Heat-resistant laser scribing with high power continuous wave laser beam sources

The magnetic properties of grain oriented silicon steel can be improved by an additional treatment method. Domain refinement techniques like mechanical scratching, laser scribing or plasma flame can be applied after the process of rolling in order to reduce the core losses due to mechanical or thermal stress that refines the magnetic domains. The most commonly used techniques is laser scribing due to its no-contact nature and the slight damage to the surface coating [1]. Therewith, the core losses can be reduced by typically 10%. However, after the annealing of laser domain refined material, the induced thermal stress is removed and the effect of the improvement of the magnetic properties is reduced dramatically [2]. Hence, such methods cannot be used for material in e.g. wound-core transformers. In this article we report about heat-resistant laser scribing of grain oriented electrical steel. The tests were performed with the LMDR (Laser Magnetic Domain Refimenent) test system and focuses on high power continuous wave laser beam sources in the near infrared with laser output power of more than 1 kW. The specific aim is a heat-resistant core loss reduction due to laser scribing by generating grooves on the sheet surface. The tests have shown that a core loss reduction of about 8% can be achieved. Therefore, the general principle of laser remote cutting was adapted to the heat-resistant laser scribing process in order to obtain suitable groove geometries, which have been evaluated in relation to their magnetic properties.