WELDING (LECTURE 1 AND 2)
By Dr. Mohammad Junaid Mir
Department of Mechanical Engineering,
Islamic university of science and technology ,
Awantipora, Kashmir
1
WELDING
• Welding is a materials joining process 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.
WELDING
•ADVANTAGES
•Different materials can also be welded
•Welding can be done anywhere
•DIADVANTAGES
•Initial investment cost is more
•Highly skilled operator is required
•To dismantle we have to break the weld
TYPES OF WELDED JOINTS
WELDING TERMS
TYPES OF WELDING
TYPES OF WELDING
• Plastic Welding or Pressure Welding
The piece of metal to be joined are heated to a
plastic state and forced together by external
pressure (Eg) Resistance welding
• Fusion Welding or Non-Pressure Welding
The material at the joint is heated to a molten
state and allowed to solidify (Eg.) Gas welding,
Arc welding
STRAIGHT POLARITY AND
REVERSE POLARITY
WELDING RODS (ELECTRODES)
• Welding rods are pieces of wire connected to the welding machine. It is where a
current is fed to enable joining of two pieces of metal by adding filler metal.
• Consumable Electrodes
• These burn slowly and get used up or melt while in use, needing replacement
at regular intervals. This is because they have a low melting point
• They are more thermally efficient than their non-consumable counterparts
• Mild, low alloy and nickel steel are the most commonly used
• Bare Electrodes: This lacks any coating of flux. They are mostly made of steel
or aluminum alloys.
• Covered Electrodes: Covered electrodes are classified as those with
cellulosethose with iron oxide, iron powder, and low hydrogen electrodes.
• Light Coated Electrodes: These have a coating factor of 1.25 where the coating
factor is equal to the diameter of the electrode divided by the diameter of the
wire.
• Medium Coated Electrodes: The coating factor in these are about 1.45,
• Heavily Coated Electrode: The coating factor here is 1.6-2.2,
WELDING RODS
(ELECTRODES)
• Flux Electrodes
• Flux electrodes are consumable electrodes that have a flux
coating. The flux produces a cloud of gas when it burns, shielding
the weld area from contamination for a smooth weld and clean
cooling process.
• Non-Consumable Electrodes
• These are also known as refractory electrodes. These are not
consumed and do not melt in the process and are more long-lasting
than the consumable electrodes.
• They are made of materials which have a high melting point such
as carbon with a melting point of 6700 degrees F and Tungsten
with a melting point of 6150 degrees F.
WELDING RODS
• Steel Welding Rods
• These are the most common as steel is the most common material that is
being used by welders
• Bronze Welding Rods
• They are used to join copper metal pieces to other metals and to repair
damaged bronze pieces by brazing
• Aluminum Welding Rods
• Aluminum welding rods are used when there is need to join aluminum
pieces and aluminum alloys that are not similar. You can use these
with MIG, TIG, and arc welding equipment
• Composite Welding Rods
• These are made of two or more than two layers of materials to produce a
stronger and quality weld. They include flux cored welding rods and
metal cored welding rods.
ARC WELDING
• Arc is initiated by touching coated electrode with workpiece.
• Gap is maintained between electrode and work-piece
• Free electrons and holes will be formed in the gas
• Temperature 6000-7000 ⁰C
• Performed on both AC and DC source
Arc Welding Equipment
1. A welding generator (D.C.) or
Transformer (A.C.)
2. Two cables- one for work and
one for electrode
3. Electrode
4. Electrode holder
5. Chipping hammer
6. Goggles
7. Protective shield
8. Gloves
9. Wire brush
ARC WELDING
ADVANTAGES DISADVANTAGES
• Most efficient way to • Manually applied,
join metals therefore high labor cost.
• Lowest-cost joining
method • Need high energy
• Affords lighter weight causing danger
through better utilization • Not convenient for
of materials disassembly.
• Joins all commercial • Defects are hard to detect
metals
at joints.
• Provides design
flexibility
References
BOOKS RECOMMENDED
• PNRAO
WEB PORTAL
• NPTEL
• shudhganga
• Slide share/scribd
