Micromilling of hardened tool steel for mould making applications

The implementation of replication techniques for mass production of microcomponents relies on the availability of tooling technologies for manufacturing of tools and moulds. Micromilling is a suitable technique for manufacturing of microstructures characterized by high aspect ratios and complex geometries as those characterizing injection moulding moulds. The realization of the micromilling process in connection with hardened tool steel as workpiece material is particularly challenging. The low strength of the miniaturized end mills implies reduction and accurate control of the chip load, which requires high positioning accuracy. Size effects, mainly related to the microstructure of the workpiece material and to the limited scalability of tool geometry and surface topography, critically influence the performance of the process in terms of part accuracy, surface roughness, cutting forces and tool wear. This paper presents the micromilling process applied to the manufacturing of microinjection moulding moulds in hardened tool steel, presenting experimental evidence and possible solutions to the above-mentioned issues.