Cutting fluids: Basics of selection, parameters, application.

Main tasks of cutting fluids

Whether we are dealing with watermiscible coolants or cutting fluids, the role of these products is always similar. Their main function is cooling and lubrication, i.e. reducing friction between the tool and the workpiece, and dissipating the resulting heat.

Other functions of the products described are:

• reducing tool wear
• providing effective corrosion protection for machine tools and parts
• flushing chips or swarf from the cutting zone (good washing of the machined surface)
• ensuring the quality of machined surfaces
• preventing adhesion phenomena

Among the required properties of the machining fluid, however, are:

• low evaporation
• proper lubrication
• good compatibility with the material
• high stability
• reduced lift-off with the material and chips
• minimized foaming
• safety for operators and the environment

In general, cutting fluids are used in classic grinding and chip machining operations, as well as in oil mist lubrication operations.
As for the chemical composition of those fluids, the composition includes base oil and additives. Among the latter are:

• additives that improve lubricating properties, such as active and inactive anti-seize (EP), anti-wear (AW)
• supporting additives such as anti-corrosion, anti-foaming, anti-oxidation, anti-fogging and others.

What to consider when choosing the cutting fluid?

The following factors are worth considering:

• what materials or alloys are being machined
• what operations are being performed
• what is the degree of difficulty of a given machining operation (depth of cut, machining regimes, etc…)
• taking into account the requirements of subsequent operations after machining (welding, painting, washing, maintenance, etc.)
• what is the expected time and conditions for storage of parts after machining
• what are the requirements on the subject of odor and other oil characteristics
• what are the previous experiences with the products and the process

However, the analysis of the above factors is just the beginning in the selection of a fluid. It is also necessary to perform technological trials. The following are illustrative examples of applications in accordance with specific requirements.

For Grinding

Machining fluids that form solutions with water work well, as do low-viscosity oils. Semi-synthetic emulsion machining agents, which form opaque, milky emulsions with water, are often used, as are transparent synthetic products. The task of the described agents will be to dissipate the intense heat, lubrication and good leaching. Also taken into account anti-corrosion properties.

For Milling

Here it is worth taking into account whether we are dealing with ordinary or fine machining. In the former case, low-concentration oil emulsions without EP additives are used. The second scenario involves using products with EP additives of high concentration. For low-speed milling of acid-resistant, heat-resistant and austenitic steels, oil agents with EP additives with a viscosity class of 46 are used. Gear milling, on the other hand, is usually carried out using formulations with EP additives with a viscosity class of 22 or 32.

For Drilling

Water-oil emulsions will be ideal. Depending on the accuracy of the process, different concentrations are used. When drilling accurately, it is worth implementing oils with EP additives with a viscosity class of 7 or 10. Water-oil emulsions are used in materials that are not prone to adhesion phenomena. However, when drilling hard-to-cut steels (for example, ductile hard steels), agents with active EP additives will be recommended.

For Cutting

This operation can also vary greatly. In the case of finishing turning, we are dealing with a small section of the cut layer and higher speeds. Therefore, the best choice will be emulsions or microemulsions with EP additives of 7 -10%. On the other hand, for coarse and medium fine turning, the same agents with a concentration of 6-8% will be completely sufficient. For ordinary steels, agents without lubricating additives or with chemically inactive additives are perfectly suitable. On the other hand, for alloyed and austenitic steels, oil formulations with chemically active lubricating additives (EP) are already required.

For cutting materials with different degrees of hardness.

If you are dealing with hard alloys, it is best to use oils with chemically inactive additives. On the other hand, in the case of machining ductile materials, agents with EP chemically active additives will be much better.

As you can see, selecting the right fluid for such specific applications is not easy. It requires considerable experience, and in this regard it is best to consult a specialist.

Properly selected lubricants for cutting bring the following benefits:

• help achieve the expected performance of machined surfaces,
• provide a safe working environment,
• bring profits in the form of a quality product obtained,
• increase the efficiency of machining processes, regardless of the type.

In the following article on machining media, we introduce and describe the FUCHS range of products that are ideally suited to customers’ requirements. We invite you to read on.