Why ? I ask out of interest, since we have only a crude spotwelder we use to make prototypes with here.
Does it depend on the metal ? We have been trying to spot weld molybdenum, with no success...

Number of welding steps number of cycles in each step and current in each step depends on type metal to be welded. Thickness of the metal to be welded and the metallurgical properties desired in weldment. Often number of steps are used for pre-heating or post-heating the job apart from actual welding. for example post heating acts as a sort of annealing/normalising and gives fine grain structure in weld bead.

No Idea about molybdenum welding. My machines are meant for welding low carbon steels, Mild steel and Galvanised steel.

Thanks & Regards,
Prahlad Purohit