Figure 1 shows a wireless signal base station indexer, there are 3 features T1, T2, T3, T1, T2 are horizontal undercuts formed by mouth of plastic part on fixed mold side, and the two undercuts face each other. Space for designing core-pulling mechanism is relatively small; T3 is characterized by inner thread inside the lower end of cover, which needs to be rotated for core-pulling, which is difficult to demold. Therefore, front and rear core-pulling of plastic parts require special demolding mechanisms.

 

Figure 1 Plastic parts
Structural features of plastic part are: main body is a dome cover, inner wall of cover has 2 circles of internal threads T3; top of cover has a groove on spherical head, there are two inverted buttons T1 and T2 on both sides of groove; Plastic parts are made of ABS plastic, with an average wall thickness of 2.2 mm and a shrinkage rate of 0.52% to 0.58%. The total production of plastic parts is 1.2 million, which requires use of multi-cavity for injection production.

Mold structure adopts layout of 1 mold and 4 cavities, as shown in Figure 2, which not only meets molding accuracy of plastic parts, but also maximizes output of a single pair of molds, so as to save the overall manufacturing cost of mold. Use side gate for pouring to facilitate gate correction and adjustment, reducing difficulty of mold manufacturing. A fixed die push-out mechanism is designed for top of plastic parts to be inverted for demoulding, and an internal thread rotation core-pulling mechanism is designed for internal threads of the lower end of plastic parts.

 

Figure 2 Mold structure layout

Using a two-plate die set, as shown in Figure 3, fixed die part of die set was modified, a fixed die push-out mechanism was added. Two plates were added to movable die part, one for installing unthreaded mechanism, and one for ejection and demoulding of plastic parts. Fixed die base plate 1, spacer block 2, and insert fixing plate 3 are assembled together by screws to form fixed die assembly of die; Core fixing plate 5, movable mold backing plate 6, spacer 7, movable mold base plate 8 are fastened and assembled together with 2 sets of screws; Pusher plate 4 is pushed out by spring 26 by being sleeved on threaded rotating core 16 , limit pull rod 27 is used to limit pusher plate 4 after pushing plastic part out of threaded rotating core 16 to prevent it from falling off mold.

 

Figure 3 Mold structure
1. Fixed die seat plate 2. Pad 3. Insert fixing plate 4. Pusher plate 5. Core fixing plate 6. Moving die pad 7. Pad 8. Moving die seat plate 9. Push plate 10. Push Rod fixing plate 11. Inclined push rod 12. Inclined push rod seat 13. Inclined push rod seat 14. Inclined push rod 15. Forming insert 16. Threaded rotating core 17. Threaded rotating core rotating sleeve 18. Threaded rotating core Gear 19. Gear fixing nut 20. Center fixing core 21. Chain gear shaft bearing 22. Chain gear shaft 23. Chain gear 24. Gear key 25. Intermediate transmission gear 26. Spring 27. Limit pull rod 28. Fixed die push plate Tie rod 29. Spring 30. Pull mold buckle 31. Gate bushing 32. Reset rod 33. Positioning ring

Casting system components include gate bushing 31 and positioning ring 33 . Gate bushing 31 is used to construct channel between gate and cavity flow channel of injection molding machine, positioning ring 33 is used for rough positioning and installation of mold on fixed platen of injection molding machine.

(1) Fixed die push-out mechanism. Stationary mold ejecting mechanism includes a push plate 9 , a push rod fixing plate 10 , inclined push rods 11 and 14 , inclined push rod seats 12 and 13 , a forming insert 15 , a fixed mold push plate pull rod 28 , a spring 29 , and a reset rod 32 . Push plate 9 and push rod fixing plate 10 are assembled with screws to form a push plate assembly, on which are installed oblique push rods 11 and 14, inclined push rod seats 12 and 13, which are used for ejection and demoulding of fixed mold of plastic part; Forming insert 15 is assembled and installed in insert groove of insert fixing plate 3 with screws, and is used for surface forming of plastic part; Spring 29 is used to push out push plate assembly, pull rod 28 is used for push plate assembly to push out limit, reset rod 32 is used for return and reset of push plate assembly. Fixed die push-out mechanism solves problem that front ends of lids are reversed in opposite direction and is difficult to demould, realizes automatic demoulding of front-end inversions.
(2) Moving die pusher plate assembly. Movable die pusher plate assembly includes a spring 26 , a limit pull rod 27 , and a pull die buckle 30 . Spring 26 and limiting rod 27 are used for pushing out and limiting position of pusher plate 4 , die buckle 30 is used for locking and closing temporary positions of insert fixing plate 3 and pusher plate 4 .
(3) Inner thread core pulling drive assembly of mold chain includes a threaded rotating core 16, a threaded rotating core rotating sleeve 17, a threaded rotating core gear 18, a gear fixing nut 19, a central fixing core 20, a chain gear shaft bearing 21, chain gear shaft 22 , chain gear 23 , gear key 24 , intermediate transmission gear 25 . Threaded rotating core 16 is sleeved in core fixing plate 5, and its unthreaded rotation is guided by threaded rotating core rotating sleeve 17. Threaded rotating core gear 18 is sleeved on the lower end of threaded rotating core 16 through gear fixing nut 19 , used to engage with intermediate transmission gear 25 to drive threaded rotating core 16 to rotate core, central fixed core 20 is sleeved in threaded rotating core 16, chain gear shaft bearing 21 is used for installation of chain gear shaft 22 on movable die base plate 8 and movable die backing plate 6; chain gear 23 is sleeved on chain gear shaft 22 to drive intermediate transmission gear 25 to rotate, and intermediate transmission gear 25 is installed on chain gear shaft 22 through gear key 24. Inner thread core pulling drive assembly of chain completes unthreading of inner thread of rear end of molded plastic part, realizes automatic disengagement of rear end thread of plastic part.

Mold is opened and divided in two times. In actual work, corresponding action process is as follows.
(1) Injection. Mold is closed, injection molding machine pours four cavities through gate bushing 31 and the side gate, waits for mold to be opened after injection.
(2) P1 parting surface is opened. After injection is completed and cooled, mold plate of injection molding machine drives movable mold to retreat, insert fixing plate 3 and pusher plate 4 are tightened by means of pull mold buckle 30. With assistance of spring 26, P1 parting surface is opened first, pusher plate 4 and core fixing plate 5 begin to separate, unthreading motor of mold drives intermediate transmission gear 25 and thread-rotating core gear 18 to rotate, so that thread-rotating core gear 18 drives thread-rotating core 16 to rotate, while rotating, hread is unthreaded and goes down. After P1 parting surface is opened to a certain distance, it is limited by limit rod 27, pusher plate 4 and core fixing plate 5 cannot continue to be separated, thread at the lower end of plastic part is demolded. During process of rotating thread, push board 4 continues to hold plastic parts, plastic parts stay forming inlaid 15 after P1 surface is divided.
(3) P2 parting surface is opened. Movable mold continues to retreat, and mold opening force forces insert fixing plate 3 and pusher plate 4 to overcome suction force of pull-die buckle 30, forcing P2 parting surface to open. When P2 parting surface is opened, push board 9, fixed board fixed board 10 is launched downward under action of spring 29, pushing inclined push rods 11 and 14, inclined push rod seats 12 and 13 to push down, plastic part is pushed out from molding insert 15, and plastic part is completely demolded.
(4) Reset. When reset, threaded mechanism at the lower end of plastic part is reset first, mold is reset in the sequence of P2 and P1, and finally fixed mold ejection mechanism is reset, mold is completely closed, next injection cycle is waited.