This paper gives a description of an experimental study of the ultrasonic welding of copper/copper. Ultrasonic welding has made possible the welding of various materials, such as copper, aluminum and magnisium at the room temperature, quickly and easily when companied to the other welding methods. The ultrasonic vibration motion is investigated of welded material by high-speed camera . For example, horn side / anvil side materials can be on together of vibration, that the friction heat is generated between materials as a result, the joining strength increases.

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By combining 6061 aluminum alloy plate same thickness (1 mm in thickness) lap welding and butt welding was carried out by friction seam welding. Effects of welding position on microstructures and mechanical properties of joints were investigated. Microstructure of near the weld interface of lap joint showed finer microstructure than that of the base metal, and Kissing bond structure was observed in weld zone of butt joint. The Maximum tensile shear load of lap joint showed about 6 kN. The tensile strength of butt joint showed 81% that of the base metal.

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Lightweight design and reliability under collision are both important matters in vehicle body design. In this study the relation between load and deformation of the thin plate hat structure spot-welded at various intervals are obtained by experiments and FEM analysis. The experimental results are in good agreement with analysis, and the shearing and tensile force caused at spot-welded point are also investigated.

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In welding of small diameter pipe, delicate control of heat input is required because of counter heat flow against the welding direction. In the process without control, the heat flow causes too much heating and over penetration at the last quarter, and wide weld bead or melt down often occurs. These defects decrease the strength of the joint. In order to avoid these problems and to obtain the uniform weld bead over the entire circumference of the pipe, a new system was developed for automatic Tungsten Inert Gas (TIG) welding of fixed pipe. In order to estimate validity of the system, aluminum alloy pipe of 38mm in diameter was used. In the welding control system, visual sensing, speed control and fuzzy logic such as human skilled welder is doing in the welding process were adopted. The visual sensing device consists of a CCD-camera and a hyperboloidal mirror which are set in the pipe and capture inner image of the molten pool. The image was processed to find the edge of the molten pool. Then, the optimum welding speed was calculated by detected width of molten pool. As a result, the effectiveness of the system was confirmed.

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Recently, welding process has been used under various environments. Under extreme environment such as vacuum, weightless and underwater condition, the need of automation technology of welding increases. In this research, the molten pool oscillation phenomenon in underwater welding was modeled. The calculated back bead width was obtained from the oscillation frequency and the dimension of the molten pool. Arc current was controlled using the difference between target and calculated back bead width. From the results of welding control experiments, the effectiveness of the system is confirmed.

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