Experimental Study On Products And Precision Design Method Of Compression Molding Mould Based On Finite Element

Compression Molding, as high pressure polymer molding technology, has an irreplaceable superiority. Compression molding products have excellent characteristics of light quality, little internal stress, small shrinkage ratio, little warpage and deformation, stable mechanical properties, especially, excellent mechanical properties. Compression molding is especially suitable for molding polymers mechanical products. Many compression products are made for substitution metal products. Thus, compression molding has a wide application prospect. But compression molding is also a low resolution molding technology. What’s more, its mould cavity design method is still the traditional one of testing die with high-cost and poor efficiency. While computer-aided technology is widely used in mould design of injection molding and extrusion molding, there is almost no computer-aided technology at compression molding. To some degree, those limit the development of compression molding.This topic is aimed to changing present situation, making some innovation in design method of compression molding mould cavity, reducing cost, improving precision of products.This paper did some studied and derivation on the stress states of material in mould cavity during compressing molding process, conclusion that, the relationship between the depth of mould cavity and axial pressure of the material closed to solid obeys decreasing power-exponent function. And guide the selection of molding pressure with the conclusion.This paper studied the influencing factors, the structure composition, the variation law of the shrinkage of products, by the method of single variable experiment which takes finite element analysis numerical simulation as auxiliary means. Research shows that, the influencing factors molding pressure, molding temperature and dwell time make more influence on shrinkage; shrinkage of product is composed by mould elastic deformation, mould thermal deformation, product elastic recovery, product cooling shrinkage and "residual shrinkage"; among them, "residual shrinkage" shows more weight; mould elastic deformation, mould thermal deformation, product elastic recovery, product cooling shrinkage respectively showed linear correlation relationship with molding pressure and molding temperature. When molding pressure, molding temperature and dwell time were in some range, "residual shrinkage" showed certain stable.The paper raises the design method of compression molding mould cavity based on Ansys Workbench numerical simulation depend on the research result of shrinkage. This method opinion that traditional shrinkage ratios have a wide range, methods calculating the sizes of mould cavity with an average shrinkage ratio can’t meet the need of different process conditions and different mould cavity structure. This method calculates the part varied with process conditions and mould cavity structure by finite element numerical simulation technology, and then, plus the varied part with the stable part, get the shrinkage ratio in corresponding process condition and mould cavity structure, finally, correct the sizes of the mould cavity with the shrinkage ratio.The paper experiment with the mould designed by the "reverse design method of the mould cavity sizes", reached a conclusion that, to some degree, the mould designed by this design method improved the product precision to traditional mould design method. The "reverse design method of mould cavity sizes" based on the structure law and the change regulation of shrinkage ratio is feasible in mould design, and is effective in improving product precision.