Types and development of ceramic inserts
The most obvious development line of the ceramic inserts is that the toughness of the inserts increases in turn: alumina ceramic inserts - composite alumina ceramic inserts - silicon nitride ceramic inserts - cubic boron nitride inserts.
In the field of metal cutting, alumina ceramic inserts and silicon nitride ceramic inserts are collectively referred to as ceramic inserts; in inorganic non-metallic materials, cubic boron nitride materials belong to the category of ceramic materials. The advent of cubic boron nitride material tools is a revolution in ceramic tools.
Properties of Ceramic Inserts and Applicable Machining Materials
Compared with cemented carbide inserts, ceramic inserts can withstand a high temperature of 2000 ° C, while cemented carbide becomes softer at 800 ° C; so ceramic inserts are more chemically stable at high temperatures and can be cut at high speed, but the disadvantage is that alumina ceramics The strength and toughness of the inserts are very low, and it is easy to break.
Because ceramic inserts are resistant to high temperatures, they are more favorable for high-temperature and high-speed cutting.
Because of the low thermal conductivity of ceramics, the high temperature is only at the tip of the tool, and the heat generated by high-speed cutting is taken away with the chips.
Therefore, most researchers believe that alumina ceramic inserts can, and it is best to cut at a linear speed 10 times higher than that of carbide cutting, in order to truly reflect the advantages of ceramic inserts.
In order to reduce the susceptibility of ceramic inserts to crushing, in an attempt to improve their toughness and impact resistance, zirconia or a mixture of titanium carbide and titanium nitride are added. Despite the addition of these additives, the toughness of ceramic inserts is much lower than that of carbide inserts.
Another way to improve the toughness of alumina ceramic inserts is to add crystal structures or silicon carbide whiskers to the material.
These special whiskers are only 1 nanometer in diameter and have an average length of 20 micrometers, which adds to the ceramic's size, toughness, strength and thermal shock resistance. Limited only by its impact toughness, it has been used in the field of finishing.
Like alumina ceramic inserts, silicon nitride ceramic inserts have higher thermal hardness than carbide inserts. It also has better resistance to high temperatures and mechanical shock. Compared with alumina ceramic inserts, its disadvantage is its insufficient chemical stability when machining steel. However, grey cast iron can be machined with silicon nitride ceramic inserts at speeds of 440m/min (1450ft/min) or higher.
Suitable machining grades for ceramic inserts: Ceramic inserts cannot be used to machine aluminum, but are especially ideal for gray cast iron, ductile iron, hardened steel, and some unhardened steels, heat-resistant alloys. However, for these materials, the successful application of ceramic inserts also requires the appearance and microscopic quality of the insert edge and the best cutting parameters.