HELICAL CUTTER TECHNOLOGY TAKES TITANIUM MACHINING TO NEW HEIGHTS
Squeaks, Not Screams: Aerospace manufacturers report significant reductions in 5-axis machining time and notable improvements in load equalization by using this cutting tool technology.
Five-axis machining is not cheap. Machining complicated aerospace parts out of solid titanium workpieces can take days, if not weeks, to complete. Couple this with burden rates of $200 an hour or higher for sophisticated five-axis machine tools, and the search for meaningful improvement in titanium machining is one aerospace part manufacturers take seriously . . . very seriously.
This is the reason why the new Mill 1-14™ helical cutter and its proprietary load-optimized insert spacing (LOIS™) concept from tooling manufacturer Kennametal Inc. (Latrobe, PA) is meeting with so much enthusiasm from the aerospace community. “One customer declined to be identified, but reported saving 20-plus hours in milling a five-axis part using this new helical cutter,” says global product manager Dennis McNamara. “They are currently reprogramming other titanium parts to take advantage of the process improvements.”
Helical cutters, which are basically helix-shaped cutter bodies with indexable inserts, are targeted at “any user that wants to take a greater axial depth of cut than can be taken with a standard end mill,” explains McNamara. “Users always want to cut deeper than the single insert height they are using today.” The Mill 1-14 represents a full range of helical cutters that provide much-needed flexibility and versatility. These helical cutters can have inserts stacked two, three and four high, and custom tools are available with up to 13 rows of inserts. “The favorite choice is going to be cutters with inserts stacked two high,” predicts McNamara. “Users receive the ability to increase the axial depth of cut with little added cost.”
Users also get a lot of versatility with helical cutting. Mill 1-14 helical cutters can be used for medium to heavy roughing and semi- up to fine-finishing in such applications as contour profiling, slotting, ramping, helical ramping from solid, and plunge milling (see Figure 1). With conventional helical cutting, the diameter, number of inserts, and the helix angle establish the maximum number of cutting edges that can be in the cut at any given time. In theory, a greater number of cutting edges in the cut at any given time can smooth out the cut but can also increase machine tool power consumption.
“In reality, with traditional helical indexable end mills, equal insert spacing often causes an uneven load demand on the machine tool,” explains Kennametal engineer Jim Waggle (see Figure 2). The response to this is LOIS™, or Load-Optimized Insert Spacing, which sets the performance of Mill 1-14 cutters apart by finding the “sweet spot” of insert spacing relative to the torque and horsepower of the machine tool. “This was not an easy concept to develop by any means,” notes Waggle, “but while appearing to be uneven, the LOIS models result in inserts spaced to optimize cutting, minimize vibrations, and reduce uneven power conditions.”
Cutting loads can fluctuate for a variety of reasons, and manufacturers familiar with milling titanium recognize the sound a helical cutter makes when profiling in a radius. A larger contact area makes the cutter react . . . LOIS does not have the same effect (see Figure 3). A technical CD is available to interested manufacturers with videos showing much lower load variation when milling steel. “When viewers hear squeaks instead of the screams, that’s when jaws start dropping,” smiles McNamara. “The reason we machined steel was so the user could see the actual tool working. If it was titanium, there would have been a picture of coolant flow.”
The Mill 1-14 inserts themselves also are specially designed to add cutting versatility (see Figure 4). Innovative micro-geometry features contribute greatly to enhanced performance, various rake angles, negative T-land, and small hone. Results include significantly reduced cycle times and lower cutting forces. Test results in producing 90 deg walls have proven excellent as well. Adding to the insert stability on these cutters are proprietary axial support pins that help align all the insert bases for improved surface finishes and tool life. The pins are spare parts and can be changed when required.
Integrated cooling nozzles further improve cutting performance (see Figure 5). Other cutters simply have drilled holes in the bodies that do not focus coolant to the cutting zone. The problem with this technique is that when the spindle starts, much of the coolant is not directed, even moving away from the cutting zone. With Mill 1-14, users can configure up to nine different coolant nozzle sizes for consistent, focused coolant flow. “With all of these helical cutters, users can purchase alternative nozzles to suit the coolant flow on their machine,” states McNamara. “As there are numerous machine styles with different coolant pumps, the user now has a choice. There’s even a nozzle opening at the end of the cutter that can also be used for cleaning the machine tool. Another advantage is that coolant pressure helps avoid any chip-packing in the cutter pockets.”
Kennametal Inc., 1600 Technology Way, Latrobe, PA 15650, 800-446-7738, www.kennametal.com.