Manufacturability Analysis of Die-casting Mold for Three-plate Hinge Connection Push Plate Bracket_H1

An Analysis of the Casting Process

The bracket part, made of ZL103 alloy, has a complex shape with numerous holes and thin thickness. This poses challenges during the ejection process, as it is difficult to push out without causing deformation or dimensional tolerance issues. The part requires high dimensional accuracy and surface quality, making the feeding method, feeding position, and part positioning crucial considerations in mold design.

The die-casting mold, depicted in Figure 2, adopts a three-plate type, two-part parting structure, with a center feed from the point gate. This design yields excellent results and an appealing appearance.

Initially, a direct gate was used in the die-casting mold. However, this resulted in difficulties during the removal of residual materials, affecting the quality of the casting's upper surface. Moreover, shrinkage cavities were observed at the gate, which did not meet the casting requirements. After careful consideration, a point gate was chosen as it proved to produce smooth casting surfaces with uniform and dense internal structures. The inner gate diameter was set at 2mm, and a transition fit of H7/m6 was adopted between the gate bushing and the fixed mold seat plate. The gate bushing's inner surface was made as smooth as possible to ensure proper separation of the condensate from the main channel, with a surface roughness of Ra=0.8μm.

The mold employs two parting surfaces due to the gating system's shape limitations. Parting Surface I is used to separate the remaining material from the sprue sleeve, while Parting Surface II is responsible for removing residual material from the casting surface. The baffle plate at the end of the tie rod facilitates sequential separation of the two parting surfaces, while the tie rod maintains the desired distance. The length of the mouth sleeve (remaining material separated from the sprue sleeve) is adjusted to aid in the removal process.

During parting, the guide post emerges from the movable template's guide hole, allowing the mold cavity insert to be positioned by the nylon plunger installed on the movable template.

The original design of the mold included a one-time push rod for ejection. However, it resulted in deformations and size deviations in the thin, long castings due to the increased tightening force on the moving mold's center insert. To address this issue, secondary pushing was introduced. The mold incorporates a hinge connection structure, allowing simultaneous movement of the upper and lower push plates during the first push. When the movement exceeds the limit stroke, the hinge bends, and the push rod's force only acts on the lower push plate, stopping the motion of the upper push plate for the second push.

The mold's working process involves the rapid injection of liquid alloy under pressure, followed by the mold opening after formation. The initial separation occurs at the I-I parting surface, where the remaining material at the gate is detached from the sprue sleeve. The mold continues to open, and the remaining material from the ingate is pulled off. The ejection mechanism then initiates the first push, wherein the lower and upper push plates move forward synchronously. The casting is smoothly pushed away from the moving plate and the fixed mold's center insert, allowing for core-pulling of the fixed insert. As the pin shaft moves away from the limit block, it bends towards the mold's center, causing the upper push plate to lose force. Subsequently, only the lower push plate continues to move forward, pushing the product out of the cavity of the push plate through the push tube and push rod, completing the demolding process. The ejection mechanism resets during mold closure through the action of the reset lever.

During mold usage, the casting surface initially exhibited a mesh burr, which gradually expanded with each die-casting cycle. Research identified two factors contributing to this issue: large mold temperature differences and a rough cavity surface. To address these concerns, the mold was preheated to 180°C before use and maintained a surface roughness (Ra) of 0.4μm. These measures significantly improved casting quality.

Thanks to the nitriding treatment and proper preheating and cooling practices, the mold's cavity surface enjoys enhanced wear resistance. Stress tempering is carried out every 10,000 die-casting cycles, while regular polishing and nitriding further increase the mold's lifespan. To date, the mold has successfully completed over 50,000 die-casting cycles, demonstrating its robust performance and reliability.