Design of thermosetting injection mold for headlight reflector

Headlight reflector is a part of the headlight lighting system to play a reflective role to avoid direct light, located on the inner side of the headlight and decorative frame, combined with the headlight, the reflector can be seen through the headlight lighting system. Plastic parts for the appearance of the parts, the surface of aluminum plating, belong to the high-gloss plating parts, the outer surface has a large area pattern, used for surface decoration. The headlight is an important safety device and decorative part indispensable to the automobile package. As the reflector has a high-temperature working environment and reflective light-gathering function, it needs to be made of prefabricated monolithic molding compound (BMC) with almost 0 shrinkage rate, which has heat resistance, flame retardant, and extremely strong creep resistance. The material has been previously used in die-casting molding process, due to low production efficiency, high scrap rate, and because the material is harmful to the human body, die-casting production requires frequent manual pick-up weighing and other processes, so it poses a certain risk to the health of the operator. In order to develop the injection molding process of BMC material to replace the die-casting molding process, the molding process of BMC has become an inevitable trend.

This paper takes the automobile headlight reflector part as an example, detailing the design points and technical summary of the automobile headlight reflector injection molding tool. Automotive headlight mirror parts as shown in Figure 1--Automobile headlight reflector parts diagram

1. Plastic part appearance requirements and structural analysis

Figure 1 shows the part diagram of a brand of automobile headlight reflector, which is made of BMC, a thermosetting plastic. This material is an extra hard material with almost zero shrinkage, and there is no need to put shrinkage in the mold design. Because it is an extra hard plastic, it has the advantages of high dimensional accuracy and good processing performance, and the disadvantage is poor fluidity. The outer surface of the plastic part needs to be plated (ordinary aluminum plating), and the plastic part is an appearance part with high surface requirements.

Plastic parts size is 216.9 × 200.8 × 161.7 mm. The structural characteristics of plastic parts are as follows:

1) Extremely high appearance requirements, the appearance does not allow spots and sprues traces, nor shrinkage depressions, fusion traces, and flying edges, and other defects.

2) Plastic parts are electroplated parts, with strict requirements for light distribution and aluminum plating on the appearance surface. The design of the appearance surface demolding slope should be reasonable, generally at least 5 ° above.

The shape of plastic parts is complex, the surface finish is high, there is no inversion inside and outside the plastic parts, no lateral core extraction is required, and the plastic parts are left and right mirror-image parts.

2. BMC material injection molding process.

Refrigerated BMC material is added to the barrel of the injection molding machine specializing in BMC material, which generates shear heat by screw rotation and melts at a lower temperature (25 degrees Celsius), and then the viscous material is injected into the mold preheated to 140-160 degrees Celsius under high pressure. Under high temperature, chemical reaction, holding pressure after curing molding, open the mold to remove the molded plastic parts, and finally the burr and debris blown by air gun, injection mold for the next cycle.

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