(SEM V) THEORY EXAMINATION 2021-22 ADVANCE WELDING

ADVANCE WELDING (KME055) – Important Answers & Notes

SECTION A (Short Answers)

a. Function of flux in welding
Flux protects the molten weld pool from atmospheric gases, removes oxides and impurities, stabilizes the arc, and improves weld bead shape and strength.

b. Principle of resistance welding
Resistance welding works on Joule’s law of heating, where heat is generated due to electrical resistance at the joint when current passes through it.

c. Weld symbols for double U and single V joint

Single V-joint: One V-shaped groove on one side

Double U-joint: U-shaped grooves on both sides for thick plates

d. Radial friction welding application
It is used to join collars to shafts or tubes by rotating one component radially, generating frictional heat and forming a solid-state joint.

e. Effect of gases in welding
Oxygen causes oxidation, nitrogen leads to brittleness, hydrogen causes porosity and cracking, all reducing weld quality.

f. Health & safety in welding
It includes protection from fumes, UV radiation, burns, electric shock, and fire hazards using PPE, ventilation, and safe practices.

g. Carbon equivalent value (CEV)
CEV = %C + %Mn/6 + (%Cr + %Mo + %V)/5 + (%Ni + %Cu)/15
It indicates weldability of steel.

h. Bend test
A mechanical test used to check ductility and soundness of a weld by bending the welded specimen.

i. Weldability of copper alloys
Affected by high thermal conductivity, oxidation, alloy composition, and preheating requirements.

j. Arc blow
Arc blow is the deflection of the welding arc due to magnetic fields, common in DC welding.

SECTION B (Long Answers)

TIG Welding Process

TIG (Tungsten Inert Gas) welding uses a non-consumable tungsten electrode and inert gas like argon. It produces clean, high-quality welds.

Advantages over MIG: better control, no spatter, suitable for thin materials
Limitations: low speed, high skill required

Residual Stresses in Welding

Residual stresses are locked-in stresses due to uneven heating and cooling.
Causes: thermal gradients, restraint, phase transformation
Effects: distortion, cracking, reduced fatigue life

Weld Defects and Distortion

Common defects include porosity, cracks, lack of fusion, slag inclusion.
Causes: poor technique, contamination, improper parameters
Remedies: correct current, clean surfaces, proper joint design

Gas-Metal & Slag-Metal Reactions

Gas-metal reactions affect weld chemistry through oxidation or absorption.
Slag-metal reactions help refine weld metal and remove impurities.

SECTION C (Descriptive Answers)

Welding Process Selection Criteria

Depends on material type, thickness, joint design, production rate, cost, and required quality.

Metal Transfer in Arc Welding

Includes short-circuiting, globular, spray, and pulsed spray transfer, each used for specific applications.

Laser Beam Welding

Uses high-energy laser beam to melt and join metals.
Advantages: deep penetration, narrow HAZ                 Applications: aerospace, electronics, automotive

MIAB Welding

Magnetically Impelled Arc Butt welding uses magnetic force to rotate arc.
Applications: pipes, automotive components               Limitations: limited material range

Heat Affected Zone (HAZ)

HAZ properties change due to thermal cycles.               Affected by cooling rate, material composition, heat input.

Weld Joints

Types include butt, lap, corner, tee, and edge joints.

Non-Destructive Testing

Dye penetrant testing detects surface cracks.                 Weld inspection ensures quality and safety.

Metallizing Process

Molten metal is sprayed on surface for protection.        Surface preparation includes cleaning and roughening.

Welding of Dissimilar Metals

Requires control of dilution, preheating, and compatible filler materials.