Theory of cutting fluid

The basic function of an effective cutting fluid is to reduce kinetic co-efficient of friction. Dr. Merchant, one of the pioneers in the theory of metal cutting, has suggested a theory to explain the penetration of cutting fluid.It is assumed that minute capillaries exist at the too chip interface as shown in figure on a sub microscopic scale.

As the chip moves up the tool face, it contacts mainly the tops of the asperities in the point contact zone creating capillaries between the chip and the tool. These capillaries draw in the cutting fluid which chemically reacts to produce a solid low shear strength film. Under the condition of high pressure and temperature at the nascent chip surface the highly reactive chemical action produces relatively weak solid providing a sandwich filling to keep the chip and tool apart thereby reducing friction.