Study on influence of angle of incidence of a CO2 laser beam on cut quality in laser beam machining

Abstract

In recent times lasers have gained popularity in machining applications. This trend has been due to the various unique properties that lasers possess which include ease of manipulation and ability to focus the beam to a small spot. There has been a lot of research on the factors that affect quality of laser machined features. The focus however, has been on laser machining with the beam perpendicular to the machined surface. In some applications, the beam is not always normal to the surface. Such applications include machining of cooling holes in engine components and engraving of freeform surfaces. The area of the workpiece that is irradiated by a laser beam of a given spot size is dependent on the angle of incidence of the beam. The effect of the angle of incidence may thus compromise on dimensions as well as the functioning of miniature components such as micro devices which are widely used today.. In this research, the effect of the angle of incidence on cut quality features is investigated. The attributes investigated are kerf width, depth of cut and the surface quality of the cut. Computer Numerical Control, CNC, is used to control the laser beam delivery system so as to guide the beam over the workpiece. Experiments are carried out on machining polymethyl methacrylate, PMMA, using a 60 W sealed, continuous wave, CO2 laser. The results of this study show that increasing the angle of incidence of the beam leads to an increase in kerf width and a decrease in the depth of cut. Increasing the angle of incidence results in deterioration of the surface finish. Increase in scanning speed results in decrease of the kerf width, depth of cut and improved surface finish. Experimental results were compared with results from analytical models for the kerf width and depth of cut. The results from the models agreed with the experimental results indicating that depth of cut can be predicted for any angle of incidence of the beam.