Understanding the process of making fuse contacts by upsetting of aluminium bars

Abstract

This paper describes the results of a study that looked at an innovative wastefree process of cold upsetting to make power fuse contacts from the commercial aluminium grade AD1. The process involves upsetting and extrusion of a workpiece cut from steel bar stock in the same die in one process step. It is proposed to use this process instead of making each separate fuse contact part, i.e. when the fuse base and the knife are notched out of a steel bar and are then stamped together. The new process is less labour intensive due to less pieces of die tooling used, less equipment required, less personnel involved and due to a significantly higher metal utilization factor – 1 instead of 0.7. Solid models have been developed for the solid part of fuse contact and for the die tooling so that this process could be performed in a die. A procedure has been developed for making fuse contacts by cutting a steel bar in the die with a flat end punch followed by upsetting and extrusion of the workpiece. The dimensions of the primary blank and the forces acting at different process steps have been determined. The upper-bound method was applied to conduct a theoretical study of kinematic parameters and forces involved in the process. Physical and mathematical modelling helped establish how a steel bar changes its shape under upsetting and extrusion. Having analyzed the block models of the extrusion process with kinematically possible velocity fields, the authors identified what conditions lead to defect formation and offered some measures to prevent such defects. Force-geometry relationships have been defined. Experimental die tooling has been made and a prototype die – designed to implement this process in practice. A pilot batch of fuse contacts has been produced.