Development of forming and product properties of copper wire in a linear coil winding process

Since electric motors are becoming more important in many application fields, e. g. hybrid electric vehicles, the optimization of the linear coil winding process is an important contribution to a higher productivity and flexibility. For the investigation of the forming behavior of the winding wire the material behavior is characterized in different experimental setups using wire diameters of 0.63 mm-3.35 mm. By comparing the results of tensile tests and compression tests, a tension-compression anisotropy of the wire behavior can be noticed. The Young's Modulus, measured in cyclic tensile tests from 99-116 GPa (dependent on the amount of strain), is used for the characterization of the elastic behavior of the copper wire. Subsequently, numerical investigations of the linear winding process in a case study for a rectangular bobbin are carried out in order to analyze the influence forming parameters have on the resulting properties of the wound coil. The wire tensile force represents a key parameter concerning the geometrical properties of the wound wire and the clearance between wire and bobbin. Numerical results show that the wire cross-section decreases through bending already at standard wire tensile forces. Additionally, the clearance between wire and bobbin increases with larger wire diameters. The aforementioned results serve as fundamentals for a comprehensive modeling of the linear winding process of noncircular coil bobbins with copper wire.