The impacts of interrupted cuts will depend on the process itself, whether it’s a roughing or finishing application. For the most part, roughing applications tend to include interruptions from forged or cast workpieces that are irregular in material or non-concentric shapes.

“However, coolant should almost always be shut off, unless machining an extremely gummy material,” said Mitchell. “When coolant is applied to an insert machining an interrupted cut, the insert undergoes extreme heat, then no heat when encountering the interruption. The hot insert is then suddenly submerged in coolant, which causes thermal cracking, shortening the tool life and potentially causing catastrophic failure.”

“In turning, everybody has the same ISO standard toolholders so it’s technology like our Steadyline anti-vibration holders, Jet Stream tooling holders and second generation Duratomic coating that makes a big difference,” said Miller. “In milling, there have been many technological advancements as well as process improvements. Today, processes like dynamic milling require high-tech tools that take a full axial DOC and a light radial DOC at an extremely high feed rate.”

Speeds and Feeds. The experts agree that one of the biggest mistakes an operator can make during interrupted turning is to reduce speed.

“If you have the corresponding toolholders in your facility already, a round insert is the strongest,” said Haid. “With a round insert, a rigid setup is necessary to take the impacts of the interrupted cuts. A square insert would be the second strongest. For the most part, diamond-shaped inserts are not well suited, but some interruptions could require a specific insert to get in and perform the cut.”

Coolant. The issue of thermal stress leads some operators to believe that running the machine with coolant is the best option.

When it comes to performance of indexable cutting tools compared with brazed PCD, CBN and carbide tip tooling, “it’s a question of cost and application,” Winter said. “Anytime you can use an indexable tool, the cost will be lower. The performance is in the cutting material (PCD, CBN, or carbide) and it’s a matter of if the tool can fit into the application.”

Haid added that it’s always better to start on the low end of the feed rate to provide a bit of wiggle room, rather than running a little bit slow. Running slow can put more impact on the insert.

According to Ewing, Iscar now offers indexable head drills from 0.157 -1.575″ (4.0-40.0 mm) dia. Most of that range is offered in 0.004″ (0.10 mm) increments. Drill bodies are offered in 1.5xD, 3xD, 5xD, 8xD and 12xD drilling depths with some bodies offering chamfer collars for combined operations. In addition, standard tooling designs are also being incorporated into special tool applications to increase productivity in medium to large quantity part runs. The special tool is often more expensive than a standard tool, but because it utilizes standard indexable carbide inserts the consumable costs can be greatly reduced.

“By pairing our patented Excelerator ball nose insert geometry with our WG-600 and XSYTIN-1 grades, we provide customers with the ability to mill hardened and difficult-to-machine materials with a full-radius ceramic indexable tool. Our Excelerator ball nose inserts with patented geometry offer better performance, longer tool life and superior cutting action across a wide variety of materials.”

For deep-hole applications, Iscar offers a line of BTA drills in single-tube and double-tube variations; indexable gun-drills including the Sumo-Gun and Tri-Deep; and standard gundrills. Indexable reaming tools include the Bayo-T-Ream, Index-H-Ream, and Solid-H-Ream.

For interrupted cuts in softer or more ductile materials, having an edge prep with a larger or wider land is a good option. With ceramic, the insert does not need to be as negative as it would for a harder material; with carbide, a medium-duty chip form will provide additional shear, which is beneficial in most cases.

They will mix and match data about chemical makeup, substrates, geometry and machine capability to advance technology the old-fashioned way—by R&D expertise, trial and error, internal testing and validation of new concepts in the field. Here’s how major cutting tool manufacturers are advancing the technology of indexable cutting tools.

Some of the impacts of interrupted cuts on the turning process can, depending on the severity of the interruption, lead to accelerated tool wear. This increased tool wear can lead to more tool changes during the process, which ultimately leads to an increase in part cycle times and an overall increase in labour and tooling costs for the job. Here are some factors to consider to help limit tool wear.

“These features have contributed to increases in operating parameters and tool life and resulted in innovations in indexable tools for holemaking,” said Craig Ewing, national product specialist-drilling for Iscar.

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Geometry. Another consideration for interrupted cutting is the geometry of the insert. Choosing an insert that has a small nose angle and long, narrow cutting edge does not offer the rigidity needed in most interrupted cutting applications.

“Indexable tooling exists for almost every type of application: milling, turning and grooving, drilling, slotting, boring, and reaming,” explained Luke Pollock, product manager, Walter USA LLC, Waukesha, Wis. “They all use different styles of inserts designed for the needs of the applications. Typically, indexable tooling is considered larger and therefore stronger, capable of taking higher horsepower cuts and higher material removal rates compared to solid tooling. As a result, indexable tools have become more competitive in applications traditionally dominated by round tools.”

Positive cutting geometry can maintain acceptable, if not increased, tool life and allows for lower horsepower cuts and less torque on the machines, according to Pollock. However, this can create a weak cutting edge.

Iscar continues to expand the line of drilling tools with new cutting geometries. In the Sumo-Cham line there are different edge preps for steel (P), stainless steel (M), cast iron (K) and non-ferrous (N) materials.

Choosing the right insert for interrupted turning can make all the difference in success of the overall process. One of the big misconceptions is that operators can just use whatever insert is available. Sometimes this may work out, but often operators will struggle.

Levels of interrupted cuts can vary anywhere from a light interruption, which might account for only 10 to 20 per cent of the overall process, to a heavy interruption which can be 60 to 75 per cent or more of the overall process. Regardless of how you define interrupted cutting, there are some points to consider when undertaking an interrupted operation.

“Tungaloy developed a technology that was able to draw the cobalt to the outer edges of the insert, giving just the cutting edge a higher concentration of cobalt,” said Mitchell. “This allowed for the best of both worlds: a carbide grade with a high concentration of tungsten to allow for higher cutting speeds and longer tool life, while at the same time providing additional concentration of cobalt at the cutting edge to provide additional impact resistance.”

“The benefit of dealing with interrupted cuts in the roughing stage is that the insert can be changed, from part to part, without an offset,” said Matthew Haid, application specialist, Dormer Pramet, Mississauga, Ont. “Dealing with interrupted cuts in finish-turning can be much more challenging. If the part has a tight finishing tolerance, operators typically need to adjust the tool wear offset on the CNC over the course of the insert’s life. When changing the insert, it's recommended not to start at zero or the regular offset, but rather do a first pass to confirm the tolerance dimension. Both interrupted roughing and finishing can be a challenge, but with roughing, there is always material left to be finished, whereas finishing tends to be more sensitive.”

“Today’s mill-turn machine offerings make it easy to combine many operations into one setup that often had to be done in multiple setups in the past. Iscar offers indexable tooling solutions that take advantage of these machine capabilities, such as multi-function tools for turning, facing and threading operations.”

“Current insert substrates and pressing technology allow for free-cutting positive geometry that doesn’t easily chip,” he said. “Positive geometry can even be added to inserts with negative basic shape or even tangentially mounted inserts.”

Pollock said that there are some machines and applica-tions where the machines can push the capability of the tools in aluminum machining. “But I think the more common point is that modern cutting tools allow machines to do more. Carbide substrates and free-cutting geometry increase the capability of smaller machines to process a wider variety of materials and large parts,” he said.

“To be fair, there are other uncertainties that could be contributing to instability—lack of rigidity and vibration dampening in the fixture, for example,” according to the team. “Comparatively few machines are also equipped with high-pressure coolant, which is extremely beneficial in the rough- and medium-turning of heat-resistant superalloys in that it greatly improves chip management (and to some extent also improves the dissipation of heat from the tool).”

“PVD coatings have a thin layer that really holds up better against the impacts of interruptions versus the CVD option,” said Haid.

“When it comes to ceramics, you want to avoid this temptation,” said Lobsinger. “It’s the first thing an operator will do when they start thinking something is going wrong, but you definitely don’t want to do that. The amount of increase in the recommended speed in severely interrupted cuts can usually be calculated. The operator can calculate the circumference of the part, then subtract the total sum of the interruptions. This will give a smaller diameter value, which increases the SFM. Essentially, when increasing cutting speed, you're reducing the time the insert spends out of the cut, thus reducing how much time the insert has to cool, ultimately reducing thermal stress and the growth of the cracks.”

Cutting tool improvements range from some actual grades that are being refined with additives in the substrate for better wet or dry machining to product upgrades. Improvements to Seco’s Perfomax indexable insert drill, for example, include an improved, highly polished body with wave pattern technology for chip evacuation, increased hardness for wear resistance and elimination of coating altogether.

Brazed tooling is generally considered to have tighter tolerances since the assembled tool can be finished (ground and polished). These harder materials in brazed form are usually limited in the cutting geometry that can be used in the tool design. Indexable inserts have the opportunity of geometry pressed into the insert so that different machining applications can be handled simply by using a different insert with different geometry or grade.

With interrupted cuts there is a greater risk for the cutting edge to break down prematurely or inconsistently, lowering part quality. It is important to choose the best cutting tool and process parameters during interrupted turning operations. Phuchit/iStock/Getty Images Plus

“We’re seeing a split in the market, a split where the indexables are being used for roughing and solid-carbide end mills do the finishing, especially as production components are becoming more near-net shape,” said Todd Miller, product marketing manager. “There is an equal need for indexables today as there is for solid tools.”

High speeds or high cutting forces amplify even the smallest instabilities in a machine, leading to deflection and, since the process is inherently cyclic, vibration. No matter how tough a ceramic is, vibration leads to irregular mechanical loads that bring about irregular wear that then translates into poor tool life.

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With carbide grades, having either a large grain size or cobalt-enriched layer as part of the substrate will make for a stronger insert. Larger carbide grains have more impact on strength compared to a fine-grade carbide.

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Lindsay Luminoso, sr. editor/digital editor, contributes to both Canadian Metalworking and Canadian Fabricating & Welding. She worked as an associate editor/web editor, at Canadian Metalworking from 2014-2016 and was most recently an associate editor at Design Engineering.

WG-600, a coated whisker-reinforced ceramic, in particular is showing “outstanding performance in turning. Finally, applications where even large-grain carbide lacks toughness (heavy interruption, impurities, forging scale) can now be addressed with XSYTIN-1 where other ceramic and carbide tools break.”

Improvements in indexable cutting tools extend to virtually every cutting process. Until the day when it will be sufficient to establish a baseline for comparative and competitive tooling performance through data analytics (a distinct future possibility of digitization and the IIoT), cutting tool manufacturers will rely on tried-and-true processes.

A rigid setup is necessary for interrupted cuts to take the impact. A round insert is the strongest, followed by a square insert. Dormer Pramet

“We are integrating the same positive cutting action and effective cutting rake angles of our single-sided insert cutters into our double-sided insert cutters. Incorporating the geometry of the single-side, four-edge square type insert into double-sided inserts allows you to get free cutting action and economy,” he said.

Another material that has not been an application area for ceramic indexable tooling is stainless steel. Duplex, 300 series and precipitation hardening steels are now being machined effectively with Greenleaf’s whisker-reinforced ceramics, according to the company.

An interruption also can be experienced not in the physical sense of material discontinuity, but by an inconsistency in material hardness or having heterogeneity in the material makeup of the workpiece. Goss explained that heterogeneity in the material can occur because of precipitates or inclusions that form during the manufacturing process of the parent material. If these precipitates or inclusions are congregated in one area of the workpiece, they can also act as an interruption during the machining process.

Within its milling family of products, Seco Tools is launching a double-sided face mill called the Double Quattromill 14, building on the success of its Double Quattromill 22 face mill for roughing and semi-finishing introduced at IMTS 2018 for heavy DOC machining.

The experts noted that some operators tend to favour a positive geometry as they think it will help take the impact, but that is just not the case. A negative geometry is going to provide a much better cut in interrupted turning.

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“A simple example of this would be 50 per cent of the material taken away by voids or interruptions at the surface,” he said. “Fifty per cent of the surface remains in contact with the tool compared to an interrupted part. So, in this case, double the SFM to compensate for that.”

“Basically, you want to look for the strongest insert possible,” said Paul Lobsinger, sales and service engineer Canada, Greenleaf Corp. “It helps to have a tough negative insert to accept the interruptions and pounding.”

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When you are considering carbide grades, having either a large grain size or cobalt-enriched layer as part of the substrate will make for a stronger insert. Tungaloy

There is still room to maximize ceramic indexable tooling. “Unless we are running on state-of-the-art, purpose-built, latest generation machines, we are limited by the rigidity, dynamics or power when applying ceramic indexable tools. In an ideal environment we are able to turn Inconel 718 at 1,476 sfm (450 m/min) with WG-300, or at 820 sfm (250 m/min) with XSYTIN-1, but with a very heavy chip,” according to the team.

“New indexable cutting tools often require faster spindle speeds, increased feed rates and multi-axis capabilities that today’s modern CNC machines are capable of to maximize their performance,” said Ewing. “For example, a 0.157″ [4[4-mm]umoCham drill can run above 11,000 rpm and up to 40 ipm [1[1 m/min]n mild steel. Even at the low end, you need more than 6,000 rpm for this tool. Some machines from 10-15 years ago would not be able to properly run this tool.

No one can accuse cutting tool manufacturers of not trying every possible combination of coating, substrate, material and geometry in their quest to gain a competitive edge for their customers.

Greenleaf’s latest advance and newest offering is the phase-toughened XSYTIN-1 ceramic which has “unprecedented edge strength, transverse rupture strength (the ability to support large forces, i.e. heavy chip flow), thermal shock resistance and toughness. XSYTIN-1 is also the most versatile ceramic in Greenleaf’s portfolio, successfully machining soft mild steel, weld-overlaid cobalt-based alloys and anything in between,” according to the Greenleaf team.

“For interrupted-style cuts on hardened material, it’s best to choose heavier edge preparations,” said Goss. “With ceramic, having a large single or compound chamfer/land, or with carbide, having a heavier-duty chip form, will ensure the insert is able to handle the abusive nature of the cut and redirect those forces appropriately to allow for maximum tool life.”

Winter pointed to Sandvik Coromant’s CoroPlus digital machining system as an example. “With the use of CoroPlus, you can use machine analytics to see exactly where you can make improvements to maximize your production. CoroPlus is data-driven process control that will push the tools and machines to the highest level of productivity possible with modern tooling,” he said.

Lobsinger explained that the smaller diameter value basically returns the operator back to the original recommended surface speed he is trying to achieve.

Indexable cutting tools are being used for innovative applications. “The biggest advancement for indexable tooling is in the application of those tools,” said Winter. “We are getting away from the ISO standard and pushing the limits of both tools and machines with creative designs. PrimeTurning is a perfect example of this. Using multi-directional turning, we see big gains in productivity and tool life. It used to be that ISO milling was the popular choice but now you would be hard pressed to find ISO milling in shops. By looking outside of ISO turning, we can push the tools, machines and the limits of the carbide inserts.”

Optimal strength is going to be realized by using a round geometry and a negative-style insert. Mitchell also noted that it’s important to pay attention to the chipbreaker selection. Some chipbreakers are designed for heavy interruptions, but others are designed to be free cutting and as sharp as possible, making them fragile and prone to chipping in an interrupted application.

One example is boring a large bore where an indexable boring bar will fit vs. using a small bore where only a brazed tipped bar can fit. The same is true of milling and drilling. “Here you can find advancements with PCD-veined tools versus brazed tools where the PCD is pressed into the tool not brazed,” he said. “This allows us to shape the PCD to the mill or drill tip, giving these tools better performance.”

Greenleaf Corp., Saegertown, Pa., is continually working to develop improvements in geometries to match the capabilities of its ceramic and carbide grades. The following is based on a written assessment of product and technology advances provided by the Greenleaf Applications Engineering Team.

Choosing the right grade depends on the type and hardness of the material, as well as the level of interruption and the machining stage, whether roughing or finishing.

Luminoso has a bachelor of arts from Carleton University, a bachelor of education from Ottawa University, and a graduate certificate in book, magazine, and digital publishing from Centennial College.

Regardless of how a shop classifies interrupted cuts, interruptions can present themselves in a couple of different ways.

“Time is money. By pushing the machines and the machines pushing the tooling, we can meet the needs of our customers and help save time and be more profitable,” Winter explained.

For drilling, along with the SumoCham and DR-Twist lines, Iscar offers the LogIQ-3-Cham, Cham-IQ Drill, Combi-Cham and Modu-Drill, as well as solid-carbide drills. The LogIQ-3-Cham three-flute drill offers higher feed rates due to the extra flute and creates more accurate holes in terms of diameter tolerance and roundness. The Modu-Drill series [1.299-1.575" (33-40 mm)] has interchangeable heads for different sizes and styles (Cham-IQ Drill, Combi-Cham and DR-DH).

For example, a hard grade of carbide will run faster and last longer but is more brittle, whereas a tough grade of carbide has impact resistance but runs slower and does not last as long.

Whisker-reinforced ceramics have sufficient hardness (and more than sufficient toughness) to machine most of the materials where carbide tools lack hardness and CBN lacks toughness. In addition, the tooling costs associated with indexable ceramics are significantly lower per cutting edge than they are for CBN.

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“There needs to be a balance,” said Goss. “You don't want to have too much negativity or a large land on some of those soft, ductile materials, which could lead to excessive cutting force. But it also needs to be heavy enough to provide adequate performance and tool life.”

According to John Mitchell, general manager, Tungaloy Canada, Brantford, Ont., carbide cutting tools are made primarily of tungsten, a very hard, wear- resistant material that is bound together with cobalt. To produce a grade capable of handling interrupted cuts, traditionally cutting tool manufacturers simply used more cobalt. On the other hand, to make the insert more wear-resistant, capable of faster cutting speeds and longer tool life, manufacturers used grades that had less cobalt and more tungsten.

Maximizing indexable cutting tool performance depends on whether or not operators are pushing their machines to their fullest potential for both tooling and process. “We need to educate our customers on best practices to be more aware of their machine utilization,” he said. “Many shop owners or plant managers can only give you an educated guess of their actual machine utilization and that utilization is sometimes much lower than they think. And on-lights, stopwatches and clipboards are being replaced by machines and tooling with sensors that can give thousands of data points.”

Indexable tools can be used in almost every application. “We are seeing more use in high-speed aluminum machining,” he said. “Advances in insert geometry and grades, as well as balanced tools and rigid holding of the insert, allow indexable tools to be used at higher rpm and sfm. Aluminum machining can take advantage of high rpm and machine tool builders have been developing spindles to run at these speeds. Traditionally, solid tools would have to be used in these applications due to balance and rigidity.”

“For roughing applications, I would like to have a tougher grade with a larger T-land or a roughing chipbreaker with a nice edge prep to maintain the interruptions as well as hold that dimensional tolerance,” said Haid. “When finishing, go with something harder rather than something tougher to hold the tolerance and not wear out as fast.”

In recent years, Iscar Metals Inc., Arlington, Texas, has made performance improvements by adjusting the alloying elements in tungsten carbide substrates, using new combinations of various coating layers and applying post-coating treatments. Iscar has also developed different edge prep geometries for a variety of material group applications.

“However, with ceramics, we would recommend opting for a silicon-carbide, whisker-reinforced ceramic insert or a silicon nitride-based ceramic over an alumina-based or white ceramic, as it will provide much more strength and reliability,” said Goss.

Coating. For interrupted turning, an insert with a physical vapour deposition (PVD) coating on the substrate will help extend tool life. PVD coatings are tougher than chemical vapour deposition (CVD) coatings.

Improvement in indexable tooling requires a holistic approach, according to John Winter, product management-East U.S. for toolmaker Sandvik Coromant, Fair Lawn, N.J. “We are pushing every aspect of the process to produce the best cutting tool solution possible, from coating technology to the macro and micro geometries that produce a stronger edge line to the post-treatment processes that give the coatings a harder, smoother surface.”

Seco Tools LLC, Troy, Mich., has developed advanced coatings such as a Niobium PVD thin coating for machining titanium and plans further advances in its Duratomic aluminum oxide-based CVD coating for general types of steel and cast-iron machining.

“Most commonly, an interruption is a break in the continuity of the material during the machining process,” said Matt Goss, applications engineer and project development, Greenleaf Corp., Saegertown, Pa. “This is where the insert engages and disengages with the workpiece, either once or a series of times. These interruptions can either be induced as part of the machining process, such as turning over bolt circles or holes, slots, or keyways, or they can be inherent to the workpiece, for example if it is out of round or has forging scale on the surface. Each of these cases presents a scenario where there's a break in continuous and uniform flow of material across the cutting tool.”

“Although positive inserts are generally not recommended for interrupted cuts, sometimes they are unavoidable,” said Mitchell. “In situations such as these, it is highly recommended to use a double-sided positive insert. Traditional positive inserts sit in a pocket and the only thing preventing them from moving is a small screw. But [some inserts] utilize a dovetail pocket, ensuring no movement even in interrupted applications, while still providing a positive cutting action.”

Interrupted cutting in turning is subjective. While some operators may look at a part with a keyway and a small depth of cut as a heavy interruption, another operator may classify heavy interruptions only as multiple interruptions with a larger depth of cut. The workpiece material, part configuration and features, and depth of cut will all come into play when determining how the interruption will affect the overall process.

Winter said that the latest developments for indexable milling, turning and drilling tools are more application-specific tools designed to perform a set operation at the highest level of performance. The processes will be optimized to maximize the machine tool, workholding and the tooling for a set application or component.

Shape. The experts agree that while different shapes of inserts may work, a round insert is the best option, followed by a square insert.

For deep-hole applications (>8xD), Iscar has also added double-margin drilling heads as well as inserts designed with self-centering, chip-splitting and flat-bottom geometries. In the DR-Twist line (four cutting edge inserts), there are geometries for general applications (medium to high feeds), soft materials (low to medium feeds) long-chipping materials (added chipbreakers) and aluminum (ground sharp edge, polished face).