VISCOELASTICITY EFFECTS OF POLYMERIC MATERIAL IN MICRO INJECTION MOLDING

摘要

An experimental study has been carried out to determine the effect of viscoelasticity in comparison to viscosity on micro-injection molded parts. In this study, two different polymeric materials- Polystyrene (PS) as a viscous material and High Density Poly-Ethylene (HDPE) as a viscoelastic material- have been selected to observe the effect of melt elasticity on the filling phase of micro molding based on cavity pressure of molded part. All process parameters except temperature are the same for both polymers. Process temperatures have been selected in order to match the viscosity for both polymers used. Polymer viscosity was characterized at different shear rate and temperature. Viscoelasticity of both polymers were investigated using rotational rheometry in the oscillation mode. The mold geometry with high aspect ratio has been used and the effect of viscoelasticity on cavity pressure has been discussed. It was observed that there is retardation on the response of pressure because of clastic response of material during filling. Despite the differences in slope, peak value, area, and cycle time between two curves, they share similar trends. The only difference is their response during solidifying because of material property.