The Research Of Precision Control Techniques In Melt Filling Flow Of Micro Injection Molding

With the development of micro-electromechanical systems, micro plastic parts are used in more fields. As an important method for manufacturing micro plastic parts, micro injection molding technology has the advantages of fast forming speed, low cost and high quality. High precision control methods are required during the injection molding procedure because the micro plastic parts always require micron level precision. Some problems have to be solved to improve the quality of the micro injection molding products. The problems include ’it is difficult to judge the start time of injection due to noise interfernces’,’bad repeatability of batch products’,’injection molding products usually have got shape defects in tiny details and possess poor surface roughness’. This article presents a series of control technologies to improve the precision and the qualified rate during micro injection molding technology. The details are as follows:First of all, according to macroscopical theory of the mold filling, the influences of surface forces and intermolecular forces that apply to the microscopic scale viscous fluid are considered. The viscosity theoretical model about the plastic melt mold filling procedure of micro injection molding is proposed. The boundary conditions are discussed. Simulations and experiments are carried out to verify the model.Secondly, an adaptive Kalman filter algorithm based on F-distribution is proposed. The algorithm can track the waveform of melt surface when it flows into the mold cavity in micro injection molding mold filling process real-timely. The algorithm is convergent in the stability analysis. It can filter various noises. Simulational and experimental results for the algorithm reveal it can track the transient signals of sudden changes during the micro injection process. The micro injection molding machine that use this algorithm can track the start time of the micro injection molding process accurately. The injection volume also can be precisely controlled to improve products’ quality. As the algorithm can deal with the mutation situation of signal waveform, it is also applicable to other hybrid systems that possess transient-state and steady-state. And then, learning control theory is led into the classical PID control method according to the repetitive motion trajectory of the plunger during the mold filling process in micro injection molding. A feedforward correction learning control method is accquried to control the repeatability of micro injection molding products. After several adjustments, the method can achieve the desired control path through repeated learning without considering the nonlinear model of mold filling process in micro injection molding. The control system of injection molding machine is set up. The analytical and experimental results prove that this method can improve the precision of injection volume control from0.01g to0.005g, real-timely. It is suitable for the high-speed demand of injection molding process and large-scale requirement of manufacturing.Finally, ultrasonic vibration is introduced into the mold filling and demoulding process to improve the quality of the products. The experiments that use the ultrasonic welding machines and Langevin-type transducer as vibrators are held to verify the advantages of the ultrasonic vibration. The ultrasonic vibration can help the plastic melt in the microchannels flowing into the mold sufficiently. It can significantly reduce the demolding force. Meanwhile, it also can decrease the adhesion between the suface of micro injection molding products and the inner surface of the micro mold during demolding process. An ultrasonic vibration micro mold model is presented. The modal simulation about the model is carried out at the ultrasonic vibration situation. Experiments on the micro injection molding prototype reveal the micro mold with ultrasonic vibration can improve the products’ accuracy during mold filling and demolding processes effectively. The surface roughness of the product is decreased from0.5μm to less than0.15μm and the micro structures are more intact and reliable.