Analysis of the Influence of Various Bending Parameters on the Resulting Electrical Properties of Bent Hairpins

Hairpin stator technology has become widely accepted in electric drive production for automotive traction drives. This technology uses rigid, rectangular, insulated copper wires as the semi-finished product. Compared to flexible round wires, this technology offers the advantage of establishing deterministic and automated bending and forming processes. The electrical properties of the insulated flat wire are typically specified by the dielectric strength for the unprocessed wire. However, especially the forming processes of bending the hairpins acts with high mechanical forces on the insulation of the wire. If damage to the insulation occurs because of these forces, this weakens the electrical properties of the motor and, in the worst case, leads to failure of the entire drive unit. Within the scope of this work, the electrical properties of the wire after processing will be investigated. A special focus of this research will lay on the influence of various parameters such as the bending radius, the bending angle, and the insulation layer thickness on the resulting dielectric strength. The wire specimens are bent on a machine which is an industrial standard for bending hairpins in a small-scale series production.