Hello all -

It's been quite some time since developing shot peen applications, but now I've been dragged back in. I've got a nickel-based part that will be peened at 4-8A, with the option of S110 or S170 (with CCW equivalent sizes allowed) ... so we'll go with either CCW 14 or CCW 20 ... but which one?

In our other shops with similar parts, the occasionally nagging problem has been edge rollover. The best solution is to generate the largest breakedge (chamfer, radius or whatever the particular requirement is) prior to peening. However, sometimes the max allowed isn't all we'd like it to be.

So the question: Does anyone have any experience as to how much affect shot size has on rollover ... if any ... given that the intensity range must be met regardless?

Thanks,
JZ

Hi JZ,

This old rollover problem seems to be a never ending one.

In my experience the people machining parts to be shot peened rarely know what "Break Edge Condition" is needed to prevent unwanted rollover, and even If they did, they may not want to incur the extra manufacturing costs involved.

Perhaps If an additional guidance Table (linked to the data provided in Tables 1, 2, 3 & 4) was to be included in ARP7488, resolving the problem may actually get a little closer.

At least the people machining parts could be made aware of what "Break Edge Condition" we (the peeners) need to enable us to meet their requirements.

Here's hoping !

Very Old Tom

A sharp edge is going to roll regardless of shot size, and a rolled edge is not something you want. in fact its strictly prohibited in most peening specifications and Nadcap requirements dictate you have method for both detecting sharp edges prior to peening and inspecting for rolled edges post peening.
If possible make your edge breaks at least .010", I've found this to be a safe minimum.