AGMA 97FTM13

Controlled Shot Peening has long been recognized as a veryeffective process to prolong the fatigue life of all types ofgears. Three recent innovations have extended the state of the art:1) by a process that provides a smooth surface after peening toincrease the resistance to surface fatigue; 2) by a coupon systemthat makes possible actual X-Ray diffraction curves to monitorproduction shot peening; and 3) by a computer program that permitsa reasonable prediction of residual stress curves. C.A.S.E.sm is anacronym for Chemically Assisted Surface Engineering. Frequently,when the bending fatigue life of very high cycle gears has beenincreased by shot peening the tooth roots, the next mode of failureis surface fatigue or pitting of the contact faces. There has beena need, particularly for automotive and aircraft transmissions, toextend the surface fatigue life beyond that provided by shotpeening alone and smoothing the surface after peening has beenfound to be very effective. The C.A.S.E. process cuts the relativefinishing time, after shot peening, down to just minutes fortypical automotive sun gears and provides a surface which, inaddition to the compressive stresses from the shot peening, canhave an Rsk value of as little as -1.1. Very significant increasesin surface contact fatigue (pitting) life have been observed.MILAMsm system. By the use of the new MILAMsm coupons, X-RayDiffraction (XRD) profiles can now be furnished in a matter of daysand at a fraction of the usual prices. The MILAM coupons aredimensionally similar to Almen strips but are thicker and made ofthe same material and hardness as the part itself. The coupons areused in the Almen fixture so that they reproduce the effect of shotpeening in the most critical locations on the part. The convenientnew system opens up the use of XRD as a production tool for theevaluation of shot peening quality and is adaptable to StatisticalProcess Control (SPC) without the need to destroy the part.Peenstresssm is a computer program, developed in conjunction withENSAM, a French engineering university, that permits theoptimization of shot peening parameters during the processdevelopment phase. The program library now contains nearly 100metals and alloys in various heat treatments and will accept inputsfor shot size, shot type and Almen intensity. Peenstress will thencalculate, and reproduce on screen, residual stressdistribution.

Edition:

97

Published:

11/01/1997

Number of Pages:

11

File Size:

1 file , 1.2 MB