Core loss reduction in grain-oriented silicon steels by excimer laser scribing Part I: experimental work

In the fabrication route of core laminations used in motors and transformers, a laser is often considered to scribe the steel surfaces after cold-rolling and annealing in order to reduce the energy losses associated with hysteresis and eddy currents. In this work, a 248 nm wavelength, 23 ns pulsed excimer laser was used to scribe the grain-oriented electrical steel grade M-4. A core loss reduction of 26% maximum has been achieved under a specific set of laser parameters. This is substantially higher than normally possible (10%) with the traditional Nd:YAG and CO2 lasers. The improved core loss reduction was attributed to the beneficial thermal stress distributions developed during short-pulsed excimer laser scribing process that in turn refined the magnetic domains and reduced the eddy current losses. Part II will describe a comprehensive, finite-difference thermal model that is capable of predicting thermal stresses and correlating the stress distributions with laser parameters. The model will facilitate obtaining the optimum laser parameters that will further reduce the core losses because there is potential for reducing the core losses up to 70% in grain-oriented steels. (C) 2001 Elsevier Science B.V. All rights reserved.