“When they invented this stuff, tooling people loved it because it just carves up cutting tools,” he said. “And the cost justification wasn’t there to go to CBN or PCD because it wears that stuff out too.”

Crystal manufactured from boron nitride under high pressure and temperature. Used to cut hard-to-machine ferrous and nickel-base materials up to 70 HRC. Second hardest material after diamond. See superabrasive tools.

Using wipers allows for increased feed rates, within the appropriate range for the finishing stage, while reducing the contact time, meaning longer tool life. The higher feed rate also leads to better chip control and evacuation, which helps to improve surface quality.

“A larger radius is typically preferred in finishing so long as the part geometry allows for it,” said Goss. “The larger radius helps to more efficiently smooth out the material and acts almost as a wiper. With a larger nose radius, you can up the feed rate slightly while still maintaining that high surface quality. In thin-walled applications however, a smaller nose radius will reduce radial cutting forces, which may lead to deflection and vibration that can negatively affect surface finish.”

Howard also noted that ceramic tools are a good choice for cutting compacted graphite iron, which he described as a fairly new type of cast iron that’s very dense and strong. Today, he said, CGI is used to make many diesel engines because it allows manufacturers to use a smaller engine block that can take more compression.

Lobsinger added that features such as full circle holes in the face of the part should be added after the finishing process rather than before. By incorporating the holes after the finishing operation, the operator does not need to perform interrupted cuts, which can be detrimental to surface finish quality.

A relatively new entry in the ceramic tool market from Greenleaf is its Xsytin-360 line of solid-ceramic endmills. Launched last year, Xsytin-360 endmills come in standard diameters down to 3/8", so they can cut much smaller features than indexable tooling.

“Some customers were using OD grinding or surface grinding for hardened materials just because that’s the traditional method that has been used,” Dillaman said. “But with ceramic inserts, you can remove large amounts of material much quicker than you could in a grinding application.”

The experts agree that tooling and fixturing play significant roles in achieving a quality surface finish. If fixturing is not rigid, it can lead to chatter, which could compromise the finish. It’s also important to make sure the toolholder has the shortest possible hangout to help keep it rigid. The workpiece and cutting tool should be adequately supported so that there is no vibration during the finishing operation.

Choosing an insert with a positive rake angle is preferred for finishing. According to Goss, a positive rake angle helps create a sharp edge for shearing off the material. For the roughing stage, he suggested working with a negative rake, because it's going to put more strength behind the cutting edge to remove more material, providing a better starting point for the finishing stage.

For finishing, Greenleaf recommends a ceramic insert with a smaller land, and a sharp edge with no hone if the material is soft. Greenleaf

Dimension that defines the exterior diameter of a cylindrical or round part. See ID, inner diameter.

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.

Cast iron having a graphite shape intermediate between the flake form typical of gray cast iron and the spherical form of fully spherulitic ductile cast iron. Also known as CG iron, CGI or vermicular iron, it is produced in a manner similar to that of ductile cast iron but using a technique that inhibits the formation of fully spherulitic graphite nodules.

“Chipbreakers are absolutely recommended,” said Andersson. “There’s no question about it. When you start looking at the macrogeometry, the top surface of the insert is in direct relationship to the material machining and the chip area. So, if you're taking a lower DOC with a lower feed rate, the chipbreakers will look different than if you take a higher DOC with a higher feed rate. You need the right chipbreaker for the material, because chipbreaking will become crucial to maintain a good surface finish consistently, especially across multiple parts.”

In addition, he noted that users of ceramic inserts in these cases aren’t limited by the form on a grinding wheel. Instead, they can program different cutting profiles to meet different requirements.

“Typically, a 0.02-in. DOC is ideal for finishing applications,” said Andersson. “It’s also important not to take too large a DOC, as most of the material should be removed in the roughing and medium stages. You generally want a light DOC and a lower feed rate.”

Another invention of late that may interest shops that haven’t tried ceramic tools in a long time is a patented material called Bidemics. Howard describes Bidemics as an advanced ceramic designed to conduct more heat away from the cutting edge.

“One thing people don't necessarily think about is how the inserts sits in the pocket,” said Andersson. “The pocket design can play a significant role. A toolholder pocket that is too open can reduce the contact area between the insert and the pocket (for example, WNMG inserts), which then introduces movement into the pocket. This leads to microvibration, which has a negative impact on surface finish.”

Even if shops aren’t put off by the higher cost of ceramic tools, shops may be unable to make proper use of the tools because their equipment can’t match the speeds for which ceramic tools have the capacity. Or shops actually may be afraid to reach those speeds.

“The direction in which the tool is cutting can also be important to pay attention to,” said Lobsinger. “You want to make sure that you are directing the forces of the operation into a well-supported portion of the part; machining away from the support can lead to vibration, which can also affect tool life, and your surface finishing will definitely be compromised.”

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Cutting tool material consisting of natural or synthetic diamond crystals bonded together under high pressure at elevated temperatures. PCD is available as a tip brazed to a carbide insert carrier. Used for machining nonferrous alloys and nonmetallic materials at high cutting speeds.

Faster cutting speeds help raise the temperature slightly, which generates a better surface finish. It also prevents that material from sticking to the top or the face of the insert. Operators should increase the speed slightly compared to roughing applications, but not so much that it will have a negative impact. If built-up edge on the flank of the insert occurs, the feed should be increased.

“The big thing with ceramic is it conducts heat better than anything else,” said Steven Howard, marketing and engineering manager at NTK Cutting Tools USA in Wixom, Michigan.

Andersson noted that one overlooked aspect of this process is how the insert grade, particularly as it relates to coatings, affects surface finish.

“Traditionally, you have to use an electrode to burn material out of a hardened workpiece,” he said. “With our solid-ceramic endmills, (you can) use the endmill to remove the bulk of that material instead of having to create an electrode to remove the full amount of material.”

“With finishing you're going to be using the higher surface footage, so faster speeds with lower feed rates,” said Matt Goss, applications engineer and project development, Greenleaf Corp. “And, generally, you're going to have a smaller depth of cut. But it's also important that you make sure the feed rate coincides appropriately with your desired surface finish. If you're using too light of a feed rate, it can cause excessive rubbing and premature wear of the insert, which is going to lead to poor surface finish.”

Using the best insert for an application helps to produce quality cuts. Speaking with insert manufacturers about new applications can help determine which insert will produce a quality surface finish in turning operations. The machining conditions and component material determine what type of insert is appropriate, but some general features can be recommended for the finishing stage.

When cutting with common tool materials, such as carbide, CBN and PCD, heat is not conducted away from the cutting edge, which eventually breaks down as a result, Howard explained. By contrast, he said, ceramics do a good job of transferring heat away from the cutting edge, thereby extending its life and the life of the tool as a whole.

When people tell Howard that they tried ceramic tools for a particular application and it didn’t work, he asks when they tried ceramics. Sometimes, it turns out that the failed ceramics experiment wasn’t even in this century. So he tells these people, “Well, we’ve invented a few things in the last 20-some years.”

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When it comes to ceramic cutting tools, don’t believe the old saying, “What you don’t know can’t hurt you.” A lack of knowledge about ceramic cutters can put a big hurt on shop productivity. What’s more, even shops that are somewhat informed about ceramic cutting tools often aren’t getting the most out of the tools because they are unaware of lesser-known applications that are a good fit for ceramic machining, let alone recent developments that make the ceramic option more attractive than ever.

Substance used for grinding, honing, lapping, superfinishing and polishing. Examples include garnet, emery, corundum, silicon carbide, cubic boron nitride and diamond in various grit sizes.

A ceramic endmill removes material much more quickly than an electrode, he said, and use of an endmill should slash the number of electrodes needed for the overall process, as well as the time spent creating them.

Lobsinger added that in cases where the operator runs into chatter, varying the RPM cycle, where the SFM varies between low and high, can help get rid of or at least reduce harmonics. This programming tip can help improve turning finishes.

Another lesser-known ceramic application cited by Howard is cutting powder metal, which is popular in the automotive industry.

Dillaman also reported that Greenleaf got good results when it pitted ceramic inserts against PCD in an aluminum-cutting application for a customer. He said the ceramic inserts that were used showed little wear and held up as well as their PCD counterparts. The biggest downside for ceramic inserts was the accumulation of some built-up edge that had to be removed.

“You may still have to do some finish work with an electrode, but the amount of electrodes consumed should be much reduced,” he said.

To ensure a high-quality surface finish, operators need to take off the right amount of material in the roughing and medium stages so that finishing can take place with few or no errors. Any issues during earlier stages can lead to poor surface quality.

As for Greenleaf’s solid-ceramic endmills, Dillaman said they can speed up machining of hardened materials normally done entirely with EDM operations.

Ceramics “run so much faster” than carbide, Howard said. “And with that comes a lot of fear. People say, ‘Wow, I can’t control this thing because I don’t have enough knowledge or skill.’”

He pointed out, however, that NTK makes ceramic tools that can cut CGI for 10 times less than the cost of carbide tools. But few in the industry know this.

“If somebody is cutting heat-resistant alloy at 125 sfm, and you bring in this new product that can do 1,600 sfm, it’s kind of like taking somebody from a horse to a rocket ship,” he said. So sometimes “the (reaction) is, ‘There’s no way I’m doing that.’”

At Greenleaf, Dillaman and his colleagues have had success using ceramic inserts to replace grinding in some cases.

Movement on the insert also makes it difficult to maintain dimensional tolerances on the component. The pocket should be suited for the insert and kept in good condition. There should be no wear or deformation, as even the slightest movement has consequences.

Andersson pointed out that many shops tend to drop the speed compared to roughing applications, which is a common mistake for finishing operations. Increasing the speed is necessary to achieve a quality surface finish.

Cutting tool materials based on aluminum oxide and silicon nitride. Ceramic tools can withstand higher cutting speeds than cemented carbide tools when machining hardened steels, cast irons and high-temperature alloys.

“When it comes to a physical vapour deposition (PVD) versus a chemical vapour deposition (CVD) coating, the CVD coating tends to be much thicker than a PVD coating,” said Andersson. “With a thicker coating, you are going to have a greater challenge of producing a quality surface finish than with a thinner coating, and this holds true every single time. PVD produces a better surface finish than a CVD coating because of coating adhesion. A PVD insert will have full coating on all surfaces of the insert, whereas CVD will have reduced coating right on the microgeometry, changing the shape of the microgeometry.”

On the downside, Howard pointed out that the hardness of ceramic materials makes them brittle, so those who make tools out of ceramics can’t put very sharp edges on them. As a result, he said, ceramic tools don’t cut as efficiently as carbide tools.

The amount of heat produced during the cutting process is a function of the cutting speed and the material being machined. So the ability of ceramics to conduct heat away from the cutting edge means that ceramic tools can run much faster than those made of carbide, CBN or PCD when cutting most materials, Howard said. He noted that while carbide tools cut heat-resistant alloys at 125 sfm, for example, ceramic tools can cut them at anywhere from 800 to 1,500 sfm.

“So people say they’re going to go really, really slow and change tools a lot,” Howard said. “But when we get a few brave people that let us play with ceramic, they go, ‘Oh, my God, I never knew I could do this.’”

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Microgeometry and edge line condition of the insert have a tremendous impact on the initial chip formation and surface finish.

1. Permanently damaging a metal by heating to cause either incipient melting or intergranular oxidation. 2. In grinding, getting the workpiece hot enough to cause discoloration or to change the microstructure by tempering or hardening.

The main advantage of ceramic tools is the effectiveness with which they handle the heat generated by the cutting process.

A chipbreaker for finishing tends to have a smaller or thinner edge profile and either a lighter or no hone; then that's followed by a narrower or deeper chip gullet, said Goss.

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However, Goss noted that coolant is not recommended for all applications. For turning hardened materials -- anything over 50 Rockwell C, using a ceramic insert -- coolant should be avoided, as it has a tendency to thermal-shock the insert, which can lead to fracturing. But if the material is on the softer side, coolant can be used with a ceramic insert.

“Wipers are so useful during the roughing and even medium stages of the turning process,” said Andersson. “When we think of wipers, we automatically think of finishing operations, but they are used to generate good surface finish in other parts of the process.”

“This creates a sharper edge for the insert, which allows it to more efficiently and effectively shear the material during the finish operation,” he added. “Ceramic inserts typically don't have chipbreakers; instead we look at the cutting edge preparation, which is usually a combination of lands and hones. For finishing, we recommend an insert with a smaller land, and a sharp edge with no hone if the material is softer. However, for any material 50 Rockwell C or higher, we typically lean towards an insert with a light hone on the cutting edge to help provide a little bit more protection and keep the edge from chipping.”

William Leventon is a contributing editor to Cutting Tool Engineering magazine. Contact him by phone at 609-920-3335 or via email at wleventon@gmail.com.

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Machining of a flat, angled or contoured surface by passing a workpiece beneath a grinding wheel in a plane parallel to the grinding wheel spindle. See grinding.

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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.

A toolholder pocket that is too open can reduce the contact area between the insert (for example, with WNMG inserts) and the pocket, which then introduces movement into the pocket. This leads to microvibration, which has a negative impact on surface finish. YG-1

Process that vaporizes conductive materials by controlled application of pulsed electrical current that flows between a workpiece and electrode (tool) in a dielectric fluid. Permits machining shapes to tight accuracies without the internal stresses conventional machining often generates. Useful in diemaking.

“That material is both abrasive and creates heat, and those are the things that wear out tools the fastest,” he said. So for this application, “people will go from carbide straight to CBN, and the cost difference between those two is astronomical.”

Jan Andersson of YG-1 and Matt Goss and Paul Lobsinger of Greenleaf Corp. offer some tips that can help operators improve turning finishes.

“Shops need to think about the turning process as a complete chain,” said Jan Andersson, director, product management, indexable inserts for Americas, YG-1, Vernon Hills, Ill. “It’s important to think of all the steps, from the roughing all the way through finishing, because they are all connected, interlinked, and interdependent.”

CoroMill® Dura dedicated solid end mills for aluminum are a stable and flexible concept, designed to work in ISO N applications. Specifically developed for roughing with finishing capabilities, for different engagements in aluminum.

Faster cutting speeds help raise the temperature slightly, which generates a better surface finish. It also prevents that material from sticking to the top or the face of the insert. Greenleaf

Lindsay Luminoso, sr. editor/digital editor, contributes to both Canadian Metalworking and Canadian Fabricating & Welding. She worked as an associate editor/web editor, at Canadian Metalworking from 2014-2016 and was most recently an associate editor at Design Engineering.

“Chip control is essential because with this process, we need to use the chip area for thermal evacuation,” said Andersson. “You have to raise the temperature so that it is both high and even, but you also need sufficient chip area. If you reduce the chip area, there is less mass to transport that heat away from the cutting zone and you will start seeing the effect of chemical, flank, and crater wear on the insert. Chip control really becomes a challenge when you're looking at surface finishing. So that's why you have to select the right geometry and maintain proper cutting parameters for a given application.”

Information about these applications usually falls into the category of what people in the machining industry don’t know about ceramic cutting tools. Equally frustrating for the firms that sell these tools, however, is what many people think they know based on outdated information.

For most turning operations, high-pressure coolant aimed directly at the cutting edge is recommended. This helps to clear chips out of the cutting zone. Chip control is essential in maintaining a quality finish. Clearing out the chips keeps the tool from recutting chips, which can damage the edge of the tool. It also prevents the chips from curling around the tool and moving across the workpiece surface, potentially leading to scratches or flaws in the finish.

“Stainless steel is an area that a lot of people never think of ceramic for,” he said. “It’s got to be hard, though — above, say, 32 to 35 Rockwell — because we’re going so fast and (therefore) cut so hot.” If the steel is below that hardness level, “you will melt it and light it on fire.”

At the finishing stage of turning operations, the last thing any operator wants to do is scrap a part because of poor surface finish quality. Shops need to take many factors into account to improve surface finish and meet customer specifications. The experts agree that proper inserts and cutting parameters are essential, but so is taking a holistic approach to producing better surface finishes.

In recent years, Bidemics has become popular with makers of larger aerospace engines, Howard said. But he added that some shops find the performance boost offered by the material a bit unsettling.

Andersson added that force management is a significant factor when it comes to the finishing stage of turning operations. The tangential force, which is axial force plus radial force, can be treated as a constant in turning. If operators increase the axial force, they reduce the impact of the radial force, which allows them to hold better tolerances and reduce microvibration because of the reduced natural instabilities. He added that this is not necessarily as much of a consideration during the roughing and medium stage of the process.

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

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.

“Coolant helps keep the part and the tool cool so you can cut at faster speeds,” said Goss. “If high-pressure coolant isn't available, conventional or flood coolant would be the next best option.”

“If you look at a green-state machining or soft steel turning machining, the operator needs to produce a good enough surface finish in early stages to achieve the necessary surface in finishing,” said Andersson. “If you start looking at hardened steel components, the surface finish of a roughing pass before heat treating will tremendously impact the final surface finish that can be produced after heat treating.”

In general, Howard believes there’s a fairly widespread lack of knowledge about ceramic cutting tools in the machining industry. So he had no trouble identifying some lesser-known applications for these tools. One is cutting hardened stainless steel.

Because they do a better job of transferring heat away from the cutting edge, Bidemics inserts can run even faster than typical ceramic cutters — close to 1,600 sfm, Howard said. He added that efficient heat transfer also lengthens the life of cutting edges.

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).

“This is especially important when we start getting into the superalloys,” said Andersson. “Many industries, like aerospace manufacturers, require the use of G- tolerance inserts versus M-tolerance inserts in finishing. The quality of the microgeometry of a G tolerance insert can really impact the surface finish, and this will help not only industry-specific applications, but anyone looking for the high-quality surface finish in difficult-to-cut materials.”

“The other thing to think about here is a directional force,” said Andersson. “In the finishing stage, you want to put as much of your force as you can axially along the component, because that will give you the stability needed. Choosing an insert that offers as close to a 0-degree entry angle will give you more force along the axis, but you also need increased back-clearance of the insert to get that quality surface finish.”

In addition, he noted that ceramic tools are more expensive than their carbide counterparts. When it comes to tools with inserts, he said this is because ceramic inserts require a good deal of grinding while carbide inserts are easily mass-produced.

Depending on the amount of material needed to make an insert, ceramic inserts could be anywhere from 1.5 to four times more expensive than inserts made of more commonly used materials, said Martin Dillaman, global manager of engineering and applications at Greenleaf Corp. in Saegertown, Pennsylvania. Dillaman added that solid-ceramic tools probably cost two to four times as much as their counterparts made of more widely used materials. He added, however, that the higher cost of ceramic tools can be justified by savings in cutting time and throughput increases at shops that use them.

“We found a way to fuse carbide and ceramic together without a cobalt binder,” Howard explained. “The carbide is introduced into the ceramic in kind of a spiderweb fashion. When heat hits the cutting edge, it runs down those little carbide trails and disperses more efficiently.”

Dillaman said these endmills are made from the company’s Xsytin-1 material, which features a “whisker,” or reinforcing material, that’s grown internally via processing rather than laid in. This makes the ceramic material much harder to break apart, he said. He added that Xsytin-1 has shown itself to be capable of handling challenging roughing applications and turning interruptions.

Determining the correct depth of the cut (DOC) will help with the stability of the turning process. A DOC that is too small leads the nose radius to put all forces into the component radially, which introduces vibration and negatively affects surface finish.

“Roughing should remove enough material so that the finishing tool is not cutting over the radius,” said Paul Lobsinger, sales and service engineer Canada, Greenleaf Corp., Saegertown, Pa. “This will help to prevent notching of the finishing tool. Roughing operations tend to use heavier feeds, which can lead to scallops on the walls of the shoulder. These scallops can be very hard and lead to very poor insert life if they are found on the part during finishing operations. Roughing tools should be programmed to remove the scallops, and steps need to be taken to provide the best possible surface for the finishing stage.”

“The best way to produce a good surface finish is to start with the insert manufacturer and look at the cutting recommendations,” said Andersson. “It will give a good starting point. You can make adjustments along the way, but the recommendations are based on years of R&D and shop knowledge, so take advantage of the expertise.”

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.

Luminoso has a bachelor of arts from Carleton University, a bachelor of education from Ottawa University, and a graduate certificate in book, magazine, and digital publishing from Centennial College.

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.