Keyhole collapse during high intensity beam drilling

In this study, we identify the conditions for the keyhole collapse during high power density laser and electron beam drilling processes from fundamental principles of thermal physics. Drilling with a high intensity energy beam becomes incapable and inefficient if the keyhole induced is collapsed. Drilling encounters in many diverse industrial application areas including biomedical devices, printers, flat-panel displays, semiconductors devices and telecommunications systems, and keyhole welding. The approach adapted is to probe the quasi-steady, one-dimensional compressible flow behavior of the two-phase vapor–liquid dispersion in a vertical keyhole of varying cross-section, paying particular attention to the transition between the annular and slug flows. Keyhole collapse is interpreted from balance of normal pressures between mixture gas, recoil, liquid and capillary pressures governed by the Young–Laplace equation. It shows that drilling is susceptible to collapse for higher Mach number and radius at the base, friction factor, and ratio of specific heats at constant pressure-to-constant volume, and lower the surface tension parameter, and liquid pressure at the base for a supersonic flow in the keyhole. A subsonic flow usually gives rise to collapse. Controlling the factors to enhance efficiency and quality of drilling therefore becomes achievable.