How important the peening is to the process depends upon the purpose of peening. If it is for paint adhesion (surface texturing) then you obviously must have a good clean surface with the proper texture or the paint will not adhere. But, if the peening is done for fatigue life reasons then this is different. You want to be sure the process is done correctly, right media, right intensity, right coverage etc.
Can you describe more about your product and the process?
Jack
