Everything you need to know about cutting fluid

Due to the advancement of technology, machining processes have brought about the usage of cutting fluid. Cutting fluid is a type of coolant and lubricant used by metalworkers to prolong the working of a cutting tool. the substance also helps to easily cut out hard material without wearing out the tool. There are various types of cutting fluids out there, which include oils, oil-water emulsions, pastes, gels, aerosols (mists), and air or other sources of gases.

Read more: Everything you need to know about cutting fluid

Today you’ll get to know the meaning, functions, types, properties, selection, applications, delivery method, and advantages of cutting fluid.

cutting fluid


What is a cutting fluid?

A cutting fluid is a gaseous or liquid substance used for improving the cutting condition during the machining process and also the save the life of the cutting tool. The term cutting fluid is also called coolant or lubricant, cutting oil, or cutting compound, well it depends on the context and the type of cutting fluid that is used. Cutting fluids are applied while machining or cutting operation is ongoing. The machining operation could be either turning, drilling, milling, etc.

Cutting fluids are made produce from petroleum distillates, plant oils, animal fats, water, air, or other raw ingredients. Cutting fluid is used generally in metalworking and machining processes. The type of cutting fluid to be used will be determined by the workpiece material. Cast iron and some brasses are materials that can be machined dry, although brass will benefit when cutting fluid is used while machining.

Read more: Understanding Foundry and Casting Process

Functions of cutting fluid

Generally, cutting fluids are known for performing two functions which include cooling and lubrication.


During the machining process, heat is generated due to friction and energy lost deforming which deforms the material. The air in the surroundings conducts heat poorly, which is called low thermal conductivity, that is, not enough coolant or poor coolant. In production work where heavy cutting is performed over long time periods, which produces more heat cutting fluid is considered rather than air cooling. Liquid coolant removes significantly more heat. It also speeds up the cutting process, so as reduce friction and tool wear.

Furthermore, both the tool and the workpiece material heat up and the excessive temperature can ruin the temper of both. That is, the tool and material will soften to the point where it fails and becomes useless. The heat will burn the adjacent material, create an unwanted thermal expansion, and can even lead to oxidation, which is known as an unwanted chemical reaction.


Apart from cooling, cutting fluids also help to lubricate the interface between the tool’s cutting edge and the chip during the cutting process. With this, friction is prevented at the surface, and also some of the heat generation is prevented. Cutting fluids that function as lubrication also prevent the chips from being welded onto the tool, which can end up interfering with subsequent cutting.

Read more: Different types of rolling mills and defects in rolled metal

Now let us briefly see the functions of cutting fluid in general.

·         It helps to dissipate heat during machining.

·         For workpiece cooling.

·         For cooling the tool.

·         To reduce friction and wear.

·         For reduction of forces and energy consumption.

·         To improve the tool life.

·         Chips are flushed away by cutting fluids

·         Good and clean surface finish is obtained if cutting fluid is used.

·         Machine surface is protected from environmental corrosion.

cutting fluid

Properties of cutting fluid

Below are the properties a cutting fluid must have in order to perform the above-mentioned functions, these properties include:

·         High flash point so that it can be used at high temperatures.

·         Low viscosity, in order to flow easily above the workpiece.

·         Stableness at high temperatures.

·         It should have a non-forming tendency.

·         Good lubricating properties in order to reduce friction between tool and workpiece.

·         High heat absorption rate so that heat can be easily absorbed.

·         It should not react chemically; that is, it has to be chemically active in nature.

·         Cutting fluids should be odorless to avoid bad smells even at higher temperatures.

·         It should be harmless.

·         It should be transparent so that the operator can see the cutting area.

Read more: Hot and Cold Rolling Process

Selection of cutting fluid

Below are the things to consider while selecting a cutting fluid and a list of materials and their suitable cutting fluid.

·         While selecting a cutting fluid, the first thing to consider is the job material as well as the tool material.

·         Secondly, the kind of cutting operation also matters.

·         Lastly, the cooling effect, that is, how the cutting fluid will react with the material.

Below is a list and diagram of material with their recommended cutting fluids and operation.

CI, BrassDry Fluid
SteelCutting oil or Cutting compound
High-speed steelwaterless cutting fluids
Hard Steel, BronzeMineral Oil

Read more: Understanding Hardness, strength, and toughness of materials

Classification of cutting fluid

There are different ways of classifying cutting fluids but there is no standardization to establish them within the industries. However, below are the most common way of cutting fluid classification.

  1. Air
  2. Water-Based Cutting Fluids:
  3. a) – water;
    b) – emulsions (soluble oil);
    c) – chemical solutions (or synthetic fluids);

III. Neat Oils:

  1. a) – mineral oils;
    b) – fatty oils;
    c) – composed oils;
    d) – extreme pressure oils (EP);
    e) – multiple use oils

Read more: Understanding the various types of residual stress

Types of cutting fluid

Below are the various types of cutting fluid and their working.


Water is one of the common ways of heat dissipation during machining but is poor in lubrication. The substance also encourages rust to the material. It is commonly used as a cooling agent during tool grinding because it’s not a long process.

Soluble oils (Emulsions):

Soluble oil-cutting fluids composes of soluble oil, emulsifiers which are comprised of sodium sulfonate, fatty, acid soap, and esters. Additives such as corrosive resistance or coupling agents and water for dilution are also included. It is one of the most common and largest types of cutting fluid used in machining operations. Let me explain how the cutting fluid works.

Emulsifiers are chemical substances that allow the suspension of tiny oil droplets. The coupling agents which are the additives provide a white emulsion with no oil or cream separating out after mixing with water 5% dilution level is the most common level of dilution. These types of cutting fluids have average lubricating abilities and good cooling properties. Although they are best suitable for light cutting operations on general-purpose machines where low metal removal rates are done.

Straight oils (petroleum or vegetable oils):

Good examples of straight oils are paraffin oils, naphthenic oils, vegetable oils, etc. Commonly, it is a petroleum or vegetable oil that is used without dilution with water. Straight oils provide excellent lubrication and for environmentally favorable requirements, vegetable oils play the role due to their ease of biodegradation and disposal. However, they are not often used because they are responsible to decompose and smell bad.

Mineral oils:

Mineral oils are another special type of cutting fluids used for heavier cutting operations because of their good lubricating properties. They are commonly used in the production of machines where high metal removal rates are performed. Also, they are best suitable for steel but should not be used on copper and its alloys since it has a corrosive effect.

Read more: Understanding petrol engine

Synthetic fluids:

These types of cutting fluids are water-based fluids and contain no mineral oil. They have a typical particulate size of 0.003mm.  because water provides excellent cooling properties but is corrosive it cannot be used on all materials and operations. This cutting fluid is not also effective as a lubricant. However, rust to the material can be prohibited when rust formation such as rust inhibitors is added. Finally,

Semi-synthetic fluids:

The semi-synthetic types of cutting fluid are a mixture of soluble oil (emulsions) and synthetic fluids (water-based fluids). In this cutting fluid, about 5 to 20% mineral oil is emulsified with water so that microemulsion is produced. The part size varies from 0.01 – 0.1mm which is small enough to transmit all incidents lightly. These types of cutting fluids are widely used because they offer the benefits of both soluble oils and synthetics.

Read more: Difference between petrol and diesel engine

Watch the video below to learn more about the working or operating of cutting fluid as well as the delivery methods:


cutting fluids are very important in metalworking and even engineering industries today since some other materials and tools also need cooling and lubrication during their cutting or machining process. In this article, we’ve learned and explained what is cutting fluid, its functions, properties, selection, classification, types, as well as delivery methods of cutting fluids.

I hope you’ve got a lot from this lesson, if so, kindly share it with other technical students. Thanks for reading! See you next time.


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