High-speed milling of AISI H13 hot-work tool steel using polycrystalline cubic boron nitride ball-nose mills: From experimental investigations and empirical modelling to functional testing of the machined surfaces

Abstract

Owing to continuous development of composite materials, the properties of polycrystalline cubic boron nitride (PCBN) can be engineered to enable their use for the manufacture of cutting edges for high-speed machining applications. This paper reports on an ‘integrative’ approach, i.e. cutting parameters—tool performance—surface integrity and residual stresses—tribological and fatigue assessment, of the high-speed milling (HSM) of AISI H13 hot-work tool steel using PCBN ball-nose end milling cutters. The experimental trials followed an experimental design (factors: cutting speed, feed per tooth, workpiece tilt angle) on which a set of key process output measures was examined: tool life, surface roughness, metallurgical integrity, microhardness, and residual stresses. Where significant variations in the output measures with the changes in the operating parameters were found, empirical models were generated; this is of particular importance for the mould/die industry to enable the prediction of critical process measures such as tool flank wear, surface roughness, and residual stresses under machined surfaces without the need for repeated measurements. It was found that only a compromise of the ‘near-best’ values of the output measures can be obtained by employing a ‘pseudo-optimal’ set of cutting parameters. Further, functional tests carried out on HSM surfaces with ‘near-best’ output measures using PCBN tools showed that superior fatigue performance (approximately 30 per cent) is expected for moulds/dies when compared with those obtained via the conventional manufacturing route (electrical discharge machining and polishing).