Machining of sinterhardened alloys is an extremely difficult proposition, with limited choices in terms of tooling and cutting conditions. The presence of martensite in the microstructure results in significant abrasion and diffusion wear on the insert, as cutting speeds and feeds increase. Increases in alloying and machining costs for sinterhardened materials have led manufacturers to reconsider heat-treated PM parts, which are rough machined in the sintered state and finish-machined or ground after the heat treatment.In the current work, a new cryogenic cooling method of machining sinterhardened materials is proposed, that has significantly reduced overall machining costs. Cryo-cooling has been shown to increase tool life significantly through a reduction of tool temperature near the workpiece-tool interface, thereby increasing the hardness and toughness of the insert. Cutting speeds and throughput can therefore be increased without the risk of tool overheating and accelerated wear. The reduced machining costs and improved dimensional tolerances of sinter-hardened parts allow this process route to remain cost-comparable to that of heat-treated material. Machining process costs could be further reduced through the addition of a small amount of Hoeganaes machining additive (MA), which has been shown to significantly enhance machinability of these sinterhardened materials over additive-free samples, as well as ones containing similar amounts of manganese sulfide (MnS).
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