Pitting when resistance welding aluminum

[Tigerdawg]

We have a application where we are resistance projection welding aluminum. We are having problems at the ground electrode with pitting. Our electrodes are RWMA class #3 copper. Is there a different material that is better suited for this type of welding? What other issues may be causing this?

 

[Goahead]

Aluminum and aluminum alloys are not recommended for projection welding. Regular spot welding should be preferred where applicable.

http://www.welding-advisers.com/

 

[Tigerdawg]

I have heard that, but do not know any details why it is not recommended. Projection welding was chosen because the process and the machine must be interchangeable with either steel or aluminum parts with minimal changeover.

Plus, we aren't having any problems with the weld. The problem is in the ground electrode. Aluminum is transferring to the ground electrode after only a dozen or so cycles. These deposits are then causing damage to the surface.

 

[Goahead]

The ASM Handbook Vol. 6 reports as follows:
..."Aluminum and aluminum alloys are very difficult to projection weld. The aluminum oxide is so tenacious that solid projection welding, in particular, is nearly impossible. In addition, it is very difficult to localize heat, because aluminum alloys soften at such low temperatures."
For resistance welding of aluminum the recommended material is RWMA Group A class 1 material. Effective electrode cooling is always needed.

http://www.welding-advisers.com/

 

[TVP]

Al has a great affinity for other elements such as Fe and Cu, and therefore sticking is problem. The other reason for difficulty in localizing heat is due to the high thermal conductivity of Al.

 

[IFRs]

Could you try a different current setting?