Temperature measurement when high speed machining hardened mould/die steel

When turning and face milling hardened (>30 HRC) mould/die steels, it is necessary to use conventional ceramic or polycrystalline cubic boron nitride (PCBN) tool materials. The use of high speed steel and cemented tungsten carbide (WC) tooling for this application is precluded due to their relatively low hot hardness values. In recent years, however, the mould and die industry has begun to utilise solid WC ball nose end mills for the high speed machining (HSM) of hardened steel cavities. Economic tool lives have been reported at high rotational speeds/feed rates.The paper details the use of 6mm diameter solid, TiCN coated WC ball nose end mills for the HSM of a hot work tool steel, AISI H13, hardened to 52 HRC. Tests were performed on a Matsuura 20 000rpm high speed machining centre and temperatures were measured using thermocouple and infrared techniques. Recorded tool /workpiece interface and chip temperatures were relatively low (200–400°C) and increased with higher cutting speed, when using worn rather than new tools and with the workpiece inclined at 60° to simulate finishing operations on the side of die cavities.