Turning Away From (Some) Tooling Conventions

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Standards are designed to help the world work more efficiently. This has long been true for manufacturing. Beginning with Henry Maudslay’s invention of the screw-cutting lathe and the resulting standardization of screw threads, industry has strived for interchangeability, predictability, consistent quality, and reduced waste, all of which are made possible through widely accepted, well-documented standards.

So it is with indexable cutting tools. Whether it’s ANSI B212.4-2002 in the U.S. or the rest of the world’s ISO 1832:2017, both sets of standards refer to clearly defined (and nearly identical) specifications for insert shape, size, thickness, and other features, all of which serve to make these critical cutting tools interchangeable, regardless of the manufacturer.

Defining CNMG

There’s no need to repeat those specifications here. Any indexable cutting tool catalog or website has a page or two devoted to them. There are also dozens of books and magazine articles explaining these standards, not to mention the countless colorful charts hanging on the walls of tool cribs everywhere, giving machinists ample resources to identify, order, and apply milling and turning inserts.

More interesting is the increasing number of cutting tool manufacturers that have begun deviating from these standards, a trend that’s particularly true for turning applications. Yes, milling tools have their share of non-standard inserts, but it’s the turning department that has seen a notable influx of tools that are not only non-standard but, in many cases, require us to completely rethink our metal removal processes.

Pittsburgh-based Kennametal Inc., for example, has introduced the FIX8, a double-sided turning insert whose tangential design quite literally flips ISO and ANSI on its side. Marketing portfolio manager Robert Keilmann explained that FIX8 does not require special programming methods, although it might force shops to reconsider their feeds and speeds.

A direct competitor to traditional CNMG (80° diamond) and WNMG (better known as a trigon) inserts, it promises up to a 15 percent reduction in cutting forces and, as its name implies, eight cutting edges per insert for lower tooling costs.

“The FIX8 reduces tooling costs and boosts productivity for manufacturers performing medium and heavy-duty turning and facing in steel, stainless steel, and cast iron,” Keilmann said. “Its lower cutting forces and extremely rigid clamping system support extremely high feed rates and DOC [depth of cut], even in heavy interruptions. Because of this, we’re seeing widespread adoption by automakers turning long shafts and tubes, although it’s a good choice for any general-purpose roughing or semi-finishing operation, regardless of the industry.”

Prime Numbers

Sometimes a turning insert appears to meet the ISO standard but is, in reality, a proprietary design. So it is with the round tools found in the CoroTurn 107 line from Sandvik Coromant U.S., Mebane, N.C., which employ a series of grooves—a rail interface—in the bottom of the insert that mate with male risers in the toolholder pocket.

John Winter, the company’s product manager for the eastern U.S., explained that the interface securely locks the insert in place, eliminating rotation during heavy cutting that can break it or the clamping screw. It also makes indexing more consistent, which leads to more predictable machining. Sandvik Coromant employs a similar interface—the iLock—on its CoroThread 266 indexable threading line and has leveraged its greater security to deliver OptiThreading, a programming method that “bounces the tool in and out of the cut,” and that Winter best describes as a sewing machine motion.

Yet it’s the company’s PrimeTurning system that has received the greatest attention in recent years. Although Winter can’t disclose the exact details, he revealed that the next generation of the unique, definitely non-ISO cutting tool system will arrive later this year. For now, CNC machinists must be content with CoroTurn Prime A, designed for light roughing, profiling, and finishing, and CoroTurn Prime B, the football-shaped roughing insert. Both styles break with convention by turning exceptionally well in the Z+ direction (away from the chuck) and do most of the heavy lifting with the backside of the insert.

PrimeTurning takes advantage of the chip thinning effect, the same phenomenon that makes trochoidal milling so effective (see sidebar). Anyone turning large quantities of shafts knows they can enjoy similar benefits by using a round or positive lead angle insert. Such conventional tools cannot turn a square shoulder or undercut, however, whereas Prime A and B are said to excel at both, as do many of the competing products that have sprung up since their introduction.

Turning Right

When asked why a machinist can’t simply use a 35° or 55° single-sided insert to “turn backward,” Winter said he worked with a shop that was doing just that during the early days of PrimeTurning. “The long, stringy chips were a constant battle and their tool life was quite poor. That’s because standard inserts are simply not built to cut in the Z+ direction. As this customer found, you can get it to work, but in most applications, the results are less than satisfactory. They’ve been using our Prime solution ever since.”

Winter added that bypassing the ISO standard gives cutting tool manufacturers greater latitude to develop innovative chip breakers and geometries that are often more productive than the status quo. This was certainly the case with Ingersoll Cutting Tools USA, Rockford, Ill., where turning product manager Raymon Avery noted that many of the products launched over the past year under the SFeedUp brand have non-ISO pockets and were designed for multidirectional turning.

As an example, Avery pointed to the company’s TurnSFeedF, a trigon-style insert that at first glance looks like an exceptionally wide grooving tool but boasts longitudinal feedrates up to 3 mm/rev in either direction. There’s also the SuperTurnZ series, whose various shapes appear to be venturing into Prime territory.

Breaking with Tradition

Avery seconded Winter’s assessment of ISO geometries. Moving away from them, he noted, allows tooling engineers to use finite element analysis (FEA) and other advanced simulation tools to optimize an insert’s metal removal capabilities, but without the constraints imposed by a decades-old standard.

Avery ticked off several additional features, such as unique locking mechanisms that eliminate insert movement during heavy loads, and insert seats with three-point contact for added stability when turning in multiple directions. When coupled with today’s high-performance coatings and the high-pressure, through-the-tool coolant now standard on most toolholders—ISO included—shops are ripping away metal at previously unheard of rates.

Yet, anyone who has stood in front of a lathe long enough likely has felt the occasional terror when a part comes flying out of the chuck, and knows that turning forces should always be applied toward the headstock. It’s a fair concern.

Said Avery, “We understand that turning away from the chuck tends to pull the workpiece out and that some applications are not viable candidates for multidirectional turning. Still, assuming you have high-quality workholding and a good grip on the material, the benefits are clear—not only can you increase metal removal rates significantly, but you’re able to use both sides of the insert, chip control is much better, and thanks to the chip-thinning effect, tool life goes up substantially.”

Adding It Up

David Essex, product manager for Tungaloy America Inc., Arlington Heights, Ill., has his own list of non-ISO product successes to share. These include the multifunctional TungBoreMini and double-sided yet positive rake MiniForceTurn, both of which (as their names suggest) are intended for smaller part turning with a lighter DOC, at least relative to the roughing inserts just described. For heavier applications, Essex might recommend the double-sided, pentagon-shaped TurnTenFeed, particularly where tooling costs are a concern, while the company’s TurnFeed is a “super high-feed” turning insert similar in shape and function to Ingersoll’s TurnSFeedF.

On the multidirectional front, Tungaloy recently released its AddMultiTurn and AddY-axisTurn systems. The former is a triangular insert that, according to the company’s website, is equally adept at front turning, back turning, profiling, and face turning. “That one has really taken off for us,” Essex said. “The AddY-axisTurn, on the other hand, is a little more limited in terms of shops that can currently use it, in that it’s made for Y-axis lathes and multitasking machines with a PSC-style (Capto) interface. We are seeing a lot more of these types of machines being purchased with Capto holders because of the benefits in accuracy and speed of tool changes.”

Essex isn’t too concerned with the possibility of parts pulling out of the chuck during multidirectional turning operations. Even so, he suggested using a live center for support whenever possible for maximum security, and as Ingersoll’s Avery indicated, grabbing the part with a high-quality chuck, preferably one with hardened top jaws.

Most important, he said, is to follow the cutting tool manufacturer’s feed, speed, and DOC recommendations, which is good advice for any machining application. “With these tools, you’re typically taking light cuts at very high feedrates. Doing so helps break up the chip and improve tool life, and in most cases, removes more metal in less time than with a heavy cut and lower feedrate. ISO-style inserts will continue to have their place, but I strongly encourage shops to look at some of the newer alternatives. Speaking for Tungaloy, at least, our customers are quite pleased with the results.”

Is G71 Dead?

Each of the tooling providers interviewed for this article noted the need for unconventional toolpaths to go with their unconventional cutting tools. Several CAM providers have begun to address this need, among them CNC Software LLC, Tolland, Conn., makers of Mastercam. Ben Mund, the company’s channel marketing manager, pointed out that these paths share many of the same qualities as those used with trochoidal milling routines, or in Mastercam’s case, Dynamic Milling.

“We worked closely with Sandvik Coromant on their PrimeTurning solution, and during that process, found it necessary to develop what I would call ‘material aware’ toolpaths,” he said. “The goal was to spread the chip load across as many surfaces as possible while keeping the chip load consistent, so we applied some of the same techniques we’d developed for Dynamic Milling to PrimeTurning.”

These techniques include arcing into and out of the cut at slightly lower feed rates, thereby reducing shock to the insert, and avoiding burying the insert in corners. Together with the tool’s positive lead angle and use of high-feed, low DOC parameters—similar to that of trochoidal milling—PrimeTurning and other multidirectional solutions make it possible to greatly increase metal removal rates.

The question then becomes: Should shops use some of these same programming methods with conventional turning tools, and skip the traditional G71 multiple repetitive roughing cycles used on Fanuc-compatible machine controls? Maybe so, suggested Jesse Trinque, an applications engineer at CNC Software.

“As a Mastercam programmer, I don’t use G71 or any of the other canned cycles found on CNC machines, and can tell you there are much more effective ways to turn a part,” he said. “Yes, for manual programming, there’s no other choice, and I understand the convenience hat comes with these routines. But for the same reasons that Dynamic Milling and other high-performance toolpaths are clearly superior to traditional milling approaches, so too is modern, CAM-generated lathe programming better than old-fashioned manual methods, especially when combined with some of the newer turning tools.”

First published here: https://www.sme.org/technologies/articles/2022/august/turning-away-from-some-tooling-conventions/