Function of Coolents in Machining

The Coolant performs three basic functions when used in drilling, milling, and threading applications:

1. to reduce the heat generated during cutting
2. to lubricate and reduce friction between the chip and the tool
3. to flush out the chips.

Coolant, which is mostly water, helps to cool the chip when it is sheared away from the work piece. It includes a small amount of oil which acts as a lubricant to improve the surface finish and evacuate cut chips from the flutes/rake surface.


Because excessive heat and friction can dull a tool, coolant helps to extend tool life. Using the recommended water/oil ratio is important. Too often, users will alter this ratio significantly in an effort to reduce cost. This can cause tool life to decrease rapidly. For example, a drill which normally yields thousand holes, may now only last for a few hundred holes.

When selecting a coolant, choose one that is suitable for both the material and the particular machining operation and follow the manufacturer’s mixing recommendations. For example, high-speed machining with carbide tools might require coolant, while tapping might require cutting oil.

S. Pradeep Kumar CMP
Kennametal Knowledge Center,
Kennametal India Limited, Bangalore.