How much does shot peening reduce material thickness? 3

[WackoJ]

Does anyone have a rough idea as to how much the thickness of a part is reduced by shot peening? Is it really measurable or only in the order of 1/10th of a thou?

If this is a substantial dimension (say .001" on a .050" thick part) is this area considered loss for a net tension analysis? Or is the material thickness pre shot peening used, at this material has only essentially been compressed and not removed?

Thanks,
Jack

 

[rb1957]

whilst obviously it depends on the intensity of the shotpeening, it shouldn't be more than the .0001" you suggest.

but, no doubt, will taylor will have something to add.

 

[WackoJ]

I am working with a part with a recommended Intensity Range (in Almen 'A') of .002 to .006 inch. I gather Almen refers to the deflection of an Almen strip when undergoing the same peening process as the part to be shot peened:

http://en.wikipedia.org/wiki/Almen_strip

 

[WKTaylor]

WackoJ...

First. At the low intensities You mentioned, I assume You are peening thin aluminum parts, probably with glass bead media. Nothing else makes sense. At these intensities, You will barely disturb the surface dimensions... more roughen it than anything else. When I worked in the field I used to specify a "poor mans" glass bead shot peening/cleaning: relatively fine beads and then blasting to attain a uniform "matte" appearance all surface and edges and holes.

Second. I sense that You're a novice to peening. Are You aware of the basic specs [MIL, SAE, AMS, ASTM, etc] and other peening data resources? There is a wealth of data available. ASK and I sumbit a list of specs & websites for You to review. Absorbing info from easy to get [free in some cases] data... then asking informed questions speeds up the process... and is my favorite teaching tool. The specs and data will define basic peening concepts and help refine any questions that might linger.

Third. Roughly speaking, variables affecting surface compression, roughness/appearance and distortion are: the "as-machined" surface finish and edge/corner radiusing/deburring of the part being peened; base material type [al, stl, etc] and hardness [strength/temper] and state of internal stresses; the shot type/size/shape/hardness; blasting velocity and angle; rigid or soft fixturing of the part; manual VS automatic processes; gun [point-shoot] VS saturation [360-deg] peening; and the ability of the peening equipment to hold parameters while extracting damaged/worn shot and loose bits-n-pieces of foreign debris, control moisture and overall cleanlieness [free from oil especially]; Coverage ["time-on targeted areas" to attain intensity with specific blast parameters and media], etc. I'm sure there are others equally important, but my brain is pooped.

NOTE.
I have not mentionioned that peening can be done using a wide variety of shot types such as glass and ceramic beads, steel and cres "spherical shot" [not steel beads] and cut-wire, and some shot comes in hardnesses equivalent to VHS tool steel. Material type dictates recommended intensities and coverage; while geometry [especially holes and fillets] dictates recommended shot sizes. Also, the latest peening methods are true rocket science such as: vibratory peening and laser shock peening.

Regards, Wil Taylor

Trust - But Verify!

We believe to be true what we prefer to be true.

For those who believe, no proof is required; for those who cannot believe, no proof is possible.

 

[tbuelna]

WackoJ,

I'll assume that you mean a shot peening process for fatigue improvement, and not a shot peen forming process.

There may be a very small amount of surface material transferred to the shot media during conventional shot peening. But generally the media size, media hardness, shot intensity, and coverage are selected such that the residual surface compression is carefully controlled. As long as corners and sharp edges are removed prior to shot peening, there should be no appreciable size change.

When it is necessary to hold a close tolerance or a controlled surface roughness on a shot peened surface (such as gear tooth flanks and roots) it is common to finish grind or hone the surface after shot peening. AMS 2430 gives the following guidance on post peening material removal: "3.5.3.1- The amount of material removed by honing, lapping, or polishing shall not be more than 10% of the minimum arc height for "A" and "C" intensities....."

Hope that helps.
Terry

 

[WackoJ]

Thanks for the help. The part is to be peened following a corrosion blendout to restore the surface finish to OEM spec. The component is a 7000 series machined item with a thickness of .070" to .115" in the area concerned.

It does appear the change in material thickness will be negligible after peening. I should be able to confirm this with NDT thickness measurement post blending. Will let you know if any drastic changes appear!!

Interesting note about the control of surface roughness of a peened part, thanks tbuelna.

Cheers,
Jack

 

[WackoJ]

Interesting result from the thickness measurements pre and post peening. Ultrasonic thickness measurement was conducted (accurate to the nearest thou) which indicated the thickness of the item POST peening INCREASED at some points by only a thou. This can be attributed to the roughening of the surface which provides higher 'peaks' during the measurement. As the increase was only seen in a few locations, the actual increase is somewhere in the region of <.001", enough to tip the measurement over to the next thou.

Cheers,
Jack