Home Forums General Discussion Shot Peening Process, Intensity, Coverage Peening on Recast Layer

I am posting this question I recently received and would like to see other's input. Please offer your opinion (if you have one). I've done a very little editing to overcome a slight language barrier.


We are working with a new product that is machined with EDM and it is going to be shot peened without removing the recast layer. The intensity is to be 20-30N (mm)

My concern is that it’s very hard to see coverage rate even with fluorescent tracer. But what I do know from the residual stress measurement is that after shot peening its at -600Mpa compared with before at +350Mpa and the customer set the limit to at least -250Mpa after the peening.

My plan to the problem to see the coverage rate is: The operator doesn't check the coverage, just looks for unusual appearance and so and of course run the Almen strip before the actual part.

The parameters are locked for editing and a technical plan for the part is signed by me and the costumer saying that the coverage isn't checked.

Would you have been satisfied with this method? Or how would you have done?

I would not be satisfied if the coverage was not checked adequately. The surface of EDM machined parts has, however, a roughness that makes coverage measurement very difficult. A pragmatic solution is to hand polish several small areas of the component before peening using wet-and-dry emery paper. This is a method that I use sucessfully on unpolished Almen C strips.

Ok, but the problem is that is a quite small part and thin material in the vanes so we have to mask 50% in the middle of the vane so that the form of the vane won´t get out of tolerance.
It is thus only the radii of mountings to be peened, its very hard to polish that area.
Does anyone else have suggestions

Five, I'm glad you were able to create an account here on the Forum. I hope to see more replies to your question.

It is difficult to imagine why you find it "very hard" to hand polish the mounting radii. With complex geometries some ingenuity is needed e.g. wrapping emery paper round a flexible ruler.

In serial production we don´t have the time to polish every hardware. Too verify the program before starting the up the serial production I manage to get hold of a casted component with the same geometry, but this is a VERY expensive solution and cant be done in real production.
I'm looking rather for a solution to the problem in the seris production, Thanks for the answer.

There was no suggestion that you should polish an area of every component. Peening intensity must, however, be checked periodically. It would satisfy most customers if you included in a batch just one component that had a polished coverage test area each time that you were checking peening intensity. That would not be very expensive.

Sine I´m working in the aviation industry we are running strips before every component (when not batch). This particular component costs roughly 50000$ before we start processing, so nothing can go wrong.
The have agreed with the final costumer not to check coverage on each part, provided that we don´t change any parameters from the residual stress measurement. I'm just curious if there was anyone else who has faced similar problems