Structure of a router antenna protective sleeve handle is shown in Figure 1, with a total production of 800,000 pieces. Plastic part is composed of two types of plastics. Base part is injection molded from a mixture of polycarbonate (PC) and acrylonitrile-butadiene-styrene copolymer (ABS) (ABS+PC), and overmolding layer is injection molded from thermoplastic rubber material (TPR). External dimensions of plastic part are 305.4mm * 21.6mm * 39.4mm. Overmolding layer thickness is 1.3mm. Overmolding area is located in the center of left end face of plastic part, and is elongated elliptical. Four bosses and one recess are provided in the center of overmolding area to ensure a tight bond between overmolded TPR part and base part. There is a 3mm wide opening at left end of plastic part for feeding material during overmolding injection. When molding plastic parts, base component is first formed using an injection molding machine and corresponding injection mold, then overmolding area is formed using an overmolding injection mold.

 

Figure 1 Protective sleeve handle

 

Figure 2 Overmolded cavity design

 

1. Support column 2. Sealing ring 3. Single-cavity core insert 4. Screw 5. Screw 6. Screw 7. Single-cavity plate insert 8. Positioning insert 9. Ejector pin 10. Positioning block 11. Guide sleeve 12. Guide pillar 13. Cavity plate insert 14. Core insert 15. Fixed mold base plate 16. Fixed mold plate 17. Main runner upper insert 18. Main runner lower insert 19. Positioning pin 20. Moving mold plate 21. Runner ejector pin 22. Pad block 23. Ejector pin fixing plate 24. Ejector plate 25. Moving mold base plate 26. Reset rod 27. Reset spring
Figure 3 Mold Structure
Shrinkage rate of base component material is 0.51%~0.58%. Recommended injection molding parameters are: mold temperature 75℃, melt temperature 265℃, ejection temperature 117℃, maximum shear stress 0.4MPa, and maximum shear rate 40000s⁻¹. Shrinkage rate of overmolding area material is 0.82%~0.94%. Recommended injection molding parameters are: mold temperature 45℃, melt temperature 210℃, ejection temperature 122℃, maximum shear stress 0.3MPa, and maximum shear rate 40000s⁻¹. During injection, melt temperature of TPR material in overmolding area is 230~240℃ to ensure a certain fusion bonding layer between it and PC+ABS material of base component.

Based on plastic part structure, when plastic part is produced using mold transfer method, base part, which is injection molded in the first mold, is placed into second overmolding mold as a plastic insert before mold is closed and injection is performed. Therefore, base part is equivalent to one molding part of overmolding cavity. However, this makes it difficult to open gate in overmolding cavity; it can only be located on the top surface of overmolding area or in a 3mm wide opening on left side of overmolding area. If material is fed from top surface of overmolding area, a point gate must be designed for injection, turning mold into a three-plate mold structure, which is complex and costly. Therefore, it is chosen to feed material from a 3mm wide opening on the left side, allowing for side gate injection. This simplifies mold to a two-plate mold structure, making it easier to manufacture and lowering costs. However, solidified material at gate needs to be removed after molding. Therefore, overmolding mold adopts a two-plate mold structure with side gate feeding, and its cavity design is shown in Figure 2.
In cavity design, positioning inserts are used to position base component. Parting surface PL of base component serves as parting surface for overmolded cavity. This parting surface is used to obtain single-cavity cavity plate insert and single-cavity core insert. Each single-cavity cavity plate insert and single-cavity core insert has an 8mm φ8mm cooling channel for cooling. Mold adopts an overlapping side gate with gate dimensions of 5.7mm * 4.5mm * 2mm. A 10mm φ10mm circular runner is used, surface roughness of runner and gate is Ra0.8μm. To ensure service life of cavity walls, single-cavity cavity plate insert and single-cavity core insert are made of H13 alloy steel, and positioning insert is made of 45# steel.

Overall mold structure is shown in Figure 3. It adopts a 1-mold 4-cavity layout, with cavities V1 to V4. Parting and structural design of each cavity is shown in Figure 2. In cooling design, water channels W1 and W3 are used for cooling cavities V1 and V2, while water channels W2 and W4 are used for cooling cavities V3 and V4. W1 and W2 are core cooling water channels on moving mold side, W3 and W4 are water channels on cavity plates on fixed mold side, all with a diameter of φ8mm. Mold's gating system includes main runner R1, primary runner R2, secondary runner R3, and gates G1~G4. Runners R1~R3 are identical for all four cavities, but gate sizes differ. Gate G1 for cavity V1 and gate G4 for cavity V4 have same dimensions as shown in Figure 2, while gate G2 for cavity V2 and gate G3 for cavity V3 have same dimensions, requiring gate balancing design. After gate balancing design, gates G2 and G3 have a width of 2.8mm and a depth of 2mm.
In design of molded parts, four single-cavity mold plate inserts 7 are combined to form mold plate insert 13, and four single-cavity core inserts 3 are combined to form core insert 14. Main runner R1 does not use commonly used cylindrical gate bushing, but instead uses upper runner insert 17 and lower runner insert 18, which together form main runner R1 when mold is closed. Ejector pin 9 pushes out plastic part and solidified material in runner. Mold's gating system design differs from that of a typical two-plate mold in opening of main runner R1, because it needs to be considered that mold is mounted on a vertical injection molding machine. Vertical mold opening structure facilitates operator's placement of base part PS. Mold's guiding mechanism uses four guide pillars 12 and four guide sleeves 11 to guide movement during mold opening.

Installation of most structural components is same as that of a commonly used two-plate mold. Difference is that installation of lower insert 18 and upper insert 17 of main runner requires positioning pins. Both inserts need to be designed with locating jaws for closing and resetting to ensure accurate resetting when mold closes. Push plate 24 synchronously pushes push rod 9 and runner push rod 21 to eject plastic part and runner solidified material. Sealing ring 2 is installed in corresponding sealing ring grooves of fixed platen 16 and moving platen 20, needs a certain thickness compression to prevent water leakage from pipes.

Mold is installed on injection molding machine for injection molding. Process is as follows:
(1) Mold Closure. After manually placing base component on mold positioning insert 8, mold closes at parting surface PL. Injection molding machine nozzle is aligned with main runner R1 inlet to inject molten plastic. After filling, holding pressure, and cooling, mold awaits opening.
(2) Mold Opening. Moving platen of injection molding machine drives fixed mold upward. Mold opens at PL surface, and plastic part detaches from cavity plate insert 13, remaining on core insert 14.
(3) Ejection. Hydraulic cylinder ejector rod inside fixed mold pushes upward, ejecting plastic part and runner solidified material from core insert 14. Plastic part is manually removed, gate and runner solidified material are simultaneously removed at gate.
(4) Reset. During reset, ejector plate 24 first resets downward. Base part is placed on mold positioning insert 8, then mold closes at PL surface, starting next injection cycle.