Laser Evaporative Heating: Influence of Laser Pulse Intensity on the Cavity Formation

Abstract

The influence of laser pulse intensity on the recession velocities of vapor-liquid and liquid-solid interfaces is examinednumerically. In order to determine the location of interfaces, the energy method is used. The mushy zone formation is considered across the zones where the phase change occurs. The energy method enables one to determine the quality of vapor and liquid qualities in the vapor-liquid and liquid-solid mushy zones. It is found that laser power intensity has a significant effect on the cavity size, particularly on the depth of the cavity. The recession velocity of the vapor-liquid and liquid-solid interfaces is high in the early heating period due to high rate of evaporation. INTRODUCTIONIn material processing, laser machining is demanding for the operations requiring precision, low cost, and a small heat affected zone. When a laser beam with sufficient power intensity interacts with the solid substrate, heating of the irradiated surface and consequent melting and evaporation processes take place. Initially, a cavity is formed, and the mass removal from the cavity takes place either by the evaporation alone or by the evaporation with the liquid ejection processes. The evaporation-only process occurs for laser short-pulses (∼10 −9 s), and liquid ejection takes place for pulses with milliseconds. The mass removal from the solid substrate through evaporation process forms the basis for the shape required in laser machining, such as a drilled hole or a cut edge. The model studies associated with laser solid substrate interactions give insight into the physical phenomenon that is involved in the process. Consequently, understanding the physical phenomenon in mass removal during laser irradiation enables us to set the appropriate controlling parameters to obtain improved end product quality, which is drilled hole or cut edges. Therefore, investigation into model studies in relation to laser machining is fruitful.Considerable research studies were carried out to examine the laser machining process. High intensity laser-induced vaporization and explosion of solid material were investigated by Dabby and Peak [1]. They formulated the heating situation analytically and obtained a temperature distribution in the vapor front with the assumption of initial temperature distribution. Steady-state and transient laser melting of solid surfaces were examined by Basu and Date [2] during laser cutting process. They indicated that the steady-state solution yielded two counter rotating circulation cells in the laser melt pool. Energy transfers and penetration velocity during a high-energy drilling process were investigated by Wei and Ho [3]. They used the enthalpy method and avoided the mushy zone in between phases through introducing temperature-correction parameters. A theoretical and an experimental study of the physical processes in relation to laser drilling were carried out by Liu et al. [4]. They discussed the hydrodynamic behavior of the vapor/plasma generated during ablation and computed the vapor expansion. The ...