Metal drilling with a CO2 laser beam. I. Theory

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Abstract
The initiation and evolution of a ‘‘keyhole’’ produced with a CO2 laser beam in a metal plate is analyzed, accounting for the following effects either exactly or by estimates of their limiting values: the spatial intensity profile of the beam, the temperature‐dependent absorptivity, attenuation of the beam intensity by the metal vapor, the exothermic reaction in the presence of oxygen, evaporative material removal and flushing of molten drops, heat conduction within the workpiece, phase transitions from solid to liquid and from liquid to gas, and heat losses at the workpiece boundaries. A study of the drilling of aluminum plates shows the relative effect of these parameters on the crater shape and penetration time. Simple criteria for initiation, penetration rate, and shift to spontaneous burning are presented. In a companion paper experimental results are analyzed to validate the formalism and to yield estimates of the interaction parameters for a specific exposure condition.