Cutting fluid is a fluid which is employed during machining operations such as turning, drilling, reaming, grinding, stamping and milling. It reduces the friction and hence reduces the power requirements. It cools the tool as well as the work piece.  Cooling of the cutting tool maintains its cutting ability and hence increases the tool life. It will also increase the rate of production. Cooling of the work piece saves it from thermal deformation and improves the surface finish. Thus rejection of the final product is reduced and also the value of product is increased because of improved surface finish. Different types of cutting fluids such as water, soap solution, oils, oil-water emulsions, pastes, gels, aerosols and air or other gases are used in different machining operations. Water is cheap and best but causes rust. Therefore something is to be added to water to make it a better cooling cutting fluid.

Functions of a Cutting Fluid

  • Does effective cooling
  • Provide good lubrication
  • Prolong cutting-tool life
  • Assure rust protection
  •  permit less heat production
  •  reduce power consumption

Desirable Qualities of a cutting fluid

  1. Good cooling capacity
  2. Good lubricating qualities
  3. No bad odor
  4. Transparent
  5. Low viscosity
  6. should be Nonflammable
  7. Non decomposable
  8.  Non- corrosive
  9. Non-toxic
  10. Easy separation from work piece and chips
  11. Quick setting of grit and fine chips so these are not recirculated along with the coolant
  12.  It should be safe to use.
  13. Resistant to fungus growth.
  14. Resistant to bacteria and mold growth.
  15. Requires no additives to preserve a fresh, clean product.


  1. Reduces rusting
  2. Reduce power requirements for machining
  3. Increases tool life
  4. Improves surface finish on the work piece
  5. Reduces the amount of heat generated during cutting
  6. It breaks the chips into small pieces.
  7. Removes the chips away from the tool.
  8. Reduces work piece rejections
  9. It permits higher speed which reduces machining time
  10. Increases rate of production
  11. Decreases cost of production
  12. Easy separation of chips from the work piece
  13. Quick setting of grit and fine chips so they are not recirculated with the cooling fluid

Examples of cooling fluids

  1. Straight oils—–Petroleum oils
  2. Soluble oils—– These oils form an emulsion when mixed with water. In this, a base mineral oil and emulsifiers produce a stable emulsion. These are used in a diluted form (usual concentration is 3 to 10%). These are widely used and are least expensive among all cutting fluids.These are available as Apex 9900, Apex 9800, Apex 9500
  3. Synthetic fluids——- Synthetic Fluids are formed from alkaline inorganic and organic compounds along with additives for corrosion inhibition. These are also used in a diluted form (usual concentration is 3 to 10%). Synthetic fluids have the best cooling performance among all cutting fluids.
  4. Semi-synthetic fluids— Semi-synthetic fluids are the combination of synthetic and soluble oil having properties of both. Their cost is in between the cost of synthetic and soluble oil fluids.
  5. Lord oil with mineral oil is used with steels.
  6. Sulphur brass oil with mineral oil is used with alloy steels.
  7. Soluble oil with 90 to 95% of water is used with copper.
  8. Mineral oil with soluble oil is used with aluminium.
  9. No cutting fluids are used with cast iron.


Refractometers are used to measure the concentration of emulsions. pH meters are used to measure the pH value. Biocides are added to reduce bacteria growth. Particulate matter is separated with a centrifuge. These degrade with the passage of time and these are rejected. Before disposal these are treated with chemicals to make these harmless to the living beings and the environment.