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 transformer s, a laser is often considered to scribe the steel surfaces after cold-roll ing and annealing in order to reduce the energy losses associated with hyst eresis and eddy currents. In this work, a 248 nm wavelength, 23 ns pulsed e xcimer 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 possib le (10%) with the traditional Nd:YAG and CO2 lasers. The improved core loss reduction was attributed to the beneficial thermal stress distributions de veloped during short-pulsed excimer laser scribing process that in turn ref ined 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 wit h laser parameters. The model will facilitate obtaining the optimum laser p arameters that will further reduce the core losses because there is potenti al for reducing the core losses up to 70% in grain-oriented steels. (C) 200 1 Elsevier Science B.V. All rights reserved.