5.7 CUTTING TOOL MATERIALS
These materials generally need to withstand high temperatures, high forces, resist corrosion, etc.
The names used for certain materials will be brand names, and so various manufacturers may be calling the same material, different names.
The List below shows some commercial tool materials
CBN - Cubic Boron Nitride
PCD - PolyCrystalline Diamond
coated WC - Tools coated with Tungsten Carbide
5.7.1 A Short List of Tool Materials
Carbon Steels
- Limited tool life. Therefore, not suited to mass production
- Can be formed into complex shapes for small production runs
- suited to hand tools, and wood working
- Carbon content about 0.9 to 1.35% with a hardness ABOUT 62°C Rockwell
- Maximum cutting speeds about 26 ft/min. dry
- The hot hardness value is low. This is the major factor in tool life.
High Speed Steel
- an alloyed steel with 14-22% tungsten, as well as cobalt, molybdenum and chromium, vanadium.
- Appropriate heat treating will improve the tool properties significantly (makers of these steels often provide instructions)
- can cut materials with tensile strengths up to 75 tons/sq.in. at speeds of 50-60 fpm
- Hardness is in the range of 63-65°C Rockwell
- The cobalt component give the material a hot hardness value much greater than Carbon Steels
- Used in all type of cutters, single/multiple point tools, and rotary tools
Stellite
- a family of alloys made of cobalt, chromium, tungsten and carbon
- The material is formed using electric furnaces, and casting technique, and it cannot be rolled, or worked.
- The material has a hardness of 60-62°C Rockwell without heat treating, and the material has good hot hardness properties
- Cutting speed of up to 80-100 fpm can be used on mild steels
- The tools that use this method either use inserts in special holders, or tips brazed to carbon steel shanks
Tungsten Carbide
- Produced by sintering grains of tungsten carbide in a cobalt matrix (it provides toughness).
- Other materials are often included to increase hardness, such as titanium, chrome, molybdenum, etc.
- Compressive strength is high compared to tensile strength, therefore the bits are often brazed to steel shanks, or used as inserts in holders
- These inserts may often have negative rake angles
- Speeds up to 300 fpm are common on mild steels
- Hot hardness properties are very good
- coolants and lubricants can be used to increase tool life, but are not required.
- special alloys are needed to cut steel
Ceramics
- sintered or cemented ceramic oxides, such as aluminum oxides sintered at 1800°F
- Can be used for turning and facing most metals, except for nimonic alloys and titanium. Mild steels can be cut at speeds up to 1500 fpm.
- These tools are best used in continuous cutting operations
- There is no occurrence of welding, or built up edges
- coolants are not needed to cool the workpiece
- Very high hot hardness properties
- often used as inserts in special holders
Diamonds
- a very hard material with high resistance to abrasion
- very good for turing and boring, producing very good surface finish
- operations must minimize vibration to prolong diamond life
- also used as diamond dust in a metal matrix for grinding and lapping. For example, this is used to finish tungsten carbide tools
Cemented Oxides
- produced using powder metallurgy techniques
- suited to high speed finishing
- cutting speeds from 300 to 7500 fpm
- coolants are not required
- high resistance to abrasive wear and cratering
