Abstract
Continuous-wave (CW) lasers are widely used in laser polishing, but with CW laser polishing, it is difficult to reduce the surface roughness to 0.2 µm from an original value exceeding 1.0 µm. The aim of this study is to develop an innovative method of laser polishing assisted by a steady magnetic field to overcome that bottleneck and produce smoother surfaces. Two experiments confirm the hypothesis that the molten pool overflows during melting peaks to flow into valleys in CW laser polishing, resulting in secondary roughness that causes the aforementioned quality bottleneck. To either reduce or eliminate this secondary roughness, a steady magnetic field is used during CW laser polishing to suppress the overflow of the molten pool. A three-dimensional surface profiler, a scanning electron microscope, and a nanometer indentation tester are used to characterize and analyze the microstructure and properties of the materials. The experimental results show that the Lorentz force due to the steady magnetic field plays an important suppression role in reducing the secondary roughness.
Highlights
Laser polishing of tool steel involves continuous-wave (CW) laser polishing and pulsed laser polishing.1–4 CW lasers are often used to polish rough surfaces, whereas pulsed lasers are used to polish smoother surfaces.2,4,5 Much of the published research concerning CW laser polishing involves tool steel, with polishing achievements of 40%–87% roughness reduction from the initial surface state
The performance of diode-pumped solid-state and CO2 lasers in CW mode for the laser polishing of DIN1.2379 (AISI D2) tool steel was evaluated by Ukar et al.,6 who developed a mathematical model to predict the resulting surface roughness,7 and both laser sources achieved comparable reductions in surface roughness (75%–80%)
Richter et al.1 demonstrated the suitability of the critical frequency and capillary smoothing prediction model for the CW laser polishing of Co–Cr–Mo alloy, providing 70% roughness reduction
Summary
Laser polishing of tool steel involves continuous-wave (CW) laser polishing and pulsed laser polishing. CW lasers are often used to polish rough surfaces, whereas pulsed lasers are used to polish smoother surfaces. Much of the published research concerning CW laser polishing involves tool steel, with polishing achievements of 40%–87% roughness reduction from the initial surface state. Much of the published research concerning CW laser polishing involves tool steel, with polishing achievements of 40%–87% roughness reduction from the initial surface state. The performance of diode-pumped solid-state and CO2 lasers in CW mode for the laser polishing of DIN1.2379 (AISI D2) tool steel was evaluated by Ukar et al., who developed a mathematical model to predict the resulting surface roughness, and both laser sources achieved comparable reductions in surface roughness (75%–80%). Hafiz et al. conducted laser-polishing tests on H13 tool steel with different overlap percentages and improved the surface roughness by 87%. Zhou et al. used a CW laser with optimized irradiation to polish S136H steel, achieving an effective surface roughness reduction of 44%–81%. In the laser micro-polishing of inclined or curved metallic surfaces, Pong-Ryol et al. proposed a method for controlling the energy density of an ultraviolet pulsed laser in real time by controlling the CW laser spot size, showing improvements in surface roughness of up to 56.4% and 57.3%, respectively
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