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The improvement of fatigue life in parts subjected to cyclic stresses by application of mechanical surface treatment processes is already well known, both in the industry and in the academy. Speaking of automotive springs, the shot peening process becomes an essential step in manufacturing these parts. In the case of leaf springs, however, a systematic investigation of the effect of shot peening on fatigue life is still required. The aim of this work is to improve the knowledge of shot peening on leaf springs for vehicles through fatigue tests on a series of samples that were subject to different peening processes. A second shot-peening after a first peening under stress (stress peening) led to a higher durability comparing to the conventional process, opening an opportunity of vehicle weight reduction.

The preset process is largely applied on coil spring manufacturing. It is mainly used to guarantee, under work load, that the spring doesn't plastically deform changing the original dimensional restrictions. However, the difficult to predict its behavior under permanent strain is a constraint on projects. All the spring calculations are based on its final geometry (after the preset process), and today the initial geometry definitions are based on empirical information. The aim of this paper, through F.E.M. and experimental work, is to comprehend the stress-strain phenomena involved on the preset process, in order to create a new methodology to design coiling tools.