Using -320°F liquid nitrogen as a coolant (as opposed to water, oil or synthetic flood coolant or dry machining) has been something that’s been closely looked at in academic and research circles as a means to lower the heat in the cutting zone — especially when working with very hard-to-turn materials. The results have been surprisingly encouraging. Now the challenge is to bring the technology out of the lab and onto the shop floor.

ELMIRA, NY — Tom Sheehy, team leader, applications engineering at Hardinge, is one of a select group of individuals working on project ICEFLY. What is ICEFLY? Well, to start, it’s not the code name for a covert government funded project involving frozen insects, nor is it an aerospace solution for conducting military sorties in Siberia. What it is, is cryogenic hard turning on Hardinge Quest CNC turning centers. And what it does will absolutely amaze anyone remotely related to manufacturing parts using hardened materials.

“Let’s start with a real world illustration,” begins Sheehy, “a few months back Hardinge was presented with a particular carbide part that our European subsidiary had been trying to cut. The carbide part was 11% Cobalt, roughly 8.500” long, 2.750” in diameter and nearly 80 RC. The part was being rough ground and then finish ground, and it was taking approximately four hours just for the rough grinding operation. It was felt that hard turning the part would be very much an advantage, if only from a time savings point of view.”

“The Europeans tried everything under the sun to try and turn the part,” Sheehy says, “and the best they could do was hard turn approximately 2” on the 8.500” piece, before the tool would disintegrate.  So, they sent the part to Elmira, NY, and we put it on a Hardinge Super-Precision Quest 8/51 with ICEFLYTM. With a little testing and adjusting the speed and feeds, we were able to take six complete passes down the length of the part for about 48”, with only one edge of the insert. We ended up with around 80 sfm and each pass was taking about four minutes. So, if we were trying to take 0.00060” off, that would be three passes, which is about 12 to 15 minutes hardturning time. This is versus four hours of rough grinding and then the additional finish grinding operation.  This is where we see ICE FLY being a huge advantage.

Sheehy notes that the goals they’re obviously looking at are decreasing machining time, thus reducing cycle time. For example, the difference between a $15 “off-the-shelf” four-tipped ceramic insert and a $50 carbide tipped insert with perhaps a single edge is pretty self-evident.  Where ICEFLY comes in is in making the ceramic insert stronger through the introduction of liquid nitrogen at the cutting zone, thus accomplishing the goals Sheehy notes above.  Similar results were found doing tests for another customer, which involved running a 0.250” round radius. The part material was 75 RC, which is not something that most people attempt to turn. However, they were able to eliminate three hours of grinding time, reducing that to 12 minutes of lathe time and then finish grind the part. And as Sheehy says, there’s considerable time/cost savings to be realized there.

The Need

Machining professionals are under enormous pressure to increase productivity and reduce costs. The challenge becomes more difficult if you're working with hard-to-machine materials like hardened steels, wear-resistant alloys, and tungsten carbide parts. If you are turning hard-to-machine metals, the revolutionary new ICEFLY machining system can dramatically reduce your cutting time and increase tool life. The unique ICEFLY machining system can help you cut parts faster, increase your throughput, and reduce your overall costs.

Traditional approaches vs. ICE FLY

Cubic boron nitride (CBN) and polycrystalline cubic boron nitride (PCBN) inserts have traditionally been the tools of choice for hard turning applications. However, many operations contemplating hard turning are turned off by their high price. The new ICEFLY extreme-temperature coolant system has been developed to offer longer insert life, faster cutting rates and more affordable hard turning insert options.

The ICEFLY cryogenic coolant system was originally developed by Air Products and Chemicals, Inc. (Allentown, PA) and is now being refined for real-world machining by Hardinge Inc. (Elmira, NY). The system delivers a jet of -320°F liquid nitrogen directly to the insert during turning operations. The liquid nitrogen raises insert hardness, which significantly reduces the thermal softening effect that an insert may experience as a result of hard turning's inherent high cutting temperatures. The steep temperature gradient between the chip/tool interface and insert body also helps remove heat from the cutting zone. In addition, the significant cooling maintains insert edge integrity to prevent “smearing” a part's hot, compressed surface layer, thus providing a quality surface finish. Liquid nitrogen insert cooling extends insert life and allows greater use of low-cost ceramic inserts for hard turning operations.

Unlike CBN and PCBN, ceramic inserts tend to wear unevenly and are prone to fracturing when hard turning dry or with water- or oil-based coolants. Increased fracture toughness resulting from low-temperature liquid nitrogen cooling provides more  predictable, gradual flank wear for ceramic inserts, as well as increased cutting speeds up to 200 percent. This predictable flank wear also allows alumina ceramic inserts to be used in critical finishing operations, where PCBN inserts are used almost exclusively today.

Option available now

IceFly is an exclusive option on Hardinge SR-Series turning centers, and is actually available today. The liquid nitrogen may be stored in a small, dedicated cylinder near a machine, or in a supply tank that would serve multiple machines. Programming is similar to a traditional coolant delivery system. A flexible liquid nitrogen line attaches to a lathe's turret via a rotational coupling. This line feeds a delivery nozzle clamped to the tool, which directs the liquid nitrogen to the insert tip.

The system works with hardened steels, hard composites and powder metal parts. Because the inert nitrogen vaporizes after contact with the insert, it doesn't leave behind residue. This is particularly helpful for porous powder metal parts, which often require subsequent part cleaning operations to remove coolant residue.

A believer

Nitrogen is a safe, noncombustible, and non-corrosive gas. In fact, 79% of the air you breathe is nitrogen. Colorless, odorless, and tasteless, nitrogen is often used as an “inert” gas due to its non-reactive nature with many materials. Companies in many different industries use nitrogen for a wide variety of applications, including food freezing and preservation, plastic and rubber grinding, inerting and blanketing, heat treating atmospheres, and tire inflation. The liquid nitrogen used in the ICEFLY machining system also quickly evaporates and returns back into the atmosphere, leaving no residue to contaminate the workpiece, chips, machine tool, or operator and eliminating disposal costs.

“Once we started to understand the process and parameter subtleties,” Sheehy says, “a lot of things, nuances, began to make sense. We’ve learned quite a bit in the past six months with this new technology. I’m a believer in it, just from seeing it cut the carbide totally knocked my socks off. I couldn’t believe it. And you know what’s next? Ceramics. Turning hardened ceramics on a Hardinge lathe.”