Patent ID: 7370784

Claim:
A method of welding a plurality of work pieces together comprising: moving a rotating tool, rotating along an axis-of-rotation; pressing the rotating tool against the plurality of work pieces at a speed sufficient to soften the work pieces due to frictional heat and weld the work pieces together, wherein the rotating tool comprises: a rotational shaft, to which the rotating tool is fixed at a tip end, and extended along the axis-of-rotation; a rotational movement drive source for rotating the rotational shaft; a hollow surrounding shaft surrounding the rotational shaft, the hollow surrounding shaft fixed against linear translation; a rotating tool holding means for rotatably holding at least one of the rotating tool or the rotational shaft and being supported movably along the axis-of-rotation; and a linear movement drive source for linearly moving the rotating tool holding means along the axis-of-rotation to cause the rotating tool linearly move along the axis-of-rotation, wherein the rotating tool includes a pin which forms said tip portion thereof and a shoulder portion coupled with the pin so as to protrude the pin toward from one end surface thereof and having a larger diameter than the pin, and wherein the apparatus is so configured that the linear movement drive source rotates the hollow surrounding shaft, the rotating tool holding means having a hole into which the surrounding shaft is inserted, and the hole is formed with an inner threaded portion which threadedly engages with an outer threaded portion similarly formed on the outer peripheral surface of the hollow surrounding shaft, thereby transmitting a rotation of the hollow surrounding shaft caused by the linear movement drive source into a linear movement of the rotating tool holding means along the axis-of-rotation and wherein the rotating tool holding means includes a bracket made of a rigid material, and wherein the bracket extends along the axis of rotation and threadedly engages the outer threaded portion of the hollow surrounding shaft at one end portion and the other portion of the bracket rotatably holds the at least one of the rotating tool or the rotating shaft.