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Cubic boron nitride CBN (Popular Science)

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brief introduction

cubic boron nitride

Boron nitride cubic

Cubic structure of boron nitride, molecular formula for BN, its crystal structure similar to diamond, hardness is slightly lower than diamond, for HV72000 ~ 98000 MPa, commonly used as abrasive and cutting tool material. In 1957, R.H. vintov America first developed into cubic boron nitride. But natural cubic boron nitride has not been found yet.

origin

Cubic boron nitride CBN (cubic boron nitride) is the 20th century 50's first by the American General Electric (GE) using artificial method under the conditions of high temperature and high pressure synthesis, its hardness second only to diamond but is much higher than that of other materials, so it with diamond collectively for superhard material, material.

data

Cubic boron nitride is composed of hexagonal boron nitride and catalyst synthesized under high temperature and high pressure, is the second after the advent of the artificial diamond and a new high technology products. It has very high hardness, thermal stability and chemical inertness, and good through red appearance and wide band width, excellent performance, its hardness only to diamond, but the thermal stability is much higher than that of diamond. The high chemical stability of iron series metal. Cubic boron nitride grinding tool grinding performance is very good, not only can be competent for the difficult to grinding materials processing, improve productivity, but also effectively improve the quality of the workpiece grinding. The use of cubic boron nitride is a major contribution to metal processing, resulting in a revolutionary change in grinding, grinding technology is the second leap.

classification

Cubic boron nitride has two kinds of single crystals and polycrystalline sintered bodies. Is the six single crystal boron nitride catalyst and the pressure of 3000 to 8000 MPa and a temperature of 800 to 1900 DEG C prepared. The catalyst selected from alkali metal, alkaline earth metal, typically tin, lead, antimony and their nitrides. Cubic boron nitride crystal tetrahedral cone, eight surface, crystal distortion and bicrystal etc.. Industrial production of cubic boron nitride has black, amber and surface plated metal, particle size is usually below 1 mm. It has superior to diamond thermal stability and chemical inertness of the metals of the iron group, to manufacture of abrasive, suitable for processing both hard and tough materials, such as high speed steel, tool steel, die steel, bearing steel, nickel and cobalt base alloy, chilled cast iron. The high grinding ratio and surface quality can be obtained by using cubic boron nitride abrasive tools.

Making method

The main method for preparing polycrystalline cubic boron nitride sintered body: using cubic boron nitride powder and a binder (such as cobalt, aluminum, titanium and titanium nitride), under the pressure of 4000 to 8000 MPa and a temperature of 1300 ~ 1900 DEG C and sintering; the cubic boron nitride powder and binder is a layer of, with hard alloy (or powder) as a layer, the pressure and temperature of the two sintering together, polycrystalline sintered body prepared with cemented carbide substrate, the sintered body with high strength, while keeping the original properties of the rational cubic boron nitride, can be made of 16 mm diameter wafers, cutting into the appropriate shape, as the knife head turning and boring, suitable for cutting hardened steel, cast iron and nickel base alloy.

Application of cubic boron nitride (CBN) in cutting process

PCBN blade finish turning of hardened steel

Processing of hard cast iron and gray cast iron

High speed boring hole

Reaming holes in hardened steel or hard casting

Cutting process for difficult to process materials

By using PCBN tool finishing of hardened steel, the hardness of the workpiece is higher than 45HRC, the best effect. Its cutting speed is generally 80 ~ 120m/min, the higher the hardness of the workpiece, the cutting speed should take low value, such as the hardness of the car for the 70HRC of the workpiece, the cutting speed should be selected 60 ~ 80m/min. Precision cutting depth in the 0.1 ~ 0.3mm, feed in 0.05 ~ 0.025mm/r, after finishing the workpiece surface roughness of the workpiece is Ra0.3 ~ 0.6 m, size accuracy of up to 0.013mm. If we can adopt rigid standards of CNC lathe machining, PCBN tool rigidity and cutting edge sharp, fine car after the workpiece surface roughness of up to Ra0.3 m, size precision of 0.01mm, achieved with NC grinder for grinding. If the machine is good rigidity, the choice of cutting speed is low, the use of PCBN composite blade can be fine car intermittent surface. Precision machining allowance is generally about 0.3mm, as much as possible to improve the size of the workpiece before quenching and reduce the size of thermal deformation, to ensure the precision machining of cutting margin uniform, prolong the service life of PCBN tool. Fine cars generally do not have cutting fluid, because in the higher cutting speed, a lot of cutting heat from the chip away, rarely stay in the workpiece surface and affect the quality and accuracy of the processing surface. Finish turning blade should use high strength and toughness of 80 DEG diamond blade, tool nose radius between 0.8 ~ 1.2mm, protect the knife edge using required before fine oil stone chamfering. Finish turning of hardened workpiece is a new process, prior to the implementation of the need to do process test, available with the workpiece material, hardness and size of the same bar, in the same type of machine for finishing or rough machining test, the key is whether there is enough rigidity test of cutting tools and cutting parameters selection and process system. The process at home has been employed such as FAW Group with PCBN cutting tools carburizing and quenching (58 ~ 63hrc) of 20CrMnTi gear shift fork groove and the technological parameters for Vc=150m/min, f=0.1mm/r, ap=0.2 ~ 0.3mm, realize the turning instead of grinding.

Processing hard cast iron

Turning of hardened steel using PCBN cutting tool, workpiece quenching hardness higher than 45 ~ 55HRC, hard machining cast iron, as long as the hardness reaches the medium level of hardness (45hrc), you will get a good processing effect. Such as automobile engine cylinder exhaust valve seat and the valve seat is adopted with the copper, molybdenum high chromium alloy cast iron material, its hardness is generally about 44 HRC, countersink (hinge), two cars process applied to a hole on the valve seat, mostly in private automatic line

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