Geometry of laser spot welds from dimensionless numbers

Recent computer calculations of heat transfer and fluid flow in welding were intended to provide useful insight about weldment geometry for certain specific welding conditions and alloys joined. However, no generally applicable correlation for the joining of all materials under various welding conditions was sought in previous work. To address this difficulty, computer models of fluid flow and heat transfer were used for the prediction of weld pool geometry in materials with diverse properties, such as gallium, pure aluminum, aluminum alloy 5182, pure iron, steel, titanium, and sodium nitrate under various welding conditions. From the results, a generally applicable relationship was developed between Peclet (Pe) and Marangoni (Ma) numbers. For a given material, Ma and Pe increased with the increase in laser power and decrease in beam radius. For materials with high Prandtl number (Pr), such as sodium nitrate, the Pe and Ma were high, and heat was transported primarily by convection within the weld pool. The resulting welds were shallow and wide. For low Pr number materials, like aluminum, the Pe and Ma were low in most cases, and low Pe made the weld pool deep and narrow. The cross-sectional areas of stationary and low speed welds could be correlated with welding conditions and material properties using dimensionless numbers proposed in this article.