, and when the skills have been met to the satisfaction of the instructor, students would use those skills to “make a project”.
When the project is completed and graded, the student moved on to another or skill, and the cycle repeated itself, in many cases until the school year was completed. In advanced courses, the process was the same, with the project becoming more complex by adding additional steps, positions, or changing the materials. In this instructional model, the main goal was the learning and mastering of skills. Consequently, the students that signed up for the class were predominantly those that were preparing themselves for a limited spectrum of career opportunities.
Arc Welding is a process that is part of a larger manufacturing model referred to as “The Design
Process”
Today, objects are being manufactured in a different way. The design does not necessarily begin by identifying the available material. Product function and behavior are incorporated into the design.

Anyone that wants to be a maker of things will have to understand much more about the materials they are using, including their structure and how they react to forces during the manufacturing process as well as the ultimate use of the part. This necessitates an understanding of the design and manufacturing of a part and, more importantly, how the final product will function and behave based on mathematical, physical, and chemical data.

Subunit 1
Subunit 2
Subunit 3
Subunit 4
The Process of Arc Welding
What is Arc Welding?
Why is Welding Important?
Why Learn to Weld?
What are the Responsibilities of a Welder?
Arc Welding Safety
Knowledge – Content
Attitude – Reactions
Skills – Performance
Work Habits – Daily Functions
Welding Safety
Material Safety Data Sheets
General Safe Practices
Fumes and Gases
Electric Shock
Arc Rays
Fire and Explosion Hazards
Noise
Hot Objects
Welding Processes
Basic Welding Circuit

Arc Shielding
Nature of the Arc
GMAW (Gas Metal Arc Welding)
MIG Welding Aluminum
SMAW (Shielded Metal Arc Welding)
A BASIC GUIDE OF ARC WELDING ELECTRODES
Joining Aluminum with TIG/GTAW
Welding Symbols
Subunit 5
Subunit 6
Subunit 7
Subunit 8
The Science of Welding
Electricity
Energy Transfers
Changes of State
Chemical Reactions
Properties of Metals
Mathematics in Welding
Welding Certification
Careers in Welding





Arc welding is a type of welding that uses a welding power supply to create an electric arc between an electrode and the base material to melt the metals at the welding point. They can use either direct (DC) or alternating (AC) current, and consumable or non-consumable electrodes. The welding region is usually protected by some type of shielding gas, vapor, and/or slag.
A welder creates an electric arc that melts the metal and filler rod to create a pool of molten metal that hardens to fuse the two pieces of metal together.
Steel Pipe – Tack Welded Root Pass or “Stringer
Bead”
Final weld after several beads are made
Many things around us are welded …
 Pipelines that bring fresh water
 Towers that carry electricity to houses
 Cars and buses that take people where they need to go

Welding is so HOT …. it’s COOL!
 Welding can help build a successful career so you can get the
things you want in life
 Skilled welders are in demand – people use things that are welded
every day!
 Welding can be fun and safe
 It is challenging and high-tech

Areas relating to people employed in the Welding Industry include:
 Arc Welding Safety
 Knowledge – Content
 Attitude – Reactions
 Skills – Performance
 Work Habits – Daily Functions
Knowledge and Content
Welding can teach you about….
 Science when applying metallurgy, chemistry, electricity, etc.
 Math when calculating angles, joint design, and weld size
 English when communicating and interpreting drawings, codes, and
procedures
 Technical areas when performing the actual welding applications
How much science and math went into the development of this bike?

Arc Welding Safety
A welder MUST always follow safe work practices:
 Students should read and understand the following before welding:
 Warning Labels
 Material Safety Data Sheets (MSDS)
 Students should also be familiar with the following information
 “Safety in Welding, Cutting, and Allied Processes” (ANSI Z49.1)
 Lincoln Electric’s ‘Arc Welding Safety’ (E205)
Attitude
The best welders demonstrate a can-do attitude when performing welding processes. This means being able to…
 Work as a team member
 Communicate ideas to others
 Listen to opinions of others
 Promote a positive attitude
 Provide solutions to problems
 Take pride in workmanship
Skills and Performance
A welder must demonstrate technical skills when performing welding processes. A welder must know how to:
 Use hand tools and materials, to operate equipment in a safe,
accurate, and consistent manner
 Acquire and evaluate information needed for problem solving
 Complete quality work
 Maintain equipment
There is no room for poor workmanship in NASCAR

Work Habits and Daily Functions
A welder must practice good working habits when performing welding processes. This means being able to …
 Follow detailed verbal and written instructions
 Maintain workspace, equipment, and tool cleanliness
 Correctly fill out, maintain and submit time cards, work assignment
cards, and other records as required
 Follow safe working practices

Because of the chemical reactions, energy transfers, and electricity involved in welding proper safety must be addressed.
Welding can be safe when sufficient measures are taken to protect yourself and others from potential hazards.
Students should read and understand the following before welding:
 Warning Labels
 Material Safety Data Sheets (MSDS).
Students should also be familiar with the following information
 ‘Safety in Welding, Cutting, and Allied Processes’ (ANSI Z49.1 from the American National Standards Institute)
 Arc Welding Safety
Understand and follow all warning labels found:
 On welding equipment
 With all consumable packaging
 Within instruction manuals

Material Safety Data Sheets
Material Safety Data Sheets (MSDS) are:
 Required by law and OSHA
 Created by the manufacturer of a product per OSHA guidelines
 Designed to inform users
 Shipped with every box of consumable product
 Available free online access at: http://www.lincolnelectric.com/enus/support/msds/Pages/msds.aspx
MSDS outlines a product’s:
 Identity and composition
 Potential hazards
 Safe use
 Handling information
 Manufacturer contact information
Protect yourself and others from potential hazards including:
 Fumes and Gases
 Electric Shock
 Arc Rays
 Fire and Explosion Hazards
 Noise
 Hot objects

Become trained and read the instructions before working on the machine or welding or cutting.
Read Material Safety Data Sheets (MSDSs) for metals, consumables, and coatings.
Wear approved safety glasses with side shields under your welding helmet or face shield and at all times in the work area.
Read and follow all labels and the Owner’s Manual carefully before installing, operating, or servicing unit. Read the safety information at the beginning of the manual and in each section.
Wear a safety harness if working above floor level.
Keep children away from all equipment and processes.
Do not install or place machine on or over combustible surfaces.
Use only genuine replacement parts from the manufacturer.
Perform maintenance and service according to the Owner’s Manuals, industry standards, and national, state, and local codes.

Breathing welding fumes can be hazardous to your health.
Keep your head out of the fumes. Do not breathe the fumes. Use enough ventilation, exhaust at the arc, or both, to keep fumes and gases from your breathing zone and the general area.
Read Material Safety Data Sheets (MSDSs) for metals, consumables, and coatings.
Use enough forced ventilation or local exhaust (forced suction) at the arc to remove the fumes from your breathing area
.
Use a ventilating fan to remove fumes from the breathing zone and welding area.
If adequacy of ventilation or exhaust is uncertain, have your exposure measured and compared to the Threshold Limit Values (TLV) in the Material Safety Data
Sheet (MSDS).
See product labeling and MSDS for ventilation and respirator requirements.

Electric shock from welding electrode or wiring can kill.
Wear dry, hole-free insulating gloves and body protection. Do not touch electrode with bare hand. Do not wear wet or damaged gloves. Protect yourself from electric shock by insulating yourself from work and ground. Use non-flammable, dry insulating material if possible, or use dry rubber mats, dry wood or plywood, or other dry insulating material big enough to cover your full area of contact with the work or ground, and watch for fire.
Do not touch live electrical parts. Disconnect input plug or power before working on machine.
Do not make input connections if color blind.
Frequently inspect input power cord for damage or bare wiring — repair or replace cord immediately if damaged. Keep cords dry, free of oil and grease, and protected from hot metal and sparks.
Be sure input ground wire is properly connected to a ground terminal in disconnect box or receptacle.
Properly install and ground this equipment according to its Owner’s Manual and national, state, and local codes.
Do not use AC weld output in damp, wet, or confined spaces, or if there is a danger of falling.
Use AC output ONLY if required for the welding process.
If AC output is required, use remote output control if present on unit.
Electric Magnetic Fields (EMF) Information
Electric current flowing through any conductor causes localized electric and magnetic fields (EMF). Welding current creates an EMF field around the welding circuit and welding equipment.
EMF fields may interfere with some medical implants, e.g. pacemakers. Protective measures for persons wearing medical implants have to be taken. For example, access restrictions for passers−by or individual risk assessment for welders. All

welders should use the following procedures in order to minimize exposure to EMF fields from the welding circuit:
1. Keep cables close together by twisting or taping them, or using a cable cover.
2. Do not place your body between welding cables. Arrange cables to one side and away from the operator.
3. Do not coil or drape cables around your body.
4. Keep head and trunk as far away from the equipment in the welding circuit as possible.
5. Connect work clamp to workpiece as close to the weld as possible.
6. Do not work next to, sit or lean on the welding power source.
7. Do not weld whilst carrying the welding power source or wire feeder.
About Implanted Medical Devices:
Implanted Medical Device wearers should consult their doctor and the device manufacturer before performing or going near arc welding, spot welding, gouging, plasma arc cutting, or induction heating operations. If cleared by your doctor, then following the above procedures is recommended.

Arc rays can burn eyes and skin.
Use welding helmet or face shield with correct shade of filter (see chart below to choose the correct shade).
Wear welders cap and safety glasses with side shields. Use ear protection when cutting out of position or in confined spaces.
Button shirt collar.
Wear complete body protection. Wear oil-free protective clothing such as leather gloves, heavy shirt, cuffless pants, and high boots.

Shielded metal arc welding (SMAW)
Gas tungsten arc welding (GTAW)
Air carbon arc cutting
(CAC−A)
Plasma arc welding
(PAW)
Plasma arc cutting
(PAC)
Torch brazing (TB)
Torch soldering (TS)
Carbon arc welding
(CAW)
Operation/Process Electrode Size
Gas metal arc welding
(GMAW) and flux cored arc welding (FCAW)
in. (mm)
Less than 3/32
(2.5)
3/32−5/32
(2.5−4)
5/32−1/4 (4−6.4)
More than 1/4
(6.4)
(Light)
(Heavy)
Arc Current
(Amperes)
Less than 60
60−160
160−250
250−550
Less than 60
60−160
160−250
250−550
Less than 50
50−150
150−500
Less than 500
500−1000
Less than 20
20−100
100−400
400−800
Less than 20
20−40
40−60
60−80
80−300
300−400
400−800
—
—
—
Minimum
Protective
Shade
7
8
10
11
7
10
10
10
8
8
10
10
11
68
10
11
4
5
6
8
8
9
10
—
—
—
Suggested*
Shade No.
(Comfort)
—
10
12
14
—
11
12
14
Oxy-fuel gas welding
(OFW)
Light
Medium
Heavy
Oxygen Cutting (OC)
Light
Medium
Heavy
Plate thickness in.
Under 1/8
1/8 to 1/2
Over 1/2 mm
Under 3.2
3.2 to 12.7
Over 12.7
Under 1
1 to 6
Over 6
Under 25
25 to 150
Over 150
3 or 4
4 or 5
5 or 6
4 or 5
5 or 6
6 or 8
* As a rule of thumb, start with a shade that is too dark to see the weld or cut zone. Then go to a lighter shade which gives sufficient view of the weld or cut zone without going below the minimum. In oxy-fuel gas welding, cutting, or brazing where the torch produces a high yellow light, it is desirable to use a filter lens that absorbs the yellow or sodium line in the visible light of the (spectrum) operation.
Guide adapted from ANSI Z49.1, 2005.
Low Current Plasma arc cutting data (0−80 Amperes) supplied by Miller Electric Mfg. Co.
10
12
14
12
14
6 to 8
10
12
14
4
5
6
8
9
12
14
3 or 4
2
14

Welding and cutting can cause fire or explosion.
Do not weld near flammable material or where the atmosphere may contain flammable dust, gas, or liquid vapors (such as gasoline). Move flammables at least 35 feet (11 meters) away or protect them with flame-proof covers (see
NFPA 51B listed in Section 7
).
Cutting sparks can cause fires. Have a fire extinguisher nearby, and have a trained fire watch ready to use it. After completion of work, inspect area to ensure it is free of sparks, glowing embers, and flames.
Do not cut on drums, tanks, or any closed containers unless a qualified person has tested it and declared it or prepared it to be safe (see AWS F4.1 listed in
Section 7).
Shielding gas cylinders contain gas under high pressure. If damaged, a cylinder can explode.
Since gas cylinders are normally part of the welding process and may be part of the cutting process, be sure to treat them carefully.
Protect compressed gas cylinders from excessive heat, mechanical shocks, slag, open flames, sparks, and arcs.
Install cylinders in an upright position by securing them to a stationary support or cylinder rack to prevent falling or tipping.
Keep protective cap in place over valve except when cylinder is in use or connected for use.
Cylinders can be heavy — use lifting device and proper methods to prevent back injury.
Read and follow instructions on compressed gas cylinders, associated equipment, and CGA publication P-1 listed in Safety Standards (see Section 7).

Ear Protection is vital while welding!
Exposure to loud noise can permanently damage welders’ hearing. Noise also causes stress and increased blood pressure, and may contribute to heart disease.
Working in a noisy environment for long periods of time can make workers tired, nervous, and irritable.
Hot parts can burn.
Do not touch hot welded or cut parts with bare hand. If handling is needed, use proper tools and/or wear heavy, insulated welding gloves to prevent burns.
Mark all hot materials with the word “HOT” and the date and time the material was hot. Metals should be marked with soapstone or chalk.
Allow cooling period before handling parts or working on equipment.

The following information is available through the Lincoln Electric Company
Arc welding is one of several fusion processes for joining metals. By applying intense heat, metal at the joint between two parts is melted and caused to intermix - directly, or more commonly, with an intermediate molten filler metal.
Upon cooling and solidification, a metallurgical bond is created. Since the joining is an intermixture of metals, the final weldment potentially has the same strength properties as the metal of the parts. This is in sharp contrast to non-fusion processes of joining (i.e. soldering, brazing etc.) in which the mechanical and physical properties of the base materials cannot be duplicated at the joint.
In arc welding, the intense heat needed to melt metal is produced by an electric arc.
The arc is formed between the actual work and an electrode (stick or wire) that is manually or mechanically guided along the joint. The electrode can either be a rod with the purpose of simply carrying the current between the tip and the work. Or, it may be a specially prepared rod or wire that not only conducts the current but also melts and
Fig. 1 The basic arc-welding circuit supplies filler metal to the joint. Most welding in the manufacture of steel products uses the second type of electrode.
Basic Welding Circuit
The basic arc-welding circuit is illustrated in Fig. 1. An AC or DC power source, fitted with whatever controls may be needed, is connected by a work cable to the workpiece and by a "hot" cable to an electrode holder of some type, which makes an electrical contact with the welding electrode.
An arc is created across the gap when the energized circuit and the electrode tip touches the workpiece and is withdrawn, yet still with in close contact.
The arc produces a temperature of about 6500ºF at the tip. This heat melts both the base metal and the electrode, producing a pool of molten metal sometimes

called a "crater." The crater solidifies behind the electrode as it is moved along the joint. The result is a fusion bond.
Arc Shielding
However, joining metals requires more than moving an electrode along a joint.
Metals at high temperatures tend to react chemically with elements in the air - oxygen and nitrogen. When metal in the molten pool comes into contact with air, oxides and nitrides form which destroy the strength and toughness of the weld joint. Therefore, many arc-welding processes provide some means of covering the arc and the molten pool with a protective shield of gas, vapor, or slag. This is called arc shielding. This shielding prevents or minimizes contact of the molten metal with air. Shielding also may improve the weld. An example is a granular flux, which actually adds deoxidizers to the weld.
Figure 2 illustrates the shielding of the welding arc and molten pool with a Stick electrode. The extruded covering on the filler metal rod, provides a shielding gas at the point of contact while the slag protects the fresh weld from the air.
The arc itself is a very complex phenomenon. Indepth understanding of the physics of the arc is of little value to the welder, but some knowledge of its general characteristics can be useful.
Nature of the Arc
Fig. 2 This shows how the coating on a coated (stick) electrode provides a gaseous shield around the arc and a
An arc is an electric current flowing between two electrodes through an ionized column of gas. A slag covering on the hot weld deposit. negatively charged cathode and a positively charged anode create the intense heat of the welding arc. Negative and positive ions are bounced off of each other in the plasma column at an accelerated rate.
In welding, the arc not only provides the heat needed to melt the electrode and the base metal, but under certain conditions must also supply the means to transport the molten metal from the tip of the electrode to the work. Several mechanisms for metal transfer exist. Two (of many) examples include:
1.
Surface Tension Transfer - a drop of molten metal touches the molten metal pool and is drawn into it by surface tension.

2.
Spray Arc - the drop is ejected from the molten metal at the electrode tip by an electric pinch propelling it to the molten pool. (great for overhead welding!)
If an electrode is consumable, the tip melts under the heat of the arc and molten droplets are detached and transported to the work through the arc column. Any arc welding system in which the electrode is melted off to become part of the weld is described as metal-arc. In carbon or tungsten (TIG) welding there are no molten droplets to be forced across the gap and onto the work. Filler metal is melted into the joint from a separate rod or wire.
More of the heat developed by the arc is transferred to the weld pool with consumable electrodes. This produces higher thermal efficiencies and narrower heat-affected zones.
Since there must be an ionized path to conduct electricity across a gap, the mere switching on of the welding current with an electrically cold electrode posed over it will not start the arc. The arc must be ignited. This is caused by either supplying an initial voltage high enough to cause a discharge or by touching the electrode to the work and then withdrawing it as the contact area becomes heated.
Arc welding may be done with direct current (DC) with the electrode either positive or negative or alternating current (AC). The choice of current and polarity depends on the process, the type of electrode, the arc atmosphere, and the metal being welded.
Arc Welding Processes
GMAW (Gas Metal Arc Welding) is also referred to as “MIG” welding.
“MIG” welding is an abbreviation for Metal Inert Gas Welding. It is a process developed in the 1940’s, and is considered semi-automated. This means that the welder still requires skill, but that the MIG welding machine will continuously keep filling the joint being welded.

MIG welders consist of a handle with a trigger controlling a wire feed, feeding the wire from a spool to the weld joint. The wire is similar to an endless bicycle brake cable. The wire runs through the liner, which also has a gas feeding through the same cable to the point of arc, which protects the weld from the air.
How MIG Welding Works
MIG weld welding requires three things, electricity to produce heat, an electrode to fill the joint, and shielding gas to protect the weld from the air. MIG welding is done using a very small electrode that is fed continuously, while the operator controls the amount of weld being done. In some cases when a robot takes over this process, it becomes automatic welding.
MIG Voltage Type and Welding Polarity
MIG welding unlike most other welding processes has one standard voltage type and polarity type. The voltage used is D/C direct current, much like the current in a car battery. Direct current flows in one direction, from the negative (-) to the positive (+).
The polarity used is also standard and that is D/C electrode (+) positive. This means that the handle is the positive side of the circuit, or it may be said, the electricity flows from the metal in to the welding handle.
The power source used for MIG welding is called a “constant voltage power supply”. In MIG welding the voltage is what is controlled and adjusted. When comparing MIG welding to Arc or TIG welding, MIG welding machines use voltage settings to set the machine. TIG and Arc welding machines use amperage to set the machine or a “constant amperage power supply”.
MIG Electrode Types
When choosing the proper MIG wire or electrode you need to match the type of wire to the type of metal being welded. Some other considerations are the type of transfer, position to be welded, and resistance to abrasion. Most of the times when working as a welder the welding engineers specify the weld size and electrode type to be used.
The most common wire used for welding carbon steel is ER 70S-6. In some cases you can weld two different metals together. An example of this is welding 304 stainless steel to A36 carbon steel using an electrode made of 309 stainless steel
“ER 309L”.

Typical MIG welding electrodes are a solid wire ranging from a thickness of .023 to .045. Some are much thicker for heavy industrial applications. The most common sizes are:




.023
.030
.035
.045
The manufactures of these electrodes use a standard code to identify the type of electrode. For example the code on the label ER 70S-6 represents the following:




ER- An electrode or filler rod that is used in either a wire feed or TIG welding.
70- A minimum of 70,000 pounds of tensile strength per square inch of weld.
S -Solid wire.
6- The amount of deoxidizing agent and cleansing agent on the electrode.
Common MIG Welding Gasses
Gas for MIG welding is what makes MIG welding possible. The name informs us of this; “Metal Inert Gas welding”. The gasses used are what shield the weld from oxygen in the air. When Carbon Dioxide or Oxygen is added to the mixture, MIG welding is not technically MIG welding anymore. This is due to the fact that both
Carbon Dioxide and Oxygen are not inert gasses. The process then becomes
GMAW or Gas Metal Arc Welding.

The type of gas uses also determines:



How deep the weld penetrates the metal welded
The characteristics of the welding arc
The mechanical properties of the weld.
When choosing the type of gas to be used, it is best to seek input from a welding supply store. Suppliers will recommend the proper gas to match the welding wire to be used. Or, one may utilize the welding wire manufacturer's recommendation.
Typically, the manufacturer will provide a few choices ranging from the best choice, to something that will provide the minimum acceptable results. The final choice in the type of gas, is based on cost.
The four most common gasses used are;




Argon
CO2 / Carbon Dioxide
O2 / Oxygen
Helium (the least common)
Most of the times these gasses are used in a mixture form, typically consisting of carbon dioxide, and Argon or Oxygen. Oxygen is what causes most weld defects, however, in small percentages, mixed with other gasses, it improves the arc characteristics. Argon and Carbon Dioxide can be used by themselves. In some case there is tri-mix shielding gas containing Argon, Carbon dioxide, and Helium, or, Argon, Carbon dioxide, and Oxygen. The more common mixtures and gasses are. o o o o
C2 or 2% Carbon Dioxide and 98% Argon
C25 or 25% Carbon Dioxide and 95%
Argon
100% Carbon Dioxide
100% Argon

Some basic guidelines for choosing the proper gas are as follows:
Welding of carbon steel can be done with Carbon Dioxide alone and it produces the deepest penetration, the most smoke and the roughest weld. A mixture of gasses ranging from 2% to 25% Carbon Dioxide and the rest Argon can be used.
However, a higher percent of Argon will result in a smoother, better looking weld, and improves the arc characteristics.
Welding of stainless steel is typically done with C2 or 2% Carbon Dioxide and
98% Argon. In some cases there is tri-mix shielding gas containing 90% Helium,
7.5% Argon, and 2.5%Carbon dioxide.
Welding of aluminum is typically done with Argon alone, with one exception. If the aluminum being welded is thicker than ½ of an inch there may be Helium added to the mix.
Argon gas by itself works well on most exotic metals like:



Copper
Copper Alloys
Magnesium



Nickel
Nickel Alloys
Titanium
MIG welding various Metals
MIG welding is a welding process that can weld almost any metal. It may not always be the best choice for weld quality but MIG welding is a fast, cost efficient, and produces results that are more than acceptable for most manufacturing and fabrication needs! Not everybody is building a space station. The three most common metals welded with a MIG welder are:



Carbon steel.
Stainless steel.
Aluminum, with a special feeder because aluminum wire is very soft.
MIG Welding Carbon Steel
Carbon steel welds are almost flawlessly done with a MIG welder. There are very few problems, beside the downside of the design of a MIG welding machine. The

wire stiffness is just right to pass through the liner from the machine with minimal friction to cause problems and has enough stiffness to be feed without coiling up.
Depending on how much voltage the MIG welding machine is running at, the weld can be set to one of three transfer types, short circuit, globular, or spray.
MIG Welding Stainless Steel
Stainless steel MIG welding does not require any special equipment. In the case of welding stainless steel, the biggest problem comes from the cord or liner of the welder. It is very important when welding stainless steel is to keep the cord as
straight as possible. Otherwise, the wire feed that feeds the weld joint will have too much friction due to stainless steel being stiffer then carbon steel. Think of trying to shove a wire hanger through a bent garden hose. Chances are if the hose is straight you can easily put it through. If the hose is bent, you will have difficulty. That is how stainless steel wire is in the liner of the welding cable. What happens is the wire is so stiff in the liner that it causes so much friction that the wire stops the feeding wheel from feeding the joint (literally spinning its wheels).
The result is a fused MIG tip. That is when the wire stops or slows down to the point that the arc melts the wire up to the MIG tip and it welds itself to it. The other major problem is again the liner. If you bend the cord to much the friction stops the wire and the wheels that are feeding the MIG gun push the wire so hard that the wire having no place to go spooling up like a birds nest before it gets pushed into the liner.
MIG welding stainless steel is mostly done in a spray transfer or globular borderline spray. The reason behind this is that stainless steel does not do to well with short circuit transfers. The short circuit transfer and globular have the wire actually hitting the metal, splashing and splattering, and that also causes friction on the liner.

Welding stainless steel requires a high percentage of Argon used in the gas mixture. If it is a critical joint that will be x-rayed, any disturbance in the transfer will cause flaws. Spray is a smooth crackle-free transfer that has no metal being violently transferred. Spray transfer also keeps spatter to the bare minimum.
With stainless steel spatter is extremely difficult to clean. The pictures below on the left is a weld were done using ER 308L wire, C2 gas, with a globular borderline spray transfer.
MIG Welding Aluminum
Aluminum MIG welding usually requires a double feed, referred to as, (a push and pull method). That is a spool of wire is pushed through the MIG handle and the handle itself has a pulley that pulls the wire. Welding aluminum is not very common for MIG welding. It is typically done when high production is needed.
Another type of feed that can be used is a spool feed MIG gun. It has a small spool of wire on the MIG gun itself. This type of feed is the most trouble free of the feeds when it comes to MIG welding Aluminum!
MIG welding aluminum is typically done with pure Argon gas using a spray transfer. On thicker joints the transfer has a fast crackle and the weld is very quick. Welding thicker aluminum out of position works well but the weld appearance is never perfect! The aluminum weld in the picture is a single pass and took about 10 seconds to do on a 3/8" bevel. It’s all about moving quickly and keeping the puddle from rolling over.

MIG Welding Cons MIG Welding Pros
MIG welding has some distinct advantages!






MIG welding does have a few problems!

Welds are clean with very little smoke.

Production is cheap and fast.

Long welds with less restarts.

The skill level needed compared to other welding processes make it easy,

Welding wire runs continuously with less down time to replace electrodes.
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Excellent for spot and tack welds.
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The welder cannot go too far from the MIG machine.
Wind is a major factor outdoors.
Always need a bottle of gas.
The cable that transfers the spool of wire through it needs to be well maintained.
Contact tips getting spatter on them, then they seize up.
Needs a clean joint.
Finally there are many parts to a
MIG welder that need to work properly and it can get very annoying sometimes trying to figure out what is wrong.
Joint Setup and Preparation
With MIG welding it is very critical that the weld area is clean. MIG welding will not be successful with a dirty joint. Unlike some stick welding / SMAW rods that can burn through rust, MIG welding has a lot of difficulties welding dirtier metals.
It also does not have slag to protect the weld when the gas is gone. When MIG welding make sure you have a clean joint by removing any foreign substance.
With MIG welding a slight bit of dirt or rust is OK but anything more is asking for trouble. MIG welding painted or coated metals does not work well at all.

MIG Welding Machine Set-Up
Set-up of a MIG welder depending on what the type of wire transfer type is chosen. There are three main ingredients, first the voltage settings, then the wire speed, and finally the type of gas. Almost any type of gas will allow you to spray transfer, but the gas type is what changes the quality of the weld!
First set the gas to flow between 25 to 35 CFH. This is only a guideline! If you are welding indoors you may need less and if you are welding in a place that may have a draft coming through you may need more.
When setting a MIG welding machine there are two major settings and they are voltage and wire speed! Before setting up your MIG machine there should be some instructions on the machine itself for the proper voltage on the inside of the panel where the wire goes. Most of MIG welding is done with the same wire diameter but what changes is the amount of heat the welder requires to heat that metal to get proper penetration of the weld.
The settings on a MIG welding machine are best set within the voltage range of what the welding machines charts have suggested for that metal thickness. The transfer type mostly changes with the wire speed and gas type. When setting your wire speed to the transfer type you need or like to use it is always best to listen to the sound of the weld. Short circuit has a fast crackle sound; globular have a few crackles or pops a second and true spray transfer has just the hum of the welder or hissing sound. Once you learn the sound, you will know the settings.
MIG welding just like any other process it also relies on two major factors joint preparation and machine set up. One of the secrets journeyman welders have to make solid welds, is based on how well they set up their welding machine!
MIG Welding Techniques
With MIG Welding just like all other welding processes it is the same techniques.
Whip, circles, or weave for most joints. Even though MIG welding is very easy to do, if you do not have basic welding skills the machine set-up can very aggravating.
There are two ways to MIG weld. The first and the most common is to push the
MIG gun toward the direction of the weld, this is called forehand method.
Forehand welding produces shallow penetration with a flat wide smooth surface.
The second is backhand method where you drag the MIG gun like a Stick welder.
This produces a deep penetration weld that is narrow and is high in the center.

To begin welding the wire stick out should be about 3/4 of an inch. Less is OK but a much longer wire stick out won’t allow the shielding gas to do its job properly.
Some general guidelines for MIG welding techniques are as follows and are only guidelines:
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Flat welding is the easiest. Typically the MIG gun will be pushed, the angle of the MIG gun can be pointing straight down to leaning toward the direction of the weld up to 35 degrees.
Horizontal welding is a little harder. The MIG gun should be pointing upward between 35 to 45 degrees and tilting about 15 to 35 degrees toward the direction of the weld.
Vertical down is also pretty easy. You start on the top and work your way down. The MIG gun needs to be tilted up between 35 to 45 degrees. There is a trick to welding vertical down. You need to stay ahead of the puddle and keep the electrode moving from side to side. Otherwise the weld will not penetrate properly.
Vertical up is a bit harder. The MIG gun handle should be between 35 to 45 degrees. When welding vertical up you need to build a shelf of weld to work upward on. The vertical up weld in MIG is typically very convex. To help with welding vertical up it always a good idea to grind a small grove where you will be welding.
Overhead MIG welding requires the MIG gun tilted 5 to 35 degrees toward the direction of the weld.
The general guidelines for MIG welding are whip when welding thin metal or making the first pass in a joint, circles for a both thicker materials and wider welds. Weave for vertical up and down.
Trouble Shooting MIG Welding
Porosity in the weld:
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Check the gas to make sure there is enough left.
Check the gas flow rate. First raise the flow rate and if that does not work try lowering it. Sometimes too much gas flow causes turbulence by pulling in air to the mix.
Check the cup of the MIG gun for excessive splatter.

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Check your stick out. It’s common for people who stick weld to allow too much stick out when MIG welding.
Check the MIG gun for leaks. Typically the MIG gun nozzle may be loose or worn out. Or the gas diffuser may be loose or have spatter blocking the gas flow.
Change your travel angle. Too much lean toward the direction of the weld can cause air getting pulled into the weld area.
Check the joint for dirt, water, or any contaminants that should not be there.
Finally check all of the connections in the gas line for leaks.
Wire Feed Jams or Uneven Wire Speed:
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Check the MIG tip.
Check the rollers for proper tension settings.
Check the rollers for a birds nest.
Check the wire spool to make sure there is wire left and nothing is catching on it. It’s common for the wire to jam on itself.
Make sure you are not bending or twisting the liner too much while welding.
If not you may need to replace the liner.
Check the rollers to make sure they are the right size for the wire being used.
Check the wire connector between the cabal and the wire feeder for a solid connection.
MIG Welding Summary
With MIG Welding just like all other welding processes it is the same techniques.
Whip, circles, or weave for most joints.. Even though MIG welding is very easy to do, if you do not have basic welding skills the machine set-up can very aggravating.
Carbon steel welds best with MIG because the stiffness of the wire is perfect for the liner. MIG welding is the best choice for spot welding and tack welds. When welding soft metals like aluminum there is special equipment that is needed to be added to the MIG welder. Harder metals like stainless steel work fine on any MIG welding machine as long as you pay attention to keeping the cord straight. Almost

any metal can be MIG welded as long as the type of wire and gas are properly chosen.
Most welding techniques that are used for other welding processes still apply here. The whip of a weld, circles, and weaves for wider welds. What changes here is typically the forehand method is used but sometimes the backhand method may be needed. To be an excellent MIG welder the main thing is to master machine set-up. This is the biggest factor when it comes to MIG welding and the one thing many people overlook.
SMAW (Shielded Metal Arc Welding)
Shielded Metal Arc Welding (SMAW) or Stick welding is a process which melts and joins metals by heating them with an arc between a coated metal electrode and the workpiece. The electrode outer coating, called flux, assists in creating the arc and provides the shielding gas and slag covering to protect the weld from contamination. The electrode core provides most of the weld filler metal. When the electrode is moved along the workpiece at the correct speed the metal deposits in a uniform layer called a bead.
The Stick welding power source provides constant current (CC) and may be either alternating current (AC) or direct current (DC), depending on the electrode being used. The best welding characteristics are usually obtained using DC power sources.
The power in a welding circuit is measured in voltage and current. The voltage
(Volts) is governed by the arc length between the electrode and the workpiece and is influenced by electrode diameter. Current is a more practical measure of the power in a weld circuit and is measured in amperes (Amps).
The amperage needed to weld depends on electrode diameter, the size and thickness of the pieces to be welded, and the position of the welding. Thin metals require less current than thick metals, and a small electrode requires less amperage than a large one.
It is preferable to weld on work in the flat or horizontal position. However, when forced to weld in vertical or overhead positions it is helpful to reduce the amperage from that used when welding horizontally. Best welding results are achieved by maintaining a short arc, moving the electrode at a uniform speed, and feeding the electrode downward at a constant speed as it melts.

The following Arc Welding Electrode information an be found at www.metalwebnews.com/howto/weldrod.html
A BASIC GUIDE OF ARC WELDING ELECTRODES by Bruce Bauerlein
INTRODUCTION
There are many different types of electrodes used in the shielded metal arc welding, (SMAW) process. The intent of this guide is to help with the identification and selection of these electrodes.
ELECTRODE IDENTIFICATION
Arc welding electrodes are identified using the A.W.S, (American Welding Society) numbering system and are made in sizes from 1/16 to 5/16 . An example would be a welding rod identified as an 1/8" E6011 electrode. This electrode is 1/8" in diameter
The "E" stands for arc welding electrode.
Next will be either a 4 or 5 digit number stamped on the electrode. The first two numbers of a 4 digit number and the first 3 digits of a 5 digit number indicate the minimum tensile strength (in thousands of pounds per square inch) of the weld that the rod will produce, stress relieved. Examples would be as follows:
E60xx would have a tensile strength of 60,000 psi E110XX would be 110,000 psi
The next to last digit indicates the position the electrode can be used in.
1.
EXX1X is for use in all positions
2.
EXX2X is for use in flat and horizontal positions
3.
EXX3X is for flat welding
The last two digits together, indicate the type of coating on the electrode and the welding current the electrode can be used with. Such as DC straight, (DC -) DC reverse (DC+) or AC.

ELECTRODES AND CURRENTS USED
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EXX10 DC+ (DC reverse or DCRP) electrode positive.
EXX11 AC or DC- (DC straight or DCSP) electrode negative.
EXX12 AC or DC-
EXX13 AC, DC- or DC+
EXX14 AC, DC- or DC+
EXX15 DC+
EXX16 AC or DC+
EXX18 AC, DC- or DC+
EXX20 AC ,DC- or DC+
EXX24 AC, DC- or DC+
EXX27 AC, DC- or DC+
EXX28 AC or DC+
CURRENT TYPES
SMAW is performed using either AC or DC current. Since DC current flows in one direction, DC current can be DC straight, (electrode negative) or DC reversed
(electrode positive). With DC reversed,(DC+ OR DCRP) the weld penetration will be deep. DC straight (DC- OR DCSP) the weld will have a faster melt off and deposit rate. The weld will have medium penetration.
AC current changes it's polarity 120 times a second by itself and cannot be changed as can DC current.

ELECTRODE SIZE AND AMPS USED
The following will serve as a basic guide of the amp range that can be used for different size electrodes. Note that these ratings can be different between various electrode manufactures for the same size rod. Also the type coating on the electrode could affect the amperage range. When possible, check the manufactures info of the electrode you will be using for their recommended amperage settings.
Electrode Table
ELECTRODE
DIAMETER
(THICKNESS)
AMP
RANGE
PLATE
1/16"
3/32"
1/8
20 - 40 UP TO
3/16"
40 -
125
UP TO
1/4"
75 -
185
OVER
1/8"
5/32"
3/16"
1/4"
5/16"
105 -
250
OVER
1/4"
140 -
305
OVER
3/8"
210 -
430
OVER
3/8"
275 -
450
OVER
1/2"
Note! The thicker the material to be welded, the higher the current needed and the larger the electrode needed.

SOME ELECTRODE TYPES
This section will briefly describe four electrodes that are commonly used for maintenance and repair welding of mild steel. There are many other electrodes available for the welding of other kinds of metals. Check with your local welding supply dealer for the electrode that should be used for the metal you want to weld.
E6010 This electrode is used for all position welding using DCRP. It produces a deep penetrating weld and works well on dirty, rusted, or painted metals
E6011 This electrode has the same characteristics of the E6010, but can be used with AC and DC currents.
E6013 This electrode can be used with AC and DC currents. It produces a medium penetrating weld with a superior weld bead appearance.
E7018 This electrode is known as a low hydrogen electrode and can be used with
AC or DC. The coating on the electrode has a low moisture content that reduces the introduction of hydrogen into the weld. The electrode can produce welds of xray quality with medium penetration. (Note, this electrode must be kept dry. If it gets wet, it must be dried in a rod oven before use.)
GTAW (Gas Tungsten Arc Welding)
The following information is available at: http://www.aviationpros.com/article/10385780/gtaw-welding-touching-on-thebasics
Gas tungsten arc welding (GTAW), also known as tungsten inert gas (TIG) welding is used in many aircraft applications. GTAW provides a clean, strong weld joint that makes it ideal for assembling and repairing various aircraft components.
In this article, we will discuss the basic theory of GTAW and cover some basic welding and setup tips.
Basic Theory
In gas tungsten arc welding, a non-consumable tungsten electrode is used to establish an arc on the base metal. The heat of the arc melts the base metal and

produces a weld pool. In contrast to normal arc welding, in GTAW an inert gas shields the weld area in order to prevent air from contaminating the weld. This shielding gas prevents oxidation of the tungsten electrode, the molten weld puddle, and the heat-affected zone adjacent to the weld bead.
In a typical GTAW setup, an AC/DC welding machine is used with a flow of shielding gas. The shielding gas goes through a regulator and flow meter and on to the torch. The torch has a collet/collet body combination that holds the electrode. A heat-resistant cup or ceramic nozzle surrounds the electrode and controls the gas shield.
Personal Protective Equipment
Although GTAW does not produce the metal spatter that is common with arc or stick welding, it still generates intense heat and light. In fact, the clearer atmosphere around the GTAW arc can cause up to twice the amount of infrared and UV rays compared to normal arc welding. Any exposed skin will be damaged similar to extreme sunburn. Welders must wear a welding helmet. Welder’s protective gloves and clothing should also be used. Fire-resistant cloth and leather clothing and accessories are recommended. Cotton should not be used as it doesn’t provide sufficient protection and it deteriorates quickly under the infrared and UV rays produced by the welding process. In addition, dark clothing should be used to reduce reflection of light behind the helmet.
Other Safety Precautions
The following general precautions should be observed to protect you and coworkers from the hazards associated with GTAW:
Ensure electrical connection leads are in good condition and tight prior to use.
They should be protected to prevent accidental damage from hangar traffic.
Make sure you have adequate ventilation. Since GTAW uses inert gases during the process, if it is used in an enclosed area it can displace breathing air and can be hazardous without proper ventilation. In addition, ozone is produced during the welding process. The amount of ozone produced varies with type of electrode used, amperage, and argon flow. In poorly ventilated areas, ozone levels can

increase to harmful levels. Whenever possible, draw fumes and contaminated air away when welding.
Flammable materials should not be carried in clothing pockets.
Shielding curtains should be placed around all jobs so that workers in adjacent areas are not exposed to the welding arcs.
Shielding Gas
In GTAW, the gas used to shield the welding arc and hot metals is an inert gas.
Inert gases are gases whose atomic structures do not allow them to react with metals or other gases. Argon, helium, or an argon-helium mixture is used as the inert gas in GTAW .
Argon is a relatively heavy gas. It has several benefits when used in GTAW. It requires a lower arc voltage than other shielding gases for a given arc length and current used (ideal for thin metal welding). It also provides easier arc starting. Its heavier weight as compared to helium provides for good shielding with lower flow rates.
In contrast to argon, helium is the lightest of the inert gases. Because of its light weight, about two to three times more helium is needed as compared to argon to shield the weld area. Despite this, helium has an advantage over argon in that it can be used with greater arc voltages. Because of this, helium is preferred when working with thick metal sections.
Another difference in the two gases is their cleaning ability. Both helium and argon allow for good cleaning action when using DC. However, when using AC, argon provides for better cleaning action. Argon also provides better arc stability than helium when using AC.
Proper Gas Selection
You want to make sure to use the right gas with GTAW. Usually, pure argon is used, although thicker welding may require an argon/helium or other specialty mix. If you use the wrong gas mixture, such as a 75 percent argon/25 percent
CO2 that is common for GMAW, the tungsten electrode will quickly be consumed or deposited in the weld puddle.

Gas Flow Rate
Setting a proper gas flow rate is another important element to successful GTAW.
Contrary to what may seem to be common sense, more isn’t better. If you are welding in a flat position, a flow rate of about 15 to 20 cubic feet per hour (CFH) is typically adequate. For overhead welding, you can start at about 20 CFH and increase the flow by small adjustments of about 5 CFH if necessary.
So why is too high a flow rate a bad thing? Well, if the gas flows out of the torch at too high a velocity, it ends up bouncing off the surface being welded and starts a swirling motion parallel to the torch cup called a venturi. This venturi effect will suck air into the gas flow, creating an impure weld atmosphere. This results in pinholes in the weld.
Accessories
The GTAW torch can either be air cooled or water cooled. If most of the welding you do is at 200 amps or less, an air-cooled torch is adequate. If welding above
200 amps, a water-cooled torch should be considered.
Controls are also offered in either foot pedal control or torch control. Foot pedal control tends to be more popular where work is done in an area that affords mobility. A fingertip control can be beneficial when working in an awkward position or where less mobility is available.
Electrodes
Many different electrode types are available including thoriated, lanthaniated, ceriated, and pure tungsten. When choosing an electrode, follow manufacturers’ recommendations and choose the one that is best for you. Some characteristics to consider in an electrode are good ignition and re-ignition properties, constant arc, long lifetime, and high current-loading capacity.
As a safety note, 2 percent (thoriated) tungsten contains thoria, a radioactive element. When grinding on these electrodes, it is advisable to use some sort of collection device in the form of a vacuum or a liquid bath so that the grinding dust does not become airborne.

Good Welding Practices
You want to get in as comfortable a position as possible. Brace your arm to allow for steady torch movement. Many GTAW welders hold the torch like a pencil to afford the best control.
You want to hold the torch at the proper angle. If the torch is perpendicular to the work piece, it will be difficult to view the welding process. The angle of the torch relative to perpendicular should be about 15 to 20 degrees. If this angle is exceeded too much, it can lead to less penetration, poor shielding gas coverage, and general arc instability.
In regards to travel direction, the torch should be pushed away from (ahead of) the weld puddle. This ensures proper gas coverage of the weld puddle and offers the welder a good view of the weld puddle.
Get comfortable with your welding equipment. Practice welding on scrap metal.
This is a good way to become familiar with the welding equipment, allowing for more confidence when doing the actual welding.
Joining Aluminum with TIG/GTAW
From http://www.millerwelds.com/resources/articles/A-comprehensive-look-at-
GTAW-TIG-welding-aluminum-for-beginners
Advice for the novice
Aluminum: beautiful, lightweight, strong, versatile...and a real challenge to weld, especially for beginning welders.
Fortunately, some newer gas tungsten arc welding (GTAW) systems have been designed specifically for aluminum welding. This article describes some of the new equipment available and its benefits, accessories required, points to consider before welding, and the techniques required to make a good weld bead.

GTAW Power Sources
In general, GTAW power sources with an AC/DC output come in four categories, which are listed here in order of lowest to highest price:
1. Light fabrication. Machines designed for light fabrication usually have an AC output from 20 to 165 amps. While they do not incorporate a square wave output or balance control technology, they do produce an arc suitable for a variety of work, including applications for the home hobbyist.
2. Light industrial, maintenance/repair, metal fabrication. This newer class of light industrial machine provides roughly a 15 to 180 AC output and a professional-quality arc. Key features include: a square wave output, a fixed balance control set for more penetration than cleaning (a 60/40 electrode negative (EN) to electrode positive (EP) ratio works best for most applications), built-in high-frequency starting for positive starts without arc wandering, and a built-in stabilizer for a more consistent arc while welding.
3. Industrial production, fabrication, aerospace, repair. Industrial production GTAW power sources have a square wave output with an adjustable balance control. Greater amounts of EN create a deeper, narrower weld bead and better joint penetration. Greater EP values remove more oxide and create a shallower, wider bead. Transformer-rectifier GTAW machines can adjust EN values from 45 to 68 percent.
Machines are available with a variety of outputs, typically rated at 250, 350, and
500 amps with a 40 or 60 percent duty cycle. The low-end amperage range listed for these machines is usually 5, 3 or 25 amps, respectively. These power sources have created millions of code-quality GTA welds.
4. Inverter-based AC GTAW machines. Also considered industrial power sources, an inverter gives the professional welder more capability to tailor the width, depth and appearance of the weld bead for an application.
Inverters can adjust EN duration from 50 to 90 percent. Adding more EN to the cycle may: increase travel speed by up to 20 percent, narrow the weld bead, achieve greater penetration, permit using a smaller-diameter tungsten (to more precisely direct the heat or to make a narrower weld bead), and reduce the size of the etched zone for improved cosmetics.
Operators can adjust the welding output frequency in the range of 20 to 250 hertz. Increasing frequency produces a tight, focused arc cone. This narrows the weld bead, which helps when welding in corners, on root passes, and fillet welds;

it also permits faster travel speed on some joints. Decreasing output frequency produces a broader arc cone, which widens the weld bead profile and provides greater cleaning action.
GTAW inverters accept single- or three-phase, 50- or 60-hertz, 230- or 460-volt input power. This provides flexibility when moving the machine between jobs sites or around a large facility. Using three-phase power and welding at 300 amps (460 volts primary), an AC/DC GTAW inverter requires only 18 amps of primary current. A 5- to 300-amp AC/DC GTAW machine weighs about 90 pounds.
GTAW Accessories
If most welding is done at 200 amps or less, an air-cooled torch works well. For welding above 200 amps, a water-cooled torch should be considered. For portability, water coolers can be mounted on a wheeled cart that also carries the power source and gas bottles.
Remote control capabilities usually include current (amperage) and contactor control (the contactor keeps the torch electrically cold until energized and starts and stops the gas flow to the torch). The most popular remote control is a foot pedal that operates much like an auto's gas pedal; the more it is depressed, the more amperage flows. Another type of control - - one that affords greater mobility but is more difficult to learn - - is a fingertip control, which is mounted on the torch.
If most work is done on a bench or around structures that permit mobility, the foot pedal remote control is probably a better option because it's easier to use.
Conversely, if most work is done in awkward positions, a fingertip control may be the better choice.
Before Welding Starts
The following suggestions address the basic areas of GTAW setup. However, they are no substitute for carefully reading the operator's manual, watching instructional videos, and following safety precautions, such as wearing protective gloves and glasses.
1. Determine amperage requirements. Each 0.001 inch of metal to be melted requires about 1 amp of welding power. For example, welding 1/8-inch aluminum requires about 125 amps.
2. Select the correct current. AC should be used for aluminum, magnesium, and zinc die cast. When exposed to air, these metals form an oxide layer that

melts at a much higher temperature than the base metal. If not removed, this oxide causes incomplete weld fusion.
Fortunately, AC inherently provides a cleaning action. While the EN portion of the
AC cycle directs heat into the work and melts the base metal, the EP portion - - where current flows from the work to the electrode - - blasts off the surface oxides.
3. Use the right gas. Usually, pure argon is employed, although thicker weldments may require an argon/helium or other specialty mix. If the wrong gas is used, such as the 75 percent argon/25 percent CO(2) mix commonly used for
GMAW, the tungsten immediately will begin to be consumed or deposited in the weld puddle.
4. Set the proper gas flow rate. More is not better, so 15 to 20 cubic feet per hour (CFH) should suffice. Argon is about 1-1/3 heavier than air. When welding in a flat position, the gas naturally flows out of the torch and covers the weld pool.
For overhead welding, the gas flow rate should begin at 20 CFH, and small increments of 5 CFH can be made, if necessary.
In any position, if the gas flows out at too high a velocity, it can bounce off the workpiece and start a swirling motion parallel to the torch cup called a venturi. A venturi can pull air into the gas flow, bring in contaminating oxygen and nitrogen, and create pinholes in the weld. Unfortunately, some operators automatically increase the gas flow when they see a pinhole, worsening the problem they tried to fix.
5. Select the right type of tungsten. For AC welding, the traditional practice calls for selecting a pure tungsten electrode and forming a ball at the end of the electrode. This still holds true for most applications and welding with a conventional power source. However, for making critical welds on materials thinner than 0.09 in., or when using a TIG power source with an adjustable frequency output, new recommendations call for treating the tungsten almost as if the weld were being made in the DC mode. Select a 2-percent-type tungsten
(thorium, cerium, etc.) and grind it to a point in the long direction, making the point roughly two times as long as the diameter. A 0.010- to 0.030-inch flat should be made on the end to prevent balling and the tungsten from being transferred across the arc.
With a pointed electrode, a skilled operator can place a 1/8-inch bead on a fillet weld made from 1/8-inch aluminum plates. Without this technology, the ball on

the end of the electrode would have forced the operator to make a larger weld bead and then grind the bead down to final size.
6. Select the right diameter of tungsten. The current-carrying capacity of a tungsten is directly proportional to the area of its cross section. For example, a 2 percent thoriated, 3/32-inch (0.093-inch) tungsten has a current-carrying capacity of 150 to 250 amps, whereas a 2 percent thoriated, 0.040-inch tungsten has a current-carrying capacity of 15 to 80 amps.
There is no such thing as an all-purpose electrode, despite the reputation of the
3/32-inch electrode. Attempting to weld at 18 amps with a 3/32-inch electrode will create arc starting and arc stability problems; the current is insufficient to drive through the electrode. Conversely, attempting to use a 3/32-inch tungsten to weld at 300 amps creates tungsten "spitting" - - the excess current causes the tungsten to migrate to the workpiece.
7. Avoid tungsten contamination. If the tungsten electrode becomes contaminated by accidentally touching the weld pool, welding must be stopped, because a contaminated electrode can produce an unstable arc. To break off the contaminated portion, the tungsten should be removed from the torch, placed on a table with the contaminated end hanging over the edge, and the contaminated portion struck firmly. The tungsten should then be resharpened.
8. Set the proper tungsten extension. While electrode extension may vary from flush with the gas cup to a distance equal to the cup diameter. A general rule is to start with one electrode diameter, or about 1/8 inch. Joints that make the root of the weld hard to reach require additional extension, although extensions farther than 1/2 inch may result in poor gas coverage and may require a special gas cup.
9. Select the filler metal. The filler rod needs to match the base metal in both type and hardness of metal. The filler rod should be the same diameter as the tungsten electrode.
10. Select a high frequency (HF) mode. For AC welding with transformerrectifier type machines, continuous HF is required to start and maintain the arc, which has a tendency to go out when the AC square wave travels through the zero amperage point. HF bridges the gap between the electrode and the work, forming a path for the current to follow.
Inverters require HF for arc starting only, as they drive the arc through the zero point so quickly that the arc does not have a chance to go out. For this same

reason, inverters produce much less arc flutter. Inverters also offer a lift arc starting method that avoids the use of HF altogether.
11. Control HF emissions. High frequency interferes with computers, printed circuit boards, televisions, and other electronic equipment but is a necessary evil.
It can be minimized by hooking the work clamp as close to the weldment as possible, keeping the welding torch and work clamp cables close together
(spreading them apart is like creating a big broadcast dish), and keeping the cables repaired to prevent current leaks.
12. Set the balance control. There are no hard rules about setting balance control, but the typical error involves over-balancing the cycle.
Too much cleaning action (EP duration) causes excess heat buildup on the tungsten, which creates a large ball on the end. Subsequently, the arc loses stability, and the operator loses the ability to control the arc's direction and the weld puddle. Arc starts begin to degrade as well.
Too much penetration (or, more precisely, insufficient EP current) results in a scummy weld puddle. If the puddle looks like it has black pepper flakes floating on it, adding more cleaning action will remove these impurities.
13. Set the frequency (inverters only). Decreasing frequency produces a broader arc cone, which widens the weld bead profile and better removes impurities from the surface of the metal. It also transfers the maximum amount of energy to the workpiece, which speeds up applications requiring heavy metal deposition (such as building up a worn part or making a fill pass).
Increasing frequency produces a tight, focused arc cone; this narrows the weld bead, which helps when welding in corners, on root passes, and fillet welds. The operator can direct the arc precisely at the joint and not have the arc dance from plate to plate. Increasing frequency also may increase travel speed up to 40 percent in certain applications.
A good starting point for general welding is 80 to 120 hertz. These frequencies are comfortable to work with, increase control of the arc direction, and boost travel speed. For a fillet weld application with full penetration in the weld without putting too much amperage in the metal, the frequency should be increased to
200 hertz or more. For buildup work, frequency should start at 60 hertz and be adjusted lower from there.

Making a Good GTA Weld
1. Get in a comfortable position and brace yourself. Maneuvering a GTAW torch properly is like trying to write neatly in a small space. It requires a braced arm, slow movements, and a mental focus on the end of the tungsten. In fact, many people grip the torch like a pencil.
2. Hold the torch at the proper angle. Travel angle is defined as the angle relative to the torch in a perpendicular position. Normal welding conditions in all positions call for a travel angle of 15 to 20 degrees. Travel angles beyond this lead to less penetration, poor direction of the weld metal, poor shielding gas coverage, and general arc instability.
For travel direction during GTAW, the push technique should always be used, which involves pushing the torch away from (ahead of) the weld puddle. Pushing ensures good gas coverage of the weld puddle and that oxides have been removed, and it offers the welder a better view of the weld puddle.
3. Practice welding on scrap. When beginning, welders should practice on a flat piece of metal rather than welding a joint or adding filler. They should also practice identifying the weld pool from the base metal, play with the amperage control to find the right amount of heat, and learn how to control the size and shape of the weld puddle.
GTAW is like welding with an acetylene torch in that, if a weld is not satisfactory, the welder can go back over it, remelt it, and repair it. However, aluminum acts as a heat sink, so if too much time is taken to get a molten puddle, a small part easily can be overheated.
4. Starting the arc. To start an arc using HF, the electrode should be held about
1/8 inch from the work and the foot pedal depressed. The electrode should never touch the work during a HF start. Many people tilt the torch and rest the gas cup against the work, establish the arc, and then shift the torch into the proper welding position. With lift arc starting, the welder touches the tungsten to the workpiece, lifts it off the workpiece, and the full welding current begins flowing.
5. Maintain consistent arc length. Arc length is usually one electrode diameter from the work. Varying this arc length produces inconsistencies. One common error that new GTA welders commit is picking up the torch, or tilting the torch too much, to get a better view of the electrode and weld puddle. For a better view, a welder should shift the position of his or her face, typically down and to the side or reposition the workpiece so that the torch is pulled toward the body.

6. Maintain a travel speed consistent with the desired bead shape. Moving the torch too quickly creates a bead that is too narrow, while moving the torch too slowly produces an excessively wide bead. With GTAW, the torch does not need to be moved forward until the weld puddle reaches the desired size.
However, holding the torch too long in one spot, especially on thin metal, can result in the arc burning through the base metal.
7. Add filler metal. Once the arc is started and a weld puddle of the desired size is established, filler metal can be added. The filler rod should be held at a 15- to
20-degree angle up from the workpiece, creating a 90-degree angle between the filler rod and the tungsten.
The torch and filler rod should be moved progressively so that the weld pool, hot filler rod end, and solidifying weld are not exposed to air. The hot end of the filler rod should not be moved from the protection of the shielding gas.
Learning GTAW
There is good news and bad news about GTAW of aluminum. The good news is that it is very difficult make a bad GTAW weld. If the welder melts the base metal and gets the filler rod into the weld puddle, a sound weld is most likely to result.
The bad news is that learning to make pretty weld beads, as well as coordinating the hands, feet and eyes, takes patience and practice. However, when a welder becomes proficient, the results are very satisfying.

Electricity is used to provide the heat needed to melt materials during the arc welding process.
Electricity is a form of energy. Electricity is the flow of electrons. All matter is made up of atoms, and an atom has a center, called a nucleus. The nucleus contains positively charged particles called protons and uncharged particles called neutrons. The nucleus of an atom is surrounded by negatively charged particles called electrons. The negative charge of an electron is equal to the positive charge of a proton, and the number of electrons in an atom is usually equal to the number of protons. When the balancing force between protons and electrons is upset by an outside force (the power source when arc welding), an atom may gain or lose an electron. When electrons are "lost" from an atom, the free movement of these electrons constitutes an electric current.
The electricity flows from the power source (Source), through the electrode and across the arc, through the base material to the work lead (Destination) and back to the power source in a “closed” pathway called a circuit.
You might have been wondering how electrons can continuously flow in a uniform direction through wires without the benefit of these hypothetical electron Sources and Destinations. In order for the Source-and-Destination scheme to work, both would have to have an infinite capacity for electrons in order to sustain a continuous flow! Using the marble-and-tube analogy, the marble source and marble destination buckets would have to be infinitely large to contain enough marble capacity for a "flow" of marbles to be sustained.
The answer to this paradox is found in the concept of a circuit: a never-ending looped pathway for electrons. If we take a wire, or many wires joined end-to-end, and loop it around so that it forms a continuous pathway, we have the means to support a uniform flow of electrons without having to resort to infinite Sources and Destinations:

Each electron advancing clockwise in this circuit pushes on the one in front of it, which pushes on the one in front of it, and so on, and so on, just like a hula-hoop filled with marbles. Now, we have the capability of supporting a continuous flow of electrons indefinitely without the need for infinite electron supplies and dumps. All we need to maintain this flow is a continuous means of motivation for those electrons, which we'll address in the next section of this chapter.
It must be realized that continuity is just as important in a circuit as it is in a straight piece of wire. Just as in the example with the straight piece of wire between the electron Source and Destination, any break in this circuit will prevent electrons from flowing through it:

An important principle to realize here is that it doesn't matter where the break
occurs. Any discontinuity in the circuit will prevent electron flow throughout the entire circuit. Unless there is a continuous, unbroken loop of conductive material for electrons to flow through, a sustained flow simply cannot be maintained.
 A circuit is an unbroken loop of conductive material that allows electrons to flow through continuously without beginning or end.
 If a circuit is "broken," that means its conductive elements no longer form a complete path, and continuous electron flow cannot occur in it.
 The location of a break in a circuit is irrelevant to its inability to sustain continuous electron flow. Any break anywhere in a circuit prevents electron flow throughout the circuit.

The electrons of different types of atoms have different degrees of freedom to move around. With some types of materials, such as metals, the outermost electrons in the atoms are so loosely bound that they chaotically move in the space between the atoms of that material by nothing more than the influence of room-temperature heat energy. Because these virtually unbound electrons are free to leave their respective atoms and float around in the space between adjacent atoms, they are often called free electrons.
In other types of materials such as glass, the atoms' electrons have very little freedom to move around. While external forces such as physical rubbing can force some of these electrons to leave their respective atoms and transfer to the atoms of another material, they do not move between atoms within that material very easily.
This relative mobility of electrons within a material is known as electric conductivity. Conductivity is determined by the types of atoms in a material (the number of protons in each atom's nucleus, determining its chemical identity) and how the atoms are linked together with one another. Materials with high electron mobility (many free electrons) are called conductors, while materials with low electron mobility (few or no free electrons) are called insulators.
Here are a few common examples of conductors and insulators
Conductors:
 silver
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 copper gold aluminum iron
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 steel brass bronze mercury graphite dirty water concrete
Insulators:
 glass
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 rubber oil asphalt fiberglass porcelain ceramic quartz
(dry) cotton
(dry) paper
(dry) wood plastic air diamond pure water

It must be understood that not all conductive materials have the same level of conductivity, and not all insulators are equally resistant to electron motion.
Electrical conductivity is analogous to the transparency of certain materials to light: materials that easily "conduct" light are called "transparent," while those that don't are called "opaque." However, not all transparent materials are equally conductive to light. Window glass is better than most plastics, and certainly better than "clear" fiberglass. So it is with electrical conductors, some being better than others.
It should also be understood that some materials experience changes in their electrical properties under different conditions. Glass, for instance, is a very good insulator at room temperature, but becomes a conductor when heated to a very high temperature. Gases such as air, which normally are insulating materials, also become conductive if heated to very high temperatures. Most metals become poorer conductors when heated, and better conductors when cooled. Many conductive materials become perfectly conductive (this is called superconductivity) at extremely low temperatures.
While the normal motion of "free" electrons in a conductor is random, with no particular direction or speed, electrons can be influenced to move in a coordinated fashion through a conductive material. This uniform motion of electrons is what we call electricity, or electric current. To be more precise, it could be called dynamic electricity in contrast to static electricity, which is an unmoving accumulation of electric charge. Just like water flowing through the emptiness of a pipe, electrons are able to move within the empty space within and between the atoms of a conductor. The conductor may appear to be solid to our eyes, but any material composed of atoms is mostly empty space!
The liquid-flow analogy is so fitting that the motion of electrons through a conductor is often referred to as a "flow."
Remember that electrons can flow only when they have the opportunity to move in the space between the atoms of a material. This means that there can be electric current only where there exists a continuous path of conductive material providing a conduit for electrons to travel through. The continuous flow of electrons requires there be an unbroken path to permit that flow.
It is interesting to note that no "wear" occurs within wires due to this electric current. Electrons do encounter some degree of friction as they move, however, and this friction can generate heat in a conductor.

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REVIEW:
In conductive materials, the outer electrons in each atom can easily come or go, and are called free electrons.
In insulating materials, the outer electrons are not so free to move.
All metals are electrically conductive.
Dynamic electricity, or electric current, is the uniform motion of electrons through a conductor.
Static electricity is an unmoving (if on an insulator), accumulated charge formed by either an excess or deficiency of electrons in an object. It is typically formed by charge separation by contact and separation of dissimilar materials.
For electrons to flow continuously (indefinitely) through a conductor, there must be a complete, unbroken path for them to move both into and out of that conductor.

We need more than just a continuous path (circuit) before a continuous flow of electrons will occur: we also need some means to push these electrons around the circuit. Just like marbles in a tube or water in a pipe, it takes some kind of influencing force to initiate flow. With electrons, this force is the same force at work in static electricity: the force produced by an imbalance of electric charge.
If we take the examples of wax and wool which have been rubbed together, we find that the surplus of electrons in the wax (negative charge) and the deficit of electrons in the wool (positive charge) creates an imbalance of charge between them. This imbalance manifests itself as an attractive force between the two objects:
If a conductive wire is placed between the charged wax and wool, electrons will flow through it, as some of the excess electrons in the wax rush through the wire to get back to the wool, filling the deficiency of electrons there:

The imbalance of electrons between the atoms in the wax and the atoms in the wool creates a force between the two materials. With no path for electrons to flow from the wax to the wool, all this force can do is attract the two objects together.
Now that a conductor bridges the insulating gap, however, the force will provoke electrons to flow in a uniform direction through the wire, if only momentarily, until the charge in that area neutralizes and the force between the wax and wool diminishes.
If we rub wax and wool together, we "pump" electrons away from their normal
"levels," creating a condition where a force exists between the wax and wool, as the electrons seek to re-establish their former positions (and balance within their respective atoms).
When the electrons are poised in that static condition (just like water sitting still, high in a reservoir), the energy stored there is called potential energy, because it has the possibility (potential) of release that has not been fully realized yet.
When you scuff your rubber-soled shoes against a fabric carpet on a dry day, you create an imbalance of electric charge between yourself and the carpet. The action of scuffing your feet stores energy in the form of an imbalance of electrons forced from their original locations. This charge (static electricity) is stationary, and you won't realize that energy is being stored at all. However, once you place your hand against a metal doorknob (with lots of electron mobility to neutralize your electric charge), that stored energy will be released in the form of a sudden flow of electrons through your hand, and you will perceive it as an electric shock!
This potential energy, stored in the form of an electric charge imbalance and capable of provoking electrons to flow through a conductor, can be expressed as a term called voltage, which technically is a measure of potential energy per
unit charge of electrons, or something a physicist would call specific
potential energy. Defined in the context of static electricity, voltage is the measure of work required to move a unit charge from one location to another, against the force which tries to keep electric charges balanced. In the context of electrical power sources, voltage is the amount of potential energy available (work to be done) per unit charge, to move electrons through a
conductor.
Because voltage is an expression of potential energy, representing the possibility or potential for energy release as the electrons move from one "level" to another, it is always referenced between two points, a positive (+) and a negative(-).

Let's take the symbol for a chemical battery and build a circuit step by step:
Any source of voltage, including batteries, has two points for electrical contact. In this case, we have point 1 and point 2 in the above diagram. The horizontal lines of varying length indicate that this is a battery, and they further indicate the direction which this battery's voltage will try to push electrons through a circuit.
The fact that the horizontal lines in the battery symbol appear separated (and thus unable to serve as a path for electrons to move) is no cause for concern: in real life, those horizontal lines represent metallic plates immersed in a liquid or semi-solid material that not only conducts electrons, but also generates the voltage to push them along by interacting with the plates.
Notice the little "+" and "-" signs to the immediate left of the battery symbol.
The negative (-) end of the battery is always the end with the shortest dash, and the positive (+) end of the battery is always the end with the longest dash.
Since we have decided to call electrons "negatively" charged (thanks, Benjamin
Franklin!), the negative end of a battery is that end which tries to push electrons out of it. Likewise, the positive end is that end which tries to attract electrons.
With the "+" and "-" ends of the battery not connected to anything, there will be voltage between those two points, but there will be no flow of electrons through the battery, because there is no continuous path for the electrons to move.
We can provide such a path for the battery by connecting a piece of wire from one end of the battery to the other. Forming a circuit with a loop of wire, we will initiate a continuous flow of electrons in a clockwise direction:

So long as the battery continues to produce voltage and the continuity of the electrical path isn't broken, electrons will continue to flow in the circuit. Following the metaphor of water moving through a pipe, this continuous, uniform flow of electrons through the circuit is called a current. So long as the voltage source keeps "pushing" in the same direction, the electron flow will continue to move in the same direction in the circuit. This single-direction flow of electrons is called a Direct Current, or DC. In the second volume of this book series, electric circuits are explored where the direction of current switches back and forth: Alternating
Current, or AC. But for now, we'll just concern ourselves with DC circuits.
Because electric current is composed of individual electrons flowing in unison through a conductor by moving along and pushing on the electrons ahead, just like marbles through a tube or water through a pipe, the amount of flow throughout a single circuit will be the same at any point. If we were to monitor a cross-section of the wire in a single circuit, counting the electrons flowing by, we would notice the exact same quantity per unit of time as in any other part of the circuit, regardless of conductor length or conductor diameter.

If we break the circuit's continuity at any point, the electric current will cease in the entire loop, and the full voltage produced by the battery will be manifested across the break, between the wire ends that used to be connected:
Notice the "+" and "-" signs drawn at the ends of the break in the circuit, and how they correspond to the "+" and "-" signs next to the battery's terminals.
These markers indicate the direction that the voltage attempts to push electron flow. This potential direction is commonly referred to as polarity. Remember that voltage is always relative between two points. Because of this fact, the polarity of a voltage drop is also relative between two points: whether a point in a circuit gets labeled with a "+" or a "-" depends on the other point to which it is referenced. Take a look at the following circuit, where each corner of the loop is marked with a number for reference:
With the circuit's continuity broken between points 2 and 3, the polarity of the voltage dropped between points 2 and 3 is "-" for point 2 and "+" for point 3. The

battery's polarity (1 "-" and 4 "+") is trying to push electrons through the loop clockwise from 1 to 2 to 3 to 4 and back to 1 again.
Now let's see what happens if we connect points 2 and 3 back together again, but place a break in the circuit between points 3 and 4:
With the break between 3 and 4, the polarity of the voltage drop between those two points is "+" for 4 and "-" for 3. Take special note of the fact that point 3's
"sign" is opposite of that in the first example, where the break was between points 2 and 3 (where point 3 was labeled "+"). It is impossible for us to say that point 3 in this circuit will always be either "+" or "-", because polarity, like voltage itself, is not specific to a single point, but is always relative
between two points!
REVIEW:
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Electrons can be motivated to flow through a conductor by the same force manifested in static electricity.
Voltage is the measure of specific potential energy (potential energy per unit charge) between two locations. In layman's terms, it is the measure of
"push" available to motivate electrons.
Voltage, as an expression of potential energy, is always relative between two locations, or points. Sometimes it is called a voltage "drop."
When a voltage source is connected to a circuit, the voltage will cause a uniform flow of electrons through that circuit called a current.
In a single (one loop) circuit, the amount of current at any point is the same as the amount of current at any other point.

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If a circuit containing a voltage source is broken, the full voltage of that source will appear across the points of the break.
The +/- orientation of a voltage drop is called the polarity. It is also relative between two points.

The circuit in the previous section is not a very practical one. In fact, it can be quite dangerous to build (directly connecting the poles of a voltage source together with a single piece of wire). The reason it is dangerous is because the magnitude of electric current may be very large in such a short circuit, and the release of energy very dramatic (usually in the form of heat). Usually, electric circuits are constructed in such a way as to make practical use of that released energy, in as safe a manner as possible.
One practical and popular use of electric current is for the operation of electric lighting. The simplest form of electric lamp is a tiny metal "filament" inside of a clear glass bulb, which glows white-hot ("incandesces") with heat energy when sufficient electric current passes through it. Like the battery, it has two conductive connection points, one for electrons to enter and the other for electrons to exit.
Connected to a source of voltage, an electric lamp circuit looks something like this:
As the electrons work their way through the thin metal filament of the lamp, they encounter more opposition to motion than they typically would in a thick piece of wire. This opposition to electric current depends on the type of material, its cross-sectional area, and its temperature. It is technically known
as resistance. (It can be said that conductors have low resistance and insulators
have very high resistance.) This resistance serves to limit the amount of current

through the circuit with a given amount of voltage supplied by the battery, as compared with the "short circuit" where we had nothing but a wire joining one end of the voltage source (battery) to the other.
When electrons move against the opposition of resistance, "friction" is generated.
Just like mechanical friction, the friction produced by electrons flowing
against a resistance manifests itself in the form of heat. The concentrated resistance of a lamp's filament results in a relatively large amount of heat energy dissipated at that filament. This heat energy is enough to cause the filament to glow white-hot, producing light, whereas the wires connecting the lamp to the battery (which have much lower resistance) hardly even get warm while conducting the same amount of current.
As in the case of the short circuit, if the continuity of the circuit is broken at any point, electron flow stops throughout the entire circuit. With a lamp in place, this means that it will stop glowing:
As before, with no flow of electrons, the entire potential (voltage) of the battery is available across the break, waiting for the opportunity of a connection to bridge across that break and permit electron flow again. This condition is known as an open circuit, where a break in the continuity of the circuit prevents current throughout. All it takes is a single break in continuity to "open" a circuit. Once any breaks have been connected once again and the continuity of the circuit reestablished, it is known as a closed circuit.
What we see here is the basis for switching lamps on and off by remote switches.
Because any break in a circuit's continuity results in current stopping throughout the entire circuit, we can use a device designed to intentionally break that

continuity (called a switch), mounted at any convenient location that we can run wires to, to control the flow of electrons in the circuit:
This is how a switch mounted on the wall of a house can control a lamp that is mounted down a long hallway, or even in another room, far away from the switch. The switch itself is constructed of a pair of conductive contacts (usually made of some kind of metal) forced together by a mechanical lever actuator or pushbutton. When the contacts touch each other, electrons are able to flow from one to the other and the circuit's continuity is established; when the contacts are separated, electron flow from one to the other is prevented by the insulation of the air between, and the circuit's continuity is broken.
REVIEW:
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Resistance is the measure of opposition to electric current.
A short circuit is an electric circuit offering little or no resistance to the flow of electrons. Short circuits are dangerous with high voltage power sources because the high currents encountered can cause large amounts of heat energy to be released.
An open circuit is one where the continuity has been broken by an interruption in the path for electrons to flow.
A closed circuit is one that is complete, with good continuity throughout.
A device designed to open or close a circuit under controlled conditions is called a switch.

 The terms "open" and "closed" refer to switches as well as entire circuits.
An open switch is one without continuity: electrons cannot flow through it.
A closed switch is one that provides a direct (low resistance) path for electrons to flow through.

An electric circuit is formed when a conductive path is created to allow free electrons to continuously move. This continuous movement of free electrons through the conductors of a circuit is called a current, and it is often referred to in terms of "flow," just like the flow of a liquid through a hollow pipe.
The force motivating electrons to "flow" in a circuit is called voltage. Voltage is a specific measure of potential energy that is always relative between two points.
When we speak of a certain amount of voltage being present in a circuit, we are referring to the measurement of how much potential energy exists to move electrons from one particular point in that circuit to another particular point.
Without reference to two particular points, the term "voltage" has no meaning.
Free electrons tend to move through conductors with some degree of friction, or opposition to motion. This opposition to motion is more properly called resistance.
The amount of current in a circuit depends on the amount of voltage available to motivate the electrons, and also the amount of resistance in the circuit to oppose electron flow. Just like voltage, resistance is a quantity relative between two points. For this reason, the quantities of voltage and resistance are often stated as being "between" or "across" two points in a circuit.
To be able to make meaningful statements about these quantities in circuits, we need to be able to describe their quantities in the same way that we might quantify mass, temperature, volume, length, or any other kind of physical quantity. For mass we might use the units of "kilogram" or "gram." For temperature we might use degrees Fahrenheit or degrees Celsius. Here are the standard units of measurement for electrical current, voltage, and resistance:
The "symbol" given for each quantity is the standard alphabetical letter used to represent that quantity in an algebraic equation. Standardized letters like these

are common in the disciplines of physics and engineering, and are internationally recognized. The "unit abbreviation" for each quantity represents the alphabetical symbol used as a shorthand notation for its particular unit of measurement. And, yes, that strange-looking "horseshoe" symbol is the capital Greek letter Ω, just a character in a foreign alphabet (apologies to any Greek readers here).
Each unit of measurement is named after a famous experimenter in electricity:
The amp after the Frenchman Andre M. Ampere, the volt after the Italian
Alessandro Volta, and the ohm after the German Georg Simon Ohm.
The mathematical symbol for each quantity is meaningful as well. The "R" for resistance and the "V" for voltage are both self-explanatory, whereas "I" for current seems a bit weird. The "I" is thought to have been meant to represent
"Intensity" (of electron flow), and the other symbol for voltage, "E," stands for
"Electromotive force. The symbols "E" and "V" are interchangeable for the most part, although some texts reserve "E" to represent voltage across a source (such as a battery or generator) and "V" to represent voltage across anything else.
All of these symbols are expressed using capital letters, except in cases where a quantity (especially voltage or current) is described in terms of a brief period of time (called an "instantaneous" value). For example, the voltage of a battery, which is stable over a long period of time, will be symbolized with a capital letter
"E," while the voltage peak of a lightning strike at the very instant it hits a power line would most likely be symbolized with a lower-case letter "e" (or lower-case
"v") to designate that value as being at a single moment in time. This same lower-case convention holds true for current as well, the lower-case letter "i" representing current at some instant in time. Most direct-current (DC) measurements, however, being stable over time, will be symbolized with capital letters.
These units and symbols for electrical quantities will become very important to know as we begin to explore the relationships between them in circuits. The first, and perhaps most important, relationship between current, voltage, and resistance is called Ohm's Law, discovered by Georg Simon Ohm and published in his 1827 paper, The Galvanic Circuit Investigated Mathematically. Ohm's principal discovery was that the amount of electric current through a metal conductor in a circuit is directly proportional to the voltage impressed across it, for any given temperature. Ohm expressed his discovery in the form of a simple equation, describing how voltage, current, and resistance interrelate:

In this algebraic expression, voltage (E) is equal to current (I) multiplied by resistance (R). Using algebra techniques, we can manipulate this equation into two variations, solving for I and for R, respectively:
Let's see how these equations might work to help us analyze simple circuits:
In the above circuit, there is only one source of voltage (the battery, on the left) and only one source of resistance to current (the lamp, on the right). This makes it very easy to apply Ohm's Law. If we know the values of any two of the three quantities (voltage, current, and resistance) in this circuit, we can use Ohm's Law to determine the third.

In this first example, we will calculate the amount of current (I) in a circuit, given values of voltage (E) and resistance (R):
What is the amount of current (I) in this circuit?
In this second example, we will calculate the amount of resistance (R) in a circuit, given values of voltage (E) and current (I):

What is the amount of resistance (R) offered by the lamp?
In the last example, we will calculate the amount of voltage supplied by a battery, given values of current (I) and resistance (R):
What is the amount of voltage provided by the battery?
Ohm's Law is a very simple and useful tool for analyzing electric circuits. It is used so often in the study of electricity and electronics that it needs to be committed to memory by the serious student. For those who are not yet comfortable with algebra, there's a trick to remembering how to solve for any one quantity, given the other two. First, arrange the letters E, I, and R in a triangle like this:

If you know E and I, and wish to determine R, just eliminate R from the picture and see what's left:
If you know E and R, and wish to determine I, eliminate I and see what's left:
Lastly, if you know I and R, and wish to determine E, eliminate E and see what's left:
Eventually, you'll have to be familiar with algebra to seriously study electricity and electronics, but this tip can make your first calculations a little easier to remember. If you are comfortable with algebra, all you need to do is commit
E=IR to memory and derive the other two formulae from that when you need them!
REVIEW:
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Voltage measured in volts, symbolized by the letters "E" or "V".
Current measured in amps, symbolized by the letter "I".
Resistance measured in ohms, symbolized by the letter "R".
Ohm's Law: E = IR ; I = E/R ; R = E/I

The electron flow you just learned about is what creates the arc in arc welding.
This is a form of electrical energy
How do we use that electrical energy to fuse metals together?

Energy transfer refers to the movement of energy from one form to another.
The energy transfers that take place in welding include:
Electrical Energy
In arc welding, the intense heat needed to melt metal is produced by an electric arc. The arc is formed between the actual work and an electrode (stick or wire) that is manually or mechanically guided along the joint. The electrode can either be a rod with the purpose of simply carrying the current between the tip and the work. Or, it may be a specially prepared rod or wire that not only conducts the current but also melts and supplies filler metal to the joint. Most welding in the manufacture of steel products uses the second type of electrode.
An arc is an electric current flowing between two electrodes through an ionized column of gas. A negatively charged cathode and a positively charged anode create the intense heat of the welding arc. Negative and positive ions are bounced off of each other in the plasma column at an accelerated rate.
In welding, the arc not only provides the heat needed to melt the electrode and the base metal, but under certain conditions must also supply the means to transport the molten metal from the tip of the electrode to the work.
Thermal Energy
Heat or, thermal energy is the total energy associated with random atomic and molecular motions of a substance. Heat is transferred in three ways. Radiation is the transfer of energy via electromagnetic waves. Radiation does not need an intervening medium to pass heat energy from the emitter to the absorber. When

radiation from the Sun is absorbed by the Earth it does work by setting molecules in motion and raising their kinetic energy level. In a solid, the molecules may vibrate more rapidly and collide with one another and transfer heat from warmer to colder portions of the mass by conduction. Though conduction is typically thought of occurring within a solid, it can occur between a solid and a fluid. When air, a fluid, comes in contact with the ground, a solid, heat can be transferred through molecular collisions. In fluids like air and water, heat is transferred by the circulation of molecules via the process of convection. Convection implies a vertical transfer of heat, like that which is occurs in a heated pot of water. As water warms it circulates to the surface. The same is true for air. When air is heated by the earth's surface it too circulates upward. While convection is applied to vertical transfer of heat, advection is a term that is applied to the horizontal transfer of heat by the wind.
Don't confuse temperature and heat; they are not the same thing. Temperature is a measure of the average kinetic energy level of a substance, in other words, the degree of hotness or coldness. Heat is the total energy associated with the motion of molecules while temperature is the average energy level. A boiling pan of water has a higher temperature than a tepid bathtub of water, but the tub contains more heat because there is more mass. The same can be said for material being welded.

During the welding process the metal changes states or forms.
What are the states of matter?
Solid
Liquid
Gas
Plasma
When a substance changes from one state, or phase, of matter to another it is said to have undergone a change of state or a change of phase.
These changes of phase always occur with a change of heat. Heat, which is energy, either comes into the material during a change of phase or heat comes out of the material during this change. However, although the heat content of the material changes, the temperature does not.

Below is a chart of the five changes of phase or state.
Description of the
Phase Change
Descriptive term for the change
Solid to Liquid Melting
Heat movement during the Phase
Change
Heat goes into the solid as it melts
Liquid to Solid
Liquid to Gas
Gas to Liquid
Freezing
Vaporization, which includes boiling and evaporation
Condensation
Heat leaves the liquid as it freezes
Heat goes into the liquid as it vaporizes
Solid to Gas Sublimation
Heat leaves the gas as it condenses
Heat goes into the solid as it sublimates
 Initially the metal is a solid
 When the arc starts the solid is converted into a liquid
 Some of the liquid is converted into a gas vapor
 When the arc stops the liquid cools to form a solid again – this is the newly formed weld joint

 During the welding process certain chemical reactions take place.
 Hydrogen, Oxygen, and Nitrogen can react in the weld puddle and cause changes in the structure of the weld weakening the weld.

(The following information is available from Integrated Publishing at http://www.tpub.com/air/1-18.htm
)
This section is devoted primarily to the terms used in describing various properties and characteristics of metals in general. Of primary concern in advanced manufacturing and advanced manufacturing and aerospace maintenance are such general properties of metals and their alloys as hardness, brittleness, malleability, ductility, elasticity, toughness, density, fusibility, conductivity, and contraction and expansion. Knowledge of these terms is essential as it helps to form the basis for further discussion of metals used in advanced manufacturing and aerospace.
Hardness
Hardness refers to the ability of a metal to resist abrasion, penetration, cutting action, or permanent distortion. Hardness may be increased by working the metal and, in the case of steel and certain titanium and aluminum alloys, by heat treatment and cold-working (discussed later). Structural parts are often formed from metals in their soft state and then heat treated to harden them so that the finished shape will be retained. Hardness and strength are closely associated properties of all metals.
Brittleness
Brittleness is the property of a metal that allows little bending or deformation without shattering. In other words, a brittle metal is apt to break or crack without change of shape. Because structural metals are often subjected to shock loads, brittleness is not a very desirable property. Cast iron, cast aluminum, and very hard steel are brittle metals.
Malleability
A metal that can be hammered, rolled, or pressed into various shapes without cracking or breaking or other detrimental effects is said to be malleable. This property is necessary in sheet metal that is to be worked into curved shapes such as cowlings, fairings, and wing tips. Copper is one example of a malleable metal.

Ductility
Ductility is the property of a metal that permits it to be permanently drawn, bent, or twisted into various shapes without breaking. This property is essential for metals used in making wire and tubing. Ductile metals are greatly preferred for advanced manufacturing and aerospace use because of their ease of forming and resistance to failure under shock loads. For this reason, aluminum alloys are used for cowl rings, fuselage and wing skin, and formed or extruded parts, such as ribs, spars, and bulkheads. Chrome-molybdenum steel is also easily formed into desired shapes. Ductility is similar to malleability.
Elasticity
Elasticity is that property that enables a metal to return to its original shape when the force that causes the change of shape is removed. This property is extremely valuable, because it would be highly undesirable to have a part permanently distorted after an applied load was removed. Each metal has a point known as the elastic limit, beyond which it cannot be loaded without causing permanent distortion. When metal is loaded beyond its elastic limit and permanent distortion does result, it is referred to as strained. In advanced manufacturing and aerospace construction, members and parts are so designed that the maximum loads to which they are subjected will never stress them beyond their elastic limit.
NOTE: Stress is the internal resistance of any metal to distortion.
Toughness
A material that possesses toughness will withstand tearing or shearing and may be stretched or otherwise deformed without breaking. Toughness is a desirable property in advanced manufacturing and aerospace metals.
Density
Density is the weight of a unit volume of a material. In advanced manufacturing and aerospace work, the actual weight of a material per cubic inch is preferred, since this figure can be used in determining the weight of a part before actual manufacture. Density is an important consideration when choosing a material to be used in the design of a part and still maintain the proper weight and balance of the advanced manufacturing and aerospace.

Fusibility
Fusibility is defined as the ability of a metal to become liquid by the application of heat. Metals are fused in welding. Steels fuse at approximately 2,500°F, and aluminum alloys at approximately 1, 110°F.
Conductivity
Conductivity is the property that enables a metal to carry heat or electricity. The heat conductivity of a metal is especially important in welding, because it governs the amount of heat that will be required for proper fusion. Conductivity of the metal, to a certain extent, determines the type of jig to be used to control expansion and contraction. In advanced manufacturing and aerospace, electrical conductivity must also be considered in conjunction with bonding, which is used to eliminate radio interference. Metals vary in their capacity to conduct heat.
Copper, for instance, has a relatively high rate of heat conductivity and is a good electrical conductor.
Contraction and Expansion
Contraction and expansion are reactions produced in metals as the result of heating or cooling. A high degree of heat applied to a metal will cause it to expand or become larger. Cooling hot metal will shrink or contract it. Contraction and expansion affect the design of welding jigs, castings, and tolerances necessary for hot-rolled material.
QUALITIES OF METALS
The selection of proper materials is a primary consideration in the development and proper maintenance and repair in advanced manufacturing and aerospace.
Keeping in mind the general properties of metals, it is now possible to consider the specific requirements that metals must meet to be suitable for advanced manufacturing and aerospace purposes. Strength, weight, and reliability determine the requirements to be met by any material used in airframe construction and repair. Airframes must be strong and as light in weight as possible. There are very definite limits to which increases in strength can be accompanied by increase in weight. For example, an aircraft frame so heavy that it could not support more than a few hundred pounds of additional weight would be of little use. All metals, in addition to having a good strength/weight ratio,

must be thoroughly reliable, thus minimizing the possibility of dangerous and unexpected failures. In addition to these general properties, the material selected for definite application must possess specific qualities suitable for the purpose.
These specific qualities are discussed in the following text.
Strength
The material must possess the strength required by the demands of dimensions, weight, and use. There are five basic stresses that metals may be required to withstand. These are tension, compression, shear, bending, and torsion. Each was discussed previously in this unit.
Weight
The relationship between the strength of a material and its weight per cubic inch, expressed as a ratio, is known as the strength/weight ratio. This ratio forms the basis of comparing the desirability of various materials for use in airframe construction and repair. Neither strength nor weight alone can be used as a means of true comparison. In some applications, such as the skin of monocoque structures (structures that utilize the “skin or external covering to help support the structural load), thickness is more important than strength; and in this instance, the material with the lightest weight for a given thickness or gauge is best. Thickness or bulk is necessary to prevent buckling or damage caused by careless handling.
Corrosive Properties
Corrosion is the eating away or pitting of the surface or the internal structure of metals. Because of the thin sections and the safety factors used in advanced manufacturing and aerospace design and construction, it would be dangerous to select a material subject to severe corrosion if it were not possible to reduce or eliminate the hazard. Corrosion can be reduced or prevented by using better grades of base metals; by coating the surfaces with a thin coating of paint, tin, chromium, or cadmium; or by an electrochemical process called "anodizing."
Working Properties
Another significant factor to consider in the selection of metals for advanced manufacturing and aerospace maintenance and repair is the ability of material to be formed, bent, or machined to required shapes. The hardening of metals by cold-working or forming is called work hardening. If a piece of metal is formed
(shaped or bent) while cold, it is said to be cold-worked. Practically all the work done on metal is cold-work. While this is convenient, it causes the metal to

become harder and more brittle. If the metal is cold-worked too much (that is, if it is bent back and forth or hammered at the same place too often), it will crack or break. Usually, the more malleable and ductile a metal is, the more coldworking it can withstand.
Joining Properties
Joining metals structurally by welding, brazing, or soldering, or by such mechanical means as riveting or bolting, is a tremendous help in design and fabrication. When all other properties are equal, material that can be welded has the advantage.
Shock and Fatigue Properties
Advanced manufacturing and aerospace metals are subject to both shock and fatigue (vibrational) stresses. Fatigue occurs in materials that are exposed to frequent reversals of loading or repeatedly applied loads, if the fatigue limit is reached or exceeded. Repeated vibration or bending will ultimately cause a minute crack to occur at the weakest point. As vibration or bending continues, the crack lengthens until complete failure of the part occurs. This is termed "shock and fatigue failure.” Resistance to this condition is known as shock and fatigue resistance. It is essential that materials used for critical parts be resistant to these stresses.
The preceding discussion of the properties and qualities of metals is intended to show why you must know which traits in metals are desirable and which are undesirable to do certain jobs. The more you know about a given material, the better you can handle airframe repairs.
METAL WORKING PROCESSES
When metal is not cast in a desired manner, it is formed into special shapes by mechanical working processes. Several factors must be considered when determining whether a desired shape is to be cast or formed by mechanical working. If the shape is very complicated, casting will be necessary to avoid expensive machining of mechanically formed parts. On the other hand, if strength and quality of material are the prime factors in a given part, a cast will be unsatisfactory. For this reason, steel castings are seldom used in aircraft work.

There are three basic methods of metal working. They are hot-working, coldworking, and extruding. The process chosen for a particular application depends upon the metal involved and the part required, although in some instances you might employ both hot- and cold-working methods in making a single part.
Hot-Working
Almost all steel is hot-worked from the ingot into some form from which it is either hot- or cold-worked to the finished shape. When an ingot is stripped from its mold, its surface is solid, but the interior is still molten. The ingot is then placed in a soaking pit, which retards loss of heat, and the molten interior gradually solidifies. After soaking, the temperature is equalized throughout the ingot, which is then reduced to intermediate size by rolling, making it more readily handled.
The rolled shape is called a bloom when its sectional dimensions are 6 x 6 inches or larger and approximately square. The section is called a billet when it is approximately square and less than 6 x 6 inches. Rectangular sections that have width greater than twice the thickness are called "slabs." The slab is the intermediate shape from which sheets are rolled.
HOT-ROLLING. -Blooms, billets, or slabs are heated above the critical range and rolled into a variety of shapes of uniform cross section. The more common of these rolled shapes are sheets, bars, channels, angles, I-beams, and the like. In aircraft work, sheets, bars, and rods are the most commonly used items that are rolled from steel. As discussed later in this chapter, hot-rolled materials are frequently finished by cold-rolling or drawing to obtain accurate finish dimensions and a bright, smooth surface.
FORGING. -Complicated sections that cannot be rolled, or sections of which only a small quantity is required, are usually forged. Forging of steel is a mechanical working of the metal above the critical range to shape the metal as desired.
Forging is done either by pressing or hammering the heated steel until the desired shape is obtained.
Pressing is used when the parts to be forged are large and heavy, and this process also replaces hammering where high-grade steel is required. Since a press is slow acting, its force is uniformly transmitted to the center of the section, thus affecting the interior grain structure as well as the exterior to give the best possible structure throughout.

Hammering can be used only on relatively small pieces. Since hammering transmits its force almost instantly, its effect is limited to a small depth. Thus, it is necessary to use a very heavy hammer or to subject the part to repeated blows to ensure complete working of the section. If the force applied is too weak to reach the center, the finished forging surface will be concave. If the center is properly worked, the surface will be convex or bulged. The advantage of hammering is that the operator has control over the amount of pressure applied and the finishing temperature, and is able to produce parts of the highest grade.
This type of forging is usually referred to as smith forging, and it is used extensively where only a small number of parts are needed. Considerable machining and material are saved when a part is smith forged to approximately the finished shape.
Cold-drawing operations for rod, tubing, and wire using a Drawbench.

Cold-Working
Cold-working applies to mechanical working performed at temperatures below the critical range, and results in a strain hardening of the metal. It becomes so hard that it is difficult to continue the forming process without softening the metal by annealing.
Since the errors attending shrinkage are eliminated in cold-working, a much more compact and better metal is obtained. The strength and hardness as well as the elastic limit are increased, but the ductility decreases. Since this makes the metal more brittle, it must be heated from time to time during certain operations to remove the undesirable effects of the working.
While there are several cold-working processes, the two with which you are principally concerned are cold-rolling and cold-drawing. These processes give the metals desirable qualities that cannot be obtained by hot-working.
COLD-ROLLING. -Cold-rolling usually refers to the working of metal at room temperature. In this operation, the materials that have been hot-rolled to approximate sizes are pickled to remove any scale, after which they are passed through chilled finished rolls. This action gives a smooth surface and also brings the pieces to accurate dimensions. The principal forms of cold-rolled stocks are sheets, bars, and rods.
COLD-DRAWING. -Cold-drawing is used in making seamless tubing, wire, streamline tie rods, and other forms of stock. Wire is made from hot-rolled rods of various diameters. These rods are pickled in acid to remove scale, dipped in lime water, and then dried in a steam room, where they remain until ready for drawing. The lime coating adhering to the metal serves as a lubricant during the drawing operation. Figure 1-23 shows the drawing of rod, tubing, and wire.
The size of the rod used for drawing depends upon the diameter wanted in the finished wire. To reduce the rod to the desired wire size, it is drawn cold through a die. One end of the rod is filed or hammered to a point and slipped through the die opening, where it is gripped by the jaws of the draw, then pulled through the die. This series of operations is done by a mechanism known as the drawbench.
To reduce the rod gradually to the desired size, it is necessary to draw the wire through successively smaller dies. Because each of these drawings reduces the ductility of the wire, it must be annealed from time to time before further drawings can be accomplished. Although cold-working reduces the ductility, it increases the tensile strength of the wire enormously. In making seamless steel

aircraft tubing, the tubing is cold-drawn through a ring-shaped die with a mandrel or metal bar inside the tubing to support it while the drawing operations are being performed. This forces the metal to flow between the die and the mandrel and affords a means of controlling the wall thickness and the inside and outside diameters.
Extruding
The extrusion process involves the forcing of metal through an opening in a die, thus causing the metal to take the shape of the die opening. Some metals such as lead, tin, and aluminum may be extruded cold; but generally, metals are heated before the operation is begun.
The principal advantage of the extrusion process is in its flexibility. Aluminum, because of its workability and other favorable properties, can be economically extruded to more intricate shapes and larger sizes than is practicable with many other metals. Extruded shapes are produced in very simple as well as extremely complex sections.
A cylinder of aluminum, for instance, is heated to 750°F to 850°F, and is then forced through the opening of a die by a hydraulic ram. Many structural parts, such as stringers, are formed by the extrusion process.
ALLOYING OF METALS
A substance that possesses metallic properties and is composed of two or more chemical elements, of which at least one is a metal, is called an "alloy." The metal present in the alloy in the largest proportion is called the "base metal." All other metals and/or elements added to the alloy are called "alloying elements." The metals are dissolved in each other while molten, and they do not separate into layers when the solution solidifies. Practically all the metals used in aircraft are made up of a number of alloying elements.
Alloying elements, either in small or in large amounts, may result in a marked change in the properties of the base metal. For example, pure aluminum is a relatively soft and weak metal, but by adding small amounts of other elements such as copper, manganese, magnesium, and zinc, its strength can be increased many times. Aluminum containing such other elements purposely added during manufacture is called an aluminum alloy.
In addition to increasing the strength, alloying may change the heat-resistant qualities of a metal, its corrosion resistance, electrical conductivity, or magnetic properties. It may cause an increase or decrease in the degree to which

hardening occurs after cold-working. Alloying may also make possible an increase or decrease in strength and hardness by heat treatment. Alloys are of great importance to the aircraft industry in providing materials with properties that pure metals alone do not possess.
FERROUS AIRCRAFT METALS
A wide variety of materials is required in the repair of aircraft. This is a result of the varying needs with respect to strength, weight, durability, and resistance to deterioration of specific structures or parts. In addition, the particular shape or form of the material plays an important role. In selecting materials for aircraft repair, these factors, plus many others, are considered in relation to their mechanical and physical properties.
SAE Numerical Index
Type
steel
Carbon of
Classification
Nickel
1xxx
Nickelchromium
2xxx
3xxx
Molybdenum
4xxx
Chromium
5xxx
Chromiumvanadium
6xxx
Tungsten
7xxx
Siliconmanganese
9xxx
Among the common materials used are ferrous metals. The term ferrous applies to the group of metals having iron as their principal constituent.

Identification
If carbon is added to iron, in percentages ranging up to approximately 1.00 percent, the product will be vastly superior to iron alone and is classified as carbon steel. Carbon steel forms the base of those alloy steels produced by combining carbon with other elements known to improve the properties of steel. A base metal (such as iron) to which small quantities of other metals have been added is called an alloy. The addition of other metals is to change or improve the chemical or physical properties of the base metal.
SAE NUMERICAL INDEX.
The steel classification of the Society of Automotive Engineers (SAE) is used in specifications for all high-grade steels used in automotive and aircraft construction. A numerical index system identifies the composition of SAE steels.
Each SAE number consists of a group of digits, the first of which represents the type of steel; the second, the percentage of the principal alloying element; and usually the last two or three digits, the percentage, in hundredths of 1 percent, of carbon in the alloy. For example, the SAE number 4150 indicates a molybdenum steel containing 1 percent molybdenum and 50 hundredths of 1 percent of carbon. Refer to the SAE numerical index, shown in table 1-1, to see how the various types of steel are classified into four-digit classification numbers.
HARDNESS TESTING METHODS.
Hardness testing is a factor in the determination of the results of heat treatment as well as the condition of the metal before heat treatment. There are two commonly used methods of hardness testing, the Brinell and the Rockwell tests.
These tests require the use of specific machines and are covered later in this chapter. An additional, and somewhat indirect, method known as spark testing is used in identifying ferrous metals. This type of identification gives an indication of the hardness of the metal.
Spark testing is a common means of identifying ferrous metals that have become mixed. In this test, the piece of iron or steel is held against a revolving stone or grinder, and the metal is identified by the sparks thrown off. Each ferrous metal has its own peculiar spark characteristics. The spark streams vary from a few tiny shafts to a shower of sparks several feet in length. Few nonferrous metals give off sparks when touched to a grinding stone. Therefore, these metals cannot be successfully identified by the spark test.

Wrought iron produces long shafts that are a dull red color as they leave the stone, and they end up a white color. Cast iron sparks are red as they leave the stone, but turn to a straw color. Low-carbon steels give off long, straight shafts that have a few white sprigs. As the carbon content of the steel increases, the number of sprigs along each shaft increases, and the stream becomes whiter in color. Nickel steel causes the spark stream to contain small white blocks of light within the main burst.
Types, Characteristics, and Uses of Alloyed Steels
While the plain carbon type of steel remains the principal product of the steel mills, so-called alloy or special steels are being turned out in ever increasing tonnage. Let us now consider those alloyed steels and their uses in aircraft.
CARBON STEELS.
Steel containing carbon in percentages ranging from 0.10 to 0.30 percent are classed as low-carbon steel. The equivalent SAE numbers range from 1010 to
1030. Steels of this grade are used for making such items as safety wire, certain nuts, cable bushings, and threaded rod ends. Low-carbon steel in sheet form is used for secondary structural parts and clamps, and in tubular form for moderately stressed structural parts.
Steels containing carbon in percentages ranging from 0.30 to 0.50 percent are classed as medium-carbon steel. This steel is especially adaptable for machining or forging and where surface hardness is desirable. Certain rod ends and light forgings are made from SAE 1035 steel.
Steel containing carbon in percentages ranging from 0.50 to 1.05 percent are classed as high-carbon steel. The addition of other elements in varying quantities adds to the hardness of this steel. In the fully heat-treated condition, it is very hard and will withstand high shear and wear and have little deformation. It has limited use in aircraft. SAE 1095 in sheet form is used for making flat springs, and in wire form for making coil springs.
NICKEL STEELS.
The various nickel steels are produced by combining nickel with carbon steel.
Steels containing from 3 to 3.75 percent nickel are commonly used. Nickel increases the hardness, tensile strength, and elastic limit of steel without appreciably decreasing the ductility. It also intensifies the hardening effect of heat

treatment. SAE 2330 steel is used extensively for aircraft parts such as bolts, terminals, keys, clevises, and pins.
CHROMIUM STEELS.
Chromium steels are high in hardness, strength, and corrosion-resistant properties. SAE 51335 is particularly adaptable for heat-treated forgings that require greater toughness and strength than may be obtained in plain carbon steel. It is used for such articles as the balls and rollers of antifriction bearings.
CHROMIUM-NICKEL OR STAINLESS STEELS.
Anticorrosive degree is determined by the surface condition of the metal as well as by the composition, temperature, and concentration of the corrosive agent.
The principal part of stainless steel is chromium, to which nickel may or may not be added. The corrosion-resisting steel most often used in aircraft construction is known as 18-8 steel because of its content of 18 percent chromium and 8 percent nickel. One of the distinctive features of 18-8 steel is that its strength maybe increased by cold-working.
Stainless steel may be rolled, drawn, bent, or formed to any shape. Because these steels expand about 50 percent more than mild steel and conduct heat only about 40 percent as rapidly, they are more difficult to weld. Stainless steel, with but a slight variation in its chemical composition, can be used for almost any part of an aircraft. Some of its more common applications are in the fabrication of exhaust collectors, stacks and manifolds, structural and machined parts, springs, castings, and tie rods and cables.
CHROME-VANADIUM STEELS.
These are made of approximately 0.18 percent vanadium and about 1.00 percent chromium. When heat treated, they have strength, toughness, and resistance to wear and fatigue. A special grade of this steel in sheet form can be cold-formed into intricate shapes. It can be folded and flattened without signs of breaking or failure. SAE 6150 is used for making springs; and chrome-vanadium with highcarbon content, SAE 6195, is used for ball and roller bearings.
CHROME-MOLYBDENUM STEELS.
Molybdenum in small percentages is used in combination with chromium to form chrome- molybdenum steel, which has various uses in aircraft. Molybdenum is a strong alloying element, only 0.15 to 0.25 percent being used in the chromemolybdenum steels; the chromium content varies from 0.80 to 1.10 percent.

Molybdenum raises the ultimate strength of steel without affecting ductility or workability. Molybdenum steels are tough, wear resistant, and harden throughout from heat treatment. They are especially adaptable for welding, and for this reason are used principally for welded structural parts and assemblies. SAE 4130 is used for parts such as engine mounts, nuts, bolts, gear structures, support brackets for accessories, and other structural parts.
The progress of jet propulsion in the field of naval aviation has been aided by the continuous research in high-temperature metallurgy. This research has brought forth alloys to withstand the high temperatures and velocities encountered in jet power units. These alloys are chemically similar to the previously mentioned steels, but may also contain cobalt, copper, and columbium in varied amounts as alloying elements.
NONFERROUS AIRCRAFT METALS
The term nonferrous refers to all metals that have elements other than iron as their principal constituent. This group includes aluminum, titanium, copper, magnesium, and their alloys; and in addition, such alloy metals as Monel and
Babbitt.
Aluminum and Aluminum Alloys
Commercially pure aluminum is a white, lustrous metal, light in weight and corrosion resistant. Aluminum combined with various percentages of other metals
(generally copper, manganese, magnesium, and chromium) form the alloys that are used in aircraft construction. Aluminum alloys in which the principal alloying ingredients are either manganese, magnesium, or chromium, or magnesium and silicon show little attack in corrosive environments. On the other hand, those alloys in which substantial percentages of copper are used are more susceptible to corrosive action. The total percentage of alloying elements is seldom more than
6 or 7 percent in the wrought aluminum alloys.
TYPES, CHARACTERISTICS, AND USES. -Aluminum is one of the most widely used metals in modern aircraft construction. It is vital to the aviation industry because of its high strength/weight ratio, its corrosion-resisting qualities, and its comparative ease of fabrication. The outstanding characteristic of aluminum is its light weight. In color, aluminum resembles silver, although it possesses a characteristic bluish tinge of its own. Commercially pure aluminum melts at the

comparatively low temperature of 1,216°F. It is nonmagnetic, and is an excellent conductor of electricity.
Commercially pure aluminum has a tensile strength of about 13,000 psi, but by rolling or other cold-working processes, its strength may be approximately doubled. By alloying with other metals, together with the use of heat-treating processes, the tensile strength may be raised to as high as 96,000 psi, or to well within the strength range of structural steel.
Aluminum alloy material, although strong, is easily worked, for it is very malleable and ductile. It may be rolled into sheets as thin as 0.0017 inch or drawn into wire 0.004 inch in diameter. Most aluminum alloy sheet stock used in aircraft construction ranges from 0.016 to 0.096 inch in thickness; however, some of the larger aircraft use sheet stock that may be as thick as 0.0356 inch.
One disadvantage of aluminum alloy is the difficulty of making reliable soldered joints. Oxidation of the surface of the heated metal prevents soft solder from adhering to the material; therefore, to produce good joints of aluminum alloy, a riveting process is used. Some aluminum alloys are also successfully welded.
The various types of aluminum maybe divided into two classes-casing alloys
(those suitable for casting in sand, permanent mold, and die castings) and the wrought alloys (those that may be shaped by rolling, drawing, or forging). Of the two, the wrought alloys are the most widely used in aircraft construction, being used for stringers, bulkheads, skin, rivets, and extruded sections. Casting alloys are not extensively used in aircraft.
WROUGHT ALLOYS. -Wrought alloys are divided into two classes-nonheat treatable and heat treatable. In the nonheat-treatable class, strain hardening
(cold-working) is the only means of increasing the tensile strength. Heat-treatable alloys may be hardened by heat treatment, by cold-working, or by the application of both processes.
Aluminum products are identified by a universally used designation system. Under this arrangement, wrought aluminum and wrought aluminum alloys are designated by a four-digit index system.
The first digit of the designation indicates the major alloying element or alloy group, as shown in table 1-2. The lxxx indicates aluminum of 99.00 percent or greater; 2xxx indicates an aluminum alloy in which copper is the major alloying element; 3xxx indicates an aluminum alloy with manganese as the major alloying

element; etc. Although most aluminum alloys contain several alloying elements, only one group (6xxx) designates more than one alloying element.
In the 1xxx group, the second digit in the designation indicates modifications in impurity limits. If the second digit is zero, it indicates that there is no special control on individual impurities. The last two of the four digits indicate the minimum aluminum percentage. Thus, alloy 1030 indicates 99.30 percent aluminum without special control on impurities. Alloys 1130, 1230, 1330, etc., indicate the same aluminum purity with special control on one or more impurities.
Likewise, 1075, 1175, 1275, etc., indicate 99.75 percent aluminum.
Designations for Aluminum Alloy Groups
Aluminum – 99.0 percent minimum and greater……………………………………………….1xxx
Aluminum Alloys, grouped by major alloying elements
Copper……………………………………………………………………………………………………2xxx
Manganese……………………………………………………………………………….………….…..3xxx
Silicon……………………………………………………………………………………………………..…4xxx
Magnesium………………………………………………………………………………………………..5xxx
Magnesium and silicon…………………………………………………………………………………6xxx
Zinc ………………………………………………………………………………………………………….7xxx
Other elements………………………………………………………………………………………….8xxx
In the 2xxx through 8xxx groups, the second digit indicates alloy modifications. If the second digit in the designation is zero, it indicates the original alloy, while numbers 1 through 9, assigned consecutively, indicate alloy modifications. The last two of the four digits have no special significance, but serve only to identify the different alloys in the group.
The temper designation follows the alloy designation and shows the actual condition of the metal. It is always separated from the alloy designation by a dash.
The letter F following the alloy designation indicates the "as fabricated condition, in which no effort has been made to control the mechanical properties of the metal,
The letter O indicates dead soft, or annealed, condition.

The letter W indicates solution heat treated. Solution heat treatment consists of heating the metal to a high temperature followed by a rapid quench in cold water,
This in an unstable temper, applicable only to those alloys that spontaneously age at room temperature, Alloy 7075 may be ordered in the W condition.
The letter H indicates strain hardened, cold-worked, hand-drawn, or rolled.
Additional digits are added to the H to indicate the degree of strain hardening.
Alloys in this group cannot be strengthened by heat treatment, hence the term nonheat-treatable.
The letter T indicates fully heat treated. Digits are added to the T to indicate certain variations in treatment.
Greater strength is obtainable in the heat-treatable alloys. They are often used in aircraft in preference to the nonheat-treatable alloys. Heat-treatable alloys commonly used in aircraft construction (in order of increasing strength) are 6061,
6062, 6063, 2017, 2024, 2014,7075, and 7178.
Alloys 6061, 6062, and 6063 are sometimes used for oxygen and hydraulic lines and in some applications as extrusions and sheet metal.
Alloy 2017 is used for rivets, stressed-skin covering, and other structural members.
Alloy 2024 is used for airfoil covering and fittings. It may be used wherever 2017 is specified, since it is stronger.
Alloy 2014 is used for extruded shapes and forgings. This alloy is similar to 2017 and 2024 in that it contains a high percentage of copper. It is used where more strength is required than that obtainable from 2017 or 2024.
Alloy 7178 is used where highest strength is necessary, Alloy 7178 contains a small amount of chromium as a stabilizing agent, as does alloy 7075.
Nonheat-treatable alloys used in aircraft construction are 1100, 3003, and 5052.
These alloys do not respond to any heat treatment other than a softening, annealing effect. They may be hardened only by cold- working.
Alloy 1100 is used where strength is not an important factor, but where weight, economy, and corrosion resistance are desirable. This alloy is used for fuel tanks, fairings, oil tanks, and for the repair of wing tips and tanks.

Alloy 3003 is similar to 1100 and is generally used for the same purposes. It contains a small percentage of manganese and is stronger and harder than 1100, but retains enough work ability that it is usually preferred over 1100 in most applications.
Alloy 5052 is used for fuel lines, hydraulic lines, fuel tanks, and wing tips.
Substantially higher strength without too much sacrifice of workability can be obtained in 5052. It is preferred over 1100 and 3003 in many applications.
Alclad is the name given to standard aluminum alloys that have been coated on both sides with a thin layer of pure aluminum. Alclad has very good corrosionresisting qualities and is used exclusively for exterior surfaces of aircraft. Alclad sheets are available in all tempers of 2014, 2017, 7075, and 7178.
CASTING ALLOYS.
Aluminum casting alloys, like wrought alloys, are divided into two groups. In one group, the physical properties of the alloys are determined by the elements added and cannot be changed after the metal is cast. In the other group, the elements added make it possible to heat-treat the casting to produce desired physical properties.
The casting alloys are identified by a letter preceding the alloy number. This is exactly opposite from the case of wrought alloys, in which the letters follow the number. When a letter precedes a number, it indicates a slight variation in the composition of the original alloy. This variation in composition is made simply to impart some desirable quality. In casting alloy 214, for example, the addition of zinc, to increase its pouring qualities, is designated by the letter A in front of the number, thus creating the designation A214. When castings have been treated, the heat treatment and the composition of the casting are indicated by the letter
T and an alloying number. An example of this is the sand casting alloy 355, which has several different compositions and tempers and is designated by 355-T6,
355-T51, and A355-T51.
Aluminum alloy castings are produced by one of three basic methods-sand mold, permanent mold, and die cast. In casting aluminum, in most cases, different types of alloys must be used for different types of castings. Sand castings and die castings require different types of alloys than those used in permanent molds.

SHOP CHARACTERISTICS OF ALUMINUM ALLOYS.
Aluminum alloys are the most workable of all the common commercial metals. It can be fabricated readily into a variety of shapes by any conventional method; however, formability varies a great deal with the alloy and temper.
In general, the aircraft manufacturers form the heat-treatable alloys in the -0 or -
T4 condition before they have reached their full strength. They are subsequently heat-treated or aged to the maximum strength (-T6) condition before installation in aircraft. By this combination of processes, the advantage of forming in a soft condition is obtained without sacrificing the maximum obtainable strength/weight ratio.
Aluminum is one of the most readily weldable of all metals. The nonheat-treatable alloys can be welded by all methods, and the heat-treatable alloys can be successfully spot welded. The melting point for pure aluminum is 1,216°F, while various aluminum alloys melt at slightly lower temperatures. Aluminum products do not show any color changes when heated, even up to the melting point.
Riveting is the most reliable method of joining stress-carrying parts of heattreated aluminum alloy structures.

The following unit on Welding Symbols was created by the Delta School of Trades
( http://deltaschooloftrades.com/welding_symbols.htm )
INTRODUCTION
Welding symbols are used on blueprints and drawings to show where the weld is to be placed and may also show the size, type of weld, number of
welds, details about the weld and even details about the joint.
Welders that fabricate or work with drawing must be able to interpret the welding symbol to prepare the joint and apply a weld that has the
required strength and soundness.
THE REFERENCE LINE AND ARROW
The reference line is one of the most important elements on the welding symbol. All the other elements that describe the weld are on or located around this line. The reference line has a leader and arrow that points to where the information applies. It may also have a tail that has information about the process, specification, or other notes that do not normally have an element that describes them. If the elements on the reference line describe the necessary details (as it does in most cases)
the tail is not used.
See the examples below:
In the above examples one of the reference lines has multiple arrows that are used to show the same weld in three locations that are relatively close to each other. There is also a reference line that has an arrow break. The break in the arrow is used to indicate the joint member that is
to receive the edge preparation.

KEY POINT: the arrow points to the bevel where the bevel needs to be prepared.
ARROW SIDE
One of the most important things about the reference line and the welding symbol is the top and bottom of the horizontal line. The actual symbol that shows the type of weld and the elements surrounding it that detail the weld can be placed either on the top of the line or on the
bottom of the line.
KEY POINTS: symbols on the bottom of the reference line mean weld the side of the joint the arrow is touching or pointing to. Symbols on the top of the reference line mean apply the weld to the other side of the joint, or the side opposite to where the arrow is pointing.
This method is used because sometimes the welding symbol must be drawn on the blueprint on the other side of the joint. When symbols appear on both sides of the reference line it means weld both sides of the joint.
If the reference line has a weld symbol on both sides of the reference line they may, or may not be the same weld on both sides of the joint.
Remember the rule to apply the right weld to the right side.
See the examples:
OTHER ELEMENTS ON REFERENCE LINE
There are two other elements that may be seen on the reference line that provide information about the weld. One is a circle around the place where the leader line connects to the reference line and indicates the weld is “ ALL AROUND ”. This means the weld extends all the way around
the joint the arrow is pointing at.

KEY POINT: The all-around element is only used when it is possible to weld all the way around a single surface. Otherwise more than on symbol is used.
The other element seen on the reference line resembles a flag and is located where the leader line joins the reference line. This element is called a field weld and means the weld will be done in another location.
For instance, this weld may be applied at the job site not in the shop.
Sometimes clarification will be given in the welding symbol tail or as a
specification on the print.
THE FILLET WELD
The fillet weld symbol is one of the most widely used symbols and the shape placed on the reference line to indicate a fillet weld is a triangle
that resembles the side profile of a fillet weld.
The examples of the weld all around and field weld above show a fillet
weld symbol so that the weld to be applied in both cases is a fillet weld.
The names of the parts of the fillet weld
KEY POINT: Fillet sounds like fill it (pronounce the T) not fillay as in fillet a fish.

The important elements added to a simple fillet weld symbol are as
follows;
1.
THE SIZE OF THE WELD.
2.
THE LENGTH OF THE WELD.
3.
THE LENGTH AND PITCH OF INTERMITTENT WELDS.
4.
THE CONTOUR REQUIREMENTS.
1.
THE SIZE OF THE WELD.
The size of the fillet weld is determined by the legs of the triangle shape
which represent the legs of the fillet.
A welded piece may have a different weld size on each side or they may
be the same size.
Sometimes (not often) a weld of unequal legs may be required. For
example: if one member of the joint is thinner than the other.
If no size is shown on the fillet weld, a size for all fillets will be given on
the drawing as a note or specification.

KEY POINT: Making the fillet welds the wrong size may lead to costly rework if you are not sure ask for clarification.
2.
THE LENGTH OF THE FILLETWELD.
The length of the weld when it is not a continuous weld is shown by a number on the right side of the fillet weld triangle. If it is not obvious the
location is detailed on the drawing.

3. THE LENGTH AND PITCH OF INTERMITTENT WELDS
An intermittent weld is one that is not continuous across the joint, but rather is a given length of weld separated by a given space between them. This method of welding may be used to control heat distortion or where the joint strength requirements allow. Intermittent welding can
save time and money if a long weld is not necessary.
Used more frequently than the length alone, the length and pitch are two
numbers located at the right of the fillet weld symbol.
The length appears first as before followed by a hyphen then the pitch is
shown.
The pitch refers to a dimension from the center of one weld to the center
of the next weld.
KEY POINT: The pitch is not the space between welds but a measurement from center to center of the welds. To get the spacing for layout subtract the length of one weld from the pitch.
The intermittent welds may be chain intermittent or staggered intermittent. Chain intermittent the welds on both sides of the joint are opposite each other and resemble a chain. Staggered intermittent the welds on the opposite side are usually started in the gap between the
welds on the first side. The welds then appear staggered.
KEY POINT: If the welds are staggered the fillet weld symbol will be staggered on the reference line.

4.
THE CONTOUR REQUIREMENTS
Some welding symbols may show a contour finish that details how the fillet weld shape must be finished after welding. The contour may be flat or convex and the element to describe this is placed above the slope on the fillet weld symbol. A letter to indicate the method of finish may be
given above the finish element.
A letter U may be used to designate an unspecified finish, when the
choice of finishing is given.

SUMMARY
When reading a fillet weld symbol always make sure you know what side of the joint the weld is applied to. Fillet weld symbols on the bottom of the reference line mean apply the weld to the side of the joint the arrow points to. Fillet weld symbols on the top of the reference line mean apply the weld to the opposite side of the joint. Fillet weld symbols on both sides of the reference line mean apply weld to both sides of the joint.
This remains the case regardless of how the break in the arrow is drawn.
The size of a fillet weld is determined by the length of the leg of the fillet weld and is shown on the symbol to the left.
If two numbers appear in parenthesis the legs are unequal, check the drawing for clarification.
When a length of weld is shown on a fillet weld symbol the dimension is placed on the right side.
When two numbers appear separated by a hyphen, the length is indicated first then the pitch. The pitch is the distance from the center of one length of weld to the center of the next length of weld.
When finishing directions are shown they appear over the slope of the fillet weld symbol.
GROOVE WELDING SYMBOLS
Groove welding symbols are used to show how butt joints are prepared for welding and to detail how the weld is to be applied. When two pieces of metal, other than sheet metal or thin sections, are butted together for welding they usually have some form of a groove to allow the weld to
penetrate into or through the joint.
The groove is formed by preparing the edges to be welded with a bevel edge, chamfer edge, double bevel edge, J groove edge or double J groove
edge.

When the butt joint has no edge preparation it is referred to as a square
groove.
The typical edge preparations are shown below:
The edge preparations may be assembled as either open root, with a
backing bar or by utilizing the back weld or backing weld application.
The open root assembly allows penetration through the joint, while the backing bar is used for easier welding. The backing bar may be removed
or may be a part of the joint.
The backing weld is applied before welding and acts as a backing bar, while the back weld is applied after welding to finish the back side of the
joint. Before applying the back weld a grinder or other method may be
used to prepare a V.

The edge preparations may be assembled in any configuration to form the groove for welding from either one side or both sides. The most
common configurations and their basic symbols are shown below.
KEY POINT: If two imaginary lines are drawn parallel to the horizontal line in the above symbols they show the joint shape, this is true for most of the symbols. This can be helpful to remember since symbols on a blueprint do not show the actual joint shape or edge preparation.
KEY POINT: The Groove welding symbols have the same placement relevance on the reference line as the fillet weld. Symbols on the bottom of the reference line mean weld the side of the joint the arrow is touching or pointing to, while symbols on the top of the reference line mean weld the opposite side of where the arrow is touching or pointing to.
If it is not clear always ask someone; reworking welds is costly and time consuming.

GROOVE WELDING ELEMENTS
GROOVE WELD SIZE
The groove weld size is given in two dimensions and like the fillet weld it
is placed to the left of the weld symbol.
The first size given is THE DEPTH OF GROOVE and is the dimension used
to prepare the edge preparation.
The depth of groove is measured from the surface of the joint to the
bottom of the preparation.
KEY PONT: The depth of groove does not include weld reinforcement or root penetration.
The second size given is the ACTUAL WELD SIZE and is enclosed in
parentheses to distinguish it from the groove size, or depth of groove.
The actual weld size is again measured from the surface of the groove through the bottom of the groove but now includes the expected
penetration of the weld. On a square groove only the weld size is given.
The weld size does not include face reinforcement or root reinforcement.
KEY POINT: The penetration into the joint shown on the weld size is not measurable by the naked eye but is given to provide information about the expected outcome.

ROOT OPENING AND GROOVE ANGLE
Two other important elements for preparing and welding the groove are
the root opening and the groove angle.
The root opening, when used, dimensions the space between the joint to
be welded and is placed inside the weld symbol.
The groove angle is also placed inside the weld symbol and is given in
degrees.
KEY POINT: The groove angle for a V groove is given as the INCLUDED angle so that means the edge bevel or chamfer for each piece is 1/2 of the degrees given. For example; A 45 degree included angle means bevel each member at 22 1/2 degrees.
J grooves angles may be detailed elsewhere on the drawing.
The root opening and groove angle are separate elements and may or may not appear together depending on the joint requirements.
On some drawings the root opening or groove angle will be covered in a note or specification on the drawing for all similar symbols, and does not appear on the symbol.
The Welder must always read all information given on a drawing.

CONTOUR AND FINISHING
The same contour symbols that apply to fillet welds may be used with
groove welding and are placed above the weld symbol.
BACKING BARS BACK WELDS AND SPACERS
As previously mentioned in this section some joint configurations may have a backing bar or spacer for easier welding or may employ the back
or backing weld technique.
The elements for these are placed on the bottom of the reference line opposite the weld symbol or in the case of the spacer on the reference
line.
KEY POINT: If the backing bar is to be removed the symbol will contain an R for remove after welding.
Since the back and backing weld symbol look the same you must look for details to see which weld applies.
Spacers may be removed before the second side is welded or they may become part of the joint.

SUMMARY
The groove weld symbols are used to provide information for preparing and welding the groove; however, they cannot always show every intended operation and often notes or specifications are used on the drawing. The welder should read the entire drawing before making a weld to avoid costly rework. Whenever you see something you are unfamiliar with check with engineering or supervision for clarification.
It is critical to produce the right size fillet and groove weld for the application so check sizes with weld gages.

The following information is derived WA Technology ( www.netwelding.com
)
Why Do Welders Need Math?
To become a highly skilled welder it is desirable to understand some welding math and basic welding physics. It is presented here in a way that doesn’t make it painful!
It Could Be Tougher
Imagine trying to do math in Roman Numerals! Actually addition is not a big problem you just put all the letters together and rationalize extra letters denoting numbers; for example if you have three V (5‟s) they would be restated as XV for
10 and 5. However division is much more difficult and a Roman “Calculator” called a „”Counting Board” is needed. Pebbles are placed in numbered boxes etc. As for fractions, the Romans didn’t have a way to write them as numbers. They would state fractions in words, for example as in the case of a ruler defining 3/16;
“three of 16 parts.” In fact maybe they made understanding fractions easier - they just said what they represented; “divide a unit in 16 parts and count only 3 of them!” You can Google Roman Numeral math if interested.
How To Read A Ruler (Includes Basics of Fractions and Common Metric
Conversions)
Reading a ruler in US Units requires working with Fractions. If the Metric
System was being used it would not - but more on Metric below.
Rulers and measuring tapes are commonly calibrated in feet and inches.
Instead of segmenting the foot into 10ths of a foot it is divided into 12 parts labeled inches.
The inch is commonly split into 8, 16 or sometimes 32 parts. Therefore working with fractions is a necessity. A fraction of an inch is a mathematical way of showing the number of the parts into which it is divided. For example, 3/8 inches is a way of showing a measure of 3 of the 8 parts into which it was divided.
This picture is an example of an inch split into 8 parts or eighths.

The yellow arrow is pointing to the third line from the start or the 3rd of 8 parts stated as 3/8. It’s shown with a division line because we could divide 3 by 8 and get 0.375 the decimal value. Now if the number of segments and the total number of segments into which the inch mark was split were always stated, fractions would be relatively easy-but it is not that easy!
This example on the shows the 4th of the 1/8 inch marks in red.
Since 4 is 1/2 the way to 8, it is the 1/2 inch mark. We could have said 4/8 which is the same as saying 1/2 . It is usually desired to display the fraction by having the lowest whole number at the bottom.
If the bottom number (called the denominator) can be divided by the number on top (called the numerator) and a whole number is the result -the fraction would have the lowest number possible in the denominator.
Looking at this picture and counting from the start or zero mark there are 6 spaces or 6/8 of an inch.

Dividing 8 by 6 produces 1.333 which is NOT a whole number (one with no decimal left over.) However both numbers can be made smaller. Any number or fraction can be multiplied or divided by 1 without changing its value. This can be accomplished by multiplying or dividing both the numerator and denominator by the same number. Both the numerator and denominator could be multiplied by 2
(actually 2/2) that would give 6 * 2= 12 for a numerator and 8 * 2 or 16 for the denominator. The fraction would become 12/16. That would be accurate and a person could be told to go cut a steel rod 12/16 of an inch long. However the objective is to have the smallest numbers. Both numerator and denominator could be divided by 2. That would give 6/2 = 3 for a numerator and 8/2=4 for a denominator. The fraction now becomes 3/4. It is the same value as 6/8 but with smaller numbers.
Notice on the ruler there are some lines longer than others. In this case the longest lines are quarters of an inch rather than eighths. Three of these longest lines could have been counted and it would be found more quickly as the third quarter or the 3/4 mark! However we must have common numbers in the denominator (bottom numbers) if two dimensions are to be added. Suppose two items are to be measured and a total length presented. If one is ¾ inches and the other 3/8 inches what is the total length? Quarters and eights cannot be added directly. It is best to convert all measurements to the largest denominator.
Therefore 3/4 becomes 6/8 (remember the numerator and denominator can always be multiplied by the same number which is really multiplying the fraction by 1.) The result is 6/8 + 3/8. The picture left shows the answer graphically. But let’s get the answer using math. To add fractions 6 of the eight parts are being added to 3 of the eight parts. So only add the numerator values (top numbers.)
Therefore 6 + 3 = 9, or 9 eights. Stated as a fraction, it is 9/8. Whenever the numerator is bigger than the denominator the numerator can be divided by the denominator to change to a whole number and possibly a fraction remainder. In this case, 8 goes into 9 once with one left over or 8/8 + 1/8 or 1 1/8 inches. This mark can be seen on the ruler as one space after 1 inch. There would be nothing wrong with saying the answer was 9/8 but suppose the result was 13 inches and
3/8 inches. It could be stated as 13 * 8 or 104/8 + 3/8 or 104 + 3 = 107/8.
However if it was necessary to measure using that dimension it would be a lot of
1/8’s for someone to count!
A 1 inch ruler mark could also be split into 16 segments.

This is a common way to make a ruler or tape. These smaller marks are still easy to read (compared to splitting it into 32 parts as is done with some steel rulers.)
The picture shows this segmentation with the 1/8 inch marks and the
1/4 inch marks shown as longer red lines.
The 1/16 inch marks shown in black are the shortest. This makes it easier to read quickly.
A tape measure is the same as a ruler except it is longer and flexible. There are also some interesting things to note about most metal tapes. This picture is a magnified section of a ruler.
This ruler is segmented into 1/16ths or 16 segments in an inch. It is also labeled in feet as well as inches. If a measurement is to be made to the yellow arrow it is located at the 12 inch or 1 foot mark plus 3 spaces. therefore there are 12 inches and 3/16 inches from the end of the ruler to the yellow mark. The mark is said to be 12 and 3/16 inches or 1 foot 3/16 inches-both would be correct.

There are a few other things that should be understood about a tape measure:
As seen in this picture there is a metal tab at the start end of the tape.
It is usually attached with two rivets. However it is loose. Do not tighten these rivets with a hammer! The tab is loose for a reason.
If you’re making what is known as an “inside” measurement after the tape is locked in position (with black button on top) the tape is pushed with a slight force into the part to be measured. The tab moves in toward the ruler and provides an accurate measurement by properly positioning the zero location.

In this photo the tape is being used to measure from the outside edge of an item.
The tape is pulled slightly away from the edge being measured and the tab moves slightly to the left in this case. It moves the thickness of the tab so that the zero point is now on the inside or from the photo the right side of the tab. This places the zero location as necessary to have it measure properly.

Another item that is often included on most tape measures is the exact width of the tape holder and it is printed on the side of the body. In the picture above it is shown as 3 inches. (it is also shown as 76 mm which is the approximate metric equivalent.) If the distance between a door jam was to be measured, for example, the tape could be placed in the space, pushing the end slightly into one door jam as defined above to have the tab properly positioned. The back of the tape holder is placed against the other side of the door jam. The tape could be read at the front (see “Read Tape Here” in above picture) and in this case add 3 inches to account for the tape holders body size. So if 33 and 9/16 inches was read then the actual dimension would be 33 + 3 added so the final dimension would be 36 and 9/16 inches. Now if the ruler was only 2 1/2 inches wide then the actual dimension would be 33 and 9/16 plus 2 1/2 inches. The whole inch measurements could be added, therefore 33 + 2=35. However to add 9/16 to ½ requires stating the 1/2 as 8/16 inches. Then 9/16 + 8/16= 17/16. Since the numerator is larger than the denominator we can divide the numerator by the denominator and obtain 1 with 1/16 left over. Then the final dimension is stated as 33+2+1 and 1/16 or 36 and 1/16 inches or dividing 36 inches by 12 in/ft = 3 feet 1/16 inches.
Metric:
Metric Units (now called SI for international Standard) are used by about every country accept the US. Many items such as cars and trucks made and purchased in the US today use SI dimensions, bolts etc!
Metric is actually a simpler system and does not use fractions! All units are in
10ths. The basic length measure is the meter (slightly longer that a yard.) The preferred unit smaller than a meter is a 1000th of a meter called a millimeter (the

abbreviation is mm.) 100rdth of a meter is called a centimeter (abbreviated as cm). A cm = 10 mm's. Everything is expressed in 10ths or multiples of
10. The ruler in the above left picture is dual dimensioned; it shows inches on top and metric on the bottom. The top is segmented in 1/16th of an inch with the number of inches displayed. The metric is labeled centimeters with segments in millimeters.
This picture shows a conversion from 20 inches to metric.
The ruler has both US Units and metric units. As noted, 20 inches must be multiplied by the conversion factor of 1 inch = 25.4 mm. Therefore 20 inches =
508 mm. Then 508 mm divided by 10 mm/cm = 50.8.
Note all we have to do to divide by 10 is move the decimal over 1 place. That yields 50.8. Or 50 cm and 0.8 cm. But a cm is 10 mm. So it could be written as
50.8 cm or 50 cm + 8 mm.

Below are some Common Welding Metric Conversions

Calculate Shielding Gas Waste
The table below provides a way to estimate MIG shielding gas waste. The data needed can be obtained from purchasing or your supplier of wire and shielding gas. Use purchases over a period of 6 months to a year to avoid introducing errors due to variable amounts of inventory.
Notes:
1) If you’re using CO 2 it probably is purchased in pounds. You'll need cubic feet
(CF) in the calculations; there are 8.74 CF per pound of CO 2
2) Argon is usually sold in CF or in 100 CF- if you are purchasing Argon in Liquid form you may be purchasing it in gallons. If so there are 113 CF of Argon gas when measured at 70 deg F and 1 atmosphere in each liquid gallon; 3) If the welding wire purchase records are only kept in dollars, you'll need the cost per pound. If needed ask your supplier as they keep the data in a form that you can use directly.
TYPICAL SHIELDING GAS TO WIRE PURCHASE RATIO
Wire
Type
Solid
Solid
Cored
Cored
Size
.035
.045
.035
.045
Typical
Lbs/hr
3.5
7.0
6.5
7.5
CF Gas/ 1 lb
Wire Purchased
10 CF
5.0 CF
5.5 CF
5.0 CF
Cored
Cored
1/16
3/32
11.0
14.5
3.5 CF
2.5 CF
Compare the typical values in the above table with your usage.
Example: You purchased 46,000 lbs of 0.045 solid wire in the past 6 months and during the same period 610,000 CF of Argon and CO2 combined:
1. Multiply the value from the far right column in the above table times the wire purchase amount; 5.0 CF/ 1 pound X 46,000 lb of wire purchased = 230,000 CF of gas you should have purchased.
2. But you purchased 610,000 CF of gas. Therefore 610,000 – 230,000 =
380,000 CF was wasted or 380,000 Wasted / 610,000 Purchased = 62% Gas
Wasted!

If you use several types of wire, treat each individually and add the total gas requirements.
Dealing With Percentages:
Reviewing a fabricators test measurement of Gas Flow and Savings when using our patented Gas Saver System shows ways to deal with percentages:
Texas Truck Storage Box Manufacturer Welds 2.7 Times More Parts with
Gas Saver System; a 63% Gas Savings
A Texas based manufacturer of various types of truck storage boxes purchased one of our patented 25 foot Gas Saver Systems (GSS) (WAT- FB25) to check for shielding gas savings. They picked a repetitive job, welding doors, and started with a full cylinder of gas. Welding with 0.035 solid wire MIG, using their standard gas delivery hose, 236 doors were completed with that cylinder. Putting on a new cylinder and the GSS, with no other changes, 632 doors were welded before the cylinder was empty! That is 632/236 = 2.7 times more parts.
The gas savings can be stated several ways. In the base test, with the normal gas delivery hose, 300 CF of gas was consumed welding 236 parts. With the GSS they consumed only 300 CF x 236/632 = 112 CF for that same number of parts.
Therefore;
300 CF - 112 CF = 188 CF is wasted with their normal system! And the GSS still provides the proper amount of extra gas at the weld start and maintains the pressure in the hose to automatically compensate for restrictions.
Calculating the gas savings as a percentage of prior use; (300 -112)/300 = 63%
gas savings. Or said another way it takes 300/112 = 268% more gas to weld the same number of parts. After these impressive results, 25 GSS's were purchased for the whole shop.
Stated another way; to weld 632 doors with their standard system they would have needed 2.7 cylinders versus only one with the GSS !! After several years of use they needed another 10 GSS's for new MIG welders. They asked for more
"Magic Hose!"
Note, there are a number of ways to use Percentage. Just be sure they are stated correctly, i.e. the same numbers yielded 268% more or 63% less etc. The same data can be presented both ways.

A Shielding Gas Leak Means Air is Leaking Back!
A phenomenon called the law of partial pressures was developed by John Dalton
(Born 1766). He found that a mixture of gases behaves as if each were separate.
Dalton‟s Gas Law: He observed that the Total Pressure of a Gas Mixture was the sum of the Partial Pressure of each gas.
P total = P1 + P2 + P3 + .......Pn
The Partial Pressure is defined as the pressure of a single gas in the mixture as if that gas alone occupied the container. In other words, Dalton maintained that since there was an enormous amount of space between the gas molecules within the mixture that the gas molecules did not have any influence on the motion of other gas molecules, therefore the pressure of a gas sample would be the same whether it was the only gas in the container or if it were among other gases.
Since there is no Nitrogen in a shielding gas hose the partial pressure of Nitrogen in the hose is 0. Since there is 78% Nitrogen in the surrounding air, the partial pressure of Nitrogen is 14.7 psia x .78 =11.5 psia. Therefore there is a driving force for the Nitrogen to reach equilibrium of 11.5 psia into the hose leak! It will not move as fast as the Argon coming out which may have a driving force of say
25 psig + 14.7 psi = 39.7 psia versus 0.009 x 14.7= 0.13 in the air. Or a driving force of 39.6 psia which is 3.4 times as much but very little Nitrogen in the gas stream is needed to cause problems.
If welding a material needing a low hydrogen deposit is being used and leaks are present in gas lines, hoses or fittings hydrogen from moisture laden air is entering back though those leaks!
Another way to think about Oxygen, Nitrogen or water vapor going back through the hole in our gas delivery hose where an Argon or CO2 based shielding gas is leaking out is to consider Dalton‟s statement.
“The gas molecules are spread far apart. The Oxygen, Nitrogen or H2O vapor will not likely hit an Argon or CO2 molecule on its journey through the hole! To provide a picture of how far apart say Argon atoms are at atmospheric pressure as they escape from a leak consider: The density of Argon at room temperature and atmospheric pressure is 787 times less than liquid Argon. Therefore the spacing between Argon atoms in the gas is 787 times larger than in Argon Liquid!
Pretty far apart!

Calculate Weld Metal Volume (and other formula)
First some formula to calculate Area:
The basic formula for the Area of Rectangle is: L (length) * W (width) = Area
(Note: We'll use * to indicate multiply since that is what is used on a
Spreadsheet.)
Here is a neat way to check your answer called Dimensional Analysis. Big word but it means checking the dimensions to be sure the result is what you are looking for and helps to be sure your formula is correct:
In this case: L inches * W inches = Area inch 2 (Since in * in = in 2 )
Dimensional Analysis verifies you correctly multiplied in * in and got in 2
Note: a Square is a special case of a rectangle where both sides are the same so the area can be stated as one side times itself or
Area = S 2 (Length of a side squared)
Let's now define the Volume of a Rectangular Block.
W in * L in * D (Depth) in = Volume in 3
We multiplied three dimensions in inches so got in 3 or cubic inches as an answer.

The following are some formula for calculating the area of additional shapes we’ll use to define weld volume in a joint:
For Triangle : Area = B * H / 2
Note it is like calculating the Area of a Rectangle and dividing by 2.
This formula works for any size and shape Triangle. Look at the Triangle below left. Below right are picture examples that help show why this equation works for any shape Triangle:
By duplicating the Blue Triangle and rearranging pieces we can construct a rectangle:
1) In the top picture the Blue Triangle is copied and turned upside down
It is shown in Green.

2) In the middle picture we make a small Red Triangle to create a straight perpendicular side on the Blue Triangle.
3) In the bottom picture the Red Triangle is moved to the left side making a straight side on the Green Triangle.
4) That makes a Rectangle with one side still equal to B and the other H.
5) The AREA as defined for a Rectangle is B * H. But remember we duplicated the Blue Triangle so to get the AREA of the Original Blue
Triangle we have to divide by 2 hence the formula: Area = B * H / 2
Area of a Segment (Weld Reinforcement)
This is one Area that is often used in calculating weld metal area and volume; it is called the area of a Circle Segment and shown in Red on the photo left. This is what is used to calculate the area of Weld Reinforcement. The accurate way to do this is to calculate the area of a segment of Radius R (that is the
combined Green and Red Areas;) use the length of the Cord W (width of weld) and subtract the area of the triangle formed by the Cord and distance from the Center of the Circle and the Cord (the Green Area.) This leaves the
Area between the Cord and the Outer Area of the Circle (Red Area) or Weld
Reinforcement in our case. However we would have to estimate the Radius of the circle making the reinforcement and the angle of that Segment. Not an easy item to estimate. Since we know the weld bead height (or the desired maximum height by code, usually 3/32 or 1/8 inch) and the weld height is much smaller than the weld width we can use a method that estimates the area and is probably better than estimating the radius.
The formula is (approximately):
Area of a Segment (Weld Reinforcement)= (2 H*W)/3+H 2/2W

Since weld reinforcement is not a perfect circle, the value obtained is sufficiently accurate for any engineering calculations needed. In fact since weld reinforcement is not a portion of a perfect circle this approach may be closer to the actual area/volume! Having checked several typical weld reinforcements dimensions you can use 72% of the Area of a Rectangle for the estimate
of reinforcement.
With these basic shapes you can calculate the area of almost all welds.
Look at the following examples of the of weld joints; the weld area can be arranged into Triangles, Rectangles and Segments.
To calculate the weld metal volume that must be added to a weld joint you simply multiply the Area times the Length in the same dimensions. Therefore if the length is given in feet convert it to inches so all dimensions are in inches.
Therefore Area in 2 * Length in = Volume in 3 . Remember dimensional analysis works to check your work in 2 * in = in 3 .
Calculate Pounds of Welding Materials Needed:
Now the Volume of weld metal you will need to add is known , how much wire will you need? The following are some material densities:
Steel weights: 0.284 lb/in3; Aluminum = 0.098 lb / in3 depending somewhat on alloy and Stainless Steel 0.29 lb / in3 again depending on the alloy.
So to get lbs of weld metal needed do you just multiply the volume by the density of the material?

Is that how much you should purchase?
No! You Must Account for Losses.
For example when Stick Welding the electrode purchased includes flux, you will also throw away the stub and some of what you are depositing will become wasted spatter.
The factor that estimates the amount of welding electrode purchased that deposit as weld metal is called Deposition Efficiency. Stick Electrodes, as you would expect, have the lowest values. Depending on the length, type of electrode and the amount of stub being thrown away the Deposition Efficiency can vary from as low as 40%, meaning only 40% of what you purchase will become weld metal to a high of 60%. For general calculations you can use 50%.
The following are some values you can use for various welding processes:
Submerged Arc Welding = 99% for wire
MIG Welding with Solid Wire = 97% with Argon Based Shielding and 96% with CO 2
MIG Welding with Metal Cored Wire = 94%
Gas Shielded Flux Cored Wire Welding = 90 to 93%
Self-Shielded (Gasless) Flux Cored Wire Welding = 78 to 80%
Stick Electrode Welding = ~50% +/- 10%
Therefore divide the weld metal needed by the Deposition Efficiency (as a decimal, i.e. 93% = 0.93) to get how much of the particular filler material being used needs to be purchased.
What Causes MIG Welding Wire to Melt?
Hint: this is what it is NOT; a) the “hot arc”, b) radiation from the arc or c) the wire passing through the arc.
Two phenomena are primarily responsible for wire melting:
1. The first reason is wire stickout. As the wire passes from the end of the
MIG gun contact tip to the arc, it is carrying all the welding current and becomes very hot. It starts at room temperature and can exceed 500 degrees F before the arc forms at the end (depending on the "sickout," the distance between the tip and the work piece.)
2. The second reason it melts is that current leaving or entering a surface, be it wire or hot puddle, requires a given amount of energy for the electrons
to enter or leave that surface. This energy, generated at the surface, melts the already hot wire. Therefore assuming Electrode Positive this is referred

to as Anode Potential (also called Work Function and measures as voltage) and is equal to the Amps x Anode Voltage.
The following equation obtained from Reference (1) page 3, defines the relationship:
Wire Melting Rate (lbs/hr) = a * Amps + b * Wire Stickout * Amps 2
Where "a" and "b" are constants and "Wire Stickout" is the distance from the torch contact tip to the work piece measured in inches. (Note, constant b has been modified to compensate for the fact that this equation was based on
"Electrode Extension” that is measured to the top of the arc.)
The values for "a" and "b" for 0.035 inch diameter carbon steel wire are: a = 0.017; b = 0.00014
These two energy sources cause the wire to melt. The first term (a * Amps) is the anode voltage times current and the second term defines the energy input due to resistance heating.
EFFECT OF CURRENT ON PENETRATION
A major implication of the wire melting relationship is with increased stickout (at a fixed wire feed speed) amperage will decrease. That has a significant effect on another parameter, weld penetration.
Weld penetration can be determined by a simple equation.
Weld Penetration (distance into the base material when making a weld on plate measured in inches) = K [Amps4 / (Weld Travel Speed; ipm * Volts 2 )] 0.333
For 0.035 inch diameter solid carbon steel wire, the constant K = 0.0019

Using these equations we find the following when we change wire stickout for
0.035 inch solid wire.
Assuming a fixed wire feed speed that produces 200 amps at 3/8 inch wire stickout: in Amps Stickout inches
3/8
1/2
5/8
200
184
172
Penetration in inches
.127
.114
.104
% Loss in
Penetration base
11%
18%
3/4
7/8
162
154
.096
.090
24%
29%
Note:
1. With a fixed wire feed speed the amperage decreased from 200 amps with a
3/8 inch stickout to a low of 154 amps when the stickout was increased to 7/8 inches. The resistance heating of the wire (the 2nd Amp 2 term in the equation) is a very efficient heating process. Therefore the current needed to finish melting the wire as it enters the arc, becomes less as the wire is hotter with longer stickout.
2. However there is a reduction in weld penetration when varying stickout in a normal range from 3/8 to 3/4 inches is 24%! If extended to 7/8 inches penetration decreases 29%.
Therefore it is very important to keep the torch stickout constant. Also the shorter the distance from tip to work for a fixed wire feed speed the greater the penetration since current also increases. When welding in the short circuiting mode it is often desirable to use a long contact tip which protrudes from the shielding gas cup. This helps assure adequate penetration is maintained by keeping current higher. It also helps visibility so the welder can stay on the leading edge of the weld puddle.
Weld Penetration Definition
For the purposes of this exercise, weld penetration is a measure of how deep the weld penetrates in a bead-on-plate deposit. Have a different wire than the 0.035 inch solid wire used in this example? No problem. In fact not only changes in wire type and size but also shielding gas and torch angle will alter the actual value.
You can generate your own constant K for what you are doing by making a beadon-plate deposit, cutting a cross section and etching it.

References:
1. AWS Welding Handbook, Volume 1, 9th Addition; pp 7
2. “The Science of Arc Welding” by C. E. Jackson. 1960 Welding Journal 39(4) pp
129-s thru 230-s
Gas Pressure / Volume Calculations
Understanding the relationship between gas pressure and volume will help when setting gas flow and understanding MIG shielding gas use and waste.
In 1662 Robert Boyle defined the basic relationship between Gas Pressure and
Volume. He stated the relationship in mathematic terms as:
P1 / P2 = V1 / V2
(Where P, pressure, is measured as absolute pressure = gauge pressure + 14.7 psi at sea level)
For example, in a MIG gas delivery hose if the initial absolute pressure is doubled the gas volume must be double. That was until 140 years later when around 1800 both Charles and Dalton independently added temperature to the relationship!
They defined the following relationship:
V1 / V2 = T1 / T2
(Where T, Temperature is measured as absolute Temperature in degrees Rankin
=Degrees Fahrenheit gauge + 460)
Applying this equation we'll see in general we need not worry about temperature effecting volume in normal ranges: i.e.V1 / V2 =T1 / T2
If T1=75 F than T1Rankin = 75+460=535 R
Assume T2 = T1 + 20% =90 deg F; then T2 Rankin = 90+460=550 R
V1/V2 due to 20 % Temp Difference =
V1 / V2 =T1 / T2= 535/550=0.97
Or at a constant pressure, an increase in Temperature of 20% measured in degrees Fahrenheit yields only 3% increase in volume. For most welding purposes and over the range of production temperatures there is not enough change in
Volume with gas Temperature to consider it significant.

The general Gas Laws can be written as:
(P1 * V1) / T1 = (P2 * V2 ) / T2
It can also be written as P * V = (nR) T where the constants nR can defined based on the gas. We'll let you find details about the nR by searching the Internet since for our purposes ratio comparisons are all we need.
MIG WELDING EXAMPLE
Assume:
1. The pressure needed in the gas delivery hose from gas source to welder/feeder to flow 30 CFH is 3 psi.
2. A regulator/flowmeter is used that employs an 80 psi regulator.
Therefore when welding stops gas continues to flow through the needle valve flow control (or orifice flow control) until the pressure in the gas delivery hose equals
80 psi.
Then the volume of excess gas in the gas delivery hose compared to the volume when welding will be:
V stopped / V welding = P stopped / P welding =
(80 psi +15) / (3 psi + 15) = 5.3 times the physical hose volume
Hose Expansion Causes More Excess Volume: Tests of a standard 1/4 inch diameter gas delivery hose showed it had a 13% increased volume due to the hose expanding with 80 psi pressure. Therefore 87% of the excess gas stored in the hose is due to the increased Pressure and 13% of the excess due to Hose
Expansion.
3. Excess Gas Blasts Out of the MIG Torch When Welding Starts: The high velocity creates turbulence in the shielding gas stream which takes several seconds to stabilize to a desirable smooth Laminar flow. The turbulence pulls in air causing excess spatter and internal weld porosity. For a typical 5/8 inch diameter MIG nozzle more than 50 CFH flow rate causes this turbulent flow. For a smaller 1/2 inch diameter nozzle flow rates should not exceed about 40 CFH.

Weld Cooling Rate
This Topic provides the math equations that estimate the theoretical cooling rates for TIG welds.
The data is presented so one can see the numbers and dimensions from each part of the equation. TIG process efficiency is shown at 0.57 (57%.)
Equation Elements and Values
R c
= Cooling rate at weld centerline; deg F/min k = Thermal Conductivity of metal;
BTU/min in deg F p = Density of metal; lb/in 3
C = Specific Heat of metal; BTU/ (lb deg F) h = thickness of metal; in
H net
= Net heat input = BTU / in [V * I / ipm * 0.57process efficiency for
T
TIG]
T c
= Temperature which cooling rate is calculated; deg F o
= Initial plate temperature; deg F
Welding Cooling Equations from pp 100 Welding Handbook Volume 1, 9th
Edition
Thick Plate Equation = R c
= - [2 * 3.1416 * k(T c
- T o
) 2 ] / H net
Thin Plate Equation = R ) 2 (Tc-To) 3 c
= 2 * 3.1416 * kpC (h/ H net
Calculate estimated cooling rate @ 1100 deg F for thin wall 4130 tube welds:
Tube = .040 in wall; V (volts) = 10; I (amps) = 70; travel = 12 ipm
Using thin plate equation:
R
H c
= -2 * 3.1416 * 0.024 * 0.29 * 0.11= - 0.00481 net
= 1.66
(h / H net
)2 = 0.000579
(T c
- T o
) 3 = 1.07 * 109
R c
= -2981 deg F / min = - 50 deg F / sec

What is a welding certification?
 Welding certifications are used to test a welder’s knowledge and welding skill
 Certifications are available for many different processes, materials, and positions.
Who certifies welders?
 Certification programs are offered by many different types of organizations:
 Postsecondary Institutions
 Community Colleges
 Companies
 Skilled Trades
 Military
 Ship Builders
 Pipelines
 The American Welding Society
How can you become certified?
 Certification testing is available at testing facilities all over the United
States
 The AWS offers many certifications including: welders, welding inspectors, and welding educators
What is the value of a welding certification?
 A welding certification proves that you have passed a test and are qualified for the job
 As an AWS certified welder your name is kept in a national database which is used to notify you of jobs open in your area
 It is a source of accomplishment and pride

Here are some possible areas you can start a career in welding
 Aerospace
 Advanced Manufacturing
 Racing
 Engineering
 Farm
 Auto Technician
 Sculpting
 Maintenance
 Iron worker
 Robotics
 Production welder
 Fabricator
 And many more…

Do you want to learn more about welding and how to weld? If so, visit the links below for more information welding, welding certification, and careers in welding. http://www.weldinginfocenter.org/sci_tech/index.html http://www.allaboutcircuits.com/vol_1/index.html http://www.lincolnelectric.com/en-us/Pages/default.aspx http://www.hobartwelders.com/ http://www.gowelding.org/ http://www.everettcc.edu/programs/bwe/advancedmanufacturing/ welding-fabrication/ http://www.aws.org http://www.sbctc.ctc.edu/general/c_index.aspx

Lincoln Electric Company
Hobart Welding
All About Circuits website gowelding.org – Welding Resource Guide
Zona Land Education website
American National Standards Institute
Miller Welding Company – www.millerwelds.com
Videos available at http://www.millerwelds.com/resources/video_library/
Welding Hazards Safety Program, Texas Department of Inusrance www.networking.com, WA Technology, Florence, SC
Integrated Publishing website : http://www.tpub.com/air/1-18.htm
Aviation Pros.com - http://www.aviationpros.com/article/10385780/gtawwelding-touching-on-the-basics