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In most laser cutting applications, the laser beam is focused to a size of 0.15 - 0.3 mm and positioned in the centre of the cutting nozzle, which has a diameter of 0.8 - 2 mm. At laser contour cutting, the focused beam spot is usually centre in the nozzle in order to obtain a constant cut quality independent of the cutting direction. A central position assures that the conditions for exhaustion of the molten material from the cut kerf, and hereby the cut quality, remains constant at changing directions of the cutting path.Compared to conventional on-axis cutting, however, investigations have shown that by positioning the focused beam spot in the nozzle towards the same direction as the cutting direction, an increased range of cutting speeds can provide a high cut quality during high pressure nitrogen cutting of stainless steel and aluminium. These investigations have been performed using a fixed, and manually adjusted, off-axis beam position during cutting in one given, and fixed, cutting direction. Naturally, this restriction is unacceptable in industrial applications where contour cutting is applied.Due to this, a method and a system has been developed which allow the position of the focused beam spot to be automatically shifted in the nozzle dependent of the instantaneous cutting direction. This means that the position of the beam spot in the nozzle will always be off-axis and placed towards the same direction as the cutting direction. The system is based on a gyroscopic mounting of the beam guiding mirror in the beam path just above the focusing lens on a Behrens 2-dimensional cutting machine (moving workpiece). Two piezo actuators position the mirror, and hereby the beam spot in the nozzle, corresponding to the movements of the workpiece. Signal acquisition, data handling, and control signals for the actuators are handled by a conventional 486-PC.In this paper, the outline and the dynamic performance of the system is described followed by a description of results obtained with the system during cutting of stainless steel in 1 & 2 mm thickness and in 6 mm mild steel. These results show that the range of the process parameters where a high cut quality can be obtained is expanded significantly by the use of the off-axis system. Furthermore, the thermal affection of the workpiece during cutting of narrow geometries usually causing material burning, is reduced by the use of a off-axis system.In most laser cutting applications, the laser beam is focused to a size of 0.15 - 0.3 mm and positioned in the centre of the cutting nozzle, which has a diameter of 0.8 - 2 mm. At laser contour cutting, the focused beam spot is usually centre in the nozzle in order to obtain a constant cut quality independent of the cutting direction. A central position assures that the conditions for exhaustion of the molten material from the cut kerf, and hereby the cut quality, remains constant at changing directions of the cutting path.Compared to conventional on-axis cutting, however, investigations have shown that by positioning the focused beam spot in the nozzle towards the same direction as the cutting direction, an increased range of cutting speeds can provide a high cut quality during high pressure nitrogen cutting of stainless steel and aluminium. These investigations have been performed using a fixed, and manually adjusted, off-axis beam position during cutting in one given, and fixed, cutting direction. Natu... |
