GATE 2016 ME (ME3) – Question 58
Two 2 mm steel sheets are spot welded with 4 kA for 0.2 s. The cylindrical weld nugget diameter is 5 mm. Steel latent heat of fusion is 1400 kJ/kg, effective joint resistance is 200 μΩ and density is 8000 kg/m³. The nugget thickness is ______ mm.
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Correct answer: 2.85 to 2.95
Explanation
Electrical heat is I²Rt=4000²×200×10⁻⁶×0.2=640J. Assuming it supplies fusion latent heat, melted volume is640/(8000×1.4×10⁶)=5.7143×10⁻⁸m³. Divide by nugget areaπ(0.005)²/4 to get thickness **2.9103mm**. Heat loss and sensible heating are implicitly neglected because the supplied data only specify latent heat.