Extracting oil and natural gas from hot, corrosive and otherwise demanding environments, such as when hydraulic fracturing or deep-sea drilling, is helping to make the U.S. energy-independent, but stresses the metal components used to get the job done. Fracking gear goes 7 miles or more into the ground, where it is subjected to pressures up to 25,000 psi (1,724 bar) and temperatures as high as 500° F (260° C). In addition, deep wells contain “sour” crude, which is highly corrosive because of its sulfur content. Even parts for above-ground applications in the energy industry experience enough stresses to make conventional metals wilt.
Therefore, designers of turbine blades, rotors, valve bodies and manifolds, pump parts, vanes and a host of other energy parts turn to exotics—primarily heat-resistant superalloys (HRSAs). “They use superalloys that can tolerate heat, corrosion, abrasive wear—just about anything,” said John Forrest, vice president and national sales manager for toolmaker Tool Alliance, Fort Myers, Fla. “Some precision components, such as for a generator or turbine system, are used in a stable environment, while others are subject to extreme conditions, such as of being part of a deep-well drilling system.”
Courtesy of Sandvik Coromant
Effectively directing high-pressure coolant to the cutting zone enhances machinability and extends tool life when cutting HRSAs, such as when making energy industry parts.
Three groups of HRSA materials exist: nickel-, cobalt- and iron-based alloys. According to a white paper from Sandvik Coromant Co., Fair Lawn, N.J., nickel-based ones are the most widely used, with common types including Inconel 718, Waspaloy and Hastelloy X. Cobalt-based superalloys, such as Haynes 25 and Stellite 31, display exceptional creep and corrosion resistance at high temperatures, similar to the nickel alloys, but are more expensive and more difficult to machine. Developed from austenitic stainless steels, iron-based superalloys, such as Inconel 909, can provide low thermal-expansion coefficients, but have the poorest hot-strength properties of the three.
Lance Hughes, industry specialist – oil and gas for Mitsubishi Materials USA Corp., Fountain Valley, Calif., added that HRSAs, such as Inconel 718 and 625, Duplex and Super Duplex, also provide antimagnetic, abrasion-resistance and high yield-strength properties and are suitable anywhere a seal surface needs to be protected against corrosion. “These parts are used in extreme environments,” he said, “and HRSAs help these products maintain their integrity.”
Machinability Matters
The structural characteristics that make HRSAs desirable for extreme applications also make them significantly more difficult to machine than run-of-the-mill metals. Nickel, for example, effectively resists high temperatures, but can also be quite gummy, reducing its machinability and increasing the prevalence of built-up edge, noted Jim Wyant, application engineer/project development for Greenleaf Corp., Saegertown, Pa. While most of the HRSA applications he sees—in the energy industry and others—are for nickel-based metals, there are many for cobalt ones, with iron alloys a distant third.
In addition, the high yield strength nickel provides causes significant heat development during machining, Hughes noted. This ultimately compounds the machining challenge.
Courtesy of Mitsubishi Materials
Mitsubishi Materials recommends its iMX exchangeable-head endmills when machining HRSAs, such as Inconel 718. Both the head and holder are made of cemented carbide.
While some are more common than others, a slew of metals are under the HRSA umbrella and contain varying percentages of up to 10 or more alloying elements, such as chromium, molybdenum, tungsten and titanium, within the same alloy group. This means machining parameters and behavior significantly vary within each group. “Every material brings its own set of obstacles to the manufacturing process,” Wyant said. “The speeds, feeds and DOCs for each material can be quite different.”
Even the same HRSA behaves differently when machined, primarily depending on whether or not it was heat or solution treated and the way in which it was produced, which includes forging, casting and as bar stock.
“Cast materials can add another machining variable that must be taken into consideration during the machining process,” Wyant said, noting many HRSAs are cast.
In addition to having a finer grain that enhances strength compared to castings, forgings have stress in them because the forging process “hammers” a material’s internal structure, said Scott Walker, president of machine tool builder Mitsui Seiki (U.S.A.) Inc., Franklin Lakes, N.J. “When you machine forged materials, they have a tendency to move around on you.”
Castings typically have a hard, visibly mottled surface, which reduces machinability and can cause notch wear on cutting tools. Bar stock is the easiest form of the three to machine, as notching is not as big a problem.
Thin is In
When notching is an issue, employing chip thinning techniques can help reduce DOC notching when roughing, Wyant said. Chip thinning is essentially using a tool’s lead angle to spread the chip over a larger section of the insert, effectively reducing tool pressures. While this helps reduce DOC notching, in many cases it allows for increased metal-removal rates because an increase in the feed is required to maintain the proper chip thickness.
Wyant added, however, that part manufacturers can increase the feed rate quite a bit when machining a material like steel, but that’s not necessarily the case with an HRSA. “With a high-temperature alloy, you can take advantage of the added benefit of increased feed rates but only to a certain point because the material will start pushing back due to its ability to withstand extreme conditions,” he said.
Courtesy of Greenleaf
Greenleaf says its WG-600 coated whisker-reinforced ceramics enable faster cutting and better resist wear and heat than carbide tools when machining HRSAs.
In addition to notching, HRSA materials tend to workharden. This requires machining them, particularly forgings, at relatively slow cutting speeds. “Speed is probably the thing we have to watch most in machining these exotic materials,” said Tool Alliance’s Forrest, noting the cutting speed for HRSAs ranges from about 75 to 150 sfm. “Speed creates heat, and heat damages tools and can workharden the material.”
He added that when a workpiece surface workhardens on a part that requires multiple passes, each subsequent pass in an already difficult-to-cut material will be even more challenging. “These multiple passes wreak havoc on your tool life.”
To lessen heat generation, prevent workhardening and effectively machine these materials when making parts for energy applications and others, Mitsubishi Materials’ Hughes recommends reducing the machining parameters four to six times compared to those for cutting alloy steels, such as 4130 and 4140. Although the reductions are not as drastic when finishing HRSAs, a 75 to 80 percent reduction in the sfm when rough turning and a 30 percent feed rate reduction when general roughing is common.
According to Forrest, peel milling is a technique that can be effective when tackling HRSAs, depending on the application. Instead of fully engaging the milling tool, such as an endmill, and taking a conventional roughing cut, the tool takes lighter cuts at higher speeds and feeds. “The radial engagement is fairly light but the feed rate is high,” he said. “Multiflute tools can be effectively used to maintain high-ipm feed rates.”
Tool Development
A high flute count helps when milling HRSAs, noted Steve Shofler, president of Superior Tool Service Inc., Wichita, Kan. In one application trimming Inconel stampings, for example, the toolmaker produced a 3⁄8 "-dia. carbide endmill with 10 flutes. The high number of flutes enables more teeth on the cutter to share the workload while taking small bites out of the workpiece.
“You almost have to file it away,” he said. “Basically, it takes a lot of patience because you have to cut it real slow.”
Shofler added that heat- and wear-resistant coatings, such as AlTiN and AlCrN, prove beneficial when cutting HRSAs.
The tool coatings might have special additives, such as silica, to allow a substrate to more effectively tolerate the demanding machining environment, Forrest pointed out. But regardless of a coating’s composition, all are moving in the direction of high wear resistance and durability, enhanced lubricity and good thermal stability.
Rather than recommending a specific coating for cutting HRSAs, Hughes emphasized the importance of a thin coating deposition, such as PVD, to maintain a sharp edge for shearing rather than rubbing the metal and minimizing heat generation. Positive cutting geometries are also effective.
“The high yield strength of these alloys creates an inordinate amount of heat during machining,” Hughes said, “and the sharper the edge, the lower the cutting forces required and, subsequently, the lower the friction and heat.”
An appropriate substrate is also critical when cutting “nastalloys” for energy applications. When applying carbide cutters, Greenleaf’s Wyant recommends one with a micrograin structure to provide the required hardness and wear resistance in such an abusive environment. Coated carbides further boost productivity by enhancing the overall substrate characteristics, allowing for increased cutting parameters and extending tool life. “Coatings supply the insert with further wear resistance and lubricity, allowing the chip to flow across the insert a little smoother,” he said.
Courtesy of Bilz Tool
Part manufacturers frequently employ shrink-fit toolholders when machining HRSAs because they provide high clamping force, high accuracy for the centerline position of a tool and minimize total indicator runout.
A more effective substrate choice, according to Wyant, is a whisker-reinforced ceramic, especially for continuous cutting because the tool material can withstand high temperatures for an extended period of time. For interrupted cuts, applying the proper edge preparation with the proper whisker ceramic grade will be most effective. Another option is a Sialon ceramic, he said. “Sialon ceramics are also designed to handle higher temperatures but only for shorter periods of time and at lower speeds than a whisker ceramic.”
Hughes agreed that ceramics are effective for roughing HRSAs. However, for applications where an HRSA, for example, is inlayed into or welded to an alloy steel body, it’s best to avoid applying a ceramic tool to simultaneously cut the two metals and go with carbide instead, he added. This is because the ceramic tool experiences a significant impact when it contacts the base metal in an inlay or welding application, resulting in premature tool wear.
Insert shape also plays a role when selecting the appropriate tools for tackling HRSAs. Being the strongest geometry, Wyant usually recommends round inserts for roughing. The shape also provides versatility. “With a round insert you can adjust the depth of cut for chip thinning benefits instead of having to change the entire tool,” he said.
Hold on Tight
Toolholders are another part of the energy part tooling package. Joe Thompson, regional sales manager for Bilz Tool Co. Inc., Lombard, Ill., noted its customers frequently use the company’s ThermoGrip shrink-fit toolholders when machining HRSAs. That’s because a shrink-fit holder provides high clamping force and high accuracy for the centerline position of a tool, and minimizes total indicator runout. “Tool position is virtually dead center from the centerline of the spindle, so there’s no deviation there,” he said, adding that the minimal TIR of 3µm at 6 times diameter maximizes the cutting edge for each flute rather than allowing one or more flutes to do more work than the rest. “That way there is even usage of each flute.”
Although rare, a tool can pull out from a shrink-fit holder during certain cutting conditions, possibly during a high- frequency cutting application where there’s a lot of vibration. “There’s always that potential, but it mostly comes down to the quality of the toolholder and the cutting tool shank,” Thompson said.
He pointed out that if the potential for tool pullout exists, Bilz offers its THD shrink-fit design, which has a thicker wall and tighter bore tolerance than the standard offering to provide an even higher clamping force and more vibration damping. That design benefits HRSA applications such as energy parts because a high level of machine horsepower and torque is needed to shear the metal while the spindle speed is relatively low, generally less than 10,000 rpm.
“Certainly shrink-fit is a wonderful way to go,” Tool Alliance’s Forrest concurred, but added that side-lock holders are still being effectively used and even some hydraulic systems have become robust enough for heavy roughing. “All the holding systems are very good,” he said. “The thing you need to look for in any application is the lowest possible runout and the greatest gripping strength.”
Cool Cutting
Another Bilz product that’s suitable for HRSA applications in energy parts is the JetSleeve coolant system, according to Thompson. The system is comprised of a shrink-fit chuck encompassed by an aluminum coolant sleeve with strategically placed holes at the nose. By utilizing coolant pressure, the system’s design enables a “tornadic-type effect,” which is created within the sleeve to supply coolant, air or oil directly to a tool’s cutting edge tip. According to the company, the system increases coolant coverage of the tool’s cutting edge tip by more than 90 percent, significantly increasing tool life while allowing the tool to impart finer surface finishes.
Courtesy of Unist
Above: When sawing 3 "-dia. Inconel bar stock with flood coolant, the cut generated excessive chatter and a burr on the edge of the stock. Below: When the same Inconel stock was cut with the same saw blade on the same machine, but using Unist’s minimum-quantity lubrication system and Coolube 210EP lubricant, the cut quality significantly improved.
Mitsui Seiki’s Walker envisions coolant usage not only being significantly reduced but essentially eliminated in a couple decades as the trend continues toward minimum-quantity lubrication, cryogenics and dry machining. Although he noted oil is the most effective metalworking fluid when cutting most hard, resilient materials, it’s flammable and not environmentally friendly, so parts manufacturers have gravitated to more environmentally sound water-based coolants.
However, dry machining HRSAs can be effective today. Walker said he’s achieved “very good results” dry milling Inconel with ceramic tools. “It almost looks like a grinding process. The Inconel comes off in flaming chips and I am very pleased with the cutting-edge tool life.”
Greenleaf’s Wyant explained that it’s best to apply coolant in continuous cutting applications and air to clear chips and cool the tool/workpiece interface when intermittent cutting, such as milling with whisker-reinforced ceramics. This is because the combination of coolant and intermittent cutting can thermally shock the ceramic as it moves in and out of the heat-generating cutting zone, reducing tool life.
In addition, vastly minimizing coolant application can enhance cut quality. For one customer sawing 3 "-dia. Inconel bar stock with a Lenox bimetal blade on a Hydmech machine, Unist Inc., Grand Rapids, Mich., reported that excessive chatter and a large burr on the edge of the stock resulted when using flood coolant (see photos above). In addition, the blade only lasted 5 days. However, when the customer installed a Unist MQL system and applied Coolube 2210EP lubricant, cut quality and blade life significantly improved.
Nonetheless, targeting high-pressure through-coolant directly at the tool/workpiece interface improves tool life and machinability when cutting HRSAs, according to Walker. He said Mitsui Seiki has built machines that provide upwards of 55 gpm through the spindle. “It’s like a hurricane inside the machine.”
Machine Designs
A current Mitsui Seiki project involves building a group of machining centers that apply up to 80 gpm at 2,000 psi for machining blades made of a superalloy with up to 30 percent nickel, Walker noted. However, instead of cutting tools, special CBN grinding wheels are used to produce the parts, and the coolant system prevents the workpiece material from binding to and gumming up the wheels.
Walker emphasized that workpiece materials dictate how machine tools are designed and built. Often, materials are introduced to improve part performance, but the metal developers do not understand how a material will shear when a cutting edge engages it. “The material guys are out of control,” he said. “They’re throwing stuff at us that end users love but is hard to machine.”
One example of a machine design change to enhance rigidity when cutting challenging exotics is the toolholder interface. Walker pointed out that he switched to the Kennametal KM4X100 spindle connection because it offers a bending moment of 35,000 in.-lbs., which compares to about 16,500 in.-lbs. for a HSK100 taper and 8,500 in.-lbs. for a BT50 taper. In test cuts, for example, a Mitsui Seiki HPX63 horizontal machine center was equipped with a high-torque, high-power spindle with a maximum 26kW of power and 1,081 Nm of torque. The KM4X100 spindle connection generated 90 kN of clamping force, more than twice that of an HSK100 and nearly four times that of a BT50 (40 kN and 25 kN, respectively).
That enhanced rigidity is especially beneficial when producing energy parts because they often are large and require extended-reach tools to access part features. “When I’m hanging out there 6 ", 8 ", 10 " from the gauge line and cutting with a lot of force,” Walker said, “I don’t pull the tool out of the spindle.”
Designing a machine tool is more application-specific when the end user is an OEM machining a specific HRSA component, such as one for a power generator, than for a job shop, which machines a variety of materials and parts. The OEM is able to specify, for instance, the frequency range for cutting, coolant-volume requirements, taper interface and thrust and torque capabilities. Walker said: “That way you build the platform around the specific material and get optimal performance for the cutting edge. That’s the appropriate way to do it, but the jobbers don’t have that flexibility. They have to work with what they have.”
As more energy deposits are harvested in the U.S. and across the globe to keep pace with virtually unquenchable demand, both OEMs and job shops will need more equipment to machine the exotic alloys that can take the heat. CTE
Contributors
Bilz Tool Co. Inc.
(800) 227-5460
www.bilzusa.com
Greenleaf Corp.
(800) 458-1850
www.greenleafcorporation.com
Mitsubishi Materials U.S.A. Corp.
(800) 523-0800
www.mitsubishicarbide.com
Mitsui Seiki (U.S.A.) Inc.
(201) 337-1300
www.mitsuiseiki.com
Superior Tool Service Inc.
(316) 945-8488
www.superiortoolservice.com
Tool Alliance
(800) 564-5832
www.toolalliance.com
Related Glossary Terms
- abrasive
abrasive
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.
- alloy steels
alloy steels
Steel containing specified quantities of alloying elements (other than carbon and the commonly accepted amounts of manganese, sulfur and phosphorus) added to cause changes in the metal’s mechanical and/or physical properties. Principal alloying elements are nickel, chromium, molybdenum and silicon. Some grades of alloy steels contain one or more of these elements: vanadium, boron, lead and copper.
- alloys
alloys
Substances having metallic properties and being composed of two or more chemical elements of which at least one is a metal.
- built-up edge ( BUE)
built-up edge ( BUE)
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.
- burr
burr
Stringy portions of material formed on workpiece edges during machining. Often sharp. Can be removed with hand files, abrasive wheels or belts, wire wheels, abrasive-fiber brushes, waterjet equipment or other methods.
- centers
centers
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.
- ceramics
ceramics
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.
- chatter
chatter
Condition of vibration involving the machine, workpiece and cutting tool. Once this condition arises, it is often self-sustaining until the problem is corrected. Chatter can be identified when lines or grooves appear at regular intervals in the workpiece. These lines or grooves are caused by the teeth of the cutter as they vibrate in and out of the workpiece and their spacing depends on the frequency of vibration.
- chuck
chuck
Workholding device that affixes to a mill, lathe or drill-press spindle. It holds a tool or workpiece by one end, allowing it to be rotated. May also be fitted to the machine table to hold a workpiece. Two or more adjustable jaws actually hold the tool or part. May be actuated manually, pneumatically, hydraulically or electrically. See collet.
- coolant
coolant
Fluid that reduces temperature buildup at the tool/workpiece interface during machining. Normally takes the form of a liquid such as soluble or chemical mixtures (semisynthetic, synthetic) but can be pressurized air or other gas. Because of water’s ability to absorb great quantities of heat, it is widely used as a coolant and vehicle for various cutting compounds, with the water-to-compound ratio varying with the machining task. See cutting fluid; semisynthetic cutting fluid; soluble-oil cutting fluid; synthetic cutting fluid.
- corrosion resistance
corrosion resistance
Ability of an alloy or material to withstand rust and corrosion. These are properties fostered by nickel and chromium in alloys such as stainless steel.
- cubic boron nitride ( CBN)
cubic boron nitride ( CBN)
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.
- cutting speed
cutting speed
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).
- depth of cut
depth of cut
Distance between the bottom of the cut and the uncut surface of the workpiece, measured in a direction at right angles to the machined surface of the workpiece.
- edge preparation
edge preparation
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.
- endmill
endmill
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.
- feed
feed
Rate of change of position of the tool as a whole, relative to the workpiece while cutting.
- flutes
flutes
Grooves and spaces in the body of a tool that permit chip removal from, and cutting-fluid application to, the point of cut.
- gang cutting ( milling)
gang cutting ( milling)
Machining with several cutters mounted on a single arbor, generally for simultaneous cutting.
- grinding
grinding
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.
- hardness
hardness
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.
- lead angle
lead angle
Angle between the side-cutting edge and the projected side of the tool shank or holder, which leads the cutting tool into the workpiece.
- lubricity
lubricity
Measure of the relative efficiency with which a cutting fluid or lubricant reduces friction between surfaces.
- machinability
machinability
The relative ease of machining metals and alloys.
- metalworking
metalworking
Any manufacturing process in which metal is processed or machined such that the workpiece is given a new shape. Broadly defined, the term includes processes such as design and layout, heat-treating, material handling and inspection.
- milling
milling
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.
- minimum-quantity lubrication
minimum-quantity lubrication
Use of cutting fluids of only a minute amount—typically at a flow rate of 50 to 500 ml/hr.—which is about three to four orders of magnitude lower than the amount commonly used in flood cooling. The concept addresses the issues of environmental intrusiveness and occupational hazards associated with the airborne cutting fluid particles on factory shop floors. The minimization of cutting fluid also saves lubricant costs and the cleaning cycle time for workpieces, tooling and machines. Sometimes referred to as “near-dry lubrication” or “microlubrication.”
- payload ( workload)
payload ( workload)
Maximum load that the robot can handle safely.
- physical vapor deposition ( PVD)
physical vapor deposition ( PVD)
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.
- sawing
sawing
Machining operation in which a powered machine, usually equipped with a blade having milled or ground teeth, is used to part material (cutoff) or give it a new shape (contour bandsawing, band machining). Four basic types of sawing operations are: hacksawing (power or manual operation in which the blade moves back and forth through the work, cutting on one of the strokes); cold or circular sawing (a rotating, circular, toothed blade parts the material much as a workshop table saw or radial-arm saw cuts wood); bandsawing (a flexible, toothed blade rides on wheels under tension and is guided through the work); and abrasive sawing (abrasive points attached to a fiber or metal backing part stock, could be considered a grinding operation).
- sawing machine ( saw)
sawing machine ( saw)
Machine designed to use a serrated-tooth blade to cut metal or other material. Comes in a wide variety of styles but takes one of four basic forms: hacksaw (a simple, rugged machine that uses a reciprocating motion to part metal or other material); cold or circular saw (powers a circular blade that cuts structural materials); bandsaw (runs an endless band; the two basic types are cutoff and contour band machines, which cut intricate contours and shapes); and abrasive cutoff saw (similar in appearance to the cold saw, but uses an abrasive disc that rotates at high speeds rather than a blade with serrated teeth).
- shank
shank
Main body of a tool; the portion of a drill or similar end-held tool that fits into a collet, chuck or similar mounting device.
- stainless steels
stainless steels
Stainless steels possess high strength, heat resistance, excellent workability and erosion resistance. Four general classes have been developed to cover a range of mechanical and physical properties for particular applications. The four classes are: the austenitic types of the chromium-nickel-manganese 200 series and the chromium-nickel 300 series; the martensitic types of the chromium, hardenable 400 series; the chromium, nonhardenable 400-series ferritic types; and the precipitation-hardening type of chromium-nickel alloys with additional elements that are hardenable by solution treating and aging.
- superalloys
superalloys
Tough, difficult-to-machine alloys; includes Hastelloy, Inconel and Monel. Many are nickel-base metals.
- tolerance
tolerance
Minimum and maximum amount a workpiece dimension is allowed to vary from a set standard and still be acceptable.
- toolholder
toolholder
Secures a cutting tool during a machining operation. Basic types include block, cartridge, chuck, collet, fixed, modular, quick-change and rotating.
- total indicator runout ( TIR)
total indicator runout ( TIR)
Combined variations of all dimensions of a workpiece, measured with an indicator, determined by rotating the part 360°.
- total indicator runout ( TIR)2
total indicator runout ( TIR)
Combined variations of all dimensions of a workpiece, measured with an indicator, determined by rotating the part 360°.
- turning
turning
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.
- wear resistance
wear resistance
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.
- workhardening
workhardening
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.
- yield strength
yield strength
Stress at which a material exhibits a specified deviation from proportionality of stress and strain. An offset of 0.2 percent is used for many metals. Compare with tensile strength.
Author
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.
