The Packing Profile Optimization Design For Injection Molding

Injection molding,a plastic processing technique,converts thermoplastic into mold cavity by high speed,and make thermoplastic into all types of products after cooling and solidified.The developments of communication and consumer electronic products require higher qualities of high precise injection molded parts.With the developments of some commercial analysis softwares for injection molding,the application of optimization based on computer aided engineering(CAE) technologies greatly improves the qualities of the components and efficiency of molding.However,it is still a challenge problem to implement effective optimization based on the computational time-consumed analysis software.Many factors may affect the quality of injection-molded parts,such as process parameters,part design,mold design,and so on.In this paper,the design of plastic injection molding is considered as a system optimization problem,which is divided into several subsystems.The important objective function of each subsystem is found out and the processing parameters which greatly affect the objective function are optimized.Firstly,the paper summarizes the histories and developments of injection molding,and introduces several optimization method and CAE technique of injection.Secondly,the uneven shrinkage which has a crucial impact on the quality of products is discussed.Proper setting of packing profile plays an important role on the uniform shrinkage of parts.However,the former scholar did not draw sufficient attention to the study of packing stage,and set the packing pressure to a constant which often leads injection parts to have an uneven shrinkage and warpage deformation.In this paper,five representative packing curves (constant,decreasing linear,decreasing step,etc) which are often used in practice are chosen. The flow,shrinkage and warpage analysis of the injection parts are simulated by Moldflow software,the Kriging model is applied to build the approximate relationship between objective function and parameters.In this study,taking a scanner model and a cellular phone shell model for example,the result of the optimization reduces uneven shrinkage effectively.Finally,the whole stage of injection molding is optimized,four subsystems are considered,gate locatiom optimization,packing profile optimization,cooling system optimization and molding process parameters optimization.During the mold filling process,a gate location design under a certain set of filling process parameters is developed to minimize the mold filling pressure,temperature difference,over packing and friction heat.An information entropy-based multi-population evolutionary algorithm in conjunction with simulation programs was used to search the optimal gate location.Based on the gate-runner design and the same set of molding process parameters as the first subsystem,the packing profile is optimized by using surrogate optimization method to minimize the uneven part shrinkage due to plastic cooling.During the cooling process,based on the previous gate-runner design,packing profile and molding process parameters,the cooling system are optimized by using decomposition optimization method.In the fourth subsystem,the molding process parameters(mold temperature,melt temperature and injection time) are optimized by minimizing the shrinkage and warpage of the product using black-box optimization methods. Taking the cover of phone and CPU-base for example,the optimization result resolved the quality defects of several subsystems,and improved the quality of injection parts effectively.The authors gratefully acknowledge financial support for this work from the Major program(No.10590354) of the National Natural Science Foundation of China.