Design of a double compound die for blanking and drawing
The double-blanking and double-drawing die design is a highly efficient forming technology developed for deep cylindrical parts (such as oil drums and fire extinguisher cylinders). By completing the three steps of blanking, primary drawing, and secondary drawing in a single stamping cycle, the die achieves continuous deformation from flat blank to deep cylindrical component. Production efficiency can reach 60-120 parts per minute, with consistent part dimensional accuracy at IT10 level. Initially, the secondary drawing parameters are determined by assigning a drawing coefficient. The primary drawing coefficient is typically 0.55-0.65, while the secondary drawing coefficient is 0.7-0.8. For a 20 steel part (3mm thickness) with a diameter of φ100mm and a height of 150mm, the primary drawing is to φ140mm × 70mm, and the secondary drawing is to φ100mm × 145mm, with a 5mm trimming allowance. Material selection must meet elongation requirements of 30% or higher and hardness ≤ HB180 to ensure crack resistance during the secondary drawing process.
The die structure adopts a progressive layout, consisting of a blanking module, a primary drawing module, a secondary drawing module, a double blank holder system, and a synchronous guide mechanism. The blanking punch and die are made of Cr12MoV steel, hardened to HRC58-62. The edge clearance is 10%-12% of the material thickness (0.3-0.36mm for 3mm thick material) to ensure burr-free edges. The corner radius of the primary drawing punch is 8-10 times the material thickness (24-30mm for 3mm thick), and the corner radius of the secondary drawing punch decreases to 5-6 times (15-18mm), guiding the gradual thinning and deformation of the material. The double blank holder system independently controls the blank holding force of the two deep drawing processes. The first blank holding force is 25%-30% of the drawing force (about 25-30kN), and the second blank holding force is increased to 30%-35% (30-35kN). The nitrogen spring is used to precisely adjust the force to prevent wrinkling and cracking.
The process coordination mechanism is key to the simultaneous execution of the two deep-drawing operations. A cam-connecting rod combination controls the timing of the two drawing punches: After blanking is complete, the primary drawing punch descends 80mm to complete the initial forming process, followed by the secondary drawing punch, which descends 70mm to complete the secondary drawing process. The interval between the two punches is ≤0.1 second, ensuring continuous material deformation. The die utilizes a split design, with the primary and secondary drawing dies connected by locating pins. The coaxiality error is less than 0.03mm. The die working surface is hard chrome-plated (0.01mm thick) to reduce the friction coefficient to below 0.1. Extreme-pressure drawing oil (viscosity 40-60 cSt) is used to minimize die wear.
The positioning and feeding system utilizes a dual control system combining “pre-positioning and precision guiding.” After leveling, the coil is fed by a servo feeder with a step accuracy of ±0.05mm. Before blanking, the material is measured using side blades (the side blade width is 0.05mm greater than the step accuracy). After the initial drawing process, guide pins are positioned to align with the process holes. Before the secondary drawing process, V-shaped positioning blocks are added to keep radial positioning errors within 0.03mm. For parts with an aspect ratio greater than 1.5, anti-wrinkle ribs (1-1.5mm in height, 0.5mm in radius) are added to the secondary drawing module to locally increase material flow resistance and suppress wrinkling in straight wall sections.
A tiered standard has been established for commissioning and maintenance. During mold trials, the coordination of each module’s movements is verified in a single step. A trial run of 100 pieces is then conducted at 50% production speed. A three-dimensional coordinate measuring machine is used to measure the diameter change after two deep draws (the diameter decrease must be uniform with a deviation of less than 2mm for each draw). During routine maintenance, the primary drawing punch is inspected for corner wear every 5,000 pieces (wear tolerance less than 0.1mm), and the secondary drawing die undergoes magnetic particle inspection every 10,000 pieces to prevent fatigue cracks. The blank holder surface is polished weekly to maintain a surface roughness of Ra 0.4μm to ensure uniform material pressing.
