Breakthroughs Expand Turning Tool Performance Envelope

Manufacturing Engineering Magazine August 2019
By Jim Lorincz

Advances in turning insert technology that promise faster processing, longer tool life and reduced cycle time are always promoted with great fanfare by suppliers and welcomed by manufacturers looking for a competitive edge.

In industries where precision and production go hand in hand, however, it makes a big difference what materials are being cut and what cutting tool innovations are being used. Today’s machine tools challenge the best efforts of cutting tool suppliers to set new standards of performance, while new cutting tool technologies promise higher optimized performance if the tools are run to new data parameters that only yesterday seemed nearly unattainable. And that requires cutting tool suppliers to educate their customers to run machines to the new highest and best performance data. ME spoke with several cutting tool experts about recent advances in insert design and manufacturing technology, as well as developments in grade, geometry, chipbreakers and coatings that are expanding the envelope of turning performance. Here are some of them.

New Approach to Turning

PrimeTurning was introduced by Sandvik Coromant, Fair Lawn, N.J., as a totally different way of performing turning more efficiently and productively. In PrimeTurning, the tool enters the component at the chuck and removes material as it travels toward the end of the component, bringing with it its own set of interesting programming challenges.

One is the application of small or shallow entering angles and higher lead angles that create thinner, wider, curved chips that spread the load and heat away from the nose radius. The result, said the company, is both increased cutting data and extended tool life due to increased feed rates. In addition, because cutting is performed in the direction moving away from the shoulder, there is no danger of chip jamming, which can be a problem in conventional turning. Entering angles of 25–30º are used to maintain chip control and tolerances.

Programming is widely recognized as a key to unlocking the potential of PrimeTurning’s processing capabilities and is available now. For example, CNC Software Inc., Tolland, Conn., developer of Mastercam CAD/CAM software, worked with Sandvik in developing programming for PrimeTurning using the principles of its Dynamic Motion engine to produce toolpaths that can drive the tool’s motion. Industries likely to benefit the most, according to Sandvik, are aerospace and automotive manufacturers, where it is necessary to perform external turning operations in large production runs or where multiple setups and tool changes are required.

Precision-Guided Coolant Jets

For machining stainless steels and superalloys such as Inconel or titanium, Walter USA LLC, Waukesha, Wis., has introduced new chipbreaker geometries with precision-guided coolant jets, according to Sarang Garud, product manager. These geometries work in conjunction with through-coolant holders to target the coolant jet directly at the cutting zone in a precise manner. This precision-guided cooling is achieved by the top clamp of the toolholder, which also acts as a coolant nozzle. The coolant exits the coolant nozzle (top clamp) onto the rake face of the insert with high pressure.

“The new ISO turning insert geometries are shaped such that the features on the rake face of the insert act as coolant channels, which further guide the high-pressure coolant to target the cutting zone. This leads to a superior cooling of the insert edge, increasing tool life up to 100 percent or more,” said Garud. Additionally, coolant is also delivered from the clearance face for additional cooling of the cutting edge.

“The clearance face blast of coolant with high pressure also acts as an extremely efficient method of chip evacuation,” Garud said. “For maximum impact it is best to use Walter’s through-coolant holders; however, a substantial benefit can also be realized by using just the precision-guided geometry inserts, which are ISO standard.”

Most of Walter’s turning geometries are less than four years old. “Some of the latest geometries, such as MS3 for medium machining and RM5 for roughing of superalloys as well as stainless steels, feature the precision-guided coolant geometry,” he said.

New Grades to Optimize Turning

YG-1 Tool Co., Vernon Hills, Ill., already one of the largest round cutting tool suppliers, has set its sights on growth in the turning insert market and invested $150 million in its insert pressing and finishing manufacturing facilities, according to Cullen Morrison, regional sales manager. YG-1 has introduced seven new grades to optimize turning. The turning grades cover most workpiece materials and chipbreakers cover a wide range of applications, including roughing and finishing as well as high-speed, low-speed and interrupted cutting applications.

Morrison explained that YG-1 has focused R&D on the science and engineering behind creating grade structures, coating technology (including adhesion of coatings and multiple-layer coatings), and grain orientation in vertical crystal configurations for strength and wear resistance.

The company has targeted the key material groups of steel, cast iron, stainless steel and more recently titanium. Technology is aimed at the problems unique to each application, including wear issues, chipping that can be addressed with micro-geometry, and locating inserts in pockets to achieve stability and consistency.

“The majority of turning applications we see involve general steel turning operations and alloy steel. We are now getting into superalloys and heat-resistant superalloys (HRSA) with new chipbreakers and grades,” said Buddy Cagle, southeastern regional sales manager. “We entered the market with a PVD grade as an “all a rounder” for cast iron, low-carbon steels and stainless materials. And now we’re developing coating and chipbreaker combinations for the superalloy materials [used in] aerospace, medical and energy industries, specifically for rust-resistant materials like Inconel,” said Cagle.

Coolant-Through, Quick-Change

The challenge of difficult-to-cut materials, especially high-temperature alloys, is being met by a combination of turning technology advances, according to Brian Sedesky, application and sales engineer, Horn USA Inc., Franklin, Tenn. Heading the list of developments from Horn are directed coolant streams and coolant-through holders, chipbreakers, edge prep and advanced coatings.

“Difficult-to-machine materials pose the challenge of controlling chips in the process with edge prep and coatings,” said Sedesky. “When heat is introduced into the materials, they get harder and stronger, making them advantageous for high-temperature applications. To effectively cut the part with carbide cutting tools, you have to generate a certain amount of heat to be able to plasticize the material and [make it] workable. There is a fine window that you need to operate within to effectively get the best metal removal rates. Coolant-through tools produce better tool life and better chip control, particularly in running unattended without stringy chips wrapping around tooling and stalling out processes.”

Horn has entered into a partnership with another German company, W&F Werkzeugtechnik, a supplier of quick-change toolholders, to provide a complete solution for Swiss-style machines, covering everything from the spindle to the tool cutting edge. Horn’s cutting tools will be utilized in the pockets of the quick-change tooling heads on a single stick tool or a round shank.

The quick-change tools with W&F’s solid, one-piece stick tool design can be mounted into the machine or the gang plate of a Swiss-style machine. The heads are interchangeable with ISO-style turning inserts, a specific Horn insert or a triangular lay down threading type tool.

“It’s a rigid system, with coolant-through capability and it answers a need with today’s skills gap of having to teach operators how to change a tool correctly, especially in a Swiss machine,” said Sedesky. “It’s as simple as removing one screw, removing the head, indexing, tightening down and locking in place. Operators no longer need to bring the tool down to a touch-off position once the initial setup for that tool position has been completed.”

The challenges of Swiss-style machining are the tight spaces, without a lot of room to remove chips as well as the need to attain the correct surface footage for small-diameter tools. “Swiss machines don’t always have the rpms to get up to the surface feet we want to run and adding coolant keeps things lubricated and material from sticking to cutting edges,” Sedesky said. “It’s always a challenge to convince shops to run harder to new performance limits, especially where running too slow—like when machining gummy stainless steels—is not the best approach.”

Steady but Subtle Changes

Travis Coomer, insert product manager, GWS Tool Group, Tavares, Fla., points to subtle but steady changes in turning insert shape, geometry and coatings as ways to improve turning operations.

“The changes have been subtle,” he said. “Substrate, geometry and coating technology have all improved steadily. Perhaps more noteworthy have been improvements in internal capabilities that allow manufacturers to improve the quality and accuracy of features like edge preparation and honing.”

A number of key material changes head the list of turning breakthroughs. “One of the most noteworthy evolutions, outside of PCD and CBN, has probably been whiskered ceramic matrix inserts for heat-resistant superalloys. Coupled with the manufacturing capability to downsize these inserts, this development has been a game changer for aircraft engine component manufacturers, from both a productivity standpoint (high metal removal) and a cost-savings standpoint due to reduced consumable spend via downsizing programs,” said Coomer.

Chipbreakers have also been subtly changed by the technologies that are being used to process them. “New laser and wire technology helps create cleaner and more accurate forms, while new coating and substrate preparation enables more control over the surface area and texture of the insert to provide either smoother or coarser surfaces,” he said. “Perhaps the biggest change is the ability to modify designs and chipbreakers specific to an application. It is possible to customize anything, from coating and substrate to chipbreakers and edge prep, to fit a particular application or address a specific problem.”

Acceptance of quick-change replacement tool bodies that are swapped in and out quickly minimizes set-up time. “As with anything, the adoption of new tool bodies typically evolves to address reduction in set-up time through speed and ease of use, along with obvious design aspects that save money in the form of extended insert life or higher metal removal rates that increase part throughput,” Coomer said.