Cold Work hole and then shot peen part or vice versa?

[RotorLiftKiowa]

Say you have an aluminum part made from 7050-T7451 material and you need to cold work a hole and shot peen the part (the hole will be plugged so that it doesn't get peened). We are wondering which step should be performed first.

I'm inclined to say that one should first cold work the hole and then shot peen the part afterwards because the shot peening would assure you that the surface around the hole is in compression. Otherwise, if you shot peened the part first and then cold worked the hole you would still likely have a circular tensile layer around the hole even at the surface and that would be a negative because cracks would want to initiate there.

What are your thoughts on this?

 

[rb1957]

either way you'll get the same result, no?

shotpeening puts the surface in compression, tension in the substrate. similarly cold working a hole puts the surface of the hole in compression and tenaion remote from the hole. in both cases the tension stresses are smaller than the compression (as there's a larger volume of material in tension than there is in compression). cold working first means that the hole surface won't be as true as it would be after cold working alone, as the bore will deform (slightly, imperceptably?) from peening. peening first means the hole will be good but there could be a far field tension issue.

if peening is directed at improving the fatigue quality of the bulk part, away from the hole, and cold-working is directed at improving the fatigue quality of the bore of the hole, you could keep the two apart by shielding not only the bore of the hole but also the surface around it (using a nut & bolt instead of just a dowel).