Tool Condition Monitoring in Machining Superalloys 85 2.3.1.3 Ceramic Cutting Tools Ceramics are nonmetallic materials.The application of ceramic cutting tools is limited because of their extreme brittleness.The transverse rupture strength (TRS)is very low.This means that they will fracture more easily when making heavy or interrupted cuts.However,the strength of ceramics under compression is much higher than HSS and carbide tools.Proper tool geometry and edge preparation play an important role in the application of ceramic tools and help to overcome their weakness.Some of the advantages of ceramic tools are:high strength for light cuts on very hard work materials;extremely high resistance to abrasive wear and cratering;capability of run- ning at speeds in excess of 2000 SFPM(surface feet per minute);extremely high hot hardness;and low thermal conductivity.To use ceramic tools successfully,insert shape,work material condition, machine tool capability,setup,and general machining conditions must all be correct. 2.3.1.4 Cermet Cutting Tools Cermets are basically a combination of ceramic and titanium carbide.The term"cermet"is derived from the words"ceramic"and"metal."The strength of cermets is greater than that of hot pressed ceramics.Therefore,cermets perform better on interrupted cuts.However,when compared to solid ceramics,the presence of 30%titanium carbide in cermets decreases the hot hardness and resis- tance to abrasive wear.The hot hardness and resistance to abrasive wear of cermets are high when compared to HSS and carbide tools.The greater strength of cermets allows them to be available in a significantly larger selection of geometries,and to be used in standard insert holders for a greater variety of applications.The geometries include many positive/negative,and chip breaker conhgurations. 2.3.1.5 Cubic Boron Nitride Cubic boron nitride (CBN),bonded to a carbide base,is similar to diamond in its polycrystalline structure.With the exception of titanium,or titanium alloyed materials,CBN will work effectively as a cutting tool on most common work materials.However,the use of CBN should be reserved for very hard and difficult-to-machine materials. CBN will run at lower speeds,and will take heavier cuts with higher lead angles than diamond. Due to the extreme hardness and brittleness,CBN should mainly be considered as a finishing tool material.Machine tool and setup rigidity for CBN as with diamond is critical. 2.3.1.6 Whisker-Reinforced Materials Whisker-reinforced composite cutting tool materials have been developed to machine new work materials and composites for improved cutting performance and wear resistance of cutting tools. Whisker-reinforced materials include silicon-nitride-based tools and aluminum-oxide-based tools, reinforced with silicon carbide(SiC)whiskers.Such tools are effective in machining composites and nonferrous materials,but are not suitable for machining irons and steels. In machining superalloys,the regularly used cutting tool materials include HSS,carbides,coated carbides,boron nitride,and ceramics.Carbide tools are the most common cutting tool material. High-speed cobalt tool steels are recommended for milling,drilling,tapping,and broaching of superalloys.Carbides are used for turning,planing,and face milling.The most commonly used carbide is the C-2 grade.Modification of tungsten carbide tools with the addition of 0.5-4%tan- talum carbide has been beneficial in improving abrasion resistance.Titanium carbide tools are not applicable for superalloys because of the high solubility of titanium carbide in nickel and cobalt [5]. Most nickel-based alloys should be machined using positive cutting geometries.Since these mate- rials are machined with carbide at 120 SFPM or less,positive rake angle geometries are required to minimize cutting forces and heat generation.In the machining of most materials.increased tem- perature enhances chip flow and reduces the physical force on the cutting edge.Adequate clearance angles must be utilized on these materials,since many of them are very ductile and prone to work hardening.When a tool is stopped and left to rub on the workpiece,hardening of the workpieceTool Condition Monitoring in Machining Superalloys 85 2.3.1.3  Ceramic Cutting Tools Ceramics are nonmetallic materials. The application of ceramic cutting tools is limited because of their extreme brittleness. The transverse rupture strength (TRS) is very low. This means that they will fracture more easily when making heavy or interrupted cuts. However, the strength of ceramics under compression is much higher than HSS and carbide tools. Proper tool geometry and edge preparation play an important role in the application of ceramic tools and help to overcome their weakness. Some of the advantages of ceramic tools are: high strength for light cuts on very hard work materials; extremely high resistance to abrasive wear and cratering; capability of run￾ning at speeds in excess of 2000 SFPM (surface feet per minute); extremely high hot hardness; and low thermal conductivity. To use ceramic tools successfully, insert shape, work material condition, machine tool capability, setup, and general machining conditions must all be correct. 2.3.1.4  Cermet Cutting Tools Cermets are basically a combination of ceramic and titanium carbide. The term “cermet” is derived from the words “ceramic” and “metal.” The strength of cermets is greater than that of hot pressed ceramics. Therefore, cermets perform better on interrupted cuts. However, when compared to solid ceramics, the presence of 30% titanium carbide in cermets decreases the hot hardness and resis￾tance to abrasive wear. The hot hardness and resistance to abrasive wear of cermets are high when compared to HSS and carbide tools. The greater strength of cermets allows them to be available in a significantly larger selection of geometries, and to be used in standard insert holders for a greater variety of applications. The geometries include many positive/negative, and chip breaker configurations. 2.3.1.5  Cubic Boron Nitride Cubic boron nitride (CBN), bonded to a carbide base, is similar to diamond in its polycrystalline structure. With the exception of titanium, or titanium alloyed materials, CBN will work effectively as a cutting tool on most common work materials. However, the use of CBN should be reserved for very hard and difficult-to-machine materials. CBN will run at lower speeds, and will take heavier cuts with higher lead angles than diamond. Due to the extreme hardness and brittleness, CBN should mainly be considered as a finishing tool material. Machine tool and setup rigidity for CBN as with diamond is critical. 2.3.1.6  Whisker-Reinforced Materials Whisker-reinforced composite cutting tool materials have been developed to machine new work materials and composites for improved cutting performance and wear resistance of cutting tools. Whisker-reinforced materials include silicon-nitride-based tools and aluminum-oxide-based tools, reinforced with silicon carbide (SiC) whiskers. Such tools are effective in machining composites and nonferrous materials, but are not suitable for machining irons and steels. In machining superalloys, the regularly used cutting tool materials include HSS, carbides, coated carbides, boron nitride, and ceramics. Carbide tools are the most common cutting tool material. High-speed cobalt tool steels are recommended for milling, drilling, tapping, and broaching of superalloys. Carbides are used for turning, planing, and face milling. The most commonly used carbide is the C-2 grade. Modification of tungsten carbide tools with the addition of 0.5–4% tan￾talum carbide has been beneficial in improving abrasion resistance. Titanium carbide tools are not applicable for superalloys because of the high solubility of titanium carbide in nickel and cobalt [5]. Most nickel-based alloys should be machined using positive cutting geometries. Since these mate￾rials are machined with carbide at 120 SFPM or less, positive rake angle geometries are required to minimize cutting forces and heat generation. In the machining of most materials, increased tem￾perature enhances chip flow and reduces the physical force on the cutting edge. Adequate clearance angles must be utilized on these materials, since many of them are very ductile and prone to work hardening. When a tool is stopped and left to rub on the workpiece, hardening of the workpiece