Manufacturing of micro-structured PVD hard coated molds and their potential use in plastic injection molding of micro-structured surfaces: a state-of-the-art review

Abstract Molded micro-structured parts offer specific enhanced functionalities and are of great relevance for a variety of technical products. The capabilities of micro-molding processes regarding achievable micro-scale feature dimensions have been lately shifted towards the submicro-metric length scale. Beside other factors, the most recent achievements are particularly related to the modification of the mold surface condition. Even though physical vapor deposited (PVD) metallic nitride hard coatings offer the potential to facilitate mold filling and to enhance part demolding, these coatings are still rarely considered as mold surface material. In traditional mold making, coating deposition onto the mold is the final step (indirect-processing). Alternatively, micro-scale features can be directly fabricated into PVD hard coatings (direct-processing) by exploiting the capabilities of micro-manufacturing. The materials and methods applied in mold manufacturing of micro-structured PVD hard coated molds directly affect their use in plastic injection molding of micro-structured surfaces. To present a state-of-the-art review on these two overarching topics, a keyword-based literature search has been carried out on research fields 1) precision mold manufacturing, 2) surface engineering, 3) direct-processing of hard coatings and 4) plastic (micro-)molding. For each research field, the state of the art is reviewed. The findings are mutually discussed with respect to manufacturing and potential use, and directions for future research are indicated. Lastly, a concept for the manufacturing of multi-level micro-structured mold is introduced. Molds realized in this manner can potentially be used for the molding of hierarchical micro-structured or multiscale structured parts, which offer a further enhanced or supplemented functionality.