'Cool' solution could save the metalworking industry billions

In a classic example of a simple idea solving a very complex problem, researchers have developed a new class of lubrication technology that could save industry billions of dollars in metalworking operations while reducing pollution and wear and tear on cutting machines and tools.

The lubricant is a solution of vegetable oil in carbon dioxide, says Steven Skerlos, assistant professor of mechanical engineering and co-author of "Vegetable Oil in Supercritical Carbon Dioxide Metalworking Fluids," which was awarded top honors last month by the International Society for Industrial Ecology in Stockholm, Sweden.

Companies around the world spend billions today on metalworking fluids, which are used as coolants and lubricants to control heat buildup during metal cutting. These fluids typically are emulsions of oil and water, where the oil is used to reduce heat generation and the water to conduct heat away from the cutting zone.

Since oil and water don't mix, current metalworking fluid systems are inherently unstable, so industry is looking for alternatives. Oil and water also are corrosive and, because of their similarity to milk, metalworking fluids can breed bacteria unhealthy to machinists.

To solve these problems, the research team substituted supercritical carbon dioxide (scCO2) for water, mixed it with soybean oil to make a metalworking lubricant, and saw a level of performance that was much higher than they had ever observed. Supercritical means the carbon dioxide is pressurized to a state where it becomes a solvent to vegetable oil.

"The level of success was somewhat surprising," Skerlos says. "For example, we found that soybean oil dissolved in supercritical carbon dioxide performs much better than straight soybean oil, even if the amount of soybean oil applied is 10 times less in the supercritical carbon dioxide system."

The scCO2 system also is a much more effective coolant because, as the pressure is released as a spray, dry ice is formed that can be thought of as a cryogenic spray. Skerlos says that this is the same phenomenon that makes a person's finger cold when the air is released through the valve on a bike tire.

The patent-pending technology is generating a buzz in the industry, particularly in the aerospace sector, which currently is trying to achieve high-speed machining rates on titanium parts. Skerlos says the technology will have applicability anywhere that metalworking fluid is used now, including automotive steel and aluminum machining.

U-M researchers are developing a business case for the patent-pending technology and selecting a launch application. Discussions regarding license agreements are active among metalworking fluid companies and businesses that can supply the scCO2-based cooling and lubrication system.

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