The unit melting energy for a certain sheet metal to be spot welded is Um = 10.0 J/mm³. The thickness of each of the two sheets to be welded is 3.0 mm. To achieve required strength, it is desired to form a weld nugget that is 6.0 mm in diameter and 4.5 mm thick. The weld duration will be set at 0.2 sec. If it is assumed that the electrical resistance between the surfaces is 125 micro-ohms, and that only one-third of the electrical energy generated will be used to form the weld nugget (the rest being dissipated into the work),​