Characterization of the effect of laser scribing on the isolation coating of electrical steel

The demand for high energy efficiency leads to an ongoing development of better material grades of grain oriented electrical steel, which is used as core material in power or distribution transformers. In order to reduce the core losses of the silicon steel after the process of rolling different methods can be used, such as mechanical scratching, plasma irradiation, spark ablation and laser scribing. All these techniques induce mechanical or thermal stress that refines the magnetic domains. Due to the no-contact nature and the ease of integration laser scribing is the most commonly used technology, but with the drawback of laser-induced damage of the isolation layer [1], [2]. In this study the material ablation of the isolation layer due to high power continuous wave CO2 (10.6 mm) and fiber laser beam sources (1.07 mm) was investigated in order to evaluate the damage threshold of the coating withrespect to the treatment parameters. The study was performed with the so-called LMDR (Laser Magnetic Domain Refinement) test system to realize industry-related process parameters with spot velocities up to 300 m/s and laser output powers up to 4000 W. The experimental results are combined with material studies to characterize the ablation process related to the difference in the absorption behavior of the material based on the difference in wavelength [3].