THE PENETRATION DEPTH IN KEYHOLE WELDING WITH PSEUDOCONTINUOUS ND-YAGAND CO LASERS INVESTIGATED MATHEMATICALLY

The laser welding of metals using continuous CO2 lasers is a well-esta blished industrial process; it has been studied in detail experimental ly and theoretically. One problem of importance is to determine the th ickness of the largest work piece that can be welded with complete pen etration occurring at all times in a reliable fashion. There is empiri cal evidence that indicates that the keyhole radius at the top of the work piece is almost exactly three times the radius at the bottom in t he case of maximum penetration. Theoretical interpretations have been constructed to explain this result and experimental evidence seems to support the predictions of models based on these interpretations in th e case of the CO2 laser operating on steel. A question of interest is whether the same mechanisms apply in the case of the pseudo-continuous Nd-YAG and CO lasers and if so what are the consequences. This paper investigates the differences in the theory and applies it to these two cases. Predictions are obtained for the type of behaviour that might be expected under such circumstances.