Minimum quantity lubrication

Mixing oil and air may be the best thing for your equipment

by S.”Mani” Manivannan

Minimum Quantity Lubrication (MQL) is a machining method that delivers a specified minimum quantity of lubricant mixed with air. Machining is done using a continuous supply of this oil/air mixture to extend tool life. This method is also called semi-dry machining or near-dry machining (NDM). This method for machining with oil/air mixtures is called MQL.

MQL makes it possible to reduce the amount of lubricant to nearly zero
In conventional manufacturing of mass produced parts that typify automotive components (engines, transmissions, brakes, etc.), a large volume of cutting fluid (coolant) is used to improve productivity and machining accuracy. Recently, the health effects of cutting fluid upon people and the environment have become a serious problem, so the reduction of coolant is strongly recommended.

The automotive industry is a major driver in the adoption of Minimum Quantity Lubrication (MQL). Chrysler, Ford and General Motors have all made plant implementations of one kind or another. Success of these first full production applications, now in their launch phase, could give the green light to more MQL applications. Getrag Ford Transmission in Cologne, Germany was the first company in Europe to put a completely MQL line into production.

A healthier way to lubricate?
The green issue identified by U.S. automotive OEMs and other industries centers on the health and safety risks associated with wet machining. Arguments raised against wet machining include the generation of dioxins, the harmful effects of coolant on skin, increased wear and tear of machine tools, increased maintenance costs and fire hazards.

In contrast, MQL generally uses vegetable or ester oils as the cutting fluid. These high-performing oils have excellent lubrication qualities and are naturally solvent. They are also environmentally friendly.

How does MQL work?
• While supporting metal cutting processes, MQL replaces the function of conventional Metal Working Fluid (MWF).
• While MQL feeds and speeds as well, tool life and work piece quality can compete against wet machining operations.
• Environment and operational costs benefit through MQL.

Other advantages come through the reduction in cutting oil consumption, resulting in improvement in plant environment and in chip recycling, reduced power consumption, increased tool life and, above all, capital investment.

Avoiding a blowout
The machining process on work pieces made of aluminum or alloy generates explosive dust of classes between category 1 and 2, depending on particle size distribution, degree of oxidation, moisture and consistency.

The process-dust contained in the crude air can be made inert if it is mixed with a limestone powder additive. Mixing of this dust with a sufficiently large quantity of calcium carbonate produces an inert dust mixture (according to VDI 2263 guidelines).

Calcium carbonate is non-combustible and a non-explosive limestone powder. The separated process-dust gets mixed with the additive and this dust mixture is non-explosive. The additive injector inside the dust container blows the dust mixture up into the filter chamber where the air stream conveys and distributes it evenly on the outer surface of the filter elements.

The XHC 241 MQL uses a minimum quantity lubrication system on the machining process. Condensed organic compounds are generated which are adsorbed by the limestone powder on the filter surface in the HANDTE dry-type separator to render them inert.

The content of aluminum dust extracted from the machining process must be kept as low as possible to avoid fire or explosion risk.

This article appeared in the April/May 2008 issue of MRO Today magazine. Copyright 2008.

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