| A thermal analysis of the multiple beam laser welding problem is presented, and includes closed form analysis, numerical simulation, and experimental studies. The objective of the study is to investigate heat flow during dual-beam laser welding and to control phase transformation after solidification.;The analytical and numerical solutions show that the cooling rates and transverse temperature gradients decrease when a preheating laser beam is applied, and is accompanied by a reduction in the formation of hard phases in the weldment. This was also verified by experiments.;The analytical solution involves both circular and elliptical Gaussian distributed heat source models of the minor heat source for preheating, while the major heat source was modeled as a line with finite penetration depth for the keyhole effect. The analytical solution shows that higher preheating power and smaller inter-beam spacing result in lower cooling rates and transverse temperature gradients, and it was also found that post-heating has better effect on reducing cooling rates, while preheating is more effective in reducing transverse temperature gradients.;The numerical simulation is based on a two-dimensional adaptive moving finite element method. Convection and radiation heat transfer boundary conditions, Gaussian distributed heat sources, latent heat effects, and temperature dependence of the material properties are included in calculating the transient temperature field during dual-beam laser welding. The simulation was applied in dual-beam laser welded tailored blanks to investigate the transient temperature field and cooling rates in joining of two metal sheets of different thicknesses. Experiments were also conducted to verify the simulation results, and there was good agreement between the experimental and simulation results.;Bead-on-plate laser welding was also done on AISI 4140 steel. Both microstructural observation and micro-hardness test were performed. The experimental results indicate that dual-beam laser welding reduces the volume fraction of martensite formed and resulting hardness of the weldment. |
