Investigation On Cold Stamping-forging Hybrid Forming Technology For Large-thickness-difference Parts

Many structural parts with large surface area and large-thickness-difference are manufactured by casting or welding method. Considering the requirement of lightweight structures, the overall plastic formation technology, stamping-forging hybrid forming technology is employed to form this kind of parts. The inside wall thickness of the double-cylinder-shaped workpiece studied in the paper is 4mm while other region only 2mm. So the stamping-forging hybrid forming technology was made that firstly forward drawing the outside cylinder, then powerful backward thickening-drawing the inside cylinder to store enough metal, and last upsetting the inside cylinder.Assuming the shell element, the FEM software eta/DYNAFORM was firstly utilized to research the material flow of the stamping process and to analyze the impact of the binder force in the forward drawing, the shape of pressure ring and binder, the velocity of the pressure ring, the binder force and the gap between punch and punch-die to the thickening result of the inside cylinder in the backward drawing. Then assuming the hexahedron element, the general FEM software MSC.Marc/Mentat was utilized to research the material flow of forging process and to analyze the impact of the binder shape and the upset ratio distribution to the upsetting result.It's shown that in the powerful backward thickening-drawing process the pressure ring and binder with a fillet can force the outer cylinder metal to flow to the interior. The minimum and maximum thicknesses of inside cylinder increase monotonously with the pressure ring velocity until they reach the peak value. And the thickening result of variable binder force is better than constant one. In the forging process the binder adding a fillet near the insider cylinder can effectively guide the material flow and avoid bulking. The insider cylinder needs a two-step upset process to reach 4mm.With referencing the forming rule by FEM, experiments were carried out to verify the thickening result of the inside cylinder, and had a good agreement with numerical simulation results.The technology that firstly storing materials by stamping and then thickening by forging will make some changes to that the sheet parts usually have a uniform thickness or slightly thinned. The theory and experiment foundation of the overall plastic formation technology were established for the big-thickness-difference parts of automotive and aerospace field.