In the design and manufacture of die-casting molds, the push rod is a key ejection component. Its fixing method and anti-rotation form directly affect the service life of the mold and the molding quality of the die-casting. The fixing method of the push rod must meet the requirements of not loosening during repeated ejection and precise positioning. Common fixing methods include step fixing, nut fixing and riveting. Step fixing is achieved by designing a step structure at the end of the push rod, which is matched with the countersunk holes on the mold push rod fixing plate to achieve positioning. This method has a simple structure and is easy to install. It is suitable for most small and medium-sized push rods, but its load-bearing capacity is limited. In high-pressure die-casting scenarios, step deformation may occur. Nut fixing is to process threads on the end of the push rod and lock the push rod to the fixing plate with a nut. This method is flexible and can adjust the extension length of the push rod as needed. It has a strong load-bearing capacity and is mostly used for large push rods or occasions that require frequent adjustments. However, the threaded connection is prone to loosening due to vibration and needs to be used with anti-loosening gaskets. Riveting fixation is achieved by riveting the tail of the push rod to the fixed plate. It has high connection strength and good stability, and is suitable for occasions with extremely high precision requirements. However, once installed, it is difficult to disassemble and the cost of maintenance and replacement is high.
During operation, the push rod not only has to withstand axial thrust, but also generates radial torque due to the shape of the mold cavity and the deviation of the ejection direction. If effective anti-rotation measures are not taken, it is very easy for the push rod to bend, break or wear more severely. Common anti-rotation forms include flat position anti-rotation, keyway anti-rotation and pin anti-rotation. Flat position anti-rotation is to machine a flat surface on the tail or middle of the push rod, which cooperates with the corresponding groove on the fixed plate, and limits the rotation of the push rod through flat contact. This method is simple to process and low in cost. It is suitable for situations where the rotational torque is small, but the flat contact area is limited, and long-term use may cause the problem of increased fitting clearance. Keyway anti-rotation is to machine keyways on the push rod and the fixed plate respectively, and achieve circumferential positioning through flat keys. It has reliable anti-rotation effect and strong load-bearing capacity. It is suitable for medium and large push rods and high torque scenarios. However, the keyway processing has high precision requirements, and the key and groove must be tightly matched during assembly. Pin-type locking is achieved by inserting a pin at the connection between the push rod and the fixed plate, using the radial restraining force of the pin to prevent the push rod from rotating. This method has a compact structure and is suitable for occasions with limited space, but the pin is prone to breakage due to uneven force and requires regular inspection and replacement.
In practical applications, different fixing methods and anti-rotation forms need to be reasonably selected based on the specific die-casting process parameters, die-casting material, and shape. For example, for die-castings made of low-melting-point materials such as zinc alloy, due to the low molding pressure, a combination of step fixing and flat anti-rotation can be used, which not only meets the use requirements but also reduces mold manufacturing costs. However, for die-castings made of high-melting-point, high-strength materials such as aluminum alloy and magnesium alloy, due to the high molding pressure and complex force on the push rod, a combination of nut fixing and keyway anti-rotation is usually required to ensure the stability and reliability of the push rod in high-pressure environments. In addition, when selecting a fixing method, the ease of replacing the push rod must also be considered. For push rods that are prone to wear, using nut fixing can reduce the disassembly workload during replacement and improve mold maintenance efficiency.
The design of the push rod’s fixing method and anti-rotation form must also be coordinated with the overall structure of the mold. In the ejection mechanism, the push rods should be evenly distributed to avoid premature failure of the fixing parts or anti-rotation structure due to concentrated force. The material selection of the fixing and anti-rotation parts is also crucial. High-strength alloy structural steel (such as 45 steel, Cr12MoV, etc.) is generally used and heat-treated to increase its hardness and wear resistance to extend its service life. For example, the step or threaded area at the end of the push rod needs to be quenched to a hardness of HRC50-55 to prevent deformation or thread stripping during repeated stress. The key or pin used for anti-rotation must be made of high-strength steel to ensure that it will not plastically deform when subjected to radial forces.
With the continuous development of the die-casting industry, the requirements for mold precision and service life are becoming increasingly higher, and innovations in push rod fixing methods and anti-rotation forms are also continuously advancing. In recent years, some new connection structures such as expansion sleeve fixing and polygonal anti-rotation have gradually been applied to high-end die-casting molds. The expansion sleeve fixing achieves gapless fixation of the push rod through friction, and has the characteristics of high positioning accuracy and easy disassembly; the polygonal anti-rotation utilizes the full contact of the polygonal mating surface to improve the load-bearing capacity and stability of the anti-rotation structure. The application of these new structures not only improves the working performance of the push rod, but also provides strong support for the efficient production and precision manufacturing of die-casting molds. In future mold design, the combination of computer-aided design (CAD) and finite element analysis (FEA) technology can further optimize the parameters of the fixing and anti-rotation structures, realize personalized and precise design, and meet the needs of different die-casting scenarios.
