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Diamond and CBN Grinding Tools |
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Grinding tools with diamond or CBN abrasive grits usually consist of a basic body on which the abrasive layer, i.e. the grits and bond, is applied in different ways.
For WENDT grinding tools abrasive and dressing grits of diamond and CBN (cubic Boron Nitride) are used. Both natural and synthetically produced diamond is used whilst CBN is always synthesised product. Besides the cubical crystal structure and its resulting cutting edge formation, the chemical and physical properties are decisive factors in the grinding applicability of the diamond and CBN grits. Diamond is considerably harder than CBN but much more sensitive to temperatures above 700°C and it is strongly reactive with iron materials. Therefore CBN is the most suitable grit for grinding steel and similar materials. Besides the grit size the influence of the grit quality which is manifold and needs a detailed analysis of the requirements. WENDT provides corresponding information to make the selection easier.
Generally valid correlation between the tool quality, grinding behaviour and the grit quality can only be given to a very limited ex-tent and in most cases only in relation to special cases of application. In general, however, the following applies: A friable grit type improves the cutting ability of the grinding wheel while it usually results in a deterioration of the achievable surface quality. Whereas a blocky grit type improves the service life of the grinding wheel and, in many cases, the achievable surface quality, however, it deteriorates the cutting ability. Often the grits are coated (Cu, Ni, Ag, Ti) to improve the bonds ability to hold the grits, the heat transfer and the chemical and mechanical properties.
The bond is of equal importance as the abrasive grit for the performance of the grinding tool. In consideration of the operating conditions applied both have to be match to each other in such a way that the abrasive grits are held in the bond as long as they still have or generate cutting edges. When the grits are worn and become unusable as an abrasive, they have to be released from the bond. A grinding wheel adapted in this way gives durability with the highest performance, low wear and reduced grinding forces.
If the worn grit remains in the bond too long, the grinding wheel loses its cutting ability after a short time. If, on the other hand, the bond wears faster than the abrasive grits or it does not hold them long enough, the abrasive grits cannot be fully utilised and the service life of the grinding wheel is reduced. In particular cases it may be necessary to adapt the grinding wheel to optimise it to the specific application parameters.
WENDT grinding tools are mainly applied in resin, sintered metal, vitrified and electroplated bonding systems.
Resin Bond
The resin bond has proved a success in almost all fields of grinding hard materials and steel. High cutting capability with low grinding forces in dry and wet grinding characterise this type of bond and allow a great scope for adaptation. The basis of this bond system are, for the most part, phenolic or polyimide resins. In particular cases special resins are also used. The extreme flexibility of the bonds properties is achieved by adding a mixture of suitable additives.
Sintered Metal Bond
Grinding tools in sintered metal bonds often consist of bronze and iron compounds to which suitable additions are admixed. They are used in applications requiring particularly high wear resistance and profile stability. Due to the generally high active forces the material removal capacity is lower than that achieved with resin bonds. The exception is the special sintered metal bonds, which are used, for an example, for profile crush forming. These bonds have a particularly good cutting ability and distinguish themselves by a high material removal capacity.
Vitrified Bond
Ceramic bonds are composed of mineral raw materials. Ceramic bonds are used in the production of abrasive layers with a defined porosity of approx. 2% to 40%. This allows for an extremely wide spectrum of applications. The tools in ceramic bond stand out for their particularly good dressing and profiling ability, low wheel wear together with low grinding forces and high qualities of the workpiece surface.
Electroplated Bond
The electroplated or galvanic bond constitutes a special type of metal bond. As bonding material mainly nickel is used, in special cases also cobalt, which is deposited electrolytically over a layer of grits on a metallic tool body in a galvanic bath. The advantage of electrolytically bonded grinding wheels is their extremely high cutting ability and grinding performance. Galvanic tools are used for pregrinding complex profiles with high material removal rates and for finish-grinding with high accuracy,
e.g. in the gear grinding industry.
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