Chapters 21/22

optimum cutting speed

this is the best trade-off between tool life and the rate of material removal in a cutting process

Titanium carbide

cutting tool materials consisting of TiC particles bonded together in a nickel-molybdenum matrix that are suitable for machining hard materials and cutting at higher speeds than those appropriate for other carbides

Dependent Variables in a cutting process

these include (A) the type of chip produced, (B) force and energy dissipated during cutting, (C) temperature rise in the workpiece, (D) tool wear and failure, and (E) surface finish and surface integrity of the workpiece

Diamond

a form of carbon that is brittle and is the hardest substance known; as a cutting tool material, it has low friction, high wear resistance, and the ability to maintain a sharp cutting edge; it has a strong chemical affinity at high temperatures and it therefore not recommended for machining plain carbon steels or titanium-, nickel-, or cobalt-based alloys

Through the cutting tool system

advanced method of applying a cutting fluid that is integrated into the tool holder itself

inclination angle

angle between the cutting tool's sharp edge and the line on the workpiece's surface that is perpendicular to the direction of cutting in a three-dimensional cutting process

relief (clearance) angle

angle between the inside surface of the cutting tool and the surface that is being cut in a two-dimensional cutting process

rake angle

angle between the outside surface of the cutting tool and the imaginary plane that is perpendicular to the cutting direction in a two-dimensional cutting process

hot hardness

characteristic of cutting tool material that means it remains hard, strong, and resists wear at high temperatures

Inert

chemically unreactive; a desirable characteristic in cutting tool material

Indirect method for cutting tool condition monitoring

correlating a cutting tool's condition with parameters such as cutting forces, power, temperature rise, workpiece surface finish, vibration, and/or chatter

emulsions

cutting fluids that are a mixture of oil and water and additives that are typically used for high-speed operations because the temperature rise is significant; the water acts as a good coolant and the presence of oil reduces the tendency of water to cause oxidation

Tungsten Carbide

cutting tool materials consisting of WC particles bonded together in a cobalt matrix that are produced using powder metallurgy techniques; cobalt increases the toughness but reduces the strength and hardness of the carbide and its composition ranges from 6-16%

(Cemented or sintered) carbides

cutting tool materials that were introduced in the 1930s in response to a growing demand for increased strength and hardness at elevated temperatures; they are among the most important, versatile, and cost-effective tool and die materials for a wide range of applications

coated tools

cutting tools first introduced in the late 1960s that have lives up to 10 times longer than traditional tools; they have unique properties such as lower friction, higher resistance to wear and cracking, and higher hot hardness and impact resistance; they are now used in 40-80% of all machining operations, particularly turning, milling, and drilling; they typically contain either titanium nitride (TiN), titanium carbide (TiC), titanium carbonitride (TiCN), or aluminum oxide (a ceramic with chemical formula Al2O3)

feed rate

distance the cutting tool travels horizontally per unit revolution of the workpiece in a turning process (mm/rev); this is also the depth of the cut in a turning process

Chip Breaker

feature incorporated in a cutting tool that assists with the breaking of large or continuous chips so they do not become entangled in the machinery

cutting fluid

fluid that is used in machining operations to reduce friction and wear, cool the cutting zone, reduce forces and energy consumption, flush away chips from the cutting zone, and/or protect the machined surface from corrosion

machining

general term denoting the removal of material from, and modification of the surfaces of, a workpiece after it has been produced

Roughing cut

general type of cutting operation that is deep and with a high feed rate and/or speed in which large amounts of material are removed from a workpiece in a short time with little regard for surface finish

Finishing cut

general type of cutting operation that is shallow and with a low feed rate and/or speed in which a nice surface finish is a priority

tool wear

gradual deterioration of a cutting tool caused by high localized stresses at the top of the tool, high temperatures along the rake face, sliding of chips along the rake face, and sliding of the tool along the newly cut workpiece surface

tool-life curve

graph of experimental data obtained by performing cutting tests of various materials under different cutting conditions, such as cutting speed, feed, depth of cut, tool machinery and geometry, and cutting fluids

flank face

inside surface of the cutting tool in a two-dimensional cutting process

machine tools

machine on which machining operations are performed

Thermally assisted machining

machining in which a source of heat (e.g. torch, induction coil, electric current, laser beam, electron beam, plasma arc) is focused onto an area just ahead of the cutting tool; it may enable machining of a metal or alloy that may otherwise be difficult to machine at room temperature

cutting off (parting)

machining operation in which a small piece is separated from the main portion of a blank; cutting a piece from the end of a part in order to produce a slug or blank for additional processing into a final product

finish machining

machining where the main consideration is the surface finish to be produced

rough machining

machining where the main purpose is to remove a large amount of material at a high rate

near-dry machining

machining with only a small amount of cutting fluid; it has become increasingly popular since the mid-1990s in response to rising concerns about pollution, air quality in factories, environmental impact, cost, and workpiece surface quality

helical

typical shape of the chips in a three-dimensional cutting process

High-pressure systems

method of applying a cutting fluid in which specially designed nozzles deliver fluid at a very high-pressure (5.5 to 35 MPa) to the cutting region (especially the relief face of the cutting tool); the high pressure acts as a chip breaker and the fluid must be continuously filtered to remove large particles that might otherwise damage the workpiece

Flooding

method of applying a cutting fluid in which the cutting fluid is essentially poured in large quantities (from 3-60 gallons/minute) into the cutting region, often under pressure

Mist

method of applying a cutting fluid in which the cutting fluid is sprayed under low pressure in small quantities into the cutting region in a manner similar to using an aerosol can; it provides good visibility of the workpiece being machined but has limited cooling capacity and requires ventilation

Oblique

neither perpendicular nor parallel to a given line or surface; slanting; sloping; the majority of machining operations involve this type of cutting

rake face

outside surface of the cutting tool in a two-dimensional cutting process

temperature rise

phenomenon that occurs in all cutting operations whereby friction between the cutting tool and chips of the workpiece convert mechanical energy into heat

cutting tool

portion of a machine tool that removes the material from a workpiece

Chip

small piece of material removed from the surface of a workpiece during machining

Insert

small, individual cutting tools (often of triangular or square shape) with several cutting edges or points (6 or 8 respectively) that are often clamped on a tool holder via a locking mechanism; a typical 0.5" example made out of (uncoated carbide, diamond) costs ($10, $100)

lubricant

substance whose main purpose is to lessen friction, especially in the working parts of a mechanism; cutting fluid that reduces the friction between the cutting tool and workpiece

coolant

substance whose main purpose is to reduce the temperature in a machine; cutting fluid that reduces the high temperatures developed in the cutting zone

Substrate

the basic material upon which another specialized material is mounted or attached; the surface or medium on which an organism grows or is attached; material upon which semiconductor devices are fabricated

high-speed steels

the most highly alloyed tool and die steels; steels that are very strong and hard at elevated operating temperatures that are used in cutting tools; they are so named because they were developed (in the early 1900s) to machine at higher speeds than was previously possible; there are two basic types--molybdenum ("M-series" with 10% molybdenum) and tungsten ("T-series" with 12-18% tungsten)

Indexing

the rotation of a cutting tool insert in its holder in order to change the cutting edge

Cubic Boron Nitride

the second hardest material known; introduced in 1962, this cutting tool material is applied as a layer on top of a carbide substrate by sintering under high temperature and pressure; the carbide provides shock resistance while this material provides very high wear resistance, cutting-edge strength, and chemical inertness to iron and nickel at high temperatures

cutting speed

the velocity of the tool along the surface of (or relative to the surface of) a workpiece that is being cut

Independent Variables in cutting process

these include (A) the tool material and coatings, (B) tool shape, surface finish, and sharpness, (C) workpiece material and condition, (D) cutting speed, feed, and depth of cut, (E) cutting fluids, (F) characteristics of the machine tool, and (G) work holding and fixturing

built-up edge (BUE)

undesirable result when layers of material from a workpiece that are gradually deposited on the tool tip in a cutting process; as it grows larger, it suddenly breaks apart only to start reforming again in a cycle of formation and destruction; it is verbally undesirable because it changes the geometry of the cutting edge and dulls it

Direct method for cutting tool condition monitoring

using a microscope or other instrument to optically measure cutting tool wear and/or observe changes in the tool shape/profile