Optimization of the Design of a Plastic Instrument Panel Push-Nut Opening Using Finite Element Analysis

One of the methods used to mechanically fasten a component such as a radio, cluster or finish panel to a plastic instrument panel substrate involves driving a screw through a metal push-nut which has been inserted into an opening in the plastic instrument panel substrate. A primary failure mode which has been observed for this type of joint is cracking of the plastic substrate surrounding the metal push-nut. Finite Element Analysis (FEA) has been employed to optimize the design of the push-nut opening in a polycarbonate substrate and minimize the potential for cracking of the plastic. For the FEA, the implicit version of the ABAQUS program was used. It was determined that the induced stress in the plastic instrument panel substrate from the fastening process can be minimized by controlling the dimensions of the push-nut opening such that push-nut recess is minimized and the thickness of the substrate in the region whether the push-nut engages is optimized. Manufacturing tolerances were also considered. By minimizing the induced stress in the joint, it is expected that the potential for cracking is also minimized