Molding method and device of step shaft die forging with flange plate in middle

The invention relates to a molding method and device of a step shaft die forging with a flange plate in the middle. The molding method comprises the steps that the diameter of a to-be-forged bar is determined according to the volume of the middle flange plate of the designed forging and the preset upsetting ratio; a tie die is adopted to pre-forge the bar with determined diameter for molding, andan intermediate blank is obtained; the intermediate blank comprises the middle flange plate and a rod part penetrating through the middle flange plate; the rod part is bent to obtain an oblique rod part, and the curvature of the oblique rod part is the sum of the inclination and the bending offset of the designed forging; the bending offset is determined according to the inclination of the designed forging and the plasticity of the bar; the oblique rod part is divided into a head part and a tail part by the middle flange plate; the head part is flattened to obtain a forged blank, and the forged blank is composed of th