Study Of The Effect Of Ultrasound On Injection Molding Quality Of The Microfluidic Chip

Because viscosity of the polymeric melt will rise rapidly with the decrease in temperature, flowing ability of the polymeric melt becomes worse at root of the micro protruding of the mold cavity insert if the cross section of the injection-molded micro fluidic chip is rectangle and has high depth-to-width ratio. Thus it is difficult to achieve high replication of the right angle turn at root of the micro protruding of the mold cavity insert during pure injection molding. How to overcome microscale effects in order to produce micro plastic parts with stable quality has been imperative for micro-injection molding. This thesis focuses on improving molding precision of the micro fluidic chip by introducing ultrasound into micro injection molding process. Contents of the work are as follows.Firstly, the research results at home and abroad are analyzed. The flow behavior of melts under microscopic size is explored, and some microscale phenomena that affect the filling of microstructure are discussed. The phenomena during micro-injection molding process, such as wall slip, viscous dissipation, etc, cannot be ignored because of their significant effect on the filling of polymeric melt flow, which is different from the macro-injection molding process. Different methods of forming microfluidic chip are described, and their pros and cons are compared. The developments of applying ultrasound during micro-injection molding process are also stated.Secondly, the mold is designed for micro injection molding aided by ultrasonic vibration. And in the mold, the ultrasonic vibrator directly forms part of the mold cavity. By the high-frequency ultrasonic vibration effect, the internal structure of the polymeric melt are changed, and viscosity of the polymeric melt are reduced, so as to promote the melt flow thus filling of the microstructure of the mold cavity. The micro fluidic chip is designed which owns aspect dimensions of 80? m×100? m, and UV-LIGA and micro-EDM methods are used to fabricate the micro-structured inserts. And then, the filling process is simulated by the software MOLDFLOW. And the stress for the key part, the ultrasonic vibrator, is analyzed by the software ANSYS.Finally, experiments of ultrasound-assisted micro injection molding are conducted to study filling of the polymeric melt in the mold cavity when the micro structure insert is still with the fixed mold plate or vibratory with the ultrasonic vibrator in the moving mold plate. Then, the effects of ultrasonic vibration on packing of the polymeric melt around the micro structure of the mold insert are researched, and the rules of ultrasonic parameters on quality of the micro structure are explored. By changing the processing parameters, it is aimed to obtain micro fluidic chips which have high quality of the micro structures and meet the requirements of certain workplaces.