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New coating makes tool products more powerful Release time：2020-08-12　　　　 Time to browse

　　Due to the high surface hardness of coating tool, grinding ratio with ordinary grinding wheel is small, heavy grinding is difficult, many operators put it as a non-regrinding tool and discarded, causing a great waste. Coating tools are used to coat a thin layer or multiple layers, even up to more than a thousand layers of refractory metal or nonmetal compounds with good wear resistance, such as TiC, TiN, TiCN, TiAlN, Al2O3, C3N4, MoS2, DLC and diamond, on the surface of hard alloy or high speed steel (HSS) with good strength and toughness. Can be coated with a single coating, can be coated with composite and multi - coating. A high speed and powerful drill bit from Sumito-Electric Corporation of Japan is interactively coated with 1000 TiN and AlN nanometer thin films on a tungsten-cobalt type cemented carbide substrate with a total coating thickness of about 2.5 m. Zx-coated end mills developed by the company have up to 2,000 ultra-thin layers, each about 1 nanometer thick, thus resolving the contradiction between the higher hardness and wear resistance of the tool material and the lower strength and toughness. The coating ACTS as a chemical and thermal barrier, reducing the diffusion and chemical reaction between the tool and the workpiece, thus reducing the depression of the crescent moon. Coated tools with high surface hardness, good wear resistance, chemical stability, heat and oxidation resistance, friction coefficient and low thermal conductivity characteristics, than uncoated cutting tools to improve the service life of 3-5 times more than 20%-70%, improve the cutting speed, improve the machining accuracy 0.5-1 level, reduce the cost of cutting tool consumption 20%-50%. Therefore, coated tools have become the hallmark of modern cutting tools. The proportion of coated tools used in industrialized countries has exceeded 70%, and 80% to 85% of the tools used in CNC machine tools (NC) and machining centers (MC) in the United States are coated tools. At present, all kinds of cutting tools, including turning tool, boring tool, drill, reamer, broach, tap, thread comb tool, hobbing head, milling cutter, forming cutter, gear hob, gear shaper and so on, can be used to improve their performance by coating process. It must be pointed out that coating tools in the use of a mistake, due to its high surface hardness, when the tool wear or coating peeling, due to the ordinary grinding wheel grinding ratio is small, heavy grinding difficult, many operators will put it as a non-regrinding tool and discarded, resulting in a great waste. The coated tool must be reground after wear. When the coated tool is resharpened, all the worn parts on the tool should be ground away. For resharpening only on the surface of the knife before cutting tools (such as forming milling cutter, broach, forming tool, the gear hob and gear shaper cutter, etc.) or just after grinding on the surface of the knife cutting tools, such as drilling and reaming, etc), if in its adjacent another knife cutting edges of the surface (such as drill screw out crumbs slot) on the coating is not damaged, cutting tool wear resistance can be improved. After the new grinding coating tool, the tool service life can reach the original new coating tool life of about 50% or longer, is still higher than the life of the uncoated tool. For grinding wheels coated with carbide tools, diamond wheels may be used. But when grinding coated high speed steel tool, the cubic borax wheel grinding has a better effect. The wear of the tool should be completely ground away. The coating should not peel off, but the tool should not be annealed. An important issue in the use of coated tools is the restoration of tool cutting performance after regrinding, that is, whether the tool can be recoated (recoated) after each cutting edge grinding (opening). Table 1 shows the wear resistance test results of coated HSS gear hob and gear shaper after regrinding and repainting the tool surface. After coating and repeated coating, the service life of gear hob and gear shaper cutter is obviously improved. The actual test shows that the film thickness does not increase obviously on the repeated coating surface of the gear hob and gear shaper, but the gear machined by the tool after repeated coating can still meet the precision requirements specified in the drawing. After the gear hob has been coated for 17 times, the cumulative total thickness of the coating film is still only 5-6 m, and the coating film is uniform on the surface of the tool, the newly coated film and the original coating form a metallurgical bond, there is no discernible boundary layer between the two, and no obvious holes. Repeated coatings are also effective for other tools such as twist drills, reamers, and end mills. Coating tool recoating, in addition to the use of the original coating material, also can use new coating material. The practical application shows that the cutting speed and the service life of the tool will be improved obviously if the new TiAlN coating material is used in the re-coating of TiN coated tool. In addition, coating tool service life and film thickness also has a certain relationship. If the tool surface wear is the reference, the tool life will increase with the increase of film thickness, but the film thickness reaches saturation at 5 m, that is, the tool life will not increase significantly. If the previous tool surface depression depth for the tool life benchmark, tool life and film thickness is proportional to no saturation phenomenon. However, when the film is too thick, it is easy to cause spalling, so now the coating thickness of the tool generally does not exceed 5-10 m. For the heavy grinding of the forming tool, also only for repainting, to ensure that the total life of the tool to increase 3-5 times more. Where the recoating tool must first according to the process requirements of the geometric parameters of the grinding, the polishing part is not allowed to exist a variety of quality defects, such as grinding, burr. When recoating, local shielding technology can be used to coat only the grinding surface. For the recoating without shielding technology, in the recoating 4-6 times, the non-edge grinding surface coating thickness of the tool will be too large, thus affecting the accuracy of the tool and the occurrence of local peeling phenomenon, at this time to take off the tool after recoating treatment. The cutting performance of the tool after recoating is generally not lower than the first new coating tool, the tool can be recoated many times, until the scrap. From the above, recoating to improve the wear resistance and productivity of the tool is a great potential. In general, cemented carbide manufacturers can generally be recoated. At present the business in mainland China and specialized coating company, for example in the joint venture on the susquehanna coating co., LTD, which is a large coating service center, with specific tool coating, grinding and painting services, the company has introduced the four sets of coating equipment, AlTiN coating S - (super nitrogen titanium aluminum), S - TiN (super titanium nitride), TiCN, DLC, CrN coating. But the coating tool after grinding whether to repaint, but also to see the tool in the technology can be repainted and whether it is economical. As far as tools are concerned, great breakthroughs have been made in coating technology, superhard materials, CAD/CAM software, etc., especially in the rapid development of coating technology. So, tool enterprises and coating enterprises in this respect have made what kind of efforts? Iska: direct to "fast metal cutting" to improve tool performance, the most basic direction of research and development is to improve tool materials. This involves two aspects: substrate and coating. The basic property of cemented carbide matrix is that the higher the toughness is, the lower the wear resistance will be. And vice versa. Therefore, when intermittent cutting, such as milling, discontinuous turning, can choose a high toughness matrix; When continuous finishing is carried out, the matrix with high wear resistance should be selected.