Effect of high-frequency orbital and vertical oscillations of the laser focus position on the quality of the cut surface in a thick plate by laser beam machining

•Multi-DOF focus positioning of laser by a 6-DOF controlled maglev lens drive actuator.•Control the formation of striations by using multi-DOF oscillation of focus position.•Orbital and vertical oscillations of focus position reduce roughness of cut surface.

In laser beam machining with oxygen gas, striations are formed on the cut surface due to the cyclic oxidization reaction, which is affected by the cutting conditions and the thermal properties of the workpiece. The formation of striations causes an increase in surface roughness. In order to reduce the surface roughness, we propose controlling the formation of striations by utilizing multi-DOF oscillation of the focus position of the laser. In this paper, we construct a laser machining system in which positioning control of the focus position is achieved by driving the focal lens. The effect of orbital oscillation of the laser focus position parallel to the top surface of the workpiece and vertical oscillation perpendicular to this surface on the formation of striations was evaluated by performing laser cutting tests on thick mild steel plates. The experimental results show that control of the formation of striations can be realized by choosing the appropriate oscillation conditions. The surface roughness with oscillation was less than half that without oscillation.