What is Cutting Fluid?: Functions, Properties, Types, Classifications, and Safety


Cutting fluid is a gas, liquid or paste that consists of high thermal conductivity and lubrication properties to use in metalworking and machineching process to cool, lubricate, and remove chips in the cutting or drilling area. “Cutting fluid”, and “cutting oil” is the same term and use for the same work and purposes.

Cutting fluid has two useful functions such as lubricating and cooling. Lubritacitng can reduce friction, and cooling can reduce the generated heat from the tool and workpiece. Additionally, cutting oil help to prevent corrosion and remove the chips of the cutting area.

Cutting oils are mainly 6 in type. Those 6 types are mineral, synthetic, semi-synthetic, soluble, neat, and environmentally friendly cutting oils. The most used cutting oils are semi-synthetic cutting oil. According to the physical form, cutting oils are mainly 3 categories. Those are liquid, paste, or gel. The “Aerosol” category is the mix of air and liquid.

When you use cutting fluid, you should follow these safety precautions such as use gloves, a face mask, eye protection, protect the floor from slippering, safely store, and avoid eating, drinking, and smoking. Else cutting fluid can affect the skin, eyes, and respiratory systems. For better physical safety machine area should be free from slippering to prevent slips and falls. Cutting oil should be stored properly and prevent form hygiene. Used cutting oil should be disposed properly.

Improper disposal of cutting fluid can cause to environmental pollution such as water pollution, soil pollution, air pollution, biodiversity loss, non-biodegradability, resource depletion, and waste generation.

What are the 2 Functions of Cutting Oil?

The two functions of cutting oil are lubricating and cooling. Lubricating can reduce friction, and cooling can reduce the generated heat from the tool and material. Due to these functions, there are benefits as below.


Cutting oil consists of lubricating material. These lubricating materials reduce the coefficient of friction at the cutting interface. Due to the lubrication of the cutting tool, there are 3 main benefits. 

  1. Cutting fluids can reduce the wear and tear resistance on the cutting tool and improve the cutting tool durability with minimum maintenance and sharpness. 
  2. When the friction is reduced, required cutting force is also reduced. Hence cutting tool can cut smoother and better surface finishes. 
  3. Lubrication help to prevent the tool from binding or getting stuck during the tapping or threading operations.


Cutting fluids consists of thermal conductivity materials. Thermal conductivity material help to remove heat generation form the workpiece and tool during the cutting operation. Due to the cooling properties of the cutting fluids there are 3 main benefits.

  1. The cutting tool and workpiece temperature can be controlled.
  2. The tool can be prevented from wearing, braking, and overheating.
  3. Fast-cutting speed can be approached.

What are the 6 Properties of Cutting Oil?

cutting oil properties

Cutting fluid has 6 useful properties such as viscosity, thermal stability, lubricity, cooling capability, and antiwear extreme pressure additives. These properties have specific definitions and benefits of using them.

  1. Viscosity
    • The viscosity of cutting oil is the thickness or resistance to flow during operation. 
    • If the oil is too thin (low viscosity), it may not adhere well, and if it’s too thick (high viscosity), it may not be distributed efficiently.
  2. Thermal Stability
    • The thermal stability of cutting oil is to retain its properties and performance at high temperatures.
    • A better thermal thermal stability cutting oil will not break down, evaporate excessively, or form sludge when exposed to these high temperatures.
  3. Lubricity
    • The lubricity of the cutting oil can reduce the friction.
    • High lubricity ensures that the cutting oil provides an effective barrier between the cutting tool and the workpiece.
  4. Cooling Capability
    • The cooling capability of the cutting oil is to absorb and dissipate heat.
    • Cooling capability help to remove some of the generated heat during the machining process. Cooling capability can protect both the tool and the workpiece from heat-related damage.
  5. Anti-wear and Extreme Pressure (EP) Additives
    • Antiwear and extreme pressure additives enhance the oil’s ability to prevent wear under high load or extreme pressure conditions.
    • These additives react with the metal surface to form a protective layer in extreme pressure conditions.
  6. Corrosion Inhibitors
    • Corrosion inhibitors are the chemicals that prevent oxidation and rusting of the machined surfaces and the machinery.
    •  They protect both the machined part and the equipment from moisture and contaminants that can cause corrosion

What are the Types and Usage of Cutting Oil?

cutting oil types

The cutting oils are mainly of 6 types. Those are mineral, synthetic, semi-synthetic, soluble, neat, and environmentally friendly cutting oils. Each cutting oil has specific properties and materials. Therefore these cutting oils are used in various operations.

Mineral Cutting Oils

Mineral cutting oils are used in their undiluted form. Mineral cutting oil primarily comprises base mineral or petroleum oils and may also contain specific additives like sulfur, chlorine, or phosphorus to enhance their lubricating properties.

  • Usage: Mineral cutting oil is typically used for operations requiring good lubrication, such as drilling, tapping, and broaching. They’re especially common in cutting and drilling in tough materials like stainless steel.

Semi-Synthetic Oils

Semisynthetic cutting oil is a blend of mineral oils and synthetic lubricants. They offer a balance between cooling and lubrication.

  • Usage: Semisynthetic cutting oil is good for a broad range of operations. Semi-synthetic oils are used in both machining and grinding processes on ferrous and non-ferrous metals.

Synthetic Cutting Oils

Synthetic cutting oil is made from non-petroleum-based components. Synthetic cutting oil don’t contain mineral oil but instead are formulated from organic and inorganic chemicals.

  • Usage: Synthetic cutting oils are often used in grinding operations, as well as in situations where staining or environmental concerns are paramount. They can also be used in high-speed machining operations on various metals.

Soluble Oils (Emulsifiable Oils)

Soluble cutting oils are mixed with water to form an emulsion. The oil content provides lubrication, while the water offers cooling.

  • Usage: Soluble oils are widely used in general machining operations, including milling, turning, and grinding, especially where cooling is as crucial as lubrication. They can be used on a variety of metals.

Neat Oils

Neat-cutting oils are non-emulsifiable oils, often fortified with polar lubricants like fats, esters, and extreme pressure additives.

  • Usage: Neat-cutting oils are generally used in severe machining operations like gear hobbing, screw machining, or deep-hole drilling, especially where a stable lubricant layer is crucial.

Environmentally Friendly Oils (Green Oils)

Environmental-friendly cutting oils are made from natural sources, such as vegetable oils, and animal oils, and are biodegradable.

  • Usage: They’re employed in applications where environmental concerns are significant, and they can be used for various machining operations, especially in places with strict environmental regulations.

What are the Classifications of Cooling Fluids?

Cooling fluids can be classifieds as mainly liquid, paste or gel, aerosols, CO2 coolants and Air and other gases. All of the cutting fluids can be classified into these categories as follow.

  • Liquid cutting fluids
    All of the liquid cutting fluids are classified in this category. The main 3 liquids cutting fluids are 
    Mineral, Synthetic, and Semisynthetic
  • Paste or gel-cutting oil
    Cutting fluid is a form of gel or paste when it is used for some applications. Especially paste/gel cutting fluid is used for drilling and tapping. This is commonly used in sawing metal. The paste is easy to stick on the saw blade.
  • Aerosols
    Aerosols are a combination of air droplets and water mixtures. It is a bad cutting fluid because it can spread surroundings, and those are not lubricate the tools and cool the workpiece and tools properly.
  • CO2 Coolant
    CO2 Coolant is used to control the cutting temperature of the workpiece and tool. Pressurized liquid Co2 is used as the coolant. CO2 coolant does not provide lubrication.
  • Air or Gases
    Compressed air is used as the cutting fluid. The discharge flow can remove the cutting chops away and it will reduce the temperature of the tool and workpiece slightly. 

What are the 7 Safety Precautions of Cutting Oil?

cutting oil safety

The 7 safety precautions of cutting oil are using gloves, a face mask, eye protection, protecting the floor from slippering, safely storing, avoiding eating, drinking and smoking and proper disposal.

  1. Skin Protection
    • Wear appropriate gloves to prevent prolonged skin contact with cutting oils. Some cutting oils can cause skin irritation or dermatitis with prolonged exposure.
  2. Eye Protection
    • Always wear safety glasses or face shields to protect against splashes, especially when pouring, mixing, or when working closely with machinery where cutting oil is in use.
  3. Respiratory Protection
    • Ensure good ventilation in areas where cutting oils are used. Inadequate ventilation can lead to the accumulation of oil mists or vapours, which can be harmful when inhaled.
  4. Prevent Slips and Falls
    • Clean up any spills immediately. Cutting oils can make floors extremely slippery, leading to falls.
  5. Safe Storage
    • Keep containers in a cool, dry place away from direct sunlight and sources of ignition.
  6. Hygiene
    • Avoid eating, drinking, or smoking in areas where cutting oils are used or stored.
    • Always wash hands thoroughly after handling or working with cutting oils before eating or touching the face.
  7. Disposal
    • Dispose of used or waste-cutting oil as per local regulations. Consider recycling or reusing where possible.
    • Do not pour cutting oils down drains or into open ground.

What are the Environmental Pollution and Effects of Cutting Oil?

The environmental pollution of cutting fluid is water pollution, soil pollution, air pollution, biodiversity loss, non-bio degradability, resource depletion, and waste generation. Each of these pollution affects the environmental effects in different ways, as below.

  1. Water Pollution
    • If cutting oils are improperly poured into drains or waterways, they can contaminate water sources. This can harm aquatic life due to the toxic components present in the oils. Additionally, oil creates a film on water surfaces, reducing oxygen exchange and potentially causing hypoxia for aquatic organisms.
  2. Soil Contamination
    • Spills or improper disposal can lead to soil contamination. The soil can absorb the harmful chemicals present in the cutting oils, making the land unfit for agriculture or other uses. Contaminated soil can also leach harmful chemicals into groundwater.
  3. Air Pollution
    • The machining process can produce oil mists and vapors. If inhaled by humans, these can be harmful, but they also contribute to air pollution. Some components in cutting oils can contribute to the formation of smog and other airborne pollutants.
  4. Biodiversity Loss
    • Contamination of natural habitats, whether water or land, can lead to a decline in the variety of species in those areas. Some species may be more sensitive to pollutants than others, and their decline can affect the entire ecosystem’s balance.
  5. Non-biodegradability
    • Many traditional cutting oils are non-biodegradable, meaning they persist in the environment for a long time if spilled or improperly disposed of.
  6. Resource Depletion
    • Many cutting oils are derived from petroleum, the extraction and processing of which has its own environmental consequences, including habitat destruction, potential spills, and greenhouse gas emissions.
  7. Waste Generation
    • Used cutting oils, contaminated rags, and filters become hazardous waste. If not managed properly, this waste can pose environmental risks.
  8. Greenhouse Gas Emissions
    • While cutting oils themselves are not major contributors to greenhouse gas emissions, the production, refining, and transportation of petroleum-based cutting oils contribute to carbon emissions.