| A micro-injection molding machine was used to obtain micro-moldings of high density polyethylene, polyoxymethylene, and polycarbonate, in order to characterize the process dynamics, and to investigate the effects of processing conditions on microstructure, mechanical properties, and thermal properties.;The samples were microtomed and examined using a polarized light microscope for investigation of morphology. Various microstructural features, such as morphological layer thickness and crystalline polymorphs, were observed and analyzed, in light of the thermomechanical history. These features were correlated with both macro and local mechanical properties.;A punch die was designed and fabricated to cut the micro molded samples precisely into tensile testing specimen. The tensile properties were measured accurately with a conventional INSTRON testing machine combined with specially designed sample holders to prevent slippage and to ensure sample alignment. Thermal characterization was performed using modulated differential scanning calorimetry. Local indentation moduli were measured with a Hysitron TriboIndenter. An effort was made to evaluate process-structure-property relations.;A data acquisition system was implemented to obtain traces of data regarding the evolution of process variables with time. Six characteristic process parameters (CPPs) and metering size were used to characterize both the cavity filling and packing stages. The method of design of experiments (DOE) was employed, in order to investigate the effects of machine variables on the CPPs. A simulation was conducted using Moldflow commercial injection molding software. The discrepancy between experimental and calculated injection pressure patterns was attributed to the utilization of the unrealistic rheological model and boundary conditions. |
