The punch fixation method for hardware molds is a core component of the high-frequency stamping process. Its stability directly impacts mold life, product precision, and production efficiency. In high-frequency stamping applications, the punch must withstand impact loads of hundreds or even thousands of times per minute. Improperly designed fixation can easily cause punch deflection, breakage, or gap fluctuations, leading to mold failure or product defects. Therefore, properly selecting a fixation method and optimizing its structural parameters are key to improving the stability of hardware molds during high-frequency stamping.
Mechanical fixation, which uses an interference fit or additional fasteners to position the punch, is the most commonly used fixation method in hardware molds. The press-fit fixation method utilizes an H7/M6 fit to press the punch into the fixed plate hole, relying on the friction generated by the interference fit to resist impact. However, under high-frequency stamping, repeated impacts can cause wear in the fixed plate hole, reducing the interference fit and causing the punch to loosen. The riveted flip fixation method, which enhances connection strength by riveting the punch tail, is suitable for thin sheet metal blanking. However, stress concentration at the riveted joint can lead to cracking, reducing fatigue life under high-frequency stamping. The screw fastening method directly locks the punch with screws, making adjustment easy. However, the screw preload may weaken under high-frequency vibration, requiring regular inspection and re-tightening.
Physical fastening utilizes the material's thermal expansion and contraction properties to secure the punch. A typical example is the shrink fit method. This method involves inserting a heated, expanding ferrule into the punch, which contracts and locks after cooling. It is suitable for high-hardness punches such as carbide. In high-frequency stamping, the shrink fit method offers advantages in high-strength connection and the absence of additional stress concentration points. However, strict control of the heating temperature and cooling rate is required to avoid residual stress between the ferrule and the punch, which can easily cause microcracks to propagate under high-frequency vibration. Furthermore, the shrink fit method requires extremely high coaxiality between the ferrule and the punch, as eccentric loading can accelerate punch failure.
Chemical fastening uses adhesives to connect the punch to the mounting plate. These adhesives are categorized as epoxy resin and inorganic adhesives. Epoxy resin bonding is simple to use, offers high bond strength after curing, and can fill small gaps, improving joint rigidity. However, under high-frequency stamping, epoxy resin may creep due to long-term vibration, causing the punch to shift. Inorganic bonding methods utilize inorganic materials such as copper oxide, which offer excellent high-temperature resistance and creep resistance. However, the bond layer is brittle and has limited resistance to impact loads. Optimizing the bond layer thickness and surface roughness requires a balance between strength and toughness.
The inclined pressure block and tapered hole plate fastening method uses a wedge-shaped structure to press the punch against the retaining plate. This method is suitable for large or irregularly shaped punches. The inclined pressure block uses screws to adjust the clamping force, automatically compensating for loosening caused by vibration during high-frequency stamping. However, the contact surface accuracy between the inclined pressure block and the retaining plate must be ensured, otherwise localized stress concentration may cause plate deformation. The tapered hole plate fastening method utilizes the self-locking properties of the tapered surface, eliminating the need for additional locking devices and resulting in a compact structure. However, the tapered angle design must balance self-locking properties with ease of assembly and disassembly. Excessively small angles can make assembly and disassembly difficult, while excessively large angles reduce the self-locking effect.
Overall, different fastening methods exhibit varying stability under high-frequency stamping. Mechanical fixing methods offer low cost and easy adjustment, but require regular maintenance. Physical fixing methods offer high connection strength but complex processes. Chemical fixing methods offer good sealing but limited impact resistance. Fastening methods using inclined pressure blocks and tapered pressure plates offer strong adaptability but require high design precision. In practical applications, the choice of fixing method should be based on a comprehensive consideration of factors such as punch shape, stamping frequency, and product precision. For example, for slender punches, shrink-fit fixing can enhance bending resistance. For multi-punch arrangements, fixing with low-melting-point alloys simplifies assembly and ensures gap uniformity. For high-frequency precision blanking, ball-lock quick-change punches, with their ball-locking mechanism, offer rapid assembly and disassembly while maintaining high repeatability, making them an ideal choice.
The impact of a hardware mold's punch fixing method on high-frequency stamping stability spans the entire design, manufacturing, and operational lifecycle. By optimizing the fixing method's structural parameters, material matching, and process control, the mold's fatigue resistance, gap stability, and product consistency under high-frequency impact can be significantly improved, thereby reducing production costs and enhancing market competitiveness. In the future, with the development of ultra-high-speed stamping technology, the punch fixing method will evolve towards high precision, high reliability and intelligence, providing strong support for the high-quality development of the hardware mold industry.
