Abstract Ceramics, as a non-metallic tool material, can be used as an industrial tooth in the field of metal cutting because it can achieve high hardness material cutting and high-speed cutting. This paper is based on the type and performance of ceramic tools (including cubic boron nitride tools). , talk about their use difference and...
As a non-metallic tool material, ceramics can be used as industrial teeth in the field of metal cutting because of its ability to cut high-hardness materials and high-speed cutting. According to the type and performance of ceramic tools (including cubic boron nitride tools), Discuss their differences in use and their suitable materials.
First, the type and development of ceramic tools
Types and development of ceramic knives: The most obvious development of ceramic knives is the enhanced toughness of the blades: alumina ceramic knives - composite alumina ceramic knives - silicon nitride ceramic knives - cubic boron nitride knives.
In the field of metal cutting, alumina ceramic tools and silicon nitride ceramic tools are collectively referred to as ceramic tools; in inorganic non-metal materials, cubic boron nitride materials are attributed to ceramic materials, and cubic boron nitride materials are available. The revolution of ceramic knives. As one of the earliest research institutes in China to study polycrystalline cubic boron nitride material tools, Henan Institute of Superhard Materials recently introduced a pure boron nitride sintered ceramic tool, which has significantly increased toughness and wear resistance.
Second, the performance of ceramic tools and its application in metal cutting
Compared with cemented carbide inserts, ceramic tools can withstand high temperatures of 2000 ° C, while hard alloys become soft at 800 ° C; so ceramic tools have higher temperature chemical stability and can be cut at high speed, but the disadvantage is alumina ceramics. The strength and toughness of the tool is very low and it is easy to break. Because ceramic tools are resistant to high temperatures, they are more favorable for high-speed high-speed cutting. Because ceramics have low thermal conductivity and high temperature only at the tip of the tool, the heat generated by high-speed cutting is carried away with the chips, so most researchers believe that alumina ceramic tools can And it is better to cut at 10 times the linear speed of the carbide cutting to truly reflect the advantages of the ceramic tool.
In order to reduce the sensitivity of ceramic tools to crushing, in order to improve their toughness and improve impact resistance, zirconia or a mixture of titanium carbide and titanium nitride is added. Despite the addition of these additives, the toughness of ceramic tools is much lower than that of cemented carbide inserts.
Another way to improve the toughness of alumina ceramic tools is to add crystalline texture or silicon carbide whiskers to the material. These special averages are only 1 nanometer in diameter, 20 micrometers long and strong whiskers, and the ceramics are considerably increased. Toughness, strength and thermal shock resistance. It is limited by its impact toughness and has been used in the field of precision machining.
Like alumina ceramic tools, silicon nitride ceramic tools have higher thermal stiffness than carbide inserts. Its high temperature and mechanical impact resistance is also good. Compared with alumina ceramic tools, its disadvantage is its insufficient chemical stability when processing steel. However, gray cast iron can be processed at a speed of 1,450 ft/min or higher using a silicon nitride ceramic tool.
Suitable processing materials for ceramic tools: Ceramic tools cannot be used for machining aluminum, but are particularly suitable for gray cast iron, ductile iron, hardened steel and some unhardened steel and heat resistant alloys. However, for these materials, the successful application of ceramic tools requires the appearance of the blade edge and microscopic quality assurance, and requires the best cutting parameters.
Third, the performance and application of cubic boron nitride tools
The hardness of cubic boron nitride cutters is much higher than that of ceramic tools. Due to its high hardness, it is also called superhard material with diamond. It is commonly used to process materials with hardness higher than RC48. It has excellent high temperature hardness - up to 2000 ° C, although It is more brittle than cemented carbide blades, but its impact strength and crush resistance are significantly improved compared to ceramic tools. At present, cubic boron nitride (CBN) tools are the best tool materials for wear resistance in the field of ferrous metal processing. It has been demonstrated that the life of cubic boron nitride tools is generally several times to several times for carbide blades and ceramic tools. Ten times, for example, Valin super-hard BN-S30 grade cubic boron nitride tool processing gray iron brake disc, cutting line speed 600M / min, 2 times better than cemented carbide blade, 6-12 times longer than roughing The life of finishing is 15-20 times that of cemented carbide inserts; and with the advancement of research, CBN tools are suitable for the processing of various high-hardness complex materials. Hualing super hard HLCBN newly developed CBN tool grade can process HRC70 The above hardness of tungsten carbide is the first in China.
In addition, some special cubic boron nitride tools (such as Valin Super Hard BN-S10 and BN-S20 grades) can withstand the chip load of rough machining and can withstand the impact of intermittent machining and finishing. Wear and cutting heat, these characteristics can meet the difficult processing of hard materials such as hardened steel with cubic boron nitride tools. The BN-K1 grade in the HLCBN series is widely used in gold processing of high hardness and wear-resistant castings such as mining machinery and metallurgical rolls because of its excellent impact toughness.
Pure Boron Nitride Sintered Blade: The latest development of Hualing Superhard is a blade made of pure boron nitride material with a CBN content of 100%. The boron nitride ceramic tool formed by pure sintering has hardness and The thermal conductivity ratio is higher. When cutting high-hardness ferrous materials, the blade edge does not suffer from common thermal cracking and chipping. Compared with CBN sintered bodies containing other bonding materials, the time of use of boron nitride ceramic tools can be Extend more than 6 times.
Cubic boron nitride cutter is suitable for processing materials: gray cast iron, all kinds of wear-resistant cast iron, cast steel, high hardness material processing (such as hardened cold work tool steel, high speed steel, bearing steel, powder metallurgy steel, high strength steel, high manganese Steel, high chromium cast iron, white cast iron, austenitic iron, hard alloy, etc.
Fourth, the difference between ceramic tools and cubic boron nitride tools
Although cubic boron nitride belongs to ceramics in material science, ceramic tools are not as good as cubic boron nitride cutters due to the difference in properties of CBN, SIN, Al2O3, and SiN materials. Therefore, according to the difference of hardness and toughness, ceramic tools are better choices when quenching steel workpieces with cutting hardness below 50HRC and small depth of cut and small feed. Cubic boron nitride tools are more suitable for workpiece hardness higher than 50HRC. In addition, it should be noted that ceramic tools and traditional inlaid boron nitride inserts are rarely used in roughing. Only some grades of boron nitride inserts such as BN-S20 are suitable for roughing and interrupted cutting.
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