Study On Some Critical Problems In Precision Injection Molding

Precision, high efficiency, and thin-wall injection molding, as the development trend of conventional injection molding, were widely studied in recent years. In this paper, a set of visualization device was designed and manufactured. A model of imbalance filling of precision injection molding in multi-cavity mold with "H" pattern runner system was established. The imbalance filling mechanism was clarified thoroughly by the visualization experimental results of melt flow behavior and the measurement results of melt temperature. A new method of ultra high speed injection molding based on giant magnetostrictive materials was proposed. A specific magnetostrictive displacement transducer used for high speed precision injection molding machine was developed. The main research results are as followed.1. Development and application of visualization experimentaldevice for injection moldingA set of visualization experimental device was developed. Theinfluence of injection molding speed and gravity on melt flow behaviorwere studied with the visualization device. The generation processes of several typical injection molding defects, such as jetting and snake flow, sink mark and bubble, were directly observed and recorded. The methods of improving these defects were proposed.2. Establishment and clarification of the model of imbalance filling mechanism in multi-cavity mold with "H" pattern runner systemOn the basis of the theory analyzing, the model of imbalance filling mechanism in multi-cavity mold with "H" pattern runner system was supposed. It is clarified that the mechanism of imbalance filling results from dissymmetrical temperature distribution on the cross-section of runner, which is strongly influenced by the shear heat and the cooling process in the runner. The imbalance filling mechanism was clarified thoroughly by the visualization experimental results of melt flow behavior and the measurement results of melt temperature. The method of improving imbalance filling named "two-step" process was proposed.3. A new method of ultra high speed injection moldingThe conventional injection molding machine to implement ultra high speed injection molding was restricted by the controlling response and precision of screw advance. Therefore, a new type of injection system with a quick response nozzle based on giant magnetostrictive materials (GMM) is proposed in this paper. The injection system is capable of implementing ultra high speed injection molding through controlling port width of nozzle, meanwhile, melts with sufficient pre-compress potential energy under under constant injection molding pressure with a hydraulic accumulator system. The method of implementing ultra high speed injection molding is never reported in the literatures.4. Development and experimental study of the key parts of foreside control ultra high speed injection moldingThe designing theories and methods of microdisplacement actuator for controllable nozzle based on GMM are proposed. The designing process of such components as microdisplacement transfer and amplifier mechanism, driving coil and control circuitry is presented particularly. Furthermore, a new type of multilevel lever mechanism was invented to transfer and magnify output microdisplacement. A sample of microdisplacement actuator based on GMM manufactured.The influence of nozzle port opening width parameter on injection speed under different injection pressures was investigated in this paper. As a result, it was found that injection speed could be increased through varying nozzle port opening width under keeping constant injection pressure. The results obtained from this study are valuable for establishment of control theory of foreside-control high speed injection molding.5. Development and experimental study of magnetostrictive displacement transducerA magnetostrictive displacement transducer special for precision injection molding was developed. Both potentiometer and magnetostrictive displacement sensor used to measure the displacement of screw. The influence of such parameters as preform and speed of screw, injection speed and back pressure was studied with orthogonal experiment method. The results showed that the higher measurement precision and higher repeatability of products can be obtained by adopting magnetostrictive displacement transducer. And magnetostrictive displacement transducer is less impacted by surrounding environment factors. The research results provide a solution method for improving precision injection molding repeatability.