Parting & Grooving: Advanced Tech Delivers Quality Parts, Results
Article From: March 2020 Manufacturing Engineering, Jim Lorincz, Contributing Editor
Coolant-through toolholders, innovative insert blade designs head list of new solutions
One thing that’s certain in developing the most cost-effective solutions for part-off and grooving applications is that there is not just one way to approach the problem and meet basic process requirements for chip evacuation, tool life and surface finish. The end result, whether in ID or OD grooving or part-off, depends on matching the right cutting tool and toolholder and coolant delivery system with the right material application.
Challenging applications range from machining difficult-to-machine materials like superalloys; micro-sized turning part applications; deep, heavy-duty grooving; and small-part machining. Small-diameter Swiss-style part-off and small-diameter ID and OD face grooving applications pose their own challenges.
What follows are examples of product families that allow insert blades to be easily changed out and a look into the future of real-time tool monitoring for micro turning applications.
Improvement Via Coolant-Through
Kyocera Precision Tools Inc., Hendersonville, N.C., has developed its JCT (Jet Coolant Through) toolholders for ID and OD grooving for improved chip evacuation, better surface finish and longer tool life, according to Todd Rucker, technical center engineering manager, Indexable Tools Division. “For ID or OD grooving, getting sufficient coolant to the cutting edge is critical. The deeper you go, the more chance there is that coolant can be shielded from the cutting edge,” Rucker explained. “Part-off is a little different animal. When you part off, you’re always going to leave a little nub on one side or the other. As you get close to center, centrifugal force will separate what you are cutting, sometimes requiring secondary processing like facing to produce a clean part with a good finish.”
Rucker pointed out that JCT cut-off and grooving toolholders not only direct coolant to the top or rake surface of the insert, but also from the bottom up to the flank below the nose of the insert. “The result is always having coolant hitting exactly where you need on the cutting edge,” Rucker said.
Kyocera offers JCT technology across many of its product lines. For example, the KGD standard dog-bone style, two-ended cut-off tooling is offered with coolant through in the universal 3 mm and 4 mm widths for grooving and cut-off. KGD toolholders without coolant-through are available in widths from 1.3 mm up to 8 mm in two styles, a single piece integral or switchblade style that can use one body for many different blades for facing, face grooving, etc.
“The advantage of coolant-through toolholders lies in achieving good chip evacuation that curls chips nicely and directs them away from the workpiece. Keeping the cutting edge cool minimizes edge wear and maximizes tool life by keeping normal flank wear from progressing too quickly,” Rucker explained.
Kyocera has also developed a line of JCT holders for small parts machining with widths from 0.5 mm to 3 mm. The KGD-JCT series for external grooving and the KTKF-JCT holders for Swiss-style automated lathe machining are for applications like turning, grooving, back turning and cut-off. “The challenge with Swiss-style machines is to keep coolant directed at the various machining processes, some of which, like cut-off, grooving and back turning, are usually done away from the spindle. It’s possible for coolant to be blocked by the subspindle. The farther they are from the coolant source, the less coolant they are likely to get,” Rucker said.
Kyocera’s KGBF-JCT triangle platform for shallow grooving delivers coolant through the top clamp. “The main grooving depths from 0.6 mm to 3 mm maximum are much less than that possible with a dog-bone style, but there are three edges and the insert can be flipped in case of damage, so there are still two usable edges,” he said.
For ID grooving, Kyocera’s SIGE system for small diameters with 8-mm minimum bore has two cutting edges in a unique L-shaped tool and is coolant-through capable for flushing chips. “We have added a new tool, the SIGC, for very deep reach in 8-mm minimum bores without deflection,” Rucker said. “The SIGC insert is a very sturdy, single-edged round insert that screws on to the end of the boring bar, providing excellent coolant-through capability for superior chip evacuation performance.”
Parting-Off Family Delivers
The Multi F Grip part-off and grooving tooling line introduced by Iscar Metals Inc., Arlington, Texas, in June 2019 has lived up to expectations to dramatically increase feed rates for parting and grooving, according to Clay East, national product manager for GRIP products. “The reasons are a robust design and high-pressure JetCut Coolant delivered right to the cutting edge. We’ve really changed how shops are parting off material with the Multi-F Grip family of products,” said East, noting that the tools are designed for part-off but can also be used for plunge grooving but not side turning.
Iscar’s blade-and-block system features different pockets for the Tang Grip single-ended blade and the Do-Grip double-ended blade. Typical applications are parting off of thicker wall parts, 0.5-4.7″ (12.7-119.4 mm). “We start with a lot more material under the pocket of the insert and have created a block that holds and supports the blade underneath so the cutting forces go back into the blade. In a typical block-and-blade system, the blade is sticking out and adapter systems don’t actually support the blade underneath,” East explained. “Depending on the diameter of the material, we’re starting off with three blades that are very tall compared with the industry standard of 32 mm.”
Tang F Grip features a high-feed (HF) chip former that is tangentially mounted in the pocket and is performance driven. “With the high-feed chip former, we are able to push feed rates of 15 to 20 thou per revolution, which is three, four, and even five times faster than your average shop, parting off steel, alloy steel and cast iron with a 3-, 4-, or 5-mm insert. We’re testing it for other materials like Inconel 718 and getting fantastic results. We have to back off the feed rate for the Inconel 718 so instead of going 18 thou per rev we’re going 12 thou per rev but that’s still three times faster than the customer was doing before we walked in the door,” said East.
Iscar’s Do Grip option is a double-ended insert like a traditional dog-bone. “What differentiates our tool is when you get up to the 4-mm width and above, we have a twisted geometry which avoids the problem with traditional dog-bone inserts. When you are parting off or plunging with the traditional dog-bone insert, once you reach a depth that is equal to the length of that insert, you’re going to start rubbing on the backcutting edges of that insert. Our twisted inserts sit in the pocket where back-side cutting edges are angled so you have clearance on either side with the result that there are no depth limits with the twisted geometry insert,” he said.
Process Stability, Chip Formation are Critical
In grooving and cut-off processes, stability in the pocket, predictability and tool life are the hallmarks of productive operations, according to Jan Andersson, director, indexable inserts, YG-1 Tool Co., Vernon Hills., Illinois. To achieve that stability, YG-1’s TD part-off and grooving platform uses a longer insert, 20 mm, that prevents twisting or movement of the insert in the pocket.
“In parting and grooving, you can’t have torsional twist or movement in the pocket,” said Andersson. “That will show up in tool wear. If you see an insert with significant flank wear on the outside of the radii or flank wear that is further back on the insert on the lower side below the cutting edge, that’s almost always due to torsional twisting. You can tell from how the insert actually wears what is happening in the pocket. A longer insert gives additional contact area and stability to avoid insert movement.
“What is probably most important in groove turning is that you plunge you turn, you plunge you turn,” he continued. “And you must have sufficient feed rate to get deflection in the blade to create clearance, without moving the insert. That’s always been the challenge in those operations.”
Chip formation and management are critical to process stability, said Andersson. “You don’t necessarily break a chip in grooving; you form the chip into a clock spring, which is slightly compressed to be narrower than the groove you are generating (to avoid chip packing). You want to steer this chip so it doesn’t wrap around the part, the tool or cause chip evacuation issues in the chip conveyor,” he said.
“Once you get within the width of the insert, the force is going to be much greater than the tensile strength of the material being machined so basically that means you are going to break the component off. So you get the pip at the very end. Also, carbide is extremely strong in compressive stresses but not in tensile stresses. In cut-off, you have compressive stresses all the way to when the part breaks off and now you go from compressive to tensile stresses,” Andersson explained.
At this point, you can start seeing chipping of the insert. As a result, programming is very important. “Once you get within the width of the insert, it’s advisable to reduce the feed by 75 percent. What that does is give full feed rate on the width of the insert while reducing the change from compressive to tensile stresses. That will add significant life to the tool,” he said.
In a groove turning operation, the operator should plunge down to depth and then retract up to 0.01″ (0.254 mm) and then do side turning, according to Andersson. “In groove turning, you actually want the blade to deflect, creating clearance and reducing the cutting forces,” he said. “With deflection, the leading corner will dig in the material. By retracting, you basically go to depth, retract a few thousandths, side turn, go to depth and do that in a zig-zag motion from left to right, right to left utilizing both corners. That’s the most efficient way to get the best quality part and maximize tool life.”
Ceramic, Carbide Inserts for the Same Toolholder
Greenleaf Corp., Saegertown, Pa., offers ceramic and carbide inserts for grooving and cut-off that can be used interchangeably in its toolholders. The benefits of having the choice are obvious for meeting one of the most important customer metrics—lowest cost per part, according to Martin Dillaman, manager applications engineering. “To achieve the best value, the highest productivity and highest metal removal rate by application, Greenleaf offers a full range of PVD- and CVD-coated carbide and coated whiskered ceramic grade inserts that are designed consistently to deliver the longest tool life.
“Ceramics are used mainly for grooving,” he continued. “You can’t use ceramic for turning cut-off except for certain diameters. Material that breaks off during the cut-off operation can be catastrophic for the ceramic. Depending on the material, whiskered grades offer high wear resistance but with some limitations on feed rate.”
Greenleaf’s whisker-reinforced ceramics include WG-300 for machining nickel and cobalt-based super alloys; WG-600 with thermal properties and shock resistance for rough and finish turning; and WG-700 whisker-reinforced Al2O3 ceramic substrate for machining difficult-to-machine materials. The newest addition is the XSYTIN-1 phase-toughened ceramic for machining steels, cast and ductile irons, high-temperature alloys (interrupted cuts), scale and abrasive casting materials.
Greenleaf continues to regard developing the next levels of inserts for higher feed rates and better wear resistance as a priority. “XSYTIN-1 inserts can be fed at a higher rate but wear resistance isn’t as good as with the whiskered grades,” said Dillaman. “One thing that is extremely helpful for our customers when building tooling—whether ceramic or carbide—is that they fit into the same holders. They don’t have to buy multiple toolholders to handle ceramic and carbide.
“With ceramics, you can’t generate a chip form as you can with carbide inserts,” he continued. “Most ceramic inserts will just have a flat top on them without a chip form. Typical applications include high-temperature alloys for aerospace applications that can be run at higher surface footage with decent feed rates to achieve high levels of productivity. Materials include Inconel, Hastelloys and Monels, materials that are very difficult to machine with carbide. Carbide can be used for finishing at a slower speed where there may be sensitivity to the heat generated by ceramics, switching the carbide insert in the same holder.”
Sensor System Monitors Ti Parting-Off Geometry
Toolmaker Paul Horn GmbH, Tübingen, Germany, and the Kistler Group, Winterthur, Switzerland, a global producer of dynamic measurement technology, have worked together to develop the Piezo Tool System (PTS) for real-time monitoring of tools used in micro-turning applications. Developed specifically for monitoring Horn’s new WT geometry for parting-off titanium, the WT geometry has proved its practical value almost immediately for parting off titanium bone screws, according to the companies. In addition to reliable chip breaking, the adapted geometry ensures a soft cut, making higher feed rates and faster machining times possible. Horn reports that tests have shown that service life is increased by up to 60 percent.
The PTS consists of a force sensor inserted into the turning tool that provides information on its condition during machining. The extremely small piezo sensor can measure even the tiniest cutting forces to a high resolution, allowing the machine operator to identify a defect in the material being cut or tool breakage immediately, resulting in minimum waste and maximum quality.
The new PTS system is suitable for use in micro range turning applications where alternative measurement methods aren’t practical and can’t detect minute variations in the drive power of the main spindle motors. Even measuring acoustic emissions would not deliver satisfactory results consistently when small workpieces like bone screws are being machined. Visual monitoring also has to be ruled out due to the use of coolant and the high rotational speeds involved in the machining process.
The new PTS solution is compatible with selected standard turning toolholders offered by Horn. It doesn’t require any adjustment to be made at the control and can be used on any machine. Sensors can be replaced quickly and easily, according to Horn. Type 224 inserts with the new WT geometry are available in increments of 2, 2.5 and 3 mm in grade IG35. They are designed for type H224 holders.
Walter Expands Grooving System Capabilities
Walter USA LLC, Waukesha, Wis., has added Walter Capto toolholders and insert widths to its Walter Cut MX grooving system. Capto toolholders feature enhanced rigidity and modularity, while the tapered polygonal shape easily handles both torsional and bending forces, according to Walter. This interface can be used for lathes, and for turning/milling centers.
With new Walter Capto monoblock tools (C3–C6), the MX system can now also be used on machines with Capto interfaces. In addition, new parting blades work with automatic lathes and multi-spindle machines. Walter has completed the range with new grooving inserts and toolholders for larger insert widths. Where previously only 0.031″ (0.80 mm) to a maximum of 0.128″ (3.25 mm) were possible, the insert width now ranges up to 0.222″ (5.64 mm)—including the very common dimensions of 0.125″ (3.18 mm), 0.157″ (4 mm) and 0.196″ (5 mm). Maximum cutting depth is 0.24″ (6 mm). These extensions are intended to make new applications possible for users of the MX grooving system, from small-parts production, where a high degree of precision is needed, to job shops, where the focus is on fast, precise tool changes and cost efficiency.
The Walter Cut MX grooving system uses dowel pin location to prevent improper assembly of inserts into the holders. The dowel pin location along with the horizontal seating surface provide positioning accuracy and diameter repeatability for the inserts. This eliminates the need for “test cuts” after every change of the cutting edge of the insert, according to Walter. The four-edge indexable inserts can be used even after one or more cutting edge breaks. The inserts also have Walter-specific precision cooling and the Tiger·tec Silver coating grades, which extend tool life, according to the company.