Molding process

The SMC composite material is a sheet molding material prepared by impregnating a fiber or a chopped fiber mat with a resin paste and covering the polyethylene film on both sides, and belongs to the range of the prepreg. SMC has high molding efficiency, good surface finish, good dimensional stability, short molding cycle and low cost. It is suitable for mass production and is suitable for the production of thin-walled products with small cross-section changes. It has been produced in the field of GFRP automotive parts production. widely used. At present, in the CFRP molding process for vehicles, SMC is mainly used for the production of sheet-like chopped fiber composite materials. Due to the discontinuity of the fibers, the strength of the products is not high, and the strength has the characteristics of in-plane isotropic. The wettability of carbon fiber in the resin paste is an important issue for the SMC process. The necessary surface treatment of the carbon fiber and the use of a suitable wetting and dispersing agent can effectively improve the wettability and uniformity of the carbon fiber in the resin paste. .

During the SMC molding process, it is important to pay attention to the control of “3 points”, that is, 3 main process parameters: molding temperature, molding pressure and molding time. The molding temperature is the mold temperature specified during molding, and this process parameter is determined. The heat transfer conditions of the mold to the material in the cavity have a decisive influence on the melting, flow and solidification process of the material. The temperature change of SMC molding compound during the molding process is complicated. Since the plastic is a poor conductor of heat, the temperature difference between the center and the edge of the material at the beginning of the molding is large, which will cause the curing crosslinking reaction to start at the same time in the inner and outer layers of the material. . The surface layer is hardened by heat to form a hard shell layer, and the curing shrinkage of the inner layer material is limited by the outer hard shell layer, so that residual compressive stress is often present in the surface layer of the molded product, while the inner layer is carried. There is residual tensile stress, and the presence of residual stress causes warpage, cracking, and strength degradation of the product. Therefore, measures are taken to minimize the temperature difference between the inside and outside of the material in the cavity, and eliminating uneven curing is one of the important conditions for obtaining high quality products.