Study Of Rheology Behaviors Of Polymer Melt In Micro-channels

With the rapid development of MEMS, micro-injection molding is widely used in many fields. It becomes more and more important to develop suitable simulation software for micro-injection molding. Determination of the rheological behavior of the polymer melt within micro-channels is vital for the accurate simulation modeling of micro-injection molding. There are evidences indicating that polymeric flows in micro-channels differ significantly from those in macro-channels. Some factors that ignored in macro-scale may have significant effect in micro-scale, such as wall slip, surface tension, micro-viscosity etc. In the paper, slip models and micro-viscosity model were introduced to simulate the flow behavior of polymer melt in micro-channels under the isothermal-steady-state and non-isothermal-unsteady-state situations. The major work and main conclusions are as following:1. On the base of macro-scale wall slip theories, the wall slip mechanisms, slip determination techniques and wall slip models were investigated. And analyzed the reasons why wall slip would easily occur in micro-channels.2. Based on the viscous fluid mechanics and flow characteristics of polymer melt in micro-channels, the reasonable simplification and hypothesis were introduced, and the mathematical model of polymer flow behavior in micro-channels was established.3. The isothermal-steady-state flow of polymer melt in micro-channels was analyzed. The micro-viscosity effect, the wall slip effect and the combined effect of two factors on isothermal-steady-state flow were investigated. The results showed that both factors were important to the flow behaviors in micro-channels, Micro-viscosity effect increased the wall shear stress and wall slip effect released the wall shear stress. When the apparent wall shear rate is high, wall slip plays a main role in the flow behavior. When the apparent shear rate is low, the flow behavior is determined by the combined effect of wall slip and micro-viscosity.4. Numerical simulation of non-isothermal and unsteady-state flow was implemented using Finite Element/Finite Difference/Control Volume method. The effects of wall slip and micro-viscosity on the flow behaviors were investigated in different temperature and pressure fields. The simulation results show that, due to the influence of pressure on wall slip velocity, the apparent wall shear stress increased with the increase of pressure within a certain range. When micro-channel is smaller than 10μm, it can be seen as isothermal flow at the wall temperature, so the wall temperature must be higher than the melt temperature. Also found that the flow became easier when apparent shear rate was increased.