Minimum Quantity Lubrication isn’t for Every Application

Minimum quantity lubrication (MQL), as the name suggests, is the technology that reduces the quantity of applied lubricant to the least amount necessary to be effective. The volume flow rate with MQL is often less than 50 mL/hr., which is a small amount compared with wet machining, which can use as much as 12,000 liters of coolant per hour (as in some grinding applications).

Knowing that lubricant savings are significant when implementing MQL, it’s no surprise that this technology allows for machining cost reduction and offers longer tool life, improved environmental protection and reduction of health risks for machine operators. Although these benefits are tangible for many applications such as turning, milling, drilling, and related operations, the technology is not well suited for deep-hole drilling; energy intensive processes such as grinding; many difficult to machine metals; and special operations such as honing and small-hole drilling.

The type of MQL used is also a critical factor in determining a proper application for use.

Through-the-tool MQL systems—which use the process of mixing metalworking fluid and air, creating an aerosol that is directly fed to the point of application—allow for rapid response to changes in settings and contain the dispersion of aerosol better than the external systems. However, they sometimes require special tooling, machine or spindle modifications and higher investments.

External MQL systems spray aerosol via a compressed gas stream into the cutting area. Although external systems are simple to use, low cost to install and do not require special tooling, they do not work well when a shadowing effect occurs (such as for deep holes or deeper cuts). Setup and adjustment options also are limited, and the nozzle can sometimes be blocked by chips.

More details about MQL can be found by reading “A Foundation for Minimum Quantity Lubrication.”