Disc springs are shallow and truncated cone-shaped components with a wide range of applications in the industry due to their large energy storage capacity in relation to the required mounting space. During their operation, they can be subjected to static or dynamic axial loads and are expected to meet high fatigue resistance demands. Operational tensile stresses can, however, limit their service life. An induction of compressive residual stresses within tensile loaded areas of the disc springs can improve their fatigue behavior. Conventional methods, like shot peening, are undesirable due to the increase in production time and costs.
In this study, the feasibility of applying the incremental sheet metal forming (ISF) technique for a selective induction of the residual stresses during forming process is investigated. Two types of metastable austenitic steels AISI 304 (X5CrNi18-10, 1.4301) and AISI 301 (X10CrNi18 8, 1.4310) were used as sheet material. The springs were produced in two geometrical categories according to the DIN 2093 standard. The parameters of interest were the geometrical accuracy and the residual stress characteristic of the incrementally-formed springs. Residual stress measurements were performed using the standard hole drilling and the X-ray diffraction methods. Furthermore, the possibility of applying micromagnetic measurement techniques to monitor the spring properties, including the residual stress distribution and the deformation-induced martensite formation, was evaluated. For this aim, the micromagnetic Barkhausen noise analysis technique was implemented.
ISF method provided the possibility to accurately produce disc springs and to integrate the residual stress induction within the forming process. In this way, the additional shot peening process could be avoided. Compared to the conventionally-produced springs, the incrementally-formed ones display a more homogenous distribution of the residual stresses. The measurements gained by means of Barkhausen noise method are in good agreement with the results gained from the conventional methods. Moreover, measurement time and costs were significantly reduced due to the elimination of sample preparation steps.