Damage failure and mapping model of PI insulation film in equivalent test of PMTMSC forming process

The polyimide (PI) film on the electromagnetic wire is an important insulation material for electronic devices, but the mechanical load during the forming process can pose a risk of damage to the polyimide film. This article studies the damage law of PI insulation film in different stress concentration areas through equivalent experiments of the forming process, and analyses the evolution law of the forming process and crack propagation. The research methods include: analysing the stress concentration area and crack initiation law based on bending loading fracture simulation method, calculating the stress and crack length based on fracture mechanics analysis method, and characterizing the crack propagation evolution law based on scanning electron microscopy (SEM) test method. Build a mapping model between the equivalent sample and the formed coil, and apply it to the forming process of the permanent magnet traction motor stator coil (PMTMSC) of China Railway High speed Train (CR450), linking the damage law of the equivalent sample to practical engineering. The results indicate that the error in residual stress between the equivalent sample and the coil prototype is 8.6 %. When the bending deflection reaches 38 mm in the equivalent test, there is a 2.8 μm crack initiation, which poses a risk of failure after passing the insulation resistance test. After optimization, the deflection of the formed coil is less than 64 mm, which can avoid insulation failure. Provide experimental basis for optimizing manufacturing and forming processes and coil structure design of electromagnetic wire electrical materials.