Thermal Engineering Study on Friction Stir Welding(FSW)

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In the academic year 2003,the holding system of specimens for FSW experiment was designed and fabricated, and by using it, fundamental data were collected. Transient temperature behaviors of the back side surface of specimen were measured by using an infrared thermometer and a mirror which were incorporated in the holding system. Data on the friction pressure and the torque applied to the specimen by the stir rod were collected by pressure sensors and dada acquisition system. A series of experiments were performed on aluminum specimens under the conditions of various tip configurations, numbers of rotations of stir rod and axial loads. Further, a new calculation method for simulating the temperature fields in the stir rod, specimens and the backing plate corresponding to the above experimental system, which applies the spread sheet of Excel was proposed and was shown effective for practical calculation purposes. From the alignment process which compares the measured temperature change … More with time and the corresponding numerical results, the coefficient of dynamic friction between the stir rod and the specimen was successfully evaluated within practical purposes.In the next academic year 2002,based on the results obtained in the previous year, the following experimental and theoretical studies were conducted. Concerning experimental study, lots of basic data, which are required for evaluation of the coefficient of dynamic friction, were collected on aluminum and other specimens, and were analyzed. The transient temperature behaviors of the specimens with translational motion were also measured. Further, the coefficient of dynamic friction between the stir rod and the specimen was evaluated by analyzing measured torques applied to the specimen. Regarding theoretical study, the unsteady-state numerical analysis which applies the spreadsheet of Excel was further developed, and a series of calculations corresponding experiments were performed. In addition, by conducting numerical calculations on such specimens as pure aluminum, aluminum alloy, copper and nickel, non-dimensional correlation equations on top and bottom surface temperatures of specimens were proposed.From the experimental and theoretical studies, a lot of valuable results have been obtained. Namely, for example, the specific values of coefficient of dynamic friction between the stir rod and the specimen which have not shown so far were made clear in this study (for instance, about 0.25 to 0.76 for aluminum alloy A7075) ; evaluation of coefficient of dynamic friction for various weld materials were shown possible by using the proposed non-dimensional correlation equation for bottom surface temperature of specimen. Less