| Flat polymer micro-device is plastic plate part with micro structures, which is widely applied in life science, chemical analysis, optical communication, etc. Micro injection molding is an important manufacturing method for flat polymer micro-devices. Melt filling is a key step in micro injection molding. The surface effect of melt will be significant to filling quality under micro-scale conditions. In this study, by taking the micro injection molding of polymeric flat micro-device as the research object, the influence of surface effect on filling flow was analyzed, and the theoretical model and core analysis module of CAE were established for the filling process of micro injection molding. In order to solve the problems of filling shortage of micro structures and warpage, the mold fabrication and process research for micro injection molding were carried out. Finally, the micro fluidic devices, typical polymeric plate micro-devices, were fabricated. The main contents of this thesis are as follows:1. Research of melt surface effect test and analysisSurface tension coefficient of polymers and static contact angle of polymers on Si, Ni substrates were tested. The influence of temperature on surface tension coefficient and contact angle was analyzed and theoretical model was established to describe the melt surface effect and filling process.2. Core model establishment and analysis of filling process in micro injection moldingBy means of the open source codes, constitutive equations were added into momentum equation to describe the surface effect of melt and micro-scale viscosity. A CAE module was built to analyze the filling process of micro injection molding. Aiming at filling process of micro grooves, numerical simulation was carried out for filling process of micro structures, and the mechanism of surface effect on filling process of micro injection molding was researched under micro-scale condition.3. Structural design and fabrication of a core-removable micro injection moldAccording to the manufacturing requirements of polymeric plate micro-devices such as small quantity and diversification, a core-removable micro injection mold was designed and fabricated. Assembly of step-like slot and fixed mold plate was adopted to realize the flexible replacement of cores. By quality improvement of mating surface in mold, symmetric distribution of various push rods and backward demould, the loads of core were more uniform and the damage probability of cores with brittle-rigid materials was decreased. An assistant vacuum structure was adopted to reduce the resistance of melt fluidic and sealing frame was used to improve sealing performance of cavity.4. Experimental research on optimization of polymeric plate micro-deviceOrthogonal experiment was adopted to investigate the effect of process parameters on filling rate of micro grooves with different widths. The primary-secondary influential order of key factors was determined and combination of optimized levels was obtained. To reduce warpage of flat device, stress distribution was adjusted by the specially designed micro structures in plate device. Experiment results of micro injection verified the validity of this technique.5. Micro injection molding and experimental test of micro fluidic devicesTwo micro fluidic devices were fabricated through micro injection molding, the micro channels boundaries of which were straight. The defect of less filling was not obvious and the warpage did not influence the bonding process. The problems such as liquid leakage, bonding failure and boundary effect of micro channel were not discovered after multi-groups parameter tests. The fabricated snake-shaped passive mixer successfully realized uniform mixing of two kinds of liquids at sample injection speed of 1μl·min-1, and the fabricated droplet generator can steadily generate liquid droplets with various diameters from 153.7μm to 69.4μm. This confirmed that the two devices achieved the requirements of application. |
PDF Full Text Request