2.2 Factors affecting the quality of PCBN blades The quality of PCBN inserts is affected by many factors. The changes in various process parameters during the sintering process have the greatest impact on the quality of PCBN inserts. The composition of the binder/catalyst material, the matrix material, and the surface cleanliness and graininess of the particles all determine the performance of the PCBN blade.
(1) Selection of substrate Since tungsten carbide cemented carbide has high hardness, good thermal conductivity and toughness, a tungsten carbide containing Co-containing carbide is often used as the PCBN blade substrate. Co as a solvent and binder can significantly improve the sintering degree of CBN and enhance the strength of PCBN [3], but the content of Co in tungsten carbide cemented carbide should not be too high, otherwise it will affect the wear resistance of PCBN inserts. Reduce tool life.
(2) Cleanliness and granularity of CBN grains The surface cleanliness of CBN grains will directly affect the sintering quality of PCBN. Therefore, CBN grains must be treated strictly before sintering to remove moisture from the surface of the grains. And impurities such as oxides. The method used is mainly heating under vacuum or a reducing gas such as hydrogen or ammonia for 1 to 2 hours. Otherwise, excessive impurities may affect the bonding between the CBN-CBN particles and the CBN and the binder, so that the strength of the PCBN blade is reduced and the wear resistance is lowered.
The size of the CBN particles not only affects the cutting surface quality of the PCBN tool but also plays a role in the sintering ability of the binder during the sintering of the PCBN. In general, the smaller the CBN particle size, the better the cutting surface quality of the PCBN tool, the better the impact resistance and wear resistance of the tool. Therefore, the hardened steel is processed and high surface quality is required (ie, the PCBN tool is realized). When the car is worn, the CBN particles in the PCBN tool used should take a small value. On the other hand, since the sintering of the PCBN insert is achieved by the "capillary phenomenon", that is, the penetration of various binder elements into the CBN particles, if the CBN particles are too small, the gap between the CBN particles is reduced, thereby The amount of penetration of the binder element is reduced. Therefore, the CBN particles should be selected to be larger when sintered. Considering the above two factors comprehensively, the mixing particle size should be selected more when CBN is sintered, and different particle size ranges are determined according to the bonding ability of the selected binder.
(3) CBN grain content CBN content has a great influence on the hardness and thermal conductivity of PCBN cutters. The higher the CBN content, the higher the hardness of the tool and the better the thermal conductivity. High-content PCBN cutters (typically 80% to 90% CBN) are based on direct bonding between CBNs and have high hardness and high thermal conductivity. These PCBN tools are suitable for processing high hardness alloys and materials with high hardness points in the structure, such as chilled cast iron, heat resistant alloys, etc. At present, such tool blades mainly include BZN6000 of GE Company, AMB90 of Element Six Company, BN100 and BN600 of Sumitomo Electric Company. Low-content PCBN inserts are mostly ceramic binders, which have good heat resistance and are easy to process hardened steel (alloy steel, bearing steel, die steel, carbon steel, etc.), and use the metal softening effect formed by heat retention in the cutting zone for cutting. GE's BZN8100, BZN8200, Element Six's DBC50, Sumitomo Electric's NB300, NB220, and Seco's CBN10, CBN100, CBN150, etc. all fall into this category.
(4) Binder required for sintering CBN: 1 The closer the physical and chemical properties are to CBN, the less the weakening of the cutting performance of the PCBN tool after sintering; 2 The temperature is easy to reach or at this temperature. It has good plasticity; 3 has sufficient chemical activity relative to CBN and has catalytic properties for converting hexagonal boron nitride (HBN) to CBN.
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