The welding of thin metal sheets with CO2, CO and pseudo continuous Nd: YAG lasers investigated by means of an integrated mathematical model

Abstract

An integrated mathematical model for the laser welding of thin metallic sheets has been developed in a previous paper and compared in detail with the results of experiments for the case where a continuous CO2 laser is used in the welding process. This mathematical model is a predictive model based only on fundamental physical processes. The model has been verified by comparison of the theory with the results of experiments for the laser welding of steel and titanium. These comparisons showed excellent agreement of the model with the results of experiments for low and moderate translation speeds of the material specimen. For high translation speeds some departure of the predictions of the model from the results of experiments has been noted and is considered mainly to arise from the increasing contribution of Fresnel absorption with rising translation speeds of the material specimen. The calculated Fresnel contribution, in turn, depends on a knowledge of the parameters describing this process and the information is poorly known, particularly in its dependence on temperature. This paper extends this model to the cases of a continuous CO laser and a pseudo continuous Nd:YAG laser. The power absorbed per unit depth in the plasma due to inverse bremsstrahlung processes is calculated using the techniques employed in the theory of the integrated model employing the finite difference approach, as well as using an analytical evaluation of this contribution based on the concept of the linking intensity. This analytical approach involving the linking intensity was developed by some of the authors in a previously published work. The calculation of the Fresnel absorption contribution in this paper explores the wavelength dependence aspect of this phenomenon. Detailed predictions are made to facilitate the comparison of the model with the results of experiments for different materials at CO and Nd:YAG wavelengths.An integrated mathematical model for the laser welding of thin metallic sheets has been developed in a previous paper and compared in detail with the results of experiments for the case where a continuous CO2 laser is used in the welding process. This mathematical model is a predictive model based only on fundamental physical processes. The model has been verified by comparison of the theory with the results of experiments for the laser welding of steel and titanium. These comparisons showed excellent agreement of the model with the results of experiments for low and moderate translation speeds of the material specimen. For high translation speeds some departure of the predictions of the model from the results of experiments has been noted and is considered mainly to arise from the increasing contribution of Fresnel absorption with rising translation speeds of the material specimen. The calculated Fresnel contribution, in turn, depends on a knowledge of the parameters describing this process and the infor...