Manufacturing meeting challenges with cutting tool advances | Manufacturing Engineering | advancedmanufacturing.org

Contributing Editor

Sharon-Cutwell engineers check a Wave-Point drill point during production. The tool can run at 70 IPM in CFRP and also tackles stacked materials.

Necessity and opportunity—including unforeseen ones—can be the mother of invention and innovation. Several creative cutting tool manufacturers, for example, used the recent industry slowdown during the COVID-19 pandemic to develop and test a host of new solutions.

Others have turned seemingly geographic disadvantages into strategic benefits.

Take today’s advanced high-strength materials, which have long bedeviled manufacturing— especially in aerospace applications. But these new cutting tool advances are up to the challenge, whether it’s for composites, titanium, Inconel or Hastalloy.

Sharon-Cutwell Co. offers a prime example, and President Jeff Prom would tell you the company’s location “in the middle of nowhere” (Belgium, Wis.) has always given it the relative quiet needed to think. Conversely, he’d add, the team at Cutwell doesn’t isolate themselves in Wisconsin: The company maintains close relationships with both customers and technology partners around the world.

Cutwell’s latest achievement is a solid-carbide, CVD diamond-coated drill family for advanced aerospace materials. Dubbed “Wave-Point,” the patented design features multiple radii along the cutting edge, alternating in and out, from the major OD to the point. Prom says the drill “allows high penetration rates and minimal exit delamination in carbon fiber, and it holds very tight tolerances.”

Cutwell also has slightly different versions optimized for carbon-fiber-reinforced polymers (CFRP), aluminum stacks and CFRP titanium stacks, as well as solid titanium, Inconel, Hastalloy and related exotics. “If you don’t want to swap out tools, you’d use the geometry optimized for the material you machine most often and the tool will still cut the other materials,” Prom adds.

The numbers bear out Prom’s performance claim. For example, tests show a 1/4" (6.35 mm) Wave-Point can drill carbon fiber at 600 SFM with a feed rate of 0.008" (0.2 mm) per revolution at 8,500 rpm, resulting in a 70-IPM feed rate. What’s more, the tool held a 0.0005" (0.013 mm) diameter tolerance with minimal delamination on entry and exit, plus it ran over 1,200" (30,480 mm). That’s one drill. The countersink portion of the tool is equally impressive.

All of Cutwell’s test are conducted with a Spike force sensing unit from Germany’s Pro-Micron, which is one of the company’s technology partners. “We get live data on all the forces—thrust, bending and torque—to help us analyze what’s going on,” Prom says. “We monitor and record all force data, make adjustments and retest until we build the best solution possible for our customers.”

In a real-world case a few years ago, Prom recounts that Boeing found a PCD drill so prone to chipping in composites that the company lowered the feed rate to 3 IPM. Boeing switched to a CVD diamond-coated tool and got up to 9 IPM, but still with poor tool life (200 holes).

“That’s when we stepped into the situation,” Prom says. “With the Wave-Point, they run at 64 IPM with an 800-plus hole tool life.”

That’s a sevenfold improvement in feed-rate with 4X longer life than the previous carbide tool. The application is drilling the holes for fastening the fuselage sections of a 787 plane. The reduction in drilling time is so significant that Boeing has saved an entire shift of drilling time on each fuselage joint, according to Cutwell.

Prom says tasks on Boeing’s latest and largest airplane, the 777X, require drills up to 1" (25.4 mm) diameter for fastening applications, and 1.4" (35.56) diameter for an access hole, all of which Cutwell can build with the Wave-Point geometry.

The patented Wave-Point design features multiple radii along the cutting edge, alternating in and out, from the major OD to the point. The drill delivers high penetration rates, excellent hole accuracy, and minimal exit delamination in both CFRP and stacked materials.

So-called stacked composites present an even bigger challenge. Prom says their recommended starting speeds and feeds for a 1/4" drill in composite and aluminum is 500 SFM x 0.008 IPR in the composite and 400 SFM x 0.008 IPR in the aluminum. “And we’ve tested up to over 800 inches (20,320 mm) of tool life, for a quarter-inch drill in this application.”

The numbers for a CFRP/titanium stack are lower: 400 SFM x 0.008 IPR in CF and 50 SFM x 0.004 IPR in titanium.

“Some applications require drilling a composite-titanium-aluminum-titanium stack,” Prom explains. “That’s four layers of different materials. It has to be done in one shot with one drill, and it has to be perfect. It’s a daunting task for one drill bit to handle all those dissimilar materials. It requires drilling each layer at a different speed and feed, so the equipment has to be highly automated and programmed for each layer of the material. It’s the hardest thing that aerospace manufacturers are doing in assembling airplanes.”

Still, Cutwell’s 0.393" (9.98-mm) diameter drill delivers 150" (3,810 mm) of tool life in a CF/Ti/Al/Ti stack that’s 1.25" (31.75 mm) thick, Prom says. “And that’s been in production for six years.”

The most predominant process, according to Prom, is to peck drill in the aluminum. “You drill straight through the composite, and then you turn on lube, generally a minimum quantity lubrication, and use that as you peck drill through the aluminum to make small enough chips that they don’t erode and damage the composite as they exit.”

Today, Cutwell has an even more advanced way of drilling aluminum. To this end, it works with Mitis (Bouguenais, France), which specializes in micro pecking, to deliver vibration-assisted drilling (VAD).

“As the drill progresses through the metallic material, it also oscillates up and down,” Prom explains, “taking the drill tip in and out of the material by only about five thousandths of an inch.” The movement is so small it’s imperceptible to the eye, but it creates “nice little chips, and it’s a much faster process,” Prom adds.

“As an example, drilling a typical composite-aluminum stack with a 1/4" tool and a standard peck process would take about twelve seconds per hole,” he continues. “When you implement the VAD process, you’ll get it down to three seconds per hole. A fourfold improvement in throughput.”

Repeated tests have shown the technology delivers the same or even better tool life, according to Prom.

While polycrystalline-diamond (PCD) drills were once the mainstay for composites, Prom says diamond-coated carbide tools have taken over most high-end applications to enable optimized geometries.

“With PCD, you don’t have the ability to create a drill tip with all the features that you’d want, or all the clearances,” Prom notes. “With a carbide drill, we can optimize the geometries and then coat it with diamond to give it a super-hard shell. You get the best of both worlds, geometry and tool life.”

But Sandvik Coromant Sweden (U.S. headquarters in Mebane, N.C.) is now using 3D printing to make PCD drills more capable and economical, lowering the resulting cost per hole and challenging carbide and diamond coated tooling.

Traditionally, PCD drills have been a combination of PCD and carbide, created by grinding slots in a carbide nib into which diamond grit is sintered, then brazing that nib onto a carbide shank. The final cutting geometry is then formed by eroding and/or grinding both the PCD and the carbide.

This approach necessitates grinding away more carbide, and consequently laying in more PCD, than is actually needed to create a flute on both sides, explains David DenBoer, an aerospace industry specialist with Sandvik Coromant. And given the cost and the inherent difficulty of then shaping PCD through erosion/grinding, the result is an expensive tool.

Tool geometry is also limited, according to DenBoer. He points out that the grind down the side of the nib must be straight, so it can’t follow the desired path of the flute. Thus, this approach works only for a short nib with a correspondingly short run of PCD.

Conversely, by 3D printing the nibs, DenBoer says it’s possible “to lay the diamond any place we want it, including farther down the side, following the flute. This gives us the ability to build a much longer nib than what we can accomplish with a standard grind.”

So there’s less PCD to remove where it isn’t needed and twice as much in targeted areas. The first point lowers the cost of the tool; the latter results in a tool that can be resharpened up to 10 times. Combined, this can yield a significantly lower cost per hole, especially as these PCD tools last through 9,000 holes.

Sandvik Coromant has introduced the technology to its 85 and 86 series drills in diameters from 0.190-0.376" (4.83-9.55 mm).

A single InoxDrill can drill multiple stainless steels, multiple nickel alloys, and both pure and alloy titaniums. Just follow the recommended feeds and speeds.

While DenBoer believes PCD drills are the right choice for “standard” composites used in Boeing and Airbus airliners, he concedes that it’s often impossible to eliminate delamination in unidirectional material with these tools. For such applications, Sandvik Coromant has developed a new diamond-coated carbide drill called TNT, which features a unique swirling flute geometry that’s compared to a soft-serve ice cream cone.

The TNT acts with “more of a slicing action than a standard drill, along a longer, curved edge than a standard PCD drill, which cuts just along the short diamond face,” DenBoer says. The design produces a significant lifting force in the material that virtually eliminates the delamination otherwise common on exit.

“In fact, sometimes we have to slow down on entry, because it lifts so much we can actually delaminate on the opposite entry side,” he notes. “No other drill that I know of can do that.”

DenBoer recounts a test of a three-flute CVD diamond-coated 1/4" (6.35 mm) TNT drill with countersink in woven CFRP. It ran without coolant at 5,000 rpm with a feed of 0.008 IPR (for both drilling and countersinking) and Vc=327 SFM. The tool held a hole diameter tolerance of Cp=3.54 and Cpk=3.33 over 3,000 holes, while delamination averaged ~0.0001" (0.0025 mm) and never exceeded 0.0018" (0.0457 mm) throughout the run. The cutter showed no signs of wear prior to an improper clamp that caused breakage at hole 3,303, ending the test, according to the company.

In the case of the F-35 fighter, DenBoer says a leading manufacturer had been forced to tape the entire underside of a large unidirectional-composite section to prevent delamination. The TNT eliminated the problem, so the manufacturer is now implementing the tool to remove “this laborious task,” according to DenBoer.

Sandvik Coromant has also demonstrated that the tool maintains a low temperature when cutting, so as not to melt CFRP material.

The carbide TNT tool costs less than a comparable PCD tool, DenBoer points out, and is offered in diameters from 0.190-0.685" (4.83-17.4 mm). But because the diamond coating wears primarily at the cutting edge, it can’t be efficiently reground. That, plus the longer life of PCD tooling, limits the TNT to the unidirectional material, in DenBoer’s view.

For its part, Emuge-Franken USA, West Boylston, Mass., used the COVID lull to test its InoxDrill “in as many materials as possible,” according to Marlon Blandon, the company’s drills and thread mills product manager. “We created a speeds-and-feeds chart that offers very specific guidance for a wide variety of materials we’ve seen used increasingly in the medical and aerospace industries.”

This enables a single tool to drill multiple stainless steels that include ferritic martensitic 440 and austenitic ferric heat-resistant super duplex; as well as nickel alloys such as Inconel 718 and 625, Incoloy 901 and 903, and Waspaloy; plus pure and alloy titanium.

The InoxDrill family is all two-flute, and either 3 or 5xD, with a proprietary monolayer PVD coating that also carries over the entire material range, Blandon says. As the drill is self-centering, Emuge does not suggest using a spot drill or any type of piloting tool prior to an application.

InoxDrill has a K-Land-style cutting edge, plus an additional hone added after the tool is ground. The result is a tool that “really likes a heavy load,” Blandon asserts. “For example, whereas you might run six thousandths per revolution with a competing drill of a given size, we would recommend seven and a half to eight thousandths per rev in the same material using InoxDrill.”

The InoxDrill was initially designed for high-temperature alloys, with a single margin. As a result, only one side of the flute has a margin for stability purposes.

“This allows you to use it in materials that are very susceptible to heat hardening, like Inconel,” Blandon says. “These materials tend to create a protective layer after you hit them, making it very difficult for the following tool, such as trying to thread after drilling.”

Thread milling is the preferred method of producing internal and external threads in many of these tough materials. This is mainly due to their edge-wearing characteristics, according to Blandon.

“High-speed steel cutting edges aren’t usually the best approach with some high-temp alloys, or a stainless steel that has a high concentration of nickel and vanadium ... or nickel alloys,” he explains. “The softer the nickel it is, the harder it is to tap it or to use a continuous cutting method for working it. So, thread milling in general is the best approach.”

Emuge boasts “excellent thread mills” that enable operations to be combined in a single tool. For example, Blandon points to the THRILLER-AERO and the THRILLER-MAX.

“These two are unique combination tools designed specifically to produce the hole and thread simultaneously in really tough materials,” he says. “As the name suggests, the THRILLER-AERO will work well in many of the high-temperature alloys, stainless steels, titanium combinations and nickels. If the hardness threshold goes beyond 46 to 50, we would probably recommend our THRILLER-MAX.”

The correct CAM approach, Blandon adds, is critical. “These tools require a left-hand spindle rotation in order to use them properly. You come in from the outside of the hole and work your way in a corkscrew-type motion.”

Dan Doiron, Emuge-Franken USA’s milling product manager, echoes this for milling in general, saying he doesn’t see enough utilization of the latest CAD/CAM toolpath methods, such as trochoidal machining, in the field. “Everyone has a wrench, but some people actually use that wrench as a hammer sometimes.”

Doiron’s main point is that even a general purpose end mill will perform much better with a proper programming approach. In particular, he explains, any end mill can be used for trochoidal machining. In some cases, a trochoidal method can solve tool life issues, allowing for more parts per tool to get out the door.

At the risk of confusing the matter, Emuge has introduced a line of end mills specifically for trochoidal machining called Trochoidal End Mills.

“A Trochoidal End Mill is a two to five times D tool,” Doiron says. “The tool is designed for light radial passes. And because of the long flute length, it has chip breakers along the flute.” That’s because cutting a deep pocket with a long flute length would otherwise produce chips that would entangle and “get wrapped up in the tool.” Breaking up the chips makes evacuation much easier. Although the tool has chip breakers, they are staggered in position along each flute, producing smooth wall finishes.

Emuge is also introducing more six- and seven-flute end mills. “You’re not going to be able to take a large radial step over, but you’re going to be able to gain speed,” Doiron says. “This fits with what a lot of machine manufacturers are doing now. Some machines are much faster than they used to be, but don’t have the horsepower they used to have. So we need to take a different direction to cut this material: Lighter radial passes at a higher feed rate.”

Another upcoming product line that excites Doiron is Emuge’s Hard-Cut End Mill, which he says is going to exceed close to 70 Rockwell in some materials. “That’s a huge step. We have re-engineered the tools and are reportedly having great results with speeds and feeds. I’m currently testing one right now on some die forgings.”

The lesson is clear: Users need to keep checking in with their cutting tool suppliers. If you’ve been doing the same thing for a few years, there’s probably a new geometry, a new coating or some other improvement that will blow older tooling away.

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Contributing Editor