Turning Stainless Made Painless

Author Mike Castner
Published
March 01,1997 - 11:00am

Turning more stainless steel but enjoying it less? Then try using the machining parameters and insert grades discussed below. You’ll probably be pleased with the results.

Stainless steel represents about 24% of the metal turned today. That percentage has been rising and will continue to rise, spurred by the growth of the chemical, oil, food-processing, and power industries, all of which crave stainless steel for its ability to withstand hostile, corrosive environments.

However, stainless steels present challenges of their own to machinists. Their machinability characteristics lead to more friction, heat, and chip-control problems than the characteristics of most traditional steels and cast irons do. Luckily, inserts designed specifically for stainless steels are available to make turning stainless easier. These new inserts provide higher positive rakes, improved coatings, and better matches for heavy roughing, medium roughing, and finishing operations. With the right tooling, a machinist can effectively apply proven turning principles and techniques to facilitate stainless-steel turning and manage the most difficult cuts.

Stainless Characteristics

There are three basic types of stainless steel - ferritic, martensitic, and austenitic - each presenting its own set of machining challenges. And for each type there are three basic issues to consider: cutting forces and the material’s workhardening and chipforming properties (Table 1).

Ferritic stainless steels, which contain 10.5% to 27% chromium and 0.013% carbon, are nonhardenable but 50% stronger than traditional steels. Because ferritic grades machine like traditional steels, an insert with a chipbreaker designed for general steel turning will suffice.

Martensitic stainless steels, which contain 11.5% to 18% chromium and more than 0.013% carbon, are heat-treated for high strength and toughness. They, too, machine like steels but with much higher cutting forces. Hardness varies within martensitic steels, causing extreme variation in cutting forces. Therefore, an insert with a very strong cutting edge is required.

Austenitic stainless steels are the most difficult to machine. They contain 16% chromium with varying percentages of nickel, molybdenum, and magnesium to build up an austenitic structure. Austenitic stainless steels are used when corrosion resistance and toughness are paramount.

 

Stainless-Steel 
Type

Workhardening

Cutting 
Forces

Chipbreaking 
Difficulty

1 = Lease Severe, 5 = Most Severe

Ferritic

1

1

1

Martensitic

1

5

1

Austenitic

5

4

3

Table 1 Machining characteristics of ferritic, martensitic, and austenitic.

Austenitic stainless steel has much lower thermal conductivity and higher ductility than other stainless steels and conventional steels. Therefore, more energy is needed to form a chip, thus generating more heat. And because the material doesn’t dissipate heat well, the workpiece, especially the cutting area, gets hotter. The resultant higher cutting temperatures increase the tendency for tool wear and plastic deformation, especially when interruptions are encountered.

To battle these high temperatures, in most austenitic stainless-steel turning applications, flood coolant is required to cool down the work area and help chips flow over the tool edge, preventing the chipwelding that can cause built-up edge (BUE). Water-soluble coolant is the most commonly used coolant for these applications, though shops typically use whatever coolant they’ve chosen for the rest of their machining operations. Dry turning of this metal is recommended in some cases when interruptions are involved to prevent thermal cracking of the inserts.

These steels also tend to produce a segmented chip rather than a smooth flowing chip, resulting in large variations in cutting forces.

Nickel and molybdenum, added to austenitic stainless steels to improve corrosion resistance and tensile strength, often work against machinability, because they deform plastically. This plastic deformation subjects inserts to extreme friction, high cutting forces, and high temperatures, causing the insert to smear and the component surfaces to workharden.

Austenitic stainless steel features a deformation-hardened layer on incoming mill stock that is considerably thicker than that found in traditional steel. The inside of the material may be only half as hard as the surface, but it’s at the surface where the cutting takes place.

To overcome these workhardened surfaces, make deeper cuts and set feed rates that ensure entry of the cutting edge past the hardened zone, which ranges from 0.003" to 0.005" deep.

When turning any of these stainless-steel varieties, observe these rules of thumb, which are based on experience in thousands of stainless-steel turning applications:

  1. Use inserts designed specifically for stainless-steel turning.
  2. Match the insert to the application to achieve better finishes and longer tool life.
  3. Learn to visually diagnose and remedy symptoms of premature edge failure.
  4. Make sure the shims are in good shape.

Insert Improvements

New developments in inserts for stainless-steel turning include improved chipbreaker geometries teamed with specialized insert geometries, stronger substrates, and more adherent coatings.

Various types of very hard, continuous chips form in most stainless-steel workpieces from excessively hard cutting action. To break up the continuous chips into smaller, more manageable sizes, select an insert with a high positive rake and aggressive chipbreaker design. A higher positive rake translates into freer cutting, longer edge life, more continuous cutting, smoother chip flow, lower cutting temperatures, and less deformation-hardening of the material.

Another important factor in an insert’s geometry is its nose radius. Be sure to select an insert with the correct nose radius for a given application, whether it is heavy roughing, medium roughing, or finishing. An excessively large nose radius can cause vibration and generate more heat. A nose radius that’s too small may be too weak and may break, resulting in a poor surface finish and inferior chipbreaking. Generally, a nose radius measuring 3/64" or larger is recommended for heavy roughing, while a 1/32" radius is recommended for medium roughing and finishing, at least as a starting point.

An insert with a geometry designed specifically for stainless steel should also possess a similarly designed chipbreaker. In the past, chipbreakers were made only for traditional steels, and users had to make compromises with machining parameters to turn stainless steels. Today, chipbreakers designed specifically for stainless steels are available. These chipbreakers feature small edge rounding, a high angle, and a positive rake. This design lowers cutting forces and, therefore, workhardening. While having a high angle and positive rake, the chipbreaker must also be strong - two requirements that seem to be mutually exclusive. However, these requirements can be met by putting a reinforced positive land on the insert geometry. This provides edge strength while keeping the rake positive. The chipbreaker must be wide and deep enough to lift the chip away from the rake surface and give the chip room to curl and break.

 

    Material CMC Number Brinell Hardness Coromant Grades
       

1025

2015

2025

2035

       

Feed fn in/rev

       

.004

.008

.012

.008

.016

.024

.008

.016

.024

.008

.016

.024

       

Cutting speed vc ft/min

Stainless Text Bars/Forged Text Ferritic/Martensitic Free Machining steel

05.10

200

1246

886

640

1017

853

771

984

820

722

525

443

394

  Non-Hardened

05.11

200

918

705

558

787

672

607

754

640

558

410

344

295

  PH-Hardened

05.12

330

525

492

476

328

262

213

295

213

164

246

180

131

  Hardened

05.13

330

689

640

640

410

328

279

344

230

164

213

148

115
Austenitic Free-Machining Steel

05.20

180

1476

1099

836

1164

918

705

968

722

541

574

508

459

  Austenitic

05.21

180

1017

771

607

820

640

508

672

508

377

394

361

328

  PH-Hardened

05.22

330

607

574

558

377

295

246

328

230

180

279

197

148

  Super Austenitic

05.23

200

705

689

656

558

443

344

443

328

246

279

246

213

Austenitic-Ferritic Non-Weldable >=0.05% C

05.51

230

918

705

558

656

558

492

689

525

394

377

312

279

(Duplex) Weldable, < 0.05 % C

05.52

260

623

541

492

492

426

377

426

377

344

476

312

197

Cast Text Ferritic/Martensitic Non-Hardened

15.11

200

--

--

--

705

574

525

672

541

492

361

295

262

  Hardened

15.12

330

--

--

--

295

213

180

246

164

131

213

148

115

   

15.13

330

--

--

--

361

279

246

295

197

148

180

131

98

Austenitic Austenitic

15.21

180

--

--

--

754

574

459

623

459

361

377

312

279

  PH-Hardened

15.22

330

--

--

--

295

213

180

279

180

148

213

148

115

   

15.23

200

--

--

--

361

377

312

377

295

230

246

197

180

Austenitic-Ferritic

Non-Weldable, >=0.05% C

15.51

230

--

--

--

607

492

443

508

394

312

344

279

246

(Duplex) Weldable, <0.05% C

15.52

260

--

--

--

443

361

328

410

344

328

426

279

180

Figure 1: Feed and speed recommendations for turning various types of stainless steel.

It is very important to choose the correct grade to suit a given application. For high-speed turning of stainless steels, a cobalt-enriched M-15 carbide grade should be used. For best results, the grade should be multicoated via medium-temperature chemical vapor deposition (MTCVD) with layers of titanium carbonitride (TiCN), aluminum oxide (Al2O3), and titanium nitride (TiN). The Al2O3 acts as a chemical barrier that prevents chemical diffusion of cobalt between the tool and the chip, which happens because carbide has an affinity for stainless steel at the high temperatures generated at high speeds. For turning at medium speeds, an M-25 grade is recommended because of its ability to handle high temperatures and varying cutting forces. For low-speed stainless-steel turning, select an M-35 grade that is straight (non-cobalt-enriched). In cobalt-enriched grades, the cobalt is drawn to the surface of the insert, so that the surface is tougher than the inner part of the insert. In a straight grade, the cobalt, and hence the toughness, is evenly distributed throughout the insert. A CVD multicoating of TiN and TiCN is recommended, though here Al2O3 is not needed.

When turning austenitic stainless steels, a strong grade of carbide, designed specifically for austenitic stainless steel, must be used. It must be tough enough to withstand the varying cutting forces, which mimic those of an interrupted cut even in straight cuts. MTCVD coatings are usually employed, because they adhere better to the substrate than CVD coatings, which tend to flake when cutting these steels. MTCVD coatings also reduce friction and BUE. For austenitic stainless steels, a cobalt-enriched grade is desirable. The grade’s greater surface toughness reduces chipping and the pull-out effects of BUE.

Parameters

In rough turning, the maximum metal-removal rate is obtained with a combination of high feed and moderate cutting speed. Machine power is sometimes the limiting factor, and in such cases the cutting speed should be lowered accordingly. Generally, when machining stainless steel, it’s better to maintain a heavy feed and depth of cut (DOC) - to get under the hardened workpiece surface - and a low cutting speed. Trying a light feed, shallow DOC, and high speed will introduce more heat and poor chipbreaking to the process.

In finishing, setting the feed at an ipr no higher than one-third of the nose radius will provide a good surface finish and dimensional accuracy.

Figure 1 lists recommended starting speeds and feeds for various stainless-steel-turning applications. These rec ommendations are conservative. Don’t be afraid to push the tooling to the limit to maximize productivity.

To minimize unacceptable tool wear, push the insert to its DOC and feed limits (determined by available power and component design) for 15 minutes, and then index the edge. This 15-minute rule of thumb helps yield more parts per edge with fewer indexing stoppages. It makes no sense economically to push the edge beyond that time. Productivity should always be the primary concern, not getting every last second of edge life out of a tool to save a few cents.

Employing appropriate machining parameters helps minimize tool wear. But it doesn’t prevent wear. Remember, tool wear is not an inherently negative process. Tools will always wear. It is not if, but when, how much, and in what manner tools wear. When a cutting edge has performed a considerable amount of metalcutting within a reasonable time, wear is quite acceptable. It is a problem when premature breakdown or tool fracture occurs, causing excessive stoppages for edge changes and, in some cases, workpiece damage.

Figure 2: Principal tool-wear characteristics in stainless-steel turning: (1) flank wear, (2) edge chipping, (3) notching, (4) BUE, (5) flaking, (6) crater wear, (7) plastic-deformation-based wear, and (8) thermal cracking.

Prevent the Avoidable

Some edge-wear patterns are normal, while others are symptomatic of improper insert application, incorrect machine settings, or inappropriate turning techniques. The latter patterns are signs of trouble ahead. It’s important to diagnose and correct these early warning signs and apply some innovative cutting techniques to minimize future tool troubles.

Tool-failure mechanisms that come into play in stainless-steel turning are similar to those found in steel-turning operations. The differences can be seen in the degree of wear (Figure 2). Here is a brief overview of the most common wear patterns and remedial actions to take to correct them early (Table 2).

Flank wear should generally be viewed as normal. It occurs at the flank or clearance face of the cutting edge along the length of engagement with the workpiece. Its occurrence can be positive in that it makes the edge sharper. However, after a certain amount of wear, continued friction against the machined surface abrades the tool and diminishes edge performance.

The solution to excessive or premature flank wear usually is to slow down the cutting speed. Another remedy is to use multicoated inserts or inserts coated with Al2O3 rather than just TiN.

Edge chipping, or breakage of the edge line, can occur when an edge has reached the end of its useful life or when the tool must execute an interrupted cut. If the edge is simply worn, you should consider indexing and changing inserts more frequently. The remedies in the case of an interrupted cut are to reduce feed rate; change the tool’s approach angle to ensure stability; and/or select a tougher, cobalt-enriched insert grade. Often, the answer is a combination of these remedies.

Notching is a type of wear in which the carbide actually breaks down, leaving a void on the cutting edge. Notch wear on the insert’s leading edge is caused by workhardening of the stainless-steel surface. During turning, the DOC line is machining harder material than the underlying nose radius of the insert, creating a notch. On the insert’s trailing edge, notching is caused by oxidation where air and coolant come in contact with the tool at high temperatures. Trailing-edge notch wear is less common than leading-edge notching in stainless-steel turning.

Notch wear is the culprit behind burr formation, which occurs when the cutting edge begins pushing the material instead of cutting it. As the notch becomes more pronounced and starts breaking down the cutting edge, the cutting forces at the DOC line rise, causing the edge to push rather than shear the chip. Along with a sharp, strong edge, larger lead angles also can help prevent this from happening.

To prevent notch wear, the remedies cited for flank wear are usually effective.

BUE is related to temperature and cutting speed. Under high temperature and pressure, the stainless-steel chips become gummy and tend to smear and stick to the insert flank. The workpiece material welds onto areas of the edge where the substrate is exposed. The BUE is torn off repeatedly, each time taking with it a chunk of the insert, leading to chipping.

Allowing BUE to grow without intervening causes premature edge breakdown and, in some instances, catastrophic insert failure. Fortunately, the temperature and cutting-speed ranges where BUE occurs are well defined and can be avoided. Much of modern stainless-steel turning takes place above the ranges where BUE occurs. And many modern insert grades are highly resistant to BUE if used properly.

Increasing cutting speed usually reduces BUE. If this isn’t possible because of machine restrictions or part specifications, a tougher grade, such as M-35, with a higher positive rake can alleviate BUE.

Flaking involves coating damage caused by an inferior coating, poor adhesion of the coating to the substrate, or plastic deformation of the workpiece. The remedy is to switch to inserts with a more tenacious coating, such as an MTCVD coating.

Crater wear occurs where the chip contacts the tool and is caused by cobalt diffusion between the tool and the chip and abrasion wear on the insert. It weakens the edge. The first recourse is to reduce speed to lower the cutting temperature. Second, reduce feed rate. And it’s a good idea to switch to an MTCVD Al2O3-coated insert with a positive geometry, which resists crater wear.

Thermal cracking is mainly a fatigue-wear phenomenon caused by rapid changes in cutting-zone temperatures and interrupted turning. To avoid it, turn up the coolant flow and select a tougher carbide grade with high resistance to thermal shock or, in some cases, turn off the coolant supply to keep the temperature level even.

Plastic deformation of the stainless-steel workpiece can contribute to notching, edge chipping, and crater wear. This problem often results from higher cutting forces and temperatures encountered when turning stainless steels, especially austenitic stainless steels, which contain nickel and molybdenum. For a tool material that can stand up to these conditions without causing plastic deformation, select an Al2O3-coated, wear-resistant grade. Al2O3 has high hot hardness and resists the cratering encountered at high speeds where plastic deformation occurs.

Table 2: Recommended remedies for the most common types of insert wear. XX = best alternative remedy; X = possible remedy.

Another weapon against improper insert wear is the shim that protects it. A proper shim in good condition is essential for turning stainless steel. It shields both the insert and toolholder from damage caused by high cutting forces. The varying cutting forces in stainless-steel turning create high pulsating pressures on the insert seat and the shim, which act as shock absorbers for the insert and workpiece. Check the condition of the shim every time you change an insert, and, when in doubt, replace it. When using a two-sided insert, watch for a shim face that has an imprint of the insert embossed on it. Such a shim must be replaced. If a shim loses its flatness, its ability to properly support the insert will suffer.

Difficult Cuts

Some new application techniques have been developed to facilitate troublesome cuts such as approaches to shoulders, uneven entering angles, and face turning.

Turning against shoulders. The approach to a shoulder presents a severe change of condition for a turning tool and can be highly stressful on the cutting edge. Chip jamming and hammering also can occur. There are several ways to overcome the risks associated with turning against a shoulder. To overcome chip jamming and hammering, increase the cutting speed when the insert is 0.040" from the shoulder. Or turn the shoulder through a number of axial cuts, forming a step-like profile that can then be finished by two radial cuts. To improve chip control and reduce cutting-edge stress, direct the tool radially in rather than feeding radially out just before the shoulder.

Uneven entering angles. When initial cuts have an uneven, acute start, the solution may be to use an extra insert for the starting process. The tool can have an entering angle of about 45° and can be used to premachine rough edges. It provides an advantageous approach for the main tool. A lower feed rate to engage into the cut is another method.

Facing toward center. Face turning is common in stainless steel and may involve facing either to the center of the workpiece or to a hole. When facing to a center, the cutting speed approaches zero at the center, upsetting the relationship between speed and feed. Higher spindle speeds in modern CNC lathes can compensate for small diameters, but only up to a point. Close to the center, the tool begins to push the workpiece material rather than cut it. Lower surface speeds also have the added disadvantage of causing smearing of the cutting edge and BUE. The best solution is to let a drill cope with the material in the center first, then follow with the face-turning operation. If there is no center hole, reduce the feed rate when the facing diameter becomes 0.400". For example, a feed of 0.010 ipr can be reduced to 0.002 ipr.

Remember, stainless steel, though difficult to turn, is still a very manageable material. Heat is the main enemy, but new inserts and properly applied turning techniques can save the day. Push the tools to the limit and follow the rules of thumb, and you’ll be piling on-spec stainless-steel parts in the bin.

About the Author

Mike Castner is product specialist, turning inserts, with Sandvik Coromant Co., Fair Lawn, NJ.

Related Glossary Terms

  • aluminum oxide

    aluminum oxide

    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.

  • approach angle

    approach angle

    Angle between the insert’s side-cutting edge and the line perpendicular to the milling cutter’s axis of rotation. Approach angle, which is also known as cutting edge angle, is used with metric units of measurement. See lead angle.

  • 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.

  • built-up edge ( BUE)2

    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.

  • cast irons

    cast irons

    Cast ferrous alloys containing carbon in excess of solubility in austenite that exists in the alloy at the eutectic temperature. Cast irons include gray cast iron, white cast iron, malleable cast iron and ductile, or nodular, cast iron. The word “cast” is often left out.

  • chemical vapor deposition ( CVD)

    chemical vapor deposition ( CVD)

    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.

  • chemical vapor deposition ( CVD)2

    chemical vapor deposition ( CVD)

    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.

  • chipbreaker

    chipbreaker

    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.

  • clearance

    clearance

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

  • computer numerical control ( CNC)

    computer numerical control ( CNC)

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

  • 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.

  • cratering

    cratering

    Depressions formed on the face of a cutting tool caused by heat, pressure and the motion of chips moving across the tool’s surface.

  • 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.

  • diffusion

    diffusion

    1. Spreading of a constituent in a gas, liquid or solid, tending to make the composition of all parts uniform. 2. Spontaneous movement of atoms or molecules to new sites within a material.

  • ductility

    ductility

    Ability of a material to be bent, formed or stretched without rupturing. Measured by elongation or reduction of area in a tensile test or by other means.

  • feed

    feed

    Rate of change of position of the tool as a whole, relative to the workpiece while cutting.

  • flank wear

    flank wear

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

  • 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.

  • interrupted cut

    interrupted cut

    Cutting tool repeatedly enters and exits the work. Subjects tool to shock loading, making tool toughness, impact strength and flexibility vital. Closely associated with milling operations. See shock loading.

  • land

    land

    Part of the tool body that remains after the flutes are cut.

  • machinability

    machinability

    The relative ease of machining metals and alloys.

  • metal-removal rate

    metal-removal rate

    Rate at which metal is removed from an unfinished part, measured in cubic inches or cubic centimeters per minute.

  • metalcutting ( material cutting)

    metalcutting ( material cutting)

    Any machining process used to part metal or other material or give a workpiece a new configuration. Conventionally applies to machining operations in which a cutting tool mechanically removes material in the form of chips; applies to any process in which metal or material is removed to create new shapes. See metalforming.

  • milling machine ( mill)

    milling machine ( mill)

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

  • plastic deformation

    plastic deformation

    Permanent (inelastic) distortion of metals under applied stresses that strain the material beyond its elastic limit.

  • rake

    rake

    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.

  • 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.

  • tensile strength

    tensile strength

    In tensile testing, the ratio of maximum load to original cross-sectional area. Also called ultimate strength. Compare with yield strength.

  • titanium carbonitride ( TiCN)

    titanium carbonitride ( TiCN)

    Often used as a tool coating. See coated tools.

  • titanium carbonitride ( TiCN)2

    titanium carbonitride ( TiCN)

    Often used as a tool coating. See coated tools.

  • titanium nitride ( TiN)

    titanium nitride ( TiN)

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

  • titanium nitride ( TiN)2

    titanium nitride ( TiN)

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

  • toolholder

    toolholder

    Secures a cutting tool during a machining operation. Basic types include block, cartridge, chuck, collet, fixed, modular, quick-change and rotating.

  • 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.

  • 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.

Author

Product Specialist

Mike Castner is product specialist, turning inserts, with Sandvik Coromant Co., Fair Lawn, New Jersey.