Heat distribution in spot welding
Besides the resistance at the interface, there are six other resistance through which the same welding current is passed. They are:
Therefore, some amount of heat is generated in these regions also (equal to I2 x R x t).The effective heat that is utilised is that due to the resistance at the metal - metal interface only, the others being losses.Among the above six resistance, R2 and R5 are high compared to the other four. These two can be minimised by properly choosing the electrode pressure and cleaning the surface well.