Home Forums General Discussion Shot Peening Process, Intensity, Coverage setting peening time with saturation curve...

Hello everyone,
I just arrived in a new company, and I have a big problem. People here adjust peening time according to almen results, When I try to explain that only coverage is time relevant, and that the peening intensity is not linked to time ("intensity"), all the people here showed me saturation curves... I tried to explain with water: no success, with SAE quotation: no success, showed the "peening time paradox" article (great one by the way!): no success.
For me it's simple https://www.electronics-inc.com/wp-content/uploads/solver.gif
with such saturation curve, my peening intensity is 9 minus 10%, if on the drawing of the part I need 8 almen, but my desired coverage is reached very soon, like time=2, I can work with no problems at 1T. Almen arc read by the worker who do control during the batch should be around 6.5 It's below the 8 specified on drawing, but we don't care, peening intensity is almost 9.
Am I crazy?

Main argument of my oponents is: almen arc due to residual stress, we want as much residual stress as possible, so if the almen does not display the wanted value, and continue arching when adding peening time, it means we should peen longer, as it clearly show that we can still provide residual stress to the plate, so why not to the product.


Do you know case where residual stress improve (deeper, better distribution, higher value) with longer exposition? (like 200, 300% coverage). I meanly know case which lead to the opposite result, as we risk overpeening...
Does almen plate arc only due to residual stress, or also other effects (maybe some effects due to the increasing surface).
Any idea to convince my peoples?

Have a nice day

You are correct. Intensity is established by creating and interpreting a saturation curve to find the 10% increase. Once established, the "intensity" of the process is the same at any point in time. The part is then peened to obtain the desired percentage of coverage. Peening beyond 100% or full coverage does not increase the intensity, 200% coverage is probably acceptable, however this is really an old way of doing things. It's my belief that before modern CNC controlled peening was available 200% was applied to drawings to be sure 100% coverage actually occurred. Peening a part too long is both detrimental to the part and is not economically a wise choice. 1) My first question to ask would be, when was the last time a saturation curve was run? I can't tell you how many times I see companies that ran the curve only when the process was first developed and never again. 2) When you run your verification arc height how far off is that valve from the saturation point or other previously established "target arc height". IMPORTANT: ARC HEIGHTS or TARGET ARC HEIGHTS ARE NOT INTENSITY only the established value from interpreting the saturation curve is the intensity. 3) If you are peening Aerospace parts and your people are adjusting the peening time or other process control values without having your frozen planning revised and approved, you're right you have a big problem.

Explaining coverage separate from saturation time is the biggest challenge we have in our classrooms.
One thing that might help is to understand that the Almen strip is unique for determining the energy of the shot stream. It is NOT used for coverage time because it is not made of the same material that you are peening. Typically 100% (or could be 200%) coverage is requested. This means that 100% of the actual part has complete denting. This has nothing to do with the saturation curve and it T1 and T2 time.
Hope this helps.