Study On PP/GMT Compression Molding Process--Molding Of Homemade Hummer's Fender

PP/GMT (Glass Mat Reinforced Polypropylene Sheet) are made from continuous glass fiber mat or needle mat reinforce modified Polypropylene matrix. GMT has high specific strength as well as excellent impact strength and can be made into large size complex component by compression molding. It has broad applications in automobile industry.Hummer is the equipment for the army of our nation in the future. Its fender is design of PP/GMT composite. The shape of the fender is composed of three inter-vertical planes, which were only 3mm thick, but the length is more than 200mm. So it is a complicate product with superior length/thickness ratio. Our research is to design the mould arid optimize the molding parameters such as temperature and pressure and finally make the fender to meet the design requirements. Also the fluidity and thermal conductivity of GMT are studied and theoretically analyzedThe fluidity of GMT is studied by compressing the round shape GMT sheet under constant temperature. First, by measure the fiber content in different radius range, the influence of pressure and temperature on fluidity is investigated. It shows that the fiber mat keeps integrity during flow and the GMT has good fluidity for molding. We also found that the rheological behavior of single layer GMT is isotropic. Temperature and pressure method has great affection on the distribution of the fiber. Second, We measure the pressure change under different molding rate and use Extensional viscosities model and Shear Force Model to analysis the data. We get the rheological parameters of GMT. By compare the experiential simulate data to the real results, the advantages and disadvantages of each model are evaluated. The calculated value of Shear force model fit well with the experimental results. It means that compare to the tensile stress during squeeze flow the shear stress can be omitted especially when the molding rate is low and distortion rate is low.Since the fender is shell like component, the dimension of the plane is muchlarger than the thickness. So we suppose it as an infinite plane and build the model to simulate the cooling process of the GMT in the mold. It shows that when GMT cooling in the mold its surface temperature and center's temperature are tend to be uniform quickly. When the mold is 80 C, the sheet cooling from 220 C and the temperature get uniform in 30 seconds, the center temperature is equal to the fringe temperature, which is 130 C.The influence of temperature and pressure on mechanical properties, surface quality and dimension precision are discussed and get the process parameters optimized. The products made by these methods have good surface quality and dimension precision and excellent mechanical properties. They meet the requests of Hummer's fender.