Laser micromachining of titanium alloy in water and ice at different temperatures

A clean cut surface with less thermal damage is typically desired in laser micromachining process. Many kinds of cooling substances can be employed to assist the laser ablation for limiting the thermal damage in workpiece and also gaining a higher material removal rate. This paper presents and compares the water- and ice-assisted laser ablation of titanium alloy, in which the effects of water/ice temperature, laser traverse speed and number of laser passes on morphology and dimensions of laser-ablated surface were experimentally investigated. A parametric model for the laser beam refraction at air-water/ice and water-gas bubble interfaces was also developed to determine the refracted distance at the workpiece surface under the different incident angles and water/ice layer thicknesses. The results revealed that the laser ablation in water can produce a clean groove on the metal surface, while only recast and spatters of titanium oxides were found on the laser-scanned track when processing in ice. A remarkable groove can be obtained by using high water temperature together with slow laser traverse speed and more numbers of laser passes. However, the laser beam scattering in water was more apparent than in ice due to water wave, the high refractive index of water and the formation of gas bubbles during the ablation. The findings presented in this study could provide a better understanding of the water- and ice-assisted laser ablation as well as their capability for damage-free fabrication of micro-/submicro-devices.