Three links of the production process is also basically the case. According to the three different specifications for the next. Sand blasting before the first, to the surface of the surface before the formation of the oxide scale removal. It is formed by hydraulic bulge forming method. Have the mold, the mold base is straight, above has the flange hole. Will into the pipe, pipe with hydraulic cylinder fixed on both sides of the filling liquid inward bulge, the tube is squeezed into a convex shape, the bulge removed from the appropriate position, also played out a groove. It must be shot through two times. Because of the machining process, there is work hardening, so the heat treatment is also required. The production process of pipe fittings is the case.