Investigation on surface smoothing of mold material by pulsed laser irradiation of 532 nm

Manual polishing has been commonly applied as finishing process for metal molds with complicated-shape, but it takes a long time to achieve required surface roughness. Thus, high-efficient polishing method and surface smoothing in micro-areas are required for precise molds. Therefore, the reduction method of surface roughness for metal mold was experimentally investigated by controlling the pulse duration and the waveform in microsecond pulsed Nd:YAG laser irradiation of 532 nm wavelength, which can achieve stable absorption of laser energy even for difficult-to-weld materials with high reflectance. The maximum height roughness can be reduced from 4.0 μm to 1.0 μm by setting an appropriate pulse duration. Excessive heat input generates the edge at the circumference of laser irradiated area due to the movement of molten material. However, control of pulse duration enables the reduction of edge formation. Shorter pulse duration from 2.0 μs to 4.5 μs can perform a wider range of power density without edge formation, compared with longer pulse duration. The range of power density without edge formation can be increased by controlling the temporal input power, which can improve the process controllability of surface smoothing of mold material.