Prediction Based On The Injection Molding Shrinkage Ratio Mold Cavity Size Generated

On account of light weight and good comprehensive mechanical properties , injection-molded parts get increasingly widely used in such industries as mechanical, electronics, aviation and so on. Meanwhile, the precision of plastic parts get more high and the shapes is also get more complicated. Using average shrinkage rates of injection-molded parts to decide the dimension of mold cavity can not satisfy the demand of high precision injection-molded parts. The existing injection mold CAD/CAM/CAE system generaly build the 3-D geometric model of injection-molded parts, then give a scale coefficient 1+S(S means the average shrinkage rates of injection-molded parts) to the 3-D geometric model of injection-molded parts to zoom in to build the 3-D geometric model of mold cavity. Aiming at it's shortage, the paper analyze the influence factor of shrinkage rates of injection-molded parts, a new method based on the prediction of shrinkage rates of injection-molded parts to decide the dimension of mold cavity is also brought forward in this paper. The scatter points of molded parts and the corresponding shrinkage is known. By building the conversion method between the dimension of injection-molded parts and dimension of mold cavity, we can get the scatter points on the surfaces of mold cavity. In order to establish the three-dimension geometric model of mold cavity in injection mold CAD/CAM/CAE system, using cubic B-spline curve surface to interpolation those scatter points. Use Visual C++6.0 and OpenGL to make the program. After the fitting of the single cubic B-spline curve surface, the outstanding reverse engineering software Imageware Surfacer is used to complete the connetion of single cubic. B-spline curve surface. Thus, the three-dimension geometric model of mold cavity surfaces is established. For the difference shrinkage of injection-molded parts is considered in the model of mold cavity, so it can reduce the deviation that caused by shrinkage, then improve the rates of success and the rates of eligibility of the mold design. In the end, an example is used to show the method that the paper has proposed. In order to validate the method, analysis of deviation is also put into use. The result shows that it can satisfies the demand of precision..