CBN, hardness after diamond.CBN is an extremely hard tool material second only to diamond and generally works best when the hardness of the material is greater than 48HRC (CBN wears out quickly when soft materials are processed). Temperature up to 2000℃ is also excellent red hardness. Although more brittle than carbide and less thermal and chemical stable than ceramic, it has higher impact strength and fracture resistance than ceramic tools and can cut hard metal for less rigid machine tools. Furthermore, the appropriate custom CBN tool can withstand the cutting load of high-power roughing, the impact of intermittent cutting, and the heat and wear performance required for fine machining.
The proper customization of the specified process includes the rigidity and edge grinding of the machine tools and fixtures large enough to prevent microscopic spalling, and the matrix of the tool is a material grade with high CBN content. A high CBN content material grade is necessary for these specified processes because they have the high thermal conductivity and toughness required for high-speed machining under heavy cutting edge loading as well as for severe discontinuous cutting. These properties allow this grade of tool material to be used for roughing hardened steel and pearlite gray cast iron.
Materials with low CBN content are more brittle than those with high CBN content, but they are better for hardened ferrous metal processing. They have lower thermal conductivity and relatively higher compressive strength to withstand the heat generated by high-speed cutting and negative rake Angle. The higher temperature of the cutting area softens the workpiece material and helps break chips, while the negative front Angle strengthens the tool, stabilizes the cutting edge, improves tool life, and allows cutting depth smaller than 0.25mm.
Because CBN cutters achieve a surface finish superior to 0.4 m and maintain a coaxiality of ±0.012mm, dry-hardened workpieces are often an attractive alternative to dirty, enhanced cooling grinding. Although CBN is a preferred tool material for hard turning and high-speed milling, the range of applications of ceramics and CBN is so strikingly overlapping that it is necessary to use cost-benefit analysis to determine who gets the best results.