The influence of nonlinear friction stir welding (FSW) tool control on joint properties was investigated. Although FSW is widely applied to linear joints, it is impossible for five-axis FSW machines to maintain all FSW parameters in optimum conditions during nonlinear welding. Nonlinear FSW joints should be produced according to an order of priority for FSW parameters. Tensile test results of butt joints with rectangular change in the welding direction on the plate plane (L-shape butt joints) change with various welding parameters. Results show that a turn to the retreating side is encouraged when the welding direction changes. The method of zero inclination tool angles is effective for nonlinear and plane welding.

Friction Stir Welding (FSW) has special properties for its low distortion, low residual stress of the joints and needless skilled worker. Application of three-dimensional FSW can apply many industry, etc automobile industry or airplane industry. However, FSW is only applicable to use linier welding at present. To realize three-dimensional FSW, it is most important to improve operation accuracy. On the other hand, it is also important to clarify "the allowance of operation" for application.In this work (A) the influence of deviation; the mismatching between the butt line and the center of tool traveling line, and (B) the influence of gap; the spacing between two plates at butt line, on tensile properties of FSW joints are investigated. A5083-O alloy plates with 3 mm thickness were welded in various deviation or gap spacing conditions by a gate type FSW machine with sufficient rigidity and accuracy. It was found that the allowance of deviation is a half of probe diameter of FSW tool in the case of the butt line was set on the advancing side of tool rotation. So we have the one-fourth of probe diameter allowance in both sides by setting the butt line from the probe center in a quarter of the probe diameter to advancing side. Beyond this allowance range, tensile properties rapidly decreased. Contrary to this, the gap spacing within 2 mm did not affect the tensile properties in this experiment, and the joint strength and ductility over 2 mm gap showed a gradual decrease.

The influence of three-dimensional friction stir welding tool-control on joints' mechanical properties was investigated. Although FSW is widely applied to linear joints, it is impossible for five-axes FSW machines to maintain all FSW parameters in optimum conditions during threedimensional (3D) welding. Such 3D FSW joints should be produced according to an order of priority for FSW parameters. Butt joints with rectangular change in the welding direction on a curved plane (curved L butt joints) were welded using different three tool-control methods, which change various welding parameters. Results show that the A and C axes shortcut method is effective for 3D welding.

The influence of roll angle of the FSW tool rotation axis on tensile properties of joints was examined to clarify the allowance of deviation from proper tool posture for three-dimensional friction stir welding. A5083-O plates of 3 mm in thickness were butt welded by three-dimensional controlled FSW machine. Transversal inclination of the tool (roll angle of the tool) was continuously changed from 0 degrees to 10 degrees for both sides. Butt joints ruptured at base metal within the range of roll angle of the tool plus/minus 2 degrees, and ruptured at the thin part made by inclined tool shoulder entering in the range by plus/minus 7 degrees. Over the range of plus/minus 7 degrees, butt joints ruptured at elongated cavities made by tool inclination at the border of stir zone and base material.

The influence of nonlinear friction stir welding FSW tool control on joints' mechanical properties was investigated. Although FSW is widely applied to linear joints, it is impossible for five-axis FSW machines to maintain all FSW parameters in optimum conditions during nonlinear welding. Nonlinear FSW joints should be produced according to an order of priority for FSW parameters. Tensile test results of butt joints with rectangular change in the welding direction on the plate plane L-shape butt joints change with various welding parameters. Results show that a turn to the retreating side is encouraged when the welding direction changes. The method of zero inclination tool angles is effective for nonlinear and plane welding.