In this study, the laser welding experiments were performed with the 1 mm thickness of Al 6061-T6 using by 5 kW fiber laser welding system. The optimum laser welding condition of the lap joint has been investigated by analyzing the penetration depth and the porosity fraction through observation of the cross-sections. Based on the test results, the sound joint was obtained from the welding condition with the power of 2 kW and the focal position of -0.8 mm at the continuous laser welding speed of 2 mpm. Also, the tensile strength of the sound joint after heat treatment(170℃, 12hr) was increased almost 87% that of the base material. Especially, the fatigue test result of the sound joint showed that the fatigue cycle was 3×10 4 at the highest test load of 100 MPa.

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.

There have been continuous efforts on automating welding processes. This automation process could he said to fall into two categories, weld seam tracking and weld quality evaluation. Recently, the attempts to achieve these two functions simultaneously arc on the increase. For the study presented in this paper, a vision sensor is made, a vision system is constructed and using this, the 3 dimensional geometry of the head is measured on-line. For the application as in welding, which is the characteristic of nonlinear process, a fuzzy controller is designed. And with this, an adaptive control system is proposed which acquires the bead height and the coordinates of the point on the bead along the horizontal fillet joint, performs seam tracking with those data, and also at the same time, controls the bead geometry to a uniform shape. A communication system, which enables the communication with the industrial robot, is designed to control the bead geometry and to track the weld seam. Experiments are made with varied offset angles from the pre-taught weld path, and they showed the adaptive system works favorable results.