Quiz 4 processing

Edge Rounding

Because of high stresses, both shear and compression, and high temperatures, sharp tools tend to become dulled and rounded during cutting operations. Alternatively, repeated formation and fracture of a built up edge tends to break off pieces of the tip of the tool, leaving it dull and round.

Oblique Cutting

Cutting is the use of a hard tool to shear away a thin strip of metal from a workpiece. It is _ if the edge of the cutting tool is not perpendicular to the direction of travel of the tool relative to the workpiece.

Orthogonal

Cutting is the use of a hard tool to shear away a thin strip of metal from a workpiece. It is _if the edge of the cutting tool is perpendicular to the direction of travel of the tool relative to the workpiece.

Notch Wear

Deformation of the metal within the tertiary shear zone leads to the formation of a hardened layer on the surface of the workpiece. In multiple pass operations, this hardened layer slides along the side of the tool at the depth of cut. Because it is harder than the bulk workpiece, this hardened layer tends to wear a notch into the side of the tool. This formation of a _ in the side of the tool is_.

Flank Wear

In a machining operation, the tool tends to wear away with time, especially at high speeds. Gradual removal of mass from the flank of the tool, by adhesive or abrasive wear,

Secondary shear zone

In cutting operations, the chips must slide along the rake face of the tool. The region near the rake face within which sliding or metal shear occurs is the _. Shear in this region is unavoidable, but does not actually contribute to removal of metal from the workpiece

Cutting Force

In orthogonal cutting, a force must be applied to the tool to force it into the workpiece. The component of the force parallel to the surface of the workpiece is the .

Flank

In orthogonal cutting, metal slides up the rake face (the secondary shear zone), and the tool slides over the new surface of the workpiece (the tertiary shear zone). The side of the tool that is sliding over the freshly exposed surface of the workpiece is the flank, or clearance edge.

Friction Force

In orthogonal cutting, there is a shear force in the plane of the rake face of the tool. This force is referred to as the _, even though it is not solely due to friction.

Primary Shear Zone

In the simplest analysis of orthogonal cutting, shear is presumed to occur within a plane, which lies at an angle to the surface of the workpiece. The _ is necessary for the cutting operation.

Clearance angle

In the simplest analysis of orthogonal cutting, the tool is wedge shaped. Its lower surface lies at an angle to the new surface of the workpiece; this angle is the

Crater wear

Metal in the secondary shear zone is moving up the tool face. Near the tip of the tool, the forces are very compressive; further up the tool, the chip is free to curl away from the tool face. Tool metal in the compressive zone tends to stay put. Where there no more compression, the chip tends to carry away tool material, leaving a crater. The heat generated in this area because of friction also contributes to the wearing away.

Cemented Carbides

They are formed from hard carbide (WC, TiC, etc) powders that are heated with Co or Fe-Ni powders. At high temperatures, this is a liquid-phase sintering process; the Co metal increases the rate of transport of the carbide, such that necks form between the particles. At lower temperatures, bonds do not really form between carbide particles; this is properly referred to as _, or liquid phase consolidation. In either case, the metal remains, and serves to help hold the particles together, forming a hard, but very tough tool material. _ generally have lower metal volume fractions; the metal content can range from 6% to 22%. The carbon is in the form of hard carbides that are held together by the Co or Fe-Ni. Cast carbides can be used to cut most metals at higher rates than can high speed steels. Cemented and cast carbides are also used for digging through rocky material.

Cast Carbides

Tool materials made by solidifying slurries containing carbides (TiC,WC, VC, etc.) in Co or Fe-Ni alloys are cast carbides. As suggested by the name, these materials are shaped by the casting process; they are often used as inserts within steel cutting tools. The carbon is in the form of hard carbides that are held together by the Co or Fe-Ni. can be used to cut most metals at higher rates than can high speed steels. also used for digging through rocky material.

Buffing

a form of abrasive machining in which the abrasive is applied to a soft surface, such as felt or other fabric; this fabric is caused to slide over the surface of the workpiece. For_, there is a semisoft binder bonding the abrasive particles to the fabric._ can be used to develop metal surfaces having mirror-like finishes.

Broaching

a multipoint machining operation whose purpose is to make shaped holes through a workpiece. The _ is a gradually tapered tool, with many teeth around its outer edges. The _ is moved through a hole, gradually widening it and possibly changing its shape. Because each cutting edge is slightly different from its neighbors, forces and pressures change along the length of the _, and_ is a multipoint machining operation.

High Speed Steels

are Fe-C alloys that contain significant amounts of the mixed-metal carbide formers, such as W, Mo, Cr. High speed steels are processed at high temperatures to solutionize these elements, shaped, then heat treated to form large volume fractions of stable mixed-metal carbides. The carbon in these allows is in the form of mixed metal carbides, such as M23C6, M3C7, or M6C._ are used to cut nonferrous alloys, such as Al, Cu, Ni, as well as mild steels and cast irons.

Hardened Steels

are Fe-C alloys that have been processed to form hard (martensitic) phases. They contain carbon as interstitial solutes within the Fe. _ can be used to cut soft materials, such as polymers, wood, and, perhaps, soft nonferrous metals, such as Pb.

Coated Carbides

are cast or cemented carbides that are coated with a vary hard surface layer, such as TiN. They are used for the metal cutting operations that are common to the other carbide tools.

Emulsions

are cutting fluids with oils dispersed in water with the aid of surface-active molecules. The surface-active molecules are organic molecules with a polar (hydrophilic) end and a non-polar (hydrophobic) end. In _, the oil droplets are large enough that the fluid is cloudy.

Cutting Oil

are mineral oils (with additives) that are used in some low speed cutting operations. The term "mineral oil" is poorly defined. It generally refers to highly purified petroleum oils that are transparent or translucent.

Ceramics

inorganic, nonmetallic materials. The ceramics that are used as cutting tools include alumina, zirconia, and silicon carbide. These materials are formed as sintered bodies, then used as inserts within steel tools. Oxide ceramics, such as alumina or zirconia contain no carbon, covalent carbides, such as silicon carbides are compounds containing carbon as an essential constituent. Tools containing ceramic inserts can be used for high speed cutting of metals.

Grinding

is a form of abrasive machining in which a solid _ wheel, composed of abrasive particles embedded in a binder is rotated rapidly as it engages the workpiece.

Grit blasting

is a form of abrasive machining in which abrasive particles are carried into contact with the workpiece by a fluid, such as air or water.

Lapping

is a form of abrasive machining in which the abrasive is dispersed in an oil-based slurry, and the slurry is carried by a soft, somewhat porous (cast iron) table.

Cutting Fluid

is a liquid used to cool a cutting tool during a machining operation. Its secondary functions include lubrication (primarily in the tertiary shear zones) and flushing away the metal chips. Because the primary function of the cutting fluid is heat transport, cutting fluids are usually composed mostly of water with oils and surfactants added to assist with the lubrication.

Drilling

is a machining operation designed to make cylindrical holes in a workpiece. A _ is a cylindrical tool with cutting edges on one end and flutes along its sides. The _ is indented into the workpiece as it is rotated about its axis. The cutting edge lift metal from the bottom of the hole, and the flutes carry it away. Because the forces and velocities vary continuously along the cutting edges, is a multipoint machining operation.

Sawing

is a machining operation in which a narrow line of cutting teeth is moved along the line of the teeth, in order to develop a groove in the workpiece or cut it off entirely. _ can be linear (reciprocating motion), cylindrical, or along the edge of a continuous, flexible band. _is a multipoint operation.

Shaping

is a machining operation in which the tool and workpiece are moved along a line relative to each other. _ usually involves a tool that engages the workpiece over an extended curved surface. Tool and workpiece are in contact over an extended length, but the forces and velocities are the same at each point along the cutting edge. It is probably most meaningful to think of _ as a single-point machining process.

Planing

is a machining operation in which the tool and workpiece are moved along a line relative to each other. _usually involves a tool that engages the workpiece over an extended straight surface. Tool and workpiece are in contact over an extended length, but the forces and velocities are the same at each point along the cutting edge. It is probably most meaningful to think of _ as a single-point machining process.

Electrochemical Grinding

is a process that uses abrasive wear and chemical machining to remove material from a surface. Most often, the surface must be very planar. In _, the abrasive particles break up the surface layers so that the underlying material can be attacked uniformly.

Filing

is a tool with a periodic arrangement of cutting edges distributed over a surface. Files may be flat, cylindrical, triangular...Filing is the use of such a tool to remove metal from an area of the surface of a workpiece. Filing is a multipoint machining operation.

Forming/Turning

is a turning operation in which a contoured tool is moved radially to the workpiece, producing a curved surface. _ is a multipoint machining operation.

Facing

is a turning operation, which produces a plane perpendicular to the axis of rotation of the workpiece by moving a single point tool radially across the axis of the workpiece. _ is a single point machining process.

rake angle

is the angle between the normal to the workpiece and the rake face of the cutting tool

Diamond

is the cubic form of carbon and is the hardest materials known to man. Diamond can be used as inserts within cutting tools; sometimes diamond needles and scribes are used for specialized single point machining operations. As a covalent ceramic composed of light elements, (This is also true for CBN.) diamond has a very high thermal conductivity. Since C is somewhat soluble in Fe, diamond is not usually used for cutting ferrous alloys. Diamond is pure carbon.

Machinablility

is the facility with which parts can be fabricated by machining operations. A machinable material is cut easily (low forces, energies, and temperatures) and gives a smooth surface finish without much effort. Tool life is long, when they are used on a machinable material. _ usually refers to the characteristics of the workpiece, but also should include the process used.

Chip Compression Factor

is the reciprocal of the cutting ratio.

Cubic Boron Nitride

is the second hardest material known to man. It is closely related to diamond. Within diamond, there are two carbon atoms, separated by <1/4,1/4,1/4> at each fcc lattice point. If one of these is replaced by B, and the other by N, the cubic boron nitride structure is obtained. As a covalent ceramic, CBN is difficult to sinter. CBN is used as a ceramic insert in high speed cutting tools. CBN contains no carbon. Boron nitride can also form as a graphite-like layered structure, which is normally used for machining.

Electrodischage machining

is the use of localized electrical discharges to ablate away small particles. The electrical discharge is a small electric arc, that is concentrated by the presence of a dielectric fluid around the tool.

Cutting Speed

is the velocity of the tool relative to the workpiece.

Built Up Edge

it is not unusual for some of the workpiece metal to adhere to the tip of the cutting tool. When this happens, the workpiece is being sheared within itself, not at its interface with the cutting tool. The _ contains a dead metal zone - a region that is not being deformed or sheared. _ normally form at moderate cutting speeds. For low speeds, forces are not large enough to deform the workpiece around the tool tip and weld it to the tool tip. At very high speeds, the _ becomes very hot, softens, and disappears.

Abrasive machining.

removal of material from a workpiece by a multitude of hard, angular, abrasive particles that are forced to slide over the surface. The abrasive particles cut small chips off of the workpiece.

Abrasive wear

the gradual removal of material from the surface of a workpiece by the cutting action of small, sharp, hard particles forced to move over the surface of the workpiece.

Adhesive wear

the gradual removal of metal from the surface of a piece of metal by (i) the formation of cold welds at points of contact with another metal, (ii) rapid work hardening of the cold welds because of the relative motion of the two bodies, (iii) exhaustion of ductility within the cold welds, (iv) fracture of the cold welds at various places.

Chemical Machining

the use of a chemical or electrochemical attack to remove matter from a workpiece. Normally, a mask or stop-off coating is applied to the areas of the workpiece that should not be attacked. Then, the chemical is applied to the workpiece. When sufficient matter has been removed, the part is cleaned, and the mask is removed.

Boring

turning the internal surface of a hollow, cylindrical workpiece. is a single point machining operation.

Electrochemical machining or polishing

uses an electrochemical attack to remove matter from a metallic surface and leave that surface with a mirror-like finish. For polishing, there must be continuous laminar flow of the electrolyte over the metal surface.