According to Garud, Walter is also adjusting design. “The need for higher volumes and reduced cycle times is always weighing down on tool manufacturers,” he said. “Walter recently introduced a new line of G4014 toolholders specifically designed for gang tooling. One of the key features of these holders is the side-access screw to clamp the insert into the toolholder.

Some trends in machining remain constant. Machine speeds continue to increase. Difficult-to-cut materials are used more frequently. The desire for better cooling, chip control and reliability remains.

“This is because both CBN and ceramic inserts can tolerate high cutting temperatures. Typically, the heat generated when performing HPT operations is distributed into the chip (80 per cent) and insert (10 per cent), with only the remaining 10 per cent entering the workpiece.”

Modern CBN inserts offer up to eight edges per insert and built-in security that enhances the bondage of CBN cutting tips on negative inserts, said Burton. Image courtesy of Sandvik Coromant Canada.

Howard added that cubic boron nitride (CBN) inserts associated with HPT are much more cost-effective than purchasing a cylindrical and centreless CBN diamond grinding wheel. Although the grinding process can achieve higher tolerances, cylindricity, and roundness, there are a number of benefits with opting for HPT.

“Concentricity and perpendicularity of the part will be much better in parts that are finished using HPT with a single setup,” said Ashok Guruswamy, product manager, grip/turn/thread, Iscar Tools Inc. Canada, Oakville, Ont. “Machining a taper and radius profile surfaces and complex contours are possible in HPT. In grinding, this would require a custom dressed wheel.”

“A part design with specific features can be generated with the standard tooling and insert geometries,” said Steve Howard, engineering and marketing manager, NTK Cutting Tools, Wixom, Mich. “A grinding wheel applied to the same part would need to be specially made with features dressed into the face of the wheel, only adding to the already costly tool. In certain circumstances, where very fine finishes are required on the part surface, grinding will be necessary.”

“A one-cut strategy is feasible for both external and internal operations,” explained Burton. “However, a stable setup is important, and tool overhang should not exceed the bar diameter in internal turning (1xD). The big advantage of a one-cut strategy is minimal cycle times, although the trade-off is reduced tool life and potential difficulties in meeting stringent dimensional tolerances.”

Horn also offers a Y-axis part-off system. “This system uses the Y axis of certain lathes as feed direction,” Kollenbroich said. “This switch in axis feed directs forces back into the holder instead of against the holder. The improved strength allows for feed rate increases of two or three times that of standard X-axis part-off applications.”

Iscar has had a series of product launches to address customer demands. “Cut Grip is one of the most complete and comprehensive grooving lines on the market,” Vanderink said. “Iscar promotes and champions the GTO (groove turn operation) as a cornerstone process for this line. Straight grooving and then turning side to side utilizing all edges of the insert reduces cycle time while producing excellent part finishes.”

Higher machine speeds are also a big part of the demand on tools. “As the machines get more capable of higher speeds and torques, and the demand to get more out of the same tool constantly increases, manufacturers have to respond accordingly,” said Sarang Garud, product manager at Walter USA LLC, Waukesha, Wis.

Tool wear depends on a number of factors, including workpiece material, CBN grade, cutting conditions, edge geometry, and machine stability. In HPT, the most common forms of CBN tool wear are crater and flank wear.

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An alternative is the two-cut strategy, which is ideal for unattended machining of high-quality surfaces. In this scenario, both inserts should have a wiper geometry. One of the main advantages of this strategy is it provides higher security, closer tolerances, and potentially longer runs between tool changes.

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One question is what to expect in the next few years. “I believe one thing we will see is machines equipped with sensor monitoring technology watching slight changes in the tool and adjusting accordingly,” Kollenbroich said. “Some machine manufacturers already have things like this, but they are not accurate or sensitive enough yet. Incorporating this sensor technology into the toolholder and tying directly into the machine control is a possibility.”

Guruswamy added that another benefit of dry machining is that during the turning process, the material becomes slightly softer as it heats, making it easier to machine. He noted that dry machining is not always advised, even though it offers economic and environmental benefits. For example, in cases of continuous turning, when high surface finish is required, coolant should be applied.

Kollenbroich described how Horn addressed that challenge with its 960 part-off system. “This is a cassette-based, coolant-through design that offers a major upgrade in blade stability,” he said. “This additional stability results in great improvement in tool life. Customers can realize gains of double or triple the tool life while showing dimensional improvements in flatness and surface finish.”

“When using standard flat top CBN without chipformers, long, unbroken chips are often produced,” said Guruswamy. “It can harm the workpiece surface finish and even interrupt the machining process. CBN inserts with chipformers will provide improved chip control at various depths of cut.”

“With crater wear, you’ll want to try and get the crater about a third or two-thirds the way up of the negative land that’s put on the inside of the insert,” said Burton. “When the crater gets too big, the edge will basically chip away and break, because it weakens the edge.”

“Also, in many aerospace applications it is a requirement to use coolant to ensure surface integrity of the component,” Burton said.

“We are seeing the increased usage of Y-axis grooving and parting-off. By using this axis of the machine, we are able to increase cutting data, allowing our customers to reduce their cycle times,” he said. “Machine tool builders are adding features to their machines that allow for the use of the Y axis. Also, builders are looking at increasing the stroke of the Y axis, allowing for increased diameters where you can use Y-axis part-off tools.”

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Applying regular cutting insert grades to hardened steel will simply fail. HPT demands CBN or ceramic grades to ensure successful processing. CBN inserts are designed to withstand the high cutting temperatures and forces associated with HPT while retaining their cutting edge. Ceramic grades can be used on materials between 50 and 60 HRC when surface finish demands are moderate. Ceramic grades offer good heat resistance and high wear resistance and can prove beneficial for light, continuous HPT.

“CBN is, however, the ultimate cutting tool material for HPT,” said Burton. “Modern CBN inserts offer up to eight edges per insert and built-in security that further enhances the bondage of CBN cutting tips on negative inserts.”

Said Winter of Sandvik Coromant, “We will see machines turning in all directions and the requirement for part-off and grooving tools is to do the same.”

The company also looks to coating for product improvement. “We offer coatings that are capable of handling heat better, which in part-off and grooving is always a challenge,” he said.

Careful preparation of the component in the soft (unhardened) state will significantly increase success in HPT. One way to achieve this is through machining as close as possible to the final dimension, leaving only a few 10ths of an inch for finishing. HPT requires a relatively small depth of cut, so tight dimensional tolerances in the soft machining stage will make all the difference.

Another example: “Heli Grip is a game changer due to its unique twisted geometry, enabling depths of cuts to go beyond the second edge of the insert without damaging it.” He said that results in “much deeper depths of cut—grooving and excellent groove turn capabilities.”

“Clamping and alignment of the workpiece are also crucial,” said Burton. “As a guide, a workpiece length-to-diameter ratio of up to 2-to-1 is normally acceptable for workpieces that are supported on only one end. If there is additional tailstock support, this can be extended.”

The two-cut strategy is ideal in situations where too much material was left on in the soft stage. If an operator is trying to remove too much material with one pass, the cutting forces and pressure involved could be detrimental. In this scenario, a two-cut strategy could be a good option.

“The insert geometry, as with any operation, should be chosen based on the strongest geometry allowable for the specific application while considering the cutting efficiency,” said Howard.

And it plays a vital factor in successful turning of hard workpieces. When it comes to insert geometry, the experts agree that with respect to insert corner geometry, a wiper configuration allows for significant process improvements and productivity gains.

Improvements in machine tools have also altered the way companies design tools. “The biggest improvement in machines that I have noticed is more machines are running high-pressure coolant,” Kollenbroich of Horn said. “Even the standard offering from most manufacturers is a considerable jump in pressure from what it was just a few years ago. High-pressure coolant offers benefits in chip breaking. Coolant-through tools, with better and more focused coolant delivery, remove chips from the work zone. This helps improve tool life and overall performance.”

Industry changes also create other considerations for toolmakers and their customers. “Geometry always plays a critical role in grooving operations,” Walter’s Garud said. “But parting-off operations typically tend to need the inserts to go all the way to the center of the bar, so cutting speeds are zero at the center, which means tougher grades are always going to be better than the harder grades. Also, chip-crimping is quite important. Not only do the chips need to curl into ‘sixes and nines’ shapes, they also need to be folded axially, so the chip breakers need to be aggressive to fold the chips.”

“The toolpath is key to an efficient cut and achieving the best insert tool life,” said Howard. “It’s important to create a program that eliminates cutting conditions that will prematurely wear or reduce tool life. Key aspects to focus on are the entry and exit angles of the insert, sudden directional changes, and interrupted-type toolpaths.”

One of the major advantages of HPT as a process is the elimination of coolant. This is because both CBN and ceramic inserts can tolerate high cutting temperatures. Image courtesy of Sandvik Coromant Canada

Kollenbroich of Horn noted that managing centerline is critical. “Centerline can be your biggest friend and your worst enemy. All manufacturers design their tools to work on center. When a machine is off, even slightly, things become unpredictable. Customers typically experience a drop in tool life, maybe poor surface finish or, worse yet, catastrophic failure. It is critical to apply part-off and grooving tools properly, and on center.”

“Jet cut tooling is vital today,” he said. “Iscar has taken great care in making sure coolant is introduced to the cutting edge of the insert even when high pressure is not accessible. Data has shown that in all cases this makes a difference in tool life and part quality.

“Flank wear is the type of wear you would want to see on any insert,” Burton added. “It is the most predictable and progresses over time. Premature flank wear is not ideal, though. Large flank wear has a negative effect on surface integrity and dimensional accuracy. Even though wear is complex, there are ways to control it and maintain a consistent and reliable machining operation.”

He also noted that HPT shares a lot of basic principles with soft turning, so machinists can easily transfer their knowledge and skill from one to the other. Alternatively, grinding requires very specific skills and an experienced machinist to perform similar tasks.

“An important element of CBN is the wiper configuration, which helps greatly to improve surface finish and quality similar to grinding,” said Guruswamy. “Wiper inserts enable work with a higher feed and good surface finish on the workpiece.”

Beyond grades and geometry, edge preparation selection is important for protecting the cutting edge and achieving good tool life. However, Guruswamy added that sharp edges are generally not recommended on CBN since a sharp edge can chip or break. In situations where cutting forces need to be reduced because of an unstable setup like in internal boring applications, machine limitations, or workpiece clamping, a sharp edge can then be used.

“As tool designers, we need to increase the pocket security of our grooving platforms to allow customers the freedom (to) turn in all directions,” said John Winter, turning specialist at Sandvik Coromant, Fair Lawn, N.J.

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Not only that, but there are significant environmental concerns when it comes to grinding, particularly in relation to the slurry left behind. The mix of coolant and grinding dust needs to be disposed of properly, and in many cases separating the coolant from the mixture can be time-consuming. Many shops will look toward HPT as an alternative to grinding because it can be dry-machined, eliminating this challenge. However, HPT has its own set of demands and challenges that need to be overcome before it can be effective. Choosing the right cutting tool for the job is necessary.

Progress in various manufacturing technologies may play a role in the future for parting and grooving, Iscar’s Vanderink said. “Additive manufacturing will be a big player from here on out,” he said. “Already, new concepts are on the way due to this technology. Additive manufacturing producing near-net shaped parts will change how removing material is viewed. This concept alone will drive the innovation needed to accommodate these types of components.”

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“Successful HPT demands not only suitable cutting tools, but also the right conditions, preparation, and environment,” said Guruswamy. “The soft state is the state in which the workpiece material is yet to be hardened to its final hardness (around 20 to 40 HRC).”

Beyond the cutting strategy, machining conditions also come into play. Having good machining stability and rigidity will help eliminate vibration, which is absolutely critical in HPT.

He also said clamping is an issue. “Using torque wrenches when clamping inserts in all parting and grooving tools is essential to maintain clamping force, tool integrity and finally part quality.”

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Added Vanderink of Iscar, “Technically, center-height position of the tool is critical. The process of a square tool plunging into a round part is very abusive. The centerline dynamic is not fiction. It is real and essential for success in these applications.”

Added Steve Vanderink, national product specialist for grip products at Iscar USA, Arlington, Texas, “Users are demanding ease of indexing of the insert with accurate repeatability while increasing productivity with rigid support and strength in the pockets—all while keeping an eye on the economics. The market wants it all. Innovation is the driving force for solutions to the market’s needs.”

The experts agree that the use of features such as chamfers and radii on the part will help with entry and exit paths to maximize tool life, especially because sharp corners can damage or break the cutting edge. Also, operators should avoid burrs and use wiper inserts to achieve superior surface finish.

According to Howard, coatings also will help protect the insert edge from the heat generating during machining and will provide an excellent surface finish on the part. For example, a physical vapour deposition coating adds wear resistance, helps to improve cutting conditions, and extends the tool life.

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“The side-lock, or ‘smart lock’ as the technology is called, allows the users to index the inserts while the tool is still clamped onto the gang tooling of a Swiss machine,” he continued. “The side access to the indexing screws allows a time reduction of up to 70 percent in insert indexing, saving valuable time on high-volume Swiss machining operations.”

“Multi-axis, multi-spindle machine tools with Y-axis capabilities are emerging to complete parts in one setup,” Vanderink continued. “The use of robots on the shop floor is increasing and is becoming a viable operation for small to medium-sized shops now.”

At Horn USA, the company is offering coolant on more of its products. “This includes part-off and grooving holders and even some inserts,” Kollenbroich said. “Getting coolant to the cutting edge has many advantages. For one, having a more accurate delivery method for the coolant direction helps in cooling the work zone. It also offers the benefit of chip breaking when used with higher pressure applications.”

Guruswamy noted that machining on an older machine versus a new CNC machine really makes zero difference in the overall output. As long as there is a high degree of stability and no vibration, HPT will be effective.

“Also, lower vibrations lead to less pitting of the tool pocket, increasing toolholder life,” Garud continued. “The new patented design by Walter for our DX18 inserts securely clamps the inserts on three sides.” It also has “a secure prismatic base: a V-shaped top groove for the top clamping finger and a small double-faceted groove at the back of the insert to seat it securely in the insert pocket.”

The high hardness of CBN enables it to machine hard materials at high speeds and feeds. However, successful HPT demands not only suitable cutting tools, but also the right conditions, preparation, and environment. Image courtesy of Iscar.

“Users are always demanding the same thing,” said John Kollenbroich, head of product management at Horn USA Inc., Franklin, Tenn. “More tool life and predictability, better chip control and surface finish. These demands have not changed in many years, nor will they change anytime soon.”

Advancements in carbide substrates are “ever changing and we are seeing new grades and coatings that are making a meaningful impact in tool life,” he added. “Industry 4.0 is expanding into tooling more and more. Tracking of tool life and wear is becoming a seamless part of the manufacturing process.”

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Last but far from least among HPT considerations is a machining strategy, with the choice made very often a balance between accuracy and productivity.

For productivity, a one-cut pass would be the best option, especially because HPT should be more of a finishing process rather than a roughing process. After the correct cutting strategy is deter-mined, proper programming will help ensure long tool life. This will be enhanced if proper soft machining strategies have been put in place.

Sandvik Coromant works to make its products flexible. Winter said that with CoroCut 1-2 “you can part-off, groove, face groove and do high-feed machining of hardened steel. The CoroCut QD platform can part-off in both the X and Y axis and face groove.”

Flank wear can be limited by increasing both the cutting speed and feed.DRY MACHINING“Of course, one of the major advantages of HPT as a process is the elimination of cool-ant,” said Burton.

“HPT provides flexible machine utilization as the same machine can be used for external and internal machining,” said Kevin Burton, turning product and industry specialist, Sandvik Coromant Canada, Mississauga, Ont. “Complex component shapes can also be machined in a single setup.”

When it comes to HPT, insert geometry should be chosen based on the strongest geometry allowable for the specific application while considering the cutting efficiency, said Howard. Image courtesy of NTK Cutting Tools

Walter USA has adjusted the way it clamps its inserts. “Usually the grooving inserts are held either through a self-clamping mechanism or through a ‘top-clamp’ screw-down mechanism,” Garud said. “The more secure the insert in the pocket, the lesser the tendency of vibration and longer the insert life.

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HPT demands CBN or ceramic grades to ensure successful processing. CBN inserts are designed to withstand the high cutting temperatures and forces associated with HPT while retaining their cutting edge. Image courtesy of Iscar

CBN grades are available for continuous cuts, light interruptions, light and heavy interrupted cuts, and heavy interrupted cuts and unstable conditions, depending on what the project calls for. The binding force between particles and grain size determines whether the insert is suited for hard or tough applications.

Hard-part turning (HPT) has many advantages to help shops achieve better accuracy more efficiently in hardened steels from 45 to 70 HRC, superalloys, sintered materials, and grey cast iron. In recent years turning has eclipsed grinding as the preferred method for producing parts in their hardened state. As a process, it has been proven to reduce machining time and costs by 70 per cent or more over more traditional methods.