Study On Molding Process Of Low Pressure Molding Compounds

In recent years, due to the improvement of manufacturing technology and reduction in production costs, the application of composite is increasing in various fields of industry. Especially, sheet molding compounds (SMC) molded at low pressure exhibits a combination of stiff and stability and a substantial saving in molds and pressure by allowing large part capability on smaller pressure and molded in some low-cost tools.Crystalline unsaturated polyester has an essential difference with MgO in thickening. The viscosity of resin will decrease rapidly when the temperature over the melting point of crystalline unsaturated polyester filled in LPMC system and turn to a solid state easily for storage below melting point. The LPMC can be molded at 1.03MPa (SMC should be at 5.5 MPa) because of its viscosity characteristic.In this paper, molding process for low pressure sheet molding compounds thickened by crystalline unsaturated polyester was investigated. Firstly, the fluidity, fiber distribution and fiber orientation was investigated. The fiber orientation was described by computer statistics technology. And, the heat exchange was investigated and calculated. Secondly, the thicken process was improved on. In use of this process, LPMC could be produced at general SMC machine. Thirdly, the area of molding temperature and molding pressure are determined. And, the relationship between the molding parameters and physical properties and finish qualities was analyzed. Furthermore, optimal molding parameters such as molding temperature, molding pressure and cure time are determined by orthogonal test. Lastly, the distribution of the heater of mold was optimized.