Classification and use of square boron nitride tools

        Cubic boron nitride tools were mainly used for finishing before, but in the past ten years, technological innovation has been carried out in terms of raw material purity and grain size, using composite materials and hot pressing processes, etc., its brittleness With major improvements, toughness is improved, and reliability is greatly improved. It can be used as a conventional tool in production, which plays an important role in improving work efficiency and ensuring product quality.

Characteristics of cubic boron nitride tool materials:

        part of the knives. Cubic boron nitride (CBN) is one of the allotropes of boron nitride (BN), and its structure is similar to diamond. It is a superhard material artificially synthesized by ultra-high temperature and ultra-high pressure technology. Its hardness is second only to diamond (microhardness can reach 8000-9000HV), and its thermal stability is high (up to 1250-1350 ℃), it is chemically inert to iron group elements, and has strong anti-adhesion ability. It can be ground with diamond grinding wheel. It is suitable for processing hard materials above 35HRC, such as various hardened steels (carbon tool steel, alloy tool steel, high-speed steel, bearing steel, die steel, etc.), chilled cast iron, cobalt-based and nickel-based High-hardness and wear-resistant materials such as superalloys, hard alloys, surface spraying (welding) materials, etc., can also be used for processing titanium alloys, pure nickel, pure tungsten and other materials. It is one of the best tools for turning and milling instead of grinding. The surface roughness of hardened steel processed by cubic boron nitride tool is Ra1.60.4μm, and the precision can reach IT7IT6.

        Cubic boron nitride cutting tools also have limitations in use, such as high brittleness, poor strength and toughness, and are not suitable for discontinuous surface machining under impact load. In addition, when it is used to process soft iron group element materials, it is easy to generate long chips, scratch the rake face of the tool and form a built-up edge, which will cause fluctuations in cutting force and damage the tool.

        In order to improve the impact resistance of cubic boron nitride cutting tools, we have developed a graphite-like hexagonal boron nitride (g-BN or h-BN) for Raw material, a new type of WBN material (WBN is BN belonging to lead-zinc ore structure) synthesized by explosion method. It has high toughness and sintering activity, and is easily converted into CBN, and can be easily co-sintered with CBN to form a polycrystal with strength and hardness close to the level of CBN.

The two-phase sintered body of WBN and CBN uses the toughness of WBN to make up for the brittleness of CBN, and its impact strength is 60% higher than that of the simple CBN sintered body, the fracture toughness is increased by 2.53 times, and the flexural resistance is improved. The strength is increased by about 1 times, the compressive strength is equivalent to that of cemented carbide, and the thermal stability is 1100~1200℃. It can be used to machine workpieces with discontinuous surfaces, such as tooth flanks of gears, surfacing surfaces or workpieces with grooves.

At present, WBN and CBN two-phase sintered body cutting tools have been widely used in the automobile industry in the United States, Japan and Russia, such as machining connecting rods, tappets, cylinder liners, brake In the process of turning, boring and milling of moving wheel, crankshaft, flywheel, and various pump casing parts.