Modelling of wear and galling in press hardening simulations

Sammanfattning: Implementation of press hardened parts in automobile responses to the requirement of reduced carbon dioxide emission because the press hardened part has very high ratio of strength to weight. Furthermore, ultra high-strength steels (press hardened parts) increases the vehicle safety. The press hardening processes are prevalently applied in global automotive industries. However, the press hardening processes corresponding to heating, forming, and cooling processes result in harsh contact conditions such as cyclic pressures, high temperatures and complex reactions between coatings and tool steels. Consequently, these harsh contact conditions increase the tool maintenance due to abrasive wear and adhesive wear. In order to study tribological behaviours in the press hardening, two kinds of the tribological experiments have been developed and used. Firstly, a reciprocating test, also called SRV test, is performed at elevated temperatures to study the wear mechanisms under press hardening conditions. However, the discrepancy between the press hardening and SRV test is obvious. To overcome the disadvantage, a sliding tribometer, also called tribolgoical test, is used as the second tribological test. A unidirectional sliding process is running under the corresponding pressures, temperatures, velocities and sliding distances. These test parameters are based on press hardening simulations. According to the present study, the abrasive wear is the predominant wear mechanism in the uncoated interface of the press hardening processes. When Al-Si coated workpieces are applied in the press hardening, severe adhesive wear, also called galling, substantially occurs in the stamping tool. The modelling of the abrasive and adhesive wear is derived from the Archard wear model in which the specific coefficients for the wear are calibrated by the tribological tests. The wear predictions implemented in the press hardening simulation have been validated by a press hardening experiment, which represents a typical geometry of vehicle components.