Page 7 - Diamond tools

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Introduction to the world of ultra-hard cutting materials
Monocrystalline diamond
Monocrystalline diamond (DM or workshop name MCD) is the hardest of all materials and is mostly used for the finest work. Extremely accurate cuts with a radius smaller than 1 μm enable surface finish accuracies lower than RZ 0.02 μm. During chip removal, the cutting edge sharp- ness creates very low cutting pressure without any heat build-up. Therefore, the monocrystalline diamond has maximum wear resistance and consequently the tool has a long service life. If, on the other hand, fillers (e.g. Si, SiC or glass fiber) are included, the cutting edge geometry can be quickly destroyed due to a lack of toughness. A monocrystalline diamond consists of pure carbon and is thermally and chemically stable up to 650°.
As diamond monocrystalline-direction-dependent me- chanical strength properties indicate, the diamonds have to be incorporated in such a way that maximum dura- bility is achieved. Diamond tools are highly suitable for machining non-ferrous metal alloys, such as gold, plat- inum, brass and silver, as well as aluminum and solid plastics.
Polycrystalline diamond
Polycrystalline diamond (DP or workshop name PCD) is a cutting material on a cemented carbide core, onto which firstly a thin metal layer and then a 0.5 to 1.5 mm thick layer of synthetic diamond powder is sinter-fused. Because of the polycrystalline structure, DP is isotropic (direction-independent) and therefore its mechanical strength properties are not direction-dependent. Cut- ting speed is virtually half that of monocrystals, but the feed rate can be increased ten times. As opposed to monocrystalline diamonds, PCD has a higher level of durability, but lower wear resistance and poorer micro-cutting edge quality.
Chemical vapor deposition (CVD)
DThis high-tech cutting material for chip removal outclasses PCD in terms of wear resistance, durability and achievable surface quality.
Synthetic crystalline diamond deposits are isolated from a gas phase which generally consists of 99% vol. hydrogen and only about 1% vol. pure carbon source (methane, acetylene).
The gases are either activated thermally or with the aid of a plasma or laser unit. Amongst other things, the excess of hydrogen suppresses the bonding of sp-hybridized carbon species (graphite, amorphous carbon).
Highly abrasive materials can be cut with the turning, mill- ing and drilling diamond tools manufactured in this way. These include electrode materials, hard coal, graphite and copper, modern lightweight materials such as alumi- num-silicon alloys, metal-matrix composites, fiber-rein- forced plastics and wooden materials.
Polycrystalline cubic boron nitride (BN or workshop name CBN)
Polycrystalline cubic boron nitride (BN or workshop name CBN) is mainly used for machining hard and abrasive ferrous materials with a hardness of up to 68 HRC, as, unlike the super-hard cutting materials DM and DP, it does not react with iron and has a heat resistance of up to 2000°C. BN is either manufactured as a coating of up to 1.5 mm in thickness by means of so-called high-pres- sure liquid phase sintering on carbide plates or as a solid body. As a rule, titanium nitride or titanium carbide are used as the binder phase.
The following overview can be used to select suitable cutting materials and cutting edge geometries. The com- bination of material group and application range indicate the appropriate cutting material.
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