Numerical prediction of hole shape in energy beam drilling of metals

A procedure for the prediction of energy beam drilling in metals is described. This procedure is based on appropriate zoning of the region to be drilled and on the assumption that as metal is melted it is forced out of the hole by forces exerted by vaporizing metal. Calculations of drilling in several metals and alloys have been made for different conditions of pulse duration, power, and number of pulses. Data were obtained for mild steel, copper, aluminium, and molybdenum. The depths, diameters and shapes of the drilled holes predicted by the proposed procedure are in close agreement with experimental results. During drilling by multiple pulses there is normally a fixed time interval between pulses. Because of heat diffusion during this time, molten metal removal does not begin immediately at the start of the next pulse. The lag time, defined as the time required to initiate molten metal removal from the hole at the beginning of each pulse, can be predicted by the proposed method. When a hole is drilled by multiple pulses, the lag time increases as the hole becomes deeper.