Generally speaking, the structure of car lights can be divided into three parts: the lamp housing, the base, and the reflector bowl (mirror). The quality of the lamp reflector directly affects the lighting effect of the car. The reflector bowl is the high-temperature (160-200 ℃) part of the car light structure. Although thermoplastic has good processability, light weight, high design freedom, and better impact strength than glass, it has gradually replaced traditional glass and metal materials, but its heat resistance and rigidity are poor. It is difficult to meet the heat resistance requirements of the reflective bowl for car lights, so the reflective bowl for car lights is mainly made of thermosetting composite material BMC, which is currently the main material for reflective bowls in domestic car light factories.
BMC composite material is an abbreviation for Bulk molding compound, which stands for bulk molding compound. Domestically, it is commonly referred to as unsaturated polyester cluster molding compound, BMC molding compound, DMC material cluster, etc. BMC composite materials are mainly made of short cut glass fibers, unsaturated resins, fillers, and various additives that are fully mixed to form a pre impregnated material in the form of pellets. BMC composite materials were first applied in West Germany and the United Kingdom in the 1960s, and then developed significantly in the United States and Japan in the 1970s and 1980s, respectively.
Due to its excellent electrical properties, mechanical properties, heat resistance, chemical corrosion resistance, and adaptability to various molding processes, BMC composite materials have the following characteristics compared to metal or thermoplastic materials:
① BMC made car light reflector can achieve an ideal smooth and flat surface, with stable reflective light pattern;
② BMC products themselves have good dimensional stability, low coefficient of linear expansion, and high heat resistance to deformation temperature;
③ BMC has good fluidity and can be formed under low pressure, making it suitable for molds with complex shapes;
④ BMC has good mechanical and insulation properties.
Especially the injection molding of car lights has the characteristics of high automation, short molding cycle, and good processability of complex parts. With the development of the domestic automotive industry, this molding process is also increasingly adopted by car light production enterprises. The process of producing automotive lighting fixtures using BMC thermosetting composite material injection molding technology involves adding pre mixed BMC thermosetting composite material into a material cylinder with a certain temperature, which is heated and softened. The material is continuously sheared and rubbed by the rotation of the screw, and continues to heat up, causing the BMC thermosetting composite material to soften into a viscous flow state. Then, under pressure, it is injected into a high-temperature mold through a nozzle and a flow channel, and heated to enter the curing process. At this time, the viscosity of the material increases sharply, reacting to form a network structure reinforced with fiberglass and filled with fillers. After a suitable period of insulation and curing, BMC automotive lighting products with a certain glossy surface and mechanical properties can be removed after mold opening.
