The characteristics of temperature variation for laser diode welding system have been analyzed with numerical investigation. The laser diode is assembled with a cap and stem by projection welding. Resistance heat, in this process, is generated by electric current at the contact surface between cap and stem within a very short time. Temperature variation of laser diode is largely affected by the welding time and the heat generated from the surface. Maximum temperature of each component in the laser diode should be lower than the melting point except for cap and stem in order to prevent welding defect. Temperature distribution of each component in the laser diode is also affected by thermal conduction mechanism. Welding defect near the insulator occurs when the resistance heat is high. Appropriate resistance heat supply to the laser diode was about 400W. The results from this study could be applicable for optimal design of laser diode welding system.

Fiber laser welding has been developed for precise welding of small and complicate components assembled on the nuclear fuel irradiation test rig. In this research, laser welding characteristics of STS316L, the main material of nuclear fuel test rig, have been studied. Several welding experiments were carried out in lap welding of the tube and the end cap made of STS316L. Process variables such as non-focal length, shield gas, laser frequency and power are optimized and compared with the results of Zircaloy-4.

Nowadays, the automotive industry has target to improve the fuel consumption due to restricted exhaust gas regulation. For this reason, the applicability of lightweight material, Al alloys, Mg alloys are also being expanded. In this concept, high strength steel, DP780 and light alloy, AL5052 are joined in the right place of the car body. However, it is difficult to join to steel and aluminum by conventional fusion welding. Generally, in respect to dissimilar metal joining by fusion welding, intermetallic compound layer formed at joint interface; hot cracking in generated. To evaluate the welding quality, tensile test and metallographic examination was carried. Especially, correlation between Heat per unit length and formation of intermetallic compound layer was minutely analyzed. Finally, optimal welding condition was selected for improvement of strength at weldment and practical use.

Numerical modeling has been carried out to analyze thermal characteristics for laser diode welding machine. Laser diode welding machine performance is largely affected by the applied current and welding period. Unsteady thermal characteristics near the laser diode welding cap has been analyzed, and most simulations were performed after applying electrical current for the duration from 0.1 to 0.5 second. Those results from this study could be applicable to the design of optimal operating condition for the laser diode welding machine system.

Laser welding is high power density welding process which is higher speed and productivity, lower thermal deformation. Recently, zinc coated sheet metal is used for many industrial due to the high corrosion resistance. This study explained that it used DOE(Design of experiment) and mathematical statistics method to optimize the conditions of high power laser welding process for zinc coated sheet metal. Finally, optimal condition for laser welding is selected for zinc coated sheet metal by alteration of welding joint width and gap.