New approach to cutting heat-resistant superalloys

Imagine machining Inconel 718 and similar heat-resistant superalloys (HRSAs) at cutting speeds normally reserved for aluminum. Melissa Singher, senior product coordinator for NTK Cutting Tools U.S.A., Wixom, Mich., said this improbable task is not only possible but becoming an accepted practice at some aerospace OEMs.

The secret is the toolmaker’s SX9 ceramic endmills, according to Singher.

“When machining superalloys, such as Inco 718 and 625, using SX9 endmills, you will typically use speeds of 2,000 to 3,000 sfm, with a minimum speed of about 1,000 sfm,” Singher said. “As an example, a ½” endmill requires a minimum of 8,000 rpm and, for optimum performance, should be run in the range of 15,000 to 20,000 rpm. Feed rates will typically range from 0.0011 to 0.0013 ipt, or more than 100 ipm for a 4-flute endmill at 20,000 rpm.”

Dust follows the SX9 endmill from NTK Cutting Tools as it cuts a workpiece made from a heat-resistant superalloy. Image courtesy of NTK Cutting Tools U.S.A.

At first glance, machining with one of these tools might have you running for the fire extinguisher. But what appears to be a glowing mass of chips that will soon ignite and a cutter that will soon be ready for the recycling bin is really an efficient metal-removal process, one that—applied correctly—offers tool life of 10 to 25 minutes, Singher said. She explained that SX9 is a SiAlON, or silicon-alumina nitride, ceramic that blends the strength of silicon nitride with the heat and wear resistance of alumina oxide. The cutting edge was reportedly developed to withstand the extreme heat and pressure generated when machining HRSAs at high cutting speeds.