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#1480 - 10/01/20 08:58 AM Tolerances of holes after shot peening
Poeli Offline
Member

Registered: 10/01/20
Posts: 3
Hi,

We have an issue with some holes which are too large after shot peening.
We do shot peening with an intensity of 0.007A inch on titanium parts. Some of the holes (38.1-38.125mm) have to be shot peened.

We have seen that, after they come back from the shot peening operation (done externally), and after a flash etch in nitric acid as decontamination (0-2.5 µm taken off), that the shot peened holes are way out of tolerance (15 and 41µm to be precise)

When shot peening these holes:
- How much deformation can we attribute to the shot peening? I know the compressive residual stress depth can be upto 200 µm, but how much would this be visible in the measurement after shot peening? Is it possible to be 41µm out of tolerance due to the shot peening alone or do we have to look elsewhere?
- After machining the dimensional control was ok. After machining we do a first etch before penetrant testing. We have measured these holes as well after the first etch ,and they were still within tolerance. After, the part is sent to the shot peener. We will measure the holes again when the part returns shot peened (before the decontamination which is done in-house).

- Is it possible at all to take the deformation of the shot peening into account when machining such tight tolerances?

It's a very interesting, yet complicated matter!
Best regards,

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#1482 - 10/01/20 10:49 AM Re: Tolerances of holes after shot peening [Re: Poeli]
Walter Online   content



Registered: 05/03/99
Posts: 167
Loc: East Hartford, CT, USA
"- Is it possible at all to take the deformation of the shot peening into account when machining such tight tolerances?"

This is done all the time when parts are sent to us for shot peen. You need to determine which process is changing the hole size( peening or cleaning), not always but most of the time peened holes get smaller not larger. Is it possible the holes could be being peened well beyond 100% coverage? If so, this would likely be the cause.

I would suggest manufacturing one part and measuring it to sure its within tolerance:

1) Then send it to the shot peen source for peening. However, DO NOT perform acid cleaning yet.
2) Once peening is complete remeasure the part.
3) If the part is within tolerance return the part for acid cleaning then measure again.
4) If the part is NOT within tolerance after peening then adjust your pre-peen dimension accordingly to factor in the changes caused by peening.
5) Manufacture another part with the new pre-peen dimensions then repeat the steps above.

Hope that helps,

Walter A. Beach
Vice President
Hydro Honing Laboratories, Inc.
d/b/a Peening Technologies of Connecticut
8 Eastern Park Road
East Hartford, CT 06108

860-969-6207

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#1483 - 10/01/20 11:18 AM Re: Tolerances of holes after shot peening [Re: Poeli]
Poeli Offline
Member

Registered: 10/01/20
Posts: 3
Hi Walter,
Thanks for the great reply. We were planning on doing these measurements.
As we don't do the shot peening in house we don't actually know what they are doing. I will ask the saturation curves.
The drawing asks for a coverage of 2.0, what they actually apply is unknown for the moment for me. Could this be the cause of being out of dimension (hole becoming too big)?

We will need to analyze further, but knowing we might have to look at their coverage would already help us a great deal.
Best regards

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#1485 - 10/04/20 12:06 AM Re: Tolerances of holes after shot peening [Re: Poeli]
Walter Online   content



Registered: 05/03/99
Posts: 167
Loc: East Hartford, CT, USA
One other thing to check. Are you sure the diameter of these holes are a post peening requirement? Often dimensions are prior to peen, and the designer realizes there will be some dimensional changes. If can tell me what specification are you working to perhaps I could help more.

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#1486 - 10/04/20 01:53 AM Re: Tolerances of holes after shot peening [Re: Poeli]
Poeli Offline
Member

Registered: 10/01/20
Posts: 3
Hi, that's als something I've been looking at a d will further look into. Spec is Bac5730

Thanks alot!

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