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Editor’s Note: This article was developed from information presented during the Horn Technology Days 2017 event held at Paul Horn GmbH in Tübingen, Germany, May 10-12.

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.

We can’t talk about coolant delivery without talking about coolant pressure. With the right coolant pressure it is possible to influence chip formation in grooving and parting off. Coolant pressure as low as 5 bar (72 PSI) can start to reduce crater wear. As the pressure increases to 20 bar (290 PSI), it can reduce BUE. Coolant pressure of 40 bar (580 PSI) can influence chip control and direction. High pressure application of 80 bar (1,160 PSI) or more can aide in chipbreaking.

The negative chip angle that works so well in free-machining brass does not work nearly the same in the lead-free version. Machining trials have shown that lead-free brass is best machined with geometries more suited for steel. For the best process capability it is important to apply the correct geometries and grades for the material you are machining. Not all brass is the same.

To cut a long story short, the advent of carbide as an effective cutting tool material caused HSS to become continuously less popular as a tool material. When appropriate, tool designers developed tool bodies to accept throwaway carbide inserts and enable machining with carbide cutting edges while reducing tool costs. But HSS’ bend-strength toughness compared to carbide’s harder and more brittle characteristics still offers advantages in some applications, and rather than always applying solid-HSS tools, the same bodies for carbide inserts accept HSS ones as well.

Chip control ensures that chips will not cause problems during the machining process. The goal is to produce short helical, spiral, comma, or tear chips (shaped like 6s and 9s). These types of chips are more likely to provide stability in the grooving and parting-off process.

Cutters tooled with HSS inserts are also suitable when machining with less-than-optimal rigidity. “High-speed steel inserts are for machining at a lower cutting speed where high toughness is required for application under unfavorable machining conditions,” said Hellmut R. Ross, president of Arno Rouse USA LLC, Harvard, Ill., which supplies HSS inserts among other tools. “I wouldn’t say the machine, but the setup might not be that rigid.”

The H-Carb Seven Flute High Efficiency Endmill specializes in deep axial trochoidal and high-speed machining applications. Offered at various lengths of cut, the 7 flute design creates a superior finish to conventional 5 or 6 flute tools.

Lundvall noted that applications exist where HSS, in general, outperforms carbide because HSS’ higher toughness is more forgiving and its sharper cutting edges prove more effective. “One good area is milling high-strength titanium, such as the new titanium 555-3 alloy where we’ve seen some spectacular results with a coated high-cobalt ASP 2060 special endmill compared to carbides,” he said.

Coolant can be supplied by an external or internal means. When external coolant is supplied via nozzles spraying on the toolholders, only a small amount of the coolant actually gets to the cutting edge so it has less of an effect on the cutting application than coolant delivered using a through-coolant toolholder delivery system. This is especially true when machining deep grooves and working with materials that are easily work-hardened, such as superalloys and stainless steels.

Coolant applied through the toolholder is precisely directed to the cutting edge, where it will have the most impact on the cutting process.

When internal coolant is supplied directly through the toolholder, it is directed precisely to the cutting edge, enabling a much more reliable process. Internal coolant, or through-coolant, holders are available in many variations. Some direct the coolant to immediately above the insert, some to immediately below.

Turning application technology has come a long way from the time when you simply clamped a piece of tool steel in place for a turning application. Today the flexibility, simplicity, increased stability or rigidity, and improved accuracy are making modular grooving systems popular.

Plastics are difficult to cut because they are typically gummy and tend to melt, burn and adhere to the cutting tool. HSS’ toughness enables toolmakers to produce inserts with a keen edge that has minimal edge preparation to reduce heat and friction at the tool/workpiece interface. “It’s a razor sharp cutting edge,” Ross said.

When finishing the periphery of screw-on inserts, Warner said the company locates the periphery off of the countersink instead of the hole to ensure accuracy. “The hole is not what centers the insert in the pocket, the countersink is,” he said.

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.

Warner added that if a customer needs more HSS inserts beyond the initial order, the subsequent ones are typically coated. For example, one of his customers was having a problem milling plastics with carbide and found that a HSS insert worked well. “In the next go-around, we coated it and it worked extremely well, so now that company regularly buys coated high-speed steel inserts,” he said.

Even with the highest-quality HSS, toolmakers have to be cautious when grinding the material—especially finish grinding—to produce good tools, according to Oscar Lundvall of Erasteel Inc. “If you do a bad grinding operation, you’ll have big scratches or grinding burn on the surface and that’ll work as a defect, so it might break,” he said, adding that the same applies to making carbide tools.

He added that, in addition to controlling chip size and the direction chips travel, the chipbreaker creates a double-positive cutting configuration to reduce heat at the tool/workpiece interface and impart a finer surface finish. As previously noted, tool bodies that accept carbide inserts also hold HSS ones, but not all bodies will work equally well. “A lot of people will buy a high-speed steel insert and put it into a negative carbide holder and it won’t work,” Warner said. “We watch that very closely whenever we’re matching high-speed steel to holders for carbide inserts.”

Consider two key points to avoid problems. One is chip forming and the other is chip control. Good chip forming ensures that the material is plastically deformed by the tooling so the chips are narrower than the width of the cutting insert to avoid damage to the groove flanks. An example is a 5-mm-wide groove insert that creates a chip that is 4.85 mm wide.

Although edge preps to minimize chipping aren’t required on HSS inserts, the inserts can have chipbreakers to enhance chip control. “Our standard chipbreaker is a 10°, 0.090 " effective-width chipbreaker, which 90 percent of the time will work sufficiently,” Warner said.

When used in lathe or screw-machine operations, this process separates a completed part from chuck-held or collet-fed stock by means of a very narrow, flat-end cutting, or parting, tool.

Tool that cuts a sloped depression at the top of a hole to permit a screw head or other object to rest flush with the surface of the workpiece.

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.

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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.

He explained that his company starts with a sheet of HSS and uses an abrasive waterjet machine to create insert profiles. For the 90 percent of the inserts that are held with screws, the toolmaker then drills a hole and creates a countersink for the setscrew. Finishing involves grinding all surfaces.

So what about cam machines that are 20 or 30 years old or older? Truth is, many companies still run older cam-style machines, and these machines aren’t being ignored. There are new options for them too.

When coated, the coating must be deposited at a temperature that’s not too high to temper HSS, which causes it to loose its hardness. Therefore, HSS inserts must be PVD coated, where the deposition process takes place at 350° to 900° F compared to 1,800° to 2,000° F for the CVD process. The same coatings found on carbide inserts, such as TiN, TiCN and AlTiN, are available on HSS inserts. Although coated HSS inserts can cut at higher speeds and feeds than uncoated ones, Warner noted that only a small percentage of the HSS inserts his company sells are coated. “Shops don’t try high-speed steel unless they’re having a particular problem with carbide and usually 10 uncoated inserts gets them out of the problem,” he said. “Eighty percent of my customers buy fewer than 50 inserts.”

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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.

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.

Intermetallic compound consisting of equal parts, by atomic weight, of tungsten and carbon. Sometimes tungsten carbide is used in reference to the cemented tungsten carbide material with cobalt added and/or with titanium carbide or tantalum carbide added. Thus, the tungsten carbide may be used to refer to pure tungsten carbide as well as co-bonded tungsten carbide, which may or may not contain added titanium carbide and/or tantalum carbide.

Cooling lubricants and cutting fluids can dramatically affect the reliability of grooving and parting-off processes. When applied correctly, cooling lubricants can reduce the temperature of the material being machined and improve chip removal. Keep in mind that no matter how much coolant is poured on an application, or how effective the coolant is, it will have little to no effect if it is not applied to the cutting edge.

The pre-plumbed systems simply bolt on to accommodate many coolant delivery options that offer quick changeover without the need to hook up coolant lines. Many of the modular systems also allow for center height adjustability that can be especially helpful when cutting difficult materials. A large number of combinations are possible with a relatively small number of components, which enables standard tool systems to be used throughout an entire production process regardless of the machine interface.

Once upon a time, HSS tools were applied for “high-speed machining,” but that’s no longer the case. In applications where carbide inserts are able to run at 300 sfm, the recommended cutting speed for HSS inserts is about 60 sfm, according to Mike Warner, president of Arthur R. Warner Co., Latrobe, Pa., which specializes in producing HSS inserts. “High-speed steel should be called slow-speed steel, but it’s amazing some of the speeds you can run,” he said. “We have some high-speed steel in applications running up to 125 sfm with coatings.”

The narrowest indexable inserts should be used in the parting-off process as this can factor into significant material cost savings. These savings multiply exponentially when you are machining alloys that have a substantially higher material cost, such as high-temp superalloys.

Not only do HSS inserts run slower in a machine tool, they take longer to grind than carbide ones. Ken King of THINBIT/Kaiser Tool Co. Inc. said that’s because a grinding wheel appropriate for HSS tends to push the insert as it is grinding. “You have to cut a little slower so the insert won’t flex away from the wheel and leave material you wanted to remove,” he said.

Ross noted that the lower machining parameters for HSS inserts, which he estimated are about half of the recommended parameters for carbide, make them suitable for machining plastics. Other suitable workpiece materials include aluminum, wrought and cast alloys, nickel alloys, copper, brass, bronze “and the outside skin on a forged part, which is really difficult to machine,” he said.

The P-style blades have many options with indexable blades that are designed to fit in existing tool blocks. Solid-carbide options allow for direct replacement of these blades for groove and cutoff applications.

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.

THINBIT, however, charges the same price for its standard HSS and carbide inserts, according to King, even though producing HSS ones requires a longer cycle time. He noted that all THINBIT HSS inserts are made of M-2 conventional HSS.

Interrupted cutting is one area where HSS offers an advantage, according to Ken King, CEO of THINBIT/Kaiser Tool Co. Inc., Ft. Wayne, Ind. The toolmaker offers standard HSS inserts for grooving, face grooving, threading and parting, as well as specials. Compared to carbide, “high-speed steel will take a lot more abuse as far as flexing and interrupted cuts,” he said. “If you do crash high-speed steel, sometimes you’ll see the inserts are actually bent or flexed. You can use that to your advantage if the application is so bad that you require the tool to bend a little bit.”

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.

Coolant supplied below the cutting edge will reduce the cutting zone temperature while minimizing flank wear. This also aids in chip removal. Reducing the temperature makes it possible to use tougher varieties of inserts while maintaining tool life and cutting parameters or, in some cases, increasing tool life and improving process reliability. This process also delivers the best results when engagement times are long and temperature is a limiting factor.

King concurred that HSS inserts cut slower relative to the same workpiece material. For example, HSS inserts can machine Teflon, or polytetrafluoroethylene, at 250 sfm with a 0.003-ipr feed rate compared to 400 sfm with a 0.003 ipr for carbide inserts, according to THINBIT. For one Teflon application, THINBIT engineered a special HSS insert design with a 60° top rake. “That gives a huge upsharp angle to help peel the Teflon away,” King said.

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.

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

Recently, cutting tool sales have been down across the board, but King indicated there’s a fairly healthy demand for HSS inserts. “When we add new products, we consider whether to offer it in high-speed steel or not,” he said. “It’s a material we still consider active and not obsolete or discontinued. We know it solves problems for people.” CTE

Groove or other tool geometry that breaks chips into small fragments as they come off the workpiece. Designed to prevent chips from becoming so long that they are difficult to control, catch in turning parts and cause safety problems.

Sometimes, it’s beneficial to put carbide and HSS inserts into the same tool body, such as a combination cutter for turning a 12 "-dia. part that requires its center to be bored. “On older machines, you can’t change the machine’s rpm during a cut, so the OD of that part has the correct surface feet for carbide but the middle of the part is hardly turning,” Warner said. “They will use high-speed steel in the middle and carbide on the outside.”

Harder tool materials, such as carbide, don’t like to bend. King used the analogy of glass and wood to compare and contrast the material properties of carbide and HSS. “You’re not going to bend a piece of glass; it’s going to break and shatter,” he said. “Whereas wood will shatter eventually, it will bend more than glass.”

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).

Because many carbide inserts have a negative clearance on the insert’s periphery, Warner noted that when end users position the insert 7° forward to provide relief on the insert edge, but without a chipbreaker, it creates a negative cutting configuration on the top. That generates a lot of heat and—like carbide—heat is no friend to HSS.

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Let’s use a lead-free brass alloy as an example of a challenging material. Brass is known for its good machinability properties. A leaded, free-machining brass is particularly popular in the production of turned parts. Tools used to machine free-machining brass have a negative chipping angle that produces small, short chips. With new laws that regulate the use of hazardous materials such as lead, new grades of lead-free brass have emerged that require a change in machining processes.

Warner explained that the depth of an edge preparation, such as a T- or K-land, on a carbide insert equals the minimum DOC the insert can effectively take. “If it’s an 0.008 " hone on an insert, you can’t take a 0.006 " depth of cut,” he said. “It would generate so much heat that your tool life would deteriorate.”

Conditioning of the cutting edge, such as a honing or chamfering, to make it stronger and less susceptible to chipping. A chamfer is a bevel on the tool’s cutting edge; the angle is measured from the cutting face downward and generally varies from 25° to 45°. Honing is the process of rounding or blunting the cutting edge with abrasives, either manually or mechanically.

Arno Rouse USA LLC (800) 943-4426 www.arno-rouse.com Arthur R. Warner Co. (724) 539-9229 www.arwarnerco.com Erasteel Inc. (973) 335-8400 www.erasteel.com THINBIT/Kaiser Tool Co. Inc. (888) THINBIT www.thinbit.com

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.

Easily access valuable industry resources now with full access to the digital edition of Canadian Fabricating & Welding.

System that uses high-pressure waterjets in combination with a slurry of fine abrasive grains to machine materials. See waterjet cutting.

Arthur R. Warner doesn’t offer carbide inserts, but Warner said its HSS inserts range from $4 to about $15, depending on type and quantity. As a comparison, he noted that a high-quality TNMC32NV carbide threading insert costs about $7. “Ours are $12, but there are 38 operations on that insert to make it and it will last a lot longer than carbide in quite a few applications,” Warner said. He added that at least until 2 years ago, his research indicated that 30 percent of milling in the U.S. is still performed with HSS tools, including inserts and round tools.

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.

Process of both external (e.g., thread milling) and internal (e.g., tapping, thread milling) cutting, turning and rolling of threads into particular material. Standardized specifications are available to determine the desired results of the threading process. Numerous thread-series designations are written for specific applications. Threading often is performed on a lathe. Specifications such as thread height are critical in determining the strength of the threads. The material used is taken into consideration in determining the expected results of any particular application for that threaded piece. In external threading, a calculated depth is required as well as a particular angle to the cut. To perform internal threading, the exact diameter to bore the hole is critical before threading. The threads are distinguished from one another by the amount of tolerance and/or allowance that is specified. See turning.

Grooving and parting-off applications present unique challenges. Unlike a longitudinal turning application that allows chips to move in three directions without restrictions, during grooving and parting-off processes you are machining between flanks, which confine chip movement to just two directions.

Coolant from above can greatly improve chip control, which is a key to longer tool life. It can also reduce built-up edges (BUE).

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.

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.

Materials are changing, and they are generally not getting easier to machine. Challenging materials such as heat-resistant superalloys, stainless steels, and lead-free alloys such as brass pose new challenges that demand modern machining strategies.

Available in two major types: tungsten high-speed steels (designated by letter T having tungsten as the principal alloying element) and molybdenum high-speed steels (designated by letter M having molybdenum as the principal alloying element). The type T high-speed steels containing cobalt have higher wear resistance and greater red (hot) hardness, withstanding cutting temperature up to 1,100º F (590º C). The type T steels are used to fabricate metalcutting tools (milling cutters, drills, reamers and taps), woodworking tools, various types of punches and dies, ball and roller bearings. The type M steels are used for cutting tools and various types of dies.

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

About the Author: Alan Richter is editor of Cutting Tool Engineering, having joined the publication in 2000. Contact him at (847) 714-0175 or alanr@jwr.com.

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

HSS also has the advantage of costing less than carbide, but that doesn’t necessarily translate into HSS inserts costing less than comparable carbide ones. Arno Rouse offers a TiN-coated carbide TCFT insert for $10 and the same one made of HSS is $37.35. “You have to get a lot more parts to justify that,” Ross said.

Other alloying elements in HSS include chromium, vanadium, tungsten, molybdenum and cobalt. Unlike cemented tungsten carbide, cobalt is not used as a binder in HSS but rather as an alloying element that’s melted with the base steel and other elements and then atomized into the finished composition. “You’re not mixing powders like with tungsten carbide,” Lundvall said. “It’s a totally different process.”

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.

Jennifer Warner, vice president of operations for Arthur R. Warner Co. (above), examines a HSS insert turning kit, containing five CCMW-3-2.5-2 screw-on, 7° positive, 0.031 " radius inserts; left- and right-hand ½ "-shank tool bodies; insert screws; and a wrench. The left-hand tool body has two pockets, with the second one providing a 50° side-cutting edge angle. Top photo: A selection of the company’s application-specific HSS special inserts.

Through-coolant holders eliminate the need to adjust coolant lines and always direct the coolant to the tool’s cutting edge. External coolant lines can be bumped out of alignment while operators are changing tools or loading parts, which can cause process variation or premature tool failure.

Similar to producing HSS, making HSS inserts is significantly different from producing carbide ones, which start as a powder that’s sintered into shape. “They press a carbide insert and—bang—they got the hole, the chipbreaker and everything they need right there,” said Arthur R. Warner Co.’s Mike Warner.

Warner added that when a machine tool, particularly an older one, does not have an adequate spindle speed to achieve the required surface footage to cut efficiently with carbide, HSS is the material of choice. “You have to slow down a little bit but your tool is going to last a lot longer and you’re going to get more parts per tool,” he said, adding that the chip load can be larger when cutting with HSS inserts vs. carbide inserts.

Tendency of all metals to become harder when they are machined or subjected to other stresses and strains. This trait is particularly pronounced in soft, low-carbon steel or alloys containing nickel and manganese—nonmagnetic stainless steel, high-manganese steel and the superalloys Inconel and Monel.

It is important to consider the economics of parting off. Since parting off is often the final operation in manufacturing a component, reliability is crucial.

A comparison of the toughness (as measured in bend strength) and hardness for Erasteel’s ASP-grade P/M HSS, conventional tool steel (CWT), conventional HSS and cemented carbide.

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.

New modular tools make it possible to produce assemblies that are tailored for specific applications while being made up of completely standard components. This can reduce the need for special tools. These systems provide a stable structure, while their modular design gives you flexibility and a large variety of tool configuration options.

Warner pointed out that HSS inserts are effective for cutting gummy and workhardening materials because “HSS actually cuts the material where carbide is meant to fracture it in front of the cut.” He added that, in some applications, HSS is able to impart a finer surface finish than carbide. “High-speed steel cuts it; it doesn’t tear it.”

To enhance HSS’ toughness while increasing its hardness, HSS producer Erasteel Inc., Boonton, N.J., is producing P/M HSS with higher alloy content, according to Oscar Lundvall, the company’s business developer. That includes alloying the material with niobium, such as for Erasteel’s ASP 2055-grade P/M HSS with about 2 percent niobium. “The powder steel is very homogenous in its structure, but with the niobium alloying we achieve even finer dispersion of carbides, which gives us a material that is even tougher than a similar steel without niobium,” he said. “It is easier to grind and produce a surface finish that is much finer than ordinary P/M steel.”