End Mills Materials
End mills are made out of either cobalt steel alloys (known as high speed steel, or HSS), or from tungsten carbide in a cobalt lattice (shortened to "carbide").
Speed Steel (HSS): Provides good wear resistance and costs less than cobalt or carbide end mills. HSS is used for general purpose milling of both ferrous and nonferrous materials. While usually inexpensive, HSS does not offer the tool life or speed advantages of cobalt and carbide end mills.
Cobalt: Cobalt is an M42 tool steel with an 8% cobalt content. Cobalt is more expensive but provides better wear resistance and toughness than HSS (M7). Because the tool can run 10% faster than HSS, metal removal rates and finish are better than HSS.
Solid Carbide: Carbide is considerably harder, more rigid, and more wear resistant than HSS. However, carbide is brittle and tends to chip instead of wear. Carbide is used primarily in finishing applications. Carbide tools are best suited for shops operating newer milling machines or machines with minimal spindle wear. Rigidity is critical when using carbide tools. Carbide end mills may require a premium price over the cobalt end mills, but they can also be run at speeds 2 1/2 times faster than HSS end mills.
The choice of tool material depends on the material to be cut as well as on the maximum spindle speed of the machine. Smaller milling machines may not be capable of reaching the spindle speeds recommended for carbide end mills.
End Mill Coatings
The use of coatings will increase the surface hardness of the tool. This will allow for greater tool life and faster cutting speed. Standard coatings include Titanium Nitride (TiN), Titanium Carbonitride (TiCN), and Aluminum Titanium Nitride (AlTiN). Long-life TiN (titanium nitride) coating is good for use on alloy steel, aluminum, and plastic. Color is gold.
Extra-life TiCN (titanium carbonitride) coating has better wear resistance than TiN coating, making it a good choice for tough-to-machine materials such as ductile cast iron, stainless steel, aluminum, and plastic. Color is blue-gray.
Super-life AlTiN (aluminum titanium nitride) coating is the best for very high feeds/speeds and high-temperature applications. Use to mill cast iron, stainless steel, nickel-based alloys, and titanium. Not for use on aluminum. Color is purple-gray.
The choice to use coated end mills is a cost versus benefit choice. If your machining benefits enough from the extra performance of a premium coating, purchase end mills with a coating.