Structure of electrical housing is shown in Figure 1, with an outer dimension of 331mm×171mm×168mm, and material is ABS.

 

Plastic part is divided into two parts, high and low, and transitioned by a circular arc, as shown in Figure 2 (a). The higher part has a square hole, the lower part has a circular pit, side of circular pit has 4 buckles, and thickness of buckle is about 4mm. Since circular pit where buckle is located is not a through hole, 4 buckles on the side of circular pit cannot be demolded by movable mold oblique push mechanism, but require a fixed mold oblique push mechanism. There is a circular side hole on the side of plastic part, which is used to install knob. In order to eliminate contour mark left by movable mold slider on plastic part, circular hole on the side is demolded by fixed mold slider structure. There are several ribs and cylindrical holes on inner surface of plastic part. Cylindrical holes are located not far from mouth of plastic part, and their axes are along vertical direction. In order to make cylindrical holes on inner surface of plastic part attach, a cylindrical hole seat is set for each cylindrical hole, as shown in Figure 2 (b).

 

For four buckle positions on inner wall of circular pit on outer surface, fixed mold oblique push mechanism is used for demoulding, which is composed of a push plate, a fixed plate, a spring, a guide column, and an oblique push rod, as shown in Figure 3. To fix fixed mold oblique push mechanism, a push plate and a fixed plate are set on fixed mold to clamp fixed mold oblique push seat. Set guide column has two functions: one is to keep push plate and fixed plate balanced during up and down movement; the other is that when mold is closed, end face of guide column supports moving mold plate, so that fixed mold oblique push mechanism, fixed mold push plate and fixed plate are reset. One end of spring is buckled on fixed mold seat plate, and the other end is buckled on fixed plate. When mold is opened, spring pushes push plate and fixed plate to move up and down along guide column to realize demolding of fixed mold oblique push mechanism. Since projection area of four buckles in mold opening direction is small, area of fixed mold push plate and fixed plate is also small.

 

Circular structure on the side of plastic part requires a slider mechanism to demold. If movable mold slider mechanism is used for demolding, slider outline will be left on plastic part. In order to overcome this phenomenon, fixed mold slider mechanism is used for demolding. Since demolding distance of slider is small, only 2.5mm, and slider size is small, in order to simplify demolding mechanism, a double-sided inclined wedge is used to drive slider to move, as shown in Figure 4. In order to improve strength of slider, slider adopts an integral structure, that is, molding position of slider and slider seat are an integral whole. Since mold opening distance of slider is small, inclined wedge adopts a double-bevel structure. When mold is closed, inner bevel of double-sided inclined wedge drives slider to reset, and when mold is opened, outer bevel of double-sided inclined wedge drives slider to open mold.

 

Several cylindrical holes are set on the side wall of inner surface of plastic part. Since axis of cylindrical hole is in vertical direction, in order to make cylindrical hole attached to side wall, a base needs to be set for each cylindrical hole, and side of base is attached to the side wall of plastic part, as shown in Figure 5 (a). In order to demold base of cylindrical hole, a moving mold oblique push mechanism is used for demolding, including an oblique push rod, an oblique push seat, screws, etc., as shown in Figure 5 (b). Since size of cylindrical hole base is small, oblique push rod adopts an integral structure. Oblique push seat adopts a T-slot structure and is fixed to push plate with screws. When oblique push rod needs to be disassembled, screws can be directly loosened or tightened from disassembly hole set on moving mold seat plate, disassembly and assembly work intensity is relatively low. Diameter of cylindrical hole is small, and its core is easy to break. In order to facilitate mold repair, core of cylindrical hole is set as an insert, as shown in Figure 5 (c). If core of cylindrical hole breaks, insert can be directly replaced, and difficulty of mold repair is relatively small.

 

Since size of plastic part is small and structure on plastic part that affects melt flow is small, one gate can meet injection requirements. According to structure of plastic part, runner is opened at a higher square hole, and material is fed on inner side of square hole. Gate type is fan-shaped, as shown in Figure 6. After assembly, gate trace is covered by other plastic parts and does not affect appearance.

 

Since opposite side of gate is movable mold push mechanism shown in Figure 5 (b), it is necessary to reserve movement space for push mechanism when opening mold. In order not to hinder movement of push mechanism, a cold material hole cannot be opened under gate sleeve. Slightly extending runner on push mechanism can play role of a cold material hole. Therefore, runner must be divided into two levels, as shown in Figure 6. Runner connected to gate is opened on movable mold core, and runner connected to gate sleeve is located on push rod. This section of runner is opened on fixed mold core.

Fixed mold adopts an integral structure. In order to facilitate installation of fixed mold oblique push mechanism shown in Figure 3 in fixed mold, space is reserved on the back of fixed mold for installing fixed mold push plate, fixed plate and spring ① and other components. Spring ① is used to push fixed mold push plate to move, as shown in Figure 7 (a). In order to separate fixed mold plate from fixed mold base plate when opening mold, a limit screw and spring ② are set between fixed mold plate and fixed mold base plate. Spring ② is used to separate fixed mold plate from fixed mold base plate, and limit screw is used to limit maximum distance between the two. Movable mold core adopts an insert structure, as shown in Figure 7 (b). Due to large ups and downs of plastic part, in order to save mold parts materials, movable mold core is composed of two pieces of material, one large and one small. Material with a smaller area is inserted in material with a larger area. Inlay position of the two pieces of material is at rib position shown in Figure 2 (b) to prevent rib position from being filled incompletely.

 

In order to demold plastic part smoothly, a push rod is used for ejection, and diameter of push rod is φ8 mm. Since there are many ribs on inner surface of plastic part, in order to avoid phenomenon of whitening and damage to plastic part, push rods are appropriately added at ribs. Since diameter of cylindrical hole on inner surface of plastic part is small, only φ3.5 mm, it is suitable to adopt ejection structure of "push rod + push rod sleeve", and ejection system is shown in Figure 8.

 

In order to make plastic part cool and solidify quickly after injection and prevent deformation of plastic part, cooling system should be designed according to shape of plastic part and structure of mold. Fixed mold of mold is an integral structure. According to shape of cavity, a straight-through cooling system is designed, as shown in Figure 9 (a). Each straight-through water channel is an independent water channel, which can effectively prevent cooling water from transferring temperature to another area during circulation process, so that mold temperature remains uniform. Movable mold adopts an insert structure, cooling water of movable mold core must enter and exit through movable mold plate through straight-through water channel. Since there are two inserts in movable mold, movable mold has two cooling circuits. Inserts with lower plastic parts use straight-through water channels, and inserts with higher plastic parts use spacer-type water well water channels, which are connected by straight-through water channels, as shown in Figure 9 (b).

 

Mold structure is shown in Figure 10. Mold is a two-plate mold. In order to demold fixed mold slider, springs and limit screws are set between fixed mold plate and fixed mold base plate. When mold is opened, they are used to separate the two, so that mold frame has function of a three-plate mold. In order to realize demolding of fixed mold oblique push mechanism, a push plate, springs and push plate guide pins are set on the back of fixed mold plate. When mold is opened, spring pushes push plate open; when mold is closed, end face of push plate guide pin buckles on movable mold plate. At this time, push plate guide pin also serves as a reset rod.

 

1. Moving mold base plate 2. Push plate 3. Push rod fixing plate 4. Pad 5. Moving mold plate 6. Cylindrical hole core 7. Guide column 8. Fixed mold plate 9. Fixed mold base plate 10. Limit screw 11. Positioning ring 12. Wedge 13. Fixed mold slide 14. Oblique push rod 15. Push rod 16. Runner condensate 17. Fixed mold push plate 18. Spring ① 19. Spring ② 20. Fixed mold fixing plate 21. Fixed mold oblique push rod 22. Fixed mold push plate guide column 23. Moving mold insert ① 24. Fixed mold insert ② 25. Support column
Figure 10 Mold structure
Mold movement process: After injection, mold is opened twice. The first mold opening is to separate fixed mold plate 8 from fixed mold base plate 9 under push of spring 19. During this process, inclined wedge 12 drives fixed mold slider 13 to demold. When distance between fixed mold plate and fixed mold base plate reaches 21 mm, movement stops under action of limit screw, and the first mold opening is completed. The second mold opening is to separate between fixed mold plate 8 and movable mold plate 5. During mold opening process, since movable mold plate no longer supports end face of fixed mold push plate guide column 22, spring 18 pushes fixed mold push plate 17 away, thereby pushing fixed mold oblique push rod 21 to demold. When movable mold is completely separated from fixed mold, injection molding machine pusher pushes mold ejection mechanism (including oblique push rod 14, push rod 15, etc.) to do ejection movement. After taking out plastic parts, injection molding machine drives movable mold to start resetting. Resetting process is opposite to mold opening process. After complete resetting, next injection cycle can be started.