Solved GATE Questions on Joining Process
Question 1. Spot welding of two 1 mm thick sheets of steel (density=8000 kg/) is carried out successfully by passing a certain amount of current for 0.1 second through the electrodes. The resultant weld nugget formed is 5 mm in diameter and 1.5 mm thick. If the latent heat of fusion of steel is 1400 kJ/kg and the effective resistance in the welding operation in 200Ω, the current passing through the electrodes is approximately
(A) 1480 A
(B) 3300 A
(C) 4060 A
(D) 9400 A
Hint 1. (Ans C)
Question 2. The strength of a brazed joint
(A) Decrease with increase in gap between the two joining surfaces
(B) Increase with increase in gap between the two joining surfaces
(C) Decrease up to certain gap between the two joining surfaces beyond which it increases
(D) Increases up to certain gap between the two joining surfaces beyond which it decreases
Hint 2. (Ans D)
Strength increases upto some certain gap and beyond this strength decreases.
Question 3. In an arc welding process, the voltage and current are 25 V and 300 A respectively. The arc heat transfer efficiency is 0.85 and welding speed is 8 mm/sec. The net heat input (in J/mm) is :
Hint 3. (Ans B)
Question 4. Two metallic sheets, each of 2.0 mm thickness, are welded in a lap joint configuration by resistance spot welding at a welding current of 10 kA and welding time of 10 milli second. A spherical fusion zone extending up to the full thickness of each sheet is formed. The properties of the metallic sheets are given as:
Ambient temperature = 293 K
Melting temperature = 1793 K
Density =7000 kg/
Latent heat of fusion=300 kJ/kg
Specific heat =800 J/kg K
Assume : (i) contact resistance along sheet—sheet interface is 500 micro-ohm and along electrode—sheet interface is zero; (ii) no conductive heat loss through the bulk sheet materials; and (iii) the complete weld fusion zone is at the melting temperature.
Hint 4. (Ans C)
Heat generated due to current,
Heat required for melting,
Since fusion zone is spherical in shape, therefore
Where r=t=thickness of sheet=2mm
Melting efficiency=70.35 %
Question 5. A direct current welding machine with a linear power source characteristic provides open circuit voltage of 80 V and short circuit current of 800 A. During welding the machine, the measured arc current is 500 A corresponding to an arc length of 5.0 mm and the measured arc current is 460 A corresponding to an arc length of 7.0 mm. the linear voltage (E)-arc length (L) characteristic of the welding arc can be given as (where E is in volt and L is in mm)
Hint 5. (Ans A)
From power–source characteristics,
Arc voltage characteristics,
Equating (i) and (ii), we get
From equation (iii) and (iv), we get b=2 a=20
Question 6. Which one of the following is a solid state joining process?
(A) Gas tungsten arc welding
(B) Resistance spot welding
(C) Friction welding
(D) Submerged arc welding
Hint 6. (Ans C)
Friction welding is clearly solid state welding.
Question 7. In arc welding of a butt joint, the welding speed is to be selected such that highest cooling rate is achieved. Melting efficiency and heat transfer efficiency are 0.5 and 0.7 respectively.the artea of the weld cross-section is and the unit energy required to melt the metal is . If the welding power is 2 kW, the welding speed in mm/s is closest to
Hint 7. (Ans B)
Welding power applied=Heating power needed
Question 8. Two pipes of inner diameter 100 mm and outer diameter 110 mm each are joined by flash welding using 30 V power supply. At the interface, 1 mm of material melts from each pipe which has a resistance of 42.4 Ω. If the unit melt energy is , then time required for welding (in s) is
Hint 8. (Ans C)
Heat energy required for welding.
Question 9. Which one of the following welding processes used non–consumable electrode?
(A) Gas metal arc welding
(B) Submerged arc welding
(C) Gas tungsten arc welding
(D) Flux coated arc welding
Hint 9. (Ans C)
Gas tungsten arc welding uses a non—consumable electrode made of tungsten.
Question 10. Match the correct pairs.
|P. Friction welding||1. non—consumable electrode|
|Q. Gas metal arc welding||2. joining of thick plates|
|R. Tungsten inert gas welding||3. consumable electrode wire|
|S. electroslag welding||4. joining of cylindrical dissimilar materials|
(A) P—4, Q—3, R—1, S—2
(B) P—4, Q—2, R—3, S—1
(C) P—2, Q—3, R—4, S—1
(D) P—2, Q—4, R—1, S—3
Hint 10. (Ans A)
1. (C) 2. (D) 3. (B) 4. (C) 5. (A) 6. (C) 7. (B) 8. (C) 9. (C) 10. (A)