Design of Flangeless Cylinder Drawing Die
The design of flangeless cylindrical drawing die is a special technology for deep drawing of flangeless cylindrical parts (such as bearing sleeves and small containers). It is suitable for materials such as low carbon steel and stainless steel with a thickness of 0.5-5mm. It can draw flat blanks into the required cylindrical size once or multiple times. The diameter accuracy of the parts can reach IT9 level and the height tolerance is ±0.1mm. The core is to control the flow rate and deformation uniformity of the material by reasonably designing the fillet radius and gap of the punch and die to avoid defects such as wrinkling and cracking. In the early stage of design, the drawing coefficient needs to be calculated according to the diameter and height of the cylindrical part. The first drawing coefficient is generally 0.5-0.65, and the subsequent drawing coefficients are increased by 0.05-0.1 in turn to ensure that the material is gradually deformed. For example, a flangeless cylindrical part with a diameter of 50mm and a height of 80mm needs to be drawn three times, the first drawing to a diameter of 70mm, the second to a diameter of 60mm, and the third to a diameter of 50mm.
The die structure is categorized as either a single-stage drawing die or a multi-station continuous drawing die, depending on the number of draw cycles. The single-stage drawing die consists of a punch, die, blank holder, discharge device, and guide mechanism. The punch is made of Cr12MoV steel, hardened to HRC 58-62, with a working surface roughness of Ra 0.4μm or less. The corner radius is 5-8 times the material thickness (10-16mm for 2mm thick material). The die is made of the same material, hardened to HRC 55-58, with a clearance of 1.1-1.2 times the material thickness (2.2-2.4mm for 2mm thick material). The corner radius is 1-2mm larger than that of the punch to guide the material smoothly into the die. The blank holder provides a force of 20%-30% of the drawing force (approximately 15-30kN) via a nitrogen spring to prevent wrinkling on the barrel wall. The multi-station continuous drawing die sets multiple drawing stations in a die, and completes multiple drawing steps in a progressive manner, which has higher production efficiency and is suitable for mass production.
The control of drawing process parameters is crucial to the forming quality. The drawing speed needs to be adjusted according to the material characteristics. The drawing speed of low carbon steel can be controlled at 100-200mm/s, while that of stainless steel needs to be reduced to 50-100mm/s to avoid overheating or cracking of the material due to excessive speed. For parts that are drawn multiple times, annealing treatment is required between each drawing (600-650℃ for low carbon steel, insulation for 1 hour) to eliminate work hardening and restore the plasticity of the material. In terms of lubrication, special drawing oil (viscosity 40-60cSt) needs to be applied between the die surface and the blank to form a uniform oil film, reduce the friction coefficient to below 0.1, and reduce mold wear and part surface scratches.
The positioning and guiding system ensures the stability of the drawing process. The blank is positioned using a combination of stop pins and guide plates. The stop pin position accuracy is ±0.1mm, and the guide plate spacing is 0.1-0.2mm larger than the blank width, ensuring accurate blank feeding. The guiding mechanism uses ball guide pins and guide sleeves. The guide pin diameter is 25-50mm, and the fitting clearance is 0.01-0.03mm. This ensures that the coaxiality error between the punch and die is less than 0.03mm, avoiding uneven wall thickness due to eccentricity. For large cylindrical parts (diameter > 200mm), an ejector device must be installed at the bottom of the mold. The ejection force is 10%-15% of the drawing force to smoothly eject the part from the die.
Debugging and maintenance must be carried out strictly in accordance with the specifications. When testing the mold, first conduct a single stroke test to check the size and surface quality of the drawn part. If wrinkles occur, the blank holder force needs to be increased; if cracks occur, the radius of the punch corner needs to be increased or the drawing speed needs to be reduced. During continuous production, check the wear of the punch and die after every 1,000 pieces, and repair the cutting edge in time if there are signs of wear. Clean the iron filings and oil stains on the surface of the mold regularly, add grease to the guide mechanism and moving parts to ensure smooth operation of the mold. For multi-station drawing dies, the relative position accuracy of each station needs to be checked regularly to ensure the continuity and stability of the drawing process.
