Prediction of Failure Mode in Hole Clinching of Al Alloy and Advanced High-Strength Steel

Abstract

Common joining methods used in automotive industry are welding, adhesive bonding, friction stir welding, mechanical fastening, self-piercing rivets, mechanical clinching and so on, for multi-material designed automotive bodies. Among different joining methods, mechanical clinching which achieves geometrical interlocking by plastic deformation has several advantages such as no need of additional joining elements and fast joining. But mechanical clinching is difficult to join a ductile material with a high-strength or low ductility material. Therefore the hole clinching as a new mechanical clinching process has been proposed to join these material combinations. In the hole clinching process, as punch force is applied to a upper sheet (a ductile material), it is indented into hole of lower sheet (low ductile material) on die and then interlocked by plastic deformation. It is very important for a successful design of hole clinching to predict the failure mode such as neck fracture and button separation and the strength of hole-clinched joint. For this an analytical approach was carried out for the hole clinching process of Al6061 and DP980. Tool geometry used in hole clinching was designed by the predicted failure mode. Preliminary finite element simulation was performed to validate the geometrical interlocking and joinability. The predicted failure mode and strength were verified by the results of cross tension test.