Computational simulation of clinching process analyzing the relationship between matrix-punch geometry and high strength steel sheet thickness

With the globally increasing demand for sustainable and pollution reduction in automobile production process, the use of advanced high-strength steels (AHSS) has been employed in order to reduce the weight of the automobile while maintaining structural strength. Thus, one of the widely used sheets joining processes is clinching, constituted by joining the sheets through plastic deformation. The clinching process has several advantages over welding process, such as the possibility of joining materials with low weldability or with coatings or painting without damaging them. However, the joint produced by clinching usually presents a lower mechanical strength in comparison to that is generated by welding process. To improve the mechanical strength, thicker AHSS can be employed in the process. More, it will lead to another consideration, which is the behavior of thick AHSS during the clinching process. In other words, the relationship between the AHSS and matrix geometry should be investigated. This work aims to investigate and analyze the influence of the matrix depth, as well as the geometry parameters of the punch and the matrix, in the clinching process. Especially their relationships with different sheet thicknesses. This investigation aims to contribute to the existing knowledge of the process and assess the joint strength in terms of unbuttoning and rupture force. For this purpose, a computational simulation model is developed, and it is validated using results from literature. Computational modelling is constituted by nonlinear material process, due to the fact that the AHSS deforms plastically. The matrix-punch assembly is discretized by a finite element approach. Further, as it is a contact problem, the governing equation is solved by using incremental-iterative procedure. The computational simulation aims to analyze the behavior of clinching joints made with sheets of different thicknesses and the matrix-punch parameters. The simulation is carried out using different sheet thickness, and the optimized parameters are obtained by comparing the size of neck and interlock of joint. The size of the neck and interlock of the joint are responsible for providing mechanical strength of the joint. It is concluded that increasing the matrix depth it will decrease the size of the neck, however, it will increase the size of the interlock. As for lateral clearance, it is necessary to evaluate whether the current joint parameters are undersized or oversized. In other words, for a set of undersized matrix parameters, increasing lateral clearance contributes to joint integrity by decreasing the neck size and increasing the interlock size. For oversized matrix, the interlock size will decrease, while the neck size will increase as the lateral clearance increases.