Post Material Removal of Shot Peened Surface

[gutboy17]

Condition: I have a 7075-T6 part that has been shot peened. However, a local surface feature of the part needs to have .050" of material removed for assembly fit.

I don't know the shot peen process (i.e. type, intensity, etc.) of the current part needing the dimensional work.

My question is, are there rules of thumb or formulas that I can show how much I'm negating the effect of the shot peening process by the post material removal that needs to be done.

Thanks.

 

[swall]

I would say that in removing .050" of surface, you are removing most, if not all of the compressive residual stresses. I'm not aware of a "rule of thumb". Every part will be different, based on geometry and the intensity imparted by the particular peening machine.

 

[metengr]

From my limited shot peening experience, the purpose is not to remove or alter the compressive stress layer that is provided by shot peening.

 

[arunmrao]

No don't remove any material,if it helps.

_____________________________________
"The richer we have become materially, the poorer we have become morally and spiritually." Martin Luther King Jr

 

[stanweld]

Agree with swall. Is the area required to be removed in the zone subject to high fatigue service?

It is noted that an incident of turbine blade failures was reported due to the shot peened surface being removed by machining at the base of the leading edge.

 

[TVP]

I agree with all of the above-- this will remove most if not all of the residual compressive stresses in that area. Definitely don't do it if this is a critical stressed region.

 

[Kwan]

Also note that this material has SCC susceptability. Shot peening can help reduce the effects. If you must remove material, I would shot peen again.

 

[rmw]

Alternatively you could remove most of what is required for the fit and then shot peen so that when you did final machining for the fit, some high percentage of the peening remains.

The benefit of the peen is the compressive stress at the base of the peen and shaving the ridges won't affect that a lot. Start removing the full depth of the "valley" of the peen, and you have lost all the goodie.

Most of what I have ever had to have peened was gearing and as the gear went into service, wear started so eventually the peening could be worn down. Still, the benefit gained increased the gear life multi-fold such that that degradation due to wear was acceptable.

Is it imperative that your fit have a solid surface (thinking of knurled surfaces for fit purposes for example)?

rmw

 

[Tmoose]

I think Some MIL spex limit material removal after peening to something like 10% of the Almen intensity achieved.
So that's a few thousandths at most.
MIL STS 13165 says:
" 3.3.1 Dimensions and condition of parts: Areas of parts to be shot peened shall be within dimensional
and surface finish requirements before peening. All heat treatment, machining and grinding shall
be completed before shot peening. All fillets shall be formed, all burrs shall be removed, and all
sharp edges and corners to be peened shall be provided with sufficient radii to result in complete
coverage without any distortion prior to peening (see 6.15). "

http://www.metalimprovement.com/PDF_DOCS/AMS-S-13165.pdf