Characteristics and common assembly forms of the push-tube ejection mechanism of the die-casting mold
The push-tube ejection mechanism in die-casting molds is commonly used for ejecting tubular, cylindrical, or deep-hole die-casting parts. Compared to traditional push-rod ejection mechanisms, it boasts uniform ejection force distribution, resists deformation of die-casting parts, and improves demolding efficiency. The push-tube ejection mechanism contacts the die-casting part through the annular end surface of the entire push-tube, evenly transmitting the ejection force to the circumferential surface. This prevents deformation or surface damage to the die-casting caused by excessive localized force applied by the push-rod during ejection. It is particularly suitable for thin-walled tubular die-casting parts, such as oil pipes in automotive engines and cylinder barrels in hydraulic systems. Furthermore, the push-tube forms a sliding fit with the core during ejection, providing guidance and protection for the core, reducing bending or wear of the core due to uneven force, and thus extending its service life.
Another key feature of the push-tube ejection mechanism is its wide adaptability. The push-tube’s shape and size can be flexibly designed to suit the die-casting’s structural characteristics. For tubular die-castings with complex exterior surfaces or irregular shapes, the push-tube’s shape can be designed to match the die-casting’s interior surface , ensuring uniform force distribution during ejection. For tubular die-castings with steps or grooves, segmented or combined push-tubes can be used to achieve step-by-step ejection, preventing shear damage during demolding. Furthermore, the push-tube ejection mechanism can be combined with other ejection mechanisms (such as push rods and ejector plates) to form a composite ejection system, meeting the demolding requirements of complex die-casting structures and enhancing the mold’s versatility and adaptability.
Common assembly forms of push tube ejection mechanisms mainly include integral push tube assembly, split push tube assembly, and nested push tube assembly. In the integral push tube assembly, the push tube is designed as an integral structure. One end of the push tube is connected to the push plate, and the other end is directly in contact with the die-casting. This assembly form has a simple structure and is easy to manufacture. It is suitable for tubular die-castings with simple structures. Integral push tubes are usually made of high-strength alloy steel (such as Cr12MoV) and are heat-treated to improve their hardness and wear resistance. The fitting clearance between the inner hole of the push tube and the core is generally controlled at 0.01-0.02mm to ensure the smooth movement and sealing of the push tube. During assembly, the connection between the push tube and the push plate is usually fixed with a step or a nut to ensure that the push tube will not loosen or fall off during the ejection process.
The split push tube assembly is to divide the push tube into two parts, the push tube body and the push tube head, which are combined together through threaded or pinned connections. The advantage of this assembly method is that it is easy to replace the push tube head and reduce maintenance costs. The push tube head is usually personalized according to the shape of the die-casting and is made of wear-resistant materials to increase its service life; the push tube body is made of high-strength steel to ensure the rigidity of the overall structure. During assembly, it is necessary to ensure that the coaxiality error between the push tube head and the push tube body is no more than 0.01mm to avoid eccentricity causing the push tube movement to jam or deformation of the die-casting. The split push tube assembly is suitable for occasions where the die-casting has a complex shape and the push tube head is easily worn, such as die-castings with irregular inner holes.
The nested push tube assembly is an ejection mechanism composed of multiple push tubes of different diameters nested together. It is suitable for complex die-castings with multi-layer steps or deep hole structures. It can achieve layered ejection to prevent the die-castings from being subjected to excessive stress during the demolding process. The inner push tube and the outer push tube of the nested push tube adopt a precise clearance fit, and the fit clearance is generally controlled at 0.005-0.01mm to ensure the coordination and synchronization of the movement of each layer of push tubes. During assembly, each layer of push tubes needs to be positioned by a guide sleeve or a locating pin to ensure its coaxiality. At the same time, a corresponding limit structure is designed on the push plate to control the ejection stroke of each layer of push tubes to avoid collision or interference between push tubes due to excessive ejection. The manufacturing precision requirements of the nested push tube assembly are high, and usually a CNC machining center is required for precision processing to ensure the dimensional accuracy and fit accuracy of each component.
The assembly quality of the push tube ejection mechanism directly affects its working performance and service life. The following points should be noted during the assembly process: First, the fitting clearance between the push tube and the core must be strictly controlled. A gap that is too large will cause the molten metal to overflow, and a gap that is too small will increase friction and wear; second, the straightness and roundness errors of the push tube must be controlled within the allowable range to avoid poor movement due to deformation; finally, the connection between the push tube and the push plate must be firm and reliable to prevent loosening during repeated ejection. In addition, the push tube ejection mechanism needs to be lubricated and maintained regularly during use to reduce frictional resistance and extend its service life. With the continuous development of die-casting technology, the design and assembly process of the push tube ejection mechanism are also being continuously optimized. For example, the use of new wear-resistant materials and precision forming technologies has further improved the performance and reliability of the push tube ejection mechanism, providing strong support for the efficient production of complex die-casting parts.
