Due to current political objectives aiming at the electrification of the automotive powertrain, electric drive production nowadays is confronted with new challenges regarding the power density and efficiency of machines and their subcomponents (i.e. stators, rotors and control units). To meet these challenges, conventional stator manufacturing methods are increasingly being replaced by novel production technologies such as the hairpin technology and the flatpack method. These technologies do achieve comparatively high mechanical copper fill factors and thus better stator performance. The flatpack method represents a bending process of a flat, comb-like assembly of numerous electrical steel lamellas with assembled prebent copper windings, providing similar copper fill ratios as the hairpin technology. In contrast to hairpin technology, however, flatpack bending does not require extensive welding operations of electrical conductors, which cause decreased robustness in mass production. Instead, the roundness of the bent inner stator geometry depends on the ability of adapting process parameters to the workpiece properties. Roundness deviations do influence possible air gaps between stator and rotor, and thus show significant impact on the performance of the electric machine. For this reason, an advanced finite element model was developed, allowing the multiple flatpack bending steps and the subsequent joining operation to be simulated as accurately as possible. The forming simulation results in a circular stator geometry with roundness deviations that depend on workpiece properties and process parameters. For validating the finite element model, three real flatpacks were bent, its ends were welded together as a ring and subsequently measured with a coordinate measurement machine. Furthermore, the numerical model was used to quantify sensitivities of bending parameters on the resulting roundness of the stator. The subsequent optimization procedure provides a systematic approach to optimize bending parameters and to reduce roundness deviations.
Numerical Simulation and Experimental Validation of Flatpack Bending and Joining Process
2020-12-08
1167952 byte
Conference paper
Electronic Resource
English