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!!!