Laser milling: Modelling crater and surface formation

Abstract

In pulsed laser-material removal systems, it is very important to understand the physical phenomena that take place during the laser ablation process. A two-dimensional, theoretical model is developed to investigate the crater formation on a metal target by a microsecond laser pulse. The model takes into account the absorption of the laser light and heating and vapourization of the target, including an adjustment to compensate for the change of state. A simple numerical technique is employed to describe the major physical processes taking part in the laser milling process. The temperature distribution in the target material during the pulse duration is analysed. The effect of the laser fluence on the resulting crater is investigated in detail. The proposed simulation model was validated experimentally for laser-material interactions between a microsecond Nd:YAG laser (λ = 1064 nm) and two different tooling materials. The measured crater depths are in agreement with the model. In addition, an analytical approach is discussed for studying the effects of crater profiles and different machining strategies on the surface formation and the resulting surface quality during the laser milling process. This approach can be employed as a tool for optimizing the process and thus broaden its use in a range of microstructuring applications. The research reported in this paper contributes to a better understanding of microstructuring capabilities of the laser milling process.