| Die casting is an advanced and efficient metal precision forming technology,which is widely used in the manufacture of electromechanical equipment,automobile and aerospace parts.Traditional die casting machines use mineral oil as working medium,which may cause pollution and flammability in high temperature working environment.Compared with traditional die casting machine,the die-casting machine driven by water hydraulics has the prominent advantages of green environmental protection and safety.Injection system is the key part to determine the performance of die casting machine.Large flow water hydraulic proportional cartridge valve is the core control component of injection system.The injection process of die casting machine has the characteristics of short duration,fast injection speed and high injection pressure,so its core control components are required to have large flow rate and fast response ability.However,due to high vaporization pressure,poor lubrication and low viscosity,there also have great difficulties and challenges in the development and application of water hydraulic control valve.1)How to increase the response speed of large flow water hydraulic proportional cartridge valve.The large diameter of the main valve leads to large inertia of movement,large load of pilot stage,and large volume of the control chamber of the main valve,which reduces the response speed of the valve.2)How to improve the control accuracy of large flow water hydraulic proportional cartridge valve.The high vaporization pressure of water medium can easily cause cavitation at the valve orifice,which can cause vibration of the valve core.In addition,the large flow rate can make the valve core subjected to large flow force,the interaction between the valve orifice cavitation and flow force,strong nonlinear effect,and reduce the control accuracy of the valve.In view of the above problems,a new structure of large flow hydraulic proportional cartridge valve driven by voice coil motor is proposed in this paper.The characteristics of flow force under cavitation were studied systematically.The mathematical model of large flow water hydraulic proportional cartridge valve was established.The key structural parameters were optimized and a prototype was developed.The major research contents are listed as follows:According to the characteristics of two different flow conditions of the pressure injection system,a new structure scheme of large flow water hydraulic proportional cartridge valve controlled by double proportional valve is proposed.The mathematical models of the main valve and the pilot valve are established,and the basic structural parameters of the main valve and the pilot valve are designed.Based on the flow requirements of the slow injection phase and fast injection phase,the flow area of the main valve is controlled by piecewise linear control to achieve the fast switching injection speed.The optimization design for the large flow hydraulic proportional valve and the pilot valve is carried out respectively.The large flow hydraulic proportional valve adopts two-stage structure.The main stage is a two-way cartridge valve,and the pilot stage is composed of 2/2 hydraulic proportional valves.The pilot valve adopts the structure of the seat valve with the lever amplifier structure,which can amplify the electromagnetic thrust of the voice coil motor.The characteristics of flow force under cavitation were studied systematically.We are focusing on the influence mechanism of several common in the poppet valve on flow forces and cavitation.A 2D simulation model of different valve s is established.The two-phase flow simulation model(water medium as the main phase and steam as the second phase)is used to reveal the mechanism and influence of cavitation and flow forces.Based on the simulation results,the main valve port adopts a non-circumferential valve port which is composed of two U-shaped ports.It can not only form a two-stage throttling effect,effectively suppress the occurrence of cavitation,but also meet the needs of the main valve ports for sectional control of the valve flow area.On the basis of determining the structure of the double U-type main valve port,the influence of the structural parameters of the double U-type valve port on the flow force is studied quantitatively by using ANSYS/FLUENT simulation software.The flow field characteristics of the valve port can be improved by selecting the optimal structural parameters of the valve port and the hydrodynamic force is compensated effectively.The flow force has been reduced by about 10%.Based on the structure characteristics and working principle of the large flow water hydraulic proportional valve,a precise nonlinear mathematical model has been established.The Simulink simulation model has been established.The influence of the structure parameters of the valve on the dynamic performance is analyzed and studied in depth.The qualitative understanding of the influence of the structure parameters on dynamic performance of the valve is obtained.The key parameters that need to be optimized are determined.The dynamic performance of the large flow water hydraulic proportional cartridge valve has been greatly improved.The maximum value of overshoot decreases from 15% to 6%(reduced about 60%)and the adjustment time decreases from 58 ms to 48 ms(the response speed increases by 17.2%).A prototype of a large flow water hydraulic proportional cartridge valve has been developed,and a test system for the thrust characteristics of the voice coil motor is built.The test system for the pilot valve performance and the whole valve performance are also set up.The thrust characteristics of the voice coil motor are simulated and tested,and the optimal thrust range of the motor is determined.The pilot valve and the whole valve have been studied by prototype test.And the experimental results show that the rising time of pilot valve is about 12~15 ms,the adjusting time is about 30~35 ms.The rising time of the main spool is about 20-30 ms,the adjusting time is about 60-110 msThe research results of this paper can provide theoretical guidance for the development of large flow hydraulic proportional cartridge valve,and lay a solid foundation for the development of full water hydraulic drive die casting machine.At the same time,the relevant research results of this paper can be further used in forging machine,steel plant metallurgical machinery,coal mine hydraulic support and other engineering equipment. |
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