I currently work for a company that took on a new project for the spotweld dept. We are welding small copper brackets to a copper plate(I don't remember the exact thickness of the material) and are having problems with the welds breaking. We are using 75 kva machines with solution boxes and chillers hooked up and are also using Molybdenum electrodes. We have tried all different settings for sq., hold, weld time, and heat% but cannot get satisfactory results. Should we be trying pre-heat or any of the slopes to aid in the welding? The part is also very cosmetic so we need to have a minimal weld mark. Any suggestions would really help. Thanks alot. Mike

-- Michael Gourlie (mgourlie@sbcglobal.net), December 29, 2003

Answers

Mike- Cu to Cu is one of the more diffcult applications to resistance weld, since cu has little resistance. All of your heat must be generated by your Moly electrodes. It can be done successfully, but the window of error is small. Have you tried projections on either piece of copper? Have you tried to resistance braze? Also, 75KVA may be undersized depending on the thickness. Pre-heat or adding upslope probably will not aid the process. Your best bet is to submit some samples into an applications and development lab, with specific requirements for nugget size and strength, proper settings can be determined. This is a free service from our company and many others. Regards, Kurt Tolliver, Unitek Miyachi Corp.

-- Kurt Tolliver (kurt@unitekmiyachi.com), December 30, 2003.

You may try our "Heat Clips" made of stainless steel. We use these clips for welding aluminum. They will increase the resistance by the tips.

-- Lennart Naslund (datawelder@prodigy.net), December 30, 2003.

We weld cu-cu wihout problems by using Medium Frequency power package (1000 Hz)and tungsten insert on the tip of the electrodes. Cemsa spa is in Resistance Wekders manufacturing since the beginning of 50's and we have accumulated a huge experience either in processes and in technology. CEMSA spa e-mail: info@cemsa.it

-- Angelo Alpago (info@cemsa.it), February 12, 2004.

Copper to copper is almost impossible. Your best bet is to have some coating of higher resistance on at least one of the 'to be welded' faces. After all this is RESISTANCE welding. Do not forget that you need heat to be localized at the weld spot. If I had to do an experiment I would start by using an iron pellet (say a disk of radius 1 - 1.5mm of 0.5mm LC steel) between the copper sheets, at the hart of the nugget. For minimal werd mark, use flat electrodes. Best of luck, you really need it!

-- Phoebus SPAROS (p.sparos@steelweld.com), February 25, 2004.