Multi-layer laser cutting of electrical steel sheets applied to electric machine laminations

by Nathan Dodd, Erica Ballantyne, Graeme Heron, Russell Goodall

With the move away from fossil fuels, the importance of electric machines is increasing. This is particularly the case within major engineering sectors such as the automotive industry. There is therefore a need to further develop processes which will allow for the diverse range of machining operations and large volume manufacture which will be required to overcome the inherent challenges in making this transition. Several critical components of an electric machine, such as the rotor and the stator, are made from electrical grade steel. This is a steel where the composition and processing acts to optimise the magnetic and other properties for the application. The steel is processed as thin sheet laminations and then stacked, to reduce the losses which occur within it due to the generation of eddy currents. The laminations need to be cut to shape, in an operation currently carried out most frequently by stamping from a sheet, but which could be done with greater flexibility by laser cutting (due, for example, to the absence of tooling). In laser cutting the possibility exists to perform cutting operations using what we call here a polystromata method, where several sheets are stacked and then cut simultaneously, increasing the efficiency of the operation. To date there have been few reports on this type of laser cutting process, and none that provide detail on the effect that the number of layers in a cutting stack has on critical parameters, such as the edge quality post cutting and the magnetic performance of the sheets. In this work we perform an experimental study of the process and report data in these measures, quantifying the decrease in performance as the stack increases in number of sheets.