Abstract: A friction stir welding device includes a table that has a placement surface on which a workpiece is to be placed and is rotatable about a table rotation axis intersecting the placement surface, a tool holder movable relative to the table in a direction along the placement surface and rotatable about a holder rotation axis parallel to the table rotation axis, and a welding tool supported by the tool holder and rotating about a tool rotation axis intersecting the holder rotation axis. A control device has a biaxial operation mode in which the welding tool in a rotating state is pressed against a welding portion of a side surface of the workpiece, the welding tool is relatively moved along the welding portion by rotating the table, and the tool holder is rotated so that the welding tool is directed in a normal direction of the welding portion.

Abstract: A friction stir welding attachment includes a body configured to be attached to a spindle of a machine tool, a metalworking shaft rotatably supported by the body and including an attachment portion configured to attach a welding tool at an end thereof, and a pair of press components supported by the body and provided at respective sides across the attachment portion. The press components are each made of disc-shaped elastic material and are each supported in a manner rotatable around a rotation axis diagonally intersecting a rotation axis of the metalworking shaft.

Abstract: A friction stir welding attachment includes a body configured to be attached to a spindle supported by a spindle head of a machine tool, a metalworking shaft rotatably supported by the body wherein a welding tool is attachable to the metalworking shaft, a plurality of air motors provided in the body, and a transmission mechanism configured to transmit a rotation of each of the plurality of air motors to the metalworking shaft. A fixing portion is provided to supply external air to the plurality of air motors. A drive air distributor is provided to distribute drive air to the air motors. A rotation sensor for detecting a rotation state is provided to the metalworking shaft.

Abstract: The present invention provides a method of improving soft ground.In this method, slurry formed by a mixture of cement-based hardener and water is supplied to the soft ground under pressure and is mixed with soft soil thereby to harden the same. Then, at least when a ground improvement machine having mixing propellers is penetrated into the above-mentioned soft soil, the cement-based hardening slurry is discharged from the mixing propellers.Further, in another method of improving soft ground according to the present invention, slurry formed by a mixture of cement-based hardener and water is supplied to the soft ground under pressure and is mixed with soft soil. Then, when deep and short walls, both consisting of mixed layer of the cement-based hardening slurry and the soft soil are formed one after the other, a plurality of deep walls are formed at a distance therebetween and then the short walls are jointly formed between a plurality of these deep walls.