Ceramics

Ceramics are essentially alumina based high refractory materials introduced specifically for high speed machining of materials and cast iron. These might withstand very high temperatures, are chemically more stable and contain higher wear resistance than other cutting tool materials. In point view of their ability to withstand high temperatures; they might be utilized for machining at very high speeds of the order of 10 m/s. This is possible to obtain a mirror finish on cast iron using ceramic turning. The major problems with ceramic tools are their low strength, poor thermal characteristics and their tendency towards chipping. The machine tools utilized for ceramic machining need to be extremely rigid to provide vibration free machining conditions. They are not appropriate for intermittent cutting or slow cutting speeds.

In spite of the pure alumina based ceramics, sometimes other materials such as titanium carbide are added to improve their transverse rupture strength. Ceramic tools are utilized for machining workpieces which have high hardness such as hard castings, case hardened and hardened steels. Typical products that can be machined are brake drums, brake discs, cylinder liners and flywheels. The correct cutting speed produces good surface finish, optimum productivity and better tool life.

Ceramic tools cannot machine some materials such as aluminum and titanium since they have a strong affinity towards them, as a result of which chemical reactions could take place.

Among other things, some of the vital requirements when machining with ceramics tools are:

1. Using the highest cutting speed recommended and preferably selecting square or round inserts with large nose radius.

2. Using rigid machines with high spindle speeds and safe clamping angles.

3. Machining rigid workpieces.

4. Ensuring adequate and uninterrupted power supply.

5. Using negative rake angles so that lower cutting stress is applied directly to the ceramic tip.

6. Using a large nose radius and side cutting edge angle on the ceramic insert reduces the tendency to chipping.

7. Avoiding coolants with aluminium oxide based ceramics.