Research On Melt Viscosity And Wall-slip In Micro-injection Molding Filling Flow

Micro-plastic parts molded by micro-injection molding technology have many advantages,such as high size precision,good consistency of quality,suitable for mass production,etc.which in bio-medical,information and communication,aeronautics and astronautics,optics and electron,etc.,show broad applied perspective.However in the process of molding of micro-plastic parts,many rheological behaviors differ from general injection molding due to the effects of micro-scale.So the study of the theoretical of micro-injection molding has become one of the hot spots.In this paper,reference the basic equations of macro-filling flow,and analyze the characteristics of micro-injection molding flow and the impact factors,then based on the Erigeen and Dkada's theory of non-linear continuity and the melt flowcharacteristics in micro-channels,the viscosity model of Cross-WLF was corrected and micro-scale viscosity model of consider the molecular orientation was build.Based on the analysis of the factors such as surface roughness and melt elasticity and the causes of wall-slip,wall-slip model considering melt elasticity was constructed,by correcting the Uhland's wall-slip model.Use the viscosity model that established above,software of Polyflow was used to simulate the material of PS in square cross-section channels of different size.The results indicate that the built micro-scale viscosity model is suitable for showing the effect of molecular oritentation that the feature size below tens of micron.For slip model,Polyflow also be used to simulate the PS,PMMA,PP,HDPE's pressure and slip velocity in circular cross-section channels of different sizes.The results indicate that wall-slip is in favor of reducing the melt flow resistance and increasing the rate of flow.The double-bowl capillary rheometer was used to measure the four polymer materials' (PS,PMMA,PP,HDPE) value of pressure and slip velocity when die diameters are 350μm, 500μm and 1000μm.The results indicate that the pressure of four polymer melts increased with the reduced of the channels size,and the HDPE has the biggest change.The wall-slip of PS,PMMA,PP increased rapidly with the increased of shear stress.The slip of the non-crystalline materials of PS,PMMA changed rapidly with the increased of the temperature and the reduced of the channel size.Finally the trial and simulation results be compared when the die diamters are 350μm and 500μm.The results indicate that the pressure of trial and simulation results of the HDPE is too far away,and the slip velocity of PP is far away too,but the velocity of PS and PMMA is close between trial and simulation results.All these show that the wall-slip model constructed in this paper is suitable for material of non-crystalline.