The role of CNC coolant and lubricant types in machining

Introduction

The use of CNC coolants and various lubricants fundamentally determines the success of machining in modern metalworking manufacturing. These specialized fluids provide cooling, lubrication, and continuous cleaning during machining operations.

The use of a professional CNC coolant not only optimizes production processes but also directly contributes to extending the service life of expensive machine tools. It also improves the surface quality of finished components. In this article, we take a detailed look at the most important types of fluids and their industrial applications.

The main types of CNC coolant options

Coolants

During CNC machining, significant heat is generated by friction between the tools and workpieces. Various types of coolants are used to dissipate this heat, helping to prevent overheating and ensuring the efficient operation of the machine. There are three main types of CNC coolants:

Water-based coolants: They are the most widely used solution on the market due to their excellent heat transfer properties. Water naturally dissipates heat quickly, making these coolants ideal for high-speed machining processes. However, these fluids do not provide sufficient lubrication on their own, which is why they are often used in the form of an emulsion, combined with oil.
Oil-based coolants: They offer excellent lubricating properties, meaning that they not only provide cooling but also significantly reduce friction. Oil-based coolants are often used in precision machining processes, where accurate and fine cutting is essential. Oil-based fluids are particularly beneficial when machining difficult-to-cut materials, as they significantly reduce tool wear.
Synthetic coolants: They are made from artificially produced compounds that provide optimal cooling and lubrication. Synthetic coolants can be more durable and effective than their naturally based counterparts, while also reducing tool wear. In addition, they can offer more environmentally friendly solutions, as they are less polluting and have a lower risk of biodegradation.

Lubricants

Lubricants used in CNC machines reduce friction between the tool and the workpiece, thereby helping to extend tool life and maintain the efficiency of the machining process. Selecting the right lubricant is critical to the machine's performance.

Cutting oils: These oils are designed to reduce friction directly between the tool and the workpiece. Cutting oils promote smooth cutting and minimize tool wear, particularly when machining at high speeds and working with hard materials. A wide range of cutting oils is available for different applications, including deep-hole drilling, turning, milling, and drilling.
Greases: These are thicker lubricants used to protect tools and machine components. Greases adhere better to machine surfaces and provide excellent protection against tool wear. They are mainly used in lower-speed machining processes or in applications where lubrication needs to be maintained for longer periods.

Emulsions and mixtures

Emulsions and mixtures provide both cooling and lubricating properties, making them particularly beneficial in applications where both are required. Base fluids are often supplemented with various additives, such as corrosion inhibitors, anti-foaming agents, and biocides, to prevent bacterial growth and extend the service life of the CNC coolant.

Oil-water emulsions: These emulsions provide excellent cooling and lubrication. Oil-water mixtures combine the properties of both fluids to optimize both heat dissipation and lubrication. Emulsions typically contain a low concentration of oil, which improves cooling performance without compromising lubrication efficiency.
Various mixtures and additives: Emulsions and other metalworking fluids are often combined with various additives that enhance their cooling and lubricating properties. These additives may include corrosion inhibitors, anti-foaming agents, and biocides, which prevent the growth of bacteria and fungi in the fluid. These mixtures are particularly important for long-term fluid use, as they extend fluid service life and improve machine performance.

How does CNC coolant work during machining?

While the types of coolants and lubricants vary, they all share a common goal: ensuring the efficient operation of the CNC machine. Let’s take a look at how these fluids support the different stages of CNC machining:

Cooling during machiningCNC machines, particularly during high-speed machining processes, generate a significant amount of heat. Coolants directed directly onto the tool and workpiece dissipate this heat, preventing the tool and workpiece from overheating, which could otherwise lead to deformation or material fatigue. In this way, these fluids ensure precise machining and longer tool life.
Lubrication to reduce friction: Lubricants used in CNC machines help minimize friction between the tool and the workpiece. This is particularly important in metalworking, where friction can generate extreme temperatures that may lead to rapid tool wear. Proper lubrication not only extends tool life but also improves the surface quality of the cut, resulting in a more precise and aesthetically pleasing finish.
Cleaning and chip removal: A properly metered CNC coolant also plays a role in cleaning, as it removes chips and contaminants generated during machining from the work area. This is particularly important in precision machining, where chip accumulation can affect the quality of the finished product. The fluids ensure effective chip removal, improving machine efficiency and reducing downtime.

Key considerations when selecting a CNC coolant

Selecting the right coolant and lubricant for CNC machines is not a straightforward process. These factors determine which fluid is best suited to the manufacturing process, taking into account costs, productivity, and product quality.

The selection of the right CNC coolant depends on several technological factors:

Type of material being machined

Different materials have different machining requirements when it comes to coolants and lubricants. The selection of the appropriate fluid depends on the material’s hardness, thermal conductivity, and sensitivity:

Metals: When machining metals—particularly carbide, steel, or aluminium—high temperatures are generated, requiring effective cooling. For these materials, oil-based or water-based emulsions are used to prevent heat-induced deformation or cracking. More difficult-to-machine materials, such as titanium, may require more specialized coolants.
Plastics and composites: These materials are generally less thermally conductive but are prone to deformation when overheated. Here, selecting the right fluid is particularly important, as oil-based coolants can easily damage the material. Synthetic or milder water-based coolants are preferable for these materials.
Precision materials: When machining materials such as stainless steel or tool steel, precise cooling during high-temperature machining is extremely important. The choice of fluid is based on the need to ensure maximum precision and long tool life.

Type of machining operation

Drilling and milling: These operations generate significant amounts of heat, particularly during high-speed machining. In drilling, proper cooling is essential for producing accurate holes and extending tool life. During milling, coolants reduce the occurrence of surface defects and improve surface quality.
Turning: During turning, fluids provide continuous cooling and lubrication, as the tool remains in constant contact with the rotating workpiece. Selecting the right fluid is crucial for achieving precision and high surface quality.
Grinding: During grinding, the primary functions of these fluids are to remove fine particles and dissipate heat. In addition to cooling, lubrication also plays an important role in preventing wear of the workpiece and tool.

Type and parameters of the machine

CNC machines have different specifications that determine the requirements for fluid application. High-speed or precision machining operations may require specialized coolants and lubricants:

High-speed machiningThese types of machines generate higher temperatures, requiring the use of high-performance coolants. Synthetic fluids can be advantageous in such applications, as they provide longer service life and dissipate heat more efficiently. An innovative and highly effective cooling method is the use of ethanol, which is delivered in atomized form directly to the tool cutting edge. Due to its high alcohol content, ethanol evaporates extremely quickly, resulting in rapid heat removal during typically high-speed machining operations. This technology is used in DATRON milling machines for aluminium machining. The result is significantly extended tool life, a clean work area, and excellent surface quality.
Precision machinesFor precision machines, lubrication and cooling are essential, particularly during fine surface finishing operations. Oil-based coolants can be an excellent choice in such applications, as they provide superior lubrication and help prevent surface defects. When using oil for cooling, the risk of fire must be taken into account. This risk typically arises from tool breakage and is particularly hazardous when machining titanium. Machine tool manufacturers specifically highlight the risks associated with oil-based cooling and lubrication systems and recommend integrating an automatic fire suppression system into the machine.Tornos SA has been working with the German company Kraft&Bauer GmbH for decades, equipping its machines with effective fire suppression systems.
Automated production lines: Automated machines designed for continuous operation also have specific fluid requirements. In such applications, fluids that remain stable over extended periods and do not cause deposits are particularly important.

Environmental and health considerations

Nowadays, the environmentally friendly and safe use of fluids in CNC machines is becoming increasingly important. Selecting the right fluid not only ensures efficient production but also helps ensure compliance with environmental and health standards:

Biodegradable fluids: Such fluids are particularly important in industries where environmental protection is a key priority. These fluids have a lower environmental impact, as they biodegrade more quickly and contain fewer toxic substances.
Toxicity: CNC coolants used in machines may contain toxic substances that can be harmful to workers’ health, particularly in cases of prolonged exposure. Therefore, it is important to use fluids with low toxicity or those that do not contain harmful substances.
Waste management: The fluids used in CNC machines need to be replaced regularly, which can generate significant amounts of waste. Environmentally friendly solutions, such as fluid recycling or biodegradation, can help reduce the environmental impact.

CNC coolant maintenance and professional management

Regular maintenance of the coolants and lubricants used in CNC machines is essential for ensuring smooth machine operation. Proper maintenance extends the service life of both the fluids and the machines, reduces the risk of breakdowns and downtime, and improves the efficiency of the manufacturing process.

Fluid replacement and system cleaning

Coolants and lubricants need to be replaced from time to time, as they can become contaminated with chips, oil residues, or other substances during use. Clean fluids ensure optimal machine performance and help prevent tool wear. They also extend the service life of high-value machine tools while providing users with a cleaner and healthier working environment.

The German company ph-cleantec GmbH. has developed specialized cleaning equipment for the professional maintenance of systems. These mobile units enable machine tools to be cleaned both internally and externally on-site, within the production facility, with exceptional efficiency. The equipment can also be used to clean machine components that are difficult or impossible to access, such as the tool magazine. With the manufacturer's equipment, the machine tool's metalworking fluids can be extracted, allowing the cleaning process to be carried out using the coolant itself. During this process, the CNC coolant flowing through the equipment is briefly heated to nearly 95°C, which destroys the bacteria present in the fluid and can significantly extend the service life of the emulsion.

Use of filtration systems

Filtration systems are used to maintain the cleanliness of fluids used in CNC machines by removing contaminants. Filtration systems can be integrated into the machine or used as external peripheral equipment.

In many cases, these filtration systems are connected to individual machine tools, but central filtration systems are also frequently used in metalworking plants to continuously filter the coolants and lubricants for an entire fleet of machines.

Filtration technology offers a wide range of options, determined primarily by the machining process. From very coarse cutting operations to processes involving the finest material removal, suitable filtration equipment is available to effectively clean metalworking fluids (MWF).

The KNOLL Maschinenbau GmbH. is one of the best-known and most reliable manufacturers of filtration equipment on the market. The wide range of KNOLL filtration systems and pumps ensures continuous cleaning of CNC coolant, whether for milling, turning, or grinding operations. The manufacturer's decades of experience provides companies involved in metalworking with a reliable solution for the management of coolants and lubricants. Its product portfolio includes chip conveyors as pre-separation units, a wide variety of filtration systems, and the pumps essential for their operation.

Recycling and environmental protection

Recycling used CNC coolants reduces costs and environmental impact. Reusing purified fluids provides a sustainable solution for manufacturing processes. The use and recycling of environmentally friendly fluids helps reduce the amount of hazardous waste.

Fluid quality control

Regular monitoring of the quality of coolants and lubricants, such as checking pH levels and temperature, helps maintain fluid effectiveness and prevent machine malfunctions.

Regular maintenance schedule

Following a regular maintenance schedule ensures that CNC machines and fluid systems always operate at optimal performance. This includes periodic fluid replacement, filter maintenance, and regular monitoring of fluid quality.

Common problems and solutions

Several common issues can occur when managing fluids used in CNC machines, and these should be avoided to ensure efficient operation:

Incorrect fluid selection: If the fluid type is not suitable for the material being machined or the machining process, it can reduce machine performance and product quality. Always consult the manufacturer or a specialist when selecting the appropriate CNC coolant.
Contaminated fluid: The accumulation of chips and other contaminants reduces fluid effectiveness. Regular cleaning and filtration are essential for maintaining fluid cleanliness.
Poor maintenance practices: Neglecting the maintenance schedule can quickly lead to breakdowns. Regular fluid replacement and filter maintenance help prevent problems and extend the service life of the machines.

Summary

Properly selected and maintained CNC coolant is a cornerstone of cost-effective and precise manufacturing. It reduces tooling costs, protects the machine fleet, and supports sustainability efforts.

If you would like to optimize your plant’s fluid management processes, contact the expert team at Premium – S Kft. for comprehensive engineering consulting and premium service support.