Tumbling self-piercing riveting of locally carburized hot stamped complex phase steel combined with a process-adapted austenitization

An established method to enhance the lightweight potential and the crashworthiness of hot stamped components is locally tailoring the part properties according to the functional purpose of the respective zones. Tailored carburization is hereby an alternative approach which offers several advantages compared to established ones, e.g. high geometrical flexibility. The process-adapted austenitization, as a lately introduced and innovative approach, showed the potential to increase the ductility of the not carburized zones while maintaining the high strength in the carburized ones. This enables an even higher grading and expands the applicability. Besides the component properties the joints between different parts of materials of dissimilar types are another crucial aspect regarding manufacturability and crash performance. Tumbling self-piercing riveting (T-SPR) is a pioneering and versatile mechanical joining process, which is a promising development of the regular process to enhance the joining capability. The combination of the tailoring approach and the mechanical joining process offers the potential to overcome current limitations in joining hot stamped parts with a component of a dissimilar material. Based on this hypothesis, the aim of this study is to evaluate this potential by investigating the impact of the material condition and combination as well as the joining parameters on the joining process, joint development and mechanical load capacity. Hereby, joints with high load capacities up to 7 kN under shear tension and an energy absorption of up to 20 J were achieved for the highest investigated tumbling velocity and a fully non-carburized upper blank.