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

Analysis of the Casting Process and Mold Design for ZL103 Alloy Bracket

Figure 1 depicts the structural diagram of the bracket part, which is made of ZL103 alloy. The complexity of the part's shape, the presence of numerous holes, and its thin thickness make it difficult to eject during the casting process and may lead to deformation and dimensional tolerance issues. Given the high dimensional accuracy and surface quality requirements, it is crucial to carefully consider the feeding method, feeding position, and part positioning in the mold design.

The die-casting mold structure, as shown in Figure 2, follows a three-plate type design with a two-part parting line. The center feeds from the point gate, providing a satisfactory effect and an aesthetically pleasing appearance.

The initial gate form chosen for the die-casting mold was a direct gate. However, it was observed that the connection area between the residual material and the casting was relatively large after part formation, making it challenging to remove the residual material. The presence of residual material negatively impacted the quality of the upper surface of the casting, causing shrinkage cavities that did not meet the casting requirements. To address this, a point gate was adopted and proved to be effective in producing castings with smooth surfaces and uniform internal structures. The inner gate diameter was determined as 2mm, and a transition fit H7/m6 was utilized between the gate bushing 21 and the fixed mold seat plate 22. The inner surface of the gate bushing was smoothed to facilitate the separation of condensate from the main channel, achieving a surface roughness of Ra=0.8µm.

Considering the limitations posed by the shape of the gating system, a two-parting surface approach was employed in the mold to address part separation from the sprue sleeve and the casting surface. Parting surface I was used to separate the remaining material from the sprue sleeve, while parting surface II broke the remaining material from the casting surface. The baffle plate 24, located at the end of the tie rod 23, facilitated the sequential separation of the two parting surfaces. Furthermore, the tie rod 23 acted as a distance fixer. The length of the mouth sleeve was optimized to ease the removal of the remaining material.

After parting, the guide post emerges from the guide hole of the movable template 29. Consequently, during mold closure, the mold cavity insert 26 is accurately positioned by the nylon plunger 27 on the movable template 29.

The initial mold design incorporated a one-time push-out using a push rod. However, this led to problems such as deformation and size out-of-tolerance in the castings. Extensive research and experimentation revealed that the thin thickness and larger length of the castings resulted in an increased tightening force on the center insert of the moving mold, leading to deformation when subjected to pushing forces on both ends. To resolve this issue, a secondary pushing mechanism was implemented. This mechanism used a hinge connection structure, in which the upper push plate 8 and lower push plate 12 were connected through two hinge plates 9 and 10 and a pin shaft 14. The pushing force from the die-casting machine's push rod was initially transmitted to the upper push plate 8, enabling simultaneous movement for the first push. Once the limit stroke of the limit block 15 was exceeded, the hinge bent, and the pushing force from the die-casting machine's push rod acted solely on the lower push plate 12. At this point, the upper push plate 8 stopped moving, allowing for the second push.

The mold's working process involves the rapid injection of the liquid alloy under pressure from the die-casting machine, followed by mold opening after forming. During mold opening, the I-I parting surface is initially separated, allowing for the separation of the remaining material at the gate from the sprue sleeve 21. Subsequently, as the mold continues to open, tension rods 23 affect the separation of the parting surface II, pulling off the remaining material from the ingate. The entire piece of remaining material can be removed from the center insert of the fixed mold. The ejection mechanism is then initiated, commencing the first push. The lower hinge plate 10, pin shaft 14, and upper hinge plate 9 enable the push rod of the die-casting machine to push both the lower push plate 12 and the upper push plate 8 simultaneously, smoothly pushing the casting away from the moving plate and inserting it into the mold center's insert 3 while activating core-pulling of the fixed insert 5. As the pin shaft 14 moves away from the limit block 15, it bends toward the center of the mold, resulting in the loss of force by the upper push plate 8. Consequently, the bolt push rod 18 and push plate 2 stop moving, while the lower push plate 12 continues moving forward, pushing the push tube 6 and push rod 16 to propel the product out of the cavity of the push plate 2, achieving complete demoulding. The ejection mechanism is reset to its initial position during mold closure, completing one working cycle.

During mold usage, the surface of the casting exhibited a mesh burr that expanded as the number of die-casting cycles increased. Research unveiled two causes for this issue: large mold temperature differences and significant cavity surface roughness. To mitigate these problems, preheating the mold prior to usage and implementing cooling during production are essential. The mold is preheated to a temperature of 180°C, and the mold cavity's surface roughness is controlled, maintaining it at Ra≤0.4µm. These measures significantly enhance the quality of the castings.

The mold's surface undergoes nitriding treatment to improve wear resistance, and proper preheating and cooling are ensured during usage. Additionally, stress tempering is performed after every 10,000 die-casting cycles, and the cavity surface is polished and nitrided. These steps significantly extend the mold's lifespan. Currently, the mold has exceeded 50,000 die-casting cycles, demonstrating its reliability and durability.

In conclusion, the analysis of the casting process and mold design for the ZL103 alloy bracket highlights the importance of considering factors such as feeding method, feeding position, and part positioning to achieve high dimensional accuracy and surface quality. The chosen gate form, point gate, proved effective in producing castings with smooth surfaces and uniform structures. The two-parting surface mechanism, alongside the hinge-based secondary push-out design, resolved issues related to deformation and size out-of-tolerance in the castings. Following proper mold preheating, controlled mold cavity surface roughness, and preventive measures such as nitriding, stress tempering, and polishing, a mold with an extended lifespan and improved casting quality was achieved. The success of this project illustrates Tallsen's commitment to quality and innovation.