Though not right for every cutting application, indexable tools have a number of inherent advantages over solid tools that account for their competitive edge in the tool market. In recent years, moreover, the competitive position of indexable tools has been strengthened by advancements that have increased tool life, improved cutting performance and sped up changeout.

Grooving and parting-off applications present unique challenges. Unlike a longitudinal turning application that allows chips to move in three directions without restrictions, during grooving and parting-off processes you are machining between flanks, which confine chip movement to just two directions.

Coolant from above can greatly improve chip control, which is a key to longer tool life. It can also reduce built-up edges (BUE).

Materials are changing, and they are generally not getting easier to machine. Challenging materials such as heat-resistant superalloys, stainless steels, and lead-free alloys such as brass pose new challenges that demand modern machining strategies.

Let’s use a lead-free brass alloy as an example of a challenging material. Brass is known for its good machinability properties. A leaded, free-machining brass is particularly popular in the production of turned parts. Tools used to machine free-machining brass have a negative chipping angle that produces small, short chips. With new laws that regulate the use of hazardous materials such as lead, new grades of lead-free brass have emerged that require a change in machining processes.

To understand how this works, consider an indexable tool with black inserts. An operator looking at the edges of one of these inserts may not be able to tell whether they have been used. As a result, the insert may be unnecessarily indexed or even replaced.

So what about cam machines that are 20 or 30 years old or older? Truth is, many companies still run older cam-style machines, and these machines aren’t being ignored. There are new options for them too.

The pre-plumbed systems simply bolt on to accommodate many coolant delivery options that offer quick changeover without the need to hook up coolant lines. Many of the modular systems also allow for center height adjustability that can be especially helpful when cutting difficult materials. A large number of combinations are possible with a relatively small number of components, which enables standard tool systems to be used throughout an entire production process regardless of the machine interface.

Another toolmaker trying to move replaceable cutting edges into solid-carbide territory is Sandvik Coromant, Fair Lawn, N.J. The company offers an exchangeable head (EH) system consisting of a removable carbide cutting tip that typically screws into a steel body. In addition to reducing the amount and cost of carbide, the EH system speeds up and simplifies the process of exchanging cutting tips because it doesn’t require the removal of the entire tool from the machine, noted Anja Redzepagic, a Sandvik Coromant sales engineer.

“There are people in this industry who have developed really bad practices when indexing inserts,” she said. “I was surprised at how little education there’s been in that area, and how many shop owners still ask us to [provide] that type of education for their employees.”

Aydt often sees such waste firsthand. When he and his Seco colleagues walk into shops and look in their used carbide insert bucket, “many times we can tell they have thrown away unused edges,” he said. “Used-edge detection can prevent this from happening.”

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In addition to the coating itself, the method of applying the coating can have a major impact on inserts. “Today, coatings are being applied so that the peaks and valleys are much smaller when you look at the coatings under a microscope,” Greenleaf’s Dillaman said.

Coolant supplied below the cutting edge will reduce the cutting zone temperature while minimizing flank wear. This also aids in chip removal. Reducing the temperature makes it possible to use tougher varieties of inserts while maintaining tool life and cutting parameters or, in some cases, increasing tool life and improving process reliability. This process also delivers the best results when engagement times are long and temperature is a limiting factor.

When internal coolant is supplied directly through the toolholder, it is directed precisely to the cutting edge, enabling a much more reliable process. Internal coolant, or through-coolant, holders are available in many variations. Some direct the coolant to immediately above the insert, some to immediately below.

The negative chip angle that works so well in free-machining brass does not work nearly the same in the lead-free version. Machining trials have shown that lead-free brass is best machined with geometries more suited for steel. For the best process capability it is important to apply the correct geometries and grades for the material you are machining. Not all brass is the same.

Today, Andersson stated, “you have a little bit of overlap” between indexable and solid tools with diameters roughly in the range of ½" (12.7 mm) to ¾" (19 mm). A key development in this area is the appearance of what Andersson calls “semi-indexable” tools with a solid-carbide front end that threads into a steel or carbide carrier. With semi-indexable tools, he noted, “you still are getting the advantage of the indexable in that you are only replacing part of the tool, and you get more of the precision you get with solid tools.”

With a chrome Duratomic coating, however, insert edges that have made any contact with a workpiece turn dark, making it easy to spot used edges. The idea is to reduce the number of insert edges that shops waste.

What accounts for the popularity of indexable tools? Fundamentally, they are efficient tools for metal removal because of their structure, which typically consists of a number of carbide inserts installed in a steel body. This structure is very strong and capable of taking high-horsepower cuts, resulting in maximum material removal rates, according to Luke Pollock, product manager at toolmaker Walter USA LLC, Waukesha, Wis.

Due to the relatively high cost of carbide compared to steel, solid-carbide tools tend to be smaller than indexable tools. While the diameter of a common solid-carbide end mill might be ½" (12.7 mm) or ¾" (19 mm), Pollock said, indexable tools normally start at ¾" (19 mm), with 2" (50.8 mm) and 3" (76.2 mm) diameter sizes more common.

From a cost perspective, indexable tools require a significant upfront investment. According to Seco Tools’ Aydt, however, the investment cost can be paid back within a few months, depending on the application.

New modular tools make it possible to produce assemblies that are tailored for specific applications while being made up of completely standard components. This can reduce the need for special tools. These systems provide a stable structure, while their modular design gives you flexibility and a large variety of tool configuration options.

Coolant can be supplied by an external or internal means. When external coolant is supplied via nozzles spraying on the toolholders, only a small amount of the coolant actually gets to the cutting edge so it has less of an effect on the cutting application than coolant delivered using a through-coolant toolholder delivery system. This is especially true when machining deep grooves and working with materials that are easily work-hardened, such as superalloys and stainless steels.

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Chip control ensures that chips will not cause problems during the machining process. The goal is to produce short helical, spiral, comma, or tear chips (shaped like 6s and 9s). These types of chips are more likely to provide stability in the grooving and parting-off process.

The narrowest indexable inserts should be used in the parting-off process as this can factor into significant material cost savings. These savings multiply exponentially when you are machining alloys that have a substantially higher material cost, such as high-temp superalloys.

The company’s small-diameter indexable milling cutters feature very small inserts. Stusak claims his company is the industry leader when it comes to five-axis pressing of inserts. “We have the ability to press and form inserts at very small diameters and hold tight tolerances,” he said.

Consider two key points to avoid problems. One is chip forming and the other is chip control. Good chip forming ensures that the material is plastically deformed by the tooling so the chips are narrower than the width of the cutting insert to avoid damage to the groove flanks. An example is a 5-mm-wide groove insert that creates a chip that is 4.85 mm wide.

Once on the job, indexables can last for longer periods of time than solid-carbide tooling. “You can keep using [an indexable tool] for three, five or even 10 years, depending upon what you’re using it for,” Aydt said. He added, however, that the carrier will always wear out eventually, with the pockets deforming over time because of the immense amount of heat and pressure applied to them.

Other developments have come in the area of coatings. One of these is Seco Tools’ latest Duratomic coatings, which feature what the company calls “used-edge detection.”

Coolant applied through the toolholder is precisely directed to the cutting edge, where it will have the most impact on the cutting process.

Much larger sizes are also possible. “You couldn’t create a 10" (254-mm) diameter cutter out of solid carbide because it wouldn’t be economically feasible,” Pollock said. “But with a steel body, it is very easy and cost-effective to do.”

Keep up to date with the latest news, events, and technology for all things metal from our pair of monthly magazines written specifically for Canadian manufacturers!

To prevent this from happening, Dillaman added, users must know the torque capability of their machine and, if necessary, adjust their cutting operation to make sure the machine isn’t overloaded. Such adjustments could include reducing the feed rate or depth of cut.

Sales figures don’t lie: indexable cutting tools—featuring removable cutting tips called inserts—are a smash hit with machine shops. According to a McKinsey & Co. report, indexable tools accounted for about 63 percent of U.S. milling tool sales in 2017, versus 26 percent for solid-carbide tools and 11 percent for solid non-carbide tools.

To extend the life of its indexable tool bodies, Sandvik Coromant prehardens the steel using a heat treatment process just before the pockets are machined. This makes it more difficult to damage the pockets when the tool is being used, according to Redzepagic.

YG-1 Tool (USA) Co., Vernon Hills, Illinois, has introduced a similar product. “Traditionally, indexable milling had its lane that it stayed in and solid tools had their lane. You used indexable tooling for roughing and went with solid for more intricate details, tight tolerances or fine finishes,” said Jan Andersson, the company’s product management director for indexables.

The H-Carb Seven Flute High Efficiency Endmill specializes in deep axial trochoidal and high-speed machining applications. Offered at various lengths of cut, the 7 flute design creates a superior finish to conventional 5 or 6 flute tools.

Redzepagic also advises shop personnel who remove inserts to make sure to clean the pockets, completely blowing out any chips that could scratch a surface and adversely affect insert fastening. If this isn’t done, the result, again, can be insert movement that wrecks the tool body.

The P-style blades have many options with indexable blades that are designed to fit in existing tool blocks. Solid-carbide options allow for direct replacement of these blades for groove and cutoff applications.

This is due to the price of steel and the relative ease of machining insert pockets into a steel body. “If you had a 10" (254-mm) diameter tool, you could easily put 10, 15 or even 18 carbide cutting edges in the steel body,” Pollock said.

We can’t talk about coolant delivery without talking about coolant pressure. With the right coolant pressure it is possible to influence chip formation in grooving and parting off. Coolant pressure as low as 5 bar (72 PSI) can start to reduce crater wear. As the pressure increases to 20 bar (290 PSI), it can reduce BUE. Coolant pressure of 40 bar (580 PSI) can influence chip control and direction. High pressure application of 80 bar (1,160 PSI) or more can aide in chipbreaking.

Dillaman added, however, that tool designers must be careful not to add so many insert pockets that there is no longer enough steel in the cutter to maintain adequate strength. In addition, users of tools with large numbers of inserts must make sure that their machines are up to the task of using all the cutters.

It is important to consider the economics of parting off. Since parting off is often the final operation in manufacturing a component, reliability is crucial.

While speed always seems to be emphasized and prized in manufacturing operations, Pollock maintains that it shouldn’t be shop personnel’s top priority when they are engaged in tool maintenance activities. “In this area, saving time isn’t necessarily the most important thing,” he said. “Doing a good and accurate job during the process is also important.”

Editor’s Note: This article was developed from information presented during the Horn Technology Days 2017 event held at Paul Horn GmbH in Tübingen, Germany, May 10-12.

Nevertheless, some companies make tools with replaceable cutting edges that are aimed at what has traditionally been solid-carbide’s turf. For example, Iscar Metals Inc., Arlington, Texas, recently introduced indexable end mills with diameters that go to 5/16" (7.9 mm). The idea is to “complement solid-carbide tools, not totally replace them,” said Bryan Stusak, Iscar’s national milling product manager.

Whether or not shops choose to upgrade their indexable tool technology, they should never miss a chance to upgrade their insert indexing and changeout practices. Many tool manufacturers now offer customer instruction in this vital area—and it’s often badly needed, according to Sandvik’s Redzepagic.

While a solid-carbide tool is very hard and resists abrasive wear, “it is also on the brittle side so you are limited as to how hard you can push it,” Pollock said. With indexable tools, however, the toughness of the steel body comes into play. “You usually don’t think about an indexable milling body breaking, but solid-carbide tools break all the time,” he noted, adding that the steel body also makes indexable tools less susceptible to vibrations.

Like the EH system, YG-1’s product in this category, called iSmart, significantly reduces carbide-related tool costs and changeout time. On the downside, however, the presence of the threaded joint means semi-indexable tools are incapable of matching the precision of solid-carbide tools. As a result, Andersson places them in the semi-finishing category, between tools designed for roughing and those capable of superfinishing.

Another technological advancement extending the life of indexable tools is the modern electrostatic press. Andersson pointed out that these presses tend to be more precise than their older counterparts in insert production. “Any time you have smaller deviation from insert to insert, you reduce runout and get longer milling-tool life,” he said.

“When you have multiple teeth in the cut, the forces required to spin the cutter go up significantly,” he said. “So you may run into instances where you will essentially stall the machine.”

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With a more uniform coating surface, cutting edges produce parts with better surface finishes, Dillaman noted. In addition, he said, coatings that lack thinner (and therefore more vulnerable) areas will do a better job of protecting insert substrates from heat.

Why do solid-carbide tools have an edge in these applications? Compared to indexable tools, “you’re going to be a lot more accurate with a solid-carbide round tool,” said Tim Aydt, indexable milling product manager at Seco Tools LLC, Troy, Mich. “Your wall finish will be better and your tolerance band will be a lot easier to maintain.” Indexables, he added, “are mainly just for metal removal and usually for larger machines making larger parts.”

Through-coolant holders eliminate the need to adjust coolant lines and always direct the coolant to the tool’s cutting edge. External coolant lines can be bumped out of alignment while operators are changing tools or loading parts, which can cause process variation or premature tool failure.

Among Redzepagic’s top suggestions in the area of insert indexing and replacement: When there is a shim in the insert pocket, take a good look at it. And if the insert has left an impression in that shim, make sure to change the shim because the insert needs to lie on a flat surface. If it doesn’t, the insert will be able to move around in the pocket—and that motion can ruin both the insert and the cutter body.

Cooling lubricants and cutting fluids can dramatically affect the reliability of grooving and parting-off processes. When applied correctly, cooling lubricants can reduce the temperature of the material being machined and improve chip removal. Keep in mind that no matter how much coolant is poured on an application, or how effective the coolant is, it will have little to no effect if it is not applied to the cutting edge.

The steel body of an indexable tool is used over and over while only the cutting edge is replaced. Normally, carbide inserts will have more than one cutting edge. When worn, the cutting edge is changed by turning or flipping the insert—i.e., indexing—to an unused cutting edge. According to Pollock, some tool designers focus on creating as many cutting edges as possible on one insert to improve the cost benefit of using their tools.

Turning application technology has come a long way from the time when you simply clamped a piece of tool steel in place for a turning application. Today the flexibility, simplicity, increased stability or rigidity, and improved accuracy are making modular grooving systems popular.

While indexable tools are the most popular choice for roughing, the situation is different for cutting applications that require smaller tool diameters or greater precision. In holemaking, for example, indexable tools have a much lower share of the U.S. cutting tool market, accounting for just 30 percent in 2017, according to McKinsey & Co., while solid-carbide tools accounted for 40 percent and solid non-carbide accounted for the remaining 30 percent.

Another advance in the indexables field is Iscar’s development of proprietary insert grades designed for machining heat-resistant superalloys used in aerospace applications. Stusak claims these insert grades normally last about 20 percent longer than a typical grade in Iscar’s portfolio. Though he wouldn’t discuss the specifics, he did reveal that there are alloying elements in the carbide substrate of the inserts that give it a higher hardness in elevated machining temperatures.

At Greenleaf Corp., Saegertown, Pa., tool designers found that adding more pockets to their face-milling tools actually adds to the life of the inserts in the tools. What makes the difference is the extra inserts in those additional pockets. More inserts stabilize the cut and reduce the forces on each insert, which in turn reduces the number of times the inserts must be indexed, explained Martin Dillaman, Greenleaf’s applications engineering manager. “You may be adding some cost by adding an insert or two to the tool, but the productivity increases outweigh that,” he said.