TIR is less than 0.0001″ (0.0025 mm) even after thousands of tool changes, and powRgrip’s rigidity and high mass minimizes harmonics, extending tool life and reducing consumable costs, according to the company. The system has five sizes, resulting in only five machine inserts the operator would ever need to use every holder, and eliminating the need to purchase machine taper mounts.

HRSA materials are machined either with carbide tools or inserts, which can offer better finishing but at comparatively lower surface feet per minute (sfm) of cutting, or else with ceramic tools that enable much higher sfm. “Ceramics are usually geared strictly towards roughing, possibly semi-finishing, but not for finishing, where carbide has the advantage,” said William Fiorenza, product manager die & mold, Ingersoll Cutting Tool Co., Rockford, Illinois. “The lion’s share of cycle-time reduction is going to be found in the roughing process and not necessarily the finishing process. But when requirements include a pristine finish, then [use] solid carbide.”

At Iscar, new carbide and ceramic grades have been developed for Inconel and other HRSAs, according to Randy Hudgins, national product manager of turning at Iscar USA. “Our IC806 carbide grade was developed specifically for Inconel 718 and it’s use spread to other heat-resistant alloys,” Hudgins said. “It was so successful that our engineers developed a grade with an even harder substrate for finishing and running at higher surface speeds—grade IC804.

Some HRSAs are also used in medical device manufacturing, not necessarily for heat resistance but for bio-compatibility as well as strength, stiffness and corrosion-resistance properties.

”After more than four years, there have been no documented cases of a tool pullout with a secuRgrip holder,” said Chris Herdman, technical field support engineer for Rego-Fix. “The only mode of failure is that of the cutting tool itself.” Unlike other systems, secuRgrip does not require purchase of specially modified end mills, but rather can accept standard 0.5–1″ (12.7–25.4-mm) carbide or HSS end mills. The system maintains 0.0001″ runout and allows users to preset tool heights.

CERASFEED Hi-Feed indexable ceramic milling cutters use 9 mm and 12 mm indexable inserts with high-feed insert geometries. The system’s strong insert clamping allows for “blistering” feed rates, according to Fiorenza. “The density of the inserts is higher for increased productivity,” he said.

These details are very important to aerospace companies, Durow noted. “They like that process security. They want to push a button and walk away knowing that the tool is going to last for a specific amount of time. They could do lights-out production. They don’t want to have to worry about something failing during the operation because the parts are extremely expensive, and the regulations they need to abide by are quite extensive.”

The same resistance to heat (and increasing yield strength with temperature) that makes HRSAs desirable for such applications is what makes them a challenge to machine. Here’s the latest on how cutting tool manufacturers are making the job easier.

Part designs that are more challenging to machine represent only one area in which manufacturers’ expectations are evolving. There is also growing pressure on them—and subsequently machine builders and toolmakers involved in HRSA machining—to enable ever-shorter cycle times and reduced tool costs.

“[We see] HRSAs as all nickel- and cobalt-based alloys that exploit the yield-strength anomaly," noted Alex Minich, applications engineer at toolmaker Greenleaf Corp., Saegertown, Pa. He is referring to when yield strength increases with temperature, contrary to most materials that get softer as they get hotter, or lower yield strength. It seems to be an anomaly—hence the name.

For maximum tool security, the Pin-Lock Collet system is available as an option. This feature works with any Weldon shank tool and guarantees pullout protection.

For that reason, heat-resistant coatings such as titanium aluminum nitride (TiAlN) or aluminum oxide (Al2O3) are applied over the substrate as part of the toolmaking process, he said.

For many generations, machining was a largely manual process with relatively slow speeds and shallow cutting depths. The most common toolholders were Weldon/sidelock chucks and ER collets, and, under these comparatively benign machining conditions, cutting tool slippage or pullout was not a serious issue.

Drew Strauchen, vice president, marketing and business development, Haimer USA LLC (Villa Park, IL), cautioned against total reliance on the ability of friction-fit holders to provide maximum tool security. “High gripping torque by itself does not equal guaranteed pullout protection,” he said. “The incredible cutting forces generated by faster machine spindles and more aggressive toolpath strategies [like full radial engagement trochoidal milling] have exposed the limitations of even the best friction-fit clamping systems.”

The aerospace industry in particular has a big stake in secure toolholding, notes Jack Burley, vice president, sales and engineering for BIG Kaiser Precision Tooling Inc. (Hoffman Estates, IL). “A number of critical components are made from titanium, which is expensive and difficult to machine. If a cutting tool slips or pulls out, the results are extremely costly, in terms of both downtime and material loss,” Burley said.

Heat-resistant superalloys (HRSAs) are nickel and cobalt-based alloys prized for applications that call for strength, resistance to corrosion and oxidation, and resistance to contact wear needed at extremely high temperatures.

One of BIG Kaiser’s newest products, the Mega Perfect Grip milling chuck, is designed specifically to prevent cutter failure. The high-accuracy milling chuck has fully concentric clamping and runout of less than 0.0004″ (0.0102 mm) @ 4×D. It accepts standard Weldon flat end mills and requires no special grinding of the milling cutter.

One solution is to direct high-pressure coolant into the cutting zone, at pressures up to 100 bar (1,400 psi) to break the chip out of the way, according to Durow. “This is a lot more than just splashing water around the cutting zone,” he said. “We have nozzles that precisely direct the coolant at high pressure into the cutting zone, creating a hydraulic wedge that pushes the chip up over the insert, essentially bending it back in order to break it.”

Another challenge to factor into the cutting process is the complexity of the design of the part being cut, pointed out Ingersoll’s Fiorenza. And, he said, there’s more complexity than ever.

Haimer is best known for its extensive line of shrink-fit toolholding. This system is a simple one-piece, highly rigid design with no moving or wearable parts. Benefits include runout accuracy up to 0.00012″ (0.00305 mm), superior repeatability, minimum vibration and chatter and excellent balance, according to the company.

“There are a number of factors that are within our control that we’ve identified as high impact when it comes to the tool life of ceramics in machining of HRSAs,” said Minich. The factors include: tool selection; rigidity and stability; grade; shape (macrogeometry); edge preparation (microgeometry), toolpath/machining strategy; cutting conditions; speed; and chip thickness. “The more difficult of these variables to maximize is certainly tool life.”

And while those software advances in CAD/CAM have made the parts—and therefore the cutting process—more complex, they are balanced by other software advances.

Greenleaf offers solutions for maximizing tool life in both milling and turning. “We meet the needs in milling, forging scale removal and heavily interrupted turning with XSYTIN-1—a unique silicon nitride-based grade. Turning, in the meantime, has been addressed with WG-600—a coated whisker-reinforced ceramic grade. At optimal cutting conditions, it’s capable of maintaining regular wear for over 20 minutes of cut time at a single point of contact in Inconel 718,” Minich said.

Krolak agreed that machining aerospace parts is particularly challenging. “Aircraft manufacturers have many applications with materials costing thousands of dollars and individual part cycle times exceeding 12 hours,” he said. “With this much invested in each machined component, tool failure is absolutely not an option.” To meet this need, Schunk recently introduced the Tendo Aviation toolholder for applications that require a secure tool that will not pull out.

In addition to the characteristics inherent the hydraulic expansion design, the Aviation toolholder employs a locking mechanism. A cutting tool with a standard Weldon shank is inserted into a special sleeve with a ball lock. The tool/sleeve assembly is then locked into place via set screws in the base of the toolholder. Finally, the holder is hydraulically actuated. As with other Tendo models, this process can be accomplished in seconds.

The Tendo holder contains an internal clamping piston that compresses hydraulic fluid into the oil chamber. The piston is manually actuated by an external clamping screw turned to a dead stop by an Allen key. A flexible sleeve immediately expands evenly against the tool shank, first centering the tool, then powerfully gripping it on the full surface. A length-setting screw can be actuated radially or axially for tool presetting.

Tool life affects both areas. Whether talking about milling or turning, carbide or ceramic, the tools used on HRSAs tend to, as the saying goes, “live fast and die young.” The life of these not-inexpensive tools is relatively short.

“When turning Inconel, [it used to be that] if you got to 100 sfm, you were doing pretty good,” he continued. “With this IC806, we’re approaching 200 sfm and getting decent tool life. Then they developed IC804, with a harder substrate, and with that we’re at over 250 sfm.

In milling applications in particular, “part and feature shapes have become more complex over the years,” Fiorenza said. “Because of advances in CAM and CAD software, part shapes are becoming more free-flowing. Where parts might have been more open in the past, designers are taking liberties with more detailed features in these different parts. Parts are being designed with smaller, tight-radius features, where cutters need to have a greater radial engagement. In situations like that, a greater amount of heat is generated due to that radial engagement. This can sometimes cause machining to be difficult. For example, the high temperatures can cause thin-walled part features to warp if proper machining techniques are not followed.”

There’s another difference between chips from standard steels and those formed from HRSAs. In turning operations, the standard steel chips break away at a size and shape that allows them to be easily removed from the cutting zone. Not so when turning HRSAs. “When you’re turning nickel materials, it doesn’t like to break a chip,” said Durow. Instead, “you’ll get these long stringers. The chip can actually wrap around your tool. Worse, it can wrap around the workpiece and damage it.” That’s not a good situation when you’re making, say, critical engine parts.

Fiorenza said he is continually surprised by customers who minimize the importance of the total cost of production in HRSA machining. “In aerospace, the most expensive item in the machining process can be the workpiece,” he pointed out. “Yes, the machining center is the most expensive thing in some cases, but landing gear, as an example, can run to over $1 million apiece. And the least expensive thing is typically the cutting tool or the insert that goes into the cutting tool. So, you would think that the greatest amount of attention would be applied to the total cost of successfully driving those inserts. That doesn’t always happen, but it should.”

The most recent product Greenleaf has created specifically with cost savings in HRSAs in mind is XSYTIN-360. “As a solid end mill made from the XSYTIN-1 material, it offers the productivity of ceramic milling at diameters previously reserved for carbide, with significantly higher tool life—as measured by the volume of material removed per tool—than best-in-class tungsten carbide solid round tools,” he said. “Because of the transverse rupture strength and impact toughness of XSYTIN-1, XSYTIN-360 is also a more accessible tool in that it can be applied at lower speeds, reducing spindle requirements. And XSYTIN-360 can also be reground, offering further cost savings,” he concluded.

An exclusive Key Grip locking mechanism provides anti-pullout protection. It is placed into the Weldon flat of the end mill shank, which is then inserted into one of the three Key Grip grooves inside the chuck. A spring functions to remove the gap between the Key Grip and the wall of the groove. Tightening a clamping nut secures the Key Grip in place, achieving dual contact between the nut and chuck body for rigidity close to that of an integral cutter.

The challenge differs depending on the cutting task, he said. “Milling and turning of HRSAs place rather different priorities on the material properties of a ceramic cutting tool. Tool life in milling benefits most from high transverse rupture strength—TRS—impact toughness, and resistance to crack growth as a result of thermal cycling. Turning requires a tool that retains chemical stability and hardness at higher temperatures, is more resistant to abrasive wear, but nonetheless has sufficiently high TRS to be able to handle the chip load and changes in the direction and magnitude of mechanical stress. Finally, any machining of HRSAs requires that the ceramic grade has appreciable resistance to crack growth.”

“CBN has typically been used in hard part machining. Very hard steels for gears and things of that nature,” he added. “But we found out this CBN material also works very well in aerospace materials. The problem was the edge performance when used on those. Whereas typically you would want a different edge prep for machining those hard steels, HRSA materials or materials like to be sheared. We needed to make a sharper edge line. So, we actually tweaked some of the geometries on those different inserts to work very well with those HRSA materials.”

While there are different types of HRSAs, they all share a major “chip challenge.” In standard metal cutting, the material is removed in the form of chips that are efficiently evacuated from the cutting zone, taking with them much of the heat generated by the cutting process, according to Bill Durow, global engineering project manager for aerospace at Sandvik Coromant, Mebane, N.C.

“The pre-pandemic years were the golden era of commercial aerospace—which we expect will return,” he continued. The [state-of-the-industry] graphs were all very green and upward-trending, and the main requirement for success was cycle time reduction.” Since the onset of the COVID-19 pandemic, however, he believes there has been a higher priority given to reducing cost.

As machining speeds increase and more difficult-to-machines alloys are introduced, machine shops need to continually re-evaluate their toolholding options. While highly secure toolholders typically cost more than their standard counterparts, the payback—in terms of the ability to machine at higher speeds and fewer scrapped parts and tools—can be substantial.

That was yesterday. Today, the productivity needed to be globally competitive requires ever increasing metal-removal rates during operations such as roughing and high-speed slotting. Process reliability is paramount, especially when working with difficult-to-machine materials. Conventional toolholders typically do not cope well with the high axial forces generated by aggressive machining, and cutter pullout can occur.

“When you’re cutting a piece of steel, for instance, it’s nice and shiny, but if you look at the chips afterwards, you’ll see they’ve turned a dark blue because of the heat they’ve absorbed from the metalcutting process,” he said. But with heat-resistant materials, that doesn’t happen. Instead of being absorbed by chips and evacuated with them, the friction-generated heat often stays within the process. “Typically, about 80 percent of the heat stays right in that cutting zone,” Durow said. “It goes back into the insert, which, if you think about it, is not a good situation for the insert.”

Probably the most prominent application for HRSAs is their use in the aerospace and defense industry, in the form of components for turbine engines used in jets, rockets and missiles. However, the materials are also widely used in the oil and gas industry. “Oil, gas and their derivatives and anything else that is corrosive and abrasive that needs to be stored, processed or transported at high pressure and temperature tend to require the strength and resistance to corrosion at elevated temperatures that only Ni-based alloys can offer,” said Minich.

Recent innovations at Ingersoll Cutting Tools center on a new ceramic line that offers two unique insert designs, according to Fiorenza. “These designs are new to the industry and the market,” he said. “Released in late 2020, this new line has been achieving a very high rate of success in many demanding HRSA rough milling applications.”

The company has also optimized its CBN—cubic boron nitride—portfolio, Durow said. “CB7014 is a high-speed CBN turning solution for nickel-based alloys.” The 7014 grade has been around for a while, but the company has recently optimized some of the geometries to better support HRSA work.

“The toolpath algorithms of today are nicely balanced and allow for high-speed machining techniques to be employed more readily. These more fluid toolpaths allow us to attack these high-temp materials in a more efficient manner, minimizing radial engagements,” Fiorenza said.

On the ceramic side, the company’s new SiAlON grade IN76N enables better throughput on demanding milling processes, he said. According to company literature, its sfm rate is up to 33 times greater than solid carbide (3,000 sfm, contrasted with 60–90 sfm for carbide).

Along with these grades, Iscar now has SiAlON grades—silicon aluminum oxygen nitrite. SiAlON is basically a ceramic—namely IS35 and IS25. “In our nomenclature, the bigger the number, the tougher the grade; the smaller the number, the harder or more wear-resistant the grade,” said Hudgins. “So, the IS35 is the tougher of the two. I usually start with IS35 because it works very well for cutting through the work-hardened scale that develops on these alloys. And with these grades, instead of 200, 250 sfm, now we’re at 600 to 800 sfm.”

There are secure toolholders for a variety of cutting operations, including milling, drilling and tapping. For example, Emuge Corp. (West Boylston, MA) offers its highly rigid FPC Mill/Drill Chuck with three tons of traction force to hold a tool securely. This is the world’s only chuck with a 1:16 wormgear, according to Emuge. The collet-cone assembly absorbs virtually all vibration, for maximum vibration dampening. With a 3×D tool length, variation in concentricity is less than 3 µm, which extends tool life and substantially improves workpiece surface finishes. All models are balanced to G2.5, 20,000 rpm. In a speed comparison with four competing chuck designs, the FPC chuck enabled the feed rate to be increased by 30% with no loss in performance.

Shops should be aware that heavy-duty machining is not the only cause of tool pullout, said Ryan Krolak, technical sales specialist for Schunk Inc. (Morrisville, NC): “It can also be the result of toolholders that do not offer concentric clamping,” Krolak said. “This often causes excessive runout, creating an uneven chip load on the cutter and premature tool failure. This shouldn’t have to be said, but it is important to make sure that all the running parameters are within the range of the material and the cutting tool being used.”'

Engineers at Rego-Fix agree that even with the highest clamping forces available, there are applications that require additional cutter retention measures. At IMTS 2012, Rego-Fix introduced the secuRgrip anti-pullout system, available for powRgrip, ER collet holders and milling chucks. A small, profiled steel locking key insert is installed in the ground flat of standard Weldon-shank cutting tools, locking the tool to the collet. A threaded friction bearing cap secures the collet in the holder and provides increased clamping force to prevent the collet from spinning.

Several years ago, Haimer developed and patented an anti-pullout system, Safe-Lock, as an optional feature on its shrink-fit holders and power collet chucks. Safe-Lock employs special drive keys in the holder and mating grooves in the tool shank, ensuring positive locking in place of the cutter and preventing spinning and pullout. Unlike Weldon flats, the mating ground grooves are perfectly symmetrical, thus eliminating issues associated with unbalance and uneven side loads. The system also provides users with the ability to adjust the axial position of the cutting tool in the holder. With 14 of the largest round tool companies as official licensed partners, tools from any number of global suppliers are readily available.

At Sandvik Coromant, recent innovations include new turning grades. “Our latest development is a brand-new turning grade that we developed for last-stage machining applications with aerospace engine components in the area of HRSA turning. It’s called S205,” said Sandvik Coromant’s Durow. “Because of coatings and new substrates, it resists heat much better than the previous grades and therefore can handle 30-50 percent higher cutting speeds. There are some new post-process treatments on the inserts as well. This CVD coated grade S205 is available in almost all of our standard insert portfolios.”

“The broad picture is that ceramic machining of HRSAs isn’t as much of a novelty today as it was in the mid-1980s, and current user objectives range from increasing throughput capacity—by increasing metal removal rates—to reducing overall cost while maintaining or improving process stability,” said Greenleaf’s Minich.

Toolholder manufacturers have responded with a variety of rigid, highly secure systems offering anti-pullout protection. These include shrink-fit, hydraulic expansion and locking toolholders. Each features high gripping torque (clamping force) for a tight friction fit on the tool shank. Many offer proprietary locking mechanisms that can guarantee up to 100% tool retention.

When milling with solid-carbide tooling, “keen edge preps need to be maintained and monitored during the process,” Fiorenza said. “Additionally, special insert designs can help optimize cutting performance—for example, specially designed rake face geometries, edge preparations and insert spotting in the cutter."

Hydraulic expansion toolholders were developed by Schunk more than 35 years ago and have been continually improved to keep pace with advancements in machine technology and carbide tooling, Krolak said. The Tendo line features a high concentric clamping force, excellent vibration dampening and runout of less than 3 µm @ 2.5×D. All commercially available tools, with Weldon, Whistle notch or cylindrical shanks, can be clamped. Micron-accurate tool changes can be made in seconds.

A way to address this is to vary the depth of cut, he said. “Let’s say you start out with a 150 thousandths depth of cut. You could then drop to 100, then to 75, then to 50. What that does is move that workhardened surface up and down the length of that carbide at different intervals. The workhardened material doesn’t have a chance to set up and start eroding away the carbide so quickly," Hudgins said.

Shrink-fit is based on the thermal expansion and contraction of metal, and uses an induction heating unit for assembly. The bore of the holder is initially slightly smaller than the outside diameter of the tool shank. When heated, the holder expands sufficiently to allow tool insertion. After cooling, contraction of the holder grips the cutting tool with up to 10,000 lb (4536 kg) of force. Tools can be changed in seconds, and operator training is minimal. As noted above, the Safe-Lock feature can be incorporated into Haimer shrink-fit toolholders.

The heat is a particularly vexing situation when using carbide tools or inserts, according to Randy Hudgins, national product manager of turning at Iscar USA, Arlington, Texas. “To form a chip, the process needs to plasticize the material, but the high nickel content in Inconel, Waspaloy and other HRSAs make them so resistant to heat that the temperatures needed to begin to plasticize them are enough be detrimental to your carbide. The binder for carbide is cobalt, and the melting point of cobalt is about 2,700°F; the temperature that it takes to plasticize these nickel-based alloys approaches over 3,000°F.” Hudgins said. “You’re in danger of melting your cobalt away.”

Minich also noted that not all alloys called HRSAs actually fill the bill. “Some would consider Jethete M152 to be an HRSA, but in our eyes it’s just a low-carbon martensitic stainless steel,” he said. “Most would also consider many titanium-based alloys to be HRSAs, because many alpha-rich titanium-based alloys are designed for service at elevated temperatures.” True HRSAs are only those nickel- and cobalt-based alloys that take advantage of the yield-strength anomaly, he stated.

The high temperatures cause trouble for carbide tools in another way. The cutting edge’s hot contact with the HRSA workpiece effectively workhardens the material, putting a scale on it. “Basically, it’s heat-treating it,” Hudgins said. “Let’s say that on every pass you’re taking an eighth of an inch depth of cut per side. What happens is, the cutting pass workhardens the material. Then you come back and take another eighth of an inch depth of cut. Well, that previous pass is now an eighth of an inch up the side of your carbide. So, now you’ve got that workhardened material in contact with your carbide and it starts to erode it. You get what we call a depth-of-cut notch. It starts notching your carbide.”

Rego-Fix Tool Corp. (Indianapolis) markets both a friction fit and a tool locking system. The powRgrip series includes holders, collets, and automatic or manual pressing systems. The collet is pressed into the holder with up to 9 tons (8.16 t) of pressure, which Rego-Fix claims to be the highest clamping force in the industry. The compression contacts the nose of the holder and not the taper.

For high production tapping, the Speedsynchro tap holder features a programmable integrated transmission of 1:4.412 to optimize thread production on CNC machines with synchronous spindles. Combined with Softsynchro’s minimum length compensation, this allows high cutting speeds at a relatively low synchronous machine tool speed, compensating for synchronization errors during the threading process. Thread production cycle time is reduced by up to 40%, and the lower spindle speed can result in significant savings in energy costs.

Emuge also produces an extensive line of tapping toolholders. The Softsynchro rigid tap holder, with minimal length compensation, is said to reduce axial force to a fraction of that required in typical tapping applications, improving thread quality and extending tool life by up to 300%. Patented elastomer springs separate the spindle from the tap, absorbing excessive axial forces and providing the tap with a significant boost in tool life and performance. Torque from the spindle is transferred to the tap via ball bearings in precision-ground grooves, promoting precision micro-correction of lead errors in a rigid tapping cycle. The modular system is adaptable to any application requiring a length adjustment screw and interchangeability for different size taps.