Heating and material removal process in hybrid laser-waterjet ablation of silicon substrates

A hybrid laser-waterjet micromachining technology has recently been developed for near damage-free micro-ablation. It uses a laser to heat and soften the target material and a waterjet to expel the laser-softened elemental material to decrease thermal damages and increase the material removal. A computational model for the hybrid laser-waterjet micro-grooving process for single crystalline silicon is presented in this paper using an enthalpy-based finite difference method. Laser heating and waterjet cooling and expelling with the temperature-dependent silicon properties are considered in the model to predict the temperature profiles of silicon and groove characteristics under different machining conditions. The simulation results show that the introduction of a high pressure waterjet enables to remove material at its soft-solid status much below its melting temperature, while the waterjet cooling effect can reduce the workpiece temperature during the laser non-pulse period and eliminate the effect of heat accumulation, so that the thermal damage induced by laser heating is minimized. The temperature field model is also used to predict the groove depth and profile, and it is found that the model can reasonably represent the machined groove characteristics when comparing to the experimental data.