As a non-metal tool material, ceramics are widely used in the field of metal cutting. This article briefly discusses the differences in their use and the materials they are suitable for processing based on the types and properties of ceramic blades and cubic boron nitride inserts.
Types and Development of Ceramic Inserts
Types and development of ceramic blades. The most obvious development line of ceramic blades is that the toughness of the blades is gradually enhanced. Alumina ceramic blades, composite alumina ceramic blades, silicon nitride ceramic blades, cubic boron nitride blades.
In the field of metal cutting, alumina ceramic inserts and silicon nitride ceramic inserts are collectively called ceramic inserts. In inorganic non-metallic materials science, cubic boron nitride materials belong to the category of ceramic materials. The advent of cubic boron nitride material cutting tools is a revolution in ceramic cutting tools. Pure boron nitride sintered ceramic blades have significantly increased toughness and wear resistance.
Performance of Ceramic Inserts and Suitable Processing Materials
Compared with carbide blades, ceramic blades can withstand temperatures of 2000°C, while carbide becomes soft at 800°C. Therefore, ceramic blades have better high-temperature chemical stability and can be cut at high speeds. However, the disadvantage is that the strength and toughness of alumina ceramic blades are very low and they are easy to break. Because ceramic blades are resistant to high temperatures, they are more conducive to high-temperature and high-speed cutting.
Due to the low thermal conductivity of ceramics, the high temperature is only at the tip of the blade, and the heat generated by high-speed cutting is taken away with the chips. Therefore, most researchers believe that alumina ceramic blades can be cut at a linear speed that is 10 times higher than that of carbide cutting to truly reflect the advantages of ceramic blades.
In order to reduce the sensitivity of ceramic blades to breakage, zirconium oxide or a mixture of titanium carbide and titanium nitride is added in an attempt to improve its toughness and impact resistance. Despite the addition of these additives, the toughness of ceramic blades is still much lower than that of carbide blades.
Another way to improve the toughness of alumina ceramic blades is to add crystalline textures or silicon carbide whiskers to the material. These special whiskers are only 1 nanometer in diameter and 20 microns long on average. The toughness, strength and thermal shock resistance of ceramics have been increased to a considerable extent. Due to its impact toughness, it has been used in the field of precision turning.
Like alumina ceramic blades, silicon nitride ceramic blades have higher thermal hardness than carbide blades. It also has better resistance to high temperature and mechanical shock. Compared with alumina ceramic blades, its disadvantage is that it is not chemically stable enough when processing steel. However, silicon nitride ceramic blades can be used to process gray cast iron at a speed of 440m/min (1450ft/min) or higher.
Suitable processing materials for ceramic blades: Ceramic blades cannot be used to process aluminum, but are particularly suitable for gray cast iron, ductile iron, hardened steel and some unhardened steel and heat-resistant alloys. However, for these materials, ceramic blades are successfully applied. The appearance and microscopic quality of the blade edge are also required, and the best cutting parameters are required.
CBN Insert Performance and Suitable Processing Materials
The hardness of cubic boron nitride blades is much higher than that of ceramic blades. Due to its high hardness, it is called superhard material together with diamond. It is often used to process materials with hardness higher than HRC48. It has excellent high temperature hardness – up to 2000℃. Although it is more brittle than carbide blades, its impact strength and anti-crushing performance are significantly improved compared with ceramic blades. In addition, some special cubic boron nitride blades can withstand the chip load of large-residue rough machining. And it can withstand the impact during intermittent cutting and the wear and cutting heat during fine machining. These characteristics can meet the requirements of using cubic boron nitride blades to rough-process hard-to-process materials such as hardened steel.
The cubic boron nitride composite layer of the welded CBN blade is relatively fragile. Therefore, it is often used to process workpieces with a single-side margin of less than 0.3mm. The integrally sintered cubic boron nitride blade can cut difficult-to-process materials with large margins. Especially in strong intermittent cutting, it leads the entire superhard material tool industry.
Pure boron nitride sintered blades. A blade made of pure boron nitride material, with a CBN content of 100%. The boron nitride ceramic blade formed by pure sintering has a higher hardness and thermal conductivity ratio. When cutting high-hardness ferrous metal materials, the blade edge will not suffer from common thermal cracking and chipping. Compared with CBN sintered bodies containing other bonding materials, the service life of boron nitride ceramic blades can be extended by more than 6 times.
Cubic boron nitride blades are suitable for processing materials: gray cast iron, various wear-resistant cast iron, cast steel, and high-hardness material processing. Such as hardened cold work tool steel, high-speed steel, bearing steel, powder metallurgy steel, high-strength steel, high manganese steel, high-chromium cast iron, white cast iron, austenitic iron, cemented carbide, etc.
The Difference Between Ceramic Inserts and CBN Inserts
Although cubic boron nitride is classified as a ceramic in materials science, due to the performance differences between CBN, SIN, Al2O3, and SiN materials, ceramic blades are not as tough and hard as cubic boron nitride blades. Therefore, according to the difference in hardness and toughness, ceramic blades are a better choice when cutting hardened steel workpieces with a hardness below 50HRC and a small cutting depth and small feed. Cubic boron nitride blades are suitable for workpieces with a hardness higher than 50HRC.
In addition, under the same flank wear, the residual stress on the workpiece surface after cutting with cubic boron nitride blades is relatively stable compared to ceramic blades. Therefore, in the processing field where ceramic blades are suitable, cubic boron nitride blades can also be selected. Users can determine which blade material is more economical based on cost-effectiveness and processing requirements.
