Metal working lubricants are important and in fact, necessary production aids to engineering industry and petroleum lubricating oils have established themselves as major constituents of such lubricants. Easy availability in wide range of viscosities and quality, as well as relatively consistent price, unaffected by vagaries of nature, has been their mainstay. The petroleum lubricating oils, lack in so many properties but lend themselves easily for supplementing with chemicals and additives to suit diversely different applications encountered in working of metals.

Cutting lubricants or cooling liquids as they are sometimes called are compounded oils or emulsions which are used wherever the cutting of metal is carried on. Cutting oils are important among metal working lubricants not only owing to their requirement in large volume but also due to important technical considerations in their development, production and usage. The sophistication and automation of machine tools is considerably influenced by the availability of right type of cutting oils.

The major function of cutting oil is to cool the cutting tool as well as lubricating the face of the tool and the chip, and preventing the chip from welding to cutting edge. In addition, cutting oils also provide a flushing action for chip removal, leave no stain or discoloration on the work, leave minimum sediment deposit on the machine, prevent or inhibit rusting of the machine and the work, resist bacterial growth, etc.

Metal working lubricants are broadly classified in the following categories:

Metal Forming and Deforming Lubricants

These types are used in operations like bar, wire, tube drawing, pressing, forging, rolling etc.

Cutting Oils

These are used in operations like turning, milling, gear cutting, drilling, grinding, broaching etc.

Heat Treatment Oils

These types are used for metal quenching and tempering.

The efficient use of cutting oil in cutting operations can result in better finish and precision of worked piece, longer tool life, higher cutting speeds lower power consumption, and easy starting of cutting operation. The main function of cutting oils is dissipation of heat and lubrication. Besides, they have important side functions. They help in removal of chip and swarf. By the combination of these functions and chemical activity, when necessary, they prevent welding of chip and tool.

There are many facts to effective & efficient metal cutting. Any change which will improve one of these areas, improves the total operation.

Cutting Oils

A wide variety of cutting oil are available in the market varying in composition and form, starting from simple solutions of soap in water to complicated well balanced formulations containing mineral oils, fatty oils, synthetic fluids, emulsifiers, coupling agents, extreme pressure agents, oxidation and rust inhibitors and bactericides. However cutting oils can be broadly classified into two main groups based on whether they contain water or not. The classification is as follows:-

 Neat cutting oil
 Water based cutting oil

Neat Cutting Oil

Neat cutting oil contains mineral oils alone or in combination with fatty oils and antiweld and antiwear additives.

Water Based Cutting Oil

Water is a very good base for cutting oil since cooling is one of the most important requirements of cutting oil and water has nearly twice the specific heat of mineral lubricating oils. In addition water is an inexpensive and readily available fluid. However, water lacks badly in lubrication, rusts and corrodes steel and other metals, and it has poor wettability. Therefore, now water is used in the form of oils, commonly known as soluble oils emulsifiers as well as solutions and dispersions of various chemical salts or soaps and synthetic fluids, along with proper additive which overcome the inherent limitation of water.

Water based cutting oils are used where cooling is more important than lubrication such as at high speed cutting. Both the emulsified oil and the synthetics are made up as concentrates which are mixed with water to the desired dilution in the user's plant. This saves transportation costs and storage space and causes no problem to the uses since the mixing requires only simple equipments. The emulsions are after cut as much as 50 to 1 with water and synthetics upto 150 to 1. These dilute emulsions are circulated over the site of the cutting operation and besides causing effective cooling, carry away the metal particles formed.

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