Welding
1. What is Welding
Welding is a permanent joining process where two or more metal parts are fused together using heat,
pressure, or both.
The base metals melt and form a strong joint after cooling.
2. Types of Welding
1. SMAW (Stick Welding)
2. MIG / GMAW (Gas Metal Arc Welding)
3. TIG / GTAW (Gas Tungsten Arc Welding)
4. FCAW (Flux Cored Welding)
5. Resistance Spot Welding
6. Laser Welding
7. Plasma Welding
8. Submerged Arc Welding
3. Welding Joints
Butt Joint – Two plates joined end to end
Lap Joint – One plate overlaps another
T Joint – Forms T shape
Corner Joint – L shape
Edge Joint – Parallel edges joined
4. Welding Positions & Angles
Positions:
1G – Flat
2G – Horizontal
3G – Vertical
4G – Overhead
Angles:
Work Angle: 45° (normal fillet)
Travel Angle: 5°–15° (push or drag)
5. Power Source and Current Types
AC – Used mainly for Aluminum (TIG)
DCEN – Direct Current Electrode Negative (Deep penetration)
DCEP – Direct Current Electrode Positive (Stable arc)
6. Polarity Selection
Mild Steel (MIG): DCEP
Stainless Steel (TIG): DCEN
Aluminum (TIG): AC
Stick Welding: Mostly DCEP
7. Welding Consumables
Electrodes – E6013, E7018 (Stick)
MIG Wire – ER70S-6, ER308
TIG Rod – ER70S-2
Flux – FCAW
8. Shielding Gases
Argon – TIG, Aluminum MIG
CO2 – Low cost MIG steel
Argon + CO2 (80/20) – Industrial MIG
Helium – Thick metals
9. Welding Parameters
Voltage – Controls arc length
Current – Controls penetration
Wire Feed Speed – Controls metal deposition
Travel Speed – Controls bead shape
Stick Out – Wire extension length
10. Welding Defects & Meanings
Porosity – Gas trapped in weld
Crack – Joint failure
Undercut – Groove near edge
Lack of Fusion – Poor bonding
Burn Through – Hole formation
Spatter – Metal splashing
11. Problems, Causes & Solutions
Problem: Porosity
Cause: Dirty metal, gas leak
Solution: Clean surface, check gas
Problem: Spatter
Cause: High voltage, wrong wire feed
Solution: Reduce voltage, adjust WFS ( Wire Feeding Speed )
Problem: Burn Through
Cause: High current, slow speed
Solution: Reduce current, increase speed
Problem: Lack of Fusion
Cause: Low heat
Solution: Increase current/voltage
12. Parameter Examples (MIG Welding – Steel 3mm)
Voltage: 18–21V
Current: 120–150A
Wire Feed: 4–6 m/min
Gas Flow: 12–15 L/min
Travel Speed: Medium
13. Robotic Welding Basics
Robot holds torch and follows programmed path.
Controller manages speed, arc start, weaving.
Sensors can correct seam position.
14. Robotic Welding Parameters
TCP Calibration
Torch Angle
Weave Width
Start/End Crater Fill
Touch Sensing
15. Common Robotic Welding Problems
Torch Collision – Wrong TCP
Uneven Bead – Wrong speed
Arc Failure – Wire jam
Bad Start – No preflow
16. Safety Rules
Use helmet, gloves, apron
Avoid fumes
Proper earthing
Fire extinguisher nearby
18. Conclusion
This manual provides complete basic to advanced welding knowledge for learning,
industrial work, and robotic welding applications.
Practice and parameter tuning are essential for quality welding.
Tig Welding
Tungsten Inert Gas (TIG) welding, formally known as Gas Tungsten Arc Welding (GTAW), uses a nonconsumable tungsten electrode to produce a weld.
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In Tig welding usually the electrode will be negative and workpiece will be positive in DC current.
The Physics: Electron Flow
In a DC circuit, electrons always flow from the negative pole (cathode) to the positive pole
(anode).
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Electrode (-): The tungsten acts as the emitter.
Workpiece (+): The base metal acts as the receiver.
When you strike an arc, electrons shoot out of the tungsten tip, travel across the plasma arc,
and smash into the workpiece at incredibly high speeds.
The Data: The 70/30 Heat Split
When those high-speed electrons collide with the positive workpiece, their kinetic energy
is instantly converted into thermal energy (heat). Because the workpiece is receiving the
brunt of this electron bombardment, the heat distribution in the welding circuit is highly
asymmetrical:
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~70% of the arc's heat is concentrated directly into the base metal.
~30% of the arc's heat remains at the tungsten electrode.
Why This Setup is the Standard
This 70/30 split provides two massive advantages that make DCEN the go-to choose:
1. Deep, Narrow Penetration: Because 70% of the heat is blasted directly into the
metal, the weld puddle melts deeply and quickly. For instance, when setting up
parameters for an automated multi-layer cladding operation, this deep, highly
predictable penetration profile is exactly what you rely on to ensure the layers fuse
correctly without excessive heat spread.
2. Tungsten Preservation: Tungsten has the highest melting point of all metals (around
$3,422^\circ\text{C}$). However, if it absorbed the majority of the arc's heat, even
tungsten would melt into the weld puddle, causing severe contamination. By
keeping only 30% of the heat on the electrode, the tungsten stays cool enough to
hold a sharply ground point, which gives you that surgical, laser-like arc focus TIG is
famous for.
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DCEN Direct current electrode negative.
It puts more of the heat on the workpiece.
But for aluminum material AC current is used in this the positive and negative voltage switch back forth
between the electrode and workpiece. It puts more heat on electrode.
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Filler metal also can be used in additional can be used if thickness of workpiece is more than 5mm.
1. When do we NOT use filler metal?
Welding without adding any filler metal is called autogenous welding [creating a weld by
only melting the base metals together].
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When it is used: Only on very thin sheet metal (typically under 2mm) and usually
only on specific joints like outside corners or perfectly tight butt joints [where two
flat pieces are pushed tightly against each other].
Why: Because the metal is so thin, melting the two edges together provides enough
volume to create a strong joint without needing extra material.
2. Why do we USE filler metal? (The "Why")
Once your metal gets thicker than 2mm, or if there is any gap between your pieces, you
must start feeding a filler rod into the puddle. Here is why:
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Adding Volume and Strength: If you just melt two 3mm plates together without
adding filler, the melted puddle will sink and become concave [curving inward, like
a bowl]. This makes the weld thinner and weaker than the base metal. Adding filler
builds the weld up so it is flush with or slightly thicker than the base metal.
Bridging Gaps: If your two pieces of metal do not fit perfectly together and have a
gap, you cannot just melt the edges—they will just melt away from each other. The
cold filler rod acts as a bridge to connect the two sides.
Metallurgy [the science of metals]: Filler rods are not just plain metal; they are
specifically engineered alloys [mixtures of metals]. They often contain extra
elements like Silicon (which acts as a "wetting agent" to make the liquid puddle flow
smoothly) and deoxidizers [chemicals that pull impurities out of the weld puddle to
prevent cracks].
Why TIG? The Advantages
There are faster and easier ways to weld (like MIG or Stick welding), but when an industry
requires absolute perfection, they choose TIG. Here is why:
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Unmatched Precision and Control: In other welding processes, pulling the trigger
feeds the wire and the heat at the exact same time. In TIG, the heat (controlled by
your foot pedal or hand dial) and the filler metal (added by your other hand) are
completely independent. This allows the welder to manipulate the puddle with
surgical precision.
Absolute Purity and Cleanliness: TIG produces zero [spatter: tiny, unwanted
droplets of liquid metal that fly off the arc and stick to your workpiece] and zero
[slag: a hard, crusty byproduct left over by flux-based welding methods that must be
chipped or ground off]. When a TIG weld is finished, it is completely clean and
requires no grinding.
Versatility of Metals: TIG can weld a wider variety of metals than almost any other
process. It easily handles carbon steel and stainless steel, but it is also the premier
choice for [exotic alloys: highly specialized metals like Titanium, Inconel, or
Chromoly] used in aerospace and motorsports.
Visual Appeal: Because of the rhythmic "dab and move" technique used to add the
filler rod, a perfect TIG weld leaves a beautiful, uniform rippled pattern often
referred to as a "stack of dimes."
What does "All Positions Available" mean?
When you build a table in your garage, you can flip the table over so you are always welding
flat on top of it. But if you are welding a pipe fixed to a ceiling, or a structural beam on a
bridge, you cannot move the workpiece. You have to move your body.
In welding, there are four primary positions:
1. Flat (1G / 1F): Welding from above the joint, like drawing a line on a table. Gravity is
helping keep the liquid metal in the joint.
2. Horizontal (2G / 2F): Welding across a wall. The metal is vertical, but your weld
runs left to right.
3. Vertical (3G / 3F): Welding straight up or straight down a wall.
4. Overhead (4G / 4F): Welding upside down on a ceiling.
Why is TIG capable of all positions?
Gravity is the ultimate enemy of liquid metal. If you are welding overhead (upside down)
and your liquid puddle gets too big and hot, gravity will pull the molten metal out of the
joint, and it will literally drip onto your head.
TIG is perfectly suited for "out-of-position" welding (anything other than flat) because of
that independent control we talked about earlier:
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If the welder is going vertical or overhead and feels the liquid puddle starting to sag
or drip from gravity, they can instantly back off the foot pedal to lower the
[amperage: the electrical current that determines the heat of the arc].
They can also dab a little extra cold filler rod into the puddle.
This instantly "freezes" the liquid metal, turning it solid before gravity can pull it out
of the joint.
Because TIG gives the operator pinpoint control over the exact freezing point of the puddle,
a skilled welder can run a perfect weld on a ceiling just as easily as they can on a
workbench.
MIG Welding
What is MIG Welding?
MIG (Metal Inert Gas) welding, formally known as GMAW (Gas Metal Arc Welding), uses a
continuously fed solid wire that acts as both the electrode [the part that carries the
electricity to create the arc] and the filler metal. A shielding gas (usually a mix of Argon and
$CO_2$) flows through the gun to protect the weld.
1. The Setup & Polarity (DCEP)
Unlike TIG, MIG welding almost exclusively uses DCEP (Direct Current Electrode Positive),
also known as "Reverse Polarity".
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The Heat Flip: In MIG, the continuously feeding wire is positive (+), and the
workpiece is negative (-). The electrons shoot up from the metal and crash into the
wire.
Why DCEP? Remember the 70/30 heat split? In MIG, roughly 70% of the heat is
focused on the wire itself. This is exactly what you want because the goal is to melt
that wire rapidly to fill the joint.
The Result: Deep penetration and a very high deposition rate [the speed and volume
at which melted filler metal is added to the joint].
2. Filler Metal (Continuous Feed)
In TIG, you manually dab cold filler rod into the puddle. In MIG, the machine automates this.
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Wire Feed Speed (WFS): You set a motor speed that pushes the wire through the gun. In MIG,
increasing the WFS automatically increases your amperage [the electrical current that provides
the heat to melt the metal].
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Voltage: You must separately set the voltage [the electrical pressure that dictates how wide the
arc is and how flat the weld puddle spreads]. Balancing WFS and Voltage is the core skill of
setting up a MIG machine.
3. Why MIG? The Advantages
While TIG is chosen for absolute surgical precision, MIG is the undisputed king of industrial
production.
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Speed: Because the wire continuously feeds, MIG is significantly faster than TIG. It is
heavily utilized in robotic automation (like ABB or KUKA cells) because a robot can
run a continuous MIG weld for meters without stopping.
Ease of Use: Often referred to as a "point and shoot" process. It requires only one
hand to operate the gun, making the learning curve much shorter than TIG.
Thick Materials: The high heat and fast deposition make it highly efficient for
welding heavy structural steel plates.
4. All Positions Available (Transfer Modes)
MIG can weld in all positions (flat, horizontal, vertical, overhead), but how it fights gravity
depends on the Transfer Mode [the specific physical way the melting wire detaches and
enters the weld puddle].
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Short Circuit Transfer: Used for thinner metals and out-of-position
(vertical/overhead) welding. The wire physically touches the base metal, creates a
short circuit, melts a small drop into the puddle, and repeats this cycle up to 200
times per second. It creates a "colder," fast-freezing puddle that won't drip on your
head.
Spray Transfer: Used for thick metals in flat positions. By cranking up the voltage
and using high-argon gas, the wire melts before it touches the puddle, spraying a
continuous mist of fine metal droplets across the arc. It is incredibly hot and fast, but
the puddle is too fluid for upside-down welding.
MIG & MAG Welding
In reality, MIG and MAG use the exact same welding machine, the exact same wire feeder,
and the exact same welding gun. They are both sub-categories of the official welding term
GMAW [Gas Metal Arc Welding].
The only difference between MIG and MAG is the type of shielding gas inside the cylinder
connected to the machine.
Here is the breakdown of the difference:
1. MIG (Metal Inert Gas)
In MIG welding, the shielding gas is 100% Inert [chemically inactive].
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The Gases Used: 100% Argon, 100% Helium, or a mix of just those two.
How it Works: Inert gases act purely as a protective bubble. They block the oxygen
and nitrogen in the atmosphere from touching the liquid weld puddle, but they do
not chemically react with the melting metal or the arc itself.
When it is Used: MIG is used for welding non-ferrous metals [metals that do not
contain iron]. The most common example is welding Aluminum. If you try to use an
active gas on aluminum, it will cause severe [porosity: tiny gas bubbles trapped
inside the solidifying weld, looking like Swiss cheese].
2. MAG (Metal Active Gas)
In MAG welding, the shielding gas contains an Active component [a gas that chemically
reacts with the welding arc and the liquid metal].
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The Gases Used: Mixtures containing Argon combined with Carbon Dioxide
($CO_2$) or Oxygen ($O_2$). A very common mixture is 75% Argon and 25%
$CO_2$ (often called "C25"), or sometimes even 100% $CO_2$.
How it Works: The active gases ($CO_2$ or Oxygen) don't just protect the puddle;
they intentionally react with the high heat of the arc. This reaction actively changes
the physics of the weld. It stabilizes the arc, allows the puddle to wet out [flow out
smoothly at the edges], and actually increases the heat and penetration of the weld
into the base metal.
When it is Used: MAG is used for welding ferrous metals [metals that contain iron].
This includes Carbon Steel and Stainless Steel.
Summary
MIG: Inert Gas (Argon/Helium) -> No chemical reaction -> Used for Aluminum and other
non-ferrous metals.
MAG: Active Gas ($CO_2$/Oxygen mixes) -> Chemically reacts to improve penetration ->
Used for Steel and other ferrous metals.
Push Pull Welding
What are Push and Pull Angles?
This refers to the angle of your torch relative to the direction you are moving. It dictates
where the arc force is directed and how the shielding gas covers the metal.
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Push Angle (Forehand): The torch leans forward, pointing in the direction you are
welding [like pushing a lawnmower]. The arc force blasts ahead of the liquid puddle.
Pull Angle (Drag / Backhand): The torch leans backward, pointing away from the
direction you are welding [like dragging a heavy box behind you]. The arc force
blasts directly down into the liquid puddle.
TIG Welding: The "Push" Rule In TIG, you almost exclusively use a Push angle (usually 10 to
15 degrees).
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Where it is used: Every material, every joint.
Why? Gas Coverage: You are manually feeding a cold filler rod into the front of the
puddle. By pushing, your argon gas flows forward, creating a protective envelope
that covers the liquid puddle and the hot tip of your filler rod.
What happens if you Pull? The gas flows backward over the finished weld. Your filler
rod is left completely exposed to the oxygen in the air, causing it to instantly
[oxidize: burn, turn black, and crumble], which severely contaminates the weld.
MIG / MAG Welding: The Choice (Push vs. Pull) In MIG/MAG, you use both depending on the
material, thickness, and wire type.
1. The Push Angle in MIG/MAG
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Where it is used: Thin sheet metal, Aluminum (you must always push aluminum),
and general solid-wire MAG welding.
Why? Flatter Bead and Visibility: Pushing directs the arc force ahead of the puddle,
which pre-heats the cold metal. This creates a wider, flatter weld bead with
shallower [penetration: how deep the weld bites into the base metal]. It also gives
the welder a very clear view of the joint line ahead.
2. The Pull (Drag) Angle in MIG/MAG
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Where it is used: Thick, heavy structural steel and specifically when using [FluxCored wire: a hollow wire filled with chemical powder that melts to create a
protective slag crust over the weld].
Why? Deep Penetration: Pulling focuses all the arc force and heat straight down into
the liquid puddle, digging a deeper hole. This creates a narrower, thicker, highly
penetrating weld profile.
The Golden Rule: "If it has slag, you drag." When using flux-cored wire, pulling
forces the liquid [slag: the hard, crusty byproduct that must be chipped off later] to
float to the back of the puddle. If you push flux-cored wire, you will drive that slag
straight into the liquid metal, causing severe internal defects.
Welding Diagrams: