When it comes to parting off and grooving processes, the long and the short of it is this: one, parting off goes deep—down to removing the pip—and two, grooving plunges are shallower and can include multidirectional turning.
Both processes depend on tooling systems that avoid the sources of catastrophic failure caused by machine crashes, poor chip control and lack of rigidity. Failure to match tooling correctly to the size and shape of material in the application can result in poor workpiece surface quality, reduced tool life, scrapped tools and wasted material in parting off. Vibration and excessive tool hang-out are especially challenging in parting off. Choices of toolholder types include modular, block and blade and integral systems with square shank, round shank, and quick-change connections.
The emergence of high-pressure, through-tool coolant systems is one way suppliers have impacted chip evacuation, especially in deep parting and internal grooving applications. Another proactive move—choosing modular style tooling—can minimize the risks associated with machine crashes that damage the whole tool assembly. In case of crash, only the insert or blade has to be replaced in a modular system.
These are among a number of ways tooling suppliers are advancing the art and science of parting off and grooving operations.
When it comes to depth of cut (DOC), the main difference is that parting off is typically a deeper process than grooving, but there are other differences as well, said Raymon Avery, product manager-turning, Ingersoll Cutting Tool Co., Rockford, Illinois. “In parting off, we often recommend a narrower insert to save material. Also, longer reach tools for deeper cutting depths make them a little weaker for grooving, so for grooving we like to shorten the tool extension as much as possible for longer tool life,” he said.
Ingersoll’s T-Clamp Ultra Plus system uses a block-and-blade toolholder style for parting off, and integral square shank toolholders for shallow grooving. The block-and-blade can be considered a modular system; it’s understood that the block is normally kept in the turret. The blade is fastened in the block and can be adjusted to accommodate the DOC. “If I’m parting off a smaller diameter, I can shorten the blade. If I’m parting off a larger diameter, I can extend the blade out. But in grooving applications we typically use a square shank integral tool with a fixed extension,” said Avery.
Width accuracy and surface finish are the main concerns when grooving. “For parting off we want to have good chip evacuation as we go down to the part center and we run out of speed. The front lead angle of the insert is important especially for those users who want a burr-free separation of the part. Right-hand and left-hand angle inserts remove the burr, or the pip, on the workpiece,” said Avery. Although burr-free parts are ideal, tool life and productivity are sacrificed when using lead angle inserts, so neutral type inserts are preferred.
In parting off operations, Ingersoll’s high-pressure T-Burst coolant-through tools channel coolant directly to the cutting edge, helping curl chips tighter to prevent jamming and insert failure.
The same types of inserts are typically used in parting and grooving toolholders. Ingersoll offers two primary geometries for parting off: one is sharp and positive cutting for gummy materials, and one isnegative for general purpose steels.
“To extend tool life in parting off, we recommend reducing the feed rate by 80 percent just before the insert breaks through to the center,” noted Avery, adding that this reduces the impact forces on the insert as the cutting speed approaches zero. “Also, for parting off larger diameter workpieces and on manual lathes, we suggest a tougher grade insert to account for damage that might occur as the part breaks free and sometimes pinches the insert,” he said.
Avery highly recommends coolant for parting off for chip evacuation, even on manual machines. “Also, the turret and tools must be properly aligned on center since cutting above or below can impact tool life, surface finish, and chip control,” he said.
Regarding stability, parting is straightforward, plunging toward the axis of the workpiece from the diameter, according to Mark Filosemi, senior product manager, Kennametal Inc., Latrobe, Pa. “When parting off you only have to worry about cutting the workpiece in one direction, but the challenge is that you may have to reach far away from the base of the tool,” he said. “In external applications, grooving involves working along the surface of the workpiece where you have more options of holding the tool, increasing process stability while moving in multiple directions.”
In 2016, Kennametal launched its Beyond Evolution system to address the challenges of both parting and grooving processes. “Beyond Evolution is a single-sided grooving and cut-off system that also performs multi-directional turning,” said Filosemi. “It incorporates a proprietary Triple-V seating feature that provides functional stability and minimizes vibration. Coolant is directed across the top of the insert precisely to the cutting zone underneath the chip to control temperature and improve chip control in grooving, cut-off, and multi-directional turning applications.”
Beyond Evolution’s Triple V creates maximum stability by clamping, not only on the top and bottom of the insert but also on the back of the insert to keep it from twisting. “Shops looking for tighter tolerances and good surface finish benefit from Beyond Evolution’s tight tolerancing and indexability,” said Filosemi. “Shops that handle shorter runs want to stock tooling that can be used in multiple applications.” Beyond Evolution covers applications including face grooving, cut off, grooving, profiling, multidirectional turning and plunging, he noted.
Filosemi stated that active coolant control improves performance by deflecting coolant not only across the front of the insert but around the corners in multidirectional turning. “Workpiece materials determine the grades that we use for inserts,” he said. “For softer materials, sharper positive cutting edges result in freer flowing material that doesn’t stick to the insert. Harder materials will need a stronger edge to prevent chipping and flaking.”
Parting off tools go deeper and groove turning tools are designed to resist axial forces, according to Sarang Garud, product manager, Walter USA LLC, Waukesha, Wis. Walter’s turning tools—available with standard ISO square shanks and boring bars, as well as with Walter Capto C3 to C6 interfaces—include three cut off and grooving style inserts and toolholder systems. They include SX single side, GX double-side, and MX style (similar to GX but with four self-aligning edges).
SX-style tooling for cut-off and deep grooves fits on mono-block tools with internal cooling for multi-spindle machines, automatic and manual lathes, while GX style double-sided tooling is the classic dog-bone style and is the “huskiest and most stable for both parting and deep grooving multiple applications,” said Garud. Geometries include sharp (UF8), positive (CF5) and universal (UF4/UD4). He noted that grooving to a cutting depth of up to 33 mm and parting off to a diameter of up to 65 mm with double-sided inserts is possible. The GX system can be used both for parting off as well as groove turning.
“Geometries are intended to get chips out of deep DOCs by curling them into clock springs. We grind the backsides of GX [tools] so they can go deeper,” said Garud. “The GX 24, for example, is a 24-mm length insert that you wouldn’t expect to go deeper than 23 mm. [But] if you take the backside off the insert it opens up the DOC and you can put a blade on it that can go quite deep in total DOC.”
Each of Walter’s three styles of grooving and part-off tools use the company’s Tiger•tec Silver PVD grades. This provides resistance to high temperature in connection with high toughness, particularly when parting-off to center, according to the company. Grooving inserts with Tiger•tec Silver PVD aluminum oxide coating, for example, are used for stainless steels, steel materials, and materials that are difficult to machine. Walter also has uses Tiger•tec CVD grades for machining steels and cast irons.
“There is a definite trend toward smaller parts, Swiss machining, and near net shape,” said Garud. “Ground geometries that are very up sharp are increasingly in demand. The insert in the MX system, for example, can be indexed easily right on the machine, a big advantage with gang tooling in Swiss-style machines.”
With the new Walter Capto monoblock tools, the MX system has been expanded to be used on machines with the Capto interface. In addition, there are new parting blades, such as those used on automatic lathes and multi-spindle machines. Walter has completed the range with new grooving inserts and toolholders for larger insert widths. The MX Insert widths range up to 5.65 mm, including the common dimensions of 3.175 mm, 4 mm and 5 mm, with a maximum cutting depth of 6 mm.
Iscar Metals Inc., Arlington, Texas, is releasing its new Multi F Grip part-off and grooving tooling line. “We’re going to change things up more than a little bit because we have figured out a way to double, triple and even quadruple feed rates for parting and grooving,” said Clay East, national product manager-Grip. “What’s involved is a complete redesign of tooling, making it more robust and making sure that high-pressure JetCut coolant is directed right at the cutting edge.”
Multi F Grip is primarily for parting but can also be used for grooving. “We’re releasing the platform in 2 mm up to 5 mm widths,” said East. Iscar is aiming for a system that is robust and rigid. “Part-off tools need a little more hang-out and require rigidity because you are parting from the outer diameter to the center for separation. We like to have the narrowest tool for the job. Larger chips than necessary add up to waste of material and money. We’ll choose a tool that is 2-3 mm wide rather than 3-4 mm wide,” he said.
Tang F Grip is a single-sided insert, single-edge tool that is tangentially mounted in the pocket. It uses the same pocket with the same inserts as in some of Iscar’s slitting tools. Multi F Grip high-feed parting has a square blade with four pockets. It fits a mounting block accepted by all types of machines for parting up to 120-mm max diameter and a minimum 2-mm insert width.
The new Tang F Grip HF (high-feed) chipformer is currently available in Tang Grip. The DoGrip option is a double-ended insert like the traditional dog bone.
“What differentiates our tool is when you get up to the 4-mm width and above, we have a twisted geometry that avoids the problem with traditional dog-bone inserts,” East said. “When you are parting off or plunging with the traditional dog-bone insert, once you reach a depth equal to the length of that insert, you’re going to start rubbing on the back-cutting 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.
Iscar’s PentaCut insert with five cutting edges is a model for other Iscar products. Introduced 16 years ago, the PentaCut concept has been extended to parting and the Logiq 5 Grip adapter with five pockets. Penta products are tangentially clamped inserts with three points of contact for rigidity. Wedge clamping provides stability and no movement in the pocket for improved feed and reduced cycle time.
“Our goal is to reduce cycle time as much as possible by pushing tools harder and faster. For machines that can’t use the higher feed rate, we look at other ways, through surface footage or application approach, rather than feed rate,” East said.
Iscar offers modular systems, standard integral shank systems, and block-and-blade systems, as well as JetCut through-the-tool coolant, directed to the cutting edge. Materials such as titanium, Inconel or austenitic stainless steel tend to strain harden during the cutting process, forming long and tangled chips. Coolant supplied efficiently to the cutting zone decreases flank and cratering rates. This leads to longer tool life and a better-machined surface finish, according to the company.
East recommends ground-edge instead of molded inserts for critical aerospace grooving. “For example, repeatability on a groove after the manufacturer is four operations and $40,000 into machining an aerospace part is essential when one little grooving failure can scrap the whole part,” he said.
Horn USA Inc., Franklin, Tenn., tackles the common problem of rigidity in part off with its modular 960 grooving system (see photo on page 82). “In part-off tools, lack of rigidity results because there is a lot of tool sticking out without a lot of material underneath,” said Edwin Tonne, training and technical specialist for Horn USA.
“The 960 system offers a higher level of rigidity than part-off blades because of the larger support under the cutting edge and its compact design. In turn, this results in flat part-ing-off surfaces, even when working larger workpiece diameters,” he said.
Components of the 960 system include the basic holder, which is configured for VDI, BMT, and other common turret specifications; an intermediate cassette holder; and a cassette containing the cutting insert. The 960 modular grooving system features various machine-specific benefits that result in the need for fewer tools and less space, leading to a reduction in tooling inventory, according to Tonne.
The 960 system offers options for coolant delivery, depending on the application. “Cassettes which are available in left-hand or right-hand options are supplied with coolant internally via the clamping finger and via the support,” he said. “Cooling via the clamping finger cools the chip-to-cutting edge interface, which has a positive impact on chip breaking and process reliability. Cooling via the support reduces flank wear and has a lubricating effect on the flanks of the grooving insert.”
The basic holder interfaces with the turret on the lathe and then the intermediate holder, which is height adjustable. The cassette is the “business end” where different insert options and chip breakers are available for various materials and applications.
“The 960 system is used by many for parting off due to its rigidity and stability, especially in machining alloys like titanium,” said Tonne. “In my experience, part-off tools are one of the most scrapped tools in a shop because of their instability.”
Applications are to be found throughout the machining spectrum, according to Tonne. “Swiss-type machines, medical applications, automotive as well as applications up to 4″ [101.6-mm] diameter parts are possible with standard cassettes. The 960 system can run on a broad cross-section of machines, including mill/turns, Swiss-style, two-axis lathes, multi-spindle and rotary transfer machines, among others,” he said.
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