Simulation of a Screw Self-tapping Process

Abstract

With the ever-increasing demand to use lightweight materials in the automotive industry, automakers are keen on using plastics across their products. Plastics are predominantly held together using adhesives, screws, or snaps. Screws are promising when axial reinforcement between the components is desired. Self-tapping screws are now the preferred type, for its ease of assembly and cost. A self-tapping screw can tap its own hole as it is driven into the material. Such screws can be broadly classified into two categories: Thread-cutting screws (woods and metals) and thread-forming screws (plastics and thin metal sheets). Thread-forming screws form the threads by local deformation by displacing the material along its travel. Generation of these threads in plastic components using FE simulation is often tricky as it undergoes severe localized plastic deformations. This calls for the use of a unique FEM approach called Combined Eulerian Lagrangian (CEL), in which the screw and the plastic screw post are modeled using Lagrangian and Eulerian formulations, respectively. The Eulerian domain allows large localized deformations to accommodate plastic flow. This approach also enables the evaluation of the tightening torque in addition to the thread-formation pattern on the plastic component.