Investigation and simulation of tool wear in press hardening

Abstract: Due to the requirements of higher strength components and lower carbon dioxide emission, press hardening becomes prevalent in the automotive industry. Heating a boron alloyed steel blank to obtain the austensite phase at high temperature and quenching it to martensitic phase enhances the strength of the products and still allows complex shapes. However, the stamping tool has to endure severe temperature changes, impacts of the counterpart and sliding processes. The wear including material transfer, surface scuffing and complicated reactions between coatings and superficial oxide layers not only shortens the service-life of tools but also decreases the productivity and the quality of the manufacturing process. Furthermore, the harsh contact conditions between the stamping tools and the work-piece, regarded as the reason for the wear, are difficult to measure in situ. The fundamental study on the tool wear in the press hardening receives insufficient attention. The present work aims at establishing an understanding of tribological characteristics in press hardening and at developing a predictive wear model by establishing a relationship between the contact conditions and the wear process. Based on these results, the extension of the service life of stamping tools through adjustment of process parameters can be possible. Sliding wear, as the dominant wear phenomenon taking place during press hardening processes, causes formation of wear particles and transfer of material fragments to the tool surface. Since the wear process is dependent on the contact conditions, finite element (FE) simulations based on thermo-mechanical calculations are used to investigate the contact conditions in a given press hardening process. Based on the results from the FE--simulations, reciprocating tests and tribolgical tests are conducted respectively under press hardening conditions to evaluate the wear coefficients of the Archard's wear model. A modified wear model is implemented in the FE--simulations to predict wear depths on the stamping tools. It is noted that most wear concentrates on the tool radius and that it correlates with the sliding distance. The correlation between the experimental set-ups and the wear predictions are analysed. An industrial experimental set-up for validation of the wear model predictions has been developed. The future work on this study is outlined.