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How Indexable Tools Keep Their Edge

By SME Media Staff

Recent developments are helping tools with inserts maintain their strong market position versus solid tools

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The NANMILL is a small-diameter, multi-toothed end mill for 90o shoulder milling.

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.

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.

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.

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.

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.

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.

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.”

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The NANMILL carries tiny triangular inserts.

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.

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.

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.

“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.”

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.

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The modular EH system makes it easier to change out cutter heads.

A Small Problem for Indexables

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.

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.”

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.

Excelerator face mills can accommodate multiple inserts.

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.

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.

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.

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.”

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.

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.

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Duratomic coatings give users a visual way of determining whether insert edges have been used.

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.

How to Make Better Indexables

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.

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.

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.

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It’s easy to create large-diameter indexable milling tools to maximize the material removal rate.

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.”

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.

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.

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.”

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.

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.

The Importance of Better Practices

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.

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iSmart end mills allow users to replace the head in the machine without removing the holder.

“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.”

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.

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.

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.”

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