Joining of high strength steel and aluminium alloy sheets by mechanical clinching with dies for control of metal flow

High strength steel and aluminium alloy sheets were joined by mechanical clinching with dies for control of metal flow. Since the sheets undergo plastic deformation for the joining during the mechanical clinching, the high strength steel sheets tend to fracture due to the small ductility. For the upper high strength steel sheet, fracture was caused by the concentration of deformation around the corner of the punch, and cracks were caused by the tensile stress generated in the bulged bottom into the groove of the die for the lower high strength steel sheet. To prevent these defects, metal flow of the sheets was controlled by optimising a shape of the die. For the upper high strength steel sheets, the depth of the die was decreased to prevent the concentration of deformation around the corner of the punch. On the other hand, the groove of the die was eliminated to reduce the tensile stress for the lower high strength steel sheets. The sheets below SPFC780 and SPFC980 were successively joined with the aluminium alloy sheet for the upper and lower high strength steel sheets, respectively.