Types of CNC Coolants: How to Choose One for Machining?

Machine operators often use CNC machine coolant to mitigate the effects of overheating of the cutting tool or materials during the CNC machining process. These coolants act as lubricants and cooling mechanisms and aid in chip evacuation.

This article explains how CNC coolant works and how it is supplied. You will also learn about the importance of coolants in a CNC machine, types, and more. Let's start!

What is CNC coolant?

CNC coolant or cutting fluid is an industrial fluid commonly used in metal cutting operations to improve efficiency. CNC machining coolants consist of special chemical additives formulated through concentrations of scientific compounds. Its main components are animal fats, water, petroleum distillates, vegetable oil and other raw materials.

These coolants improve the ability of CNC machines to cut materials such as high-density plastics, fiberglass, and metals while reducing the generation of high temperatures.

How do refrigeration systems work?

During CNC machining, a coolant mixture from the CNC machine flows over the work area. The coolant flushes chips and particles from the work area like a flood. It then flows into the sump at the bottom of the machine, where it needs to be pumped out and returned to the work area for continued use.

The coolant cools the workpiece during machining at high speeds and lubricates the cutting tool at low speeds. Therefore, CNC coolant increases the life of the cutting tool, protecting it from corrosion and preventing deformation of the part. To ensure maximum performance, you must monitor, maintain and adjust the central and individual cooling systems of CNC machines.

However, a small refrigeration system uses a less efficient component for oil separation and filtration, resulting in constant changes and greater fluctuations in concentration levels. Therefore, it would be better to use coolants that are less susceptible to chip contamination in small systems.

Various Coolant Supplies on CNC Machines

Different CNC machines use coolants with different properties and pressures. Therefore, choosing the ideal coolant supply mechanism for your CNC machine is crucial. If you don't choose the right quantity, workshop resources can quickly run out, while the wrong pressure can damage the part or CNC cutting tools. Here are some of the common coolant supply types on CNC machines:

Mist cooling mechanism

This coolant delivery method uses low pressure and is suitable for operations where heat and chip removal are not a priority. Mist cooling does not place any additional stress on the tool or workpiece because no high pressure is applied.

Air cooling mechanism

Air cooling technology is not ideal for lubrication reasons, but it helps reduce heat and remove chips. Air cooling is less effective because it does not contain oil or water-based coolant.

Furthermore, the air cooling mechanism is ideal for direct contact with the workpiece when processing more delicate materials. However, it is suitable for plastic materials that are susceptible to thermal shock or rapid expansion, as direct coolant often causes the part to contract.

Minimum Quality Lubricant Mechanism (MMS)

The priority of every CNC shop is to gain a competitive advantage by improving shop efficiency, increasing production and reducing costs. For this reason, CNC shops often turn to MQL for its environmental benefits.

MQL engines reduce costs and material waste by using the required amount of coolant. They usually come in the form of a very fine mist or aerosol and provide enough refrigerant to perform a specific operation efficiently.

High pressure mechanism

The high pressure CNC machine coolant supply uses pressure in excess of 1,000 psi to remove chips during machining operations. This method is ideal for vacuuming and draining chips, as it moves them away from the material.

The pressure used in this method can damage a microdiameter tool, although it can cool the part quickly and effectively. Therefore, this method is compatible with CNC drilling or deep cavity operations and is easy to transport using the built-in coolant or coolant tank.

Types of Coolants for CNC Machining

Machining coolants are divided into four main categories with corresponding compositions. However, it is helpful to select a coolant based on its overall efficiency and performance, taking into consideration the material and machining process. Below are common types of machine coolants.

Synthetic fluids

These coolants are the cleanest as they do not contain petroleum or mineral oil. Synthetic fluids contain rust inhibitors and chemical lubricants that dissolve in water. These fluids are mixed with water to form a metalworking fluid. Therefore, these CNC coolants have high cooling performance, anti-corrosion, easy maintenance and lubricity.

Furthermore, due to their excellent cooling performance, synthetic fluids are mainly used in high-temperature and high-speed machining processes such as surface grinding. High-performance synthetic fluids are ideal for carrying out various machining operations.

Depending on their composition, synthetic substances are divided into simple and complex synthetic or emulsifiable substances. Simple synthetic fabrics or real solutions are often used for light sanding work. Complex synthetic concentrates, on the other hand, contain synthetic fluids suitable for medium to heavy duty machining processes. Most importantly, complex synthetic lubricants enable high speeds and advances in machining operations.

Per

• Synthetic fluids have high microbial control and excellent resistance to rancidity.
• These lubricants offer excellent corrosion resistance and high cooling performance.
• They offer greater stability after mixing with water.
• Plastics are easy to maintain because they are clean and suitable for a variety of machining operations.

Disadvantages

• Machine fluids, such as lubricating oils, can easily contaminate synthetic fluids. Therefore, you must manage and maintain these fluids effectively.
• Synthetic fluids produce fine mist or foam due to moderate to high agitation conditions, although they are less prone to problems associated with oil-based fluids.

Semi-synthetic fluids

Semi-synthetic fluids are a hybrid of synthetic substances (polymers) and soluble oils. These liquids contain about 2 to 30% minerals or petroleum in a water-dilutable concentration. The remaining percentage of a semi-synthetic fluid consists of water and emulsifiers. Other elements in the concentrate include biocidal additives, wetting agents and corrosion inhibitors. They are commonly called finished chemical emulsions because water is their main ingredient and they emulsify with water during the preparation of the concentrate.

These semi-synthetic fluids are generally translucent. However, its properties can vary from slightly translucent to opaque. Furthermore, many of these semi-synthetic fluids have good heat sensitivity. Therefore, semi-synthetic oil molecules surround the cutting tool, providing better lubrication.

Per

• They are excellent lubricants for medium to heavy duty applications.
• Semi-synthetic fluids enable cutting at faster feeds and higher speeds due to their excellent wetting and cooling properties.
• These liquids have low viscosity and therefore allow for better settling and cleaning properties.

Disadvantages

• Water hardness affects the stability of semi-synthetic liquids and leads to the formation of limescale deposits.
• These liquids foam easily because their cleaning additives have less of a lubricating effect than soluble oils.

pure oil

These oils are derived from petroleum, mineral oil, animal oil and other elements, such as compounds, plants and fats. These pure oils sometimes contain other ingredients such as phosphorus, sulfur, and chlorine additives. Pure oils are typically insoluble in water and provide the best lubrication, rust protection, longest reservoir life and easy maintenance.

Since bacteria only thrive in liquids with water content, pure oils do not become acidic. These oils reduce the force created by the cutting tool when cutting the material and provide clean cuts that ensure a smooth surface on the workpiece.

Per

• Pure oil provides good lubrication and reduces friction during machining operations.
• They guarantee excellent surfaces and minimize tool wear.
• These oils are usually affordable and have high compatibility with various materials, such as bronze, steel and iron, commonly used in machinery and equipment.

Disadvantages

• Pure oils have poor cooling performance.
• Due to their high aging properties, they generally require more maintenance and oil changes.
• These oils are not ideal for certain heavy-duty applications.
• When pure oils are not disposed of properly, they have a negative impact on the environment.

Soluble oils

Soluble oils, also called emulsions or water-soluble oils, are excellent coolants for general machining purposes and are often used among water-soluble cutting fluids. Water-soluble oils often form emulsions when mixed with water. The resulting mixture consists of base mineral oil and emulsion to create a metalworking fluid. It works well in diluted form and provides excellent lubrication and heat transfer performance.

Soluble oils are inexpensive and often used in metal processing. They consist of 60-90% petroleum, emulsifiers or mineral oil and adhere to the part during processing. They are ideal for lubrication and provide excellent rust resistance when mixed with a specific amount of rust inhibitor.

Per

• These oils allow for better cooling and lubrication due to the water-oil mixture.
• Soluble oils are versatile and ideal for light and medium applications, including a variety of ferrous and non-ferrous applications.
• You can supplement operations such as thread cutting and broaching that are performed with direct oil by using heavy-duty water-soluble oils.

Disadvantages

• If not maintained properly, the coolant tank promotes microbial growth of bacteria and fungi.
• Oil in the mixture leads to problems with rust protection, evaporation losses and residual oil contamination.

Understanding Coolant Concentration in CNC Machines

Using the wrong coolant concentration in your CNC machine can lead to several complications. Therefore, it is important to know how to use the correct coolant ratio for the CNC machine to obtain the best results. There are certain risks associated with using a coolant concentration below the minimum CNC machine requirements. That includes:

• Microbial growth
• Faster wear of cutting tools
• Corrosion of parts and machines

On the other hand, the risks of excessive coolant concentration include:

• Foam
• toxicity
• Concentrated waste
• Reduced heat conduction
• Poor lubrication
• Discoloration of machines and machined parts
• Tool wear due to residue formation

CNC Coolant Concentration Table

Below is a coolant concentration table showing the variations of CNC coolant concentrations:

Water-Based Cutting Fluids Versus High-Pressure CNC Coolants

Water-based cutting fluids and high-pressure coolants for CNC machines are common in metal machining processes. These fluids efficiently lubricate tools and cutting materials.

Water-based fluids have excellent heat dissipation and lubricity properties. They are generally environmentally friendly and economical alternatives to high-pressure machine refrigerants. However, water-based coolants are susceptible to bacterial growth and can promote corrosion in certain metals.

In the meantime, it would be helpful to invest in a system that can increase speeds and feeds, improve tool life, and prevent chip control issues if your machine uses high-pressure CNC coolants. As a result, a high-pressure CNC coolant significantly increases productivity. You can experience pressures in excess of 1,000 psi, essential for tapping and deep drilling operations.

However, high pressure CNC coolants are expensive and require a lot of maintenance to ensure optimal functionality. Furthermore, these systems require specialized knowledge to ensure safe and efficient operation.

Concluding

CNC machine coolants help achieve optimal efficiency in a CNC shop. These coolants help reduce heat generation, lubricate the cutting tool and prevent discoloration and defects during machining processes such as CNC milling, turning or drilling.

Common questions

When is the right time to change the coolant on a CNC machine?

Several factors usually influence the interval at which you need to change your engine coolant. Consideration must be given to the material being processed, the type of coolant and the operating conditions of the CNC machine. However, most CNC machine manufacturers recommend every 6 to 12 months as a rule of thumb.

How to kill bacteria in CNC machining coolant?

You can prevent or stop bacterial growth in CNC machine coolant by injecting ozone directly into the coolant. It kills viruses, bacteria or mold and eliminates odors in the coolant reservoir.

What causes foam to form in a CNC coolant?

Lack of minerals in water is one of the main causes of foam formation in soft drinks. However, it is advisable to check the hardness of the water using hardness test sticks.