Figure 1 Two-dimensional structure of shell

 

Figure 2 3D modeling of shell

Structure of shell is shown in Figure 1. The whole is disc-shaped and structure is more complicated. There are three cylindrical structures on both sides of disc surface, and each cylindrical structure has its own internal structure. Its three-dimensional shape is shown in Figure 2. Show. Among them, there are two ϕ2mm small holes in the center of φ14mm small cylinder. External grooves with a height of (3±0.05) mm and a depth of 0.75mm (see B-B cross-sectional view in Figure 1), 4 inner grooves with a width of 3mm, a depth of 0.5mm and 3 inner grooves with a width of 3mm and a depth of 0.5mm. Two groups of inner grooves are located on both sides of parting surface Ⅰ-Ⅰ. Material of plastic part is PA1010, inner groove is not suitable for forced demoulding, core pulling mechanism needs to be used for demoulding. Appearance quality and dimensional accuracy of plastic parts are high, defects such as gate marks, welding marks, shrinkage holes, and depressions that affect appearance quality are not allowed.

According to structure and technical analysis of shell, shell has an outer groove and inner groove structure, two groups of inner grooves are located in fixed mold part and movable mold part of mold. Mold structure needs to use outer core pulling and inner core pulling mechanisms to form grooves to meet molding requirements of shell. Combined with needs of automated mass production, mold is designed as a 2 cavity structure, using ordinary runner latent gate feeding to achieve automatic separation of gating system to meet appearance quality requirements of plastic parts.

 

Figure 3 gating system

Design of gating system is shown in Figure 3. Mould gating system is mainly composed of main runner, sub runner, gate and cold cavity. Main runner is directly composed of a sprue sleeve. End of main runner adopts a hook-shaped cold cavity to collect melt condensate in injection molding process. After mold is opened, main runner condensate can be pulled out to stay on moving mold, and ejector can be ejected by ejector rod to complete ejection. Sub runner is set on parting surface where core meets, with a circular cross section to ensure that melt has good fluidity. In order to ensure appearance quality of plastic parts, latent gate is set on moving mold, submerged in moving mold into cavity along oblique direction, and material is fed from inside of plastic parts to be formed. Position of gate is hidden in the back of plastic parts, and channel is set by end of push rod in cavity. Angle between latent gate and center line of runner is 45 °, gate taper is 17 °, and diameter is ϕ1. 5mm. In the process of pushing out, gate is automatically cut off by its lower push rod to ensure that pouring material and plastic parts of gating system are automatically separated after mold is opened.

 

Figure 4 Core pulling mechanism inside forming slider

1. Forming slider 2. Fixed mold round core 3. Fixed model core 4. Base 5. Fixed mold plate 6. Insert 7. Fixed mold seat plate
There are four internal grooves with a depth of 0.5mm on the inside of plastic column (see left side of B-B cross-sectional view in Figure 1). Fixed part is formed by inner core pulling mechanism of forming slider, as shown in Figure 4. Mechanism is mainly composed of molding slider 1, fixed mold circular core 2, fixed mold core 3, base 4, and fixed mold base plate 7. Core pulling structure of four internal grooves on fixed mold side is designed as 4 shaped sliders with an angle of 3 ° from axis of base, which is connected with I-shaped groove in sliding connection and is symmetrical on 4 surfaces of base distributed. After injection molding of plastic parts, base 4 retreats in axial direction, forming slider 1 slides on I-slot relative to base 4. Under restriction of square hole of fixed mold circular core 2 and forming slider 1 , molding slider 1 does not move axially relative to plastic parts, and only performs contraction movement in radial direction of central axis. Maximum contraction distance is L = 20 * tan3º = 1mm, so as to realize core-pulling molding of 0.5mm inner groove of plastic parts of fixed mold part.

 

Figure 5 Inside core pulling mechanism of inclined push rod

1. Push plate 2. Push rod fixing plate 3. Inclined top seat 4. Cylindrical pin 5. Inclined push rod 6. Movable template 7. Movable model core 8. Movable mold circular core
There are 3 internal grooves with a depth of 0.5mm inside other cylinder of plastic parts (see right side of BB cross-sectional view in Figure 1), which is formed in moving mold part. Since core pulling force and core pulling distance are not large, core pulling mechanism inside oblique push rod can be used for forming, as shown in FIG. 5. Push-out mechanism is mainly composed of push plate 1, push rod fixing plate 2, slanted top seat 3, cylindrical pin 4, oblique push rod 5, and movable mold circular core 8. Section of inclined push rod 5 is a square structure. When push plate 1 pushes inclined top seat 3 to move, forming end of inclined push rod 5 moves in the direction of 3º inclined plane in circular core 8 of movable mold, and the other end is connected to cylindrical pin 4 to move in T-shaped groove structure of inclined top base 3. In the process of pushing out, oblique push rod 5 moves out of plastic part while pushing out plastic part in an oblique direction, maximum demolding distance is 20 * tan3º = 1mm, which realizes core-pulling molding of 0.5mm inner groove of plastic part of moving mold part.

 

Fig. 6 Core pulling mechanism on the outside of inclined guide plate slider

1. Fixed mold plate 2. Forming block 3. Inclined guide 4. Spring 5. Slider 6. Wear-resistant stop 7. Limit screw 8. Moving mold plate
Shape of plastic part has an annular side groove with a depth of 0.75mm, and core guide mechanism of inclined guide plate slider is used for demoulding, as shown in Figure 6. In order to ensure that side groove can be demolded smoothly, mechanism is composed of fixed mold plate 1, forming block 2, inclined guide plate 3, spring 4, slider 5, wear-resistant stop 6, limit screw 7, and movable mold plate 8. Optimal inclination angle of inclined guide plate 3 is 16º, effective height is 25mm, maximum core pulling distance is 25 * tan16º = 7mm, end of inclined guide plate 3 is designed with a 10º reverse slope, which cooperates with wear-resistant stop 6 to lock slider to prevent slider from being stretched by injection pressure during injection process and plays a reverse locking role. Molding block 2 is assembled on slider; slider 5 cooperates with T-shaped guide groove of moving mold plate to ensure that it slides smoothly in guide groove without stagnation and jumping. Under action of spring 4 and limit screw 7, slider 5 stays in a certain position after mold is opened.

 

Figure 7 shell injection mold structure

1. Movable mold base plate 2. Push plate 3. Push rod fixing plate 4. Spring 5. Reset lever 6. Guide 7. Movable template 8. Movable model core 9. Fixed model core 10. Round core 11. Fixed template 12 .Fixed mold base plate 13. Pull rod 14. Positioning ring 15. Sprue bush 16. Spring 17. Limit screw 18. Guide bush 19. Guide post 20. Insert 21. Screw 22. Base 23. Forming slip Block 24. Fixed mold round core 25. Moving mold round core 26. Push rod 27. Oblique push rod 28. Cylindrical pin 29. Inclined top seat 30. Screw 31. Forming block 32. Inclined guide plate 33. Slider 34. Spring 35. Limit screw 36. Wear-resistant stop 37. Support column
Overall structure of mold is shown in Fig. 7. Inner core pulling mechanism of forming slider is used to form inner groove of plastic part in fixed mold part, inclined push rod core pulling mechanism is used to form inner groove of plastic part in moving mold part, inclined guide plate slider core pulling mechanism is used to form plastic side groove. Aiming at side grooves of different parts of plastic parts, design of mold core pulling mechanism ensures that plastic parts are smoothly formed and demolded.

As can be seen from Fig. 7, injection mold of shell is composed of multiple groups of core-pulling mechanisms, and each action operates in coordination.
Working principle of mold: After mold is closed, molten plastic melt enters mold gate sleeve 15 through nozzle of injection molding machine, enters mold cavity through latent gate. After heat preservation, pressure maintenance, and cooling, mold is opened. Working process of mold: ① When mold is opened, first, under action of spring 16, Ⅰ-Ⅰ parting surface is opened, fixed mold base plate 12 and fixed mold plate 11 are separated first. Fixed mold base plate 12 drives base 22 to move, under action of I-shaped matching chute, base 22 drives forming slider 23 to contract in radial direction until large end of limit screw 16 fits bottom surface of fixed mold plate 11. At this time, fixed mold base plate 12 and fixed mold plate 11 are separated by 20 mm, and the forming slider 23 is contracted by 1 mm in the radial direction. Forming slider 23 is completely detached from inner groove of plastic part, so as to realize core pulling of inner groove of fixed part; ② Continue to open mold, parting surface Ⅱ-Ⅱ is opened, fixed mold plate 11 and movable mold plate 7 are gradually separated, inclined guide plate 32 installed on fixed mold plate 11 is moved. Under action of inclined guide plate 32 and spring 34, slider 33 is driven to move laterally, molding block 31 is driven away from outer concave of plastic part until slider 33 contacts limit screw 35 and stops moving. After inclined guide plate 32 completely disengages from slider 33, movable and fixed molds are completely opened, separated by at least 90 mm to allow length of main runner condensate and space of inclined jack to eject; ③ Ejector rod of injection molding machine pushes push plate 2, push plate 2 drives inclined top base 29 to move. Under guidance of oblique square hole, oblique push rod 27 pushes out plastic part in oblique direction while leaving groove in plastic part of movable mold part, push rod 26 cuts off latent gate under action of push plate 2 to realize separation of flow runner aggregate and plastic part. Finally, plastic part is completely pushed out under action of inclined push rod 27 and push rod 26, mold opening is completed.
When mold is closed, ejector rod of injection molding machine is reset, push rod 26 and inclined push rod 27 are reset under action of spring 34; then mold is closed, movable mold plate 7 and fixed mold plate 11 are first closed, inclined guide plate 32 drives slider 33 and forming block 31 to reset. Finally, under action of clamping force, spring 16 is compressed, fixed mold base plate 12 and fixed mold plate 11 are pressed together, base 22 is driven to reset molding slider 23; mold is locked to form a closed cavity, and mold is closed, ready for next injection molding cycle.