Bit of a messy finish...We usto clamp between to copper blocks and twist and st reach till rope parted...was a big lump of a machine would weld anything up to 48mm
The sparks are called expulsion. Expulsion in resistance welding is molten metal leaving the weld zone. There are lots of factors that affect expolsion in resistance welding. In my experiance having little to no expulsion is the best/most consistant weld process.