Nd:YAG welding of Cobalt to mild steel 1

[concutter]

Hi, we have a process where we are pusle welding heat-treated (hardened) mild steel to pure Cobalt. The weld area is ~0.040" in diameter and we are not using a shield gas. We are, however, using two air knives in series between the weld surface and the laser optics. We have been using this process for some time and have had some very clean, uniformed, and smooth welds in the past, but recently our welds are heavily pitted and spitting all over. I am told nothing has changed on the material end, and I have tried cleaning the weld surfaces in various solvents, but to no avail. Does anyone have any idea why this process would be so messy?? It creates a lot of soot, carbon, fume, etc. There are no coatings, contaminants, or other periphial considerations on the metals. In addition, to get good weld strength, we need to run the laser pretty hot. It we turn down the power in the least bit, our weld strength plummets (we are shooting for weld strength, not trying to seal anything).

Does anyone have any ideas of how to approach this issue? Should I try to TIG the same materials together under a shield gas to see if it is the materials themselves??

Let me know... thanks!!!

 

[vic81]

Sounds like your focus has degraded. Did you have to increase the power recently, and did the problem occur then? A poor focus will cause a broader, shallower weld with poor penetration. Operators will compensate by upping the laser power. Higher powers will often cause material ejection from the weld pool. Try a focus trial where you move the lens up and down to achieve best weld strength (or weld area at the interface if you don't have a way of testing strength). Then optimize power at this focus.