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Research On Microscale Effects Of Filling Flow And Key Technology Of Micro Mold In Micro Injection Molding

Posted on:2011-12-21Degree:DoctorType:Dissertation
Country:ChinaCandidate:B XuFull Text:PDF
GTID:1101360332456984Subject:Mechanical Manufacturing and Automation
Abstract/Summary:PDF Full Text Request
The feature size of micro-injection molded plastic products is becoming increasingly tiny with the enlarging application field. Micro scale filling flow of polymer melt shows obvious scale effect within micron size range. Many impacting factors which are neglected in macroscopic scale are likely main elements, including rheological behavior, wall slip, viscous dissipation, double electric layer effect, surface tension, etc. Due to the role of above-mentioned factors, the filling theory and analysis method of traditional injection molding has not fully applicable to the micro molding process. Therefore, there are the momentous significances in both theoretical and practical for revealing the role of microscale effect, establishing the micro-dynamic model of melt filling flow, guiding mold design, improving the quality of molding products to investigate the filling factors in micro scale. In the paper, the main research contents are as follows:1. According to the measurement principle of capillary rheometer, the mechanism that the increasing ratio of surface to volume in microscale influences polymer melts rheological behavior was suggested and a mathematical model of micro-scale viscosity was developed on the base of Kelvin—Voigt constitutive model. The model characterizes the relationship between the characteristic size of micro channel and melt viscosity. The melts rheological tests were conducted with different feature size capillary dies.2. Based on the micro scale viscosity model and Mooney measurement method of wall slip velocity, micro-scale effect on the impact of wall slip velocity was analysied. Considering scale factor, a micro-scale model of wall slip was developed by modifying the slip coefficient of the traditional wall slip model. With none-modified model and modified model, the pressure drops in micro channels were carried out at different shear rate through numerical simulation and compared with testing value. In view of this, the influence of wall slip on melt filling flow was investigated.3. On the foundation of theoretical analysis of polymer melt viscous dissipation, a microscale measurement of polymer melt viscous dissipation was proposed. The viscous dissipation measurement device was developed on two-cylinder capillary rheometer and the temperature rises due to viscous dissaption were gauged when polymer melt is extruded steadily through various feature size capillary dies. The radial temperature distribution equation of capillary die was established with micro wafer. Thus a calculation model of average temperature for cappliary dies exit was obtained and the comparison of the experimental results with those predicted from the simulations at different melt temperatures was analysied. Besides, the influence of viscous dissipation on melt viscosity was studied.4. A cell container micro injection mold with two cavities was designed and made. Using micro-EDM milling, a three-dimensional mold cavity was machined. Variotherm technology with the combination of oil, water and electricity was realized. Temperature and pressure sensors were installed at the front gate and melt temperature and pressure changes during injection molding process can be detected timely. After sealling the mold cavity, the air in mold cavity was eahausted with vacuum and the influence of vacuum on the quality of products was investigated.5. The molding process of cell container was conducted with single factor test with the consideration of five process parameters, including mold temperature, melt temperature, injection speed, packing pressure and packing time. Thus the influence sequence of process parameters was obtained by extremely poor analysis for three polymers.The molding process characteristic of micro products was investigated through qualitative analysis.
Keywords/Search Tags:Micro Injection Molding, Scale Effect, Rheological Property, Wall Slip, Viscous Dissipation, Micro Injection Mold, Injection Molding Process
PDF Full Text Request
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