Structure of router safety protection lock cover is a disc cover, as shown in Figure 1. Average wall thickness of plastic part is 2.8 mm, and the overall dimensions are 162.5 mm*202.2 mm*58.6 mm. Disc part of plastic part is main structure, disc height is 3.3 mm, maximum outer edge diameter is φ162.5 mm, maximum diameter of cylindrical wall Z1 set under disc is φ158 mm, and depth of cylindrical wall Z1 is 23.3 mm. 4*φ3 mm side holes H1~H4 are set on cylindrical wall Z1, but center directions of holes are different, they are symmetrically arranged on both sides of center line L1 of plastic part at angles of 10° and 30° respectively. Center of disc is another cylindrical wall Z2, outer wall of Z2 is provided with a straight knurling pattern T1, and inner wall is provided with a rotating lock T2. Buckle handle Z3 is a rectangular thin shell, with two countersunk holes H5 and H6 and a rectangular through hole H7 inside, outer wall is also provided with a straight knurling pattern T3. Plastic material is ABS+PC, and shrinkage rate is 0.48%~0.56%.

 

Figure 1 Plastic part structure
Design difficulties of injection mold for molded plastic parts: ①H1~H4 holes are located on one side of plastic part, concentrated in a small space, and core pulling direction of hole center is inconsistent. It is difficult to realize core pulling and demolding of four holes using general inclined guide column slider core pulling mechanism; ②There are multiple characteristic holes in local area of buckle handle Z3. Molded parts of these characteristic holes are not easy to process, and inserts need to be split to reduce processing difficulty.

Mold cavity is parted by a plane parting surface (PL surface). After obtaining cavity plate insert 1 and core insert 2, part details are designed according to processing, pouring, cooling, etc., as shown in Figure 2. In mold part design, in order to facilitate processing of cavity plate insert 1, cavity plate insert 1 is divided into inserts 3 to 6 for external surface features of molding handle Z3. Correspondingly, corresponding position of core insert 2 is also divided into inserts 7 to 9. In order to facilitate processing of molding part of cylindrical wall Z1 of plastic part, inner wall insert 14 is divided twice on core insert 2, two side gates G1 and G2 are opened in the center of insert 14. In order to solve molding difficulty of holes H1 to H4, hole inserts 10 to 13 are set accordingly, and inserts 10 to 13 are centrally set on slider 16. Material of cavity plate insert 1 and insert 3~6 is H13, with heat treatment hardness of 53~58 HRC; material of core insert 2, insert 7~9, and insert 14 is SKD61, with heat treatment hardness of 48~52 HRC; material of insert 10~13 is T8A high-quality carbon tool steel, with heat treatment hardness of 45~48 HRC. Cavity plate is cooled by φ8 mm cooling water pipe. Both cavity plate insert 1 and core insert 2 are provided with cooling water pipes, and pipe spacing is 20 mm (average value).

 

Figure 2 Parting surface and molded part design
1. Cavity plate insert 2. Core insert 3~14. Secondary split insert 15. Cover plate 16. Slider

For core-pulling movement of molding hole inserts 10~13, a double-oblique guide column four-way core-pulling composite slider mechanism is designed, as shown in Figure 3. A corresponding small slider is arranged at tail end of each insert 10-13 in mechanism, which are small sliders 17-20 respectively. Under limitation of cover plate 15, small sliders 17-20 can only slide in groove at the front end of slider 16 in F5 direction and opposite direction F5′. Therefore, when slider 16 moves in F6 direction for core pulling, it can synchronously drive inserts 10-13 to move in F1-F4 directions respectively. Tail end of insert of each forming hole can move with corresponding small slider without being stuck, so that one slider drives four inserts 10-13 to synchronously implement core pulling in different directions, and movement is opposite when resetting. Slider 16 is driven by double inclined guide pillars with a driving angle of 20°. Core pulling distances of small sliders 17~20 in their respective guide holes are not equal. After calculation, core pulling distance of slider 16 in F6 direction needs to be more than 7 mm to ensure that four inserts are completely demolded. At the same time, in order to ensure that inserts 10~13 can be reset, inserts 10~13 cannot be separated from four holes set on core insert 2. Therefore, core pulling distance of slider 16 in F6 direction needs to be guaranteed to be 7 mm≤s≤9 mm.

 

Figure 3 Double inclined guide pillar four-way core pulling composite slider mechanism
10~13. Inserts 15. Cover plate 16. Slider 17~20. Small slider

Mold structure is shown in Figure 4. It uses a two-plate structure, uses two gates G1 and G2 shown in Figure 2 for casting. Cavity plate is cooled by φ8 mm pipe cooling. Cavity exhaust groove is opened on parting surface and located on the side of cavity plate insert 1. Exhaust groove depth is 0.02 mm and width is 5 mm. Mold uses 8 evenly arranged 48 mm push rods 30 to push out molded plastic parts, and uses 1 pull rod 31 to pull out main channel solidified material.

 

Figure 4 Mold structure
(a) Two-dimensional structure (b) Moving mold; 1. Cavity plate insert 2. Core insert 10. Insert 14. Insert 15. Cover plate 16. Slider 17. Small slider 21. Fixed mold base plate 22. Water nozzle 23. Fixed mold plate 24. Moving mold plate 25. Guide column 26. Reset rod 27. Push rod fixing plate 28. Push plate 29. Moving mold base plate 30. Push rod 31. Pull rod 32. Positioning bead 33. Locking block 34. Screw 35. Inclined guide column 36. Gate sleeve 37. Positioning ring

Working principle of mold is as follows.
(1) Mold is installed on injection molding machine and closed after debugging to wait for injection molding of plastic parts.
(2) Injection molding machine nozzle moves forward and injects molten material into cavity through gate sleeve 36. After filling, pressure holding and cooling, mold is ready for opening.
(3) Slider of injection molding machine drives movable mold to move, and mold is opened at PL surface. At the same time, inclined guide column 35 drives slider 16 to drive four inserts 10~13 to pull core.
(4) After mold is opened, injection molding machine pusher pushes push plate 28 and push rod fixing plate 27 to push out push rod 30 and pulling rod 31 on it, pushes molded plastic part and runner condensate from core insert 2, and plastic part is demolded.