About this previous year paper
ADVANCE WELDING TECHNOLOGY (EME-022)
Section-Wise Solved Answers
SECTION – A (Short Answer Questions)
(10 × 2 = 20 Marks)
(a) Brazing
Brazing is a joining process in which two metals are joined by melting a filler metal having melting temperature above 450°C but lower than the base metals. The filler flows by capillary action and forms a strong joint without melting base metals.
(b) Arc blow
Arc blow is the deflection of welding arc from its normal path due to magnetic fields created by current flow. It causes uneven weld bead and poor quality weld.
(c) Spray welding
Spray welding is a process where molten metal droplets are sprayed onto a surface to form a coating. It is mainly used for surface repair and build-up.
(d) Importance of Schaeffler diagram
The Schaeffler diagram is used to predict microstructure of stainless steel weld metal based on chromium and nickel equivalents. It helps in selecting proper filler metal and avoiding cracks.
(e) Electroslag welding
Electroslag welding is a vertical welding process where heat is generated by electrical resistance of molten slag. It is used for welding thick plates in a single pass.
(f) Importance of welding
Welding provides permanent joints, saves material, reduces weight, and gives high structural strength. It is widely used in construction, automobiles, shipbuilding, and pipelines.
(g) Life prediction of welded structures
Life prediction involves estimating fatigue life of welded components by stress analysis, crack growth rate, and loading conditions to prevent failure.
(h) Modes of metal transfer
Modes of metal transfer in arc welding include: Short-circuiting transfer
Globular transfer Spray transfer
Pulsed spray transfer
(i) TIG and MIG
TIG (Tungsten Inert Gas): Uses non-consumable tungsten electrode.
MIG (Metal Inert Gas): Uses consumable wire electrode.
Both use inert shielding gas to protect molten weld pool.
(j) Hard facing
Hard facing is the process of depositing a wear-resistant layer on a metal surface to increase hardness, abrasion resistance, and service life.
SECTION – B (Long Answer Questions)
(Attempt any FIVE – 5 × 10 = 50 Marks)
2(a) Principle of LASER and Laser Beam Welding
LASER stands for Light Amplification by Stimulated Emission of Radiation. Laser works on three principles: Stimulated emission
Population inversion Optical resonator
Laser Beam Welding (LBW) uses a focused laser beam to melt and join metals.
Applications: aerospace, electronics, medical devices.
Advantages: deep penetration, narrow heat affected zone, high precision.
2(b) Electron Beam Welding (EBW)
EBW uses a high-velocity electron beam to produce heat on impact with workpiece. Welding is performed in vacuum.
Problems:
High equipment cost Vacuum requirement
Solutions:
Partial vacuum systems Improved beam control
2(c) Ultrasonic waves and Ultrasonic Welding
Ultrasonic waves are high-frequency mechanical vibrations above 20 kHz. They are generated using
piezoelectric crystals.
Ultrasonic welding joins materials by frictional heat produced from vibrations.
Applications: plastics, thin metal foils, electronic components.
2(d) Explosive welding
Explosive welding uses controlled explosion to join two metals at high velocity.
The collision creates a wavy interface providing strong bond.
Parameters: Explosive velocity
Stand-off distance Collision angle
Applications: cladding, heat exchangers, bimetal plates.
2(e) Hardfacing – theory and applications
Hardfacing is similar to simultaneous alloy steel making and heat treatment during arc welding. Alloying elements are deposited and rapidly cooled.
Processes used: SMAW
TIG MIG
Plasma arc welding
Advantages: increased wear resistance, longer component life.
Applications: crusher rolls, cutting tools, valves.
2(f) Plasma Arc Welding
Plasma is an ionized gas capable of conducting electricity.
Transferred mode: Arc between electrode and workpiece
Non-transferred mode: Arc between electrode and nozzle
Advantages: high temperature, stable arc, deep penetration.
2(g) Welding defects, distortion, causes and remedies
Defects: cracks, porosity, slag inclusion Distortion: angular, longitudinal
Causes: improper heat input, poor joint design Remedies: preheating, proper sequence, controlled cooling.
2(h) Friction welding – advantages and limitations
Advantages: No filler metal
High joint strength No fusion defects
Limitations:
Only rotational or linear parts Equipment cost
Process parameters include pressure, speed, friction time.
SECTION – C (Very Long Answer Questions)
(Attempt any TWO – 2 × 15 = 30 Marks)
3. Lap joint and butt joint – design & life prediction
Lap joints overlap plates while butt joints join edges.
Design considerations include: Load type
Weld size Stress concentration
Life prediction is done using fatigue analysis, S-N curves, and crack propagation models.
4. Arc and power source characteristics
Arc characteristic shows relation between current and voltage of arc.
Power source characteristic may be:
Drooping Constant current
Constant voltage
Stability is achieved by matching arc and power source characteristics.
5. Temperature distribution, heating & cooling rate
Temperature distribution around weld shows highest temperature at weld center.
Heating rate: rate of temperature rise Cooling rate: rate of temperature fall
They affect grain size, hardness, residual stress, and weld strength.