Cutting Oils That Provide Better Surface Finish & Increase Tool Life

Posted by Mary Kimbro on Jul 14, 2020 11:40:46 AM

Enhanced Cutting Fluid Formulations with Specialty Additives

Historically, conventional straight oils consisted of only oil or a mixture of oil and lard that didn’t last very long when used for machining metal. However, with current technology there is a wide selection of high performance oil Cutting Oilssoluble additives that help improve performance and prolong the life of these oil based cutting fluids. These enhanced cutting oils provide significantly better surface finish and increased life of the machine tool. This reduces scrap and the overall tool demand: increasing the return on investment of the machining process.

Lubricity Additives

Specialty lubricity additives for oil based cutting fluids dramatically helps reduce surface tension and friction providing more consistent metal surface finishes that facilitates the production of parts that require tighter specs. Lubricity additives perform by:

  • Absorption onto the surface providing protection in metal removal and protecting fluids
  • Increasing the viscosity index of the straight oil with specialty esters allows for less change in viscosity when there are fluctuations in temperature and an increase in the film strength
  • Providing a physical separation in metal forming fluids

Extreme Pressure Additives

Extreme pressure additives are highly effective in forming a sacrificial film that fills asperities on metal surfaces to:

  • Eliminate surface wear and welding
  • Help prevent metal to metal contact
  • Reduce friction allowing for low shear strength

Other Additives

Because straight oils run hotter and are traditionally a combination of mineral oils, oxidation is a big concern for fluid life. Naphthenic oils or even Group I paraffinic oils, which are less oxidatively stable, require an antioxidant be added to help extend the functional life of the oil. Some additive chemistry can stain the metal being machined. Active sulfur is a commonly used extreme pressure additive that will stain yellow metals. Fortunately, stain inhibitors have been developed to help protect the metal surface.

Misting of cutting oils was once a big health and safety concern because as mist was introduced into the shop air, operators were subjected to breathing in droplets of oil. With antimist additives, misting is reduced or even eliminated from the shop air.

All of these additives work together to provide features and benefits to the end user.

Features Benefits
Improved finish due to lubricity and extreme pressure additives Less scrapped parts
Minimizes misting, smoke, and odor Providing a healthier, safer, and more pleasant work environment for machine shop operators
Viscosity optimization: a product that is not too trick and not too thin Providing a balance dialed into specific applications which will allow for the best tool-life and part finish
Provides solvency Giving better penetration of the oil to the machine tool/workpiece interface where lubrication is essential


Choosing the Best Formulation

When selecting the best formulation of an oil based metalworking fluid the following conditions are important to consider:

Choosing the Best Formulation chart 2

Always refer to the fluid manufacturer’s guidelines to ensure the proper match of oil and chemistry with the application.


Straight oils with the proper additives are best in low speed applications when machining gummy metals, such as aluminum, or harder metals like stainless steel. These superior metalworking fluids encompass:

  • Honing Oils
  • Tapping Oils
  • Reaming Oils
  • Grinding Oils
  • Deep Hole Drilling Oils
  • Pipe Threading Oils
  • Gear Hobbing & Cutting Oils
  • Internal Broaching Oils

Straight cutting oils provide many advantages due to their superior lubricity, good corrosion protection, and extended sump life. The excellent lubrication properties of neat oils help to reduce frictional heat as the cutting tool penetrates the metal or drags against the freshly machined surface and newly generated chips. In addition, the reduction in cutting forces helps to decrease energy consumption. Oil based cutting and grinding fluids perform best in critical heavy duty machining operations where lubricity is the most important criteria of the fluid.

Download the paper below to learn how specialty lubricity additives for cutting oils provide significantly better surface finish and increased tool life.

Cutting Oils for Cutting & Grinding

Topics: Cutting Oil, cutting fluid

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