This page covers a minimum quantity lubrication (MQL) system for machining: a total-loss, air-and-oil package delivering 5 – 60 ml/hour of oil as 1 – 50 micron droplets to the cutting zone, externally or through the tool. This is a near-dry machining page; centralized oil mist lubrication for bearings and spindles sits elsewhere on this site. For oil-storage coil tubing, see helical coil nylon pipe; for a low-pressure feed pump, see the BRB trochoid pump.
How MQL Works
MQL meters a small oil flow into compressed air and atomizes the mix at the nozzle. The aerosol lubricates the tool-chip interface with an oil film, convects heat away and clears chips with high-velocity air, and adds modest evaporative cooling. The oil is consumed at the cut: the principle is total-loss.
Specifications
| Parameter | Value |
|---|---|
| Oil output | 5 – 60 ml/hour, adjustable by needle valve or metering pump |
| Common working setting | 20 ml/hour for tools under 40 mm |
| Droplet size | 1 – 50 microns |
| Compressed air | 4 – 10 bar typical; up to 16 bar on high-performance systems |
| Air-to-mist differential | about 1 bar minimum |
| Reservoir | 1 – 4 liters |
| Nozzle forms | single focused nozzle / dual nozzle coverage |
| Nozzle position (external) | 20 – 40 mm from the cutting edge |
| Oil viscosity | 10 – 100 cSt at 40°C optimal; up to 200 cSt on some systems |
| Ambient temperature | 0°C to +50°C |
| Air supply quality | clean, dry, filtered air |
| Mounting | fixed or magnetic base; PROFINET or PROFIBUS machine interface on some models |
External vs Internal MQL
External MQL mounts one or two nozzles outside the tool, aimed at the cutting edge from 20 – 40 mm, and retrofits to almost any machine, manual or open. Internal MQL routes the aerosol through spindle, tool holder and tool bore; the stronger choice for deep-hole drilling and high-speed machining, but it needs through-channels in all three.
Operations and Materials
Typical operations: milling, drilling, turning, tapping, sawing and grinding, on aluminum, steel, stainless steel, cast iron, titanium and hard alloys such as Inconel. It runs on CNC machining centers, lathes, milling machines and manual machines, open or enclosed.
MQL vs Flood Coolant
Flood coolant moves 10 – 100 liters/minute; MQL moves 5 – 60 ml/hour. Even at the highest MQL setting against the lowest flood setting, 10 liters/minute = 600,000 ml/hour and 600,000 / 60 = 10,000, so flood moves roughly ten thousand times more liquid. In return, MQL avoids heat shock at the cutting edge, leaves chips and workpieces nearly dry at typically less than 2% oil residue, and removes sump maintenance and coolant disposal.
Components and Installation
The package: reservoir, air regulator with needle valve or metering pump, atomizing nozzle and mounting base. Feed lines typically use 4 mm nylon pipe. The base is fixed or magnetic, and some models offer a PROFINET or PROFIBUS machine interface. For a machine-matched configuration, request a system quote.
Honest Limitations
- MQL is not an equal-volume substitute for flood coolant; heat removal and chip evacuation are weaker, so deep-cavity work, heavy roughing and high-heat-load grinding need process validation first.
- Internal MQL requires through-channels in spindle, holder and tool; machines without them run external MQL only.
- Oils are limited to the three near-dry classes listed below; anything above 200 cSt needs atomizer confirmation first.
Frequently Asked Questions
Is this the same as oil mist lubrication?
No. MQL on this page is metered oil atomized at the cutting zone for near-dry machining. Centralized oil mist systems feed bearings and spindles continuously and are a different category on this site.
How do I choose between external and internal MQL?
External MQL suits machines without through-tool channels, large solid tools and open setups, and is the easier retrofit. Internal MQL suits deep-hole drilling and high-speed work in enclosed zones, but needs channels through spindle, holder and tool.
What does the 5 – 60 ml/hour oil rate mean in practice?
It is the metered oil volume per tool per hour, set by needle valve or metering pump. A common working value is 20 ml/hour for tools under 40 mm; harder cuts move toward the upper end.
What air pressure does the system need?
Typical systems run on 4 – 10 bar; high-performance systems reach up to 16 bar. Keep about 1 bar of differential between air and mist lines for consistent aerosol formation.
Why does droplet size matter?
The 1 – 50 micron range governs transport, wetting and mist escape. Smaller droplets travel further with the air; larger ones wet the tool faster. Match it to a nozzle distance of 20 – 40 mm from the edge.
Which operations benefit most?
Milling, drilling, turning, tapping, sawing and grinding run on MQL; deep holes need internal feed, heavy roughing and high-heat grinding need validation first, and sawing sits at the upper oil range.
How is MQL different from flood coolant?
Flood recirculates 10 – 100 liters/minute; MQL applies 5 – 60 ml/hour consumed at the cut. Chips and workpieces come off nearly dry, typically less than 2% oil residue, with no sump to maintain, but heat removal and chip evacuation are weaker.
Which oils can I use?
Three near-dry oil classes: synthetic esters, fatty alcohols and vegetable-oil-based fluids. Optimal viscosity is 10 – 100 cSt at 40°C; some systems accept up to 200 cSt. Above that, confirm against the atomizer specification.
What happens to line oil after shutdown?
Residual oil settles in the lowest tubing sections. Coiled storage tubing holds a small reserve so restarted air flow picks up oil immediately; that tubing has its own page here.
Who supplies this system?
IsoHiTech Lubrication Systems supplies MQL systems and matching components, founded in 2023, engineering since 2006. Share machine, tooling and operation details through the contact page or write to inquiry@isohitech.com for a configuration proposal.
