Figure 1 shows structure of face cover and bottom cover of breast shield, and plastic part is made of ABS.
As shown in Figure 1 (a), there are 3 circular holes at the front end of face cover, 1 U-shaped notch at rear end, 2*φ2mm vertical cylindrical holes at the bottom of inner surface, and 2*φ2mm oblique cylindrical holes at the front end. Angle between axis and horizontal direction is 20°. Since these two cylindrical holes are tilted downward and inclination angle is large, it is not suitable to demold with an oblique push rod, and an inner slider is required for demolding. As shown in Figure 1 (b), there is a U-shaped notch at the rear end of bottom cover, multiple reinforcing ribs on inner surface, and a φ2mm*13mm cylindrical hole at the bottom.

 

In order to produce face cover and bottom cover as a set, two plastic parts are placed in same mold for molding. Layout is shown in Figure 2, where inner surface of face cover is molded by movable mold insert, and inner surface of bottom cover is molded by fixed mold insert. Since structures of two plastic parts are quite different, in order to maintain force balance of mold, parting surfaces of face cover and bottom cover are not in same plane.

 

For two oblique cylindrical holes on inner surface of face cover, it is suitable to use inner slider structure for demolding, which consists of an oblique wedge and an inner slider. Oblique wedge and inner slider are connected by a T-slot, as shown in Figure 3. Oblique wedge is fixed on support plate, and inner slider is fixed on movable mold core. When support plate is separated from movable mold core, inner slider moves obliquely downward along inclined surface, thereby demolding cylindrical hole.

 

1. Support plate 2. moving mold core fixing plate 3. moving mold core 4. Wedge 5. Inner slider
Figure 3 Inner slider structure

Face cover has three small holes. In order to prevent plastic parts from having welding marks, fixed mold slider structure is used for demoulding, which is composed of an inclined wedge, a slide groove strip, a slider seat, a small hole core, etc., as shown in Figure 4. Inclined wedge and slider seat each have two inclined surfaces, which also serve as inclined guide pillars and wedge-tightening blocks. When mold is opened, outer inclined surface of inclined wedge contacts slider seat to drive slider to demould. At this time, inclined wedge acts as an inclined guide pillar; when mold is reset, inner inclined surface of inclined wedge contacts slider seat, and inner inclined surface presses on slider seat to drive slider to reset. At this time, inclined wedge has function of a slider wedge-tightening block.

 

1. Small hole core, 2. Pressure plate, 3. Slider seat, 4. Wedge, 5. Plastic part, 6. Slide strip
Figure 4 Fixed mold slider structure

Due to buckle position of U-shaped notch on face cover, it is not suitable to use pillow position as parting surface of U-shaped notch. Slider molding is required, in which slider and slider seat are a whole. In order to ensure balance of slider movement, two springs are set on slider seat, as shown in Figure 5.

 

There are two ribs on inner surface of cover, with a maximum depth of 37mm and a wall thickness of 1.0mm. Core of rib is set as an insert, which mainly plays three roles: ① Increase exhaust effect to prevent phenomenon of insufficient cavity filling; ② Facilitate mold repair and modification; ③ Facilitate polishing. Insert structure is shown in Figure 6.

 

For U-shaped notch of bottom cover, parting surface adopts a pillow structure, as shown in Figure 7.

 

There are several ribs and a cylindrical hole on inner surface of bottom cover. In order to prevent ribs on inner surface of bottom cover from being insufficiently filled, core of ribs and cylindrical hole is set as an insert, and structure is shown in Figure 8.

 

A good cooling system is conducive to rapid cooling and shaping of plastic parts, so that shape of plastic parts remains stable and does not deform. In this mold, front cover and bottom cover use different cooling water channels: front cover is arched, fixed mold of front cover uses two independent straight-through water channels on upper and lower layers, so that distance between straight-through water channel and cavity surface is basically same; fixed mold of bottom cover uses a water channel that combines straight-through and water wells, with water wells at pillow and middle positions and straight-through water channels at other positions, as shown in Figure 9 (a). Since movable mold of front cover has an inner slider and two reinforcing rib core inserts, it is not suitable to open a water well. Movable molds of front cover and bottom cover both use straight-through water channels, as shown in Figure 9 (b).

 

Both plastic parts are cast using direct gates, and mold uses a three-plate mold. Each plastic part corresponds to a gate, and material is fed directly on plastic part to be molded, as shown in Figure 10. In order to facilitate personnel to trim gate condensate, gate position is set to a concave position so that gate condensate is lower than surrounding horizontal plane after trimming, which does not affect assembly of other parts and can avoid appearance of flow marks and other undesirable injection phenomena on the surface of plastic part.

 

In order to drive inner slider of face cover to demold after movable mold core fixing plate is separated from support plate, an auxiliary mold opening mechanism is set at each end of push plate. Its structure consists of a guide block, a push bar, a movable block, a spring (function is to push movable block to reset), etc. One end of push bar is fixed on push plate, and the other end is buckled on movable blocks at both ends of movable mold core fixing plate, as shown in Figure 11. When movable and fixed molds are completely separated, when injection molding machine push rod drives push plate to move, push bar pushes against movable blocks at both ends of movable mold core fixing plate, so that movable mold core fixing plate is separated from support plate, and inner slider is driven to demold.

 

When moving mold core fixing plate and support plate are separated by a certain distance, inclined surface of movable block contacts inclined surface of guide block, and movable block is compressed. When movable block is fully retracted, push bar is separated from movable block and no longer pushes moving mold core fixing plate to move. At this time, moving mold core fixing plate and support plate are no longer separated, but mold ejection system continues to move, and push rod pushes plastic part out. When mold ejection system is fully reset, spring at the end of movable block pops out movable block.

Both face cover and bottom cover are cast by direct gate, so mold adopts a three-plate mold structure, a push plate is set between fixed mold base plate and fixed mold plate, a support plate is set between moving mold core fixing plate and pad to drive inner slider of face cover to demold. Mold structure is shown in Figure 12.

 

1. Moving mold base plate 2. Push plate 3. Push rod fixing plate 4. Pad 5. Support plate 6. Moving mold core fixing plate 7. Push tube 8. Slider 9. Fixed mold core fixing plate 10. Inclined guide column 11. Push plate 12. Fixed mold base plate 13. Positioning ring 14. Wedge 15. Inner slider 16. Fixed mold slider core 17. Fixed mold slider seat 18. Inner slider wedge 19. Support column 20. Screw 21. Cylindrical pin 22. Limit column 23. Reset spring 24. Push bar 25. Guide block, 26. Movable block 27. Spring 28. Bottom cover moving mold core 29. Reinforcement rib core insert 30. Bottom cover fixed mold core 31. Pull rod 32. Surface cover fixed mold core 33. Surface cover moving mold core 34. Limit screw 35. Push rod 36. Support column
Figure 12 Mold structure
Mold is opened in three steps. Specific movement process is as follows: After injection is completed, mold is opened between push plate 11 and fixed model core fixing plate 9 for the first time, and inclined wedge 14 drives fixed mold slider core 16 to demold; mold is opened between fixed mold core fixing plate 9 and movable mold core fixing plate 6 for the second time; the third time is opened after movable mold moves to limit position. When ejection system of injection molding machine drives mold to move, push bar 24 separates movable mold core fixing plate 6 from support plate 5, and inner slider inclined wedge 18 drives inner slider 15 to demold. When separation distance between movable mold core fixing plate 6 and support plate 5 reaches 35mm, it stops moving, and then push plate 2 pushes push rod 35 to move until plastic part is completely pushed out. After taking out plastic part and runner condensate, mold is reset. Reset step is opposite to mold opening step. After reset is completed, next injection is performed.