Ceramic insert grades, coated or uncoated, are based on silicon-nitride or aluminum-oxide formulations. Silicon-nitride-based cutting tools often contain toughening agents and are well suited for turning and milling of ductile, malleable and nodular cast iron, other difficult-to-machine irons and high-strength alloys. Silicon-nitride tooling is used to machine cast irons and steels up to Rc 65.
Economical tool life in gray cast irons can be achieved at speeds of up to 5,000 sfpm in single-point and milling operations.
Aluminum-oxide (Al2O3)-based ceramic has high-abrasion-wear resistance and moderate strength. It is best suited for applications in which interruptions, impacts or extreme hardness are not factors.
The high compressive strength of these grades makes them good to use for cast-iron grooving. Coolant should not be used in this application because of the grades’ low resistance to thermal-shock.
Aluminum-oxide ceramics reinforced with silicon carbide (SiC) single crystals, or whiskers, have high melting points, high hardness, chemical inertness and wear and thermal-shock resistance. The whiskers enhance the fracture toughness of these grades.
It is unusual for reinforced-ceramic tools to fail catastrophically as conventional ceramic inserts can. Instead, movement or failure of reinforced ceramic inserts can result in edge chipping or delamination of the rake face. Usually, these ceramic tools are consumed gradually in a predictable wear pattern.
Reinforced-ceramic grades are well suited to machining high-temperature alloys. They also can be used to machine hardened steels, hard irons and plasma spray and welded overlays. Reinforced-ceramic tooling works well in interrupted-cut turning, milling and die/mold work.
Whisker-reinforced ceramic tools can be run dry, wet, or intermittently cooled without fear of failure from thermal cracking.
Coated whisker-reinforced ceramics work well in light to medium-duty applications such as semi-finishing and finishing operations in which extended tool life is needed. Coated-ceramic tool life is up to three times that of uncoated ceramics. Coated ceramics are not recommended for abusive milling or interrupted cutting.
Machining of titanium with ceramic tools is not recommended because the high heat necessary for the process, coupled with the flash point of titanium, could create the risk of fire.
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