Method of producing bulge-shaped pipe

摘要

A method that produces an inexpensive and high-quality male side pipe by forming a seal groove for holding an O-ring only by means of press machining is disclosed. A male side pipe is pressed to form an expanded part at an intermediate part thereof. This expanded part is pressed to form a bulge part. Furthermore, the portion of the male side pipe from a tip end to an intermediate part of the bulge part is contracted to form a seal groove side face and a seal groove bottom face at the side of the bulge part. In addition, the portion, of the male side pipe from the tip end to the point S is pressed for thinning to facilitate the machining on male side pipe. Then, the thinned portion is widened to form a seal groove side face at the side of the tip end. By forming the seal groove side face roughly perpendicular to the axial direction of the male side pipe during these processes, the askew assembly or slanting of the O-ring can be prevented.