ABSTRACT
What is Friction Stir Welding?........................................................................... 138 Solid-State Welding ........................................................................................ 138 Advantages of Friction Stir Welding ........................................................... 139
Origins and Development of the Process ........................................................ 140 The Welding Institute Patent ........................................................................ 140 The Retractable Pin Tool ................................................................................ 140 The Self-Reacting Tool ................................................................................... 140 Current Status of Friction Stir Welding ....................................................... 141
Metal Flow in Friction Stir Welding ................................................................. 141 Plastic Flow Stability and Instability ........................................................... 141 The Shear Interface and the Rotating Plug Model .................................... 142 Sticking and Slipping at the Tool-Metal Interface ..................................... 143 The Wiping Mechanism of Metal Transfer ................................................. 144 The Mechanism of Welding .......................................................................... 145 Flow Oscillations and Banding .................................................................... 145 Streamlines and Flow Traces ........................................................................ 146
Pressures and Forces ........................................................................................... 150 Torque .............................................................................................................. 150 Drag .................................................................................................................. 152 Plunge Force .................................................................................................... 154
Defects................................................................................................................... 154 Lack of Fill Defects: Trenches, Surface Fissures, and Wormholes ........... 155 Tears ................................................................................................................. 156 Residual Oxide Defect ................................................................................... 156 Galling .............................................................................................................. 157 Lack of Penetration ........................................................................................ 158 Allowable Parameter Window ..................................................................... 158
Tool Design........................................................................................................... 160 Tool Materials.................................................................................................. 161 Tool Geometries .............................................................................................. 162
Conclusion ........................................................................................................... 163 Acknowledgments .............................................................................................. 164 References ............................................................................................................. 164
The friction stir welding (FSW) process joins metal by moving a rotating pin along a seam. The pin literally stirs the metal together. At the surface of the weld metal is a shoulder rotating with the pin and pressing against the workpiece surface. Without the shoulder, metal would be free to flow up the pin and the pin would plow the metal to produce a cut rather than a weld. Figure 6.1 illustrates a FSW tool embedded in a metal seam. The workpiece rests on an anvil not shown in the figure.
