WELDING
1. Definition
Welding is a fabrication process of joining materials (metals/thermoplastics) by heating
to fusion temperature, with or without pressure and/or filler material, to form a permanent
joint.
Difference from brazing/soldering: In welding, the base metal melts, whereas in
brazing/soldering only filler melts.
2. Classification of Welding Processes
A. Fusion Welding (with melting of base metal)
1. Arc Welding
o Shielded Metal Arc Welding (SMAW / Stick Welding)
o Gas Metal Arc Welding (GMAW / MIG)
o Gas Tungsten Arc Welding (GTAW / TIG)
o Submerged Arc Welding (SAW)
o Flux-Cored Arc Welding (FCAW)
2. Gas Welding
o Oxy-Acetylene Welding (OAW)
3. Advanced Energy Beam Welding
o Laser Beam Welding (LBW)
o Electron Beam Welding (EBW)
B. Solid-State Welding (without melting of base metal)
1. Resistance Welding
o Spot welding
o Seam welding
o Projection welding
2. Friction Welding
o Friction stir welding (FSW)
o Rotary friction welding
3. Ultrasonic Welding (USW)
4. Explosion Welding
3. Welding Joints
Butt joint – end-to-end
Lap joint – overlapping plates
T-joint – perpendicular plates
Corner joint – plates at right angles
Edge joint – parallel plates
4. Detailed Welding Processes
(a) Shielded Metal Arc Welding (SMAW)
Uses a flux-coated electrode that melts and deposits filler.
Arc struck between electrode and base metal.
Flux → generates shielding gas & slag to protect weld.
Advantages: Simple, portable, cheap.
Limitations: Slag removal needed, lower productivity.
Applications: Construction, pipelines, shipbuilding, repairs.
(b) Gas Metal Arc Welding (GMAW / MIG)
Uses a continuous wire electrode and shielding gas (Ar, CO₂, or mixture).
Higher deposition rates than SMAW.
Advantages: High productivity, no slag.
Limitations: Costly equipment, sensitive to wind.
Applications: Automotive, fabrication shops, thin sheets.
(c) Gas Tungsten Arc Welding (GTAW / TIG)
Uses non-consumable tungsten electrode with inert gas (Ar/He).
Filler can be added separately.
Advantages: High quality, precise, clean welds.
Limitations: Slow, requires skill.
Applications: Aerospace, stainless steel, thin sheets, nuclear industry.
(d) Submerged Arc Welding (SAW)
Arc and weld zone are submerged under a blanket of flux.
Continuous wire electrode used.
Advantages: High productivity, deep penetration.
Limitations: Only in flat/horizontal positions.
Applications: Thick plates, pressure vessels, pipelines.
(e) Oxy-Acetylene Welding (OAW)
Flame produced by burning acetylene in oxygen (~3200°C).
Filler rod used when needed.
Advantages: Simple, portable.
Limitations: Slower, not for thick materials.
Applications: Maintenance, repair, thin sheets, jewelry.
(f) Resistance Welding (Spot/Seam)
Heat produced by resistance to electric current at joint.
Pressure applied → weld formed.
Advantages: Fast, no filler, automation possible.
Limitations: High equipment cost, limited thickness.
Applications: Automobile body panels, sheet metal industry.
(g) Friction Stir Welding (FSW)
Rotating tool stirs and joins materials in solid state.
No melting, no filler.
Advantages: No porosity/solidification defects, good for aluminum.
Limitations: Limited to linear welds, costly.
Applications: Aerospace, shipbuilding, railways, aluminum structures.
(h) Laser Beam Welding (LBW)
Uses highly focused laser beam for localized heating and welding.
Advantages: Narrow heat affected zone, high speed, precision.
Limitations: Very costly, safety concerns.
Applications: Electronics, medical devices, aerospace, automotive.
(i) Electron Beam Welding (EBW)
Beam of high-velocity electrons under vacuum melts material.
Advantages: Deep penetration, high quality.
Limitations: Requires vacuum chamber, expensive.
Applications: Aerospace, nuclear, precision instruments.
5. Advantages of Welding
Permanent strong joint.
Can join different shapes & thicknesses.
Lighter than mechanical fasteners.
Versatile (manual, semi-auto, fully automated).
6. Limitations of Welding
Residual stresses & distortions.
Heat affected zone (HAZ) may alter properties.
Skilled labor required.
Inspection (NDT) needed for critical jobs.
Safety hazards (arc radiation, fumes, explosions).
7. Applications of Welding
Construction: Bridges, pipelines, structures.
Automotive & aerospace: Frames, body panels, jet engines.
Shipbuilding & railways: Hulls, wagons.
Power plants: Boilers, turbines, pressure vessels.
Electronics & medical: Precision welding of components.
Repairs & maintenance of machinery.
