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!