Thermal Aspects of the Split-Beam Laser Welding Concept

Abstract

The high cooling rates normally encountered in the application of high intensity welding processes such as laser beam welding is often detrimental to the weldment, especially for high hardenability steels. To minimize this effect, the split-beam laser welding concept is proposed and analyzed. The analysis shows that even when the intensity of the single heat source is the same as the intensity of each of the dual heat sources, the resulting cooling rate at any specific temperature is lower for the dual source process than the single source process. For example, for mild steel, the cooling rate at a point 25 mm behind the heat source (where the temperature is 1364°C) was determined to be 382°C/s for the single source system, while that for a point 40 mm behind the major source (where the temperature is 1377°C) was determined to be 206°C/s for the dual heat source system. When the heat inputs for the dual system are reduced such that the total heat input is equal to that of the single source system, the resulting temperature rise is lower at all points of the weldment for the dual system. That also means a smaller weld pool size and heat affected zone. To maintain the same weld pool size and penetration as for the single heat source system then requires an increased total heat input for the dual heat source system, with the additional input depending on the spacing between the two heat sources.