Influences of separation and joining processes on single tooth laminated stacks

Rotor and stator stacks consist of laminated electrical steel sheets and represent the essential components of an electric drive. The process chain for the production of laminated stacks comprises two core steps: first, the separation of the final contour of the electrical sheets and, second, the joining of individual sheets to a laminated stack. Both steps can be executed by different technologies. In this contribution, the influences of the separation technologies stamping and laser cutting on material properties of the individual sheets were investigated. In addition, different joining possibilities for stacking of the electrical sheets were also part of the study. Here, gluing, interlocking, baked varnish joining and laser welding were considered. For the laminated stack, a single tooth geometry was chosen, which was produced in three different lengths. In addition, a wide variety of sheet material was used - given a range of material thicknesses between 0.1 and 0.35 mm. Sheets and single teeth were measured with respect to their mechanical, geometrical and electro-magnetic properties, respectively. The measurements of the sheets, for instance, comprised burr height, contour and microhardness. In all stamped materials a significant increase in microhardness can be seen at the stamped edge. The geometrical properties of the laminated stack, namely dimensions, form and orientation are relevant for the assembly of the electric drive and were measured with tactile coordinate metrology. These measurements show that gluing as well as stamping lead to an increase of manufacturing variances with increasing length of the laminated stacks. On the other hand, baked varnish stacking shows very stable results with low deviations. Laser welding shows good results in the geometric measurements as well. Depending on the application, laser welding can thus be seen as a future alternative to common stacking technologies. The measurement of the electro-magnetic properties reveal a higher increase in power loss on stacks produced from laser cut sheets than on those made from stamped material. This difference is visible only on measurements of stacked sheets such as laminated ring cores or single teeth. Non-laminated sheets measured at the Epstein frame show no difference in deterioration of the electro-magnetic properties between both separation technologies.