machine

.   So   the   molding   process   and   system are

cooling cycle time, high quality of products and low cost. Especially, WAIM can produce larger void spaces and longer hollow sections in parts than GAIM[1–3]. All the advantages lead the applications of WAIM to a broad   field

* Corresponding author. E-mail: zzm.zju@gmail。com

This project is supported by National Basic Research Program of China (973 Program, Grant No. 2006CB705405), National Natural Science Foundation of China (Grant No. 507优尔99), and Zhejiang Provincial Science and Technology Plan Program of China (Grant No. 2007C21057).

designed to make injection water supplier work well    with

injection machine. On the other hand, if the injection water pressure is changed largely, the eddy and interfacial instabilities will be caused. There is reason to control pressure increasing step by step[6–7]. The injection water flow rate is large and the compensation flow rate replacing melt shrinkage is small. The energy saving and control performance  are  required  in  system design  based  on the

CHINESE JOURNAL OF MECHANICAL ENGINEERING ·419·

intermittent periodic work cycle of WAIM. The present experimental and commercial WAIM systems  are developed from GAIM and water is pressurized by compressed gas[1,4]. The pressure and flow control of injection water are low-stiffness and slow-response. Also low efficiency is induced by the additional air compressor and exhaust valves. These problems can be solved when the injection water is supplied by water hydraulic system directly.论文网

The water hydraulic technique using filtered tap water or seawater as working fluid offers advantages, such as low cost for medium, environmental friendliness, cleanness and non-flammability[10]. The typical application fields include water mist fire fighting, high pressure water cleaners, underwater operation, water treatment, nuclear, mining, steel, ship, food processing industry, etc[11–12]. The fast response, high control stiffness, constant viscosity and low temperature-induced drift are highly praised in water hydraulic proportional control technique, for the reason of high bulk modulus and thermal capacity of water. Another benefit is high efficiency coming from low viscosity[12–15]. However, the nonlinearity in water hydraulic control systems may be great due to the seal and lubrication in components. The static friction and leakage flow will cause large dead band and poor linearity in control valves, cylinders or other actuators as disturbance additionally[12–14]. The steady-state accuracy of control valves  can  be increased by static compensation as well as the dynamic performance will not be affected. Simultaneously, the anti-disturbance performance may be improved through closed-loop control. Besides, the throttle valves, accumulator, and wide variation of flow rate change parameters and equilibrium points during process of water injection. Generally, hydraulic plants exhibit significant nonlinearities and parameters varying with time, whereas the linear controller is classical, mature and easy to design. The set of rules and methods is well developed in linear control. The injection parameters are  different  for variations of polymer materials, mold, process approaches. The simple control scheme design based on linear control theory contributes to the convenience of parameter adjustment and industrial process.

The application of water hydraulic technique in WAIM shows a perfect combination of green transmission and novel injection molding technology with energy  saving, high efficiency and low operation expense. So on the basis of the analysis of the WAIM process and load characteristic, a novel design of the water hydraulic system was designed and modeled in MATLAB. The problems of linearization, load characteristic and multi-point feedback need to be discussed in terms of tracking errors and stability. Then the experiments of proportional pressure control on  WAIM were conducted on compensated static control of water hydraulic proportional pressure relief valve.