Exploring Advanced Manufacturing Technologies. Steve Krar
inserts work best on hard ferrous metals and nickel base alloy; they are not effective on ferrous metals below 42Rc.
▪About 80% of reinforced ceramic usage is on nickel alloys and aerospace alloys such as Inconel, Waspoloy, Hastelloy, and others.
▪Ceramic’s melting point is 3700°F (1678°C), higher than sintered carbide, allowing it to be used at higher speed rates on hard materials.
▪Machining time is reduced because of the higher speeds possible and the long tool life.
▪Accurate part size is possible because of the greater wear resistance.
▪The surface finish on machined parts is better than what is produced by other cutting tools.
▪Turning is an ideal operation for reinforced ceramic inserts; milling can be compared to interrupted machining in turning.
▪Hard milling operations require much higher spindle speeds to generate the heat equivalent of a single-point turning tool.
Table 3-2-7 The composition and application for various ceramic grades. (Kennametal, Inc.)
Disadvantages
A few of the disadvantages or cautions that a user should be aware of:
▪Ceramic insert are brittle and tend to chip if not set up or used properly.
▪Considerably more power and higher cutting speeds are required for ceramics to cut efficiently.
▪The initial cost of ceramics is higher than carbides; however this is offset by higher productivity.
▪The machine tool used must be more rigid than those using carbide tools.
PART 5 CERMET CUTTING TOOLS
Continued research aimed at improving the strength of ceramic cutting tools led to the development of cermet tools that are a combination of various ceramic and metallic materials. They combine the ceramic properties of hardness, wear resistance, temperature, and oxidation, with the properties of metals that include toughness, impact strength, and ductility. The multi-component alloy cermets, made up of different hard materials and binder elements, have high wear-resistance qualities that result in long tool life. The properties of cermet tools are shown in Fig. 3-2-18.
Types of Cermet Tools
There are two main types of cermet tools: those composed of titanium carbide (TiC) based materials and those containing titanium nitride (TiN) based materials.
Titanium carbide (TiC) cermets have a nickel and molybdenum binder and are produced by cold pressing and sintering in a vacuum. They are used extensively for finishing cast irons and steels that require high speeds and light-to-moderate feeds.
Titanium nitride (TiN) has been added to titanium carbide to produce titanium carbide-titanium nitride (TiCTiN) cermets. Other materials such as molybdenum carbide, vanadium carbide, zirconium carbide, and others may be added, depending on the application.
Because of their high productivity, cermets are considered a cost-effective replacement for coated and uncoated carbide and ceramic tools. However, cermets are not recommended for use with hardened ferrous metals (over 45 Rc) or nonferrous metals.
Fig. 3-2-18 The properties of cermet insert tools. (Kelmar Associates)
Characteristics of Cermet Tools
The main characteristics of cermet tools are:
▪They have great wear resistance and permit higher cutting speeds than do carbide tools.
▪Edge buildup and cratering are minimal, which increases tool life.
▪They possess high hot-hardness qualities greater than carbide tools, but less than ceramic tools.
▪Excellent chemical stability at conventional (carbide) speeds.
Advantages of Cermet Tools
Cermet tools have the following advantages:
1.The surface finish is better than that produced with carbides under the same conditions, which often eliminates the need for finish grinding.
2.High wear resistance permits close tolerances for extended periods, ensuring accuracy of size for larger batches of parts.
3.Cutting speeds can be higher than with carbides for the same tool life.
4.When operated at the same cutting speed as carbide tools, cermet tool life is longer.
5.The cost per insert is less than that of coated carbide inserts and equal to that of plain carbide inserts.
Use of Cermet Tools
Titanium carbide cermets are the hardest cermets and are used to fill the gap between tough tungsten carbide inserts and the hard, brittle ceramic tools. They are used mainly for machining steels and cast irons where high speeds and moderate feeds may be used. See Table 3-2-8 A to F for recommended cutting speeds for machining various material groups.
Titanium carbide-titanium nitride inserts are used for semifinish and finish machining of harder cast irons and steels (less than 45 Rc) such as alloy steel, stainless steel, armor plate, and powder metallurgy parts.
For more information on CUTTING TOOL TECHNOLOGY see the Websites: www.carboloy.com www.cormorant.sandvik.com/us www.kennametal com www.niagaracutter.com
Table 3-2-8 Cermet grade inserts with recommended material applications and suggested speed ranges. (Hertel Carbide Ltd.)
(Arthur Gill, Consultant – Kelmar Associates)
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