Patent ID: 7264764

Claim:
A method of manufacturing a branching pipe having a first pipe and a second pipe, the second pipe being branched off from the first pipe, the manufacturing method comprising: an extrusion step of extruding a first extruded tubular member and a second extruded tubular member, the second extruded tubular member being substantially parallel to the first extruded tubular member; a first forming step of conveying molds arranged on both sides of the first extruded tubular member and the second extruded tubular member and forming the first extruded tubular member and the second extruded tubular member corresponding to molding surfaces of the molds, so as to mold the first pipe and the second pipe; a second forming step of thermally welding part of the second extruded tubular member with an outer wall of the first extruded tubular member and closing parts of the second extruded tubular member to form a welding joint portion; a hole formation step of forming a connection hole for connecting a conduit of the first pipe with a conduit of the second pipe in the welding joint portion; wherein the first forming step has a step of blowing a compressed gas into the first extruded tubular member and the second extruded tubular member; and the second forming step has a step of stopping the blow of the compressed gas into the second extruded tubular member, while blowing the compressed gas into the first extruded tubular member to expand the first extruded tubular member, so as to form the welding joint portion.