Plastic part structure is shown in Figure 1, where structure formed in fixed mold direction is shown in Figure 1 (a) and (b), and structure formed in movable mold direction is shown in Figure 1 (c). Its bottom is elliptical and has a size of 80mm*73mm*26mm. There is a protruding sheet along contour of outer cylindrical surface. Sheet is 46mm wide and 100mm high. There are 4 square holes on outer surface of sheet, 2 cylindrical holes and several reinforcing ribs on inner surface. There are 4 cylindrical holes and 4 buckles in movable mold direction of plastic part. Inner diameter of cylindrical hole is φ2mm and height is 20mm, as shown in Figure 1 (d). Since inner and outer surfaces of protruding sheet of plastic part need to be designed with a slider demolding, preventing sheet on plastic part from deforming is a difficult point in mold design.

 

According to structure of plastic part, mold adopts a 2-cavity layout and a two-plate mold structure, and runner is set on upper surface of moving mold plate. Sheets of two plastic parts are arranged facing each other, a latent gate is used for feeding, and gate is set on the side of protruding sheet, as shown in Figure 2 (a). Since position of latent gate feeding is protruding sheet, width is 5mm, height is 9mm, and thickness is 0.5mm, in order to increase fluidity of melt after entering cavity, material is added to inner surface of protruding sheet. Specific method is to set a square columnar structure, as shown in Figure 2 (b). Adding material to sheet can prevent plastic part from being underfilled.

 

Inner surface of protruding sheet of fixed mold part of plastic part is distributed with several reinforcing ribs and two horizontal cylindrical holes. Fixed mold oblique push mechanism driven by inclined wedge is used for demolding, as shown in Figure 3. Inclined wedge is fixed on fixed mold base plate, fixed mold inclined push block slides in slide groove on fixed mold plate, fixed mold inclined push block and inclined wedge are connected by an inclined T-shaped groove. When opening mold, mold is first opened between fixed mold plate and fixed mold base plate, so that inclined wedge drives fixed mold inclined push block to perform demolding movement.

 

There are 4 square holes on outer surface of protruding sheet of fixed mold part of plastic part. Demolding is carried out by a slider mechanism driven by an inclined guide column, and assembly position of gate sleeve is opened between two cavities of slider. In order to enhance stability of slider, two raised positionings are set on the side of slider and one recessed positioning is set on the top surface, as shown in Figure 4 (a). In order to keep slider stable during movement, three guide grooves are opened at the bottom of slider, as shown in Figure 4 (b).

 

There is a square hole on other side of plastic part, which requires design of an inclined guide column + slider for demolding. Core of square hole is designed on slider. According to structure of plastic part, structure of this slider is similar to that of slider 1, but it is thinner than slider 1. Similarly, two recessed positionings are set on the side of slider, one recessed positioning is set on the top surface, and three guide grooves are opened at the bottom of slider, as shown in Figure 5.

 

Movable and fixed molds are set as inserts. According to structure of plastic part, fixed mold insert is set as a step. Two raised positionings are set on fixed mold insert. An inclined surface with same inclination as clamping wedge is set before and after protrusion, and an assembly position of fixed mold oblique push mechanism is set on each of two cores, as shown in Figure 6. Movable mold core of plastic part is set on movable mold insert. Unlike step-shaped fixed mold insert, surface of movable mold insert is a plane, and two grooves are opened on plane as guide grooves for movement of two sliders, as shown in Figure 7.

 

Movable mold insert corresponding to latent gate is designed as a small insert structure, as shown in Figure 8. There are two main reasons: ① Since sheet corresponding to latent gate is lower than parting surface and size of sheet is small, in order to facilitate processing and polishing, corresponding core is set as an insert; ② Since condensate at latent gate is easy to break in flow channel and is not easy to clean, it will cause phenomenon of insufficient filling in subsequent production. After removing corresponding small insert from movable mold insert, gate condensate in latent gate can be removed.

 

There are 4 buckle positions on inner surface of plastic part, and 4 movable mold oblique push mechanisms need to be designed for demolding. Each oblique push mechanism consists of an oblique push rod + an oblique push seat. Oblique push rod and oblique push seat are connected by a T-shaped position, as shown in Figure 9. Oblique push seat is fixed to push plate from bottom with screws, which is convenient for disassembly. When repairing, oblique push mechanism can be taken out from front of movable mold by loosening screws from bottom of oblique push seat, and disassembly workload is small.

 

Although size of plastic part is small, there are many reinforcing ribs on inner surface of plastic part. In order to smoothly eject plastic part, 9 push rods are set on each plastic part, and push rods are set next to reinforcing ribs. Since there are 4 cylindrical holes on plastic part, inner diameter of cylindrical hole is only φ2mm and height is about 20mm, core of cylindrical hole is easy to break. In order to facilitate mold repair, cylindrical hole core is set as a push tube assembly. Push tube assembly is a standard part. If cylindrical hole core breaks, it only needs to be replaced, and maintenance workload is small. Ejection mechanism of plastic part is shown in Figure 10.

 

Plastic part material is PP, which is easy to deform. Wall thickness of plastic part is uneven, and there are several reinforcing ribs on plastic part, which is easy to shrink after molding. In order to overcome above phenomenon, a cooling water channel with good cooling effect must be designed. According to shape of plastic part, mold structure and layout of 2 cavities, a straight water channel with a diameter of φ10mm is used, an independent circuit is set for each of two sliders of moving and fixed mold inserts, as shown in Figure 11. Cooling water channel of fixed mold must avoid fixed mold oblique push mechanism on fixed mold insert, cooling water channel of movable mold must avoid push rod and movable mold oblique push mechanism on movable mold insert.

 

Mold adopts a two-plate mold structure, which is a secondary mold opening, the first mold opening is set between fixed mold plate and fixed mold base plate. A limit screw is set between fixed mold plate and fixed mold base plate, and first mold opening distance is set to 50mm. In order to prevent dust and other impurities from falling into bottom of push plate, causing mold ejection mechanism to be unable to reset and plastic parts to have flash, etc., a limit column is set at the bottom of push plate so that bottom of push plate cannot be close to movable mold base plate, providing space for dust and other impurities to enter. Mold structure is shown in Figure 12.

 

1. Moving mold base plate 2. Push plate 3. Push rod fixing plate 4. Pad 5. Push plate guide column 6. Moving mold plate 7. Push rod 8. Oblique guide column 9. Slider 1 10. Fixed mold insert 11. Fixed mold plate 12. Fixed mold base plate 13. Fixed mold wedge 14. Fixed mold oblique push mechanism 15. Oblique guide column 16. Slider 2 17. Moving mold insert 18. Oblique push rod 19. Oblique push seat 20. Push plate reset limit column 21. Support column 22. Pull rod 23. Gate sleeve 24. Positioning ring 25. Limit screw 26. Guide column and guide sleeve
Figure 12 Mold structure
Mold movement process: After injection is completed, mold is first opened between fixed mold base plate 12 and fixed mold plate 11. Since fixed mold wedge 13 is fixed on fixed mold base plate 12, fixed mold wedge 13 will drive fixed mold oblique push mechanism 14 to perform demolding movement. After fixed mold base plate 12 and fixed mold plate 11 are separated by 50 mm, fixed mold oblique push mechanism 14 completes demoulding. Then mold is opened between fixed mold plate 11 and movable mold plate 6, that is, second mold opening, and at the same time, oblique guide pillars 8 and 15 respectively drive slider 9 and slider 16 to perform demoulding movement. When movable mold moves to limit position, ejection mechanism of injection molding machine pushes ejection mechanism of mold (push plate 2, push rod fixing plate 3, push rod 7, oblique push rod 18, pull rod 22, etc.) to perform ejection movement. After plastic parts are taken out, ejection mechanism of mold is reset under action of reset spring. When ejection mechanism of mold is reset, ejector of injection molding machine pushes movable mold part of mold to reset. When mold is completely reset, next injection can be started.