Hi,
I have been reading the forum for several years, it has been very useful for me to learn about thermal spraying processes.
Now, I'm facing a problem and I have no clue on what it's happening, maybe you could give me some idea.
We are spraying a part made from an aluminium alloy with a WC17Co superfine grade coating by air plasma spray, thickness aprox. 0.30 - 0.35 mm (.012-.014 inch). The coating is finished by dry turning with CBN.
Up to now, we have been obtaining a smooth surface finish after machining (see attached picture).
However, since a few weeks ago, the appearance of the coating has been getting worse after machining, the last one the worst of them. The surface seems rougher than usual, in all the sprayed area (see atached picture 2)
It is as if the turning tip is not finding enough material, -but it did, comparing the original as-sprayed dimension and the finished one there is around 0.15mm (.006 inch) of difference. Or as if the coating is more porous.
However the metallography seems correct (see attached picture 3)
Any idea on what is going on? Apparently, there has not been any change in the thermal spraying nor machining process.
Powder feed rate is done before all sprayings and it's correct.
Spraying parameters are monitored and ok.
So, probably something has changed but I'm not sure what...
Thanks for your help, best regards,
Pablo Arriola