SMC molding process

SMC composite material is a kind of sheet molding material made of resin paste impregnated fiber or chopped fiber mat and covered with polyethylene film on both sides, which is a kind of prepreg material. SMC has high molding efficiency, good surface finish, good dimensional stability, short molding cycle and low cost. It is suitable for mass production and thin-walled products with little change in cross-section. It has been obtained in the field of GFRP auto parts production. widely used. At present, SMC is mainly used for the production of sheet-shaped chopped fiber composite materials in the CFRP molding process for vehicles. Due to the discontinuity of the fibers, the strength of the products is not high, and the strength has the characteristics of in-plane isotropy. The wettability of carbon fibers in the resin paste is an important issue faced by the SMC process. The necessary surface treatment of the carbon fibers and the use of appropriate wetting and dispersing agents can effectively improve the wettability and uniformity of the carbon fibers in the resin paste. .
In the process of SMC molding, it is necessary to pay attention to controlling “3 points”, that is, 3 main process parameters: temperature, pressure and time. The molding temperature is the mold temperature specified during molding. This process parameter determines the direction of the mold. The heat transfer conditions of the material in the cavity have a decisive influence on the melting, flow and solidification of the material. The temperature change of SMC molding compound in the molding process is more complicated. Since plastic is a poor conductor of heat, the temperature difference between the center and the edge of the material is large at the beginning of molding, which will cause the curing and cross-linking reaction to start at the same time as the inner and outer layers of the material. . The surface layer material forms a hard shell layer due to the early curing of heat, while the curing shrinkage of the inner layer material at a later time is limited by the outer hard shell layer, resulting in residual compressive stress in the surface layer of the molded product, while the inner layer has a There is residual tensile stress, and the existence of residual stress will cause product warpage, cracking and strength reduction. Therefore, taking measures to minimize the temperature difference between the inside and outside of the material in the mold cavity and eliminating uneven curing is one of the important conditions for obtaining high-quality products.