The main concern was to remove 0.200-0.400 in. of stock fast without overloading the auxiliary spindle, especially laterally.  In flange work, low lateral forces are essential to keeping the flanges perfectly flat, preventing leaks when the valves go into service.

Greenleaf’s GF1 chip form also contributes to finishing success. The form is ground into the top of the insert, up to the cutting edge, and is offered on all Greenleaf’s whisker grades. “It helps reduce cutting pressure, which reduces the chance for any type of failure during the quality inspection,” Dillaman said.

The price difference can easily be 25-30%, he added, citing the case of a whisker-reinforced ceramic having a seven-minute tool life, versus six minutes for the SiAlON. But, with a 25% lower price, that works out to a 7% savings in favor of the SiAlON. “Over a year of usage, that’s a huge savings,” Navarrete asserted. “Ceramics aren’t cheap.”

“The Mazak had the power to cut faster; the bottleneck was the tool,” Ingersoll field rep Darrell Boatwright observed during a plant walk-through.  He brought in a Gold-Duty cutter he had in the trunk and they tried it out on the spot. By the end of the day, parameters were optimized at 100SFM/0.014IPR/0250 DOC.

Ceramics remain an excellent solution for high-temp alloys and abrasive materials, with the ability to achieve eye-popping rates. In fact, milling speeds in high-temp alloys range from 2,800 to 4,400 surface feet per minute (SFM), according to Robert Navarrete, national product specialist for parting, grooving, and turning at Iscar USA.

Micor Industries, Decatur, Ala., reduced rough-turning cycle time on titanium from 45 to 30 minutes with another Gold-Duty insert, shipping a rush order three days sooner. They’ve since standardized on that tool for all rough OD work, and are collaborating with Ingersoll to develop an ID-machining version — projecting the savings at around $500,000 per year.

The Gold-Duty tool easily handled the 33% higher machining rates with no pounding or scraping, the usual forerunners of an insert about to rupture.  “We slowed the surface speed but fed faster and cut deeper,” explained Micor programmer Joey King.

Development of breakthrough carbide-grade opportunities in machining is practically tapped out, according to Bernie McConnell, executive vice president, commercial, of Greenleaf Corp., Saegertown, Pa.

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Despite having no previous experience with ceramics, the company worked through the required deviations from its carbide methods quickly. There were just two problems. The first, explained Brian Shaffer, vice president of operations and quality, was wheel wear.

Micor standardized on those settings for the balance of the job, and delivered the job three days early as a result.  “Despite the higher removal rates, the inserts lasted 33% longer,” King added.  He estimated that, with an annual volume of 400-500 pieces, Micor would save $13,000 a year on that one titanium job.  Consequently Micor is standardizing on Gold-Duty tooling for all rough turning and facing, for a projected $60,000 annual savings.

It should come as no surprise that live turning speeds up a roughing operation on any machine with a C axis.  The process gets two spindles working simultaneously, with tools having multiple cutting edges rather than just one.

So, there you have it. Ceramics offer outstanding solutions to difficult machining challenges, and the challenge of machining ceramics themselves can also be met with the right technology and a willingness to push the limits.

“Outside of doing different things with coatings, geometry, and edge preps, there are only so many ways you can mix and blend the carbide materials,” he said. “Most of the exciting technology development is coming on the ceramic side of the business.” That’s for both cutting tools and parts. “Whether you are talking about going super fast, facing extreme heat, or abrasive wear characteristics, ceramics are pushing the envelope in diverse applications. Today’s ceramic capabilities are unbelievable, and continue to get better.”

Meanwhile, Greenleaf’s premium performance whisker-reinforced ceramics continue to have value-added applications, owing to their higher hot hardness and wider feed-rate capabilities, according to Martin Dillaman, the company’s global manager for engineering and applications. For example, he said, “you typically would not finish with a SiAlON in heat-resistant alloys, because they run at a higher feed rate that exceeds the surface finish requirement for the part. So you have to use a whisker-reinforced ceramic if you want to keep the speed up and finish.”

With its advanced design, substrates, and coatings, the Ingersoll Gold-Duty line of rough turning inserts is a generation ahead of the field in large scale turning, according to Ed Woksa, Ingersoll national turning product manager.  The inserts are physically much thicker and stronger than conventional turning inserts.  Their unique seating scheme enables more efficient top-face geometries in two-sided inserts for the first time.  ‘Rest pads’ on the insert faces mate with bumps in the seat pocket to lock them in place (see diagram).  It’s the rest pads that bear the clamping forces, not the cutting edges on the reverse side. This is what enables 5-7 degree positive rakes and aggressive chipbreakers in a two-sided insert. Recessed clamping provides a flush surface for unimpeded chip evacuation.

Danobat conquers these challenges with its Overbeck IRD machine, equipped with a four-spindle wheel head. Grinding the form requires three-axis interpolation (X, Z, and B0), as well as all four spindles. For example, grinding the outside of the form requires a large OD wheel, while much smaller ID wheels tackle the inner form. Getting the required surface finish also necessitates using multiple abrasives for roughing as well as finishing, added Beavers.

“Many people don’t appreciate how tight the dimensional and form tolerances are on these parts,” observed Daniel Rey, president of Danobat distributor Rey Technologies, St. Charles, Illinois. “And one reason Overbeck has been successful in meeting them is by using solid natural granite as a machine base. Among other things, this manages any temperature fluctuations in a shop. Overbeck also uses linear motors, which is another edge over some of the competitors.”

The second problem with grinding ceramic is that it produces a fine, milky swarf that clogs coolant filters faster than carbide. Better Edge addressed this by changing filters more frequently, but decided that if they were to continue grinding ceramic they’d have to dedicate a filter to that application.

Neither Greenleaf nor Iscar shares the secrets of how their tools are made. But Scottsdale, Pa.-based Better Edge gives a glimpse into the challenge of grinding the final cutting geometry. While the company focuses on specialized carbide cutting tools, Better Edge recently got a project to grind a half-inch diameter, short-LOC, six-flute end mill for an aerospace customer. The tools came in worn, so Better Edge cut off the cutting portion, then ground a new geometry into the remaining blank.

The same types of tooling also increased OD removal rates, enabling the whole fleet of screw machines to reach the shop managers’ goal of 30% higher capacity with no capital expenditures.  “Even in miniature precision screw machine work, today’s higher-rake, chipbreaking inserts with advanced coatings can make a material difference,’ said Ingersoll’s Matt Hagenow, who worked on this project.

You may think of rough turning as a bottleneck operation, maybe even a hazardous one, and rightly so.  But, across the country several alert machine shops have found different ways around both problems, according to Ingersoll Cutting Tools.  Users report material-removal rate improvements anywhere from 30% to 6-to-1 in OD and ID work, reliably longer tool life, and relief from ‘shrapnel’ flying from shattered tools.

If you need a third example, you can’t do much better than a line that produces 2,000 aluminum beverage cans per minute. According to Jim Beavers, sales manager for Danobat Group in Rolling Meadows, Illinois, the necking die that forms the can’s walls to accept the lid was traditionally made of carbide, “but over the years, they’ve discovered that HIP (hot isostatically pressed) ceramic has a longer life, because they have better heat transfer and wear capability.” The version Danobat sees most often is yttria tetragonal zirconia polycrystal (YZTP), which Beavers reported as “coming in at 81 on the Rockwell scale, and 1,300 on the Vickers. So certainly a challenging material.”

DeZurik-APCO-Hilton, in Sartell, Minn., improved a host of valve-turning operations with the move to live turning at rates some people think could damage the spindle.  On the first job, facing time on a large valve flange was reduced from 18 minutes to three, yet the spindle load reading rarely exceeded 50%. The C-axis spindle is equipped with an Ingersoll Hi-Quad F high-feed face mill that doubles as a full-depth face mill capable of depths of cut up to 0.200 in.

Now, the DeZurik operation runs securely, cutting cycle time for a typical 36-in. flange from 18 minutes to three and leaving a perfectly flat mating surface. As the part rotates slowly on the machine table, the facemill works much like a woodworking router, rotating at 785 SFM and feeding outward from the center bore at 403 IPM. Synthetic oil is delivered through the spindle.

The Hi-QuadF face mill features an extra-thick insert with the usual high-feed radius, extremely rigid seating, free cutting geometry and a 12-degree lead angle for lower lateral forces at entry and exit.  It is so free-cutting that, in similar applications elsewhere, it has doubled throughput without the spindle-load needle even budging.

Micor, which built its reputation machining difficult metals, was only midway through a 150-piece rush job turning titanium, and was running late already.  But, the tools they were using, with conventional two-sided negative rake inserts, broke whenever they tried to run any faster than 130 SFM/0.010 IPR/0.200 DOC. That operation, on a Mazak Quik Turn 450, was taking 45 minutes per piece, while the finishing machine nearby stood idle, waiting for feedstock.

That’s not all. The die has a fairly complex form, inside and out, plus a slot. “The profile tolerance is two tenths. And the other important aspect is the tangency on the radius versus the angle where they intersect,” explained Beavers. It gets worse. “Customers are requesting the inner bore come from the machine down to two micro inches. So we have to deliver a polished finish.”

Such printed parts are usually cut off the build plate with wire EDM, leaving 0.200-0.300" (5.08-7.62 mm) of support structure to remove, Bronson said. “Then they want to clean up the base plate so they can print again. So they’ll take 15 or 20 thou off the plate.”

The main obstacle in the New England rebuilder’s effort to raise capacity of its screw machine fleet was the boring sequence, which represented more than half the total machine time.  The shop still used conventional, negative-rake boring tools, a carryover from the time when most of the work they took in involved free-machining mild steels.  When more work came in that called for long-chipping 8620 steel, they simply accepted as an unavoidable detail the 100% operator attention for chip clearance.

Switching to Ingersoll TCMT boring inserts with higher rakes, more aggressive chipbreakers and the proprietary TT8125 coating led directly to 30% higher machining rates.  It also completely eliminated any ‘bird nests’ of chips and the labor involved to clear them.  Chips flow out as uniform C’s, easily cleared with a shot of compressed air.

The newest call for ceramic cutting tools comes from the need to clean up the build plates after metal 3D printing. Bronson listed cobalt chrome for medical products, Inconel 718 for aerospace, Haynes 282 for rocket engines, Rene 220 for power generation, and Rene N2 as difficult alloys the company is being asked to deal with. These are difficult to machine materials when forged, and Bronson explained that printing them adds another degree of difficulty because the laser-sintering process leaves scale between the layers.

“For milling, I’d typically start at around 3,400 SFM, gauge the wear on the insert and adjust the parameters accordingly,” he explained. “For turning, depending on machine capability, you’d be between 600 and 1,100 SFM in high-temp alloys.”

Of course, all this depends on having the proper edge prep to begin with. “For finishing cuts in high-temp alloys, we’d spec out a honed edge,” Navarrete said. It’s the most free cutting. For “intermediate cutting, like semi-finishing or semi-roughing, we’d go with a chamfer, which we call a T-land. It’s a little stronger. If it’s purely roughing, with a lot of material coming off, or we’re going to machine scale or crust, we go with what we call a TE edge prep. That’s a chamfer and a hone. It’s an even stronger edge, but it also means more tool pressure. It’s meant to take the beating.”

Ingersoll’s Brian Winterlin made a counterintuitive recommendation: a Hi-QuadF high-feed style cutter and taking off the stock in a single pass.  That’s definitely beyond the ‘comfort zone’ for conventional high-feed cutters, which are known for fast feeds and shallow cuts.  But the tool — though primarily a high-feed insert — had worked in similar high-depth applications “This is really an all-purpose cutter,” Winterlin added.

A 2021 Manufacturing Engineering article on carbide tools, “An Improbable but Powerful Solution,” included the curious fact that ceramic inserts can look like hell and still cut well. The key to this capability, Navarrete explained, is the condition of the edge. “There is so much heat thrown into these inserts, especially if you’re running them dry, they look burnt. But the edge prep is still there. You might take it out and observe that it’s dark or charred, but once you start to cut again, it burns off—you could almost say—like a barbecue grill. Once the machining temperature threshold is reached, material residue heats up and comes off the ceramic and the edge prep is engaged again.”

In a live-turning setup like this, the cutting forces are lighter than you might think, Winterlin explained. “As the tool rotates, its eleven inserts engage sequentially, dividing the cutting forces uniformly over them all. The stock comes off as a lot of small chips rather than the fewer thumb-size chips they were getting by turning with a stick tool.”

Rather than worry about the misleading appearance of the insert, or focusing your attention on the edge, Navarrete recommended simply setting a time limit. “Ceramics are very shock sensitive, but also predictable.” He suggested starting with a relatively short, programmed time in cut (TIC) and then inspecting the edge. “I typically start with three and half minutes as a starting gage point. Once we find a sweet spot where everybody is comfortable, we can adjust accordingly by either adding or decreasing the insert time in cut.

As mentioned earlier, ceramics can also serve as wear parts, or other components that must survive tough conditions. Greenleaf operates a “technical ceramics” division for such applications, and trains its tooling staff to keep an eye open. McConnell said one engineer recently noticed an operator changing out the carbide guide wheels on the measuring device for a large roll-turning mill. This gauge must continuously ride along a huge steel surface, measuring roundness and size, so there is significant wear. As a solution, Greenleaf offered the customer ceramics that last 10 to 15 times longer.

With the original Hi-Quad F insert, edges lasted through two complete parts, or four flanges.  Recently the company switched to a tougher insert grade with an improved coating treatment, IN4005.  The change notched edge life up another 50% at the same removal rates. Edges now last through three complete parts.

In general, the higher hot hardness of whisker-reinforced ceramics, versus SiAlONs, enables WG300 to run in heat-resistant alloys at 10 to 20% higher speeds, but at a reduced feed rate, which is required for finishing, according to Bronson. “Our coated WG600 would go another 20% faster, so you’d be about 30-40% higher than a SiAlON. And our nano-coated WG700 is another 20% faster, so you’d be close to 50-60%. You can run in Inconel with WG700 as high as 1,500 SFM, and SiAlONs are going to melt long before you get to that point,” Bronson said, adding that WG700 also excels in interrupted cutting of Rene.

Oddly, he added, the softer stainless material presented an even bigger challenge for carbide. Once a tool designed for the tougher material hit the stainless steel, it would fail. That’s probably because the gumminess of the stainless steel inhibited chip formation. Greenleaf’s solution was to use the XSYTIN-1 ceramic in a small face mill with RNG45 inserts. The strength of XSYTIN-1 allows the user to “get away with a sharper edge,” Bronson said. “That allows you to get through the hard material, yet it doesn’t smear in the softer material, thanks to the sharper geometry.”

However, many auxiliary spindles are designed for light duty, unable to deploy the full capabilities of the high-performance face mills available today.  “The trick in live turning is to find a cutter able to take deep cuts, yet hold down cutting forces,” said Ingersoll field engineer Brian Winterlin, who worked on the DeZurik live turning project.

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While chemically similar to a SiAlON, Greenleaf’s well-known XSYTIN-1 ceramic is a phase-toughened silicon nitride. “The way it’s pressed causes a crystalline structure to grow inside the material,” Bronson explained. As a result, he said, the company can “generally run 20-30% higher feed rates with XSYTIN-1 than most SiAlONs,” even though XSYTIN-1 has a similar speed limit, because the binders break down at a similar temperature.

What’s more, where the abrasive nature of the material had forced the customer to take very shallow depths of cut, amounting to only 0.015" to 0.025" (0.38-0.635 mm), Greenleaf increased the depth of cut to between 35 and 50 thou. “And instead of having to take maybe five, or six or seven passes with carbide, we can take two or three with ceramics and clean up the entire plate,” Bronson said. In fact, on six such projects on which he’s worked, edge damage usually required indexing the carbide tool after a single pass through the laser-sintered material. Whereas the ceramic “lasted through every pass we had to make,” Bronson observed.

“Initially, we were using a Toolgal wheel with a harder, high-performance hybrid bond, RM644, our ‘go-to’ bond when looking for longer wheel life for fluting. But in fluting ceramic tools, it was wearing faster than we would have liked.”

Dillaman added that many aerospace companies perform sonic testing on their heat-resistant alloy parts, checking for minor imperfections in the surface. But in every case he knows of, “the surface finish left by a SiAlON will not pass sonic testing, whereas our WG300 and coated WG600 whisker-reinforced ceramics have been approved for this testing. So there are definitely some areas where whiskers are not going to be replaced by a SiAlON.”

“The Mazak is a big ticket item with a high hourly burden, so it’s vital to get the most out of it,” said Chandler Commerford, manufacturing engineer.  But, the Minnesota shop had no experience with the live turning process.

Greg Bronson, Greenleaf’s sales director for the Americas, elaborated. “Because the edge of whiskered-grade ceramics holds up better, you don’t get the same level of heat generation and the smearing of material that could cause parts to fail additional surface testing.”

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As another example, McConnell pointed to guide bushings for deep hole drilling. “In the past, these would have been carbide or a hardened steel. Now we’re making them out of ceramics and they last 20 times longer. So the possibilities are sort of limitless.”

Up in New England, a screw machine reconditioning shop boosted capacity by 30% on its fleet of Swiss Automatics using Gold-Duty CNMX 43.52 inserts.  Their applications involve OD and ID work on wrought 8620 steel.

“Titanium just complicates ID work with conventional tooling because of its unhelpful chipping characteristics,” said Ingersoll’s Darrell Boatwright. “The aggressive chipbreakers on the new Gold-Duty tool make short work of long chips in OD turning, and soon for ID work as well.”

We want to find a TIC where we can then safely index each time and know it’s not going to fail. Milling can be anywhere from seven to 10 minutes, predictably.”

In addition, Danobat’s Beavers said paying the “utmost attention” to the thermal stability of the machine means incorporating liquid cooling in the workheads. Coolant filtration also must be at “the highest level,” he said. So, in addition to a standard system, the company adds canister filters rated down to five microns, plus chillers to maintain a constant temperature.

Iscar offers “tough” SiAlONs and “hard” versions. The latter is advertised as “whisker-like,” because it mimics the hard, brittle nature of whisker-reinforced ceramics.

“That beats up carbide significantly. You get a lot of chipping and excessive wear. So customers were hoping ceramics could get through that.”

Another plus: SiAlONs are “much more forgiving than a whisker,” he continued, and as a result they can run at lower speeds, without the plasticization that is normally required for whisker ceramics to cut. “If I had a part with an interrupted cut, like a forging with a scale or any type of crust, I would run a SiAlON, as opposed to a whisker.”

The incoming castings had the usual, wide piece-to-piece dimensional variations and yet needed a lot of stock removed depending on those inconsistencies. “Definitely not the ideal candidates for a first stab at a new kind of process,” said Commerford.

Until mid-2014, DeZurik rough-turned their big valve body workpieces with conventional stick tools on a heavy-duty VTL. Then, the company installed a large, five-axis Mazak mill/turn machine, which opened the door to live turning.

Greenleaf’s first foray was removing 31-35 HRC Haynes 282 printed on a stainless steel plate. Owing to the part configuration, the print required a highly variable set of gates, risers and support structures, Bronson recalled. “Some of them were thick, some thin. Some were tall. They were all over the place. So, by nature, it was very interrupted. Plus, Haynes is very abrasive.”

However, he pointed out, the fragility of ceramics is often exaggerated. “Ceramics can take a beating, you just have to program it and approach it properly.” On that note, he cautioned, any switch from carbide to ceramic tooling requires reprogramming the cut. “You should not plug a ceramic tool into a carbide program.”

To help solve the problem, Better Edge reached out to David Ginzburg, who is the president of Elberton, Ga.-based Toolgal USA Corp. Ginzburg advised trying the newer RM769G hybrid-fluting bond. That might have seemed counterintuitive, because RM769G is a softer bond, but it actually worked better and delivered longer wheel life. According to Ginzburg, the wheel’s different diamond quality and the bond’s better diamond retention was more free cutting and suitable for fluting ceramic. Cycle times were just a bit slower than carbide, roughly a half-hour per tool, Shaffer added.

But this isn’t anything new. Navarrete noted that a number of shops are familiar with these capabilities based on experience with whisker-reinforced ceramics, which is a decades-old technology. Instead, he touted newer silicon, aluminum, oxygen, nitrogen (SiAlON) ceramics. “You can run the same whisker-like parameters at a lower cost, because SiAlONs are cheaper to produce than whiskers,” Navarrete said. “I’ve never gone into a shop, spec’d out and quoted a SiAlON and been more expensive than a whisker. It hasn’t happened.”