Project: Icefy Cryogenic Hard Tuning

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 of lowering the heat in the cutting zone — especially when working with very hard-to-turn materials. The results have been surprisingly encouraging. Now, the real challenge is to bring the technology out of the lab and onto the shop floor.

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 funding 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.

Let's start with a real world illustration, says 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 in. long and 2.750 in. in diameter. The part was being rough ground and then finish ground, and it was taking approximately four hours just for the rough grinding operation. We 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 turn the part," Sheehy says, "and the best they could do was hard turn approximately 2 in. on the 8.500-in. piece, before the tool would disintegrate. So, they sent the part to Elmira, NY, and we put it on a Hardinge Quest 8/51 with ICEFLY. With a little testing and adjustment to the speed and feeds, we were able to take six complete passes down the length of the part for about 48 in., with only one edge of the insert. We ended up with around 80sfm, and each pass was taking about four minutes. So, if we were trying to take 0.0006 in. off, that would be three passes, which is about 12 to 15 minutes hardturning time. This is where we see ICEFLY being a huge advantage."

Sheehy notes that the goals they're obviously looking at are decreasing machining time, reducing cycle time, while also reducing costs. 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 selfevident. Where ICEFLY comes in is in making the ceramic insert stronger through the introduction of liquid nitro gen at the cutting zone, accomplishing the goals Sheehy notes above.

Similar results were found doing a test for another customer, which in volved running a 0.250-in. round ra dius with a 0.500-in. diameter tool. The part material was 75 RC, which is not something that most people attempt to turn. However, they were able to eliminate four hours of grinding time, reducing that to 15 minutes of lathe time, and then finish grinding the part. And as Sheehy says, there's consider able time/cost savings to be realized there.

TRADITIONAL APPROACHES VS. ICEFLY
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 put off by their high price. The new ICEFLY extremetemperature 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 (Lehigh Valley, 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 the 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, providing a quality surface finish.

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%.

OPTION AVAILABLE NOW
ICEFLY is an exclusive option on Hardinge Quest turning centers, and is available today. The liquid nitrogen may be stored in a small, dedicated cylinder near a machine, or in a sup ply tank that would serve multiple ma chines. Programming is similar to a traditional coolant delivery system. A flexible liquid nitrogen line attaches to a lathe's turret via a rotational cou pling. 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 does not leave behind residue.

The ICEFLY machining system aims a small amount of liquid nitrogen directly at the cutting insert engaged in material removal. The ice-cold jet of liquid rapidly removes heat without affecting the workpiece dimensions. Due to the superior cooling of liquid nitrogen, tool wear rates diminish significantly, even at high cutting speeds. More importantly, if you are machining with ceramic inserts, the ICEFLY system can reduce insert fractures.

A BELIEVER
Nitrogen is a safe, noncombustible, and noncorrosive gas. In fact, 79% of the air we breathe is nitrogen. Colorless, odorless, and tasteless, nitrogen is often used as an "inert" gas due to its nonreactive 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, which eliminates 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."