Shower head handle is shown in Figure 1. Its following features will affect mold structure design: ①External thread feature. Due to limitation of upper shower head cover, thread can only be removed by rotating external thread core; ②Annular groove. Demolding here can only be done by forced core pulling. Depth of single-side groove is 0.15mm, and an annular undercut is formed in demolding direction. According to calculations, forced demolding will not damage local features of plastic part under structural dimensions here; ③Handle elbow. Center line of sweep path of circular hole in inner wall section is an arc. Elbow core pulling is required to realize demolding of center hole of inner wall of elbow; ④Plastic casting problem. It is difficult to find the best balanced pouring point. Although there is an optimal gate opening area after mold flow analysis, this area cannot be selected due to mold structure; ⑤Plastic part structure is complex, wall thickness distribution in local area is uneven, and it is easy to produce defects such as shrinkage marks; ⑥Surface of plastic part is required to be smooth and bright, and surface roughness inspection requirements are high. Plastic parts are to be molded by injection molding of engineering plastic ABS modified by fireproofing and antistatic, with a shrinkage rate of 0.52%~0.58%, material grade HFA-451, and a production of 1.2 million pieces.

 

Mold structure is shown in Figure 2. For demoulding of plastic parts' external threads, due to design space limitations, a single plastic part can only be demoulded by rotating thread core 21. To ensure that thread core 21 can rotate around its axis, its upper end is mounted on cylindrical central core 18, and the lower end cooperates with thread pair of thread guide ring 20. When external thread is demoulded, rack 11 drives gear to drive transmission gear 15 to rotate, and transmission gear 15 drives gear 16 to rotate, so that thread core 21 rotates and removes thread under guidance of thread guide ring 20, while moving downward along its own axis, to achieve complete separation from external thread of plastic part.

 

1. Fixed mold base plate 2. Fixed mold plate 3. Push plate 4. Moving mold plate 5. Moving mold pad 6. Gear partition 7. Pad 8. Moving mold base plate 9. End cover 10. Guide wear strip 11. Rack 12. Bearing 13. Bearing 14. Gear shaft 15. Transmission gear 16. Gear 17. Press plate 18. Central core 19. Locking nut 20. Threaded guide ring 21. Threaded core 22. Pull rod 23. Positioning pin 24. Bend pipe groove seat 25. Locking block 26. Cylindrical pin 27. Bend pipe slide 28. Core insert 29. Cavity plate insert 30. Insert plate 31. Drive plate
Figure 2 Mold structure

Molding and demolding of circular groove are completed by central core 18. Upper end of central core 18 participates in molding of inner wall of center hole of plastic part. When demolding, central core 18 is forced to pull core from center hole of plastic part to realize demolding of circular groove.

Inner hole core pulling mechanism assembly of elbow includes parts 23 to 31. Front end of elbow slide 27 is provided with elbow core, which slides in elbow groove seat 24. Center line of elbow groove of elbow groove seat 24 and center line of center hole of elbow of plastic part are same arc. When mold is in closed state, locking block 25 locks elbow slide 27. Bending slide 27 is provided with a cylindrical pin 26. When driving plate 31 moves downward and separates from bending groove seat 24, cylindrical pin 26 is driven downward through driving grooves on both sides thereof. Cylindrical pin 26 drives bending slide 27 to slide in bending groove of bending groove seat 24, so that bending core at its front end is pulled out from molded plastic part.

As shown in Figure 2, mold is parted with bottom edge of φ29mm cylindrical shell of plastic part as main parting line. Outer wall molding parts above parting surface are cavity plate inserts 29, and inner wall molding parts below parting surface include core inserts 28, threaded core 21 and central core 18. Bottom edge of shell is separately provided with an insert plate 30 for molding. This is not only convenient for mold part processing, but also requires push of insert plate 30 for final separation of plastic part from core insert 28.

Demoulding of molded plastic parts is achieved in following steps: ① Piston rod of hydraulic cylinder drives thread core 21 to rotate through rack 11 to complete demoulding of external thread of plastic part; ② Mold parting surface P1 is opened, central core 18 is forced to be pulled out from center hole of plastic part, thread core 21 is away from plastic part, movable mold pad 5 drives drive plate 31 to move downward and separate from elbow groove seat 24, and drive groove on drive plate 31 drives cylindrical pin 26 to drive elbow slider 27 slides in bend slot seat 24, so that bend core at the front end of bend slider 27 is pulled out from bend hole of plastic part, and inner wall of bend hole is rotated to pull core out of mold; ③ Mold parting surface P2 is opened, outer surface of plastic part is pulled out from cavity of fixed mold plate 2 and remains on core insert 28; ④ Mold parting surface P3 is opened, pull rod 22 pulls upper push plate 3 to drive core insert 28 to separate from plastic part, plastic part is left on insert plate 30 in upper push plate 3 and automatically falls off.

Function of mold frame is mainly to carry various functional system parts and ensure that plastic parts can be automatically injection molded. Therefore, mold frame can be simplified to be composed of pieces 1 to 8 stacked and combined. Installation of mold frame auxiliary mechanism is shown in Figure 3. To facilitate installation of mold structure, movable mold pad 5, gear partition 6, pad 7 and movable mold base plate 8 are combined together using screws and positioning pins; upper push plate 3 and movable mold plate 4 are movable plates that move relatively, opening and closing movements between mold plates are guided by guide pillars 43 and guide sleeves 40, 41, 42. When mold parting surface P1 is opened, movable mold plate 4 and movable mold pad 5 are opened by spring 34, and separation distance is set by long tie rod 38, which is 120mm; when mold parting surface P3 is opened, separation distance between upper push plate 3 and movable mold plate 4 is set by tie rod 44, which is 50mm; opening distance of mold parting surface P2 is 45mm, which is controlled by tie rod 22, and hydraulic cylinder 32 is installed on the side of mold frame.

 

1. Fixed mold base plate 2. Fixed mold plate 3. Push plate 4. Moving mold plate 5. Moving mold pad 6. Gear partition 7. Pad 8. Moving mold base plate 32. Hydraulic cylinder 33. Long pull rod 34. Spring 35. Drawer buckle 36. Elastic pin 37. Gate sleeve 38. Drawer rod 39. Positioning ring 40. Guide sleeve 41. Guide sleeve 42 Guide sleeve 43. Guide column 44. Pull rod
Figure 3 Installation of mold frame auxiliary mechanism

Mold uses a latent side gate for casting, with a gate diameter of φ0.8mm. Runner of casting system is opened on insert plate 30. When mold parting surface P1 is opened, runner condensate escapes from main flow channel of gate sleeve 37. As mold parting surface P3 is opened, pull rod 38 pulls out runner condensate and separates it from plastic part. Runner condensate is finally left on insert plate 30 and is ejected by ejector pin 36. Mold fixed plate 2 opens a φ8mm cooling water channel to cool cavity, and movable mold side opens a cooling water channel on insert plate 30 to indirectly cool core.

Mold is a 8-cavity layout, as shown in Figure 4. 8 cavities are V1~V8, which are directly processed on cavity plate insert 29, and insert plate 30 is mounted on 8 core inserts 28. Fixed mold and movable mold each have a water channel W1 and W2. Piston rod of hydraulic cylinder 32 drives rack 11 to drive two transmission gears 15. Two transmission gears 15 drive four threaded cores 21 to rotate and pull cores. Each cavity is independently provided with a bend pipe groove seat 24, a bend pipe slider 27 and a core insert 28. Mold is provided with five pull rods 38, which are respectively arranged at flow channel diversion. Four guide pillars 43, pull rods 22, 44 and long pull rods 33 are arranged evenly to ensure smooth opening and closing movement of mold. Gate sleeve 37 is installed on fixed mold plate 2, which can effectively shorten flow channel length. Positioning ring 39 is additionally installed on fixed mold base plate 1.

 

11. Rack 15. Transmission gear 21. Threaded core 22. Tie rod 24. Bend pipe groove seat 27. Bend pipe slide 28. Core insert 29. Cavity plate insert 30. Insert plate 31. Drive plate 32. Hydraulic cylinder 33. Long tie rod 37. Gate sleeve 38. Pull rod 39. Positioning ring 43. Guide column 44. Tie rod
Figure 4 Mold cavity layout

(1) Mold closing and injection. After mold is installed on injection molding machine and mold is closed, injection molding machine nozzle injects molten ABS plastic into cavity through gate sleeve 37, and mold is opened after filling, pressure holding, cooling and other processes.
(2) External thread core pulling. Piston rod of hydraulic cylinder 32 drives threaded core 21 of 8 cavities to rotate and pull core through rack 11.
(3) Mold parting surface P1 is opened. As movable mold descends, mold parting surface P1 is opened by spring 34 and stops after opening 120mm. Central core 18 is forced to pull core out of center hole of plastic part, and threaded core 21 is away from plastic part. At the same time, movable mold pad 5 drives drive plate 31 downward to drive bent tube core at the front end of bent tube slider 27 to be pulled out of bent tube hole of plastic part, realizing rotary core pulling and demolding of inner wall of bent tube hole.
(4) Mold parting surface P2 is opened. Movable mold continues to descend. Due to locking of pull die buckle 35 and pushing of elastic pin 36, mold parting surface P2 is opened, outer surface of plastic part is pulled out of fixed mold plate 2 cavity and remains on core insert 28. Mold parting surface P2 is opened by a distance of 134mm.
(5) Mold parting surface P3 is opened. Movable mold continues to move downward, pull rod 22 pulls push plate 3, and core insert 28 is pulled out from plastic part. When mold parting surface P3 is opened by 50mm, plastic part remains on insert plate 30 and automatically falls off.
(6) Reset. Before resetting, piston rod block of hydraulic cylinder 32 drives threaded core 21 to reset first, then mold resets in sequence according to P2→P3→P1, waiting for next injection cycle.