A Close-loop Multivariable Quality Control Strategy For Injection Molding Process

Injection molding is widely used for manufacturing plastic materials into various products inplastics industry. Injection molding is a typical multi-variable, multi-phase batch process. Productquality control is critical to an injection molding process, which has been attracting a lot of attentionsin both academia and process industry. After consulting a lot of relevant literatures, the thesis firstpresents a review on the major theoretical and technical methods for quality control of injectionmolding process. A novel multi-variable closed-loop quality control strategy is then developed, whichcan regulate product quality by adjusting the set-points of process variables when quality is deviatingfrom its target value. Four major issues addressed in the developed quality control strategy are studied,and the major work done in the thesis is summarized as below.Firstly, orthogonal experimental design is done to generate sufficient process data, and analysisof variance (ANOVA) is used to determine the influences of process variables to the product quality.The initial set-points of process variables can be obtained for customer-defined quality specifications.Secondly, the multilayer group method of data handling (GMDH) algorithm is used to develop thequality model. Thirdly, a local optimization method, the sequential quadratic programming (SQP), isadopted in the quality controller design, where the optimal parameters are calculated cycle by cycleaccording to the observed quality deviation. Finally, a multi-way partial least squares (MPLS) modelis proposed to provide online quality measurements. The developed quality control strategy is testedby an injection molding quality control simulation procedure. The results can show the feasibility ofthe proposed quality control strategy.