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:

1. Resistance of the upper electrode - R₁
2. Resistance of the upper electrode metal contact - R₂
3. Resistance of the top metal - R₃
4. Resistance of the bottom metal - R₄
5. Resistance of the metal - bottom electrode contact - R₅
6. Resistance of the bottom electrode -R₆

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.