Stellar Precision Components is used to meeting demanding requirements. Among the work orders it has completed have been components for RAM Block II anti-ship missiles; the CCtCap crew transport vehicle, 155-mm Long Range Land Attack Projectile (LRLAP) advanced gun systems; and rocket motor cases for the Atlas Five launch vehicle, among others. However, one of the shop’s most recent projects tested the mettle of machinists and management alike.

Frieze explained that Stellar had just received a purchase order for a handful of Inconel 625 prototypes. The raw material blanks for the job measured 18 in. square x 3 in. thick (457x457x76 mm), and each one weighed nearly 300 lb. (134 kg). The project team was not deterred by the tough material’s poor machinability; Stellar routinely cuts Inconel and other nickel-based superalloys, as well as tungsten, maraging steels, 60 Rc 4340 (300 M), and tool steel.

Nor was tolerance an issue. Frieze pointed to one recent titanium part that called out a 0.005 in. (0.127 mm) profile tolerance over its 12 in. length (304 mm), the equivalent of holding “a couple tenths” in parts that cost over $5,000 each before machining. Meeting the relatively wide-open tolerances on the Inconel part was not a concern.

The problem was one of raw material removal: when finished, the Inconel plates weighed 30 lb. (13.6 kg), 90% lighter than their starting weight. Frieze knew there are not enough hours in the day to remove that much material using conventional carbide tooling, not if Stellar were to meet the deadline. He needed a better solution.

Seminar notes — A few months before, Frieze and several of his coworkers had attended a learning event sponsored by a local National Tooling and Machining Association (NTMA) chapter, hosted at the Kennametal technical center in nearby Latrobe, Penn. There he met product manager Matthieu Guillon, who introduced him to a cutting tool that made Frieze skeptical, at first. “It looked and felt like a plastic toy end mill,” he laughed as he recalled the details.

The tool was Kennametal’s series of four- and six-flute, high-performance full ceramic end mills. Constructed of SiAlON KYS40 grade ceramic and designed specifically for roughing in nickel-based high-temperature alloys, these end mills often out-produce carbide by up to 20 times. Said Guillon, “We recommend a starting speed of 825 SFM up to 3,300 SFM (250 to 1000 m/min), and feed-rates starting at around 0.001 IPT (0.03 mm), depending on the tool diameter and other conditions. Despite the far higher cutting speeds, we have some customers who have reported two to three times greater tool life than carbide.”

Stellar didn’t have any immediate use for the ceramic tools, but after making some quick feed-and-speed calculations, Frieze knew they would be an effective solution given the right application. Several months later, that application arrived with the Inconel plates. He called Guillon to say he might have a good use for those ceramic cutters they had talked about, and wondered how soon he could get some.