Numerical Simulation And Experimental Study Of Shape Change In Polymer Micro-extrusion

In recent years, people’s attention gradually shift from the macro objects to the phenomenon occurred in small-scale and rapid response process and its corresponding device due to the development requirements of modern high-tech as well as the increase awareness of macro-and micro-physical phenomena, the miniaturization has become an important trend in natural science and engineering. It is an effective way to use micro-extrusion technology for producing products such as interventional catheter, micro fiber, micro gear which are widely used in health care, transportation, and other industries, however, product miniaturization has also brought a series of problems, the rheological behavior of polymer melt in the micro flow channel has been changed, many factors such as microscale effect and wall slip phenomena which needed be considered in tradition extrusion must be considered, even the effect of surface tension can not be ignored. And these products are mostly belong to irregular profile, the complexity of the die tunnel brought a lot of trouble to our research, so the study of shape change mechanism in polymer micro extrusion has important theoretical value and practical significance for the parameter design of the micro-extrusion die.Based on the theory of tradition extrusion and polymer rheology, wall slip and surface tension based on the micro-size effect in the process of polymer micro-extrusion are studied, the material’s surface tension model and Navier wall slip model are determined which provide the basis of model for the numerical analysis.With the ellipse and trefoil section die as the object of study, the die structure parameters are designed according to the traditional extrusion die design theory and experience, the flow process considering both the established surface tension model and wall slip model is numerical simulated, the effects of the die parameters including the compression ratio, compression angle and the lengh of stereotypes section on the product flow and shape change are analyzed, two dies are designed and manufactured whose structure parameters are determined according to numerical simulation. Using the reverse extrusion molding technology of POLYFLOW software, the inverse extrusion of elliptical and trefoil section die are numerical simulated, the corresponding die shape is obtained, the results are analyzed, the theoretical guidance and design basis for extrusion die design is provided also.Finally, extruding experiments are conducted using the designed dies, the influence of different processing parameters on shape change of extrudates ia analyzed, die structure parameters are further revised according to the results of experiment and numerical simulation.