CO2 laser cutting of metallic coated sheet steels

Sheet steels with zinc and aluminium coatings, such as GALVABOND, exhibit an anomalous behaviour when subjected to laser light and pose some severe machining limitations by virtue of the high light reflectivity and thermal conductivity of the coatings as well as the difference in physical properties between the coating and substrate materials. An investigation of the machinability of GALVABOND using CO2 laser cutting technology is presented. It shows that by proper control of the cutting parameters, good quality cuts are possible at high cutting rate. Visual examination indicates that when increasing the cutting rate to as high as 5000 mm/min, kerfs of better quality than those produced using the parameters in an early study can be achieved. Some kerf characteristics such as the width, heat affected zone and dross with respect to the process parameters are also discussed. A statistical analysis has arrived at the relationships between the cutting speed, laser power and workpiece thickness, from which a recommendation is made on the selection of cutting parameters for process control and optimization