Cutting Fluids


Reading Assignment

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Cool workpiece and tool

  • Temperature is an important factor in tool life
  • Influences surface integrity


  • Reduces power requirements
  • Increases production rates
Corrosion Protection
Inhibit bacterial growth
Chip removal

Oil Vs. Water

Main Advantages
Oil – Lubricity
Water – Cooling Capacity
  • Water is capable of dissipating heat 2.5 times faster than oil.


Surface reaction can be:

  • Hydrophobic
  • Hydrophilic

Contact Angle

Should a cutting fluid’s reaction with the surface be hydrophobic or hydrophilic?

Types of Cutting Fluids

Inactive Cutting Oils

Mineral Oils
    • Straight Mineral Oils
    • Compounded Cutting Oils
      • Blended with additives such as animal and vegetable oils.  Increases wetting ability.  Alows fluid to penetrate too/chip interace.
    • FattyMineral Oils
      • Improve surface finish in machining steel, brass, copper, and aluminum

Active Cutting Oils

  • Cause a film to develop on tool surface and provide anti-weld properties.
  • Contain
    • Sulfur
    • Chlorine
    • Phosphorous

Emulsified Oils (Soluble Oils)

  • Oil droplets suspended in water by blending the oil with emulsifying agent.
  • Advantages:
    • Greater heat reduction, higher cutting speeds
    • Potentially cleaner working conditions
    • More economical (diluted with water)
    • Better operator acceptance (cleaner, cooler parts)
    • Improved health and safety benefits
      • Not a fire hazard
      • Misting and fogging are reduced

Chemical Fluids

Contain no petroleum oil
True-solution Chemical fluids contain no wetting agents, usually clear
Surface-active chemical fluids have wetting agents.

Semichemical Fluids

Contain mineral oils
Advantages of Chemical and Semichemical Fluids

  • Rapid heat dissipation
  • High degree of cleanliness
  • Light residual films are easy to remove
  • Ease of mixing, little agitation needed


  • Lack of lubricity
  • High detergency, irritates hands
  • Tend to foam
  • Disposal problems

Gaseous Fluids

  • Air
  • Compressed Air
  • Argon, helium, nitrogen have been used, but are expensive.

Pastes and Gels

  • Waxes, soap-like lubricants, graphite compounds
  • Used where lubrication is much more important than heat removal.
    • Tapping
    • Drilling
  • Used when working against gravity

Factors in Cutting Fluid Selection

  • Machining time per part
  • Number of rejects from unacceptable surface finish
  • Machine downtime due to tool changes and maintenance
  • Cutting fluid consumption per part
  • Cutting fluid batch life
  • Cutting fluid disposal or recycling costs
  • Compatibility (workpiece and tool)

Application of Cutting Fluid

  • Manual
  • Flood
  • Mist
  • High pressure – through tool

Maintenance Considerations

Clarification/Separation Methods

  • Tramp oil skimmers
  • Settling (Weirs)
  • Centrifuge
  • Magnetic Separators

Storage of Concentrate

Water Quality

  • Hardness/Softness

Rancidity Control

Bacteria found in fluids

  • Aerobic
  • Anaerobic

Physical Tests

  • Concentration  (refractometer)
  • Viscosity
  • Flash Point
  • Stability
  • Emulsion Stability
  • Residue
  • Foaming

Chemical Tests

  • pH
  • Corrosion

Microbiological Tests

Health and Safety

Types of Risk

  • Oral Toxicity
  • Inhalation Toxicity
  • Dermal Toxicity
  • Skin Irritation
  • Eye Irritation

Rule of thumb: Minimize contact with workers!

Additional Resources

Curran, K. and Blohowiak, C.  Cutting Fluid Types and Uses Wisc-Online []

Cutting Fluid Brands

Trim (Master Chemical) E206 is good general purpose cutting fluid


Liquid Ice

Valenite Valcool

Primrose (Extreme Pressure Lubricant)

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