Cutting Fluids:
Big amount of heat is produced during metal cutting, and it softens the tool and workpiece both. Tool softening is measured to the tool life; however workpiece softening helps in its machining by decreased force needs. Cutting fluid carries away heat, and decrease friction (among chip and tool, and among tool and workpiece). This is observed that some cutting fluids (surface active cutting fluids) decrease cutting forces, surface roughness, & the degree of tool wear. Cutting fluids are extremely effective in machining tough, highly plastic metals subjected to work hardening. Although, cutting fluid influenced is decreased with an enhanced uncut chip thickness and cutting speed. Therefore, cutting fluids are imagined to give high cooling influence, lubricating effect, stability, and high anticorrosive properties, but they must be less toxic.
The cutting fluids are categorized in two groups: those utilized for cooling influence and those utilized for lubrication. The primary group of cutting fluids are low viscosity liquids along high heat conductivity and high heat capacity. Usually these are aqueous solutions of mineral electrolytes (sodium nitrate, soda ash etc.) and emulsions. Latter are colloidal solutions of organic acids and soaps in mineral oils, stabilized by water or water and alcohol. A good cutting fluid must have good oiliness along good cooling properties. It can be attained by adding surface active elements as, oleic, stearic ,palmitic, etc. These substances decree the surface tension and enhance its wetting power (oiliness).
Cutting fluids of second group (lubricant type) along high oiliness, comprise oils (vegetable oils and mineral, or their mixture), kerosene and solution of surface- active substances. These cutting fluids are utilized when very low value of surface roughness and high dimensional accuracy are attained.
Generally Cutting fluids are in the liquid form however sometimes gaseous are also utilized. Air is utilized in very restricted cases due to its poor cooling capabilities. CO2 is comparatively more common. In some of cases, sub-zero cooled air is also utilized as a coolant.