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.
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.”
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.
Related Glossary Terms
Fluid that reduces temperature buildup at the tool/workpiece interface during machining. Normally takes the form of a liquid such as soluble or chemical mixtures (semisynthetic, synthetic) but can be pressurized air or other gas. Because of water’s ability to absorb great quantities of heat, it is widely used as a coolant and vehicle for various cutting compounds, with the water-to-compound ratio varying with the machining task. See cutting fluid; semisynthetic cutting fluid; soluble-oil cutting fluid; synthetic cutting fluid.
- cubic boron nitride ( CBN)
cubic boron nitride ( CBN)
Crystal manufactured from boron nitride under high pressure and temperature. Used to cut hard-to-machine ferrous and nickel-base materials up to 70 HRC. Second hardest material after diamond. See superabrasive tools.
- gang cutting ( milling)
gang cutting ( milling)
Machining with several cutters mounted on a single arbor, generally for simultaneous cutting.
Machining operation in which material is removed from the workpiece by a powered abrasive wheel, stone, belt, paste, sheet, compound, slurry, etc. Takes various forms: surface grinding (creates flat and/or squared surfaces); cylindrical grinding (for external cylindrical and tapered shapes, fillets, undercuts, etc.); centerless grinding; chamfering; thread and form grinding; tool and cutter grinding; offhand grinding; lapping and polishing (grinding with extremely fine grits to create ultrasmooth surfaces); honing; and disc grinding.
Machining operation in which metal or other material is removed by applying power to a rotating cutter. In vertical milling, the cutting tool is mounted vertically on the spindle. In horizontal milling, the cutting tool is mounted horizontally, either directly on the spindle or on an arbor. Horizontal milling is further broken down into conventional milling, where the cutter rotates opposite the direction of feed, or “up” into the workpiece; and climb milling, where the cutter rotates in the direction of feed, or “down” into the workpiece. Milling operations include plane or surface milling, endmilling, facemilling, angle milling, form milling and profiling.
- 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 flood cooling. The concept addresses the issues of environmental intrusiveness and occupational hazards associated with the airborne cutting fluid particles on factory shop floors. The minimization of cutting fluid also saves lubricant costs and the cleaning cycle time for workpieces, tooling and machines. Sometimes referred to as “near-dry lubrication” or “microlubrication.”
Workpiece is held in a chuck, mounted on a face plate or secured between centers and rotated while a cutting tool, normally a single-point tool, is fed into it along its periphery or across its end or face. Takes the form of straight turning (cutting along the periphery of the workpiece); taper turning (creating a taper); step turning (turning different-size diameters on the same work); chamfering (beveling an edge or shoulder); facing (cutting on an end); turning threads (usually external but can be internal); roughing (high-volume metal removal); and finishing (final light cuts). Performed on lathes, turning centers, chucking machines, automatic screw machines and similar machines.