Cutting fluids - Role in machining and classification

Studies conducted around 1883 on work organization and metal cutting were the first to report the use of soapy water to cool workpieces during machining. This increased cutting speeds by 30 to 40% and reduced the frequency of tool sharpening.

Soapy water laid the foundations for the use of cutting fluids in machining, fulfilling the essential functions of effectively assisting the material removal process, namely:

• cool the cutting area thanks to the high specific heat capacity of water;

• lubricate the tool/material interface by reducing the coefficient of friction thanks to the soap's fat content;

• Rinse the cutting environment thanks to the density of the fluid, which carries the machined material (chips and machined material) away from the cutting area and the machined surface.

In addition, soapy water was more "wetting" than pure water. However, it did not prevent corrosion and stained parts and machines. Soapy water was replaced by vegetable or animal oils, then by mineral oil emulsions, and finally by mixtures of mineral oils and fats to which additives were added to give them additional properties. The technique for distributing cutting oils changed. A central tank in each workshop was used to distribute the liquid to the various machines. Coolants were referred to as cutting oils because, whether soluble or not, these liquids always contained oils and, in most cases, a significant percentage of mineral oils.

A new step forward was taken when cutting fluids that no longer contained any type of oil became available on the market. This is why it is more appropriate to use the term "cutting fluid," as it encompasses the wide technical diversity of all cutting liquids available on the market. The NF ISO 6743-7 standard establishes a classification of cutting fluids according to the "aqueous fluids" family and the "full oils" family.

The global market for industrial lubricants, which includes cutting fluids, is experiencing sustained growth, driven by increasing demand in the manufacturing, energy, transportation, and construction sectors. In 2024, global consumption of industrial lubricants is estimated at 22.07 billion liters: it is expected to reach 26.06 billion liters by 2029, representing an annual growth rate of approximately 3.4%.

In a context of sustained demand and increased environmental responsibility, cutting fluids are being reinvented to be more virtuous, while maintaining or improving their effectiveness. This has given rise to the following concepts.

• Clean machining: this allows the full potential of cutting fluid...