
Welding is a joining process of materials which
produces coalescence of materials by heating them to
suitable temperatures with or without the application
of pressure or by the application of pressure alone,
and with or without the use of filler material.

Welding is used for making permanent joints.
It is used in the manufacture of automobile bodies, aircraft
frames, railway wagons, machine frames, structural works,
tanks, furniture, boilers, general repair work and ship
building.


Plastic Welding or Pressure Welding
The piece of metal to be joined are heated to a
plastic state and forced together by external
pressure
(Ex) Resistance welding

Fusion Welding or Non-Pressure Welding
The material at the joint is heated to a molten state and allowed
to solidify
(Ex) Gas welding, Arc welding
(i). Arc welding

Carbon arc

Metal arc

Metal inert gas

Tungsten inert gas

Plasma arc

Submerged arc

Electro-slag
(ii). Gas Welding


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Oxy-acetylene
Air-acetylene
Oxy-hydrogen
(iii). Resistance Welding

Butt

Spot

Seam

Projection

Percussion
Thermit Welding
(v)Solid State Welding
Friction
Ultrasonic
Diffusion
Explosive
Newer Welding
Electron-beam
Laser
i)Related Process
Oxy-acetylene cutting
Arc cutting
Hard facing
Brazing
Soldering



Resistance welding is a fusion welding process
in which coalescence of metals is produced at
the faying surfaces by the heat generated at the
joint by the resistance of the work to the flow of
electricity.
Force is applied before, during, and after the
application of current to prevent arcing at the
work piece.
Melting occurs at the faying surfaces during
welding.

Resistance welding depends on three
factors:
Time of current flow (T).
 Resistance of the conductor (R)
 Amperage (I).


Heat generation is expressed as
Q = I2R T, Q = Heat generated.
Heat = I2 RTK
Where
I = Current (Amps)
R = Resistance (Ohms)
T = Time (Cycles 1/60
Second)
K = Heat Losses
Is a function of:
Transformer Tap Setting
Material Prop., & Pressure
Control Setting
Conduction, Convection,
Radiation
Electrodes
or Welding
Tips
Upset Weld
After Welding
Electrodes
or Welding
Wheels
Electrodes
or Dies
Projection
Welds
Flash Weld
After Welding

Adaptability for Automation in High-Rate
Production of Sheet Metal Assemblies

High Speed

Economical

Dimensional Accuracy

Difficulty for maintenance or repair

Adds weight and material cost to the product, compared with
a butt joint

Generally have higher cost than most arc welding equipment

Produces unfavorable line power demands

Low tensile and fatigue strength

The full strength of the sheet cannot prevail across a spot
welded joint

Eccentric loading condition
contactor
Main Power Line
Spot Weld
Upper Electrode Wheel
Workpiece
What is fusion welding..?
A process in which parts are melted and
fused or joint together is called fusion welding.
or
Fusion welding is a group of processes that bond metal
together by heating a portion of each piece above the
melting point and causing them to join together.
Types of fusion welding include:
 Arc welding.
 Oxy-fuel welding.
 Metal Inert Gas (MIG).
 Tungsten Inert Gas (TIG).
 Heat is supplied by various means
o Oxyacetylene gas
o Electric Arc
o Plasma Arc
o Laser
 Filler metal may be added
What is Arc 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.
Equipments:









A welding generator (D.C.) or Transformer (A.C.)
Two cables- one for work and one for electrode
Electrode holder
Electrode
Protective shield
Gloves
Wire brush
Chipping hammer
Goggles
Transformer:
A welding transformer is an
electrical transformer used in
welding
power
supply.
It pulls relatively low current
drawn from the mains power
typically limited to 15 A and
converts it to the typical 50 A
to 500 A used in arc welding
and higher currents used in
spot welding.
Electrode holder:
The insulated handle that clamps
onto the electrode. The welder
holds this during welding to
control the arc
Electrode:
Filler metal coated with flux in the
form of a rod or heavy wire
Electric cables:
Cables are used in welding to
connect work piece with
electric supply.
Welding shield (hood):
This is the mask which is worn to protect the
person welding from the bright flash of the
arc.
Welding gloves:
These are special, insulated leather gloves
that reach about 6 inches above the wrists,
and protect the hands and lower arms of the
welder (the person welding).
Welding leathers:
This is an apron like leather jacket that
covers the shoulders and chest of the welder,
used for overhead work where sparks might
ignite the welder's clothing, or cause burns.
 Gather the tools and materials you will need to begin
welding.
 Set up a safe work area, preferably with a table constructed
of steel or other non-flammable material.
 Prepare the metal to be welded.
 Attach clamps to hold your metal pieces together.
 Attach the ground clamp to the larger piece of stock that is
being welded.
 Select the correct rod and ampare range for the work you
are attempting.
 Turn on your welding machine.
 Hold the stinger in your dominant hand by the insulated
handle.
 Select the point where you wish to begin your weld.
 Strike the electrode against the surface of the metal, pulling
it back slightly when you see an electric arc occur.
 Practice traveling across the path of your weld with the
electrode until you can keep a consistent arc, moving at a
consistent speed.
 Complete Your weld.
 Clean your finished weld.
 Paint your weld with a suitable rust-preventative primer to
protect it from corrosion.
Advantages





Most efficient way to join
metals
Lowest-cost joining
method
Affords lighter weight
through better utilization
of materials
Joins all commercial
metals
Provides design flexibility
Limitations




Manually applied, therefore
high labor cost.
Need high energy causing
danger
Not convenient for
disassembly.
Defects are hard to detect at
joints.
Types Of Flames:
1. Neutral Flame.(5600 to 5900 F)
In neutral flame both gases are in equal proportions.
2. Oxidizing Flame (Excess of oxygen)(6000 to 6300F)
An oxidizing flame is caused by increasing the oxygen from a
neutral flame.
3. Reducing Flame (Excess of acetylene)(5400 to 5500F)
If the oxygen is reduced, a carbonizing flame is created from a
neutral flame.
Three basic types of oxyacetylene flames used in oxyfuel-gas welding and
cutting operations:
(a) neutral flame; (b) oxidizing flame; (c) carburizing, or reducing flame.