here is that harder tool substrates are more brittle and more likely to fracture or break under adverse operating conditions. Softer tool substrates mean the tool will be tougher, allowing successful machining even under adverse conditions. Although, tougher substrates are less likely to fracture or break, they operate at lower performance parameters and so tool life is not as long. An ideal cutting tool material should resist flank and point wear, as well as deformation, be tough to resist breakage, does not chemically interact with the work piece material, resist oxidation and diffusion and have good resistance to sudden thermal changes. Inserts are made from tungsten carbide, which is the most commonly used material for indexables. Other available material used for inserts includes cermet (CT), ceramics (CC), cubic boron nitride (CBN) or polycrystalline diamond (PCD). CT has good flank and crater wear resistance and is not prone to built-up-edge. Because of this, the cutting edge maintains its sharpness over a longer time. CC has a wide application area in cutting hard materials (45-55 HRc) and has high resistance to abrasive and thermal conditions. CBN is an excellent cutting tool material and offers extremely hard high thermal resistance. CBN is utilized in materials such as hardened steels and cast iron. PCD exists in two types (natural diamond or industrial diamond) and is utilised for non-ferrous materials, such as high silicon aluminium due to its high resistance to wear. As PCD is extremely hard and brittle, it is not a good choice for high hardness or impact applications. Material – rotary Round tools are traditionally made from high speed steel (HSS), high speed cobalt (HSCo or HSS-E) or solid carbide. Carbon, chromium, tungsten, molybdenum, vanadium and cobalt all make up the main alloy elements used within high speed steel cutting tools. HSS is a medium alloy that has good machinability and performance. It offers toughness and is a cost-effective option for a wide variety of large scale drilling and threading applications in multiple materials. However, it is not very wear resistant and so not suited to demanding, difficult conditions. Cobalt high speed steel offers a good combination of toughness and hardness, providing good machinability and wear resistance. This makes the material suitable for drills, taps, milling cutters and reamers. Solid carbide is the most widely used and wear resistant cutting tool material today and is suitable for both round tool and indexable applications. Performance and versatility – indexable From a cost perspective, indexable inserts and tool holders represent a significant investment, however, they have the potential to last for longer periods of time. Also, when a replacement is needed, this is more time and cost efficient because of the need to only rotate or change the insert. To support the long-term investment of indexable inserts, they are also Milling machine working on steel. The new turning chip breaker HR2 is for heavy roughing. www.engineeringnews.co.nz 25
EN feb17 Digi5
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