Jun S. Lee

Evaluation of novel tooling for nanoscale injection molding

Injection molding technology is one of the most promising candidates for the economically viable manufacturing of nanoscale parts, but the composition and surface properties of tooling materials become more critical as the size of the molded features decreases. In the study, the effect of novel tooling with micro and nanoscale features was investigated by employing this tooling as inserts for micro injection molding of polycarbonate. Parts molded from etched silicon wafers with pattern depths of 300 nm and widths of 200 to 980 nm showed a significant decrease in replication quality with the size the features, probably because polymer adhered to the tooling surface. Silicon tooling from a different source and titanium-coated gallium arsenide tooling produced higher quality replication. The replication quality from the silicon tooling, however, was constant over 3000 molding cycles and coated gallium arsenide inserts survived the molding pressures; (the uncoated gallium arsenide fractured). These findings suggest that modifications to the insert surfaces will allow for viable tooling for injection molding of plastic parts with nanoscale features.

Enhancement of surface replication by gas assisted microinjection moulding

Abstract Achieving perfect replication of micro- and nanostructured surfaces without creating sink marks in the parts is challenging. Therefore, gas assisted injection moulding (GAIM) was investigated as a method to enhance moulding quality in polypropylene, polymethylmethacrylate (PMMA) and thermoplastic polyurethane (TPU) parts. For all three polymers, the GAIM did not improve replication (depth ratios) of low aspect ratio microfeatures moulded using tooling with positive features, but did significantly enhance replication of higher aspect ratio trenches and tapered holes. The enhanced replication was attributed to better filling, and with the semicrystalline polymer, significantly less shrinkage. GAIM sometimes enhanced the edge definition of the features, and as expected, reduced sink marks in the polypropylene surfaces.