Materials Science and Manufacturing Engineering Miscellaneous
Direction: Resistance spot welding of two steel sheets is carried out in lap joint configuration by using a welding current of 3 kA and a weld time of 0.2 s. A molten weld nugget of volume 20 mm3 is obtained. The effective contact resistance is 200 micro-ohms. The material properties of steel are given as (i) latent heat of melting 1400 kJ/kg, (ii) density 8000 kg/m3, (iii) melting temp 1520°C (iv) specific heat 0.5 kJ/kg°C. The ambient temp is 20°C.
- Heat (in Joules) used for production weld nugget will be (assuming 100% heat transfer efficiency)
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I = 3000 A
t = 0.2 sec
R = 200 μΩ
V = 200 mm3
LH = 1400 kJ/kg
ρ = 8000 kg/m3
C = 0.5 kJ/kg °C
Heat Generation = I2 RT
= 3000 × 200 ×10-6 × 0.2 = 360 Joules.
Heat utilised for production of weld Nugget
= m [LH + C∆T]
800 × 20 × 10-9[1400 + (1500 × 0.5)] × 1000
= 344 JoulesCorrect Option: C
I = 3000 A
t = 0.2 sec
R = 200 μΩ
V = 200 mm3
LH = 1400 kJ/kg
ρ = 8000 kg/m3
C = 0.5 kJ/kg °C
Heat Generation = I2 RT
= 3000 × 200 ×10-6 × 0.2 = 360 Joules.
Heat utilised for production of weld Nugget
= m [LH + C∆T]
800 × 20 × 10-9[1400 + (1500 × 0.5)] × 1000
= 344 Joules
- Aluminium strips of 2 mm thickness are joined together by resistance spot welding process by applying an electric current 6000 A and 0.15 second. The heat required for melting aluminium is 2.9 J/mm3. The diameter and thickness of the weld nugget are found to be 5 mm and 2.5 mm respectively. Assuming the electrical resistance to be 75 micro ohms, the percentage of total energy utilized in forming the weld nugget is
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hn = 2.5 mm, I = 6000 A
R = 75 µΩ, t = 0.15sec
dn = 5 mm Energy/Volume = 2.6 J/mm3
Energy generated = I2 R t
= 60002 × 75 × 10-6 × 0.15 = 405 J
Energy Required = 2.9 × volume of Nugget= 2.9 × π d2nhn 4 = 2.9 × π 522.5 = 142.35 joules 4 Efficiency = 142.35 × 100 ≃ 35% 405 Correct Option: B
hn = 2.5 mm, I = 6000 A
R = 75 µΩ, t = 0.15sec
dn = 5 mm Energy/Volume = 2.6 J/mm3
Energy generated = I2 R t
= 60002 × 75 × 10-6 × 0.15 = 405 J
Energy Required = 2.9 × volume of Nugget= 2.9 × π d2nhn 4 = 2.9 × π 522.5 = 142.35 joules 4 Efficiency = 142.35 × 100 ≃ 35% 405
- Consider the following statements: The magnitude of residual stresses in welding depends upon
1. Metal melted/deposited
2. Design of weldment
3. Support and clamping of components
4. Welding process used
Which of the statements given above are correct?
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Residual stress depends on welding parameters such as current, voltage, speed, current.
Correct Option: B
Residual stress depends on welding parameters such as current, voltage, speed, current.
- Two 8 mm thick steel plates are placed 5 mm apart and welded by a butt joint. Welding is carried out at 20 V and speed of 5 mm/s. Heat transfer efficiency is 0.80. If the heat required to melt steel is 10 J/mm3 and melting efficiency is 0.625. The weld current (in amperes) will be
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t = 8 mm, Gap = 5mm
V = 20 volts, v = 5 mm/s
ηHt = 0.8, H = 10J/mm, ηm = 0.625
I =?
Volume of weld pool = 8 × 5 × x
= 40 x mm3
Heat Required = 10 × 40 x = 400 x J
Heat Generated= ηHtηm VIx v = 400= 0.625 × 20 × I × x × 0.8 5
I = 200 ACorrect Option: B
t = 8 mm, Gap = 5mm
V = 20 volts, v = 5 mm/s
ηHt = 0.8, H = 10J/mm, ηm = 0.625
I =?
Volume of weld pool = 8 × 5 × x
= 40 x mm3
Heat Required = 10 × 40 x = 400 x J
Heat Generated= ηHtηm VIx v = 400= 0.625 × 20 × I × x × 0.8 5
I = 200 A
- In a fabrication shop, a T-joint is to be made between two plates using a chin intermittent, double fillet weld of 6 mm leg length. The intermittent welds are 40 mm long and spaced 80 mm apart, edge to edge. The welding symbol of the joint is
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Correct Option: D