Mechanical properties of an innovative shear-clinching technology for ultra-high-strength steel and aluminium in lightweight car body structures

Abstract

Comfort- and safety-related requirements lead to weight increase of automotive structures. Modern constructions in automotive body in white (BIW) production confront this upward weight spiral with multi-material design. This restricts conventional thermal joining technologies. The basic idea of mechanical joining technologies is a force- and form-fitting joint. Clinching technologies create a joint only by plastic deformation. The formability of the joining partners limits this technology, especially when joining ultra-high-strength steels (UHSS) in multi-material design. State of the art to realise this is multi-stage clinching with pre-hole. Industrial applications in BIW are, e.g. the brackets for mouldings in the upper windscreen frame of Daimler’s S-class and the battery holder of Daimler’s M-class. Innovative shear-clinching enables joining by forming hot formed UHSS and ductile aluminium in a single-stage process. The spherical punch-sided tool set prevents any harm of the punch-sided ductile material. The cutting die initialises a crack in the die-sided material with limited formability. This paper presents detailed studies on the mechanical behaviour of state of the art multi-stage clinching with cylindrical and tapered pre-hole under quasistatic and fatigue testing methods to evaluate the influence of the interlock. These results were compared to the single-stage shear-clinching technology to derive further recommendations.