Characterisation of micro injection moulding process for replication of micro/nano features and micro components

Polymeric micro parts and micro/nano scale features, as typically found on miniature medical devices and microfluidic chips, are mainly produced by the micro injection moulding process, because of its mass production capability. Because of high surface to volume ratios, filling small cavities and tiny features requires high temperature and high speed in order to prevent short shots from premature solidification. The polymer melts are consequently subject to high shear rates and thermal gradients. This thesis has characterized the micro injection moulding process, polymer rheological behaviour at the micro scale, micro/nano feature replication, and morphology development and mechanical properties of micro parts and micro features.An in-line process monitoring system was developed to characterize filling, packing, and cooling of a typical micro component having a large sprue and runner. A shot size optimization method was proposed, which successfully eliminates the effect of machine switchover and holding pressure on the cavity filling process. Using a slit flow model, polymer melt viscosity at the micro scale was found to be dependent on cavity thickness and was lower than conventional viscosity, which is attributed to wall slip and non-isothermal flow. Replication of multi-scale features, ranging from hundreds of microns to as small as 100nm, has been successfully achieved by micro injection moulding using Bulk Metallic Glass tool inserts. Feature replication is characterized with respect to the moulding process and to the material, design, and feature configuration. Bulk Metallic Glass tools can successfully retain mould patterns for ~20,000 moulding cycles. Poly (ether block amide) micro parts exhibit some unique morphological features: spherulite-free core, larger spherulites between a skin layer and fine-grained layer/core layer. Shear stress was shown to be a successful threshold for the onset of an orientated structure by comparing the micro injection moulding process to a "short-term shear protocol". The morphology of the micro features was found to be similar to that of the core region, and the skin layer deformed into micro feature cavities depending on local pressure. Process-morphology-mechanical properties are correlated for micro parts.