Comparison of Rotary Draw Bending and Pipe Bending Processes in the Context of Hairpin Technology

The growing sales of electric traction drives applied in both hybrid and all-electric drivetrains results in a high demand for precise and robust production technologies. Hairpin technology, which is distinguished by a high level of automation, has become the most relevant and reproducible manufacturing process for powerful stator windings. Consequently, various bending processes for the manufacturing of stator windings, in particular hairpin coils, have become established in automotive production lines. Nevertheless, the state-of-the-art industrial bending processes still show technological limitations in terms of process stability and interactions with the insulation of the rectangular wires. For example, different bending processes result in varying springback effects or a tool-dependent damage of the insulation of the bent hairpin coil. In order to compare the bending processes, it is necessary to analyze the mechanical forming properties as well as the interaction between the bending tool and the insulation of the rectangular wire. Against this background, this paper presents a comparison of rotary draw bending and pipe bending for insulated rectangular wires.