| Posted: December 27, 2007 |
Dry machining enhanced by superhard nanocomposites |
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(Nanowerk News) Dry machining is cost-saving in a sense that neither coolants nor lubricants are involved in the machining progress, hence saving 20% to 30% of total machining costs.
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For dry machining, high hardness and high oxidation-resistance are both important. That's why superhard nanocomposites, which represent a new, advanced generation of wear protective coatings boosting such advantages as high hardness and high oxidation, are important to dry machining, according to Professor Stan Veprek of the Department of Chemistry at the Technical University of Munich.
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Speaking at the recently held 2007 International Conference & Exhibition on Nanotechnology and Advanced Materials, Professor Veprek referred superhard nanocomposites to those that consists of 3-4nm small nanocrystals of a hard transition metal nitride "glued" together by one monolayer of thin Si3N4 interfacial "tissue".
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When correctly prepared and free of impurities, the superhard nc-TiN/a-Si3N4 composites attain high hardness of at least 100 Gpa while featuring high elastic recover, high elastic limit, high resistance against brittle fracture, high thermal stability and oxidation resistance.
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Professor Veprek said that in dry drilling and milling of steel, for instance, the lifetime of the nc-(Ti1-xAlxN)/a-Si3N4 coated tools is typically three to four times longer than that of the same tool coated with (TiAl)N coatings. The resulting reduction of the maintenance and personnel costs further improves the productivity.
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In the case of hobs, which are used for machining the wheels of gears, the lifetime of the hobs coated with nACRo [superhard nanocomposites
(nc-(Ti1-xCrx)N/a-Si3N4] is significantly longer than that of their counterparts coated with AlCrN (=Al1-xCrxN), and about seven times longer than that of hobs coated with TiCN-TiN. The advantage of the nc-(Ti1-xCrx)N/a-Si3N4 nanocomposites as compared with the solid solution (Al1-xCrx)N coatings is a second hardness maximum of not less 40Gpa at a low content (3% to 5%) of chromium, which is of some environmental concern.
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Used in hole drilling in Airbus 380
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Professor Veprek also mentioned, as an interesting example, the drilling of holes in the wings of the new Airbus 380 airplanes. The wings are made of a material consisting of a combination of graphite fibers reinforced carbon and aluminum alloy, and the only tools that can be used so far are drills made of cemented carbide and coated with polycrystalline diamond. To increase the life of the drills, UNIMERCO developed special nanocomposite coatings that can be used two times longer than polycrystalline diamond coatings.
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Moreover, the nanocomposite coatings, after reaching their lifetime, can be stripped off, and the drills, which cost several hundred euros, can be re-grinded and re-coated several times. This is not possible with the diamond coatings. In such a way, the actual lifetime of the tool is increased by a factor of 7 to 10 as compared with the same tool coated with the diamond coatings.
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