In Plastics Machining, One Sharp Tool Does It All - carbide end mills for plastic

Allied’s new GEN3SYS XT Pro drills feature dual gundrills with four outlets for increased coolant flow and material-specific inserts with coatings developed in-house. “A unique connection design offers superior torsional loads while still allowing the convenience of insert swaps while the tool remains in the spindle,” Pisorn said.

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.

Rather than producing CVD-coated inserts at a temperature of 1,000 degrees C (1,832 F), which was typical in the past, Wilshire said CVD coatings generally are deposited using the medium-temperature CVD method in which the temperature ranges from about 700 to 950 C (1,292 to 1,742 F).

Each layer can have a different thickness, he said, adding that an aluminum oxide layer that’s thicker than the other ones enhances heat and wear resistance.

In terms of drilling, the number and type of holes to be made is generally the key determinant for opting to use replaceable-tip tools, according to Allied’s Pisorn. The more holes (from 1,000 to 50,000 or more) and the shallower (up to 13×D) the better.

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.

Reducing the time required to deposit a CVD coating is one way to increase cost efficiency. Czettl said Ceratizit’s target is a deposition rate of better than 2 µm (0.00008") per hour.

PVD coatings are most common for smaller diameter tools, he added, “because they help maintain sharper edges than thicker CVD coatings. Kyocera’s R&D efforts in PVD coating technology have resulted in our Megacoat coatings. With high oxidation temperatures and high hardness, they are ideal for running at higher speeds, resulting in reduced cycle times.”

In those situations, Wilshire said the only way to shorten cycle time is to increase cutting speed, and the CVD-coated insert can run at a faster cutting speed than PVD-coated or uncoated cermet and impart the needed surface finish.

Often used as a tool coating. AlTiN indicates the aluminum content is greater than the titanium. See coated tools.

“The end goal is a finer-grain structure with a precise grain alignment to improve the wear resistance, rigidity and toughness of the coatings,” Wilshire said. “If a crack does start, it is more easily arrested instead of letting it run through the coating and down to the substrate itself.”

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

Machining vertical edges of workpieces having irregular contours; normally performed with an endmill in a vertical spindle on a milling machine or with a profiler, following a pattern. See mill, milling machine.

For example, Sandvik Coromant Co. manufactures its diamond coating using hot filament CVD, a technology that is “totally different” from the one used to manufacture other CVD coatings, said Doug Evans, grade development specialist for Sandvik Coromant’s facility in Mebane, North Carolina. “These technologies cannot be compared.”

Tough, difficult-to-machine alloys; includes Hastelloy, Inconel and Monel. Many are nickel-base metals.

For deeper, large-diameter applications, the Iscar ModuDrill is a combination of replaceable head and indexable insert drills in larger diameters for depths beyond 12×D. The ChamIQ 700 family is offered in a diameter range of 33-40 mm in 0.5 mm increments and “some common fractional-inch increments,” he said. “The HFP carbide blades, which look more like a spade drill, fit into a range of steel adapter heads (MD-DFN), which also mount onto a long steel drill body (MD-BODY). A combination of two drill bodies and seven adapter heads cover the entire diameter range.”

Toolholding is vital to precision holemaking with replaceable-tip drills, he continued. “You have to remember that you have collective tolerances—of the body itself and then a tip on top of it.”

High-temperature (1,000° C or higher), atmosphere-controlled process in which a chemical reaction is induced for the purpose of depositing a coating 2µm to 12µm thick on a tool’s surface. See coated tools; PVD, physical vapor deposition.

At Mitsubishi Materials U.S.A. Corp., Schaumburg, Illinois, the company’s DIAEDGE STAW indexable drills “are unique in that they have cutting edge geometry that is the same as the edge geometry on our DIAEDGE WSTAR solid-carbide drill,” said Barry Griggs, assistant business development manager of cutting tools. “The wave designed cutting edge and center point gash is aimed at improving machined hole accuracy.”

Another drill that’s been on the market a while is the CoroDrill 870 series by Sandvik Coromant. But since its introduction in 2012, numerous refinements have been made. “We found that the body material was wearing, so we made it more wear-resistant, making the drill more rigid,” explained Loughney.

The initial release of the I-One will feature a single grade for the energy industry, with general-purpose grades and geometries to follow. I-One’s multilayer coating is geared to high or low speeds and is designed to tolerate heat and abrasion and prevent sticking. It is fully coolant-through.

While a small minority of the carbide inserts that the company sells are uncoated, Wilshire said about half of the cermet products don’t wear a coat.

However, any time an operator makes changes in the machine, something can always go wrong. For instance, they must take care not to drop wrenches and screws into the machine while replacing tools.

“You can push it more,” he said, “but usually there is a trade-off. If you push it too much, you get more scattering in coating thickness.”

Tool-coating process performed at low temperature (500° C), compared to chemical vapor deposition (1,000° C). Employs electric field to generate necessary heat for depositing coating on a tool’s surface. See CVD, chemical vapor deposition.

Replaceable-tip tools can also provide users with a significant reduction in setup times, Loughney added, for instance on transfer lines for automotive manufacturing. And, with the ever-pressing shortage of experienced manufacturing labor, quick and easy tool switchouts instead of more intensive setups help ease that burden.

Tool-coating process performed at low temperature (500° C), compared to chemical vapor deposition (1,000° C). Employs electric field to generate necessary heat for depositing coating on a tool’s surface. See CVD, chemical vapor deposition.

Wilshire said end users typically are locked into a particular feed rate to maintain a specified surface roughness.

Extremely hard material added to tungsten carbide to reduce cratering and built-up edge. Also used as a tool coating. See coated tools.

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.

“Playing with the coating thickness helps as well,” he said. “The thinner the coating, the less time you are spending in the chamber at the high temperature.”

To more than double the depths of cut previously available in its Multi-Master line of end mills, Iscar Metals Inc., Arlington, Texas, added replaceable-tip mills capable of reaching depths up to 1.5×D, said Tom Raun, chief technical officer.

“Some smaller sizes come in smaller shank diameters and shorter OAL (overall length) without a flange for Swiss lathe and live tool applications,” he added. “There are also drill bodies with integrated chamfering inserts.”

To minimize stresses in the CVD alumina, or Al2O3, coating, Evans said Sandvik Coromant developed a technology called Inveio to control the orientation, or structure, of the crystals in the coating. With the technology, the crystals are arranged in a uniform direction that points toward the cutting edge in a tightly packed structure that improves coating strength and extends tool life 25% to 30%, according to the company. The inserts are aimed at cutting ISO P steel and are suitable for machining stainless steel and cast iron.

Unlike PVD coatings, which are composed of multiple layers of coatings a few nanometers thick to achieve a coating that’s from 1 to 7 µm (0.00004" to 0.00028") thick, CVD coatings are usually from 5 to 20 µm (0.0002" to 0.00079") thick and sometimes thicker.

However, Evans said CVD is not suitable for brazed products because the process still reaches a temperature that melts the brazing. In addition, he said Sandvik Coromant does not offer solid-carbide, round-shank tools with nondiamond CVD coatings because those tools are typically long and slender, especially small-diameter ones, and tend to experience shape deviation at CVD’s elevated temperatures, which is not an issue with PVD.

Kyocera Precision Tools takes a different approach to tightly controlling the fine-grain structure of its CVD coatings by “continually playing with the compositions of the gases as they are introduced” to the coating chamber, Wilshire explained.

YG-1 touts its 7×D drill as the only one of its type on the market, Pulvermacher noted. “People really like it because 8×D gives up so much rigidity.”

He said the aerospace industry also cuts a significant amount of composites and stacked materials, and the thinner PVD coating helps maintain a sharp edge to avoid fraying the workpiece. Uncoated inserts might be suitable as well, he said.

The current crop of replaceable-tip milling and drilling tools features a host of new substrates, geometries, PVD coatings and coolant solutions geared for a range of applications across numerous industries and materials. As always, the decision to use a particular tool is application specific.

When drilling difficult-to-machine materials like stainless steel or titanium, steel bodies for replaceables might torque too much, Pulvermacher cautioned. For that reason, fabricators have tended to split their use of solid and replaceable tools for those materials about 50-50, depending on the diameter. For that to change, he said, replaceable-tip tools would have to outperform solid in the 0.5-0.75" (12.7-19.05 mm) range. Replaceable-tip drills might get the nod in larger diameters, where solid drills could cost up to $750; however, replaceables struggle under 7/16" (11.11 mm) because they are somewhat expensive relative to solids—and the small tools, screws and inserts tend to get lost.

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).

In contrast, PVD processes are based on purely physical response methods. A material vapor condenses on the substrate surface, and to ensure that the vapor particles reach the components and are not lost through the dispersion of gas molecules, the process takes place under vacuum conditions.

He estimates that at least 60% of turning inserts are CVD-coated. Milling and grooving, however, involve interrupted cuts, and he said at least 60% of the tougher PVD-coated inserts are used for those applications.

“We usually do that with a dry-blasting process,” he said, “which is better than wet-blasting processes.”

On the larger side, Iscar’s LogIQ-3-Cham is a three-flute, interchangeable-head drill in 14-23.9 mm diameters, in 0.1-mm increments and bodies in 1.5×D, 3×D and 5×D. “Eventually, the line will include all head sizes from 12-25.9 mm. The three-flute design will provide extended tool life and/or increased feed rates,” mostly for ISO-P and ISO-K materials, Ewing said.

SumoCham is available from 4-32.9 mm diameter in 0.1 mm increments, Ewing explained. Heads are offered in 10 geometries for various material groups and applications, and bodies are offered in 1.5×D, 3×D, 5×D, 8×D and 12×D through most of the diameter range. Each body accepts a range of head diameters: from 4-14.9 mm, bodies come in 0.5 mm increments, and from 15-32.9 mm, bodies come in 1-mm increments.

Inserts are available in sizes from 10-18.1 mm, and the VP15TF and DP5010 PVD coated grades feature tough carbide substrates and proprietary crystal coating technology. For machining a wide range of materials, from alloy steels to various types of stainless steel and cast iron, the VP15TF grade ranges from 100-400 sfm, Griggs added. “The drill body is made resistant to corrosion and abrasion by using a superior high-heat resistance alloy and a special surface treatment suitable to counter new hard-to-machine work materials.”

“Clearly, a small replaceable insert or tool head made of carbide costs less than an entire solid drill of the same diameter,” noted Andrew Pisorn, solid carbide product manager at Allied Machine & Engineering Corp., Dover, Ohio. And, by extension, using a range of replaceable-tip tools with a smaller number of steel body holders greatly improves operational and cost efficiencies by cutting down on one’s inventory of unique solid-carbide tools. “If your shop can minimize the amount of carbide in your tool cribs and drawers, you’re minimizing inventory costs.”

In contrast, he said markets big on machining heat-resistant superalloys and titanium alloys (ISO S), such as aerospace, apply more PVD-coated inserts to better shear those challenging materials.

Also for hard-to-machine materials, Sandvik Coromant’s recently introduced CoroMill 316 exchangeable milling heads are optimized for titanium and nickel-based metals. For titanium, grade 1745 with its 1.5×D cutting edge “is a little bit longer of a replaceable-tip end mill compared to our standard 316s,” explained Scott Lewis, aerospace industry specialist for Sandvik Coromant. To be released in the near future is grade 1710 for nickel alloy, which will also have 1.5XD capabilities. Both grades feature unique substrates and geometries and are currently available in the company’s solid-carbide end mills. These replaceable-tip end mills “can run, cutting data wise, quite close to what a solid is, with a solid being perhaps more rigid because it is shorter—a stouter setup,” Lewis said. “We also have very short, stout adapters for our 316s.”

“In the future, I can see CVD becoming more dominant,” Evans said, “because there’s more technology that’s coming that will allow us to put sharper edges on CVD-coated inserts.”

Replaceable-tip cutting tool suppliers offer numerous examples of how those tools surpassed solid-carbide versions. For instance:

Fabricators seeking smaller diameters can look to Iscar’s SumoCham line, now available down to 4 mm in up to 5×D applications, said Craig Ewing, national product specialist for Iscar Metals.

In addition to TiCN and Al2O3, nondiamond CVD coating materials generally are restricted to TiC and TiN. Although a single-layer CVD coating is possible, virtually all CVD-coated inserts have two or three layers. Brian Wilshire, technical center manager for Kyocera Precision Tools Inc. in Hendersonville, North Carolina, said most of the toolmaker’s CVD-coated grades start with a TiCN layer on the substrate, followed by an Al2O3 layer and topped with TiN.

Turning operations, in which an insert continuously cuts a workpiece material, enable CVD coatings to shine. Czettl said CVD-coated inserts are still dominant in turning because they effectively resist abrasion and wear and have a high level of hot hardness to combat carbide’s worst enemy: high temperature.

But what about performance? Ultimately, using replaceable-tip drilling tools generally does not mean sacrificing much penetration rate or tool life—to a point—experts assert.

Workpiece is held in a chuck, mounted on a face plate or secured between centers and rotated while a cutting tool, normally a single-point tool, is fed into it along its periphery or across its end or face. Takes the form of straight turning (cutting along the periphery of the workpiece); taper turning (creating a taper); step turning (turning different-size diameters on the same work); chamfering (beveling an edge or shoulder); facing (cutting on an end); turning threads (usually external but can be internal); roughing (high-volume metal removal); and finishing (final light cuts). Performed on lathes, turning centers, chucking machines, automatic screw machines and similar machines.

Almost all indexable inserts — estimated at about 90% to 95% — are coated, either with the physical vapor deposition or chemical vapor deposition coating method.

Aluminum oxide, also known as corundum, is used in grinding wheels. The chemical formula is Al2O3. Aluminum oxide is the base for ceramics, which are used in cutting tools for high-speed machining with light chip removal. Aluminum oxide is widely used as coating material applied to carbide substrates by chemical vapor deposition. Coated carbide inserts with Al2O3 layers withstand high cutting speeds, as well as abrasive and crater wear.

These drills are being used heavily in structural steel applications like beams and bracketing in areas such as bridge towers, Pisorn said. Planetary gears with flanges might feature 20 to 50 shallow holes; bearing rings for wind energy can feature 50-100 holes. Tube sheets for heat exchangers is another sound application. And, a filtration system plate for the paper industry might feature thousands of shallow holes.

“Typically, the harder, more wear-resistant grades go with a thicker coating,” Wilshire said. “If you are trying to improve toughness, you go with a thinner coating.”

XT Pro carbide inserts have a combination of substrate coating and geometry engineered to survive the wear of high-penetration drilling, which “inherently produces significant heat,” Pisorn noted. “Combating that heat well is critical to extending tool life and increasing drilling rates. We have worked closely with our coating team and partners to develop several new material-specific, proprietary, multilayer coatings designed to withstand increased heat thresholds.”

For the CVD process, the base substances used for the coating are vaporized before being supplied to the coating zone, reports toolmaker Ceratizit USA Inc. in Warren, Michigan. The vapor then either decomposes or reacts with additional base substances to produce a thin film on the cutting tool substrate.

While PVD-coated inserts have an edge over CVD-coated ones when it comes to market share, that may not always be the case as toolmakers work on developing technologies to improve the performance of CVD coatings.

“The key is making sure the initial coating layer adheres to the carbide and subsequent layers adhere to each other,” Wilshire said. “Obviously, if the coating doesn’t stick to the insert, it’s not going to do you any good.”

“It’s a niche product,” he said about CCX, “but we’re seeing steady growth as people find out about it and see the benefit of shortening the finishing process.”

Carbide isn’t the only cutting tool substrate being CVD-coated. CVD-coated cermet inserts are also available, such as Kyocera Precision Tools Inc.’s most recent advancement: the CCX CVD-coated cermet insert for finishing. Technical Center Manager Brian Wilshire explained that the thermal expansion rates of the cermet and the CVD coating enable the coating to achieve a strong residual compressive stress that prevents cracks.

Wilshire said the split is likely greater, with 70% to 75% of turning inserts being CVD-coated and only 10% of milling inserts being CVD-coated.

“For milling,” he said, “with the constant interruption, we have found — and everyone else has found as well — that PVD coatings for the most part are unrivaled in those applications.”

Reduction in clearance on the tool’s flank caused by contact with the workpiece. Ultimately causes tool failure.

“Most of the CVD-coated inserts we offer have a post-coating process to smooth the coating, such as polishing and brushing,” Wilshire said.

“Various grade options allow better flexibility and optimization vs. solid carbide tools” and feature proprietary Sumo Tec PVD post-coating technology that provides “improved toughness, improved flaking, and chipping resistance, which in turn provides very reliable and repeatable results.” Those grades are:

Slated for release midyear is YG-1’s I-One drill. “We’re performing extensive testing with it in the energy industry, with very good success,” Pulvermacher noted. It will exist alongside the company’s well-established I-Dream drill, which currently has several geometries: Dream Drill General for general purpose (carbon steel, iron); one for stainless (Inox); Dream Drill Alu (aluminum), High Feed (carbon steel, iron); and High Hard (up to 70 HRC).

Ability of the tool to withstand stresses that cause it to wear during cutting; an attribute linked to alloy composition, base material, thermal conditions, type of tooling and operation and other variables.

High-temperature (1,000° C or higher), atmosphere-controlled process in which a chemical reaction is induced for the purpose of depositing a coating 2µm to 12µm thick on a tool’s surface. See coated tools; PVD, physical vapor deposition.

For more information from Kyocera Precision Tools about its CVD-coated inserts, view a video presentation at cteplus.delivr.com/2bn2e

As a result, the DIAEDGE STAW demonstrates “excellent chip disposability and achieves high-efficiency machining,” Griggs noted. “STAW replaceable carbide tips/inserts are designed for extreme sharpness, precision, positioning and rigidity in our unique clamping system. The wavy edge design delivers a sharp peripheral edge to enhance cutting performance, complemented by a strong center point geometry for initial cutting at entry. A high helix offers a low-resistance drill pocket design that improves chip breaking for superior chip disposal.” The STAW’s clamping system has more material behind the tip for added strength and durability.

“You cannot compare CVD and PVD because the coating textures and chemistries are different,” said Christoph Czettl, R&D manager of cutting tools for Ceratizit Austria GmbH. “For example, with PVD on the inserts, the most common coating is TiAlN. With CVD, the most frequently used coating architectures are TiCN and aluminum oxide, so those are completely different types of coatings.”

For large-diameter applications, true helical flutes are the key to the success of the SRH series of replaceable mills by Carmex, said White. Helical flutes cut freer than straight-flute tools, he explained, although “solid thread mills are still the most efficient choice for anything under 1" (25.4 mm) thread diameter because you get more flutes in the cut and the geometry allows for higher cutting speeds and faster feed rates.” The SRH has been most successful in the oil and gas market, threading buttress and Acme threads in large diameters, he added.

“We went to a fine-grain cermet and refined the binder material so that it could accept a CVD coating,” he said.

Materials composed of different elements, with one element normally embedded in another, held together by a compatible binder.

The result is a TiCN layer with a strong columnar shape that’s perpendicular to the top surface of the insert, an alumina layer with tightly aligned small grains, and a top TiN coating where the small grain size enhances stability.

Strip or block of precision-ground stock used to elevate a workpiece, while keeping it parallel to the worktable, to prevent cutter/table contact.

Drilling sometimes takes a hybrid approach. Wilshire explained that the outer insert can be a CVD-coated one to better resist wear at a high speed when drilling while the center pocket accepts a PVD-coated insert, which has a 0 sfm at the center, and the surface footage only increases away from the center.

Abrasive process that improves surface finish and blends contours. Abrasive particles attached to a flexible backing abrade the workpiece.

Currently in the fundamental stage, Czettl said Ceratizit is researching zirconium-based CVD coatings, such as ZrCN, to replace TiCN. With three other people, he authored a paper that stated that some reports suggest that there are advantageous mechanical and thermal properties of Zr(C,N) over Ti(C,N) coatings. One of the main questions involves costs: Are there deposition rates that make this economical?

The workpiece material also determines which type of coating to select. Evans said industries that machine a lot of carbon steel (ISO P and ISO K materials), such as automotive and heavy equipment, use a lot of CVD-coated inserts because of the heat protection they provide to the carbide substrate while resisting crater and flank wear. The coatings are effective even when cutting stainless steel (ISO M), he said.

Metal-removing edge on the face of a cutter that travels in a plane perpendicular to the axis. It is the edge that sweeps the machined surface. The flat should be as wide as the feed per revolution of the cutter. This allows any given insert to wipe the entire workpiece surface and impart a fine surface finish at a high feed rate.

Substances having metallic properties and being composed of two or more chemical elements of which at least one is a metal.

Meanwhile, Kyocera Precision Tools Inc., Hendersonville, N.C. is noting increased demand for smaller, modular indexable end mills, said Technical Center Manager Brian Wilshire.

“Wiper inserts can be used for some of those applications,” he said, “but only if you are machining parallel or perpendicular to the centerline. Anything with profiling cuts or angled cuts, the wiper won’t really help.”

Post-treatment also helps reduce stresses that can cause cracking as the coating shrinks more than the carbide during the CVD process, Czettl said. In addition, Ceratizit tries to convert the residual tensile stresses into a crack-resistant compressive stress, which is a topic of numerous peer-reviewed publications as well.

The modular part of the system “is that there are indexable insert heads that also mount onto the two drill bodies,” said Ewing. They are offered in eight metric sizes (33-40 mm) and two inch sizes (1.375" and 1.5") and use standard SOMX inserts from the DR Twist line. “They also use guide pads from the BTA Deep Drill line. The drilling depth of this system is in the 16.5-17" [419-432 mm] range.”

In addition, some solid-carbide, round-shank tools are CVD-coated with diamond, which is a special form of CVD coating.

The option of smaller diameter, high-feed end mills is “a popular option for harder tool and die steels, especially in the aerospace and mold industries,” Wilshire continued. “Customers tend to run the replaceable-tip drills and indexable end mills faster than their solid-carbide counterparts to shorten cycle times because the replacement costs are less and the time to index is shorter.”

To effectively coat cermet via CVD, Wilshire said the toolmaker had to upgrade the substrate’s grain structure and minimize leaching of the binder.

Wilshire added aluminum and plastics to the list of materials that can be cut effectively with highly polished, uncoated inserts.

Machining grooves and shallow channels. Example: grooving ball-bearing raceways. Typically performed by tools that are capable of light cuts at high feed rates. Imparts high-quality finish.

“The biggest thing we’ve done is introduced new grades optimized for steel, stainless steel and cast iron,” he continued. “Our Zertivo technology uses a PVD process, and we are able to achieve better bonding between the substrate and coating to where we have significant improvements in edge line security—resulting in longer, predictable tool life.” Grades include –PM 4334 for low alloyed and carbon steels, –MM2334 for stainless and –KM3334 for cast iron. While there is no grade specifically for heat-resistant materials, Loughney added, “we can cross over our geometries into those areas” for multiple industries.

Jim White, national sales manager for Carmex Precision Tools LLC, Richfield, Wis., concurred. “The reason most customers go with indexable is versatility—using one holder for multiple pitches—or cost,” he said, adding that “indexable thread mills are more cost effective in large-thread diameter applications or low-volume jobs where cycle time is not a consideration.”

The Mini-Mill series of tools—including Nanmill, Nan3feed, Heli4mill, Heli3mill and Micro3feed—complement Iscar’s solid-carbide tools with diameters starting at 0.312-0.75" (7.92-19.05 mm) with multi-edged inserts for 90o milling and fast-feed milling, he explained.

Carmex recently introduced new coatings for its Slim MT line. “This nano coating can handle temperatures 30 percent higher than TiAlN and is 25 percent harder than other coatings typically used for indexable cutters,” said White. “These coatings outperform others in high-temperature alloys like inconel and titanium.”

“Because of the temperature difference in the furnaces,” Evans said, “you can put a sharper edge on a PVD-coated insert.”

“For example, if I would expect to get a thousand inches of tool life with a solid, then I would expect the same from a modular tool—but of course exceptions apply,” said Bill Pulvermacher, director of marketing for YG-1 Tool Co., Vernon Hills, Illinois. “I would expect the overall penetration rate of the solid to be just a little bit higher.” Furthermore, some users say replaceable-tip drills over 0.5" (12.7 mm) tend to perform better in lathe applications “because they are much more tolerant of the misalignment that lathes tend to have.”

“So you can increase the speeds, shorten cycle time and increase throughput,” he said about the combination of coatings.

When weighing the choice of replaceable-tip mills and drills or solid-carbide tools, consider this succinct statement from one industry expert: carbide equals cost.

Generic term for a curve whose shape is controlled by a combination of its control points and knots (parameter values). The placement of the control points is controlled by an application-specific combination of order, tangency constraints and curvature requirements. See NURBS, nonuniform rational B-splines.

“In some cases,” he said, “in low-carbon steel we are able to run twice the cutting speed with CCX compared to our PVD-coated cermet.”

Because carbide and coatings have different rates of thermal expansion and contraction, Wilshire said the CVD coatings deposited with the older, high-temperature CVD method tended to develop microcracks. MTCVD helps reduce or eliminate residual cracks in the coating.

“These screw-in heads are available from 8 mm up to 32 mm in diameter and can be mounted on extensions of various lengths,” he explained. “The smaller diameters have replaced solid-carbide tools in many instances. The advantages of both the replaceable-tip drills and modular, indexable end mills are similar: lower replacement costs, because instead of the entire tool being composed of carbide, only the portion actually doing the cutting contains carbide; less variability in position after indexing; the ability to easily change grades or geometries when cutting different workpiece materials; and less downtime when replacing worn tools.” However, he added, solid-carbide tools still provide better rigidity, deep-hole drilling and greater depth of cut capabilities when milling.

Besides keeping deposition time as short as possible, toolmakers try to keep the coating temperature as low as possible to prevent the process from damaging the carbide substrate, such as by brittling it. However, he said too low of a temperature risks creating adhesion problems.

Another inventory factor to consider: Shops that routinely send solid-carbide tools for regrinding must keep an adequate supply of solid tools in reserve to maintain production, said Patrick Loughney, a product manager at Sandvik Coromant, Fair Lawn, N.J.