Die-casting is widely used in automobiles, 3C products, hardware parts, etc. due to its advantages of high efficiency, high material utilization, and high forming accuracy. For specific die-casting parts, corresponding die-casting molds need to be designed. Shell needs to be formed using a side-gate die-casting mold. Design and manufacturing of side-gate die-casting mold is the key to ensuring quality of aluminum alloy die-casting parts. Taking aluminum alloy parts of shell as an example, design of die-casting mold for aluminum alloy horizontal cold chamber die-casting machine is introduced.
Process analysis of a shell aluminum alloy die-casting part was carried out, structural design of die-casting mold for horizontal cold chamber die-casting machine was introduced in detail, including parting surface selection, pouring system design, side core-pulling design and demoulding mechanism design. Working principle and structural characteristics of die-casting mold are explained, providing a reference for structural design of die-casting mold for horizontal cold chamber die-casting machines.

Shell structure is shown in Figure 1 and Figure 2. This casting requires high strength, light weight, works in a high temperature and high humidity environment above 100℃. Therefore, YL102 aluminum alloy is selected, its melting point is 650℃. Due to high Si content, a metal crucible is selected for smelting furnace. There are two φ6mm through holes and φ8mm blind holes on this casting. Shape is φ56mm cylindrical surface. Two φ6mm through holes have a center distance requirement of 280-0.2mm. Dimensional accuracy of casting is not high. Casting has good formability and requires a smooth surface. There must be no casting defects such as cracks, cold seals, or pores inside. Drafting angle of inner and outer surfaces is 1°, wall thickness of casting is 4mm. transition between inner and outer cylindrical surfaces is set with rounded corners, and radius is 1mm; injection specific pressure is 65MPa, filling speed is 42m/s, pouring temperature is 630℃, mold preheating temperature is 160℃, filling time is 0.1s, and sodium fluoride water is used as coating. Mold clamping force is calculated based on projected area method, and J1110A horizontal cold chamber die-casting machine is selected for die casting. Inner diameter of die-casting machine is φ40mm, outer diameter is φ90mm, and injection stroke is 0 to 120mm.

 

Figure 1 Shell plan view

 

Figure 2 Three-dimensional view of shell

 

Figure 3 Shell parting surface plan
(1) Scheme I: Large core of die-casting mold is set in core fixed plate, cavity and small core are set in cavity plate. Advantage is that push-out force of die-casting part is small. Disadvantage is that it is difficult to ensure symmetry between the two φ6mm small holes in die-casting part and center line of φ56mm outer circle and φ48mm inner hole of die-casting part; parting surface of die-casting mold is the lower plane of die-casting part (assembly reference plane), there are flash edges on it, accuracy of dimensions of 20mm and 16mm cannot be guaranteed (see Figure 1). Obviously, quality of die-casting parts with this solution is difficult to guarantee.
(2) Scheme II: Part of cavity and large core of die-casting mold are placed in core fixing plate, the other part of cavity and small core of die-casting mold are placed in cavity plate. Disadvantage is that it is difficult to ensure symmetry between the two φ6mm die-casting parts, outer circle φ56mm of casting, and center line of inner hole φ48mm. Parting surface of die-casting mold is set on a plane with an outer circle, which artificially causes flash on the outer circle of die-casting part, resulting in poor appearance quality of casting.
(3) Scheme III: Die-casting mold cavity and large core are located in cavity plate, and small core is located in core fixing plate. Advantage is that flash of casting is not on mounting datum plane of casting. Disadvantage is that the two φ6mm small holes in casting have a certain impact on symmetry of outer circle φ56mm and center line of inner hole φ48mm, but quality of casting can basically be guaranteed; upper plane of die casting is used as parting surface, and there is flash on upper plane of die-casting part. Since flash of die-casting parts is blocked by other parts during assembly, it does not affect appearance quality of castings after assembly. This solution is more reasonable.
(4) Plan IV: Die-casting mold cavity and large and small cores are all located in movable mold. Advantage is that it can ensure symmetry between the two φ6mm small holes in casting and center line of φ56mm outer circle of casting and φ48mm inner hole. Disadvantage is that parting surface is set on the lower plane of die casting (assembly datum), and there is flash on assembly datum of casting. This surface is assembly reference surface and cannot have flash, so this solution is unreasonable.
(5) Plan V: Part of cavity of die-casting mold is located in movable mold, the other part of cavity is located in fixed mold, large and small cores are all located in movable mold. Advantage is that it can ensure symmetry of the two φ6mm small holes in casting and center line of inner hole φ48mm. Disadvantage is that symmetry between the two φ6mm holes in die-casting part and φ56mm centerline of die-casting part's outer circle cannot be ensured, φ5mm outer circumferential surface is used as parting surface, artificially causing flash on outer circumferential surface of die-casting part and poor appearance quality. Based on above analysis, option III is selected, using upper plane of shell as parting surface.

 

Figure 4 Shell gating system

 

Figure 5 Assembly diagram of shell die-casting mold

4. Hexagon socket head screws 2. Limiting plate 3. Wedge block 5. Slider 6. Inclined guide post 7. Ejector screw 8. Spring 9. Side core 10. Movable mold core 11. Small core 12. Ejector 13. Large core 14. Sprue sleeve 15. Diverter cone 16. Copper pipe 17. Fixed mold base plate 18. Fixed template 19. Moving mold plate 20. Support plate 21. Push rod fixed plate 22. Push plate 23. Moving Mold base plate

 

Figure 6 Die-cast shell parts