Water Hydraulic Proportional Pressure Control For Cavity-Filling Process Of Water-Assisted Injection Molding

Water hydraulic proportional control technology is an important developing direction of 'green' water hydraulics.As well,water-assisted injection molding(i.e.WAIM) has attracted much attention in the field of injection molding technology,due to the advantages such as high efficiency,high quality,low cost and so on.However,water hydraulic proportional control technology is high-cost and has high environmental requirments.It is the main reason that there is nearly no application in common industry.Also WAIM research and industrialization are very difficult because of the restriction of low-level equipment development.The organic combination of WAIM reaearch and water hydraulic proportional control technology is a great idea to develop the WAIM system and extend the applications of water hydraulics.The water pressure control for cavity-filling process of WAIM is the key influence factor of forming effect, and is the key problem in the application research of water hydraulic proportional control in WAIM.The low-cost water hydraulic proportional pressure control valve is developed,whereas, it doesn't meet the requirements of the injection water pressure control due to the great nonlinearity and poor performance.Meanwhile,the research on WAIM is not promoted on equipment development to solve problems of process improvement,system control,saving energy etc.For these reasons,there are two key problems in this thesis.Firstly,the control performance of the low-cost water hydraulic proportional pressure control valve should be improved.Secondly,the water hydraulic system is required to fit the process and load characteristics and the new control strategy should be proposed to control the water injection pressure.Based on these two researches,the experimental study is carried on aiming at fine molding effects.In this thesis,an innovative control method is proposed to decrease the dead zone and hysteresis of the water hydraulic proportional valve based on the sectional linear hysteresis model of the valve.That is a feed-forward static hysteresis compensation strategy with one-side pulse modulation.A novel differential pressure control of pressure cylinder is proposed to regulate the accumulator pressure,aiming at matching the intertiment work cycle and load characteristic of WAIM.The water hydraulic pressure control valve is used to regulate the back pressure in one chamber of the pressure cylinder opposite to another chamber connected with accumulator.The linear WAIM load model is built through flow field simulation on WAIM cavity-filling process. And the model-based feedback of accumulator pressure is provided to eliminate the differentiation element of the pressure control system.At last,the influence of pressure control on WAIM forming effect and the WAIM applicability with various geometrical conditions are investigated through experiments.These contribute to industrialization of water hydraulic system for WAIM.The thesis is outlined as following.In chapter 1,the state of the art of water hydraulic proportional control and WAIM technology is introduced.Key problems of this thesis are analysed.Purpose,significance and main contents are outlined.In chapter 2,the sectional linear hysteresis model of the water hydraulic proportional pressure control valve is built.The main factors influencing the valve static characteristic are analysed. The large dead zone and hysteresis are reduced significantly by feed-forward static hysteresis compensation with one-side pulse modulation.In chapter 3,the model of cavity-filling process in WAIM is built based on the time dependent analysis,turbulence models,and viscoplastic constitutive equations etc.Main process control parameters and linear load model are investigated in simulation.In chapter 4,a novel water hydraulic system is developed based on the differential pressure control of pressure cylinder and accumulator.A linear model of pressure control system is built. Model-based feedback and closed-loop control of load pressure with integral compensation are proposed and investigated.In chapter 5,the influence of flow resistance on system pressure control and molding effects with different water pins are investigated.WAIM applicability with various geometrical conditions and the influence of pressure control on WAIM forming effects are investigated by experiments.A novel method on water injection is provided with partial mould modification. In chapter 6,all the research ontents are summarized,and the future research developments and outlooks are proposed.