Welding is a fabrication process used to join metals or thermoplastics by applying heat, pressure, or both.
It melts the materials at the joint and allows them to fuse together as they cool.
Welding is widely used in construction, manufacturing, and repair work.

Welding

Welding is one of the most important manufacturing processes used to join two or more metal parts permanently. Here’s a clear and detailed explanation suitable for study and exams.

1. What is Welding?

Definition

Welding is a fabrication process in which two or more parts are joined by heating them to a suitable temperature, with or without pressure and filler material, to form a strong joint.

2. Basic Principle of Welding

Heat is applied to metal surfaces
Metal melts at the joint
Molten metal solidifies
Forms a strong permanent bond

Sometimes:

Filler material is added
Pressure is applied (in some processes)

3. Types of Welding Processes

(A) Fusion Welding (Melting Type)

Metal is melted to form the joint.

1. Gas Welding

Uses flame (oxygen + acetylene)
Example: oxy-acetylene welding

2. Arc Welding

Uses electric arc to produce heat

Common types:

Shielded Metal Arc Welding (SMAW)
Gas Metal Arc Welding (GMAW/MIG)
Gas Tungsten Arc Welding (GTAW/TIG)

(B) Pressure Welding (Solid State Welding)

No melting, pressure is used.

Types:

Forge welding
Resistance welding
Friction welding

(C) Resistance Welding

Heat generated by electrical resistance
Pressure applied

Types:

Spot welding
Seam welding

(D) Solid-State Welding

No melting involved
Atoms bond directly

Examples:

Friction welding
Diffusion welding
Ultrasonic welding

4. Welding Joints

Common types of joints:

Butt joint → end-to-end
Lap joint → overlapping plates
Corner joint
Edge joint
T-joint

5. Welding Positions

Flat position
Horizontal position
Vertical position
Overhead position

6. Equipment Used in Welding

Power source (AC/DC)
Electrodes or filler rods
Welding torch or holder
Protective equipment (helmet, gloves)
Gas cylinders (for gas welding)

7. Advantages of Welding

Strong permanent joints
Lightweight structures (no bolts/rivets)
Can join complex shapes
Leak-proof joints possible
Economical for many applications

8. Disadvantages

Cannot be disassembled
Heat affects material properties
Requires skilled labor
Possibility of defects (cracks, porosity)

9. Applications of Welding

Construction (bridges, buildings)
Shipbuilding
Automobile industry
Aerospace
Pipelines
Manufacturing industries

10. Common Welding Defects

Cracks
Porosity (gas holes)
Slag inclusion
Incomplete fusion
Distortion

Summary

Welding = permanent joining process using heat/pressure
Two main types:
- Fusion welding (melting)
- Pressure welding (no melting)
Common methods:
- Arc welding
- Gas welding
- Resistance welding
Used widely in construction, automotive, and manufacturing