GATE 2021 ME (ME2) – Question 48

Casting, Forming and Joining Processes · Welding, brazing, soldering and adhesive bonding · 2 marks · Numerical answer

A spot welding operation performed on two pieces of steel yielded a nugget with a diameter of 5 mm and a thickness of 1 mm. The welding time was 0.1 s. The melting energy for the steel is 20 J/mm³. Assuming the heat conversion efficiency as 10%, the power required for performing the spot welding operation is _____ kW (round off to two decimal places).

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Correct answer: 39.07 to 39.47

Explanation

Nugget volume is π(5)²(1)/4=19.63495 mm³. Useful heat is 392.699 J; at 10% efficiency input energy is 3926.991 J.

Divide by 0.1 s and 1000 W/kW to obtain **39.27 kW**. Both efficiency and weld duration must be included.