Figure 1 Drawer structure of refrigerator

Structure of refrigerator drawer is shown in Figure 1. Dimensions are 434mm * 401mm * 134mm, average wall thickness is 3mm, volume is 902979mm³, material is transparent GPPS, and mold adopts a 1 cavity structure. Shape of plastic parts is relatively large, and there are undercuts on the outside and inside. Deepest undercut inside is 26mm, and outside is a circular arc.

 

Figure 2 Gate

It can be seen from analysis of structure of plastic parts that the most suitable gate method is single-point valve pin hot runner direct injection. Hot nozzle valve pin directly contacts surface of plastic part to be molded, and gate trace left on the surface of molded plastic part is small, which has little effect on its appearance, gate does not require secondary processing. Gate is shown in Figure 2 .

 

Figure 3 Parting design

Shape of plastic part is formed in a fixed mold, it needs to use 3 sliders to complete its molding, and inside needs to be formed with a lifter block. Parting design is shown in Figure 3. Difficulty of mold design is rotary core pulling structure of slider 1 .

 

Figure 4 Fixed mold structure

 

Fig. 5 Moving mold structure

 

Figure 6 mold structure

1. Insulation board 2. Fixed mold base plate 3. Fixed template 4. Fixed model cavity plate 5. Push plate 6. Dynamic model core 7. Dynamic template 8. Pad block 9. Push rod fixing plate 10. Push plate 11. Movable mold base plate 12. Support column 13. Limit nail 14. Oblique top rod 15. Oblique top slider 16. Circular core rotating shaft 17. Circular core fixing block 18. Hydraulic cylinder fixing plate 19. Hydraulic cylinder 20. Connecting rod 21. Slider 22. Arc core 23. Sloping top block 24. Positioning ring 25. Hot nozzle
Fixed mold structure is shown in Figure 4. Fixed mold is relatively simple. Main parts are fixed model cavity plate, slider pressure block and guide post. Moving mold structure is shown in Figure 5. Key structure of mold is in moving mold part, and its main parts are moving mold core, lifter block, slider and hydraulic cylinder. Mold structure is shown in FIG. 6, and core part of mold is circular arc core-pulling structure of combination of hydraulic cylinder and slider in "E" area in FIG. Design of arc core pulling structure makes mold structure simple, safe and reliable, realizes problem of demolding arc reverse button. At the same time, internal reverse button of plastic part to be molded is formed by a lifter block, which solves core pulling problem of mold and trapped gas when plastic part is pushed out. Mold cools evenly, and melt easily fills cavity during injection molding, shortening injection cycle.

 

Figure 7 First stage core pulling

After injection molding is completed, slider of injection molding machine moves to open mold, fixed mold and movable mold are separated, core pulling action of slider 2 and slider 3 (see FIG. 5) is completed by inclined guide column installed in fixed mold. Then, connecting block of hydraulic cylinder drives connecting rod slider to move S1, and then drives circular core to rotate S2 through connecting rod to complete rotary core pulling of circular core. The first stage of rotating core pulling is shown in FIG. 7. During this process, both slider 1 and arc-shaped core fixing block are in a static state to ensure that core-drawn core of arc-shaped core does not damage plastic parts.

 

Figure 8 Second stage core pulling

After arc-shaped core rotates S2 to complete core pulling of undercut of handle position, connecting rod slider moves to limit position of slider 1, and slider 1 is driven to translate S3 under action of hydraulic cylinder connecting block, and finally core pulling of plastic part is completed. Core pulling in second stage is shown in FIG. 8. In this process, slider 1, arc-shaped core fixing block, arc-shaped core and connecting rod move synchronously with connecting rod slider and hydraulic cylinder connecting block.

 

Figure 9 State of plastic parts after being pushed out

After core pulling of slider 1, slider 2 and slider 3 is completed, push plate and push rod fixing plate are pushed by ejector rod of injection molding machine, so that push rod drives push block and lifter slider drives lifter top rod to move. Plastic part is pushed out of moving mold core through combined action of pushing block and lifter rod. State of plastic parts after being pushed out is shown in FIG. 9, and finally it is taken out by robot. Lifter component also completes core pulling action at the same time as plastic part is pushed out, see "F" in Figure 9. Lifter rod translates S4 while pushing out plastic part, and lifter slider also moves S4. At this time, all undercuts have completed core pulling. Before closing mold, reset ejection system to ensure that lifter block and lifter rod return to initial position, then drive slider 1 through hydraulic cylinder connection block to reset, slider 2 and slider 3 are reset by action of inclined guide post. After completing mold clamping action, next injection cycle begins.

 

Figure 10 slider 1 design details

Shape of mold is 800mm*600mm*664mm. It is produced on a 780kN injection molding machine. Cooling time is 30s, and injection cycle is 60s. Mold production is normal, and a successful mold trial. In order to prevent slider 1 and connecting rod slider from moving together when mold is rotating and pulling in the first stage, two springs are designed between hydraulic cylinder fixing plate and slider 1 to prevent slider 1 from moving when arc core of the first phase is rotated, as shown in FIG.

 

Figure 11 Design of insertion angle between slider and lifter block

Due to large size of mold, push plate and push rod fixing plate are slightly deformed, so that lifter block cannot be completely reset. In order to completely reset lifter top block, a 10° insertion is designed between slider 1 and lifter block during design of mold to ensure that lifter block does not collide with slider 1 at the same time, as shown in "H" in Figure 11 Shown.

 

Figure 12 Inductive switch design

Due to insertion design of slider 1 and lifter block, there is a requirement for order of mold clamping. After push plate and push rod fixing plate are reset, hydraulic cylinder connecting block can drive slider 1 to reset, and movement sequence is controlled by electronic induction switch, as shown in Figure 12.