| Plastic injection molding machine (IMM) is the key factor that ensuresthe precision of the molded part. According to the analysis of precisioninjection molding principle, the influences of clamping unit's performance onproduct quality, and the summaries of the existing clamping technologies, anew kind of internal circulation mold-clamping cylinder and its hydrauliccontrol system were developed based on the patent "internal circulationtwo-platen clamping unit". A novel internal circulation two-platen IMM,especially a clamping unit with the new cylinder was manufactured. Theclamping unit is mainly composed of a stationary platen, a moving platen, twomold-moving cylinders, four tie bars, four patented mold-clamping cylinders,a mold-adjustment device and an ejector. The rod of the mold-clampingcylinder was integrated with the tie bar of the clamping unit, simplifying thestructure of the clamping unit. The cylinder tubes of the mold-movingcylinders and the mold-clamping cylinders are fixed in the stationary platen,and the rods of them are connected with the moving platen. Themold-adjustment device and the ejector are mounted on the moving platen.When mold-moving, the internal circulation function of the mold-clampingcylinders becomes effective and thus the two cavities are connected, achievingthe internal flow of the oil. The internal circulation of the hydraulic oil in themold-clamping makes machine energy-saving during the mold-moving phase.At the moment of mold-clamping, the internal circulation function is switchedoff and the inlet of the mold-clamping is pressed, building up the clampingforce. On the basis of the advantages of the conventional clamping units, thenovel clamping unit further overcomes the shortcomings of the conventionalclamping units, such as high energy consumption and complex structure. Thecharacteristics of the internal circulation two-platen clamping unit can besummarized as "direct clamping by four cylinders","two-platen withmold-adjustment function" and "internal circulation". Five aspects of workwere conducted around the novel internal circulation two-platen clamping unit,and some research conclusions were obtained as follows:(1) Research of the theoretical model for the internal circulationtwo-platen unit. The clamping stiffness model and energy-consumption modelduring the mold-moving phase were established repectly, and the main factors affecting the stiffness model and the energy-saving principles of the clampingunit were investigated. Results show that the structure size, material of theclamping unit, and oil property are all the main factors of influencing systemstiffness. Comparing with the external circulation clamping unit, the novelclamping unit is energy-saving by eliminating the oil-filling energyconsumption and lowering the resistance energy consumption because of theuse of the internal circulation cylinder.(2) Simulation and optimization on the hydraulic system of the internalcirculation two-platen clamping unit. The working performance of thehydraulic system was investigated through the software AMESim.Displacement curve of the moving platen, pressure curve in themold-clamping cylinder and flow curve in the cartridge valve for releasingpressure were gained. It was found that the large flow in the cartridge forreleasing pressure was the main cause of the prototype CHH200's poorstability. An optimization scheme was proposed. The determining principle ofkey parameters in the optimization scheme was demonstrated. Theoptimization scheme can improve the operating efficiency and the stability ofthe hydraulic system.(3) Research on the working principles of the internal circulationclamping cylinder. The working conditions of the internal circulation clampingcylinder during the mold-moving phase was investigated by the softwareFLUENT. Results show that the pressure is relatively high at the front of thepiston of the mold-clamping cylinder and it is negative at the back of thepiston. The high pressure displayed as the resistance of the mold-moving,corresponding with the resistance energy consumption in the energyconsumption model. The resistance increases with the increasing of themold-moving speed. The velocity field nearby the piston in the mold-clampingcylinder is intensive. The maximum velocity occurred in the holes of thepiston and the flow behind the piston is turbulent. The turbulent flow is goodfor the heat exchange of the mold-clamping cylinder.(4) Research on the clamping property of the internal circulationtwo-platen clamping unit. The clamping property was investigated from twoaspects: clamping uniformity and clamping repeatability. The former wasinvestigated by simulation method and the latter by experiment method. Whenclamping uniformity was investigated, the mold cavity strain of as theevaluation index of clamping uniformity was proposed innovatively, differentfrom platen strain mentioned in the existing literature. The research resultsshow that the clamping property of the internal circulation two-platenclamping unit is higher than that of the toggled three-platen.(5) Research of the precision IMM standard. Based on the aboveresearches of precision injection molding and the status of existed plasticsIMM standards, the corporate standard "Precision Plastic Injection MoldingMachine" was developed. The standard not only proposes higher technical requirements for IMM, but also provides performance requirements. Theperformance requirement includes individual indicators and comprehensiveindicator. The comprehensive indicator is the weight repeatability and it is1‰according to this standard. The comprehensive indicator is the key index thatdetermines whether an IMM is precise or not.Based on the above researches, the prototype of the internal circulationtwo-platen IMM CHH200was developed and CHH90was manufactured inseries. The performances of the internal circulation two-platen IMMs weretested according to the standard "Precision Plastic Injection MoldingMachine" and "Plastic IMM Energy Consumption Testing and RatingStandard of China". The test results show that the IMM with the internalcirculation two-platen clamping unit is precise and is of the highest rank interms of energy-saving. The characteristics of the internal circulationtwo-platen clamping unit could be summarized in the following: materialsaving, energy saving, high molding precision, high production efficiency andhigh performance-cost ratio.The above researches make the internal circulation two-platen clampingtechnology relatively perfect and mature. The new technology is beingindustrialized by Ningbo Haitian Group, Ningbo Haida Plastic Machinery Co.,Ltd. and Zhejiang Sound Machinery Manufacture Co., Ltd.
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