Blanking die screws and pins
Screws and pins in blanking dies are key connectors in die assembly, securing mold components and ensuring their relative positioning accuracy, respectively. Their performance and assembly quality directly impact the mold’s overall rigidity, precision, and service life. Screws primarily fasten mold components (such as the punch retaining plate, die, and stripper plate) together, transmitting force and torque. Pins primarily serve as positioning components, preventing relative displacement during assembly and operation and ensuring uniform clearance between the punch and die. The design and selection of screws and pins requires determining the appropriate type, specification, and material based on the mold’s structural characteristics, load capacity, and precision requirements.
Screws primarily serve as fasteners in blanking dies. Their type and specifications should be determined based on the size of the die components, the loads they are subject to, and the assembly position. Commonly used screws in blanking dies include hexagon socket head screws, countersunk socket head screws, and bolts. Hexagon socket head screws are easily assembled and disassembled, offering strong holding power and are widely used to secure die components. Countersunk head screws are suitable for applications requiring smooth surfaces, such as connecting stripper plates to retaining plates. The screw diameter should be determined based on the thickness of the connected parts and the loads they are subject to. It is generally 0.5-0.8 times the thickness of the parts being connected, and the length should ensure a penetration depth of at least 1.5 times the screw diameter to ensure a secure connection. For example, when connecting a 20mm thick punch retaining plate to the upper die base, M8-M10 hexagon socket head screws should be used, with a penetration depth of at least 12mm and a tightening torque of 30-50 N · m to prevent deformation of the parts due to overtightening or loosening of the connection due to overtightening.
Pins in blanking dies primarily serve a positioning function, ensuring accurate relative positioning of mold components after assembly and preventing displacement due to forces during use. Commonly used pins in blanking dies include cylindrical pins and conical pins. Cylindrical pins offer high positioning accuracy and are suitable for secure positioning; conical pins are self-locking and suitable for applications requiring frequent disassembly. The diameter of a pin is generally equal to or slightly smaller than the diameter of the screw it connects to, and its length should ensure penetration into two or more parts simultaneously to a depth of at least 1.5 times the pin diameter to ensure reliable positioning. For example, if an M10 screw is used to locate the punch retaining plate and the upper die holder, a cylindrical pin with an 8mm diameter and a length of 30-40mm can be used, ensuring the pin is embedded at least 12mm deep in both the retaining plate and the die holder. The pin-part fit is a transition fit (H7/m6), which ensures both positioning accuracy and ease of assembly.
The arrangement of screws and pins is crucial to the mold’s connection strength and positioning accuracy. A proper arrangement ensures uniform force distribution and accurate positioning. During mold assembly, screws should be evenly distributed across the stress-bearing areas of the part to avoid deformation caused by excessive localized forces. For large mold parts, the number of screws should be at least four, and they should be symmetrically distributed. Pins are typically placed inside the screws or in areas subject to greater stress. They are paired with the screws to form a “one-nail, one-pin” positioning and fastening unit, ensuring sufficient positioning accuracy at every connection point. For example, in the connection between the die and the lower die base, a set of screws and pins are typically placed at each of the four corners of the die, with the screws on the outside and the pins on the inside. This ensures both secure fixation of the die and accurate relative positioning of the die and the lower die base.
The material and heat treatment process of screws and pins directly affect their strength and wear resistance. Screws and pins in blanking dies are typically made of high-strength alloy structural steels, such as 45 steel and 40Cr. Screws require tempering to a hardness of 28-32 HRC to ensure sufficient strength and toughness, while pins require quenching to a hardness of 50-55 HRC to enhance wear resistance and shear resistance. For dies subject to significant impact loads, such as thick sheet blanking dies, screws and pins can be made of higher-strength materials, such as 35CrMo, which achieves a hardness of 32-36 HRC after heat treatment to improve fatigue resistance. Furthermore, the surfaces of screws and pins should be treated with rust-resistant treatments, such as galvanizing or oxidation, to prevent rust from forming in humid environments, which could affect assembly and disassembly and the service life of the die.
The assembly process for screws and pins significantly impacts mold precision and service life. Precision machining of screw and pin holes is required before assembly to ensure dimensional and positional accuracy. Pin holes are typically drilled and reamed to ensure precise fit between the pin and the hole. During assembly, the pins should be installed first, followed by tightening the screws to prevent component displacement and loss of positioning accuracy. Screws should be tightened evenly across diagonal planes to avoid uneven force and deformation. For large molds, tightening can be performed in stages: pre-tightening first, then gradually increasing the force to the specified torque. Pins should be installed using a press, applying a uniform pressure to avoid bending or deformation. For tapered pins, the insertion depth should ensure that the large end of the pin is slightly above the surface of the part to facilitate removal. A sound assembly process ensures that screws and pins perform optimally for fastening and positioning, improving overall mold performance.
