Research On Filling Flow Theory And Processing Experiment In Micro Injection Molding

Micro plastic pans molded by micro injection molding technology have manyadvantages, such as light quality, small volume, great corrosion resisting and insulatibity, highreplication precision, high production efficiency, etc. which in aeronautics and astronautics,precision instrument, biology and genetic engineering, pharmaceutical engineering,communication and information, environmental engineering and military field, etc., showbroad prospects in application. The filling flow process of polymer melt during microinjection molding directly influences on the molding quality of micro plastic part andproduction efficiency, and is deemed to be the most important phase in micro injectionmolding. So, polymer melt filling flow behaviors in microscale in special microscale effectswere researched, and distributions of temperature, pressure and velocity, etc. were gained. Onthis basis, numerical simulations were carried out and molding process experiments werestudied, all of which are momentously theoretical and practical significance on optimizationdesign of micro injection mold and on improving the quality of micro plastic part.In this paper, according to the fundamental theories of viscous fluid dynamics andpolymer rheology, the basic equations for filling flow of polymer melt during micro injectionmolding were constructed with reference of the research methods of conventional injectionmolding,. With non-linear fitting modeling method, microscale viscosity model was built tocharacter the relationship between the melt viscosity and the characteristic dimension ofmicrochannels. Using Navier's slip model, the influencing rules of wall slip in microscale onmelt velocity field and temperature field were obtained. In terms of analysis for themechanism of heat transfer between melt and channel wall, melt temperature distributionsemploying the transient convection heat transfer coefficient model were shown. Then, thedistinct effects of viscous dissipation on polymer melt filling flow in microscale were given.This theoretical research of micro injection molding offers important theoretical foundationfor the structure design of micro injection mold and the setup of micro injection moldingprocess.On basic of theoretical research results of micro injection molding and combining thenumerical methods in finite element analysis, the rheology equation and the thermodynamicscondition boundary were corrected, and the single effect and the couple effect of themicroscale viscosity model and the transient convection heat transfer coefficient model onmelt velocity and temperature were systematically analyzed. The influencing rules of moldtemperature, melt temperature, injection pressure, injection speed and injection stoke onvolume fill percentage of microstructure part were gained under the condition of consideringmicroscale effects. The injection mold of dumb-bell shape microstructure part for validating and moldingprocess experiments was designed and fabricated. In reference to structure characteristics ofmicrostructure part and micro injection molding features, the variotherm mold of whichpattern is of electric-heating and water-cooling was designed. The micro cavity with channelof width 100μm was fabricated by no back plate process of UV-LIGA technology and themicro cavity with channel of width 500μm was fabricated by micro electrical dischargemachining technology.The on-line device measuring polymer melt pressure based on the theory of slitrheometer was developed, and the melt pressure data at entrance of microchannel weremeasured. Correcting and calculating the experimental data, the validity of the builtmicroscale viscosity model was proved. Then, with Taguchi experiment design method themolding experiments for dumb-bell shape microstructure parts were performed. The influencesequence and optimal level combination of process parameters were obtained by the analysisof means and the analysis of variance, and the simulational method is feasible and valid. Theinfluencing rules of material property and surface roughness of cavity on the volume fillpercentage of microstructure parts were researched, which is of important application valueon improving the molding quality.