Minimum Quantity Lubrication Machining Process Maximizes Environmental, Cost Savings

To machine its power train, Ford Motor Co. uses CNC equipment requiring minimal lubricants and coolants. Not only does this reduce Ford’s fluids consumption, it eliminates the need for their disposal—along with the accompanying costs.

A good deal of attention is paid to the use of biobased coolants and oils as a means of implementing sustainability in metalworking. Companies are replacing base oils with organic or highly engineered petroleum oils to reduce the volatile organic compound (VOC) content and vapor pressure of coolants and lubricants to meet strict environmental standards.

However, there are costs associated with buying, filtering, separating, and disposing of these reduced-VOC fluids. These costs can represent as much as 16 percent of a machine tool’s life cycle cost.

Another approach to fostering sustainability in metalworking lubrication is to use a process called minimum quantity lubrication (MQL). MQL eliminates large quantities of water and oil-based coolants and replaces them with a small quantity of lubricant mixed with air. This air-oil stream is precisely metered and delivered to the cutting tool’s edge. MQL is based on a simple principle: Use only what is needed for the application, reducing consumption and waste, and deliver the lubricant precisely where it is needed.

How MQL Works

MQL is a nearly dry machining process that uses a through-tool oil mist, tailored to provide just the right volume for ideal lubricity at the interface of the tool and work surface. The process controls the amount of lubricity for the particular machining operation and tool, such as tapping or face milling. MQL reduces metalworking fluid flow from gallons per minute (as in traditional wet machining) to milliliters per hour.

In CNC machines designed for MQL, the cutting program for a part controls the amount and duration of the aerosolized oil spray. This is important

because different parts are made using a variety of machining processes, and each needs a different amount of lubrication. For example, milling, a surface operation, requires a small amount of lubricity; however, tapping and thread cutting require much more lubricity because of the high surface pressures involved.

The CNC program controls a dosing valve, which meters out the precise amount of lubricant. The lubricant is then mixed with air to form the required aerosol, which is fed through the cutting tool to the cutting edge. To minimize the amount of lubricant used, the aerosol switches off as the spindle moves from one cut to another.

How MQL Is Green

Workers benefit from the MQL machining process, both in the short and long term. Operators, skilled tradespeople, and engineers are not exposed to the toxicity, bacteria, and fungi risks that come with traditional wet machining. Coolant mist almost always fouls the plant air and equipment.

The small amount of oil used with MQL generally is vegetable- or ester-based.

The environment is cleaner because no used cutting fluids remain that require stringent disposal. Oil and other wastes present significant disposal impacts and implications to the environment.

Furthermore, the metal chips produced during MQL machining are nearly dry and virtually clean. The near-dry chips are easier to recycle and are more valued as a recycled material.

The process helps change the “dirty” perception of manufacturing, particularly in machine shops where splashed coolants and metal chips no longer litter the floors and condensed oils/coolants no longer drip down the walls.

Cost Benefits Too

So with all of the benefits of MQL technology, why aren’t more manufacturers implementing it? Some may believe the myth that sustainability adds cost.

However, when one considers the total cost of investment, including operating expenses, it becomes clear that MQL machining systems can be cost-competitive, considering that no transferring, recycling, and pressurizing coolants and their accompanying costs for coolant supply, filtration, and mist collection equipment are required.

In addition, considering additional life cycle costs in the form of lower energy consumption, minimal chemical maintenance, water makeup, used cutting fluids disposal, and replenishing consumed fluids, MQL presents even more cost benefits.

Thinking in terms of life cycle costs can be a real challenge, but doing so is a mainstay of sustainability.

So, what is the worst thing that can happen? The answer is that manufacturers may miss the next technology opportunity to restore American manufacturing leadership—and no one can afford that.

Case Example: Green Machining at Ford Van Dyke Transmission Plant

Green machining has a double meaning at the Ford Van Dyke Transmission plant, Sterling Heights, Mich.

Since installing the nearly dry MQL machining process, the company has netted green savings of seven figures in initial cost, and the machines are producing parts at a lower variable cost. Ford no longer has the cost of unneeded coolant tanks and high-pressure supply systems. The process reduces operating costs too.

Since installing MQL, the Van Dyke Transmission plant has finished first in Ford’s North American Powertrain Environmental Performance Awards, and the plant was awarded Quality Magazine’s 2008 Quality Plant of the Year Award.

MAG Powertrain horizontal machining centers, equipped for MQL machining, produce a family of valve bodies and transmission cases for Ford.

The facility currently uses more than 120 MAG CNC machines equipped with MQL or hybrid systems combining CNC and special machines.

The plant’s most recent green-machine installation included horizontal machining systems configured for 4- and 5-axis work to produce aluminum parts for the 6F midrange front-wheel-drive transmission. The high-speed machines work with MQL using a proprietary real-time temperature compensation system that constantly monitors the machine, the part, and ambient air to ensure consistently precise work. The steeply angled interior of the machines, coupled with a Handte chip evacuation system, eliminates the need for chip-flushing coolant and the resulting cost for pumps, filter media, and chip drying.

The second meaning of green machining applies to air quality. Plant air quality is improved compared to conventional wet machining, as well.

The machining envelope is kept under negative air pressure, with chips and oil mist pulled out in an airstream, then through a centrifuge and filter system. Dry chips collect in a hopper, and clean air is returned to the plant or back to the machine enclosure.

Van Dyke Transmission conducted a study that showed that the filtered air from the chip evacuation system is as clean as typical office air, contributing to an improvement in overall plant air quality.

Ford Motor Co., One American Road, Dearborn, MI 48126, [email protected], www.ford.com