At present, the most widely used in automotive market is rigid instrument panel, while slush-molded instrument panel is standard equipment of middle and high-end models. Hidden airbag frame is inside instrument panel assembly. From appearance of entire vehicle, surface of entire slush-plastic instrument panel is clean and seamless, surface quality is very high. Airbag is installed in airbag frame, pops out from airbag frame in an emergency, tearing airbag frame and slush plastic skin, thereby protecting human body. In modeling stage, it is necessary to consider cleanliness of slush-molded instrument panel and whether airbag blasting can meet requirements in test. Therefore, a hidden airbag frame was used on a certain model of Chang’an, key points were checked in mold design stage from gate layout and ejection layout. Hidden airbag frame introduced in this article checks key technical points of CAE simulation and mold design to avoid risk of failure of airbag frame blasting test due to mold or mold flow.

As shown in Figure 1, because airbag frame, instrument panel frame, etc. are hidden in slush plastic skin, from perspective of modeling, plastic part has a simple profile and a high-end feeling. Airbag is installed in concealed airbag frame 3, and concealed airbag frame 3 is installed on the dashboard frame 2 with its own clamping structure. Slush-molded skin 1 is adhered to surface of dashboard frame 2 and hidden airbag frame 3, then front defrosting cover 5, other decorative parts and functional parts are installed on dashboard frame 2, and overall installation of dashboard is basically completed.

 

Figure 1 Partial view of dashboard assembly
1. Slush plastic skin 2. Instrument panel frame 3. Hidden airbag frame
4. Air duct 5. Front defrosting cover
As shown in Figure 2, blasting tear line is in installation frame. Plastic part has 12 snap connections for installation to dashboard frame 2, and there are 7 installation holes for installing airbag. Mold design of this paper is to study this part.

 

Figure 2 Information diagram of plastic parts

Plastic part size: 262*183*94mm, plastic part material: high heat-resistant PC+ABS.
Plastic part shown in Figure 3 is a non-appearance part, which is a precision plastic part. Mold design needs to be in accordance with precision mold design. Outer ring line of plastic part is the largest contour and is also parting line (PL line). There are installation points on all sides, and a 4-side core-pulling design of slider is required.

 

Figure 3 Plastic part structure

Main wall thickness of plastic part is 3.5mm, thickness of ribs in a circle of "mouth" is 3mm. Plastic part is a non-appearance part and has low requirements on appearance. Due to safety characteristics of plastic part, airbag needs to be ejected from blasting tear line to protect safety of passengers. Therefore, position of tear line must be controlled by weld line. If it is unavoidable, as shown in Figure 4, direction of weld line and tear line should be same as possible; as shown in Figure 5, plastic part adopts a 2-point open hot runner to directly enter surface of plastic part, which can complete filling very well. Technical indicators are excellent and fully meet performance and molding requirements of plastic part. Conclusion is shown in Table 1.

 

Figure 4 Schematic diagram of welding line

 

Figure 5 Schematic diagram of plastic part filling

 

Mold adopts non-standard mold base CI6068A210B290, plastic inlet is two-point open, cavity adopts original retention method, and core adopts method of inserting molds. 4 sliders envelop all installation structures of plastic part, the whole structure is compact and simple.

Fixed mold part is shown in Figure 6, which is mainly composed of fixed mold plate 1, hot runner plate 2, fixed mold seat plate 3, hot runner system assembly 4, cooling system 5, slider clamping block 6, inclined guide post 7 and pressure bearing piece 8. Fixed mold part adopts an integral design, slider is integrally wrapped in A plate, which is beneficial to slider not to retreat during injection process, and at the same time, it will increase service life of mold.

 

Figure 6 Fixed part structure
1. Fixed template 2. Hot runner plate 3. Fixed mold base plate 4. Hot runner system assembly
5. Cooling system 6. Slide block wedge 7. Inclined guide post 8. Bearing piece

Movable mold part is shown in Figure 7. There are many mold parts. Slider system, cooling system, and ejector system are separately deployed. Fixed mold part is mainly composed of movable mold plate 1, movable mold seat plate 2, ejector fixed plate 3, ejector pad 4, mold foot 5, guiding system 6, core 7, ejection system 8, cooling system 9, and accessories 10. Plastic part has an inclination, so 4 sliders are designed according to inclination of plastic part ejection. 3 adopts cylinder core pulling, one adopts inclined guide pillar core pulling, When four-sided slider is in process of opening and closing mold, operating side and opposite side have priority to open and close mold. Delayed opening and closing of mold at the fixed side is beneficial to control deformation of plastic part and prolong life of slider.

 

Figure 7 Partial structure of movable mold
1. Movable template 2. Movable mold base 3. Ejector fixed plate 4. Ejector pad 5. Mold foot
6. Guiding system 7. Core 8. Ejection system 9. Cooling system 10. Accessories

Cooling system is shown in Fig. 8, and it is mainly composed of 3 parts: fixed mold water path 1, 4 slide block water path 2, movable mold water path 3 of movable mold core. Water path adopts a diameter of ϕ 10mm and is evenly arranged. Temperature of inlet and outlet water paths is controlled at ±3°, the entire plastic part is cooled without dead ends, cooling temperature is controlled uniformly and effectively.

Ejector system is shown in Figure 9. It consists of two parts, ejector rod 2 and ejector block 3. Ejector rods are layout in “mouth”-shaped rib with a diameter of ϕ 12*6mm. Because rib is above 60mm, core holding force is very large, so four top blocks are arranged on the ribs, entire ejection system is arranged uniformly and reliably, which is beneficial to safe demoulding of plastic parts.

 

Figure 8 Cooling system

1. Fixed mold waterway 2. Slider waterway 3. Dynamic mold waterway

 

Figure 9 ejection system
1. Plastic parts 2. Ejector 3. Top block

Concealed airbag frame mold has been successfully applied to many models of Chang’an, and mass production has been verified by market. Mold structure introduced in this article can be widely used in mold design of safety precision parts, or structure of plastic parts with similar raw materials.