Searchlight cover product is shown in Figure 1. Maximum external dimension of product is 362.40 mm * 256.70 mm * 74.09 mm, average thickness of plastic part is 3.00 mm, material of plastic part is ABS, shrinkage rate is 1.005, weight of plastic part is 282.3 grams. Technical requirements for plastic parts are that there shall be no defects such as peaks, underfilling, flow lines, pores, warpage deformation, silver lines, cold materials, and spray lines.

 

Figure 1 Product map of searchlight cover
Searchlight cover is a plastic part with high appearance requirements. As can be seen from Figure 1, plastic part is shaped as a flat triangle with arc-shaped corners, appearance is smooth and flat, and structure is simple. There is a cooling groove at one corner of plastic part, and slider core needs to be designed. There is a column at the top of inner side of plastic part, root of which is suspended and supported by only three bones. Size of plastic parts is large, outer surface is appearance surface, and there should be no gate marks. Edge of plastic part cannot be designed with side gates. Therefore, it is necessary to design a flip-chip mold to solve difficult problem of gating system design.
Reverse mold refers to mold in which pouring system and ejection system of injection mold are located on the side of fixed mold. Reverse mold is an important form of injection mold. For some plastic parts, such as notebook computer A shell , LCD computer monitor bottom case, lampshade and other plastic parts, plastic products have high appearance requirements, and no glue marks are allowed on outer surface. Due to limitation of surface quality requirements, gate cannot be set on outer surface and side of plastic parts. At this time, glue feeding from the back of the plastic part can meet product requirements. After mold adopts flip-chip structure, core is set in fixed mold, cavity is placed in movable mold, plastic parts need to be pushed out from fixed mold side, and structure of the entire mold is relatively complex. In this case, structure of flip-chip mold will be adopted. Flip-chip mold is much more complicated than positive-load mold. Flip-chip mold is generally a two-plate mold + hot runner structure. Three-plate mold can also design a flip mold, but mold structure is more complicated. If you encounter a second ejection, it will be even more difficult.
Flip-chip molds need to reverse fixed and movable molds of mold base. Original moving mold is used for fixed mold, and original fixed mold is used for moving mold. Its structural feature is that main runner is very long, plastic parts remain in fixed mold after mold is opened, and ejection mechanism is also fixed. Because injection molding machine has no push-out power on fixed mold side, difficulty in designing a flip-chip mold is to solve problem of a long sprue and no push-out power on fixed mold side. As an important type of injection mold, flip mold is usually used on molds that directly feed glue and gate cannot be on the surface of product.
3D drawing of searchlight cover mold design is shown in Figure 2.

 

Figure 2 3D mold design

 

Figure 3 Flip-chip mold structure
Size of plastic parts is large, mold design cavity layout is 1 cavity, and mold base is a non-standard mold base 5565. Structure of flip-chip mold is shown in Figure 3 and Figure 6.
Main points of flip-chip mold design are as follows;
1) Flip-chip molds basically use a hot runner pouring system. If a cold runner is used, plastic is designed to be fed directly into main runner in sprue sleeve, and mold structure is relatively simple. If a three-plate mold is designed, glue is fed into gate at fine nozzle, there is disadvantage that it is inconvenient to take out condensate in gating system. The more gates and the longer runner, the harder it is to remove runner aggregate.
2) Flip-chip molds generally use oil cylinders to provide power source for ejection, because ejection side of mold is installed on fixed mold of injection molding machine, and ordinary injection molding machine cannot provide ejection action on the side of fixed mold plate.
3) Main problem of flip-chip mold is that it is easy to produce a circular halo imprint on outer surface facing gate, and color depth is inconsistent with other places, which seriously affects appearance of plastic part. Temperature is high and cooling part of mold is uniform. Therefore, cooling around hot nozzle is very important. For this reason, hot nozzle insert is designed to transport water independently. Cooling system diagram of hot nozzle is shown in Figure 7.

 

Figure 4 Parting surface design

 

Figure 5 Gate and ejection method

 

Figure 6 Flip chip structure diagram

 

Figure 7 Hot nozzle inserts carry water independently
4) Small flip-chip molds can also use a button machine to achieve sequential parting, such as this set of molds.
Gate design of flip-chip mold usually has four situations, and difficulty of mold design is shown in following table: