Hi kristof
Here is a couple of joining processes you can use.
1.TIG
A 140amp DC is ample,the filler wire you need is a
1.6mm C7 (copper),Try using helium as this cheaper and a lot cleaner.As your only welding 1mm sheet you should be looking at using a 2.4mm tungsten with a sharp point.
The amps you should weld on are about 30-100 depending on users experience.
2.Brazing
This method is also used to join copper sheet
especially in decorative fabrication.The equipment you need is a suitable brazing torch running on oxy and acceteylene or propane,the filler wire is silver solder(flux coated)simply heat the copper sheet at the join till its a cherry red colour and then apply the silver solder without flame and leave to cool.
