Spot hole - Resistance welding 1

[roberto1brazil]

Hi everybody
I would like to have your opinion in the following issue: We had to weld two parts, one with 0,5 mm thick (Stainless Steel 321) and the other with 0,8 mm thick (Inco 625). The process was Resistance Spot Welding. The welding was performed making use of the following machine features and parameters:

Welding machine MP-10 BAMTECH – Nominal power – 10 KVA
Power Percentage – (0 – 99% ) – 49% (parameter chosen)
Pulses amount – 1 (NOTE -value setup for Stainless material according to the machine manual)
Cicle time – (0 – 1,6 seconds) - 22% (parameter chosen)

Those parameters were achieved making use of a test piece and so we have performed welding of many parts with those parameters succesfully, but unfortunately (for some reason) we had a part that a spot hole through (0,5 mm or .020” diameter) was introduced during the process. Please, have you some idea of what could be the cause of damaging the part (hole) as it was described?
Thanks for any tip.
Roberto

 

[berkshire]

The most likely, but not the only cause, is some volatile contaminant either on the surface of the two parts being joined or in the metal itself.
Check the part for oil on the surface, check the heat settings. The stainless steel is more likely to flash out than the inconel.
B.E.

 

[roberto1brazil]

Berkshire, thanks for your advices. We are going to simulate a situation like described (in a scrap part of course) in order to be sure about what to be aware when executing this welding.
thanks
Roberto

 

[EdStainless]

also look at the condition of the electrodes.
Though I have seen more of them related to foreign material on the surface (or between the pieces).

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