Structural Analysis of the Forming Process for Hairpin Windings for Electric Motor Applications: Torsional-Flexural Instability Issues

Electric motor manufacturing technology is evolving due to automotive transport development. Besides, environmental issues and the need of CO2 emission reduction have led to an increasing demand for electric drives efficiency. Permanent magnet synchronous machines are widely employed for traction systems and distributed windings produced by using insert techniques are growing in popularity. These methods require preformed wires such as the well-known hairpin shape. The advantages of hairpins are discussed in the pertinent literature. In the present paper, the manufacturing process of a hairpin is investigated by analysing its mechanical behaviour via Finite Element simulations. In fact, many problems might occur during the forming of a hairpin, depending on the shape required. In particular, this study aims at describing the influence of the geometry of the wire cross-section on the resulting final shape of the formed hairpin. Suitable ranges of geometrical and manufacturing parameters are identified to avoid torsionalflexural instabilities.