Influence of CO2 in the Ar process-gas on the heat-conduction mode laser beam welding process with Nd:YAG and diode lasers

Ar-CO2 mixtures are used as process-gases to optimize welding results. However, the mode of action of the gas mixture is not yet well-understood and practical applications of active gas components strongly depend on empirical experiences. This work identifies the effects of Ar-CO2 mixtures on the welding process. The influence of the variation of CO2 in the Ar process-gas on the melt-pool temperature, the alloy, the seam geometry and the absorption-coefficient is experimentally analysed. A Nd:YAG and a diode laser system have been used for the experiments to determine the dependence of the process-gas / melt-pool interaction on the laser wavelength and the beam profile. Two significant effects have been observed. First of all a higher rate of CO2 can bring more energy into the welding se am. Secondly the cross section profile can be altered. A simulation model is presented which explains some details of the mode of action and can support the choice of adapted Ar-CO2 mixtures for laser applications.