A Comprehensive Guide to Machining Coolants: Principles, Types, Applications

Machinists often use CNC machine coolants to mitigate the effects of overheating on cutting tools or materials during CNC machining. These machining coolants effectively act as machining lubricants and machining coolants and aid in chip removal.

This article discusses how machining coolants work and their delivery techniques. You will also learn about the importance of coolants in CNC machines, their types, and more.

1.What is machining coolant?

Machining coolant or cutting fluid is an industrial fluid that is commonly used in metal cutting operations to improve efficiency. CNC machining coolants consist of special chemical additives that are scientifically compounded and concentrated. Its main ingredients include animal fats, water, petroleum distillates, vegetable oils, 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 high temperature buildup.

2.How does a coolant system work?

During CNC machining operations, a CNC machine coolant mixture flows through the work area. The coolant washes away chips and particles from the work area like a flood. The coolant then flows into an oil pan at the bottom of the machine, where you must pump and circulate it to the work area for continuous use.

The coolant cools the workpiece during high-speed machining and lubricates the cutting tool during low-speed machining. As a result, machining coolant protects the cutting tool from corrosion and prevents deformation of the workpiece, thereby extending the life of the cutting tool. To ensure optimal performance, you must monitor, maintain, and adjust central and individual CNC machine coolant systems.

However, small coolant systems use less efficient components for oil separation and filtration, resulting in constant and variable concentration levels. Therefore, using coolant that is less susceptible to contamination by debris is best in small systems.

3.Various machining coolant delivery in CNC machines

Different CNC machines use coolants with different characteristics and pressures. Therefore, it is critical to select the ideal coolant delivery mechanism for your CNC machine. Failure to select the appropriate amount can cause your shop’s resources to be quickly depleted, while the wrong pressure can damage the workpiece or CNC cutting tool.

Here are some common coolant delivery types in CNC machines:

1) Mist Cooling Mechanism

This coolant delivery method uses low pressure and is suitable for operations where heat and chip removal are not the main considerations. Therefore, mist cooling does not put additional stress on the tool and workpiece because high pressure is not applied.

2) Air Cooling Mechanism

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

In addition, when processing more sensitive materials, the air cooling mechanism is ideal for direct contact with the workpiece. However, it is not suitable for plastic materials that are susceptible to thermal shock or rapid expansion because direct coolants usually cause the part to shrink.

3) Minimum Quality Lubricant (MQL) Mechanism

The top priority of every CNC shop is to gain a competitive advantage by improving shop efficiency, increasing production, and reducing costs. Therefore, CNC shops often adopt MQL because of its environmental advantages.

The MQL mechanism reduces costs and material waste by using the required amount of coolant. They are usually in the form of an extremely fine mist or aerosol, providing enough coolant to effectively perform the defined operation.
High-Pressure Mechanisms

High-pressure CNC machine coolant delivery uses pressures greater than 1,000 psi to remove chips during machining operations. This method is ideal for extracting and evacuating chips because it blows the chips away from the material.

The pressure used by this method can damage micro-diameter tools, even though it can quickly and effectively cool the part. Therefore, this method is suitable for CNC drilling or deep cavity operations and can be easily transported using coolant or built-in coolant tanks.

4.Types of CNC Machining Coolants

There are four major categories of machining coolants, each with its own formulation. However, it helps to select a coolant based on its efficiency and overall performance, considering the materials and machining processes involved.

The following are the common types of machining coolants:

1) Synthetic Fluids

These coolants are the cleanest because they do not contain petroleum or mineral oils. Synthetic fluids include rust inhibitors and chemical lubricants that break down in water. These fluids are mixed with water to produce metalworking fluids. Therefore, these machining coolants have high cooling capacity, corrosion protection, easy maintenance, and lubricity.

In addition, synthetic fluids are mainly used in high-heat, high-speed machining processes such as surface grinding due to their excellent cooling capacity. Heavy-duty synthetic fluids are ideal for handling a wide range of machining operations.

Based on the composition of the synthetic, synthetics can be classified as simple synthetics, complex synthetics, or emulsified synthetics. Simple synthetics or true solutions are generally used for light grinding.

On the other hand, complex synthetic concentrates contain synthetic fluids suitable for medium to heavy machining procedures. More importantly, complex synthetic lubricants allow for high-speed and feed machining operations.

① Advantages

1. Synthetic fluids have high microbial control and excellent anti-acidity.
2. These lubricants have excellent anti-corrosion properties and high cooling capacity.
3. After mixing with water, their stability is higher.
4. Synthetics are clean and suitable for a variety of machining operations, so they are easy to maintain.

② Disadvantages

1. Mechanical fluids (such as lubricating oils) can easily contaminate synthetic fluids. Therefore, you must manage and maintain these fluids effectively.
2. Although less susceptible to the problems associated with oil-based fluids, synthetic rubbers can still produce fine mist or foam under moderate to high agitation conditions.

2) Semi-synthetic oils

Semi-synthetic oils are a mixture of synthetic oils (polymers) and soluble oils. These fluids contain about 2-30% mineral oil or petroleum oil in a concentration of water-swellable oil. The remainder of the semi-synthetic oil consists of water and emulsifiers.

Other ingredients in the concentrate include biocide additives, wetting agents, and corrosion inhibitors. They are often called pre-chemical emulsions because water is their main ingredient and is emulsified with water during the concentrate production process.

These semi-synthetic oils are usually translucent. However, their properties can vary from slightly translucent to opaque. In addition, many semi-synthetic oils have good heat sensitivity. Therefore, the semi-synthetic oil molecules surround the cutting tool, ensuring better lubricity.

① Advantages

1. They are excellent lubricants for medium to heavy-duty applications.
2. Semi-synthetic fluids can cut at faster feeds and higher speeds due to their excellent wetting and cooling properties.
3. These fluids have low viscosity and have better settling and cleaning properties.

② Disadvantages

1. The hardness of water can impair the stability of semi-synthetic fluids, resulting in hard water scum deposition.
2. These fluids tend to foam because their cleaning additives provide less lubrication than soluble oils.

3) Straight oils

These oils are extracted from petroleum, mineral oils, animal oils, and other elements such as compounds, plants, and fats. These straight oils sometimes contain other ingredients such as phosphorus, sulfur, and chlorine additives. Straight oils are generally insoluble in water and provide optimal lubrication, rust prevention, longer sump life, and easy maintenance.

Since bacteria can only grow in liquids containing water, straight oils do not become sour. These oils reduce the force generated by the cutting tool when cutting the material, resulting in clean cutting and ensuring a smooth workpiece surface.

① Advantages

1. Straight oils have good lubricity and can reduce friction in machining operations.
2. They ensure excellent surface effects and minimize tool wear.
3. These oils are generally affordable and highly compatible with a variety of materials such as bronze, steel, and iron commonly used in mechanical equipment.

② Disadvantages

1. Straight-run oils have poor cooling properties.
2. Due to their higher degradation characteristics, they generally require higher maintenance and oil change costs.
3. These oils are not suitable for specific high-performance applications.
4. Straight-run oils can have adverse effects on the environment if not properly handled.

4) Soluble oils

Soluble oils, also known as emulsions or water-soluble oils, are excellent coolant options for general machining purposes and are often used in water-soluble cutting fluids. Water-soluble oils usually form emulsions when mixed with water. The result of the mixture includes base mineral oil and emulsion to form a metalworking fluid. It performs well in diluted form and provides excellent lubricity and heat transfer properties.

Soluble oils are inexpensive and commonly used in the metalworking industry. They consist of 60-90% petroleum, emulsifiers or mineral oils that adhere to the workpiece during machining. It is ideal for lubrication and has excellent rust prevention properties when mixed with a specific amount of rust inhibitor.

① Advantages

1. Due to the mixture of water and oil, these oils facilitate better cooling and lubrication.
2. Soluble oils are widely used and are ideal for light and medium-duty operations, including various ferrous and non-ferrous metal applications.
3. You can use heavy-duty soluble oils to match operations such as tapping and broaching that are handled with pure oil.

② Disadvantages

1. If the coolant tank is not properly maintained, it will encourage microbial growth of bacteria and fungi.
2. The oil in the mixture can cause rust prevention problems, evaporation losses and tramp oil contamination.

5.Understanding CNC machine coolant concentration

Using the wrong coolant concentration in CNC machine tools can cause a variety of complications. Therefore, it is crucial to understand how to use the appropriate CNC machine coolant ratio for best results. Using coolant concentrations below the minimum requirements of CNC machine tools carries certain risks.

These risks include:

1. Microbial growth
2. Faster wear of cutting tools
3. Corrosion of parts and machinery

On the other hand, risks posed by too high a coolant concentration include:

1. Foaming
2. Toxicity
3. Concentrated waste
4. Reduced heat transfer
5. Poor lubrication
6. Discoloration of machinery and machined parts
7. Reduced tool performance due to residue buildup

6.Coolant concentration chart

Below is a coolant concentration chart that includes varying levels of coolant concentration:

7.Water-based cutting fluids vs. high-pressure machining coolants

Water-based cutting fluids and high-pressure CNC machine coolants are common in metalworking processes. These fluids effectively lubricate cutting tools and materials.

Water-based coolants have excellent heat dissipation and lubricity. They are often an environmentally friendly and cost-effective alternative to high-pressure machine coolants. However, water-based coolants are prone to bacterial growth and can cause corrosion on some metals.

At the same time, if your machine uses high-pressure machining coolant, it can be helpful to invest in a system that can increase speeds and feeds, extend tool life, and prevent chip control issues. Therefore, high pressure machining coolants can significantly increase productivity. You may experience pressures above 1,000 psi, which is critical for tapping and deep hole drilling operations.

However, high pressure machining coolants are expensive and require extensive maintenance to ensure optimal functionality. In addition, these systems require skills to ensure safe and efficient operation.

8.Conclusion

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

If you need professional help in determining the ideal lubricant type and pressure for your CNC machine, feel free to contact Xavier. We are a one-stop CNC shop for all your manufacturing needs, and we provide you with reliable and professional CNC machining services.