Home Forums General Discussion Media, Shot, Beads, etc. Specifying mixed shot sizes

Hello, everyone. I'm rather new to shot peening, so this question may be fundamental.

I am being advised to allow the use a mix of three shot sizes in a single-pass shot peening process, where our usual specification explicitly calls for a single size of cast shot. The supplier claims this will improve the surface finish achievable at our required intensity and coverage on a critical part.

Multiple resources advise against using mixed shot sizes for the reason of process inconsistency, but there are also references to mixing unused shot sizes in production to simulate well-used shot (a "commissioning mix") as well as a small amount of literature on size mixes that corroborates the supplier claim of improved surface finish. It seems to me this will increase equipment cost (more screening to keep the relative fractions of the sizes stable) as well as potentially increasing the fraction of damaged shot in the charge, but I don't know if it's significant enough to care about. What are your thoughts? Are there any other practical ramifications to allowing this vs. single shot size peening?

Thanks,
Zach

Using three sizes of shot at the same time would make creating a saturation curve impossible. Each size of shot would produce a different intensity value. A "mix" is a term used in shot blasting (cleaning operation) a mix is never ever used in peening period.

Did the person who was asking you to use three shot sizes specify the sizes to use and the percentage of each?
Did they suggest how you would maintain the mix ratio?
Did they indicate an inspection method to identify acceptable or unwanted results?
Is this person accredited in the shot peening process?