Polishability of tool steels : Characterisation of high gloss polished tool steels

Abstract: The manufacturing of plastic components, like a majority of other mass produced discrete parts, require well designed dies and moulds. Complex geometries and increasing demands on final surface appearance, which is strongly connected to the quality impression, are pushing for high demands on mould-makers and polishers as well as steel producers. Moulds for production of shiny plastic components require tool steels with low defect levels to achieve highly gloss and very smooth mould surfaces (roughness levels in the nm-range). It is the ability to achieve those mirror-like surfaces, the polishability of tool steels, that is the central part in this study. To increase the understanding of how material properties and different surface preparation techniques impact the polishability, a selection of high gloss polished tool steel qualities were characterised using non-contact 3D-surface texture analysis. A first step towards a grading system of the polishablility was made based on a classification of surface defects detected on included steel samples. 3D surface parameters based on interferometer measurements seemed to be useful for a characterisation, even though further studies (involving different filters and segmentation methods) are needed to find less and more precise parameter values to grade tool steel qualities. Future work will include analysis of surface measurements of test moulds and plastic parts, as well as studies of how quantitative parameters can be linked to qualitative estimations in order to better understand how surface features on the mould are transferred into the surface of plastic components.

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