Design of the small hole punching die with ultra-short punch
The design of impact-type ultra-short punch small hole punch is a difficult technology in the field of precision stamping. It is suitable for punching small holes with a hole diameter of 0.5-3mm. It is widely used in industries such as electronic components and precision instruments. Its ultra-short punch structure can effectively solve the bending and breaking problems of traditional long punches. The key challenge of small hole punching is the insufficient strength of the punch and the difficulty of chip removal. Therefore, the mold design needs to adopt an impact structure to achieve material separation through high-frequency impact, while shortening the punch length (usually 3-5 times the hole diameter) to improve rigidity. In the early stage of design, the punching force needs to be calculated based on the small hole diameter and material thickness (such as 0.3-1mm brass or phosphor bronze). The formula F = Lσb t (L is the punching circumference, σb is the material tensile strength, and t is the thickness) is used. For example, for punching brass with a diameter of 1mm (σb≈370MPa), the punching force is about 1.16kN. Based on this, an impact device with an impact frequency of 100-150 times/second is selected.
The core structure of the mold consists of an ultra-short punch, die, guide sleeve, and discharge device. The ultra-short punch is made of high-speed steel (W18Cr4V), achieving a hardness of HRC 63-65 after quenching and low-temperature tempering. The working diameter is equal to the hole diameter, and the length is only 3-10mm (for example, a 1mm diameter punch is 5mm long). The tail is connected to the die handle through a transition fit with a clearance of 0.005-0.01mm. The die is made of cemented carbide (WC-Co alloy, 8%-10% Co content), with a hardness of HRA 89-91. The die hole is machined using electrospark perforation, with a wall roughness of Ra 0.1μm and a cutting edge radius of ≤0.01mm, ensuring a smooth hole after punching. The guide sleeve is made of bronze, with a clearance of 0.002-0.005mm between the inner hole and the punch, ensuring precise guidance and preventing radial deviation of the punch.
The chip removal and lubrication system design directly affects the stability of blanking. A chip removal hole is set at the bottom of the die, with a diameter 0.2-0.3mm larger than the punching hole diameter, and the length of the chip removal hole does not exceed 1.5 times the thickness of the die, so that waste can be discharged easily. Oil-gas lubrication is adopted, and compressed air carries lubricating oil (extreme pressure emulsion is selected) into the gap between the punch and the guide sleeve through the micro oil hole on the guide sleeve. The oil volume is controlled at 0.1-0.2ml/min, which ensures lubrication and avoids oil pollution of the workpiece. For continuous blanking, an elastic unloading plate can be set on the upper surface of the die, and polyurethane rubber is used as the elastic element. The unloading force is 10%-15% of the blanking force to ensure that the workpiece is separated from the punch in time to prevent waste accumulation.
The impact mechanism and buffer design need to match the characteristics of small hole punching. The impact drive mechanism adopts electromagnetic or hydraulic drive, and realizes high-frequency impact through cam or eccentric wheel. The impact speed is 5-10m/s. The impact energy is calculated according to the punching force and stroke to ensure that the material separation can be completed with a single impact. The buffer device is set under the die, using a disc spring group, with a buffer stroke of 1-2mm, which can absorb 30%-40% of the impact energy and reduce the impact of mold vibration on the punch. The mold mounting seat is made of cast iron HT300 with a thickness of not less than 100mm. A shockproof pad (rubber material, hardness 60 Shore A) is set at the bottom to further reduce the vibration transmission of the equipment.
Precision control and mold maintenance must be strictly controlled. When testing the mold, an optical microscope is used to detect the aperture accuracy, and the tolerance is controlled at IT8-IT10 level (such as a 1mm diameter hole tolerance of ±0.014mm), and the verticality error of the hole wall does not exceed 0.01mm/mm. The wear of the punch needs to be checked for every 1,000 pieces punched, and the diameter is measured through a tool microscope. When the wear exceeds 0.01mm, the punch needs to be replaced. The die cutting edge is repaired every 5,000 pieces, and a diamond grinding wheel is used to grind to keep the cutting edge sharp. After long-term use, the wear of the guide sleeve needs to be detected. When the fit clearance exceeds 0.008mm, the guide sleeve should be replaced in time. When stored, the punch needs to be hung vertically or loaded into a special sleeve to avoid collision and deformation, and anti-rust paste is applied to the die hole to prevent rust and clogging.
