Design and Application of Two-color Injection Mould for Slider Blade

Time：2022-03-31 09:02:42 / Popularity： / Source：

【Abstract】Structural characteristics of two-color plastic parts are introduced, mold gating system, cooling system, exhaust system and ejection system are analyzed, and structure of two-color injection mold for slider blade is designed.

1 Introduction

For two-color plastic parts, in addition to a small number of two hard plastic two-color parts, most two-color plastic parts are composed of hard plastic parts and soft plastic parts. Hard plastic parts are generally made of PP, ABS, PC and other materials. Hard rubber part is generally made of PP, ABS, PC and other materials. Strength and hardness of this kind of hard glue material are good. When plastic part is assembled, it can meet strength and use requirements of plastic part itself, but for contact parts, hand feel and texture are relatively poor; soft rubber part is generally made of TPU, TPE, characteristics of this type of soft rubber material are that material strength and hardness are low, but material is soft and softness of hand is very good. As a result, two-color molds are widely used in automotive exterior parts and are also highly recognized by customers.

2 Characteristics of plastic parts

Through measurement of dimensions of plastic part in Figure 1, it can be seen that length of plastic part is 994.5313mm, material of hard plastic part is PP+30% GF, material of soft plastic part is TPU, and structure of hard plastic part is relatively complex. If rotary two-color injection molding is designed, machine used for injection molding will be very large, weight of mold is calculated in tons, general rotary two-color injection molding machine cannot meet production requirements. If overmolding or translation two-color is designed, then two sets of molds with same size need to be designed, which will greatly increase cost of mold, is not conducive to automation and high-efficiency production. If slider blade two-color injection mold is designed, selection of injection molding machines, efficient production of plastic parts, and realization of automated production are possible, but mold design ideas, complexity of mold structure, mold processing, process and tooling requirements are higher. Design, as front end of mold production, can only make mold realization possible with perfect design. Therefore, mold needs a big breakthrough in design.
Figure 1 Maximum dimensions of plastic parts

Two-color Injection Mould for Slider Blade

3 The overall structure of mold

A major feature of slider blade mold is that size of mold can be minimized while achieving two-color molding. This feature has a particularly obvious advantage in large-size automotive plastic parts. One is that you can choose an ordinary injection molding machine instead of a dedicated two-color injection molding machine, the other is to improve production efficiency and achieve automation.
As shown in Figure 2, mold does not have a complex rotating structure, realizes a 1+1 ejection of soft and hard rubber in a compact size. From the overall perspective of mold, mold is compact in structure, and can meet production requirements of 1,200t ordinary injection molding machines required by customers.

Figure 2 Schematic diagram of mold structure
1. Water transport 2. Fixed mold cavity 3. Plastic parts 4. Blade slider 5. Top block 6. Movable mold insert 7. Movable mold core 8. Oil cylinder 9. Mandrel 10. Limit block 11. Movable mold seat Plate 12. Ejector backing plate 13. Ejector fixed plate 14. Support head 15. Square iron 16. Movable mold plate 17. Slider limit block 18. Slider 19. Inclined guide column 20. Fixed mold plate 21. Catchment block 22. Hot runner plate 23. Fixed mold seat plate 24. Green column 25. Hot runner system 26. Pump mouth 27. Positioning ring

4 Pouring system

Slider blade two-color injection molding is to complete injection molding of two materials in same cavity, so blade two-color mold is same as rotating two-color mold, with two sets of gating systems, as shown in Figure 3 and Figure 4.
Hot runner gating system shown in Figure 3 is filled with hard rubber. Nozzle of runner system is generally designed on panel of mold to match main barrel of injection molding machine.
Hot runner system shown in Figure 4 fills soft rubber part, and nozzle is designed on non-operating side of fixed mold part. Soft rubber pouring system is generally not originally equipped with injection molding machine. It needs to be equipped separately and has mobility, which is also a major feature of slider blade two-color injection molding to reduce costs and improve efficiency.

Figure 3 Hard glue hot runner system

Figure 4 Soft glue hot runner system

5 Plastic injection molding system

Injection molding system mainly refers to parts or mechanisms that are in contact with plastic surface of plastic part. Generally, there are core parts, cavity parts, insert parts, slider parts and inclined top parts. These parts are core parts of mold. It is directly related to appearance, shape and structure quality of plastic part. Therefore, in mold design, this part will be designed separately, using better steel materials, even nitriding and heat treatment processes are required to make molded parts reach strength and service life required by mold production.
Figure 5a shows cavity part. This structure is in direct contact with appearance surface of plastic part. In trial and production, it directly reflects appearance of plastic part. Figure 5b is core part. This part mainly forms non-appearance surface part of plastic part. Therefore, bone position of plastic part and ejection mechanism of mold are all designed in core part. Determination of appearance of plastic part is directly related to choice of cavity, which is also directly related to customer's requirements for plastic part. Figure 5c shows slider mechanism, slider mechanism mainly solves undercut structure that cannot be directly demolded on the side, but in this mold design, slider not only needs to complete side undercut, but also design a blade inside slider to realize two-color molding through blade structure, as shown in Figure 5d.

Figure 5 Plastic molding system
a — — Cavity b — — Core c — — Slider structure d — — Slider blade

6 Cooling system

A very important part of cooling system mold structure, it is directly related to molding cycle of plastic part, appearance of plastic part and accuracy of plastic part. In blade mold design, this is also a design difficulty, because blade structure has already occupied a large space of mold, and because slider needs to be embedded with blade structure, space for slider to be designed to transport water becomes smaller. If water transport is not designed, or designed water transport is insufficient, resulting in uneven cooling of water transport, it will directly affect production efficiency of plastic parts and quality of plastic parts.
Figure 6 shows cooling system. Water transportation in all directions of plastic parts is relatively uniform in theory. There is no obvious glue plane far away from water transportation. Cooling system can uniformly cool mold, water transportation direction is horizontal. Arrangement direction is beneficial to optimize deformation of plastic part by adjusting temperature difference of water during injection, thereby increasing injection molding window of plastic part.

Figure 6 Cooling system
a — —Overall diagram of the cooling system b — —Fixed model water transportation system c — —Moving model water transportation system d — —Slide water transportation system

7 Mold exhaust system

Exhaust system of mold is mainly to solve problem of air trapping in plastic part. Since plastic part is injection molded, in order to avoid occurrence of flare, in the design of mold parting surface and actual fitter assembly, movable and fixed molds are fitted. If there is no vent, trapped air in cavity will be concentrated to the end of filling when plastic part is filled, resulting in lack of glue or even scorching. It will also make welding line at bonding position more obvious. Therefore, exhaust design in mold design is very important. As shown in Figure 7, mold cavity is evenly designed for exhaust, so that during filling process, cavity gas is exhausted along exhaust position.

Figure 7 Exhaust system

8 Ejection system

Mold ejection system is to ensure that mold can be removed from mold smoothly after injection molding, without straining, no topping, no topping, no topping, no topping, etc. In slider blade mold design, there are also places that need to be paid attention to, especially ejection of soft rubber part. In design of mold, after many detailed reviews and inspections, as well as customer's requirements for soft plastic parts to not allow ejector mark, ejector and ejector block are only designed at hard plastic position. Soft rubber can be ejected together with hard rubber because of its own soft characteristics. Ranking of plastic ejector rod is shown in Figure 8.

Figure 8 ejection system

9 Mold opening and closing effect and slider action

Figure 9 shows mold opening state. Two-color blade moves through position of slider blade. In one molding cycle of plastic part, injection molding of soft rubber and hard rubber is completed at the same time. In selection of injection molding machine, this injection molding machine is smaller than rotary two-color injection molding machine. In terms of mold processing cost and molding cycle, it has more advantages than translational two-color and over-coated two-color, can realize automatic production. Therefore, blade two-color injection mold has more and more prominent advantages in design and development of large-scale automotive plastic molds. Figure 10 shows movement process of slider in different injection molding stages of soft and hard rubber. Figure 10a shows names of various parts of plastic part of slider and schematic diagram of cross-section of slider.
The first hard rubber molding: As shown in Figure 10b, blade slider is positioned forward and contacts the fixed mold cavity to seal glue. At this time, hard glue is injected through hot runner for the first time, so that hard glue is formed according to designed shape and size.
Second soft rubber molding: when hard rubber molding stage is completed, slider blade moves backward under control of oil cylinder, as shown in Figure 10c, as slider blade moves backward, cross section of hard rubber is in contact with cavity of soft glue. At this time, melted glue of soft glue enters cavity through hot runner system to complete forming of soft glue.

Figure 9 Fixed and movable mold opening state

Figure 10 Movement process of blade slider

10 Summary

Slider blade two-color injection mold not only enables complex two-color plastic parts to be ejected, but also improves quality of plastic parts. Its characteristics are: ①Size of mold is minimized, manufacturing cost of injection molding machine and mold is controlled; ②Production efficiency is improved, soft and hard plastic parts are formed in same cycle in same pair of molds at one time, with a short production cycle and high efficiency; ③High-quality plastic parts, since plastic part is formed on the mold at one time, two materials are formed by moving position of blade, bonding degree and appearance quality of joint position are better. As a result, slider-blade two-color injection mold is more and more widely used in practical applications.

Gud Mould Industry Co., Ltd