Coolant Management

Coolant Management Best Practices


Machining coolants are an important component of metal working operations. Coolant is essential for preserving tool life, improving machinability, and ensuring part finish and quality.  Machining coolants are an important component of metal working operations. Coolants improve machinability, increase productivity, and extend tool life by cooling and lubricating the part and cutting tool. When performing these functions, coolants can quickly become contaminated with foreign materials, causing coolants to lose effectiveness and develop foul odors. For this reason, most coolants are used only for a short time before being discarded.

The practice of discarding and replacing coolants is costly and wasteful. Developing and implementing a coolant maintenance program can help you minimize contamination, prolong coolant life, and reduce costs. MnTAP’s fact sheet, Coolant Maintenance for Machining Operations, can help guide you in your efforts to develop a maintenance program. Additionally, we provide a list of equipment and supplies for coolant maintenance to help you with this project.

Regularly Check and Maintain Machine Coolant Levels

Ensure that operators monitor and adjust the volume and concentration of coolant in machines daily. This is an important first step towards optimizing coolant usage. In addition, maintaining a record of concentration, volume, and pH levels can help your business track trends over time and reduce instances of coolant-related problems. When concentrations are too high, coolant is wasted and may not provide adequate cooling to the part; when concentrations are too low, decreased tool life, coolant spoilage, and product defects can occur. 

Maintaining sump volume at 85-100% helps to minimize fluctuations in concentration and pH. Monitoring and maintaining the appropriate coolant concentration will help to save costs in coolant usage, tool life, product defects and quality, labor, and time. Be sure to make checks and additions while the machine is not running, as there can be significant apparent volume changes in the sump during operation. Adding too much coolant while the machine is operating runs the risk of overflowing the sump and can result in costly time spent on clean up.  

Dose Machines Individually and at the Right Concentration

It may seem convenient to have a one-size-fits-all approach when it comes to supplying coolant to machines. For some shops, this can be practical if the machines are all of a similar type, run the same materials, and perform similar jobs. However, there is considerable variety in how machine tools operate; factors such as feed rates, cutting tool speed and material, machine model quality, part tolerances, part material, and size all play a factor in the resulting parts produced. Due to the number of competing forces at play, it is crucial that each individual machine is dosed appropriately according to the manufacturer’s recommendations. 

Check with your supplier to ensure that you are running at the recommended concentration and with the appropriate coolant. Generally, it is advisable to target a coolant concentration between 5-10%. There are exceptions for being outside of this range; for instance, cutting aluminum often requires a higher concentration closer to 12%. In most cases, however, coolant concentrations should not exceed 10%. If you find that your tool life seems to be low when running in the 5-10% range, it may be a sign that you need a coolant with a higher lubricity. 

Some suppliers offer twist compression testing capabilities, which is a method of quantitatively evaluating and comparing the friction and lubricity of fluids under varying loads. This testing can help you to choose the optimal coolant for the job. 

Recycle Coolant When Possible

Coolant recycling is another opportunity that can help your business achieve significant cost savings. There are varying degrees of sophistication for reusing coolant, from simply dumping coolant separated out from metal chips back into the machine to incorporating a larger centralized recycling systems. 

One simple solution is to use a sump filter that connects directly to the machine sump. These filters have the capability to remove solids and oils, and can be a simple solution to help prolong the life of your coolant.

A more complex and higher duty solution may be to implement a centralized recycling system. Systems of this type usually consist of a collection tank for holding used coolant and a second tank for cleaned coolant ready to be returned. Oil skimmers, centrifuges, or coalescers may be used to remove tramp oils, while filters remove metal fines and other suspended solids. 

Consider the coolant currently in use and whether recycling is feasible. Machine shops with significantly large volumes of coolant may find it economically advantageous to switch to a different fluid with greater potential for recycling. Certain fluids are developed with properties such as bio-stability or emulsion resistance that can allow for greater recycling potential. In some cases, recycled coolant is mixed with a proportion of virgin coolant before returning to the machine. In other cases, an additives package offered by the coolant vendor may be added. These additions are made in order to replenish depleted components in the fluid, ensuring that the recycled fluid is able to maintain optimal pH, bacterial control, and lubricity. 

When cost justifying these systems, the cost savings from reduced purchasing of coolant and decreased waste disposal costs are essential to include. However, there can be additional factors to include, such as improved uptime of machines, fewer sump and machine cleanouts, and extended tool life. Tracking these costs can help to illuminate the true value that fluid recycling brings to the table.  

Consider Automated Coolant Dosing

Automation is an important step towards achieving a superior level of control, consistency, and efficiency in your machine shop. There are numerous advantages that automated dosing can achieve, including labor savings, coolant concentration optimization, and uptime. 

Labor is a significant benefit that can be maximized from automation. Workers spend an average of 15 minutes to check coolant levels, access the coolant, titrate the appropriate solution dose, and finally haul the coolant into the machine sump. This represents time lost that could otherwise be spent on the next production run. In an industry with tight margins, maximizing productivity is key to building a competitive advantage.  

Consistency in the coolant tank is another significant benefit from automation. Removing the element of human error from the dosing procedure can result in better coolant concentration control. Remaining in the target range means that the tool life can be maintained without the danger of overdosing and wasting coolant. Automation also offers the ability to individualize the target dose range for each machine, as mentioned above. This can further improve the performance and quality of the product. 

Further automation in your machine shop can help achieve a significant increase in your overall throughput. Automated coolant dosing can be the difference maker in being able to run certain jobs overnight or even 24/7 without any operator oversight. Depending on the machining capabilities and jobs that are run at your facility, this can be a primary consideration for implementing this type of technology.