VOL. 9 November ISSUE YEAR 2008

Shot Peening in the Automotive Industry

in Vol. 9 - November Issue - Year 2008
Recent news in shot peening applications to automotive components

Recently I was in Tokyo to attend the International Conference on Shot Peening (ICSP10) where, between a sushi and a sashimi, I listened to many presentations about shot peening simulation, shot peening effect on mechanical behaviour (not only fatigue behaviour!!) of machine parts made of different materials, fine particle bombarding and other new treatments derived from shot peening. All them were really interesting and allowed listeners to appreciate how powerful shot peening can be to improve the performances of components and, consequently, to reduce the weight of complex systems. I was not surprised that many papers (perhaps more than one half) were about  automotive industries and automotive elements: gears, shafts, springs were the object of many papers and research. Most of them were coming from Japanese industries, but this is probably due to the fact that the conference was in Japan, and I want to underline that many papers related to automotive components and materials were devoted to the investigation of  new efficient solutions of shot peening. First of all the so called "fine particle bombarding", that allows many advantages in terms of surface finishing and residual stress field and that was applied for improving fatigue behaviour of spring steels. There was also the application of shot peening on nitrided steels. This is of interest for high performance gear manufactures that would like to avoid grinding after carburizing by substituting carburizing with nitriding. The results are interesting, both as fatigue strength and contact fatigue strength are concerned. Indeed many questions remain open, but the correct choice of the type of test and experiment seems able to open the way for the definition of design approaches that consider both the strength of the nitrided and shot peened case and of the presence of the internal inclusions. This last factor can strongly influence the effect of shot peening on nitrided components.

Another fact that I would like to underline is that most of the papers show experimental results of tests carried out on peened and not peened parts or specimens: the tests were well described, the peening conditions too, and the comparison generally showed the great advantage that can be taken by the application of shot peening. It is ok, but, in my opinion, it is a little bit limited. I expected to listen to more analytical methods and approaches to predict the peening results as a function of treatment parameters, that is to say that I expected to see more approaches able to relate the influence of shot peening execution modes to the improvement of the strength (fatigue, contact fatigue, fretting or other) obtained by peening. This is very important, because it means that, at least for the materials and the loading conditions tested, the effect of shot peening is clearly understood and experimental investigations can be reduced (not eliminated, of course!!).

What does it mean? Why were only few of these approaches presented? There are two  possible interpretations. The first one is that when you are designing a component and you want to improve its mechanical behaviour you look only for the result that has to be good enough to support the service load. No matter if, with the same cost and the same effort, you can get a more pronounced advantage simply by looking in depth at the process. No matter if you can apply the results also to other cases, by obtaining, in the average/long term, also an economical advantage. You want only to solve your particular problem because you do not have enough time to develop a systematic approach.

The second interpretation is that companies developed such approaches but they are jealous of them and they do not like to let others know. For sure every company is afraid that its know-how and knowledge can be used by others without paying any costs. But there are many ways to present interesting results without showing reserved data and the company has an advantage in terms of promotion and  gains popularity by being able to solve that problem. John Almen worked for an automotive company and wrote papers and books read and used all over the world, but not all the readers were able to conveniently use his knowledge.  It is not sufficient to know, it is more important to know how to use knowledge.

Shot Peening in the Automotive Industry
by Mario Guagliano
Contributing Editor MFN and
Associate Professor of Technical University of Milan
20156 Milan, Italy