The effect of temporal pulse shape on drilling efficiency

A previously developed 1-D transient laser uniting model with variable properties is used to investigate effect of temporal pulse shape on drilling efficiency during laser uniting. 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 irnmobilization transformation. The final solution is obtained by an iterative scheme to satisfy the energy balance along the solid-liquid and liquid-vapor interfaces. An Energy balance is implemented by calculating the energy reflected, E_r, the energy loss due to convection and radiation at the boundaries, E_loss the energy storage, E_g, energy removal by vaporization, E_v, and energy removal by liquid expulsion, E _l at each time step. These energies sum up to the total incident energy from the laser with less than 0.1% error. Using this drilling model, we perform a study of the effect of different pulse shape on drilling efficiency as defined by mass removal per unit laser energy per pulse. Simulations are done using mild steel properties. Results for top hat and ramp temporal laser pulse shapes are presented and discussed. Energy partition and threshold are calculated. It was found that the ramp temporal laser pulse shape is more efficient in material removal.