Many factors are leading the most important players in the automotive field to experiment and use new materials, both metallic and non-metallic. Perhaps the most important factor is the environmental emergency, with ever stricter international rules for reducing pollution and fuel consumption, where respect for such rules makes necessary the development of new and lighter solutions. But this is not the only reason to experiment with new materials and to develop new design solutions: the ever increasing demand of performance, safety, and reliability that characterizes the global market requires development of new(er) and light(er) cars and this can be achieved only by using new materials.

On the other hand, cars nowadays have many accessories that seem to be necessary for selling a competitive product: electronic devices for vehicle control, servo-equipment for more comfortable driving, and safety accessories such as anti-intrusion bars are required by customers but add weight to the car.

By summarizing and without having the ambition to include all the aspects of interest, I would say that today car design is influenced by contrasting exigencies that make the work of the engineers more difficult and more stimulating at the same time.

A solution able to satisfy all the diverging requirements is to use light materials, both metallic and non-metallic. And in recent years, an increasing use of light alloys such as aluminium alloys, have been proposed for producing everyday cars and not only special, expansive models, produced in a few units. And other materials are object of research: for example, magnesium alloys are being considered for anti-intrusion bars and other important structural parts. The problem is that, if we compare the mechanical behaviour and the strength of traditional steels and light alloys, the advantages of the latter are not so evident. Indeed the discussion about the convenience of using lighter materials that need larger sections or steels (heavier but with better mechanical characteristics) is not new, and the answer is in continuous evolution.

In this contest, the use of mechanical treatments and, in particular, the use of shot peening, could result in an important factor for the choice of the material. Since the mechanical properties are strongly influenced by the surface state, it is evident that the ability of shot peening in improving the behaviour of metal parts could increase the efficiency of light alloys, making them more competitive. And this is particularly true in critical points, like notched parts, connections, welds and so on. In these situations, shot peening is able to strongly influence mechanical strength and it is expected to be a great advantage for aluminium, magnesium and other light alloys. But, if we look at public data, scientific and technical papers, books and datasheets, we note that what we can find about the effects of shot peening on the mechanical behaviour of these materials are not exhaustive. The documents refer to standard specimens and are focussed on fatigue (that is of primary importance but not the only factor to take into consideration). And only a few data can be found on connections and joining technologies used with these materials: for example, it is rare to see experiments and research about the application of shot peening on friction stir-welding, an emerging technology derived from aeronautical systems.

This is a strong limitation, since the safe and reliable application of shot peening requires a deep knowledge about its effect on machine elements and on the structural parts, that is to say, that a lot of experimental data must be acquired and elaborated on regarding both the materials (by means of tests carried out on laboratory specimens) and on real parts (possibly full scale parts) under loads similar to the in-service ones. And, as for all technological processes, it is necessary to relate the effect of the shot peening parameters on the mechanical behaviour of the treated parts, that is to say, that research must be performed to find the optimal treatment parameters with respect to particular applications. The last step is the ability to develop reasonable approaches for assessing, in the production lines, the uniformity of the treatment and its repeatability.

These are just some ideas and considerations; I know that many other suggestions could be proposed. But definitely, the application of shot peening in the automotive industry could be increased: it is a long-term project, the costs would be significant, but this would be a sound investment. A good opportunity could be to propose a strategic research program supported by some international organization, or the defining of a consortium able to share the results. This approach has given good results in other fields; will it be used also in this case?

Shot Peening in the Automotive Industry
by Mario Guagliano
Contributing Editor MFN and
Associate Professor of Technical University of Milan
20156 Milan, Italy
E-mail: mario@mfn.li

Author: Mario Guagliano