Warpage

Posted by: shotgirl

Warpage - 01/18/18 01:51 PM

Good Morning All,

Is it possible to correct a part that has been warped post shot peen and be acceptable? The part was only shot peened on one side of the part. The other side was completely masked off.

Thank you,
Shotgirl
Posted by: Dave Barkley

Re: Warpage - 01/18/18 04:36 PM

I think the first option would be to peen the other side, but the other side was masked off for a reason. Even if allowed, the part may not return to its original shape.

More important is learning why it warped. Was it peened with too high of an intensity? If so, that would be the larger issue and cannot be undone. If the peening procedure allowed for the intensity used, then the process design is in question. Since that is often not the case you should verify the part was dimensionally correct (Was it too thin?) before being peened. Next, double-check that your arc height measurements and intensity calculation are correct.

In the end, any corrective action would need approval from the part owner and/or design authority.

Please let us know your findings, or additional information. I would appreciate reading a follow-up.
Posted by: shotgirl

Re: Warpage - 01/22/18 06:45 PM

Exactly what we did...peened the other side. It was optional but nerveless did not return to original shape.
The intensity was within the allowable range as was the arc height measurements and calculations.
The part was to thin and that is why masking was required in those areas but only required on one side of the part.
I personally haven't seen that requirement before. Just makes sense to me whatever you mask and peen on one side of the part should be done to the other. Process design is checking into it. I will let you know.
Thanks, Shotgirl
Posted by: Dave Barkley

Re: Warpage - 01/23/18 03:46 PM

It sounds like nothing can be done for the part you've already done.

Future attempts should be done by peening both sides at the same time with blast streams directly opposing each other. If that is not possible, peen one side with light coverage, then do the same for the other side. Repeat this until you've obtained the desired coverage.
Posted by: shotgirl

Re: Warpage - 04/25/18 03:29 PM

Would a warped part be rejectable as an unacceptable part in the shot peen process or in final inspection? If shot peen rejects the part, how do we back it up if it isn't covered in our specification.

Thanks in advance,
Shotgirl
Posted by: Jack Champaigne

Re: Warpage - 04/25/18 04:57 PM

It sounds like you have an opportunity to make improvements in the quality or inspection procedures practices. There should be guidelines for acceptance/rejection of components coming into the shot peen department and again after peening.
There is a special burden on the shot peening operator. If he/she properly peens to the required peening parameters and then if the part warps (often because of thin cross section) then who is at fault? The designer or the operator?
Is the operator expected to recognize if the part is warped prior to peening thus rejecting it? Are drawings complete with dimensions and accept/reject levels for both pre and post peening?
Perhaps some additional training for designers, inspectors and operators could help address this issue.
Posted by: shotgirl

Re: Warpage - 04/25/18 06:40 PM

You make a good point regarding additional training Jack. We do have guidelines for acceptance/rejection criteria but they are straight out of the spec. Our customer is taking responsibility if the part warps as long as it is masked and shot peened according to the model(CATIA)which it is. Then they will inspect it on there end and make the decision.
My concern is us stamping the part as acceptable because here isn't anything in the shot peen spec that addresses accept/reject criteria for a slightly warped part.
Thanks again for your valuable response.
Shotgirl