Supercool: Turning Performance

Find out more about a cryogenic lubrication technology based on supercritical CO2 in this month's Look Ahead feature.

December 15, 2011By Alan Richter

It’s an ongoing challenge to effectively cool and lubricate the tool/workpiece interface. After 8 years of research at the University of Michigan laboratories of Dr. Steven Skerlos, the university developed a dry, environmentally friendly, single-channel cooling and lubrication technology that simulta- neously enhances both functions, according to Thomas E. Gross, CEO of Fusion Coolant Systems. The company was formed last year to commercialize this technology through the University of Michigan’s Technology Transfer Office.

Marketed as CHiP Lube (Composite High-Pressure Lubrication), the technology is based on supercritical CO₂. Gross explained that above its critical temperature of about 90° F and pressure of 1,200 psi, scCO₂effectively dissolves lubricants, turning CO₂ into a solvent. “Carbon dioxide goes into a kind of mushy base and then you can dissolve oil and other things in the solution,” he said.

The higher the pressure, the better the cooling capability, Gross added, noting 2,500 psi is a typical pressure.

When the supercritical solution exits a coolant delivery system, it rapidly expands, releasing the oil and sending chilled microparticles of lubricant at the cutting zone with high velocity. The coolant nozzle or through-coolant orifice on the tool is positioned no more than 1 ” from the cutting zone to maximize cooling effectiveness, Gross added.

Chip Lube White Paper 31aug11-5.tif

Courtesy of Fusion Coolant Systems

Machining an Inconel casting with CHiP Lube near-dry cryogenic lubrication technology from Fusion Coolant Systems.

He noted that only a small amount of lubricant is used. “The CO₂ evaporates and what’s left is basically a dry chip.”

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Because of that, CHiP Lube is similar to minimum-quantity lubrication, but MQL doesn’t cool the cutting zone, according to Gross. “We call it MQL on steroids,” he said.

Although CO₂ is a relatively inexpensive gas, it can be recycled, or repurposed, as a byproduct of other industrial processes, such as smelting. “There’s no effect on the environment because it’s already been created long before we use it,” Gross said.

The technology eliminates the risk of shop personnel breathing coolant-laden air, but a HEPA-filter mist collector is needed to extract the dry ice-like mist that contains atomized oil droplets, he noted.

To achieve the full potential of scCO₂ in through-coolant applications, the company is working with toolmakers to develop cutting tools with coolant orifices from 0.006 ” to 0.010 ” in diameter rather than the typical 0.020 ” to 0.030 ” holes, as well as ones that provide flank and top jet cooling. The smaller holes restrict flow to build pressure and minimize oil and CO₂ consumption.

In addition, Gross pointed out that spindles must be modified by spindle retrofitters or machine tool builders. “To really have complete acceptance in the marketplace, the machine tool guys have to get onboard with this,” he said.

The company has a retrofitted turning center in its new downtown Detroit technology center for demonstration purposes and has achieved impressive results, according to Gross. For example, in a standardized test by an independent third party, the company reported that CHiP Lube nearly tripled tool life compared to the baseline when milling titanium using externally mounted coolant jets. The company has also conducted grinding tests, including one for Inconel 700 using a CBN wheel.

For more information about Fusion Coolant Systems, Ypsilanti, Mich., call (248) 693-4223 or visit www.fusion coolant.com.

Glossary terms in this article

minimum-quantity lubrication
Use of cutting fluids of only a minute amount—typically at a flow rate of 50 to 500 ml/hr.—which is about three to four orders of magnitude lower than the amount commonly used in f…