PURPOSE: To stably prevent water infiltration under the stoppage of gas supply by providing an opening/closing mechanism which is structured to slide in the axial direction of a machining nozzle with divided shut-off plates superposed at the ends.
CONSTITUTION: Ar gas is released from a machining nozzle 1, after the foot 18 of a solid partition which is flexibly provided in the outer circumference of a shut-off nozzle 2 comes into full contact with the surface of a member 6 to be machined and, at the point of time when an approach sensor 3 at the tip end of the outer circumference of the shut-off nozzle 2 comes into contact with the member 6. Then, the opening 2a of the shut-off nozzle 2 is raised slidingly with the opening opening, and its end is raised at least to the end 1a of the machining nozzle so as to open fully. At this point, arc is generated from a tungsten electrode 5 and machining is started. Meantime, upon completion of the machining, the opening 2a of the shut-off nozzle is sealed as it is lowered slidingly by an electrical signal from a temperature sensor 4 provided inside the shut-off nozzle 2. Concurrently, the release of the gas is stopped.
OKAMURA HISANOBU
OMORI TSUNEHIKO
