Question

Two metal sheets are joined using resistance spot welding. A welding current of 4500 A is applied for 0.2 s. The effective contact resistance at the sheet interface is \(400 \times 10^{-6} \, \Omega\). The thermal efficiency of the welding process is 50%. The amount of heat, in J, used for producing a spot weld is ................. (in integer).

• A. 810
• B. 850
• C. 900
• D. 950

Hint:

The heat generated in resistance welding is proportional to the square of the current, the resistance, and the time of application, adjusted by the thermal efficiency.

Answer 1

The Correct Option is A

The heat generated in the spot welding process is given by: \[ Q = I^2 R t \times \eta \] where:
- $I = 4500$ A is the welding current
- $R = 400 \times 10^{-6} \, \Omega$ is the effective contact resistance
- $t = 0.2$ s is the time
- $\eta = 50% = 0.5$ is the thermal efficiency
Substitute the values into the formula: \[ Q = (4500)^2 \times (400 \times 10^{-6}) \times 0.2 \times 0.5 \] \[ Q = 20250000 \times 400 \times 10^{-6} \times 0.2 \times 0.5 \] \[ Q = 810 \, \text{J} \] Thus, the heat used for producing the spot weld is 810 J.