Shrinkage Control Strategy Of Thick-walled Plastic Parts Based On Injection-Compression Molding And The Agent Model

The thick-walled plastic parts tend to produce large volume shrinkage deformation after molded,which results in internal shrinkage holes or surface sink mark.However,the Injection-Compression Molding(ICM)can make the plastic dense and reduce shrinkage due to the compression of mold cavity by external force during compression stage.In order to solve shrinkage problem of thick-walled plastics,ICM process was applied to its molding process.Starting from the shrinkage mechanism of the compression melt and the law of the influence of process and mold parameters on the shrinkage,a shrinkage control strategy based on the agent model and genetic algorithm was proposed to control and optimize the shrinkage deformation of thick-walled parts.The main research contents and results are as follows:Firstly,based on the comparative analysis of injection molding and injection compression molding of thick-walled plate,the melt shrinkage mechanism during compression stage of the ICM process was explored.The CIM and ICM numerical simulation of thick-walled plate were completed by using Moldflow.And the simulation results were compared and analyzed including filling time,clamping force and injection pressure,volume shrinkage and warpage deformation.The results proved that the volume shrinkage of thick-walled plate formed by injection-compression process could be reduced significantly.And the melt shrinkage mechanism was obtained by analyzing melt flowing and density change in mold cavity.Secondly,the effects of ICM process and mold parameters on volume shrinkage of thick-walled plate was investigated.For improving the efficiency of parameter optimization and screen the key factors,the paper adopted the orthogonal experimental design and range analysis to study the effects of process and mold parameters on shrinkage to obtain the main factors.With the maximum volume shrinkage rate as the target,the influence law of process and die parameters on the integral shrinkage rate and internal shrinkage distribution of thick-walled parts were analyzed.And the results showed that melt temperature,die temperature,compression time,compression gap,cooling pipe spacing and gate size are the main factors affecting the shrinkage deformation of thick-walled parts.Furthermore,a shrinkage control strategy for thick-walled parts based on process and mold parameters was established.In order to reduce the probability of shrinkage defects and improve the quality of in thick-walled parts,a new evaluation model based on shrinkage uniformity and shrinkage tendency was built.And a shrinkage control strategy for thick-walled parts with a combination of Latin Hypercube(LHS),Kriging model,non-dominated genetic algorithm(NSGA-II),and multiple attribute decision making(TOPSIS)was proposed.LHS sampling was used to obtain sample data,Kriging model between parameters and indicators was established by MATLAB and the overall accuracy was tested.Then the NSGA-II and TOPSIS methods were used to find the optimal solution and obtain the optimum Pareto solution,and the effectiveness of the optimized solution was verified by finite element analysisFinally,the effectiveness of ICM process,evaluation model and shrinkage control strategy were verified by using plastic crankshaft as an example.The numerical analysis and comparison indicated that the volume shrinkage of plastic crankshaft can be effectively reduced by ICM process.Then based on the plastic crankshaft,the CIM molding simulation and production experiment were compared and verified.The results demonstrated that the proposed evaluation model can effectively determine the trend of shrinkage defects in plastic parts.At the same time,the proposed shrinkage control strategy was applied to the ICM molding of the plastic crankshaft,and the optimized shrinkage evaluation indexes were improved by 38.25% and 17.24% respectively,which revealed that the shrinkage control strategy of thick-walled parts is effective.