Analysis of the coupling efficiency of grain-oriented electrical steel using fiber laser

Laser scribing of electrical steel used for transformers improves their efficiency. In particular, the laser-induced thermal stress reduces the core losses of grain-oriented (GO) electrical steels by a refinement of the magnetic domains. A reliable process control needs precise information about the narrow temperature range, which ensures the desired transformations of the material. Therefore, optimized process designs benefit from thermal simulations of the temperature field during the laser treatment. The accuracy of such computations depends upon the knowledge of the coupling efficiency of laser radiation into the processed materials. Therefore, a combined approach of experimental measurements and numerical calculations is applied to get reliable coupling efficiency data for GO electrical steels. The results show very high coupling efficiencies in a range of about 80% for solid-state laser radiation with a wavelength of 1070 nm. Subsequent investigations on coated and uncoated sheets reveal potential reasons for the high coupling efficiency.