THE LASER-WELDING OF THIN METAL SHEETS - AN INTEGRATED KEYHOLE AND WELD POOL MODEL WITH SUPPORTING EXPERIMENTS

An integrated mathematical model for laser welding of thin metal sheet s under a variety of laser material processing conditions haa been dev eloped and tested against the results of experiments. Full account is taken in the model of the interaction of the laser-generated keyhole w ith the weld pool. Results calculated from the model are found to agre e well with experiment for appropriate values of the keyhole radius. T he analysis yields values for power absorption in the metal. In a comp lementary calculation the total absorption of the laser energy is dete rmined from detailed consideration of the inverse Bremsstrahlung absor ption in the plasma and Fresnel absorption at the keyhole walls. To te st these results, experiments were performed on 1 mm mild steel using a high-speed video camera, which measured the surface dimensions of th e melt pool. Processing parameters were varied to study the effect on the melt pool; parameters considered included traverse speed, laser po wer and shroud gas species. The general shape of the weld pool was fou nd to depend on whether penetration was full, partial or blind; only t he results for full penetration were compared with the theory, which i s for complete penetration only. The melt pool changed shape as the de gree of penetration reduced, from tear-drop shaped to a more parallel- sided oval. Changes in processing parameters were seen to affect the l ength of the weld pool more than the width or shape. Experimental resu lts on the melt pool dimensions correlate well with the theoretical pr edictions. To verify the absorption predictions a simple calorimetric technique was used to monitor both absorption and transmission of the laser beam by the weld sample.