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.
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Heat (in Joules) used for production weld nugget will be (assuming 100% heat transfer efficiency)
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- 324
- 334
- 344
- 354
Correct 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
