A key factor in reducing the energy consumption of modern vehicles is lightweight construction, which is frequently implemented using multi-material design. In this context, mechanical joining processes such as clinching are increasingly being used. The aim of the investigation is to increase the accuracy of clinching process simulations to ensure the acceleration of product development cycles. Due to the importance of friction in clinching process simulation, a friction test bed is developed, which maps the local joining process parameters. Based on the experiments, a friction model is derived. In particular, the contact between extensible die segment and joining part as well as the contact between extensible die segment and anvil are considered. Since geometry and kinematics of extensible die segments do not permit an axisymmetric 2D process simulation, the numerical investigations are carried out using a 3D model. Subsequently, the friction is modeled mathematically and validated via inverse numerical simulations.