Tag: coolant management

Coolant in CNC Machines – What Is It and Why It Is Used?

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Written by Peter Jacobs, CNC Masters

During machining operations, overheating can have detrimental effects on the workpiece and the equipment, which could be avoided by cooling them down post-usage. Therefore, cooling is crucial for most machines to function efficiently and effectively. 

Hence, this article covers a wide range of aspects related to the usage of coolants in CNC machining, including their purpose, the many kinds of coolants utilized, and their characteristics. Let’s delve deeper.

What’s the Significance of Coolants in CNC Machining Operations?

While executing a milling or turning operation using a desktop CNC mill, the heat gets produced as a byproduct of the materials being sheared off the workpiece and by the friction of the chip moving across the cutting tool. Rapid tool wear occurs at high temperatures, and undesired changes in the workpiece’s metallurgical properties and toughness, thermal expansion, and chemical reactions like oxidation can only materialize at high workpiece temperatures. Since this is the case, you should employ a coolant to maintain a steady temperature between the workpiece and the tool.

Vital properties of coolants include-

  • Enhanced lubrication and cooling performance,
  • The surface of the workpiece gets protected from corrosion,
  • They aid in maintaining chemical, physical, and technical stability,
  • They prevent excessive forming. 

The primary purpose of coolants is-

  • Cooling- While in the case of very mild cuts and moderate duty cycles, air may also be employed as a coolant. However, this time-consuming and labor-intensive cutting process occurs during production. Therefore, liquid coolant is used to quickly evacuate heat from the tool, which aids in speed cutting and reducing friction and tool wear, making it possible to maintain a steady production stream.
  • Lubrication- Cutting fluid is not only utilized for cooling but also as a lubricant between the workpiece and the tool’s cutting edge. The heat created during machining can cause chips to weld themselves to the tool if they aren’t lubricated first.

Common Types of Coolants

There are four primary classifications for coolants, and within each of those, there is a wide range of possible compositions. When choosing a coolant, you should base your decision on the comprehensive performance & efficiency it offers concerning the machining operation and the materials being utilized.

  • Soluble Oils: The most prevalent type of water-soluble cutting fluids, soluble oils, are also an excellent alternative for general-purpose machining because of their versatility. The disadvantage of these systems is that when the coolant sump is not well treated, they are more likely to experience the microbial proliferation of bacteria and fungi.
  • Synthetic Fluids: These are the cleanest cutting fluids as they do not include any mineral oil and repel tramp oil. Additionally, synthetic coolants offer the least amount of lubrication.
  • Semi-Synthetic Fluids: They are regarded to provide the best combination because they contain fewer oils than emulsion-based fluids, have a less putrid odor, and, nevertheless, retain most of the lubricating properties of emulsion-based fluids. Given all such features, they are suitable for a greater variety of machining applications.
  • Straight Oils: Straight oils are distinguished from other types of oils as they are insoluble in water; they are made up of a mineral or petroleum oil base and include lubricants such as fats, vegetable oils, and esters. They have the best lubricating properties but the worst cooling properties.

How Do Coolants Get Delivered to CNC Machines?

Cutting fluids can be applied in various ways; the most effective method will vary depending on the operation at hand and the equipment at disposal. Coolant is typically supplied at high pressure and volume straight to the chip-tool contact in a metal cutting process, with valves surrounding the machine to confine the splash and others to reach the filter and recirculate the fluid. The probability of flooding is reducing as technology improves. The novel method incorporates a variety of liquids, aerosols, and gas delivery options. One technique is to use cryogenic cooling on the tip of the tool to lubricate it with a minimal amount of oil.

A through-spindle coolant system uses the spindle and the tool themselves as channels to transport coolant to the cutting interface. Nowadays, high-pressure coolant systems are also used.

Importance of Maintaining Appropriate Coolant Concentrations

Many problems might arise if coolant concentrations are not kept at the right amounts. There’s a significant risk if the coolant concentration is lower than the minimum ratio required by the machine coolant supplier, which may include:

  • Corrosion of machinery and workpiece
  • Tools wear out faster
  • Microbial growth

However, if the coolant concentration is excessive, the following will occur:

  • Lowering of heat conduction
  • Foaming
  • Weakened lubrication
  • Concentrated wastage
  • Degradation of tools owing to residue buildup
  • Discoloration of machinery and machined components

Therefore, it is essential to keep a log sheet of concentration levels for every CNC equipment since this provides insight into the system operation and the degree to which concentration levels fluctuate daily.

Conclusion

Learning about the various types of coolants and how they function will help you choose one that is ideal for your equipment and machining operation. Also, the life of your tools and machinery, as well as the coolant itself, can be dramatically increased with regular monitoring of coolant concentration. Twin Specialties has been supplying metalworking fluids since 1955. We have years of expertise to assist you in selecting the right fluids for your machining needs.

 

About the Author:

Peter Jacobs is the Senior Director of Marketing at CNC Masters. He is actively involved in manufacturing processes and regularly contributes his insights to various blogs on CNC machining, 3D printing, rapid tooling, injection molding, metal casting, and manufacturing in general.

 

Considerations for Coolant Selection

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Finding the optimal metalworking fluid is a difficult task because no fluid is “one-size-fits-all.” Each shop has its own unique set up of machines, operations, metals, etc. Operators have to consider many factors before selecting the optimal fluids or fluids for their shop. The optimal fluids should successfully perform the following core functions:

  • Lubricate the cutting edge
  • Disperse heat from the cutting edge and workpiece
  • Flush away chips from the cutting edge

Additionally, there are secondary functions a coolant can improve your operations. These include:

  • Corrosion protection
  • Extending tool life
  • Reducing energy consumption and machining forces
  • Improve surface finishing

To find a coolant that can perform these functions, you should take the following factors into consideration.

Machine Requirements

The types of machines in your shop will determine what type of fluid you will need. Older, swiss-type lathes can use neat oils. Whereas newer and more sophisticated CNC mills and lathes perform better with a water-soluble product. This is because higher speeds and higher pressures need more cooling than swiss-type lathes. The water does an excellent job cooling the cutting edge and workpiece. For neat oils, the cutting diameter plays a key role in determining the appropriate viscosity. The smaller the diameter, the lighter the viscosity should be to maintain and improve flow characteristics.

If your machine is operating at high speeds and/or high pressures, it is wise to consider a low-foam coolant or a specialized “high-pressure” coolant to use. Synthetic coolants are also an option as they tend to have lower foam rates than semi-synthetic and soluble oils. If your shop has a wide variety of machines and operations, you can consider using different fluids that are tailored to each operation. Over-consolidation can cause issues and may not be worth the savings. Fluids can be bought in smaller quantities and be used in limited cases to ensure performance and tolerances are met.

Shop Preferences

Machines do the heavy-lifting in metalworking, but there are still people behind each operation programming the CNC or working the lathe. Operators always get coolant spray on their skin and could be subjected to mist or spray. Finding a product that does not cause irritation nor spray/mist is paramount to keeping your operators safe and happy.

Shops have to consider the costs and labor involved in changing fluids as well as maintaining fluids. Cheaper fluids may save money, but will require more maintenance, monitoring, and change-outs. If your time is limited, investing in higher cost fluids will free up time to complete other machining tasks.

The ancillary equipment in the shop also can influence what type of fluid you need. If your sumps are equipped with oil skimmers, paying extra for a fluid with advanced tramp-oil-rejection characteristics may be unnecessary. Automatic mixers makes synthetic coolants a more attractive option since the concentration control required for synthetics is much more stringent than semi-synthetics and soluble oils. Understanding what is in your shop will help determine what fluid is appropriate for you.

Operations and Water Quality

As mentioned before, operations with higher speeds and pressures will call for a fluid with robust extreme-pressure (EP) additives to cut the toughest metals. In slower operations, a soluble or neat oil can be sufficient.

Your shop’s location will play a key role and fluid selection since the tap water is different in each town. If your shop has harder tap water, your machining might be negatively affected with higher chloride and sulfur content. Softer water is susceptible to more foaming. Avoid using softer water in higher pressure machining to limit foaming issues. It is recommended to charge up a sump with tap water and then use deionized (DI) water for topping off the sump and maintenance.

Shops can install a DI-Water line that can hook right up to an automatic mixer and improve coolant mixing. Distributors, like Twin Specialties, offer water testing services in the context of metalworking fluids. We can learn more about your water and make product and operational recommendations to improve coolant performance.

Workpiece Materials

Not all metals are the same. Some are soft, some are hard. Some metals are more reactive and require more care and specialized fluids. Magnesium requires certain additives or fluids that designed to machine magnesium. When machining carbide, it is best to use an amine-free coolant that does not react with the carbide and result in cobalt leaching. Harder metals like Inconel or titanium require coolants with EP additives and superior cooling to ensure heat is dispersed and friction is reduced. If you machine titanium or exotic metals in limited circumstances, it may be beneficial to keep a pail or a few gallons of a robust coolant in storage used specifically for those jobs and operations.

Potential Contamination

Contamination can occur frequently and in many forms. The main contaminants to watch for are: oxidation, tramp oil, and biologics. To combat oxidation, many fluids have anti-oxidant additives. It is key to monitor temperature as excessive heat will oxidize the oil. Antioxidants are limited in coolants; once all of the additive is consumed, the oil degrades quickly and will need be replaced sooner rather than later.

Tramp oils can change the oil’s viscosity, thus its flow characteristics. Having coolants with tramp-oil-rejecting compounds will help, but using oil skimmers is an excellent option to combat tramp oil. The skimmers remove the oil off the top of the sump and limits tramp oil being circulated through the machine. Oil filters are recommended to keep tramp oil from circulating through the system. Neat oil systems should use 5 micron filters and coolant systems should use 15 micron filters.

Outside biological contamination like bacteria can wreak havoc on your machine and cause clogs and ruin your fluid. Many fluids contain biocide additives to combat bacteria, but many factors allow it to grow uncontrolled. Be mindful to thoroughly clean your machine before recharging it. Any remnants of bacteria will multiply and ruin your fluid. Hot operating environments spur bacteria growth so it is recommended to implement as much climate-control in your shop as possible. Circulating the coolant will also make it tougher for bacteria to grow. Tank-side biocide additives like Grotan can supplement fluids and fight bacteria. Ensuring your coolant has proper concentration will ensure there is enough biocide to prevent bacteria growth.

Concentration

Monitoring concentration is key for maintaining your fluid. Some fluids, like synthetics, require tighter control and more monitoring. If you are limited by time, using a soluble or neat oil will reduce the time needed to monitor your fluid. Coolants typically run between 5 to 15% concentration. Using a refractometer to regularly track concentration is the best way to monitor and maintain coolants. Technical data sheets include refractometer charts and BRIX factor information to ensure the coolant is mixed optimally. If the line in the refractometer is blurry, that is a sign of contamination in the sump. Automatic mixers are ideal for charging sumps and eliminate human error or measuring biases that may occur when mixing coolant.

Takeaways

Selecting a metalworking fluid is a thorough and long process. Taking these considerations into account will set you up for long-term stability and success. Working with a metalworking fluid distributor and/or manufacturer is strongly recommended to help select to correct product. Twin Specialties offers a wide range of metalworking fluids and fluid maintenance resources to ensure you get the most out of your fluid.

7 Steps for a Successful CNC Restart

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After an extended production shutdown, it is imperative to get restarted quickly and efficiently. Maintaining your coolant can be the difference between success and failure. It is key to clean, refill (if necessary), and run according to the manufacturer’s recommendation.

These steps will depend on whether you emptied the sump before the shutdown. If you have emptied the coolant, ensure that the machine is cleaned out; Astro-Clean A can be used to clean the machine and remove and residual coolant and contamination in tough to reach places.

If your coolant remains in the sump after the shutdown, follow these steps for a successful restart:

  1. Inspect the coolant sump/tank for any problems.
    • Remove any tramp oil by using skimmers.
    • Remove any swarf or solids with filters or skimming nets.
    • If there are significant solids, the tank and machine should be cleaned out before proceeding.
  2. Do not add any coolant unless there is not enough to circulate through the machine. If you need to add coolant, add coolant at or above the target concentration.
  3. Circulate coolant through ALL pumps for 60 minutes to ensure all nozzles are flushed out.
  4. Check the concentration from the nozzle using a refractometer (either manual or digital).
  5. Top off the sump to 95% capacity to the target concentration + 2%.
  6. Check the pH and odor. Test the pH from the nozzle.
    • If it is too low (8-9 pH), add 3% volume of coolant and circulate for 30 minutes. Repeat until pH is acceptable.
    • If pH is below 8, the coolant is spent and must be replaced. Use Astro-Clean A to clean out machine.
  7. Add fresh coolant to bring tank/sump volume to 100%.

Bonus Tip: To keep coolant fresher during shutdowns, run skimmers and fish-tank fans to prevent tramp oil contamination and coolant breakdown. Circulating the sump coolant may reduce odor.

Following these steps will ensure a successful restart. Equally important is continuous monitoring of the sump/tank. One individual should check concentration daily and pH weekly. If something is off, act accordingly and quickly. Keep records in a coolant log for each machine to ensure continued success.

Contact Twin Specialties about our coolant guide for information about success coolant management. Twin Specialties has over 65 years of experience with metalworking fluids and is your go-to source for metalworking fluids, cleaners, and rust preventatives/inhibitors.