These are acronyms for Minimum Quantity Lubrication (MQL) and Near Dry
Machining (NDM). They both employ the use of minimum quantities of "neat" or
"straight" lubricant or a lubricant and emulsifier combined with water . However ,the fluids are dispensed (sprayed) in combination with compressed air up to the available "shop air" pressures .

The degree of atomization is dependent, to some degree, on whether the
inexpensive fluids are basically oil or water. Since the use of "water" is primarily to remove heat, it is used very generously ---and broken up in very fine particles to enhance its ability to absorb heat (heat of vaporization).

Whereas use of an oil (vegetable derivative) is applied very sparingly in larger particles which allow them to wet-out in extremely thin films, dramatically reducing friction and heat.

WHEN DID IT START?

The use of "Venturi type" systems for dispensing water base materials became common during World War 11. ln the mid 50's in the U.S., it was realized that Venturi systems were "fogging up" the workplace, causing breathing problems and other environmental issues.

High speed steel tools and some inserts were being used. Thermal shock on the carbide was initially unrealized problem causing a breakdown of the cobalt binder in carbide tools .

Soon thereafter, it was realized that if fluid could be delivered to a nozzle tip in a controlled low volume it could be combined with compressed air of an equal or lesser pressure. This dramatically reduced airborne particles and their negative effect on the' working environment.

WHY IS IT USEFUL?

NDM and MQL are being used for basically two reasons:1) environmental and
2) monetary.

Environmentally: lf used and applied properly it will clean up slippery floors , reduce or eliminate breathing and skin related problems (depending on fluid used and application volumes).

Monetarily: Reduce floor space, eliminate coolant pumps, eliminate coolant testing, treatment and disposal, it will bring higher scrap value, provide faster machining. yield better finishes. Allow the operator to observe performance during machining.

WHEN AND WHERE IS IT USEFUL?

It is doubtful there is a metal cutting operation that could not benefit, even forming tools such as dies and swaging tools. Substantially yield increased tool life and better parts and finishes when fluid is applied uniformly to all surfaces.

ARE THERE ANY LIMITS?

The limits have not been reached. There is no metal cutting operation that cannot benefit from NDM/MQL. it could be that the challenges of some grinding operations may require a little more ingenuity than has been applied to date .But sanding, some surface grinding and most tool and cutter grinding could benefit.

All metal forming operations irregardless of material being formed can benefit.
Mold release applications in vacuum forming and many injection molding operations find it beneficial.

IS WATER BETTER THAN OIL?

Water is water ---or is it ? it is wet, it evaporates when heated and it contains "contaminates". Are the contaminates harmful? Possibly. What improvement does the lubricant, emulsifier, rust inhibitor and other additives (totally 5-10%) do for your coolant ? l do not know , but the potential negatives are there.

A highly refined vegetable oil of consistent highly-refined world-wide quality will not cause thermal shock and can handle friction and heat better (by 2 times) than any mineral oil product. Usage can be so slight it cannot be detected by the human eye. My vote would be for vegetable oil over water unless there were overriding circumstances.

HOW IS IT APPLIED?

Since water based fluids are normally applied in volumes of 10-20 times that of vegetable oil, its metering is less critical. Normally metering it under pressure using a metering flow valve is sufficient. It is then usually combined with air pressure that is lower than the fluid pressure.

Since a good vegetable oil is used at about the rate of 5% of a water based fluid its metering is critical. Normally small air operated pumps intermittently inject the oil into the air stream at or close to the cutting tool. Depending on the quality of the oil stickiness can be eliminated while non toxicity and high bio-degradability are common to most vegetable oils.

WHAT IS ITS FUTURE?

Most everyone you meet who has a "connection" to machining says" it's the future---it has to be".

And so why is it taking so long to implement?

The best answer I have is that to optimize it requires collaboration between machine builders,tool makers, tool designers, fluid supplies and application system engineers.

It would require (1)some minor machine revisions, (2)Revised tool materials, coating and geometry probably at lower cost and (3)Dramatic loss of existing "coolant" business---to be offset somewhat by lower volumes of more expensive lubricants.