【Abstract】Analyzed structure of automobile fuel filler plastic parts, determined injection molding scheme and way of glue feeding, introduced process of demolding plastic parts through cooperation of slider and mold opening action.

Figure 1 shows plastic part of automobile fuel filler. Plastic part has a sandwich structure, is covered with TPE on the top and bottom of hard plastic PP. Soft rubber at fueling port has a closed all-around undercut (see Figure 1 I). Surface A should be matted, and no gate marks are allowed. Plastic part has a complex structure, and a full-circle undercut is added on the basis of two-color, which puts forward high requirements on mold opening sequence and mold structure.

 

Figure 1 Fuel filler plastic parts

Plastic part has two-color soft plastic parts in movable and fixed molds. Generally, there are two options: one is to eject core and rotate while replacing movable and fixed mold to form soft plastic; the other is overmold. After forming hard plastic PP, plastic part is taken out and placed in soft plastic cavity to form soft plastic. Since our company does not have ready-made in-mold rotation equipment, considering cost of mold, we decided to adopt solution of overmolding.

Because mold structure is complex, especially soft rubber part, hot nozzle and runner need to pass through middle of slider. When arranging position of hot nozzle, in addition to ensuring balance of glue feed according to mold flow analysis, it is also necessary to consider that runner cannot affect mold movement. Therefore, glue feeding method as shown in Figure 2 is adopted.

 

Figure 2 Glue feeding method

As shown in Figure 3, plastic part has undercuts in many places, a special structure should be designed on mold to ensure smooth release of plastic part. Two problems need to be solved for undercut A, which is a closed undercut and a full circle of undercut at the same time. Closed undercut adopts a strong release method. Plastic part of undercut A is made of TPE, which is relatively soft, can be deformed enough to ensure smooth release of plastic during demolding; because space of undercut B gradually becomes smaller in moving direction of slider, it is necessary to design sequential action slider to ensure that there is space for slider to escape from plastic part.

 

Figure 3 Inverted structure
Figure 4 shows structure of slider here. By controlling mold opening sequence, fixed mold cavity inserts 1, 2 and movable mold core 8 are released from plastic part, sliding block 5 is first released under action of inclined guide column 6 to make room for strong release. A delay design is made on slider 3, so when slider 4 is released for a certain distance, slider 3 is pushed by oblique guide column 6 to force off and close undercut. After sliding block 3 and sliding block 4 are pulled out, a space is left for sliding block 5 to go out, sliding block 5 is pulled out of plastic part in an oblique direction under action of oil cylinder 7 to realize smooth demolding of sliding block.

 

Figure 4 Slider structure
1. 2. Fixed mold cavity insert 3. 4. 5. Slide block 6. Inclined guide post 7. Oil cylinder 8. Movable mold core

Since mold has a relatively complex structure, slider movement requires a sequence, and at the same time, considering that soft glue should not stick to mold, it must be achieved through mold opening sequence. As shown in Fig. 5, under action of shutter 5, parting surface III is opened first. In Fig. 4, movable mold core 8 is disengaged, leaving space for sliding block to be softened and reversed. Then parting surface I is opened, fixed mold insert 1 in Fig. 4 is pulled out of plastic part to prevent soft glue from sticking to fixed touch. After parting surfaces I and III are opened, push plate is pushed out by oil cylinder 6 to realize sequential action of slider in FIG. 4.

 

Figure 5 Mold opening sequence

Mold assembly structure is shown in Figure 6.

 

Figure 6 Mold assembly structure