SECTION 3.1
Heat Removal

The relative importance of each function of the coolant depends upon (a) the material being machined, (b) the cutting rate, (c) the tool geometry, and (d) the finish required. No matter how you look at it, however, the primary function of a cutting fluid is to control heat near the cutting edge.

An inverse exponential relationship between the temperature at the cutting edge and the life of the tool was first defined by Taylor, and subsequently expressed as:

where

• T = tool life in minutes,

• t = temperature at the tool/chip interface (degrees C),

• n = an exponent dependent upon the tool material (approx. 20-25), and

• k = a constant dependent upon the workpiece and tool material.

This equation has been substantiated by experimentation. Small changes in the tool/chip interface temperature will produce large changes in tool life. A cutting fluid with a high specific heat and a high thermal-conductivity, that provides good surface contact, can increase tool life simply by reducing the tool temperature a few degrees. A coolant does this in two ways: (1) by straight forward heat transfer, and (2) by reducing friction.