The threshold and efficiency of material removal

A transient one-dimensional laser drilling model with variable properties is developed for a finite thickness material. The model contains three different physical domains, solid, liquid and vapor. The material properties such as absorptivity, thermal conductivity, and heat capacity can be functions of temperature. The governing equations in each domain are solved numerically using the boundary immobilization transformation. The final solution is obtained by an iterative scheme to satisfy the energy balance along the solid-liquid and liquid-vapor interfaces. The temporal laser power can be arbitrary. Sub-minute solution times are typical, permitting the rapid investigation of a design space. In this presentation, the numerical model is used to predict the removal threshold, mass removal rates and drilling efficiency for various laser parameters. A specific simulation is performed using mild steel properties. The physics of material removal and removal threshold will be discussed and results will be presented.