The invention provides a
swelling pressure composite forming method for a large-section-difference special-shaped section
pipe fitting and relates to a forming method for a large-section-difference special-shaped section
pipe-shaped part. The
swelling pressure composite forming method comprises the main steps that 1, the perimeters and the equivalent diameters of a plurality of cross sections on the to-be-formed large-section-difference special-shaped section
pipe fitting are determined, and the structure of a
swelling pressure composite forming mold and the inner
cavity size and initial position of a side
extrusion mold are determined; 2, an equal-
diameter circular-section pipe blank with a certain length is
cut and put into the swelling pressure composite forming mold; 3, the equal-
diameter circular-section pipe blank is filled with a pressure medium with a certain pressure through a pressure medium inlet, and a variable-
diameter circular-section pipe blank is obtained through swelling; 4, the side
extrusion mold is driven to extrude the variable-diameter circular-section pipe blank, and the large-section-difference special-shaped section
pipe fitting is obtained; and 5, the pressure is released, and after the swelling pressure composite forming mold is opened, the formed
pipe fitting is taken out. The swelling pressure composite forming method is used for forming large-section-difference special-shaped section pipe fittings.