The traditional ceramic materials are generally derived from nature, for example, soil of Jingdezhen can be made into various commodities after mixing, forming and roasting. However, the modern high-tech ceramics (also called special ceramics), of which the material is synthetic. For example, silicon nitride powder, which has high purity, can be made into products that have high hardness and high temperature resistance by using modern powder metallurgy technology.
The variety and development trend of ceramic tip
The tenacity of ceramic tip will enhance successively in the following sequence: aluminum oxide ceramic tip-composite aluminum oxide ceramic tip-silicon nitride ceramic tip-cubic boron nitride ceramic tip, this can be regarded as the development trend of ceramic tip.
In the metal cutting field, aluminum oxide ceramic tip and silicon nitride ceramic tip are collectively known as the ceramic tip; in the inorganic nonmetallic materials, cubic boron nitride materials can be attributed to ceramic materials. The appearance of cubic boron nitride cutting tool can be regarded as a great revolution of ceramic cutting tool. Ceramic cutting tools can be generally divided into aluminum oxide series, silicon nitride and boron nitride. Compared with traditional cutting tools, ceramic cutting tools have excellent heat resistance, wear resistance and chemical stability when it is used in high speed cutting field and cutting difficult-to-process materials. Although ceramic cutting tool has good machinability, it can have great effect only when it is properly used. With the development of ceramic technology as well as wider and wider application of numerical control machine tool and machining center, ceramic cutting tool will be more and more widely used. As the raw material of ceramic cutting tool is very rich in the earthcrust, new type ceramic cutting tool will have very broad application prospect.
High purity ceramics
High purity ceramics can be regarded as the earliest ceramic. In order to improve the tenacity, it should emphasize on improving the micronization and densification of crystals. High purity ceramic can be formed by cold pressing and hot pressing. Ceramic that is formed by cold pressing will appear to be white, while those ceramics that formed by hot pressing will appear to be black. This kind of ceramic can be used in turning, planing, boring, milling and producing screw. The processing materials mainly include soft cast iron, hot rolling as well as cold-drawn carbon steel, brass, bronze and aluminum.
Composite ceramic is mostly commonly used currently, which can be used in high speed heavy cut (the cutting speed can reach 800m/min) and milling. The processing materials include hardened steel, chilled cast iron, superalloy and other similar hard metals.
Silicon nitride ceramics
Silicon nitride ceramic is mainly composed by Si3N4 powder and is added with certain amount of Al2O3. It is made by atmospheric pressure sintering method or hot pressing method. It can be used in high speed heavy cut (the cutting speed can reach 600m/min), milling cast iron and cutting nonferrous metals.
Boron nitride ceramics
Boron nitride ceramic is a kind of new type high-tech ceramic, which is mainly used in turning, milling and boring superhard materials. Cubic boron nitride blade has much higher hardness than ceramic tip and also can be collectively known as superhard materials with diamond due to its high hardness. It is often used in processing materials that have the hardness higher than RC48. Besides, it has excellent high temperature hardness. When the temperature is more than 2000 degrees Celsius, although it is more brittle than carbide blade, the impact strength and crushing resistance will be obviously improved compared with ceramic tip. In addition, some special boron nitride blades can resist the swarf load of large allowance rough machining, besides, it can bear the impact of intermittent as well as the abrasion and cutting heat of finish machining. Due to these characteristics, cubic boron nitride blade can be used in the rough machining of hardened steel and other difficult-to-process materials.
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