Considering microtexture geometry to improve micro-injection molding fidelity

Abstract Micro-injection molding ( μ IM) is an attractive manufacturing technique to produce microstructured parts at low cost and high throughput. However, due to the small feature sizes to be molded, μ IM presents unique engineering challenges to overcome. Accordingly, extensive research has focused on improving the mold design and molding parameters in order to improve the limitations and ultimately the replication fidelity of the process. In this report, we investigate one variable that has not yet been considered: the microstructure’s geometric pattern. Hence, we used laser micromachining techniques to inscribe geometric arrays of hierarchical micropillars in the shapes of squares, rhombuses, hexagons, and triangles. By developing a novel analysis protocol based on the roughness of ‘microbumps’ transferred from the mold to the replicates, our results demonstrate that triangular and hexagonal microstructure arrays lead to higher replication fidelity due to their improved air drainage properties compared to the other geometries tested. In addition, to put the geometry’s influence into a broader perspective, we also tested several molding parameters including the holding pressure, melt temperature, mold temperature, and choice of polymer resin. We found that the use of high holding pressure is most strongly correlated with high replication fidelity, whereas the temperature and resin variables had a relatively small impact on our molding process.