Ultrafast Heavy Cutting of Difficult Superalloys

Imagine burying a roughing tool in a block of Ti-6Al-4V titanium and ripping away more than 1,000 cm³ (61 cu in) of material in only one minute. Using a 95 mm (3.74 in) axial depth of cut, 20 mm (0.78 in) radially, and a feed rate of 423 mm/min (16.65 ipm), the 80 mm (3.15 in) diameter HARVI™ Ultra 8X helical milling cutter from Kennametal Inc. (Pittsburgh, PA) can plow through this difficult aerospace superalloy for nearly three minutes straight without flinching. The limits of the HARVI Ultra 8X cutter has been pushed on everything from 15-5 PH to cast iron to Aermet 100 (high strength steel), with outstanding results on each. “We developed this cutter to meet two distinct needs,” says Tim Marshall, a senior global product manager for indexable milling at Kennametal. “Thanks to the large numbers of aircraft being built today the first came from the aerospace industry, which requires the highest metal removal rates possible but still achieving excellent tool life. At the same time, machine tool builders and users alike are asking for tools able to withstand higher cutting speeds but generate lower machining forces, so as to reduce wear and tear on machine components during extreme cutting conditions. This cutter does all that and a lot more.”

Massive piles of chips notwithstanding, your shop almost certainly wants its tools to stay in the cut far longer than three minutes. The HARVI Ultra 8X is designed to predictably remove 20 cu in (328 cm³) of Ti-6Al-4V each minute while attaining 60 minutes of tool life per cutting edge. To do this, a number of innovative technologies are combined in this highly engineered cutting tool system:

• A double-sided yet positive rake insert delivers the lowest cost per edge possible and simultaneously reduces power consumption by up to 50 percent.
• A unique AlTiN+TiN PVD coating provides robust resistance to thermal fatigue so that the high performance KCSM40 carbide grade enjoys much longer tool life than competitors.
• The cutter body is constructed of a higher quality steel than competitors for improved stiffness and rigidity under high cutting forces.
• A unique BTF46 (bolt taper flange) connection provides the ultimate deflection resistance compared to traditional shell mill type holders.
• The variable helix design breaks up the harmonics that lead to chatter, further improving tool life, part quality, and throughput.

Variable helix geometry greatly reduces carbide-killing vibration. Using 12 mm and 10 mm inserts also helps because their smaller size means more inserts in the cutter body, more inserts engaged in the workpiece, and more inserts to absorb the pounding of a heavy machining operation. Yet the HARVI Ultra 8X has even more tricks up its sleeve: Precision through-the-tool coolant nozzles direct cutting fluid where it’s needed most. An enhanced flute design assures maximum chip evacuation. Oversize M4 Torx Plus screws for greater insert stability. The option with a KM4X adaptor brings greater toolholding stability. Specially-prepared double-sided insert edges optimized for the KCSM40 grade greatly extend tool life. Corner radii from 0.8 mm to 6.4 mm (in both inch and metric) means there’s little that can’t be machined.

“The flutes and the coolant nozzles assure maximum chip flow, something that’s very important when you’re removing this much material – without it, the chips get jammed up and you face catastrophic failure,” notes Marshall. “Our KCSM40 grade is a top performer in high-temp alloys, but we also offer several equally excellent grades for other workpiece materials. And eight cutting edges per insert? Nobody else has that in a helical cutter.” Double-sided inserts not only mean lower cost per edge, but the ability to increase speeds and feeds beyond what was previously possible. And because the HARVI Ultra 8X is available with an integral shank or the “crazy strong” BTF46 mount, users can adapt the cutter to virtually any machine tool spindle with no loss of rigidity.

Kennametal Inc., 600 Grant Street, Suite 5100, Pittsburgh, PA 15219, 800-446-7738, www.kennametal.com.