Experiment Research On The Influence Of Melt Viscosity On The Filling Flow In Micro-injection Molding

For the tiny size of the runner and mold cavity,as well as the scale-effect in the process of micro-injection molding, polymer melts demonstrate many rheological phenomena different from macro-injection molding,so as to affecting the forming quality of micro-parts.Hence,it has been becoming the research hotspot in the field of micro-injection in recent years.This dissertation,based on deep analysis on the flow theory and research status of micro-injection,found on polymeric rheological theory,aiming at the influence of polymeric viscosity to mold filling in micro-injection molding,adopting the simulation software of POLYFLOW and double-barrel capillary rheometer,has simulated and measured the characteristics of three kinds of polymer melt(PS,HDPE,PP) flowing through rectangular and round dies of several length-to-diameter ratio and equivalent diameter,which areΦ350μm(with the section of 320×300μm andΦ350μm),Φ500μm (with the section of 500×400μm andΦ500μm) andΦ1000μm (with the section of 1000×785μm andΦ1000μm) respectively.Compared to the numerical simulation,the rheological experiment show that,the viscosity of three kinds of polymer melt decreases with the melt tempareture and the shear rate rising,among which the viscosity of PS and HDPE melt are thehas maximum and minimum change,respectively;At the same tempareture, whereas,the viscosity of three kinds of polymer melt decreases with the size of micro-scale dies minishing;Under the codition of the same equivalent diameter,the viscosity of polymer melts flowing through rectangular dies are larger than that of the round dies;The non-Newtonian index of the three kinds of polymer melt decreases with the shear rate increasing,among which PS and HDPE melt are the minimum and maximun respectively.The experimental viscosity of the three kinds of polymer melt flowing through the rectangular and round dies with the same equivalent diameter and diameter of 350μm and different length-to-diameter ratio at different tempareture and shear rate, comparing with the theoretical values from the two kinds of micro-scale viscosity model, the results show that, the theoretical value of the micro-scale viscosity model considering the length-to-diameter ratio is much closer to the experimental result.