Structure of elastic sleeve is shown in Figure 1. Material is PC+ABS and shrinkage rate is 0.53% to 0.59%. Main body of plastic part is a two-layer cylindrical pipe fitting. Diameter of top circular cone is φ97.5mm, and bottom end is a tapered tube with a height of 40.2mm. There are two types of spines with different orientations spaced between conical tube and top truncated disk. One has an outer diameter of φ65.3mm, and the other has an outer diameter of φ48.6mm. Each type is divided into 3 groups, and each group contains 4 thorns. Middle part of plastic part is a small casing with a diameter of φ20mm and a height of 87.9mm. There are two design difficulties for mold that forms this plastic part: ① Setting up pouring system; ② Demolding molded plastic part.

 

In view of structural characteristics and molding difficulties of plastic parts, parting shown in Figure 2 is used to divide cavity into three layers with P1 and P2 surfaces. In order to facilitate demoulding of molded plastic parts, molded parts above P2 surface are divided into upper center core insert 1 and upper push-out insert 2. Taking 1 group as an example, molded parts include an upper side insert 3 and a lower side insert 5. Upper side insert 3 and lower side insert 5 are fastened together using screws when installed in mold. Molded parts below P1 surface are core inserts, which are also divided twice into lower core inserts 7 and lower center core inserts 8.

 

1. Upper center core insert 2. Upper push-out insert 3. Side upper insert 4. Side upper insert 5. Side lower insert 6. Side lower insert 7. Lower end core insert 8. Lower center core insert 9. Push rod 10. Slide push rod 11. Slide push rod
Figure 2 Parting design
Based on above-mentioned parting design, demoulding of molded plastic parts can be completed according to following steps: plastic parts are pushed downward from upper center core insert 1 by upper push insert 2; then 6 sets of side inserts are pushed out by each push rod, and side core pulling is performed while inserts are pushed out. Taking upper side insert 3 and lower side insert 5 as an example, when slider push rod 10 pushes upper side insert 3 and lower side insert 5 upward, upper side insert 3 and lower side insert 5 push molded plastic part out from lower center core insert 8 and lower core insert 7; while being pushed out, side upper insert 3 and side lower insert 5 simultaneously pull cores to left side. In order to ensure that center part of plastic part is pushed out of mold, lower center core insert 8 is also provided with a push rod 9 to assist in pushing out. Plastic part will automatically fall off after being pushed out of lower center core insert 8 to achieve complete demolding.

Combining plastic part output requirements and mold manufacturing costs, it is more reasonable to arrange mold structure into 1 cavity, as shown in Figure 3. A three-plate mold base is used as mold base. A push plate push-out action must be implemented on fixed mold side. Therefore, mold opening action control mechanism components that need to be added on fixed mold side include long tie rods 12, spring fixed distance tie rods 13, stripper plate pull rod 14, and sequential opener 15. Mechanical components that need to be added on the side of movable mold include die buckle 18, return lever 16, and return spring 17. Since demoulding of outer wall between parting surfaces P1 and P2 requires use of 6 sets of side core-pulling slider mechanisms, six mechanisms M1~M6 are arranged on the side of movable mold for demoulding of outer wall of plastic part. Action that is synchronized with demoulding of outer wall is that plastic part is pushed out from lower core insert by central push rod 19 and small push rod 20. Considering that there are many branches on outer wall of plastic part and mold cavity is difficult to fill, pouring of mold cavity is divided into six areas to ensure that ends of each branch receive sufficient filling pressure. As shown in Figure 3(a), cavity is poured with 6 point gates evenly distributed above it, namely gates G1~G6, with a gate diameter of φ0.8mm. Since there are many side core-pulling mechanisms around mold cavity, size of each side core-pulling mechanism is small, it is difficult to install cooling pipelines. After comprehensive analysis, it was determined that C1 and C2 waterways are used for cooling of mold cavity. C1 waterway is used to cool upper push-out insert 2, C2 waterway is used to cool side inserts 3 and 4.

 

2. Upper end push-out insert 3. Side upper insert 7. Lower end core insert 8. Lower end center core insert 10. Slider push rod 12. Long pull rod 13. Spring fixed distance pull rod 14. Stripper pull rod 15 .Sequential opener 16. Reset lever 17. Reset spring 18. Die buckle 19. Center push rod 20. Small push rods C1, C2. Cooling water channel G1~G6. Point gate M1~M6 slider mechanism number
Figure 3 Mold structural layout

Mold structure is shown in Figure 4. Upper center core insert 1 is fastened and installed in fixed mold plate 27 by wedge block 24 and positioning pin 37. Upper end push insert 2 is installed on its outer cylindrical surface and is designed in shape of a push plate. Upper side inserts 3 and 4 are designed in the form of slide blocks and are fastened to lower side inserts 5 and 6 respectively. They are installed on inclined wedge 35 by sliding with T-shaped guide rail on wedge 35. Upper end of inclined wedge 35 is provided with a locking block 36 for limiting position of slider to prevent slider from falling off after being ejected. Six sliders and their corresponding driven inclined wedges 35 are installed in movable template 28. Lower core insert 7 is fastened to movable mold backing plate 29 with screws, and is also used to fasten the lower center core insert 8 to movable mold backing plate 29. Push rod 9 and slide push rods 10 and 11 are installed on push rod fixed plate 32. Stripper plate 26, fixed mold plate 27 and upper push-out insert 2 are respectively provided with guide sleeves 39~41 and guide posts 38 for sliding cooperation, which are used for sliding guidance of mold plate. Mold is opened in 4 times, and mold opening sequence is PL1→PL2→PL3→PL4. Mechanical components that control mold opening sequence include long tie rod 12, spring fixed distance tie rod 13, stripper plate tie rod 14, sequential opener 15, and die buckle 18. Mold opening principle is as follows: slider of injection molding machine drives movable mold to retreat. Since sequence opener 15 locks fixed mold plate 27, upper end of insert 2 and movable mold plate 28, mold buckle 18 also pushes upper end of insert 2 and locks movable mold plate 28. Mold is first opened at PL1 side. As movable mold continues to retreat, long pull rod 12 will pull stripper plate 26 to retreat. PL2 side opens, and stripper plate 26 cannot continue to retreat until it is pulled by stripper plate pull rod 14. At the same time, sequential opener 15 unlocks, fixed mold plate 27, upper end pushes out insert 2, and movable mold plate 28 separates. As movable mold continues to retreat, movable platen plate 28 pulls upper end to push out insert 2 through friction of die buckle 18, overcomes elastic force of spring fixed distance pull rod 13 and opens on PL3 surface, upper push-out insert 2 pushes molded plastic part from upper center core insert 1, leaving plastic part on the side of movable mold. As movable mold continues to retreat, upper push-out insert 2 cannot continue to move downward. Upper push-out insert 2 separates from movable template 28, PL4 surface opens, elastic force of spring fixed distance rod 13 forces upper push-out insert 2 and fixed mold plate 27 to close simultaneously, leaving plastic part on movable mold side.

 

1. Upper center core insert 2. Upper push-out insert 3. Side upper piece 4. Side upper piece 5. Side lower piece 6. Side lower piece 7. Lower end core insert 8. Lower end center core insert 9 .Push 10 slider push 11. slider push 12 long pull 13. spring distance pull rod 14. stripper plate pull rod 15 sequence opener 16. reset rod 17. reset spring 18. die buckle 19. center push 20. small Push rod 21. Gate sleeve 22. Positioning ring 23. Pulling rod 24 Wedge block 25. Fixed mold base plate 26. Stripper plate 27. Fixed template 28 Moving template 29 Moving template pad 30. Screws 31. Spacer block 32. Push rod fixed plate 33. Push plate 34. Moving mold base plate 35. Incline 36. Locking block 37. Positioning pin 38. Guide post 39. Guide sleeve 40. Guide sleeve 41. Guide sleeve 42. Reset rod
Figure 4 Mold structure

Working principle of mold is as follows.
(1) Mold is closed to complete injection process and wait for mold to be opened.
(2) Movable mold of mold retreats, first opens at PL1 surface, and gate condensate at 6 points is separated from plastic part.
(3) Movable mold continues to retreat, PL2 surface opens, stripper plate 26 pushes flow channel condensate from pull rod 23 and falls off.
(4) Movable mold continues to retreat, PL3 surface is opened, upper end push-out insert 2 pushes molded plastic part from upper center core insert 1 and remains on the side of movable mold.
(5) Movable mold continues to retreat, PL4 surface is opened, PL3 surface is closed simultaneously, and plastic part is completely separated from upper push-out insert 2.
(6) Movable mold continues to retreat to a certain position. Ejector pin of injection molding machine pushes push plate 33 out. Slider pushrods 10 and 11 push slider, pull core sideways and simultaneously push molded plastic part from lower center core insert with push rod 9 until plastic part automatically falls off, achieving complete demolding.
(7) When resetting, push plate 33 is reset first, then mold is closed in the order of PL1→PL2→PL3→PL4, and mold starts next injection molding.

A pair of six-point gate three-plate molds is designed for automatic injection molding of plastic parts. Mold structural features: ① Push plate is used to push push rod and side core pulling slider is driven to perform side core pulling and demoulding; ② Multi-point gates are used to pour mold cavity to ensure that cavity is completely filled; ③ An upper push-out insert 2 is added to fixed mold side to assist in pushing out molded plastic parts from fixed mold side to ensure stable demoulding of plastic parts. Mold is changed from 3 mold openings of ordinary three-plate mold to 4 mold openings, simplifying structure and realizing automated production.