The latest cutting tool materials promote the deve

2022-08-21
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New tool materials promote the development of cutting technology

over the past decade, high-speed machining technology has been developed from research and development to promotion and application in production, as well as the rise of dry cutting and hard machining to the gradual expansion of application fields, which marks the great progress of cutting technology. The application of these advanced cutting processes has greatly improved productivity and machining accuracy, significantly reduced manufacturing costs, and promoted the simplification of parts manufacturing process flow and the reform of production mode

The great progress of cutting technology is the inevitable result of the continuous development and considerable progress of tool materials. Due to the optimization of tool materials, the improvement of manufacturing process and grain refinement, especially the rapid development of coating technology, the tool performance is continuously improved, and then the cutting speed is continuously improved (Fig. 1) and the spindle speed of machine tool is continuously improved. The combination of cutting tool technology and machine tool technology promotes cutting technology to enter a new stage of development

it can be seen that the popularization and application of new tool materials plays a decisive role in promoting the development of cutting technology. Ideal tool materials have both extremely high hardness and high toughness (Fig. 2), and tool materials are always developing towards this goal

Figure 1 development of cutting speed of different tool materials

Figure 2 performance of tool materials

superhard tool materials

polycrystalline diamond (PCD) and cubic boron nitride (CBN) are increasingly becoming "ordinary" tool materials

pcd has particularly high hardness (hv30:5000) and wear resistance. It has high productivity and process reliability when used to process non-ferrous materials such as aluminum alloys. For example, the WWS cutter factory of Mapai company has launched a PCD face milling cutter with a cutter body made of high-strength aluminum alloy, and its cutting speed can reach 6500 m/min (cutter diameter 80mm) and 8600 m/min (cutter diameter 200mm)

the hardness of CBN (hv30:4300 ~ 4600) is second only to that of PCD. Due to its good thermal stability, CBN is suitable for processing hardened steel, chilled castings and spray welding materials. At present, when machining castings with CBN tools, the cutting speed can be as high as (2000 ~ 4000) m/min, and the cutting speed for machining nickel base alloys can also be as high as 300m/min. Some tool factories developed fine grain CBN (2 m), CBN content (50 ~ 55)% and ceramic bonding, which further improved the strength of the blade, making CBN tools more suitable for hard machining (45hrc ~ 63hrc) and dry cutting

cbn is used in grinding. The circumferential speed of CBN grinding wheel is (90 ~ 250) m/s, which greatly improves the grinding rate of materials, significantly shortens the grinding time, and makes the precision technology used to manufacture high-quality functional surfaces develop into a general processing technology for a long time. For example, when grinding camshaft on Centerless Grinder, the grinding allowance is 4.1mm, the grinding speed is 90m/min, and the grinding time is only 12s, while the shaft diameter tolerance can reach 20 m, the roundness is 8 m, and the surface roughness Rz is 40 m. The number of workpieces processed during the service life of the grinding wheel exceeds 500000 camshafts

ceramic tool materials

among ceramic tool materials, alumina (Al2O3) is mainly used for rough and finish machining of castings. In addition to Al2O3, mixed ceramics also contain tic or tin, which improves the hardness, heat resistance and wear resistance. In addition, it also improves the heat shock resistance and blade strength. At present, the developed mixed ceramic tools with fine grain and high toughness and tin coating can be used for wet and dry hard turning or milling hard materials. Silicon nitride (Si3N4) ceramics have good toughness and heat resistance, and are suitable for turning, milling and drilling castings. When milling the cylinder block with the milling cutter made of this tool material, the cutting speed can reach 1500m/min; Using an integral Si3N4 drill bit to drill a hole with a diameter of 14.5mm and a depth of 35mm on the brake disc of a truck, the cutting speed is 410m/min, and when the feed rate per revolution is 0.16mm, the basic time for machining a hole is only 1.46s. At present, due to the improvement of the properties of Si3N4 based ceramic materials, the cutting tools of this material are also used for high-speed machining of nickel resistant alloys (inconel706, Inconel718, udimet720), and can obtain very strict manufacturing tolerance and high machining reliability

Table 1 performance of coated cemented carbide tools

Ultra Fine Grain Cemented Carbide + TiAlN coated hard milling and hard drilling

cutting speed m/min

feed per revolution (mm/r)/feed per tooth (mm/z) 0 2 0.. 1

average roughness Rz m

cemented carbide

tungsten cobalt (WC) based cemented carbide mainly has two development directions, one is to develop fine and ultra-fine grain cemented carbide; The second is to develop coating technology to improve the hardness and toughness of cutting tools through the combination of Fine Grain Cemented Carbide and hard coating. In the past, the toughness of cemented carbide was improved by increasing the content of CO, but with the increase of CO, the hardness of cemented carbide will decrease. Nowadays, more and more refined grains can be manually operated by the common hydraulic universal testing machine to compensate for the negative effect caused by the increase of CO content

the bending strength of ordinary cemented carbide is (1000 ~ 3400) n/mm2, while the bending strength of ultra-fine grain cemented carbide can reach 4300 n/mm2. This is higher than high-speed steel [(2500 ~ 3800) n/mm2]. Therefore, this kind of ultra-fine grain cemented carbide has high hardness, fatigue strength and impact resistance, and the blade can be ground very sharp. It can be used to make small-scale drill bits (diameter can even be as small as 0.5mm) that used to be made of high-speed steel, end mills, screw threads and other tools. Thus, the application range of hard Gongfu alloy is greatly expanded

at present, the hardness and toughness can be greatly improved by nano grain cemented carbide, but this kind of cemented carbide is very expensive and difficult to be popularized and applied

The combination of Fine Grain Cemented Carbide and coating is another important aspect of the development of cemented carbide tools at present. The fine grain tool matrix with high toughness deposits different coatings for specific processing tasks through CVD or PVD process, so that this coated cemented carbide tool has both high bending strength and wear-resistant surface. If TiAlN hard coated cemented carbide tools with high high temperature hardness and poor thermal conductivity are used, they can be used for hard milling and hard drilling (Table 1), and can replace CBN tools, which obviously expands the application range of cemented carbide

due to the coordinated development of cemented carbide tool materials and coating technology, it accounts for the vast majority of the current tool materials. According to the statistics of 1998, cemented carbide accounts for 78% of the total tool materials (excluding high-speed steel) in the world, of which CVD coated tools account for 43% and PVD coating accounts for 10%

at present, the hardness and toughness can be greatly improved by nano grain cemented carbide, but this kind of cemented carbide is very expensive and difficult to be popularized and applied

tic/tin based cemented carbide

tic/tin based cemented carbide has experienced several generations of development, mainly by increasing the content of nitrogen to improve the hardness and bending strength. Compared with WC based cemented carbide, it has better high-temperature hardness, high blade strength and small friction coefficient. It is especially suitable for finishing or semi finishing steel parts and castings with high cutting speed and small cutting depth. It can obtain high surface quality, stable dimensional accuracy and long tool life

this kind of cemented carbide tool can finish turning steel parts with a cutting speed of up to 400m/min (milling: 300m/min), and the turning speed of gray castings can reach 450m/min (milling: 250m/min)

Table 2 performance comparison of hard coating and soft coating

coating material coating thickness m microhardness hv0.05 oxidation resistance ℃ friction coefficient

hard coating

tin -500 -0.4

ticn -400 0 4

TiAlN -800 0.. 4

TiAlCrYN -950 0.. 4

CrN -1750 its excellent toughness helps to ensure that the rib parts of the water inlet (outlet) fasteners of the polimotor 2 can maintain a reliable seal without cracking -700 -0.5

soft coating

WC/C -1100 -300 2500hv), and the soft coating has a very small friction coefficient

fraisa company of Switzerland has developed a new coating process, which should slowly and safely rise to the regular voltage value when applying voltage. Different coatings are deposited in front and behind the tap, that is, a heat-insulating hard coating is applied behind the tap, which is mainly subject to abrasive wear, and a nano sliding layer is applied in front of it. In this way, most of the heat generated by the tap during tapping can be taken away by the clinging spiral chips

multi coating is more and more widely used. At present, the number of coatings is even more than 20. Through the combination of different coating materials, it can inhibit chip buildup, cracks and edge collapse, improve the wear characteristics of the tool and improve the heat shock resistance

among the multi coatings, titanium based (ti-) coatings are mostly used: tin+ticn+tialn, tin+ticn+al2o3, etc. For example, the multi coating tool with TiAlN as the covering layer has high hardness and outstanding oxidation resistance by only operating for a few minutes, which makes this multi coating tool particularly suitable for dry milling of steel parts (cutting temperature>600 ℃)

as another example, depositing a layer of zirconium carbonitride on tin+ticn+al2o3 can inhibit the propagation of cracks

at present, the combination of hard coating and soft coating applied to dry cutting is an important way to make the dry cutting strategy a reality. For example, a layer of wc/c soft coating with medium hardness is covered on TiAlN. Because the friction coefficient of this soft coating is very small, it helps to prevent chip buildup and reduce cutting force when processing plastic metal materials

with the development of nanotechnology, manufacturing nano coatings can further improve the hardness and thus improve the wear resistance of tools, which makes it possible to abandon welded cbn/pcd tools. For example, cemecon company in Germany adopts diamond nano coating to significantly improve the durability of cutting tools

conclusion

the continuous development, popularization and application of new tool materials have greatly improved productivity and extended tool life. Promote the development of cutting technology to high-speed machining, hard machining and dry cutting. Mark cutting technology is undergoing profound changes. The grain refinement of tool materials, especially the development of nanotechnology, will bring changes to tools. The combination of coating technology and Fine Grain Cemented Carbide Tool Matrix greatly expands the application range of cemented carbide

The innovation of cutting technology, the substitution of different tool materials and different machining processes, the simplification of process flow and the continuous development of machine tool technology all fully reflect the technological progress brought by the development of new tool materials

therefore, strengthening the development and application of tool materials and coating technology is an important condition for accelerating the development of machinery manufacturing industry

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