Finite element analysis of material flow in die-less clinching process and joint strength assessment

In the present work, a numerical investigation of the effect of the blank holder parameters on material flow and the final geometry of the die-less clinched joint is conducted. Various blank holder designs as well as different process parameters are used to obtain clinched joints. Axisymmetric finite element (FE) model was developed to simulate die-less clinching experiments. A hybrid material model with a weight function between the two common used hardening laws, Swift and Voce, was utilized to better represent the material behavior in the FE model. Another hybrid material model, referred to as extended-Voce model, was also utilized in the FE simulation and the results compared with the weight function approach. The weight function material model resulted in smaller geometric interlock compared with the experiment, whereas, the extended-Voce model led to better prediction of experimental geometric interlock with an error of less than 5%. The results showed that the interlock forms due to a large material flow in the axial and radial directions. The interlock can be maximized by controlling the material to flow in radial direction instead of axial direction, by decreasing blank holder depth. Also, distortion of the bottom of the die-less clinched joint can be avoided by achieving a bottom thickness of at least 10% of the total sheet thickness. Lastly, finite element models were also developed to predict the joint strength in shear and peel failure modes.