Problem with welding one pure nickel strip on another

Hello,

I am building huge 12S14P battery pack. To do this i have got access to professional spot welder in academic laboratory with ADP3 weld power supply (300 Joule, dual pulse, stored energy welding power) and WBT-Q03 welding head.
I am using 0.2 mm thick and 7 mm wide pure nickel strips.

I had no problem with doing series welds. Connections were nice and neatty.

https://imgur.com/Z7FQV0l[

I had problem with welding second nickel strip to do the parallel conection of the cells. I had a lot of sparks, scorched cell and almost punctured 18650 tube. I was trying to enlow current, but there was no junction.
On the image is parameters setup:

https://imgur.com/plUSEJn

The guy in laboratory who usually operate this spot welder was not able to give me good advise. He mentioned only that he had never had anything like that, he tried to weld it by himself and had the same sparks I had.
Do you have any idea what might have gone wrong?

Best guess is you are shorting out cells.

I can't see your pictures, but if you can attach images using the attachments tab showing your actual pack layout, top and bottom, and then showing how you wish to make the parallel connections, we can see if you are creating a short with the welding probes or nickel strips that's causing the problem.

increase the head pressure. sparks means bad contact if you have real nickel. did you test it?