In search of turning&#39;s sweet spot - metal lathe carbide insert

 2024-06-22 10:31:12

To try and prevent further crashes, Odekirk consulted with CNC Broach Tool’s John Gardner, who recommended a larger cross-hole for the relief, but the customer didn’t want any revisions to the part design. “They said, ‘We’ll manufacture them ourselves if you guys can’t figure it out,’” Odekirk said. “We said, ‘We’ll figure it out, no problem whatsoever.’”

The duMONT Minute Man tooling system allows users to broach through and blind keyways, keyways in a tapered bore and shaped or splined holes. Image courtesy of duMONT.

Alan holds a bachelor’s degree in journalism from Southern Illinois University Carbondale. Including his 20 years at CTE, Alan has more than 30 years of trade journalism experience.

When blind-keyway broaching, CNC Broach Tool recommends creating a relief area in the part to push chips into and prevent chip packing. The types include cross-hole (top), groove (middle) and notch (bottom). Images courtesy of CNC Broach Tool.

Whichever approach is most economical, Gardner emphasized the need to make a mental leap when it comes to broaching on CNC lathes and mills. “People have this whole backwards notion about broaching on a CNC machine,” he said. “They just can’t visualize a different way of doing it, so they have a resistance to doing it on their lathe or mill.”

Muthig began single-point shaping with CNC Broach indexable-insert broaches after it quoted producing the crank adapters complete in the lathe without manually loading parts into the machine. “We load bar stock into a machine and out comes a finished part that’s ready for packaging and shipping,” Odekirk said, adding that the job involves annually producing 40,000 to 60,000 of each adapter.

While the vast majority of indexable inserts are disposed of or recycled once they are worn, Sanieski said duMONT’s broaching inserts, which contain 13 percent cobalt and are heat-treated to a hardness greater than 68 HRC, can be resharpened up to five times, depending on insert condition and, therefore, how much material must be ground off.

When broaching blind keyways, Ron Odekirk at Muthig Industries emphasized that it’s critical that chips don’t pack together at the end of an indexable-insert tool’s stroke. This essential element was reinforced after the multifaceted parts manufacturer experienced three “pretty significant crashes” when applying indexable-insert broaches from CNC Broach Tool to produce, for an OEM, ¼"-wide × 2"-long (6.35mm × 50.8mm) blind keyways in a family of two different crank adapters made of cold-rolled steel.

Tapered tool, with a series of teeth of increasing length, that is pushed or pulled into a workpiece, successively removing small amounts of metal to enlarge a hole, slot or other opening to final size.

Engagement of a tool’s cutting edge with a workpiece generates a cutting force. Such a cutting force combines tangential, feed and radial forces, which can be measured by a dynamometer. Of the three cutting force components, tangential force is the greatest. Tangential force generates torque and accounts for more than 95 percent of the machining power. See dynamometer.

CNC Broach Tool offers indexable-insert tools for broaching blind keyways. The tools have setscrews on the side, but the inserts are open face. Image courtesy of CNC Broach Tool.

Sanieski added that the broaching system is not only suitable for generating keyways but also splines, squares, hexes and other internal and external features. “Anything you can think of, we can match a profile.”

Runs endmills and arbor-mounted milling cutters. Features include a head with a spindle that drives the cutters; a column, knee and table that provide motion in the three Cartesian axes; and a base that supports the components and houses the cutting-fluid pump and reservoir. The work is mounted on the table and fed into the rotating cutter or endmill to accomplish the milling steps; vertical milling machines also feed endmills into the work by means of a spindle-mounted quill. Models range from small manual machines to big bed-type and duplex mills. All take one of three basic forms: vertical, horizontal or convertible horizontal/vertical. Vertical machines may be knee-type (the table is mounted on a knee that can be elevated) or bed-type (the table is securely supported and only moves horizontally). In general, horizontal machines are bigger and more powerful, while vertical machines are lighter but more versatile and easier to set up and operate.

Nonetheless, Gardner pointed out that even though the operation involves taking a light DOC, it’s essentially a “controlled crash. You’re blasting the tool in there. Broaching is a very shocking operation.”

Minute Man broaches from duMONT accept keyway inserts, as well as slotting and special inserts, for application on CNC lathes and machining centers. Image courtesy of duMONT.

Milling cutter held by its shank that cuts on its periphery and, if so configured, on its free end. Takes a variety of shapes (single- and double-end, roughing, ballnose and cup-end) and sizes (stub, medium, long and extra-long). Also comes with differing numbers of flutes.

Cutter rotation is opposite that of the feed at the point of contact. Chips are cut at minimal thickness at the initial engagement of the cutter’s teeth with the workpiece and increase to a maximum thickness at the end of engagement. See climb milling.

Odekirk said he learned about the benefits of CNC Broach Tool’s broaches online and, after watching a demonstration video, determined “if they can do it, we can do it; we just need to get a broach in here and figure it out.”

Space provided behind a tool’s land or relief to prevent rubbing and subsequent premature deterioration of the tool. See land; relief.

Uncoated inserts are acceptable for some applications, such as when broaching aluminum, but Sanieski recommends recoating inserts when cutting materials such as stainless steel and other challenging-to-machine materials.

Although Archambault estimates that trochoidal milling can reduce cycle times by 20 to 30 percent, he emphasized that the bigger benefit comes from extending tool life. In a titanium milling application, for instance, one customer was conventionally milling with the full diameter of a ½" (12.7mm) VariMill solid-carbide endmill. “They were happy with it,” he said. “We tried trochoidal milling and got five times the life on that cutter.”

CNC machine tool capable of drilling, reaming, tapping, milling and boring. Normally comes with an automatic toolchanger. See automatic toolchanger.

Space provided behind the cutting edges to prevent rubbing. Sometimes called primary relief. Secondary relief provides additional space behind primary relief. Relief on end teeth is axial relief; relief on side teeth is peripheral relief.

Machining operation in which metal or other material is removed by applying power to a rotating cutter. In vertical milling, the cutting tool is mounted vertically on the spindle. In horizontal milling, the cutting tool is mounted horizontally, either directly on the spindle or on an arbor. Horizontal milling is further broken down into conventional milling, where the cutter rotates opposite the direction of feed, or “up” into the workpiece; and climb milling, where the cutter rotates in the direction of feed, or “down” into the workpiece. Milling operations include plane or surface milling, endmilling, facemilling, angle milling, form milling and profiling.

Fluid that reduces temperature buildup at the tool/workpiece interface during machining. Normally takes the form of a liquid such as soluble or chemical mixtures (semisynthetic, synthetic) but can be pressurized air or other gas. Because of water’s ability to absorb great quantities of heat, it is widely used as a coolant and vehicle for various cutting compounds, with the water-to-compound ratio varying with the machining task. See cutting fluid; semisynthetic cutting fluid; soluble-oil cutting fluid; synthetic cutting fluid.

Tangential velocity on the surface of the tool or workpiece at the cutting interface. The formula for cutting speed (sfm) is tool diameter 5 0.26 5 spindle speed (rpm). The formula for feed per tooth (fpt) is table feed (ipm)/number of flutes/spindle speed (rpm). The formula for spindle speed (rpm) is cutting speed (sfm) 5 3.82/tool diameter. The formula for table feed (ipm) is feed per tooth (ftp) 5 number of tool flutes 5 spindle speed (rpm).

The dimensions (in inches) for when a chip breaks out of a cross-hole and when it starts to touch the other side of the hole, along with a selection of chips produced when broaching blind keyways. Image courtesy of Muthig Industries.

Odekirk said the crashes, the first of which happened a day or two after production began, didn’t damage the main spindle on the company’s Doosan 2600SY lathe, but they did permanently damage three tool bodies when the insert popped out. After each "full, hard crash," the machine was out of alignment, which required half a day to correct, he added.

Gardner suggested that maybe a chip was sticking to the end of the insert, causing the insert to pop out. Odekirk thought that scenario would be difficult to verify, but, sure enough, one day he was watching the machine when broaching suddenly stopped. “And there it is; I’m looking at this chip stuck to the end of the insert,” Odekirk said. “Any time you get material welding to your cutting tool, you have a problem. It significantly increases the cutting load.”

Angle of inclination between the face of the cutting tool and the workpiece. If the face of the tool lies in a plane through the axis of the workpiece, the tool is said to have a neutral, or zero, rake. If the inclination of the tool face makes the cutting edge more acute than when the rake angle is zero, the rake is positive. If the inclination of the tool face makes the cutting edge less acute or more blunt than when the rake angle is zero, the rake is negative.

The company did and produced five samples of each part, which the customer approved, without any issues, according to Odekirk. To break the chips and prevent them from packing at the end of the blind keyway, Muthig machines a cross-hole relief in each part, which is more suitable for this particular family of parts because adding a groove or notch relief would create a thinner wall that could reduce part strength.

The OEM, which had been producing the adapters in-house, turned the parts in a lathe and then moved them to a vertical machining center for broaching, he noted.

Cone-shaped pins that support a workpiece by one or two ends during machining. The centers fit into holes drilled in the workpiece ends. Centers that turn with the workpiece are called “live” centers; those that do not are called “dead” centers.

The insert was relatively fresh, with its coating still intact, so Odekirk said he examined the coolant line. Coolant was flowing through an ER32 collet, but spraying along the length of the tool without a clearly defined coolant jet directed at the chip. The company changed the coolant line so the flow was directed at the tool/workpiece interface and not just spraying everywhere. “Before, it was like cutting underwater,” he said.

“We want to have enough relief space so you’re not pounding chips in there,” Gardner said. “That’s the ultimate goal for blind-keyway broaching.”

Enlarging a hole that already has been drilled or cored. Generally, it is an operation of truing the previously drilled hole with a single-point, lathe-type tool. Boring is essentially internal turning, in that usually a single-point cutting tool forms the internal shape. Some tools are available with two cutting edges to balance cutting forces.

That mentality can quickly change, however, after a shop outsources, say, a couple hundred parts that need blind keyways to be EDMed at $25 a part and receives the parts with incorrect keyways 2 or 3 weeks later. “If you can blind-keyway broach in your own house, you’re saving money, time and the chance that somebody won’t scrap your parts,” Gardner said. “How do you beat that?”

Archambault noted the VariMill series is effective for trochoidal milling materials as hard as 60 HRC, and the toolmaker recently introduced the 7-flute VariMill II ER. “More flutes makes it even faster.” The ER stands for eccentric relief, in contrast to the primary relief and secondary relief found on most endmills, he added. “It’s one continuous form for the cutting edge clearance. That relief makes the edge much stronger.”

Machining operation in which material is removed from the workpiece by a powered abrasive wheel, stone, belt, paste, sheet, compound, slurry, etc. Takes various forms: surface grinding (creates flat and/or squared surfaces); cylindrical grinding (for external cylindrical and tapered shapes, fillets, undercuts, etc.); centerless grinding; chamfering; thread and form grinding; tool and cutter grinding; offhand grinding; lapping and polishing (grinding with extremely fine grits to create ultrasmooth surfaces); honing; and disc grinding.

“If you are paying attention and don’t run them too long and start chipping them, you can sharpen them quickly and won’t remove too much material,” he said.

2-D or 3-D path generated by program code or a CAM system and followed by tool when machining a part.

Odekirk added that Muthig also increased coolant concentration to enhance its lubricity and antiweld characteristics.

For shops that resharpen their inserts in-house, duMONT offers an accessory called a sharpening stem. It holds an insert at the correct angle—the angle of the face originally ground into the insert. “You just screw the insert onto the end [of the stem] and buzz it with a grinding wheel,” Sanieski said.

Machine designed specifically to run broaching tools. It is typically designated by operating characteristics (pull, push, rotary, continuous, blind-spline), type of power used (hydraulic, mechanical) and tonnage ratings. Broaching is also performed on arbor presses (manual and powered).

With those corrective measures in place, Odekirk said Muthig Industries continues to apply the broaches from CNC Broach Tools to produce crank adapters and has not experienced any crashes or other issues. “We are definitely familiar and comfortable with the technology and the manufacturer.”

Steve Archambault, senior applications engineer at WIDIA Products Group, Latrobe, Pa., explained that trochoidal milling is a technique where the cutting tool, either a solid or an indexable one, takes a light DOC while following a circular motion, enabling users to engage more of the flute length in the workpiece than conventional milling while increasing the surface footage. When machining a 52 HRC workpiece via conventional milling, for example, the surface footage might be 80 to 125 sfm (24.4 to 38.1 m/min.), whereas trochoidal milling can achieve 500 to 600 sfm (152.4 to 182.89 m/min.).

Machining, normally milling, that creates slots, grooves and similar recesses in workpieces, including T-slots and dovetails.

Trochoidal milling a full slot requires a tool that has a diameter (D) approximately 70 percent of the width of the slot (b) being cut, where (F) is direction and the WOC (ae) is approximately 5 to 15 percent of the tool diameter, depending on the material and its hardness. Illustration courtesy WIDIA Products Group.

A chip became welded to an insert during blind-keyway broaching at Muthig Industries. Image courtesy of Muthig Industries.

Wheel formed from abrasive material mixed in a suitable matrix. Takes a variety of shapes but falls into two basic categories: one that cuts on its periphery, as in reciprocating grinding, and one that cuts on its side or face, as in tool and cutter grinding.

That’s according to Kevin Sanieski, CNC tooling system lead for The duMONT Co. LLC, Greenfield, Mass. One effective method is to use broaches that accept inserts, and the toolmaker offers those in its Minute Man line for application on CNC lathes and machining centers.

Hardness is a measure of the resistance of a material to surface indentation or abrasion. There is no absolute scale for hardness. In order to express hardness quantitatively, each type of test has its own scale, which defines hardness. Indentation hardness obtained through static methods is measured by Brinell, Rockwell, Vickers and Knoop tests. Hardness without indentation is measured by a dynamic method, known as the Scleroscope test.

Gardner compares blind-keyway broaching with an indexable-insert tool on a CNC machine to chopping down a tree with an ax. “If you swing the ax really slowly, the ax bounces off of the tree, but if you swing it fast, the ax bites and cuts,” he said.

Added to titanium-carbide tooling to permit machining of hard metals at high speeds. Also used as a tool coating. See coated tools.

Using a shaper primarily to produce flat surfaces in horizontal, vertical or angular planes. It can also include the machining of curved surfaces, helixes, serrations and special work involving odd and irregular shapes. Often used for prototype or short-run manufacturing to eliminate the need for expensive special tooling or processes.

When broaching on a lathe, the workpiece is positioned horizontally and gravity causes chips to fall down and away. Not so when broaching on a mill. With a mill, Gardner recommends creating a cross-hole, groove or notch relief in the part—an open area to push the chips into. The relief area needs to be large enough that coolant doesn’t simply flush and pack the chips into it, however. If the relief area is not large enough, the tool will pound into those packaged chips and potentially cause a crash, he said, adding that coolant flushes the chips right through a cross-hole and avoids that.

Being able to broach a blind keyway while keeping the part on the same CNC machine tool used to perform the other machining operations provides a significant improvement in setup, reliability and accuracy, compared to moving the part to a dedicated broaching machine.

Operation in which a cutter progressively enlarges a slot or hole or shapes a workpiece exterior. Low teeth start the cut, intermediate teeth remove the majority of the material and high teeth finish the task. Broaching can be a one-step operation, as opposed to milling and slotting, which require repeated passes. Typically, however, broaching also involves multiple passes.

Flexible-sided device that secures a tool or workpiece. Similar in function to a chuck, but can accommodate only a narrow size range. Typically provides greater gripping force and precision than a chuck. See chuck.

In addition, Odekirk explained that he examined where the broach was stopping within the cross-hole and determined that a chip breaks out of the hole at 1.9096" (48.5038mm) of the cut length and starts to touch the other side of the hole at 2.1504" (54.6202mm). “So we were stopping about 0.1" past the end of the cutting stroke. I said I’m only going to stop 0.04" past and see if that corrects the issue, because the chips were packing the backside of the hole.”

The duMONT sharpening stem holds an insert securely in place as the cutting edge of the insert is resharpened at its original angle. Image courtesy of duMONT.

For example, Muthig Industries applies broaches from CNC Broach at 550 ipm (13.97 m/min.) when producing blind keyways in parts made of relatively soft cold-rolled steel. (See sidebar below).

The company states that it designed the insert to pop out of the tool pocket to protect the machine spindle if there is not enough relief space. “Don’t get mad and blame the tool,” Gardner stated. “This is a clue that you do not have enough relief space or the chips are not evacuating the relief space and you are pounding into them.”

Resharpening inserts doesn’t suit everyone. Odekirk said Muthig Industries doesn’t resharpen its inserts, which average about 250 keyways per edge, because resharpening changes an insert’s dimensions and makes it nonstandard. “Then you have to either cut, measure and recut to get a good part or retouch the tool off every time you change it,” he added. “I don’t like to live in that world, which is why we also do not sharpen endmill diameters.”

Turning machine capable of sawing, milling, grinding, gear-cutting, drilling, reaming, boring, threading, facing, chamfering, grooving, knurling, spinning, parting, necking, taper-cutting, and cam- and eccentric-cutting, as well as step- and straight-turning. Comes in a variety of forms, ranging from manual to semiautomatic to fully automatic, with major types being engine lathes, turning and contouring lathes, turret lathes and numerical-control lathes. The engine lathe consists of a headstock and spindle, tailstock, bed, carriage (complete with apron) and cross slides. Features include gear- (speed) and feed-selector levers, toolpost, compound rest, lead screw and reversing lead screw, threading dial and rapid-traverse lever. Special lathe types include through-the-spindle, camshaft and crankshaft, brake drum and rotor, spinning and gun-barrel machines. Toolroom and bench lathes are used for precision work; the former for tool-and-die work and similar tasks, the latter for small workpieces (instruments, watches), normally without a power feed. Models are typically designated according to their “swing,” or the largest-diameter workpiece that can be rotated; bed length, or the distance between centers; and horsepower generated. See turning machine.

Grooves and spaces in the body of a tool that permit chip removal from, and cutting-fluid application to, the point of cut.

Microprocessor-based controller dedicated to a machine tool that permits the creation or modification of parts. Programmed numerical control activates the machine’s servos and spindle drives and controls the various machining operations. See DNC, direct numerical control; NC, numerical control.

Inserts from CNC Broach, which come coated with TiN, can also be resharpened, sometimes up to nine times, and most of its customers do not recoat them after resharpening, Gardner said. “I feel the coating helps get maybe two extra keyways per cutting edge, but with our product you’re already getting 100 to 200 keyways per cutting edge.”

When the tool comes out of the hole, the insert shouldn’t touch any metal, Odekirk said, noting the rectangular toolpaths get wider and wider as the broach progresses and makes the keyway deeper and deeper.

Main body of a tool; the portion of a drill or similar end-held tool that fits into a collet, chuck or similar mounting device.

To achieve the most-effective cutting speed, Gardner suggests holding the broach body in an ER collet with the backstop held directly in a CAT 40 or 50 spindle. He recommends to never hold the shank of the ER collet in a VDI boring bar sleeve to avoid generating taper in the ceiling of the keyway.

Value that refers to how far the workpiece or cutter advances linearly in 1 minute, defined as: ipm = ipt 5 number of effective teeth 5 rpm. Also known as the table feed or machine feed.

“You can basically run them in any lathe or milling machine,” Sanieski said. “Obviously, the bigger and more rigid the machine, the better the tools will operate.”

Despite being a fairly well-established technique, misconceptions about trochoidal milling persist. “A lot of people say it can’t be fast because you’re only in the cut 50 percent of the time, based on the circular motion,” Archambault said. “That’s not true.” This is because a tool might be going one speed when cutting and, as it is coming around to take the next cut, the tool is programmed to go five times as fast while traveling through air. “Eight-five percent of the time you are actually in the cut.”

Distance between the bottom of the cut and the uncut surface of the workpiece, measured in a direction at right angles to the machined surface of the workpiece.

Essentially a cantilever beam that holds one or more cutting tools in position during a boring operation. Can be held stationary and moved axially while the workpiece revolves around it, or revolved and moved axially while the workpiece is held stationary, or a combination of these actions. Installed on milling, drilling and boring machines, as well as lathes and machining centers.

Alan holds a bachelor’s degree in journalism from Southern Illinois University Carbondale. Including his 20 years at CTE, Alan has more than 30 years of trade journalism experience.

Measure of the relative efficiency with which a cutting fluid or lubricant reduces friction between surfaces.

“Specifically, in the blind-keyway situation, you didn’t really have an option before CNC systems came along,” he said. “We have found that ramping that tool out at a 45° angle, or thereabouts, helps keep that insert intact and clears the chip out of the way.”

Milling metals hardened to 52 HRC and harder with solid-carbide cutters doesn’t require a heavy-duty, high-performance machine tool when a machinist employs trochoidal milling and applies cutting tools with an appropriate substrate, coating and geometries.

For workpieces up to and above 65 HRC, WIDIA offers Vision Plus solid-carbide endmills. Archambault explained that those tools have a negative rake and an AlTiN coating, allowing them to effectively hard-mill with only an air blast or coolant mist rather than flood coolant because the coating oxidizes at a high temperature and creates a heat barrier. “The coating doesn’t work unless you get it hot,” he said, “and the heat tends to stay in the chip.”

“Speed is your friend” when broaching, Gardner added, but many users are afraid of hurting their CNC machines when applying the tools. Depending on the workpiece material, “I have to constantly remind them that they’re only taking a 0.001" depth of cut,” he said. “It’s just a very light shave. There is virtually no force involved. You could push that through with your hand.”

The challenge when applying this type of tool is that if a user cuts a blind keyway, simply retracts the tool from the cut and then continues to broach, the chips continue to build up at the bottom of the keyway and the insert inevitably becomes damaged, Sanieski explained. Therefore, the company provides a CNC program with its keyway broaching system that promotes continuous tool movement and cutting while eliminating the need to manually clear chips.

CNC Broach’s tools have setscrews on the side, but the carbide inserts are open face, Gardner explained, and the design of the insert directs the cutting force down into the tool centerline and seats the insert down and back in the tool body’s pocket. This design protects the machine if the insert, which has two cutting edges, experiences a lot of pushback or chips buildup in the relief area, he said.

John Gardner, owner of CNC Broach Tool LLC, Marina Del Rey, Calif., agreed that users can ramp, or taper, an indexable-insert broach out of a blind keyway when broaching it, but maintains that the programming required to do so is difficult to perform. In addition, the design of the broaching tool CNC Broach Tool offers isn’t well-suited for ramping out of the cut.

Ron Odekirk, production manager for Muthig Industries Inc., Fond du Lac, Wis., a parts manufacturer that applies tools from CNC Broach to broach blind keyways, described the toolpath as rectangular, and said the tool is fully withdrawn from the workpiece when it retracts from the hole after each cut.

In search of turning&amp;#39;s sweet spot - metal lathe carbide insert

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In search of turning's sweet spot - metal lathe carbide insert