Topic: Manufacturing Processes
A resistance spot-welding operation is performed on two pieces of 1.5 mm thick sheet steel using 12000 amps current for a duration of 0.20 second. The electrodes are 6 mm in diameter at the contacting surfaces. Resistance is assumed to be 0.0001 ohms and the resulting weld nugget is 6 mm in diameter and 2.5 mm thick. The unit melting energy for the metal is 12 J/mm³. What portion of heat generated was used to form the weld?
- A. 29.4%
- B. 70.6%
- C. 58.8%
- D. 41.2%
Answer: A. 29.4%
Explanation: Total heat generated H = I² * R * t = (12000)^2 * 0.0001 * 0.2 = 2880 J. The volume of the cylindrical weld nugget is V = (pi/4) * d² * h = (pi/4) * 6^2 * 2.5 ≈ 70.686 mm³. The heat required to melt this volume is Q = V * Unit energy = 70.686 * 12 = 848.23 J. The portion of heat utilized is (848.23 / 2880) * 100 ≈ 29.45%, which is closest to 29.4%.