Comparison between Aluminum and Copper Hairpins on the Torsional-Flexural Instability Phenomenon in the Bending Process

Design for manufacturing is crucial in developing sustainable electric drives, as aligning a product's design with its production process enhances assembly efficiency and reduces material waste. Focusing on hairpin technology for stator windings of electrical machines, this study aims to define the hairpin cross section geometrical constraints introduced by the bending process, during which the straightened pin is shaped into the characteristic U-form defining the hairpin structure. In particular, the onset of torsional-flexural instability is examined, which occurs when undesirable pin twisting combines with the intended pure bending during the process, thus compromising the geometric control of the final hairpin shape. The instability is examined on two conductor materials: copper and aluminum, with the latter being more sustainable, despite its higher electrical resistivity. The research evaluates whether the sustainable aluminum solution offers higher stability, and consequently, more flexibility in the design stage for the definition of the hairpin cross-sectional dimensions, when accounting for manufacturingrelated constraints.