Design of compound die for blanking, deep drawing twice and edge extrusion
The design of a composite die featuring blanking, double-drawing, and edge extrusion is a highly efficient die technology that integrates multiple forming processes. It is suitable for parts requiring multiple deep-drawing cycles and requiring smooth edges, such as deep cylindrical containers with smooth edges. Blanking, primary drawing, secondary drawing, and edge extrusion can be completed in a single stamping process, increasing production efficiency by over 50% compared to single-process dies. Part verticality tolerance is less than 0.1mm/m, making it suitable for mass production. Initially, the parameters for the double-drawing process are determined based on the part’s final height, diameter, and material thickness (typically 1-4mm). The primary drawing coefficient is set at 0.55-0.65, while the secondary drawing coefficient is set at 0.7-0.8 to ensure gradual material deformation and avoid cracking. For example, a part with an 80mm height and a 50mm diameter undergoes a primary drawing to a diameter of 65mm and a height of 35mm, followed by a secondary drawing to a diameter of 50mm and a height of 75mm. Finally, edge extrusion is used to adjust the height to 80mm while ensuring smooth edges.
The die structure consists of a blanking punch and die, a primary drawing punch, a secondary drawing punch, a side extrusion die, a blank holder, a discharge device, and a guide mechanism. The blanking punch and die are constructed from Cr12MoV alloy tool steel, hardened to HRC58-62. The blanking clearance is 8%-12% of the material thickness to ensure part quality. The corner radius of the primary and secondary drawing punches decreases in sequence: the primary drawing punch has a corner radius of 6-8 times the material thickness, while the secondary drawing punch has a corner radius of 4-6 times the material thickness. For a 2mm thick material, the primary corner radius is 12-16mm, and the secondary corner radius is 8-12mm, guiding the gradual deformation of the material. The side extrusion die utilizes carbide inserts with a hardness of HRA89-91 to ensure a smooth edge after side extrusion. The clearance between the die and the side extrusion punch is controlled to 0.01-0.02mm.
The force and stroke control of each process are crucial. The blanking force, the second drawing force and the extrusion force need to be reasonably distributed, and the total punching force needs to match the tonnage of the press. The blank holder is divided into the first drawing blank holder and the second drawing blank holder, which provide corresponding blank holder forces respectively. The first drawing blank holder force is 20%-25% of the first drawing force, and the second drawing blank holder force is 25%-30% of the second drawing force to prevent wrinkling of the material in each drawing stage. The extrusion force is 15%-20% of the total drawing force to ensure sufficient edge extrusion and consistent height. The stroke of each punch is designed according to the process sequence. After the blanking is completed, the first drawing punch moves downward to complete the first drawing, and then the second drawing punch continues to move downward to complete the second drawing. Finally, the extrusion punch moves downward to achieve extrusion, and there is no gap between each stroke.
The guiding and positioning system ensures precise positioning during each process. It utilizes dual guide pins and guide sleeves, with a diameter of 25-35mm and a clearance of 0.005-0.01mm, to ensure synchronized movement of all mold components. Blanks are positioned using retaining pins and guide plates, with a positioning accuracy of ±0.05mm. A positioning step is provided between the two drawing stages to ensure accurate positioning during the secondary drawing. A ejector device, comprised of multiple ejector pins, is installed at the bottom of the mold. This device lifts the workpiece after each process is completed, facilitating subsequent steps. Observation windows are also provided on the side of the mold to monitor the stamping process and identify any problems promptly.
Commissioning and maintenance must be carried out strictly in accordance with specifications. During mold trials, the forming quality of each process is checked step by step. The blanking dimensional deviation must be less than 0.2mm, the height deviation of the first and second deep drawing must be less than 0.15mm and 0.1mm, respectively, and the edge flatness error after extrusion must be less than 0.05mm. During continuous production, five parts are randomly inspected every hour, and key dimensions are measured to ensure compliance with requirements. After every 1,000 parts, debris is cleaned from the mold, and the wear of each cutting edge and punch is inspected. The drawing punch surface is polished if wear exceeds 0.03mm, and the carbide inserts of the extrusion die are replaced promptly if wear is observed. The guide mechanism is regularly greased to ensure flexible mold movement and extend its service life.
