Comparison of Different Upsetting Processes for the Production of Copper Coils for Wheel Hub Engines

Abstract

The electric wheel hub engine is a promising technology for the development of future urban electric mobility and offers different advantages. Conical shaped copper coils offer the potential for a better exploitation of the available coil assembly space, causing a higher power density of the electric engine. The production of these copper coils using casting technology is possible, but expensive. Thus, an economical serial production process for such coils using metal forming technology is highly desirable. In this paper, different manufacturing approaches for the production of conical shaped copper coils are presented and compared. In total, four approaches for the production of these copper coils were investigated. The basis for all approaches are pre-bended ETP-copper coils, which are further compressed to a conical shape. The investigated processes are: a single-stage upsetting process with a constant geometry constraint on the outer side of the coil, a multi-stage upsetting process with adjustable geometry constraints on the outer side of the coil in each stage, an upsetting process with a steel coil as an additional forming tool and an upsetting process using an additional counter punch. The most homogeneous wire cross section was achieved by the upsetting process with a steel coil as an additional tool. However, the extraction of the copper coil from the steel coil after forming is difficult. Thus, the multi-stage process, which could enable greater productivity, and the process using the additional steel coil will both be considered in future work.