Positive lead angle tooling increases metal removal rates and extends tool life

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With ten cutting edges and a recommended feedrate up to 2.0 mm/rev (0.079 ipr) in ISO P materials, Tungaloy’s TurnTenFeed ranks among the lowest cost per edge in roughing inserts.  IMAGE: Tungaloy

By Staff Writer

The WNMG-432 turning insert, more commonly known as a trigon, is a staple of many machine shops. It can face, turn, and bore with equal aplomb, and thanks to its six corners, ranks among the lowest cost per edge of indexable tooling (second only to round inserts). Similar praise can be heaped on the older, more established 80° diamond. It shares in the trigon’s capabilities, and despite its having two fewer corners, is probably even more popular.   

The Walter Lock W1011 and W1010 copy turning system boasts a triangular, multidirectional, non-ISO insert that reportedly supports up to 60 per cent faster feedrates in “back turning” operations. 
IMAGE: Walter Tools

Except for one thing: these and other industry standard turning tools have a negative lead angle and so don’t take advantage of the chip-thinning effect. And as any machining centre operator can tell you (those using trochoidal milling strategies, at least), this generally means shorter tool life and significantly lower rates of metal removal. 

Accelerated machining

David Essex, product manager for Tungaloy America Inc., ticked off several products that avoid this status quo and utilize a positive lead-angle, chip thinning insert to increase feedrates, in some cases alarmingly— for example, when using the company’s TurnTenFeed pentagonal (POMG) roughing insert and HF (High Feed) holder, the recommended feedrate in ISO P materials is up to 2.0 mm/rev (0.079 ipr), fast enough to have most reaching for the emergency stop. 

Although shaped like many other trigon-style insert, Ingersoll’s TurnSFeedF is oriented in such a way to provide longitudinal feedrates up to 3.0 mm/rev (0.120 ipr) in either cutting direction. IMAGE: Ingersol

And Tungaloy’s new AddMultiTurn multidirectional turning tools come close to that with feedrates of 1.2 mm/rev (0.047 ipr) or more when reverse turning S45C steel (equivalent to AISI 1045), albeit at a conservative 0.25 mm (0.0098 in.) depth of cut. To achieve productive tool life and part quality at these rocking fast feedrates, however, it’s important to follow the cutting tool manufacturer’s recommendations, even if they might seem outlandish compared to traditional, ISO-style inserts. 

“I was working with a customer on the 6C version of our AddMultiTurn, which is a double-sided, positive rake, TOMG-style insert designed for light roughing applications,” says Essex. “I then switched to one of the 6V finishing inserts but neglected to adjust the feed and speed. The tool survived, but the part surface finish was horrible, and you could tell we were really just ripping the material out instead of efficiently cutting it.”

Skip the template

Walter USA LLC has a similar solution, one that also relies on chip thinning for its success. As with Tungaloy’s AddMultiTurn, the Walter Lock W1011 and W1010 copy turning system boasts a triangular, multidirectional, non-ISO insert that, according to product manager Sarang Garud, supports up to 60 per cent faster feedrates when turning away from the chuck.

But what does the term “copy turning” mean? Machine shop veterans might recognize it from the days of tracer lathes, where an arm and roller mechanism is used to follow a template part, thus copying its shape onto a series of workpieces. 

Garud says Walter’s more modern definition of copy turning encompasses the various profiling, recessing, and back turning or grooving operations possible on a CNC lathe—until Walter and other cutting tool manufacturers developed non-ISO alternatives, though, machinists had to perform these operations using V- or D-style, diamond-shaped inserts applied in the Z- direction, or with turn-groove inserts able to cut toward or away from the spindle. Neither approach, he notes, leverages the chip-thinning effect or supports particularly high feedrates. 

“Due to the insert’s patented seating system, it’s also far more rigid than traditional profiling solutions,” says Garud. “The holder has a precision through-coolant feature that cools the cutting edge, leading to increased insert life, efficient chip evacuation, and a very reliable process.”

Extreme feeding

Ray Avery is another of the chip-thinning effect’s biggest fans. A turning product manager for Ingersoll Cutting Tools USA, Avery points to the company’s SuperTurnZ and TurnSFeedF as two examples of multidirectional turning inserts that run circles around their traditional ISO-style counterparts. 

The latter of these looks much like any other trigon-style insert, but has been rotated to bring its broad face perpendicular to the Z-axis; it’s the wide relief area that would normally sit right behind the tool tip in a traditional setup that does all the work with the TurnSFeedF, however, providing longitudinal feedrates up to 3.0 mm/rev (0.120 ipr) in either direction. 

Here again, such expeditious, multidirectional material removal requires above-average clamping capabilities and generous cutting fluid delivery. Ingersoll has addressed both. Any potential for insert twist has been eliminated by locking it in place with a special three-point contact screw hole and three raised grooves on the insert’s bottom side, while the toolholders support top-down and bottom-up coolant (as do most turning tools today). 

Perhaps the only downside to unconventional turning offerings is the programming: none can use that old standby, the G71 roughing cycle. Says Avery, “for shops that are still programming manually, this might be a fair criticism, but any additional programming time is easily justified by the huge jump in metal removal rates. And for everyone else, a decent CAM system has no problem generating the required back-and-forth toolpaths. Either way, our website has operating guidelines and we have plenty of knowledgeable people on hand who can help with any questions.”

After Prime Time

John Winter, product manager for the Eastern U.S. at Sandvik Coromant is familiar with such considerations. He, too, is unconcerned. The company’s CoroTurn Prime turning system has been on the market since late 2016, and even though the toolpath recommendations associated with it are typically much more complicated than the back-and-forth motions described earlier, the CAM community has done an excellent job supporting them. 

Regardless, it’s entirely possible that these programming recommendations are about to gain in complexity. Winter is mum about the details but suggests an upgraded Prime Turning will soon be coming. “We continue to look for additional ways to increase tool life and productivity, and have begun to adjust some of the angles and other geometry used on CoroTurn Prime. This will eventually become the next generation of Prime B.” 

Sandvik Coromant’s CoroTurn 107 platform uses a round insert and a unique locking system that prevents spinning during dynamic toolpaths. Image: Sandvik Coromant

Until then, Winter recommends shops wishing to leverage the chip-thinning effect look to Sandvik Coromant’s CoroTurn 107 platform, a round insert with a locking system that prevents spinning during dynamic toolpaths. “I’d also suggest applying some programming methods used with Prime Turning to their traditional turning tools. We’ve found techniques like gentle arcing into and out of the cut, not burying the insert in corners, and adjusting the depth of cut slightly to reduce depth of cut notching, can have a positive effect on tool life, regardless of the insert style or geometry.” SMT

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