Minimum Quantity Lubrication
What is Minimum Quantity Lubrication?
Minimum Quantity Lubrication (MQL) or near-dry machining is a narrow stream of atomized lubrication that lubricates the cutting tool without creating a mist. MQL dramatically reduces fluid use, replacing gallons of coolant with just a few ounces of renewable lubricant.
At Unist, our mission is to design and build innovative products that solve manufacturing problems. For metal cutting operations we believe there is a better alternative to traditional flood coolant. MQL not only reduces fluid use and saves money, but improves tool life, promotes cleaner shops, and eliminates the need for fluid circulation, treatment and disposal - all while utilizing an environmentally-friendly product that's safe for your workers.
Use only 2–4 ounces per shift with MQL
Minimum Quantity Lubrication Myths
How Minimum Quantity Lubrication works
Primary shear zone: shearing action of the material causes heat buildup as the material deforms and eventually flies away as a chip.
Secondary shear zone: The sliding friction between the workpiece and the cutting tool generates heat as the tool plunges into the material.
Minimum Quantity Lubrication (MQL) is effective because it focuses on managing heat rather than eliminating it. Both carbide and HSS tooling perform best within a specific temperature range. MQL applies a small amount of high-quality lubricant directly to the cutting tool/workpiece interface, forming a lubrication boundary that reduces friction and minimizes heat generation. Most of the heat generated by material deformation is carried away by the chips, allowing the tool to maintain a steady temperature. Unlike traditional cooling methods, which can quench the tool and create thermal cracks at the cutting edge, MQL promotes consistent thermal stability.
Choosing a Minimum Quantity Lubrication Solution
Minimum quantity lubrication systems are made up of a system, single-line or dual-channel (co-axial) tubing, and a nozzle.
Minimum quantity lubrication demands precise microliter output with consistent performance. Unist uses positive-displacement pneumatic metering-pumps to guarantee accuracy and reliability. Positive displacement means the same amount of fluid is dispensed with each stroke, regardless of external variables. Unist’s systems are reliable, accurate, and tested to 12 million pump cycles.
- Continuous or intermittent output
- Dispense fluids between 30-5000 SUS, NGLI grade 00 and grade 000 greases
- Micro-adjustments, tune as accurately as .02 mL per pump stroke
- Up to 12 separate fluid outputs
- Manual, air pilot, solenoid, or fully integrated PLC actuation
Minimum Quantity Lubrication systems can use single-line or dual-channel (co-axial) hose. Your choice depends on where the fluid is atomized within the airflow.
In a single-line system, the fluid is atomized within the MQL system. The mixture is carried through the tubing and sprayed out the nozzle. In a single-line tube, oil can collect around hosebends and cause dripping at the nozzle.
In a dual-channel or co-axial hose, the air-supply-line runs within the fluid delivery line, and atomization occurs at the nozzle tip. Dual-channel systems provide the most uniform droplets and spray pattern, resolving many of the performance issues associated with single-line hoses.
Key factors like blade type, spray pattern, adjustability, and machine vibrations are important considerations when choosing a nozzle. Unist offers a wide range of spray tips, loc-line, and rigid nozzles to suit most applications. For OEM needs, we also offer custom nozzle configurations specific to your machine.
Choosing the Right Fluid
Typically, MQL fluids are synthetic ester oils or fatty alcohols. Synthetic ester oils are best for maximum lubrication. They offer a high boiling/flash point and generate less vapors than conventional mineral oils. In addition, ester oils have very good biodegradability and a very low toxicity.
Wetting and viscosity are key properties of a successful MQL lubricant. "Wetting" is a fluid's ability to spread itself on the cutting surface. The better the wetting property, the better the lubricant will work. Generally, better wetting properties mean lower fluid viscosities. However, it’s important to find the perfect balance as lower viscosities are more prone to generating a mist. It’s recommended to use a fluid with a higher viscosity and flash point above 150°C or 300°F.
Why Coolube?
We created Coolube®, an environmentally-friendly cutting oil specifically designed for MQL applications. With excellent wetting properties and a higher viscosity (75-85 SUS), Coolube® 2210 minimizes emissions thanks to its high flash point (>400°C or >200°C). Available in three varieties, it's ideal for machining ferrous and non-ferrous metals and most plastics. We’re so confident in Coolube® that we offer a lifetime warranty on all pumps used exclusively with it. Tested to 12 million pump cycles, Coolube® delivers performance and durability you can trust.
Want more data?
The MQL Handbook combines 15 engineering case studies, articles, and experiments into 55 pages on the science of MQL.
Download now