Router safety lock cover is disc-shaped, as shown in Figure 1. Average wall thickness is 2.8 mm, and the overall dimensions are 162.5 mm * 202.2 mm * 58.6 mm. Disc portion of part forms main structure, with a height of 3.3 mm and a maximum outer diameter of 162.5 mm. Beneath disc is a cylindrical wall Z1 with a maximum diameter of 158 mm and a depth of 23.3 mm. Cylindrical wall Z1 is provided with 4 * 3 mm side holes H1 to H4, but hole centers are oriented in different directions, symmetrically arranged on either side of part's centerline L1 at angles of 10° and 30°, respectively. Center of disc is another cylindrical wall Z2, whose outer surface features a straight knurling pattern T1 and its inner surface is equipped with a rotating lock latch T2. Handle Z3 is a thin rectangular shell with two countersunk holes H5 and H6 and one rectangular through-hole H7 inside. Outer wall also features a straight knurled pattern T3. Plastic part is made of ABS+PC, with a shrinkage rate of 0.48% to 0.56%.

 

Figure 1 Plastic Part Structure
Following are some of difficulties in injection mold design for this part: ① Holes H1 to H4 are located on one side of part, concentrated in a small space. Furthermore, core pulling directions of hole centers are inconsistent, making it difficult to pull and demold all four holes using a conventional inclined guide-slide core pulling mechanism. ② Multiple characteristic holes are located in a local area of handle Z3, making molded part difficult to machine. Therefore, inserts need to be split to reduce machining difficulty.

Mold cavity is parted using a planar parting surface (PL surface). After obtaining cavity plate insert 1 and core insert 2, detailed part design is then performed based on machining, pouring, and cooling, as shown in Figure 2. During mold component design, to facilitate processing of cavity plate insert 1, it was subdivided into inserts 3-6 to form external surface features of handle Z3. Correspondingly, corresponding position of core insert 2 was also subdivided into inserts 7-9. To facilitate processing of cylindrical wall Z1 of plastic part, inner wall insert 14 was subdivided from core insert 2, and two side gates G1 and G2 were opened at the center of insert 14. To address molding difficulties of holes H1-H4, corresponding hole inserts 10-13 were provided, and inserts 10-13 were centrally mounted on slider 16. Cavity plate inserts 1 and inserts 3-6 are made of H13 with a heat-treated hardness of 53-58 HRC; core inserts 2, 7-9, and 14 are made of SKD61 with a heat-treated hardness of 48-52 HRC; inserts 10-13 are made of T8A high-quality carbon tool steel with a heat-treated hardness of 45-48 HRC. Cavity plate is cooled using φ8 mm cooling water pipes. Both cavity plate inserts 1 and core inserts 2 have cooling water pipes, with an average spacing of 20 mm.

 

Figure 2 Parting Surface and Molded Part Design
1. Cavity Plate Insert 2. Core Inserts 3-14. Secondary Split Insert 15. Cover Plate 16. Slide

A double-inclined guide pin four-direction core-pulling composite slide mechanism was designed to support core-pulling motion of molded hole inserts 10-13, as shown in Figure 3. A corresponding small slider is set at the tail end of each insert 10~13 in mechanism, namely small slider 17~20. Under limit of cover plate 15, small slider 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 follow corresponding small slider to move 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. Sliders 16 are driven by dual inclined guide pins at a 20° drive angle. Core pulling distances of small slides 17-20 within their respective guide holes are unequal. Calculations show that core pulling distance of slide 16 in F6 direction must be at least 7 mm to ensure complete demolding of four inserts. Furthermore, to ensure that inserts 10-13 can reposition and remain within four holes provided in core insert 2, core pulling distance of slide 16 in F6 direction must be 7 mm ≤ s ≤ 9 mm.

 

Figure 3: Dual-Inclined Guide Pin Four-Direction Core Pulling Composite Slide Mechanism
10-13. Inserts 15. Cover Plate 16. Sliders 17-20. Small Sliders

Mold structure is shown in Figure 4. It utilizes a two-plate construction, using the two gates G1 and G2 shown in Figure 2 for casting. Cavity plate is cooled using φ8 mm ducts. A cavity venting groove is located on parting surface, on one side of cavity plate insert 1. Venting groove is 0.02 mm deep and 5 mm wide. Mold uses eight evenly spaced 48 mm ejector rods 30 to eject molded part, and a single pull rod 31 to pull solidified material out of main runner.

 

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. Dynamic mold plate 25. Guide column 26. Reset rod 27. Push rod fixing plate 28. Push plate 29. Dynamic 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, injecting molten material into mold cavity through sprue sleeve 36. After filling, holding pressure, and cooling, mold is ready for opening. (3) Injection molding machine slider drives movable mold to move, and mold opens at PL surface. At the same time, inclined guide column 35 drives slider 16 to drive four inserts 10-13 to perform core pulling. (4) After mold is opened, injection molding machine push rod pushes push plate 28 and push rod fixing plate 27 to push out push rod 30 and pulling rod 31 on it, pushing molded plastic part and runner condensate from core insert 2, and plastic part is demolded.