Numerical and experimental studies on the clinch-bonding and riv-bonding process
By combining mechanical joining and adhesive bonding interactions exist between these elementary joining methods. Tooling and process parameters that have been determined as optimum, separately, can not be transferred to the hybrid technology, directly. Mutual interactions lead to the necessity of fitting the respective process parameters of both elementary joining methods in order to achieve best results in the combined joining process. Optimizing parameters for the overall system is required in every case. Therefore accurate statements concerning dependencies in terms of quality production are needed, such as clear guidelines for adhesive properties and adhesive processing or adjustment of process kinematics. Understanding of the process can be accomplished not only by experimental studies, so the numerical description of hybrid joining processes and the generation of additional knowledge from simulations has to be worked out. Subjects of investigation are the mechanical joining processes clinching and self-pierce-riveting in combination with adhesive bonding, below called clinch-bonding and riv-bonding. In extensive experimental studies the influence of various parameters on the clinch-bonding process are studied. These studies are focussed on the influence of adhesive viscosity and process kinematics on the joint quality for several joining applications with identical overall gauge. A key parameter of process kinematics is the relative axial positioning of punch and blank holder at the beginning of the joining process. Another parameter is a non-continuous joining process with a defined stopping time during the joining process. For the hybrid bonding and mechanical joining technologies clinch-bonding and riv-bonding FEA reference models are developed regarding elementary joining by forming processes. These reference models are expanded with the displacement of the liquid adhesive to describe the hybrid joining processes. The influence of the described parameters is investigated in a variety of simulations. Positioning the punch 0.5 mm till 1.0 mm in front of the blank holder leads to significant improvement of the joint quality for clinch-bonding processes by reducing the adhesive bags in the joint area. Thus a greater undercut can be realised. Stopping the joining process for about 1.0 s can provide an increased undercut value in the same dimension. Based on the increased process knowledge based on simulations, options for process optimization are derived. The developed simulations go beyond the state of the art, how-ever, are associated with numerical instability and high computational times. The principal numerical calculation of hybrid joining processes is demonstrated and provides a basis for further numerical investigations for hybrid joining technologies.