What is a minimum or micro lubrication system?

MQL, or minimum quantity lubrication, systems are designed to apply a very fine amount of high quality lubricating oil to metal cutting/machining operations. The typical MQL application system consists of a reservoir, pump, valves, hoses or tubing, and a nozzle which delivers the oil to the cutting surface in the form of an atomized spray. MQL is a term and process used specifically for machining and metal cutting operations.

basic MQL Minimum Quantity Lubrication system

Do you always need lubrication for cutting metal?

In general, yes. Sometimes, dry cutting with no lubrication can be done, but if you’re trying to make a lot of parts efficiently, this is not effective. In repetitive, demanding production machining environments, dry machining will result in premature tool wear, The surface finish after dry cutting or dry machining will not be as smooth. This is because of the extreme heat that’s generated in the process without any lubrication. The chief purpose of the oils used in MQL is to lubricate. MQL is an alternative to the common practice of flood coolant.

Machining clean with MQL - Reduce friction and avoid heat - neatly apply ounces of lubricant per shift with no fluid cleanup or disposal
Machining with coolant - Cool down hot tools and work - flood with gallons of coolant - recirculate/treat fluid, clean up fluid mess, pay for disposal.

Coolant’s chief purpose is to remove heat. Lubricants are designed to reduce friction and therefore reduce heat generation in the first place. Friction between the cutting tool and the workpiece material is a main source of heat in any metal cutting or machining operation. Another source of heat is from material deformation while cutting, however, when using MQL the majority of the heat caused by the bending and shearing of the material is carried away with the chips. The main purpose of lubricant in MQL is to reduce heat in the first place by reducing friction. Alternatively, a coolant’s main purpose is to remove heat by quenching.

What is the difference between dry machining and minimum quantity lubrication?

You can cut metal and machine dry, but the results are less desirable. For low volume production runs, it may be fine. But the more volume or parts you’re working with, the worse it will be for wear. Drill bits, saw blades, and other tools can all wear down very quickly with dry machining. Dull cutting tools and dry machining result in a less desirable surface finish or surface quality. Dry machining results are more prone to surface markings or defects, and generally not as smooth or appealing of a finish as with parts created using an MQL system.

Near-dry machining

Near-dry machining is another term sometimes used for MQL. Since such a minute quantity of lubricant is used and mostly consumed in the process, the result is a dry or near-dry part. The chips produced are also dry or near-dry when using MQL systems. This eliminates mess, simplifies chip storage and means chips have more value when recycled.

If cleaning is required, any residual lubricant from MQL can usually be removed with a common alkaline based cleaner such as Simple Green or common dish soap. Some applications don’t require cleaning of the finished part, and it can just be wiped down. Is an MQL system a mist lubrication system?

Some people refer to MQL systems as mist lubrication, misters, or mist lubrication systems. MQL commonly uses compressed air to break up or atomize the lubricant and propel it to the cutting tool. These misting technologies and applicators are also used to dispense water-based coolants in some machining operations, but these coolants differ in purpose and function from cutting lubricants. Sometimes, additives are included in water-based coolants that serve to add a small amount of lubrication, but removing heat through cooling remains the primary function of these mixtures. When compared to flood coolant, MQL has proven to be better concerning air pollution in machining environments, as coolant systems can actually create more unwanted mist & air pollution.

How is lubricant applied in an MQL system?

When compared to a pressure fed MQL system, a positive-displacement-pump based system provides more consistent and repeatable delivery of the MQL oil to the cutting zone. Pressure-based systems can be difficult to calibrate since lubricants become more or less viscous in different temperatures. Positive-displacement-pump fed systems move the same volume of oil with each pump stroke no matter the temperature.

positive displacementPositive Displacement
An easy way to understand the concept of positive displacement is to think of a syringe. When the syringe's plunger is pulled back, a known volume of fluid is drawn into a cavity. This known volume of fluid is dispensed when the plunger moves forward and displaces it. This is the same concept found in an MQL system's pumps and provides the advantage of being able to control the lubricant quantity dispensed.

Some MQL systems provide a continuous flow of lubricant to the cutting zone and this is appropriate for continuous operations such as sawing, milling, and drilling. Sometimes, an intermittent flow of lubricant is desired for operations such as tapping. With each hole tapped, a discrete amount of lubricant is applied to the tap before the tapping cycle. MQL systems are commonly configured to dispense in either a continuous or intermittent manner. In both of these cases, the pump delivers the lubricant to a nozzle where it is mixed with air and delivered to the cutting area.

What kind of fluid is used in MQL systems?

coolube lubricants for mqlDifferent types of MQL oils—such as our Coolube® Lubricants—are available depending on the material being machined. The MQL fluids are tailored with different additives depending on the application. Most MQL fluids are nontoxic and environmentally friendly, meaning they are biodegradable and made of natural ingredients.


What makes a cutting oil high quality?

The most critical component in an MQL cutting oil is its lubricity. Oil-based lubricants have higher lubrication qualities and water-based or water soluble lubricants. Other important qualities of an MQL lubricant are a high flash point to avoid evaporation and polar properties that help it wet out, or adhere to surfaces. A high quality MQL fluid will lubricate well and also cling effectively to the surfaces requiring lubrication.

Unist's line of Coolube® lubricants for lubricants for MQL systems are all environmentally friendly products. Another important feature of Coolube products is that they do not oxidize like other oils. If you’ve ever left some vegetable oil sitting in a pan, you know how it can turn sticky or gummy - that’s due to oxidation, a reaction between the oil and the oxygen in the atmosphere. A high quality MQL lubricant is one that is inert and doesn’t react with oxygen. The highly refined quality of Coolube prevents sticky and tacky buildup common with cutting oils of lower quality.

Can you reuse MQL cutting oil?

In theory, yes you can, but there is not meant to be any left over. Using the minimum quantity of oil means that it should be entirely consumed by the process. MQL is unique in this way, it’s designed so that you don’t have overspray and waste. Chances are that if you have enough oil left over to collect, you are putting too much on to begin with, or missing the target.

How do you configure an MQL system?

Depending on your process, tools, and material, different elements of a MQL system are recommended. For instance, specialty nozzles exist for drilling, tapping, circular sawing, band sawing, etc. Also the nature of your machine - whether manually or computer numerically controlled (CNC) will influence the system recommendation.

Unist's product builder tool can help determine your ideal system. We are happy to talk to you about your process so we can find the products you’d need. As with any of our products and systems, there is always support available as well as documentation and installation guides.

What are the benefits of minimum quantity lubrication?

MQL increases performance

Some have found that speeds and feeds of cutting tools can be increased using MQL compared to flood coolant. MQL sometimes has a smaller sweet spot for optimal running conditions than flood coolant, but within that range, the performance ends up much higher than the results with flood coolant systems. MQL is a more precise process than flood coolant and therefore can take a little more adjusting to get just right, however there are performance benefits to be had.

MQL decreases mess and waste

The mess is much less with MQL. Flood coolant can be a messy and hazardous process. With flood coolant, excess coolant is flung from tooling, splashes on equipment and can create hazardous work environments. For example, cutting tube stock on a band saw with coolant can result in coolant travelling through the length of the stock and creating a mess elsewhere. Parts machined with coolant can come out of a CNC dripping wet and leave their messy trails all over the floor. It can be hard to contain the spray, dripping, and mess of flood coolant.

When properly adjusted, MQL systems apply such a small amount of lubricant in such a neat fashion that there's no excess fluid to contend with. This results in cleaner parts, cleaner floors, and cleaner machines.

How does MQL prolong tool life?

Tool life can be increased using MQL. Imagine if every cutting tool could cut even 10 more parts before needing replacement or sharpening. That really adds up over time. MQL systems use high quality lubricants that lubricate better than flood coolant or dry machining. Also, MQL reduces the effects of thermal shock in carbide tools. Thermal shock is caused by cycling between hot and cool temperatures, which can cause premature failure in carbide tools.

cutting tool life

Tools are consumables items. More parts per tool is always beneficial. Also, when changing out tools, the machine is powered down, which creates loss. We’ve seen pretty incredible tool life gains after switching to MQL.

What are the maintenance needs for an MQL system?

Maintenance requirements are minimal on an MQL system. If the system runs dry, it may need to be reprimed, but this is easily avoidable by keeping the reservoir full of oil. Oil and airflow are easily adjusted for your process. Unist MQL pumps can run for years of operation before needing replacement. If you buy a Unist MQL system and only use Unist Coolube®, the systems and parts are warranted for life.

Alternatively, maintenance requirements for flood coolant systems are very high. There is chemistry and upkeep required to keep bacteria growth down in the coolant. You must maintain filters and recirculating pumps. You have to remove chips and debris from cutting that can get into the filters and pumps. No oil is recirculated with MQL systems.

Is it difficult to switch from flood coolant to an MQL system?

It is a process. Flood coolant is the most popular form of metal cutting & machining lubrication now. Flood coolant is easy to implement, set up, and apply. It doesn’t matter how much coolant is used using flood coolant. It’s similar to throwing a bucket on a fire. However, there are many other costs associated with this method.

MQL can be more complicated to set up and it may require process changes to switch from flood coolant to MQL. The degree of difficulty to change increases with the level of sophistication of the machining operation and the tools and machines used. However, the benefits are well worth it, and the change is a one-time occurrence. There are significant issues with flood coolant that can be avoided by changing over to MQL.

Dangers of flood coolant

All flood coolant solutions have a shelf life. Flood coolant disposal is expensive since flood coolant can be toxic. Workers frequently exposed to flood coolant can develop dermatitis. Flood coolant introduces more coolant mist into the air and environment than MQL. Spilled coolant leads to slip hazards as well. Simply put, flood coolant is toxic and messy, when compared to MQL systems. MQL lubricants from Unist are high quality and won’t cause the health issues flood coolant does and an MQL system applies the oil neatly avoiding the mess.