Joining polymer parts with self-tapping screws: an improvement of the screw thread geometry

In the present article, the influence of the self-tapping screw’s geometry during the thread forming processes in polymer types used in several industries was studied and analysed using experimental measurement and the finite element method. A number of parameters, such as assembly, type of materials and geometry, were studied. Several commercial screw topologies were also studied, and it was demonstrated that the geometry of the self-tapping screws could be optimised. A new geometry was proposed and then compared against the commercial self-tapping screws. The proposed screw obtained a smaller installation torque and a greater stripping torque, which resulted in a greater clamp load in the self-tapping joining. The clamp load loss due to relaxation was reduced up to 10% compared to the best existing geometry.