Laser cutting of metallic coated sheet steels

This paper discusses the laser-beam machining of metallic coated sheet steels such as ZINCALUME, ZINCANNEAL and GALVABOND of 1 mm thickness. These materials are essentially zinc and aluminium coatings of varying skin thickness on steel. The experimental work explores some methods for reducing thermal damage of the coatings vis-a-vis the parent!base metal which impose severe machining restrictions by virtue of their high reflectivity and thermal conductivity. A 500 W continuous-wave, 10.6 mu m CO2 CNC laser centre was used to improve the cut quality in terms of good surface finish, reduced kerf width and dress. An analytical model was developed to establish the finite-element characteristic of the cutting process and it has been clarified that an efficient choice of the process parameters is a pre-requisite for minimum thermal damage of the coatings. The topographical characteristics of the uncut-through. kerf and surface roughness are discussed. Some visualisational experiments were also performed for further understanding of the micro-and macro-mechanics of the cutting process. It is proven that the cutting speed is a function of the input power and that the laser processing of these materials is a commercially viable option. (C) 1998 Published by Elsevier Science S.A.