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machine tool

machine tool, power-operated tool used for finishing or shaping metal parts, especially parts of other machines. An establishment that is equipped with such tools and specializes in such work is known as a machine shop. Machine tools operate by removing material from the workpiece, much as a sculptor works. Basic machining operations are: (1) turning, the shaping of a piece having a cylindrical or conical external contour; (2) facing, the shaping of a flat circular surface; (3) milling, the shaping of a flat or contoured surface; (4) drilling, the formation of a cylindrical hole in a workpiece; (5) boring, the finishing of an existing cylindrical hole, as one formed by drilling; (6) broaching, the production of a desired contour in a surface; (7) threading, the cutting of an external screw thread; and (8) tapping, the cutting of an internal screw thread. In addition there are operations such as sawing, grinding, gear cutting, polishing, buffing, and honing. The tools themselves vary in size from hand-held devices that can be used for drilling and grinding to large stationary tools that perform a number of operations. Many machine tools have a name that indicates their principal function, e.g., drill press, broach machine, milling machine, and jig borer. The lathe can perform turning, facing, threading, drilling, and other operations. In order to withstand the great heat that this work generates, the materials used in machine tools must be extremely hard and durable. Thus, their working surfaces are made of such substances as high-speed steels, sintered carbides, and diamonds. To help dissipate the heat, the area of contact between the working surface and the workpiece is usually lubricated with a fluid that may also improve the finish of the workpiece's surface. Modern machine tools are often numerically or computer controlled; where a human operator can be distracted, and is limited by the speed of human reflexes, a numerically controlled machine is more reliable and accurate. See boring mill.

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machine tools

machine tools Power-driven machines for cutting and shaping metal and other materials. Shaping may be accomplished in several ways, including shearing, pressing, rolling, and cutting away excess material using lathes, shapers, planers, drills, milling machines, grinders, and saws. Other techniques include the use of machines that use electrical or chemical processes to shape the material. Advanced machine-tool processes include cutting by means of laser beams, high-pressure water jets, streams of plasma (ionized gas), and ultrasonics. Today, computers control many cutting and shaping processes carried out by machine tools and robots.

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machine tool

ma·chine tool • n. a nonportable power tool, such as a lathe or milling machine, used for cutting or shaping metal, wood, or other material. DERIVATIVES: ma·chine-tooled adj.

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Machine Tools

Machine Tools

Milling machines

Turning centers or lathes

Boring machines

Planers

Shapers

Drilling machines

Sawing machines

Grinding machines

Resources

A machine tool is an electrically powered tool that is used to remove material, usually metal, at a controlled rate to achieve a desired shape or finish. A machine tool typically holds the workpiece and a cutting tool, and moves either the workpiece, tool, or both to provide a means of machining the material to the desired shape. Machining, another term for metal-cutting, is performed by shaving away the metal in small pieces called chips. An average machining operation can reduce the original workpiece weight by approximately 50%. The modern machine tool is a precision piece of equipment designed to cut metal and produce thousands of parts to an accuracy of millionths of an inch, which is approximately equal to 1/300 of the thickness of a human hair. Machine tools range from very small bench mounted devices to large complex machines weighing hundreds of tons. The major operations performed by machine tools are milling, turning, boring, planing, shaping, drilling, power sawing, and grinding.

Milling machines

Milling machines comprise one of the largest categories of machine tools with many different varieties and configurations available. A milling machine is considered essential equipment in any machine shop because of its wide variety of machining operations and its high metal removal rates. The workpiece, mounted on a movable machine table, is fed against one or more multiple-tooth rotating tools called milling cutters, or mills. The workpiece is usually held in vises, special holding fixtures, or clamped directly to the machine table and fed at right angles to the axis of the milling cutter to produce flat, recessed, or contoured surfaces.

Classifications

Milling machines can generally be classified according to the orientation of the spindle, either vertical or horizontal. Vertical milling machines can also have what is called multiaxis capability where the vertical axis can tilt and swivel to enable the machining of closed angles and contoured surfaces. Vertical milling machines are extremely versatile and can machine horizontal surfaces, vertical surfaces, angular surfaces, shoulders, grooves, fillets, keyways, T-slots, dovetails, and precision holes.

Horizontal milling machines are available in plain and universal types. Plain milling machines have tables that are fixed at right angles to the knee. Universal milling machines have a table that can be pivoted in a horizontal plane. This allows the machine table to be swiveled to different angles for milling helical grooves.

The universal milling machine is widely used by maintenance machinists and toolmakers because of its versatility. Computer numerically controlled (CNC) mills or machining centers are available in vertical and horizontal configurations and come with automatic tool changers that can store many different tools in carousels. The major components of a typical milling machine include the following: base, column, knee, elevating screw, saddle, machine table, ram, head, and spindle. The base is the heavy foundation member of the machine that can also be used as a reservoir for coolant or cutting lubricant often used in machining operations. The base is a massive casting that helps to absorb and dampen vibration from the machining process. The column, which is either cast with the base or keyed and bolted on, supports the functioning members of the machine. Horizontal ways on top of the column support the ram and head while vertical ways on the column front face support the knee, saddle, and machine table. The knee moves along the vertical ways of the column and is the basic work-supporting member. The knee is equipped with ways on top to allow horizontal movement of the saddle to and from the column face. The elevating screw provides additional support for the knee and allows the knee to be raised and lowered. The saddle mounts on the ways of the knee and has horizontal ways at right angles to the knee ways to support the machine table.

The machine table moves longitudinally on the ways of the saddle and supports the workpiece. Combined movements of the knee, saddle, and machine table allow for precise positioning and feeding of the workpiece left and right, in and out, and up and down. This is called 3-axis movement (X = left and right movement, Y = in and out movement, and Z = up and down movement). A rotary table can be added to a 3-axis mill to give it 4-axis capabilities (typically rotation is about the longitudinal or X-axis), while 5-axis mills are able to tilt and swivel about the vertical axis. The ram is mounted on the horizontal ways at the top of the column. It supports the head and provides horizontal movement and positioning of the head at varying distances from the column face. The head includes the motor, stepped pulley, belt drive (or in the case of heavier duty mills, the gear drive), and the spindle. The head assembly provides for rotation of the spindle and spindle feeding along the vertical axis using a quill. The spindle contains the toolholding mount and drives the cutter.

Turning centers or lathes

Lathes are considered to be one of the oldest machine tools in existence. Lathes were typically foot-powered until water and steam power were harnessed. One of the first machines driven by Scottish inventor and engineer James Watts (17361819) steam engine was a lathe that is how it came to be known as an engine lathe. The lathe operates by holding the workpiece in a rotating holder, usually a chuck or collet, and then a single-point cutting tool is fed into the workpiece. If the tool is fed along the axis of rotation of the workpiece, it is considered to be a turning operation and any desired cylindrical contour can be made. If the cylindrical contour is produced on the inside of the workpiece, the operation is called boring.

In addition to turning and boring, the lathe is also used for threading, tapping, facing, tapering, drilling, reaming, polishing, and knurling. Some typical parts a lathe may produce are pins, bolts, screws, shafts, discs, pulleys, and gear blanks. Different attachments allow a lathe to perform milling, grinding, and broaching operations. With the right combination of attachments, it is said that the lathe is the only machine tool capable of reproducing itself. The size of a lathe is given in terms of the maximum swing and length of bed. The swing refers to the maximum diameter of work that can be rotated in the lathe. The length of the lathe bed refers to the maximum length of the lathe ways, not the maximum distance between centers of the chuck and tailstock. Many different varieties of lathes are available ranging from the small precision lathe used for making watch parts to the extremely large lathes used in producing mill rolls and rocket casings.

Lathes can generally be classified in one of the following five basic groups: engine lathes, speed lathes, turret lathes, vertical lathes, and automatics. The engine lathe, sometimes referred to as a geared-head lathe, is the most commonly found lathe model. Speed lathes are used where the workpiece is polished or formed (e.g., spinning) rather than cut. Turret lathes have a turret tool changer that rotates to permit a number of different tools to be used in a certain sequence. Vertical lathes have a vertical axis of work-piece rotation rather than horizontal. Automatic lathes consist of high production turning machines such as screw machines and single or multiple spindle chucking and bar fed machines.

All of the five basic lathe groups can also be found in a computer numerically controlled version, sometimes called a turning center. The main components of a typical engine lathe include the following: bed, headstock, feedbox, tailstock, and carriage. The bed is the base of the lathe that supports the other components. The precision ways are the part of the bed on which the carriage travels. The bed is a massive casting in order to absorb and dampen vibration from the machining process. The headstock is mounted rigidly on the bed and houses all the gearing and mechanism for the spindle drive and power takeoff source for the feed-box. Controls for selecting and changing spindle speeds are also part of the headstock. The feedbox, which may be an integral part of the headstock or a separate unit, drives both the feed rod and the lead screw for the feed rate or thread lead required.

A direct mechanical connection with the spindle drive is required to provide the proper relationship for feeding or threading operations. The lead screw is a precision part and is usually only used for threading operations to avoid unnecessary wear. Most engine lathes incorporate a feed rod that is used to drive the carriage for operations other than threading. The headstock spindle supports a faceplate, chuck, or collet, which in turn holds and drives the workpiece. There are four types of standard spindles, all identified by the type of nose: threaded nose, camlock, taper nose key drive, or flanged nose. The threaded nose spindle is usually only found on smaller and less expensive lathes. The camlock type allows faster changing of faceplates or chucks. The taper nose key drive type provides greater support to the workpiece while the flanged spindle nose permits mounting of special chucks or power operated equipment and can be found on turret lathes and automatics. The tail-stock is mounted on the bedways and may be positioned and clamped to support work for turning. It may also use a tool mounted in place of the tailstock center so that boring, drilling, or reaming can be done. The tailstock must be perfectly aligned with the head-stock spindle in order to produce good parts. The carriage is the tool platform of the machine. It supports and feeds the cutting tool over the work. The carriage consists of the cross slide, which bridges the ways to support the compound and tool post, or toolholder, and the apron. The lead screw and the feed rod pass through the apron and transmit feeding power to the carriage. The main controls for positioning and feeding the tool are also located on the apron.

Boring machines

Boring machines are similar in construction to milling machines except they are generally more massive and built lower to the floor, use different tooling, and feed differently along the axis of the spindle. Boring machines are typically located in very clean, climate controlled environments and are massive for extra rigidity and vibration damping to ensure close tolerance hole sizes and locations, one example being automobile engine piston bores.

Jig boring machines are primarily intended for tool room use and are used to produce precision dies, jigs, and gages, which are used to ensure the accuracy and interchangeability of high volume production parts. There are three common designs of jig boring machines in use, the open-sided or C-frame, adjustable-rail, and fixed-bridge construction. Variations of the jig boring machine include jig grinders, which are used to realign holes after hardening, and the horizontal jig boring and milling machine, which is utilized for general production operations.

The base of the jig boring machine supports a saddle that moves in and out from the operator to the column. A table moves right or left on the saddle to complement the saddle movement. A massive column supports the spindle housing, which adjusts to the work location by moving up and down the column ways. The spindle moves inside a quill that is supported by the housing or spindlehead.

The quill also moves up and down inside the housing to give a telescoping mechanism which adds rigidity to the spindle. The spindle, quill, and housing are manufactured under very careful and exacting conditions to eliminate any lost motion. The housing is usually made of Invar cast iron to minimize errors due to thermal expansion. Stability of the housing is extremely critical because any expansion would change the tool location relative to the column.

The spindle is hardened, ground, and lapped. Preloaded ball bearings also help to eliminate lost motion of the tool and its driving mechanism. Spindle speeds range from 30 to 1,500 rpm (revolutions per minute) on an average machine. A digital readout (DRO) system is used to provide a continuous numerical readout of the table position. Jig boring machines may also be computer numerically controlled (CNC). CNC control permits many additional jobs that would be impossible with a manually operated machine. One example would be to produce precise, irregularly curved forms to be generated on cams or master templates without operator involvement.

Planers

Planers remove metal in a series of straight cuts by reciprocating (moving back and forth) the workpiece as the single-point tool feeds. The fixed tool is rigidly supported while the workpiece moves on precision ways for the full length of the cut, thus ensuring maximum accuracy. The rigidity of the tool allows the use of powerful motors, up to 150 hp (horsepower), which permits higher production speeds and the use of multiple tooling with extremely heavy cuts and feeds. Planers are typically big machines used for handling the largest and heaviest work that can be supported on the machine table, as much as 75 tons (68 tonnes). Planers may be fitted with hydraulic tracing attachments to enable them to cut curved surfaces.

There are two distinct types of planers, the single-housing, or open-side planer, and the double-housing planer. Double-housing planers are the most widely used and provide the greatest tool support rigidity. The major components of a double-housing planer are the bed, table, housings, arch, cross rail, and heads (side and rail). The bed is the foundation to which the housings are attached. The bed is provided with precision ways over its entire length and supports the reciprocating table.

The table supports the workpiece and reciprocates along the ways of the bed. The table is slightly less than half the length of the bed and its travel determines the dimensional capacity of the machine in length of stroke. The housings are rigid box-type columns placed on each side of the bed and table. They are heavily braced and ribbed to absorb the large cutting forces encountered in planing. The arch joins the housings at the top for greater rigidity of construction and, also, houses the drive mechanism for tool feeding. The cross rail is a rigid horizontal beam mounted above and across the table on the vertical ways of the columns. It supports the rail heads and provides for horizontal feeding of the cutting tools.

The heads carry the cutting tools and are equipped with clapper blocks that lift the tools clear of the work on the return stroke of the table. Single-housing or open-side planers support the cross rail from a single column. This permits wide workpieces to overhang the table on the open side if necessary.

Planers require many strokes of the workpiece to complete a cutting operation. Horizontal and vertical mills are much more efficient at metal removal than planers and have replaced planers for production work.

Shapers

Shapers utilize a reciprocating single-point tool with the workpiece clamped on the machine table. The workpiece position and feeding are controlled to produce the desired shape or surface as the tool passes back and forth along a fixed path taking a series of straight cuts. Horizontal shapers are used for machining flat surfaces, which may be horizontal, vertical, or angular. Vertical shapers or slotters are used for machining slots, keyways, and splines. Shapers may be fitted with hydraulic tracing attachments to enable them to cut curved surfaces. The size of a shaper is designated by the maximum length of stroke or cut it can take.

There are many different types of shapers, but the most common is the horizontal plain shaper, which consists of a bed, column, cross rail, table, ram, and the head. The bed is the rigid base of the machine that supports the column and sometimes an outrigger table support, which is used to increase the rigidity of the workpiece mounting. The column houses the motor and drive mechanisms, and it is equipped with two sets of precision ways that support the ram and cross rail. The cross rail is a horizontal member that travels vertically on the ways of the column to be adjusted, and clamps in place in the desired position. The cross rail supports the table on precision ways. The table supports the workpiece and feeds along the cross rail. The ram is the tool driving member and reciprocates on precision ways on top of the column. The length of stroke, rate of reciprocation, and overhang at the extreme end of the ram travel are all adjustable. The head, which is mounted on the forward end of the ram, supports the toolholder and provides for vertical feeding or swiveling of the tool 30° either way from vertical.

Shapers require many strokes of the tool to complete a cutting operation. Horizontal and vertical mills are much more efficient at metal removal than shapers and have replaced shapers for production work.

Drilling machines

Drilled holes are required in the manufacture of almost every product and drilling is one of the most common machining operations. Drilling machines are similar in construction to milling machines except they are used exclusively for making holes.

All drilling machines are characterized by a rotating cutting tool that advances along its axis into a stationary workpiece producing a hole. Six common operations that can be performed on a drill press are drilling, reaming, boring, counterboring, countersinking, and tapping. Drilling machine capacity is determined by the size of the largest workpiece over which the spindle can be centered, the maximum clearance under the spindle, and the maximum drill diameter that can be fed at a practical feed rate through mild steel. The five major classifications of drilling machines are uprights, radials, horizontals, turret drills, and multiple-spindle machines. Each classification represents a family of machines that is further subdivided.

Upright drills comprise the largest group and are characterized by a single vertical spindle rotating in a fixed position and supported in a modified C-frame structure. The major components of the upright drill include the base, column, spindle, motor, head, table, feed mechanism, and quill.

Radial drills are designed to accommodate large work. These machines are arranged so that the spindle can be positioned to drill anywhere within reach of the machine by means of movement provided by the head, the arm, and the rotation of the arm about the column. Some types of radials and portable horizontal machines allow the entire machine to be moved to the workpiece.

Horizontal drills are characterized by the position of the spindle. Way-type and spindle-feed horizontals are self-contained units consisting of motor drive, gearing, and spindle which may be mounted at any predetermined drill angle and are used extensively to meet high production needs.

Turret drilling machines provide a number of tools mounted in a turret designed to handle a sequence of operations. The turret drilling machine is also available as a computer numerically controlled machine.

Multiple-spindle drilling machines include those designed with fixed spindles for single-purpose production and those where the spindles are adjustable, either by means of universal joints or by traversing along a worm or spiral drive in a straight line. Multiple-spindle drilling machines are primarily used for high production rate workpieces.

Sawing machines

Sawing machines Sawing machines are primarily used to part material such as rough-cutting excess material away before machining or cutting curved patterns in sheetmetal. Sawing machines substitute mechanical or hydraulic powered motion for arm motion to achieve the speed necessary for production operations. The cutoff operation is usually one of the first requirements in any production process before any machining, welding, or forging is done. The saw blade has individual teeth that track through the workpiece, each tooth deepening the cut made by the preceding tooth in the direction of feed. The saw or work may be fed and by controlling the direction of feed, either straight or curved cuts can be made. The width of the cut (also known as kerf) is approximately equal to the thickness of the saw blade and because of this saw blades are made as thin as possible but with adequate tool strength and rigidity.

There are three common types of sawing machines, reciprocating or hack saws, band saws, and circular saws. These machines all perform the same operation but vary in capability, capacity, and application. Power hacksaws use a reciprocating stroke where on the cutting stroke the saw blade teeth are forced into the metal either by gravity or hydraulic pressure while on the return stroke the pressure is automatically removed to prolong saw blade life. Most of the machines come equipped with a chip tray and a cabinet base that contains the coolant reservoir and its circulating pump. Heavy-duty power hacksaws come with automatic bar feeds where the stock is loaded on a carriage that automatically moves forward the necessary distance when the cutting is finished. Hydraulic pressure automatically operates the vise jaws, gauges the material, and raises and lowers the saw blade.

After being set up for cutting material to a specified length, the power hacksaw will operate automatically without need for an operator until all the material loaded on the carriage has been cut. Horizontal band saws are one of the most widely used sawing machines for cutoff operations. These band saws range from small manually operated machines to large, fully automatic production machines. Vertical band saws are also used but are primarily manually controlled machines used in tool rooms and shops for maintenance and low production work.

Band saws have several advantages over other kinds of cutoff machines. The saw blade cutting width, or kerf, is 1/16 in (0.16 cm) compared to 1/8 in (0.33 cm) for power hacksaws and abrasive disc circular saws, and 1/4 in (0.64 cm) for cold saws. This can represent a sizable savings especially when cutting large or expensive material. The thinner saw blades also require less power to cut through material making them more economical to operate. Because bandsaws have endless blades (band saw blades are welded together to create an endless loop) that cut continuously, the cutting rates are much higher.

Two of the most popular circular saws are the cold saw and the abrasive disc cutoff saw. Cold saws are low rpm circular saws for metal cutting. These saws range in size from hand-operated bench-top models with 8 in (20 cm) blades to fully automatic machines with blades of 3 in (7.6 cm) diameter and larger. Light duty manual or automatic machines are sometimes equipped with a swivel head that enables cuts to be made at different angles. These saws are mostly used for cutting structural shapes such as I-beams, angles, and channel sections because the circular blades can complete their cuts with less travel than straight blades. Heavy-duty machines are available with bar feeds and can be used for cutting solid bars up to 10 in (25 cm). Material larger than this size would require excessively large blade diameters, which must be more than double the cutting capacity, which would become too costly along with the machine necessary to drive them. Different speed ranges are provided for cutting metals of different hardness and toughness, and built-in coolant systems help produce better finishes and prolong blade life.

Abrasive cutoff saws utilize an abrasive disc to separate material by using a grinding action. Abrasive cutoff saws are built for either manual operation or with power feeds, with either fixed or oscillating wheel heads. Oscillating wheel heads are used when cutting thick sections of tough materials such as titanium, nickel-based superalloys, and other high alloy steels. Sizes range from small bench-top machines with 8 in (20 cm) wheels to bigger machines with 20 in (50 cm) or larger wheels. Abrasive cutoff saws are very useful for rapidly cutting small sizes of bar stock, tubing, and structural shapes and also for cutting tough or hardened materials that cannot be cut efficiently with other types of saws.

Grinding machines

There are many different types of grinding machines available that are used to obtain very close tolerances and fine finishes. Grinding machines are used for grinding flat surfaces, external and cylindrical surfaces, tapered surfaces, and irregular surfaces. Production parts are typically ground to tolerances of plus or minus 0.0001 in and special parts for precision instruments are ground to plus or minus 0.000020 in (20 microinches). All grinding machines utilize a rotating abrasive wheel or moving belt in contact with a workpiece to remove metal. Various combinations of wheel feed, either along or normal to the axis of wheel rotation, and also rotary or linear workpiece motion, are provided by the different types of grinding machines. To produce shapes of cylindrical section, workpiece and wheel both rotate on parallel axes while one or the other is fed along its own axis of rotation. Contact between workpiece and wheel is on the outside diameter of the wheel and the work is mounted between centers, chucked, or rotated without centers by a back-up wheel (this is called centerless grinding). To produce flat surfaces, the workpiece is mounted on a table. It is, then, traversed along a line parallel to the surface to be ground or rotated about an axis at right angles to the surface to be ground. The axis of grinding wheel rotation can either be parallel or perpendicular to the surface to be ground, applying either the side or face of the wheel. Complex shapes are routinely ground such as thread forms, cam contours, gear teeth, and cutting tool edges. The same basic devices that control motion between the cutting tool and workpiece in other machine tools are also used in grinding machines such as lead screws, cams, special fixtures, and tracer mechanisms. Grinding machines have limitations as to how fast and how much material can be removed but modern manufacturing, with the help of more accurate castings and forgings, is utilizing grinders more and more for both sizing and finishing operations. Some finished parts are produced by grinding only.

KEY TERMS

Accuracy How close measurements are to the true value.

Carousel A rotary tool holder used to hold many tools as part of an automatic tool changer on a CNC mill.

Dies High precision tooling primarily used in production presses.

Gages Extremely accurate tooling used for measuring.

Jigs Tooling which is used for locating parts and also for guiding cutting tools such as in a drill jig.

Precision How close repeated measurements are to each other.

Quill Rotating toolholder.

Spindle Assembly that contains a flange mount housing, bearings, and a tapered nose tooling holder.

The major types of grinding machines available are cylindrical grinders, internal and chucking grinders, universal grinders, centerless grinders, surface grinders, face grinders, disc grinders, and tool and cutter grinders.

See also Industrial Revolution.

Resources

BOOKS

Bruce, R. Gregg, et al., eds. Modern Materials and Manufacturing Processes. Upper Saddle River, NJ: Prentice Hall, 1998.

Curran, Kelly, and Jon Stenerson, eds. Computer Numerical Control: Operation and Programming. Upper Saddle River, NJ: Prentice Hall, 2001.

Gill, Arthur. Machine Tool Technology Basics. New York: Industrial Press, 2003.

Kalpakjian, Serope, and Steven R. Schmid, eds. Manufacturing Processes for Engineering Materials. Upper Saddle River, NJ: Prentice Hall, 2003.

Society of Manufacturing Engineers (SME). Tool and Manufacturing Engineers Handbook, Desk Edition. Dearborn, MI: Society of Manufacturing Engineers, 1998.

Glenn G. Whiteside

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Machine Tools

Machine Tools

INDUSTRIAL CODES

NAICS: 33-3512 Machine Tool (Metal Cutting Types) Manufacturing, 33-3513 Machine Tool (Metal Forming Types) Manufacturing, 33-3514 Special Dies, Tools, Jigs, and Fixtures, 33-3515 Cutting Tool and Manufacturing Tool Accessory Manufacturing

SIC: 3541 Machine Tools, Metal Cutting Types, 3542 Machine Tools, Metal Forming Types, 3543 Industrial Patterns, 3544 Special Dies, Tools, Jigs and Fixtures

NAICS-Based Product Codes: 33-35121 to 33-35129, 33-3512A, 33-35124W, 33-3513, 33-35131, 33-35133, 33-35135, 33-35137, 33-3513W, 33-35140, 33-35151, 33-35153, 33-3515W

PRODUCT OVERVIEW

Machine tools play the same central role in metalworking that computers play in data processing. They shape and process metals into components. Manufacturers then assemble these components into durable goods and also use parts in many other products. At the foundation of industrial activity are the extraction industries by means of which we obtain our fuels and our ores. We refine the fuels and smelt the ores. The primary metal industry produces basic shapes—bars, billets, ingots, sheets, tubes, rails, bars, wires, and some fifty other recognized intermediate or final products. The first three differ only in their widths. Foundries remelt such shapes to make castings; hot metal is poured into dies. Other products of primary mills are ready to use immediately. Wire products, reinforcing bars, and steel beams used in construction are examples. A substantial portion of primary output, however, moves on to fabrication plants in semi-finished forms. There, battalions of machine tools await to transform them into final components.

The terminology commonly used in the industry may cause confusion. A machine tool should not be confused with a cutting tool. While the machine tool is a large structure, the cutting tool is a relatively small device attached to the machine's working arm. By analogy to hand tools, the electric drill is the machine tool, the drill bit is the cutting tool. Cutting tools may be changed to do different kinds of work and are replaced as they wear out. Indeed, the market for cutting tools is much larger than the market for machine tools, and each kind of product is produced by its own industry. Machine tools also come in two basic types: cutting machines remove metal and forming machines shape it. The object on which a machine tool operates is known as the workpiece; it is the metal that is being shaped or modified.

Cutting Machines

Cutting machines shape metal by separating pieces of it using saws or removing metal selectively from the surface or the body of a workpiece. The machine itself holds and moves the piece and directs the cutting tool. The tool itself may be a saw, drill bit, broach, milling cutter, reamer, tool bit, or another specialized device. Broaches are tapered, serrated, hole-making tools. Milling cutters are further differentiated below. Tool bits are used in lathes. Grinding and buffing machines may use abrasive wheels instead of cutting tools. In many applications, the tool is stationary while the workpiece is in motion. In others, for instance when drilling multiple holes into a block or broaching several openings on a single piece, the block may be held still while the drills descend to do their work. On a lathe the workpiece rotates. In drilling, boring, and milling, the cutting tool itself is rotating and the workpiece may be held still or may be moved horizontally. The cutting edge used in all applications must be made of a material harder than the workpiece. Three other fundamental requirements are: appropriate motion to achieve the desired cut, heat control provided by cutting fluids, and guidance systems to ensure precision. In complex modern machines, guidance is achieved by electronic systems that communicate with servomotors—a servomotor being an electromechanical device that uses electrical inputs to direct the position of the armature of a motor.

Forming Machines

Forming machines shape metal by using dies or by bending, drawing, and shearing the workpiece. In a typical die-based approach, the operator brings the workpiece to a high temperature. While it is red-hot and glowing, it is hammered into shape between simple dies while confined in place or manipulated mechanically. The hammer is lifted hydraulically and is powered by weight or assisted by fluid power. Alternatively the die may be in two pieces that approach the red-hot metal and sandwich it between the die pieces. High pressure exerted by the machine causes the two halves of the die to close. Explosive metal forming, also called high energy rate forming, or HERF, uses controlled explosions instead of hammers to move the metal into the die. The explosive force is exerted through a medium like water, oil, or air. The strength and design of the dies used in forming machines is crucial. Dies must withstand the impacts or pressures applied. They must also be shaped in such a way that the metal from the hot blank reaches the deepest and least accessible parts of the die. The product of these machines is called a forging. Some forgings, depending on shape, may require additional machining in a cutting machine to finish them. Other types of forming machines shape metal by punching, bending, and shearing. Such machines are referred to as presses; hammer-and-die machines are forges.

Evolution

Forming machines represent the automation and extension of the traditional smithy. The smith usually shapes hot metal by hammering it on an anvil. The anvil—with one or two rounded and tapered horns, a narrow step at one or both ends enabling the smith to create angles, a wide face for general use, and two holes (the smaller pritchel and the larger hardy hole) used for additional implements or as aids in bending metal—represents an all-purpose die. In forming machines, human judgment necessary to know when to stop, how hard to hammer, when to reheat the workpiece, and so on are translated for each object into appropriate die design and settings on the machine, which guide the force, timing, and duration of the impacts.

Historians of technology trace cutting machines back to the hunting bow and to the potter's wheel. Early humans used bow-string wrapped around a stick to make fire. Holding the stick straight they caused it to rotate rapidly by moving the bow back and forth. The tight string caused the stick to whirl on a piece of soft, dry wood until the latter heated, began to smoke, and threw sparks that the fire-maker could ignite by blowing. It is believed that in this same way people also discovered how to drill holes. The potter's wheel was the first invention to cause a workpiece to rotate while the hands, working on the clay, served to shape it and to remove excess material. The earliest machine tool was the lathe, essentially a potter's wheel turned ninety degrees to one side. Instead of turning clay, the early lathe turned a piece of wood. A blade applied to the wood could uniformly carve it with little effort and pleasing precision.

The Cutting Edge

The cutting tool must be harder than the workpiece upon which it is designed to work. The machining of metals improved as advances in metallurgy delivered harder types of steel. Ultimately the discovery of tungsten and of tungsten carbide produced the means of cutting the hardest steel. Nature gives us iron in oxidized form mixed with minerals. To get the iron out we must remove the oxygen. We do this by burning coke mixed with ore. The iron in the ore melts. Carbon combines with oxygen and removes it from the iron. In this process, however, a fair amount of carbon remains in the resulting pig iron, typically 3.5 percent. Carbon at these levels makes pig iron strong but brittle. In steel-making most of the carbon is removed. To make the strongest steels, however, some of the carbon in the metal is left but rearranged by various processes such as tempering. Steel is tempered by cooling and reheating it in sequence. Tempering causes carbon to align itself uniformly within the crystalline lattice of steel. Ultra-high carbon steel will have a carbon content of 1 to 2 percent; it is extremely hard but also difficult to weld.

Axel Fredrik Cronstedt, a Swedish chemist and mineralogist, discovered tungsten in 1758. The word itself is a form of the Swedish terms for heavy and for stone. Tungsten is a metal and present in nearly every home as the filament of incandescent bulbs, but more than half of all tungsten mined is used in cutting tools. By 1855 tungsten had been introduced as a hardening agent for steel. By 1926 it had been developed into cutting tools as tungsten carbide, the hardest material available to all those who cannot afford to use diamonds. The hardest cutting tools are tipped with industrial diamonds.

NC/CNC Controls

Automatic methods of controlling machine tools emerged from the pioneering efforts of John T. Parsons in 1949 in work conducted by Parsons Corporation for the U.S. Air Force. Parsons, working with Frank L. Stulen, one of his employees, developed the complex mathematical descriptions of tool movements in three dimensions (X,Y,Z) with the aid of early IBM calculators. The Massachusetts Institute of Technology (MIT) participated in this work and eventually developed servomotors that became standard in so-called numerically controlled (NC) machine tools. NC devices came of age in the mid-1960s when computer-generated machine instructions began to replace operator skills. The instructions were held in the form of punched paper ribbons that could be read by the machine tool to guide its servomechanisms. Operators needed only to change the workpiece and to activate the NC tool. After electronic circuitry directly talking to the servomotors replaced punched paper, automatic cutting came to be called CNC, for computerized NC, although the shorter abbreviation persists, as for instance in the reporting of the U.S. Bureau of the Census. In the twenty-first century, NC machining and CNC machining have essentially the same meaning: software is guiding the cut.

Functional Classifications

Cutting machines come in five major functional categories. The industry produces milling, drilling and boring, turning, gear cutting, and grinding and polishing machines:

  • Mills utilize a cutter with multiple teeth that eat away material. The three basic cutters used are called slab, face, and end mills. A slab cutter is shaped like the tire on a car and moves over the workpiece surface like a wheel; the spindle of the cutter is parallel to the workpiece surface. If the blades cut on the downward motion the method is called down-milling; if the cut is from the bottom of the workpiece upward, the method is called up-milling. Face cutters have relatively wide surfaces and sit on top of the workpiece like a cup on a table, with the bottom of the cup carrying the blades. The spindle of the cutter is perpendicular to the workpiece. An end cutter is shaped like a drill bit. It is a rod pointing down at the surface to be milled. End mills are typically used to produce indentations in the workpiece. The sides of the indentation may be tapered because end mills can be tilted to selected angles. Variations on such tools can produce all manner of shapes including slits, slots, and shaped forms on the workpiece surface. Milling is the most widely used cutting technique, although most milling machines are multi-functional devices. Approximately 40 percent of machine tools are mills or have milling functions alongside others.
  • Drilling and boring machines make holes in the workpiece. Drills rotate as they penetrate the piece. Boring heads are used to enlarge a hole. As the drill bit penetrates, the material it is removing leaves the opening in the free space between the spiraling cutting blades of the bit. Freestanding drilling and boring machines are 10 percent of the cutting tool category.
  • Turning machines, or lathes, represent 16 percent of the machine tools made. In these devices the workpiece itself is rotated as cutting blades touch it and remove material. The blades can be moved from point to point along the rotating workpiece; multiple blades may be used at the same time. The method is well suited for the machining of cylindrical surfaces.
  • Gear cutting is a specialized type of milling known as hobbing. As the workpiece, the future gear, is turned, the cutting bit turns at the same speed, its multiple blades removing metal from the gear forming one tooth at a time. Gear cutting machines represent 7 percent of the market.
  • Grinding and polishing machines differ from other forms of cutting because they use wheels of abrasive materials to give workpieces their intermediate and final finish. Grinding, polishing, buffing, honing, and lapping are specific functional activities. Honing uses abrasive rods to smooth surfaces including borehole interiors. Lapping is a fine-finishing step using very fine abrasives. Grinding and polishing is a large category and accounts for 28 percent of all machine tools in the cutting machine sector.

Metal forming machines divide into two basic types: forges and presses. Forging of metals can be hot or cold and may involve repeated hammering of the piece using flat dies in order to achieve a desired dimension or die-stamping. In the latter operation metal is forced into dies. Most forging processes are hot and operate at temperatures of 2,300 degrees Fahrenheit. Three general methods are in use:

  • Impression die forging compresses metal between two halves of a die. Variants involve pressing metal into a die relatively slowly at uniform pressure to ensure that all hollows are filled.
  • Open die forging, which is equivalent to hammering the piece until it is shaped correctly, uses flat dies without internal profiles—protrusions or cavities—of any kind. The workpiece may be held and moved between blows of the hammer by a mechanical manipulator executing pre-programmed rotations and advances of the piece or the process may involve successive steps in which different flat dies are applied to the piece.
  • Cold forging, which may take place at room temperature or in the presence of several hundreds of degrees of heat, is used with softer metals. As the Forging Industry Association describes the general method, "cold forging encompasses many processes [including] bending, cold drawing, cold heading, coining, extrusion, punching, thread rolling and more to yield a diverse range of part shapes." Cold drawing pulls the metal and cold heading increases the cross-sectional area of a workpiece, thus making it wider, longer, or both.

Metal presses typically operate on cold metals and on sheet or plate metals. They form their workpieces by punching, shearing, and bending the metal into various shapes.

Metal forming machinery represented 24 percent of all machine tools in use in the United States in the middle of the first decade of the twenty-first century. Within that category itself, forges of all types were 30 percent and metal presses 70 percent of the market.

MARKET

In 1997 domestic producers of machine tools shipped product valued at $6.9 billion; in 2005 shipments were $4.6 billion. Within this category cutting machines declined from $4.7 billion to $3.3 billion and forming machines from $2.2 billion to $1.3 billion in the 1997 to 2005 period. If cutting tools as well as dies, fixtures, and jigs used by the machines are included, the market is larger but trends do not change. Cutting tools had shipments of $5 billion in 1997 and $4.5 billion in 2005; special dies and fixtures declined from a level of $8.8 billion to $8.4 billion in this period. All growth rates were negative. Machine shipments declined at the rate of 5.1 percent, 4.5% in cutting machines and 6.4% in forming machines. Cutting tools declined at 1.3 percent and special dies and fixtures at 0.5 percent yearly. Declines in the more recent 2000 to 2005 period were uniformly steeper reflecting the brief 2001–2002 recession from which recovery in 2005 had not yet returned sales to levels experienced in 2000. The general picture is presented in Figure 128.

Data on imports and exports of these industries were available for the 2000 to 2005 period only and provide a means of calculating apparent consumption in the United States. Apparent consumption is calculated by starting with domestic production, reducing it by the level of exports, and adding the level of imports. In the period under consideration, apparent consumption exceeded domestic production uniformly and across the board—the consequence of imports exceeding exports in every year. Apparent consumption, however, declining from $22.7 billion in 2000 to $20 billion in 2005, also exhibited negative growth of 2.5 percent per year. Total exports declined at the rate of 0.6 percent, total imports at the rate of 0.1 percent. Figure 129 presents these data.

The Machine versus Its High Priced Parts

In 2005, with apparent consumption valued at $19.98 billion, machine tools represented $6.3 billion, or 32 percent, of this total, and parts (tooling, dies, and fixtures) $13.7 billion. For every $1 buyers spent on machine tools they spent $2.18 on the parts and devices to use in these machines. The machine tool is bought once and used for a long time. The market for parts or changeable tooling that are used with the machine tool are a far larger market than is the market for machine tools themselves. Machine tool parts wear out and must be replaced at frequent intervals. Users of these devices can more readily delay upgrading machines than replacing tools so that, in consequence, sales of cutting tools, dies, and accessories have been declining at much lower rates than sales of machine tools.

The Global Picture

The U.S. manufacturing industry was the top consumer of machine tools in the period from 1993 to 2002—and in most earlier decades as well throughout the twentieth century. U.S. consumption dipped in 2003 and has been heading down so much so that in 2007 (using preliminary estimates), the United States was the third-largest consumer in the world. China had emerged as the top purchaser of machine tools, followed by Japan in second place, and the United States in third.

In 1981 the United States was the top producer of machine tools in the world. It had also had the lead across the globe in earlier decades, competing for top rank with Germany which out-performed the United States in some years. The U.S. industry began declining after 1981. By 1992 the country had fallen to fourth place behind Japan, Germany, and Italy. By 2003 the U.S. industry ranked fifth, with China out-producing the United States and in fourth place. By 2006 U.S. producers had dropped to seventh place. In that year the major producing countries were Japan, Germany, China, Italy, South Korea, Taiwan, and then the United States. Switzerland, not usually ranked among giants in heavy industry, was ranked eighth in 2006, just behind the United States with shipments equivalent to 78 percent of U.S. production.

The general decline both in the use and production of machine tools is a reflection of the decline of manufacturing as part of the U.S. economy. Using data from the World Resources Institute, based on compilations of the World Bank, in 1996 manufacturing was 18.2 percent of Gross Domestic Product (GDP) in the United States, 22.2 percent in Germany, 23.3 percent in Japan, and 33.5 percent in China. The GDP to manufacturing relationship in 2004, eight years later, showed decline of this sector in three of the four cases cited. The U.S. manufacturing share of GDP had dropped to 14.2 percent, Germany's had increased to 22.7 percent, Japan's had dropped to 21 percent, and China's to 32.4 percent. The largest loss in manufacturing was that of the United States.

Other factors producing negative growth appear to involve rising technological competition and slow or inadequate response to global challenges by the domestic industry. In a 1994 study prepared for the U.S. Office of Science and Technology Policy, a part of the White House, Rand Corporation gave six reasons for the decline of the U.S. industry as follows:

  • Insufficient number of large firms and little cooperation among small companies. Global competition requires large companies able to invest in technology and export marketing. A national mechanism to stimulate foreign trade, drawing smaller companies into it, must also be present.
  • Difficulty obtaining capital for investment. In the 1990s investors viewed the U.S. industry as too small and not profitable enough to invest in. Although not stated by Rand, investment capital was flowing into hotter markets like computers and Internet start-ups.
  • Inadequate supply of skills and disincentives to invest in training. Rand found that the skills of the U.S. labor force were inferior to those of the industry's competitors elsewhere. U.S. producers used CNC machines to replace skilled with less skilled operators whereas Japanese firms used CNC machines to train machinists. U.S. companies also abandoned expensive apprentice training programs to avoid training machinists for other companies that avoided training costs.
  • Poor performance in translating technological research into marketing advantage. Links between universities and industry were weak, according to Rand, and government research was focused on very sophisticated devices with few widely-marketable applications.
  • Unsophisticated domestic demand, thus slow acceptance by domestic users of advanced technology. Manufacturers in the United States were not investing in innovation but making do with older tools.
  • Weak export capacity and export infrastructure.

Developments in the market since the mid-1990s have not removed these barriers. Foreign companies, however, intending to exploit the U.S. market more effectively, have been drawn to acquire U.S. producers, simultaneously gaining access to the domestic market and adding to their overall capacity.

KEY PRODUCERS/MANUFACTURERS

Companies participate in this industry by specializing in one of its chief technological sectors rather than producing all systems and tools that make machining and metal forming possible. The three sectors are: machine tools; electronic control systems providing the CNC guidance; and cutting edges (tooling narrowly viewed), a sector that depends on metallurgical know-how.

MAG Industrial Automation Systems

MAG Industrial, headquartered in Sterling Heights, Michigan, is the largest machine tool company in the United States, and is the principal enterprise in the holdings of Maxcor, Inc., a privately-held investment company. In 1981, the peak year in U.S. machine tool history, the top five companies were Cincinnati Milacron, Bendix, Cross & Trecker, Giddings & Lewis, Ex-Cell-O, and F. Joseph Lamb. These leaders held 40 percent of the market that year. MAG Industrial unifies elements of all of these companies except Bendix. MAG Industrial's portfolio also includes foreign acquisitions. Maxcor, headquartered in New York, New York reported that MAG Industrial had sales of $1.2 million in 2006 and was the fifth largest machine tool company in the world. Although MAG Industrial is a single segment under Maxcor and its largest holding, it consists of eleven different corporate units operating in the United States, Germany, Korea, Brazil, France, and the United Kingdom. As a private investment company Maxcor does not file reports with the Securities and Exchange Commission (SEC); hence, its general corporate strategy, and the degree of coordination of its holdings, is difficult to discern.

Yamazaki Mazak

The world's largest machine tool builder is the Japanese company, Yamazaki, operating worldwide and, in the United States, as Mazak Corporation based in Florence, Kentucky. Yamazaki has made significant investments in the United States. Yamazaki's reported sales in machine tools was $1.58 billion in 2005.

Smaller U.S. participants include Hardinge Inc., of Elmira, New York and the Bridgeport brands, a company it acquired. Hardinge had sales in 2006 of $326 million. Ingersoll Machine Tools Inc., owned by Camozzi Group of Italy, had sales of approximately $62 million in the middle years of the first decade of the 2000s. Ingersoll was one of the top 15 companies in 1981. Camozzi reported sales in 2004 of €110 million ($145 million). Textron describes itself as a multi-industry corporation, a conglomerate with sales revenues of $11.6 billion in 2006. The company participated in gear cutting machine tools as part of its $3.1 billion industrial segment. The world leader in gear cutting machines in 2006 was the German Liebherr Group.

Kennametal Inc.

Kennametal is the largest tool-bit manufacturer in the United States and ranked second globally in the tools and accessories market. The company, originally McKenna Metals Company, owed its growth to a tungsten-titanium carbide alloy developed by its founder, Philip M. McKenna, in 1938 which produced significant productivity increases in machining. Headquartered in Latrobe, Pennsylvania, the company reported total sales revenues of $2.4 billion in the fiscal year ended June 2007. Two important foreign tool makers are Mitsubishi Material, with sales in tooling of approximately $1.2 billion in the fiscal year ended March 2007, and Toshiba Tungaloy, with sales in tooling of approximately $414 million in the same period.

General Electric

Through its GE Fanuc Automation Corporation, General Electric is a leading worldwide producer of computerized numerical control and computer-assisted manufacturing systems. The company had 2006 sales revenues of $163.4 billion, but its filings with the SEC subsumes sales of its automation products beneath its broader industrial segment (20.5% of revenues).

Rockwell Automation, Inc.

Rockwell acquired Allen-Bradley in 1985, a leader in numerical control. Rockwell had revenues in 2006 of $5.6 billion, of which control systems accounted for $4.6 billion. Both GE and Rockwell are major exporters of control systems.

MATERIALS & SUPPLY CHAIN LOGISTICS

Machine tools are assembled from engineered products, major subsystems of which are purchased from other industries. Machine tool producers are major consumers of metal components. The top three inputs into the industry in the middle years of the first decade of the 2000s were castings, fabricated metal products, and sheet steel. Hydraulic (fluid power) devices were the fourth-ranked input. Electronic systems used in CNC guidance were fifth in importance. Cutting and forming machines have similar materials requirements; the chief difference is that the latter do not use CNC guidance systems to the same extent because forming operations are far less complex, on average, than machining processes. From a logistical point of view, the industry is located around areas of industrial concentration in the Upper Midwest (near the automobile producers, a major buying group), the Northeast, California, and Texas.

The largest input to the cutting tool and accessories industries is tungsten carbide metal powder, other metal powders, and industrial diamonds—materials that impart hardness to cutting tools. Although the United States has reserves of tungsten ore, the country does not mine the metal and instead relies on secondary tungsten recovered from cutting sludges and from tungsten alloys. Cutting operations are typically cooled by liquids. As cutting edges wear away, the metal is carried off in the coolant. These sludges are inherently valuable because they contain tungsten and are routinely recycled, often traveling hundreds of miles to specialized recycling centers. The world's largest producers of tungsten are China, Russia, and Canada. The largest reserves are in China, Canada, and Russia. Most tungsten imported into the United States comes from Canada.

DISTRIBUTION CHANNEL

The selling of machines, cutting tools, and accessories calls for the services of sales engineers able to understand and to respond knowledgably to the special needs of the customer. For this reason the industry relies heavily on distributors appropriately staffed with engineers intimately familiar with the machinery of the manufacturers they represent. The American Machine Tool Distributors' Association has 300 members; each organization has substantial technical staffing.

Distribution arrangements somewhat depend on the size of the seller and of the buyer. Large companies maintain direct sales staffs calling on the customer directly and assisting distributors; many small companies operate through manufacturers' representatives and distributors. In 2002, as reported by the Census Bureau, the cutting sector had 342 companies; of these 140 had fewer than twenty employees. The forming machine sector had 169 companies, ninety-eight of which were small. Tool sellers use distributors and also deploy extensive Web sites where buyers can identify and also buy cutting devices and auxiliary equipment online.

A significant part of dealer operations is selling used machine tools. There is also a business in making parts and tools for lines of old equipment that are no longer supported because the manufacturers that made them went out of business during the shrinkage of this industry from 1981 to 1990.

KEY USERS

Industrial buyers in the metal fabrication business buy 97 percent of all machine tools; the remainder, in the form of small machines made specifically for these markets, are sold to garages, laboratories, and home workshops. The dominant buying sectors are automobiles, farm and construction equipment, aerospace, and a wide range of industries making heavy metal equipment.

ADJACENT MARKETS

Cutting fluids used to cool all cutting, drilling, and boring operations represent an important adjacent market to machining. These substances are classified as mineral, synthetic, or semi-synthetic. Mineral products are oils usually derived from petroleum. Synthetic cutting fluids are water-based liquids holding alkaline substances like ethanolamine and amber alongside corrosion-inhibitors. Semi-synthetic coolants are oil-water emulsions. Cutting fluids typically contain extreme pressure (EP) additives such as chlorine, sulfur, and phosphorus that help the fluid hold up under the pressures present at the point where the tool and workpiece meet. Synthetic coolants provide the best service.

Abrasives used in grinding, polishing, and lapping applications are another important market. Aluminum oxide is the most widely used abrasive on ferrous metals and silicon carbide is the most widely used on nonferrous metals. Zircona alumina, a mixture of zirconium oxide and aluminum oxide, is used to grind and polish very hard carbon and stainless steels. Abrasives are delivered in mounted forms as bonded or coated abrasives, adhering to a carrying surface and formed into wheels or plates. They also reach the end user in powdered form.

Indirectly adjacent to machining are high-performance plastics, in that these substances are gradually making inroads to replace metal parts in applications that require high strength. Examples of such plastics are polyamidimide, polyimide, polyetherimide, and polyetheretherketon (PEEK). These materials are relatively expensive but lend themselves to forming by injection molding and thus need no machining.

RESEARCH & DEVELOPMENT

Research and development in this industry at the basic level, which is often pursued by university departments, is aimed at improving the accuracy of results, novel forms of cutting, improvement in servomotors, automation of machining steps not yet achieved, and further development in CNC methods. Considerable R&D expenditure at the corporate level is dedicated to support specific applications categories for customers, frequently with the financial participation of the customer.

One example of basic research in achieving higher accuracy comes from MIT where a research team headed by Alexander H. Slocum introduced, in 1995, platforms for machining supported on a thin layer of water to reduce vibrations. At the extremely low tolerance required in certain modern applications, even fractional reductions in surface vibration are beneficial to achieve higher rates of accuracy. MIT, which pioneered servomotors in this industry in the 1940s and 1950s, continued to make contributions to the industry in the twenty-first century. Laser cutting of metal was under intense study in the latter half of the first decade of the 2000s. The technology, already in use as an alternative to plasma arc cutting of metal, was still relatively new in the twenty-first century but developing rapidly. In the far distant future, but already much discussed, is the promise of nanotechnology, which may permit the build-up of parts from the molecular level or, minimally, modification of surfaces by rearranging atoms.

CURRENT TRENDS

Trends in this industry were dominated by global developments as the first decade of the twenty-first century was drawing to a close. The most striking of these was the rapid industrialization of China, India, and other major Asian markets that, half a century back, ranked among the most under developed economies of the world. In the latter half of the first decade of the 2000s, China had emerged as the largest single consumer of machine tools, as well as having become a leading producer. From a U.S. perspective, it is noteworthy to see that European industries have shown competitive strength and were holding on to market shares whereas the United States was continuing to yield its share.

The evolving technological landscape suggests that machine tools are being ever more integrated into larger automated complexes. With but a few exceptions, Yamazaki Mazak being one, most major producers are diversified systems manufacturers and machine tools are but one of many major product lines they offer. Materials competition, especially the erosion of metal markets under the onslaught of plastics, has not yet reached deeply into major durable goods, but trends suggest that more competition in the future is likely to affect machine tools.

TARGET MARKETS & SEGMENTATION

The industry's products divide two major segments: stand-alone and single-purpose machines which do one thing well, drilling or boring; and multi-function devices which offer more than one machining function on the same machine, drilling, milling, and grinding, for example. Such machines, installed in automated lines, are very flexible when guided by CNC functions—capable of changing their own tools and capable, in conjunction with video sensors, and of recognizing different products approaching them on the assembly line. In the most complex computer-assisted manufacturing systems, machine tools become components of systems that function as mere organs in a manufacturing process. Marketing approaches—sales methods and requisite cooperative work with the ultimate buyer—depend largely on the function and complexity of the product.

RELATED ASSOCIATIONS & ORGANIZATIONS

American Machine Tool Distributors' Association, http://www.amtda.org

The Association of Manufacturing Technology (AMT), http://www.amtonline.org

Forging Industry Association, http://www.forging.org

Industrial Tungsten Industry Association (ITIA), http://www.itia.org.uk

The Metal Forming Machinery Makers' Association, http://www.mmma.org.uk/page.asp?node=1&dec=Home

National Tooling & Machining Association, http://www.ntma.org/eweb/StartPage.aspx

BIBLIOGRAPHY

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Cho, Dan. "Cut by Numbers. John Parsons Paved the Way for Computer-Aided Manufacturing." Technology Review. Massachusetts Institute of Technology. May 2004. Available from 〈http://www.technologyreview.com/Infotech/13598/?a=f〉.

Darnay, Arsen J. and Joyce P. Simkin. Manufacturing & Distribution USA, 4th ed. Thomson Gale, 2006.

Feingold, David et. al. The Decline of the U.S. Machine-Tool Industry and Prospects for Its Sustainable Recovery. Rand Corporation. 1994.

"GDP: Percent GDP from Manufacturing." EarthTrends, World Resources Institute. Available from 〈http://earthtrends.wri.org/searchable_db/index.php?theme=5&variable_ID=217&action=select_countries〉.

"History." Industrial Tungsten Industry Association. Available from 〈http://www.itia.org.uk/Default.asp?page=35〉.

Joshi, Amit Mukund. "Explosive Forming—An Overview." Indian Institute of Technology. 15 April 2000. Available from 〈http://www.metalwebnews.com/howto/explosive-forming/explosive-forming.html〉.

"Standard Metal Cutting Processes: Laser Cutting vs. Plasma Cutting." Tesko Laser Division. Available from 〈http://www.teskolaser.com/laser_cutting2.html〉.

Thomson, Elizabeth A. "MIT Researchers Win Again in R&D Competition." Massachusetts Institute of Technology. 8 November 1995. Available from 〈http://web.mit.edu/newsoffice/1995/researchers-win-1108.html〉.

"Tungsten Carbide—An Overview." Azom.com. Available from 〈http://www.azom.com/details.asp?ArticleID=1203〉.

The U.S. Machine Tool Industry and the Defense Industrial Base. National Research Council, National Academy Press. 1983.

Warsh, David. "How and Why America's Machine-Tool Industry Lost Control." The Washington Post. 24 July 1991.

"What Are the Types of Forging Processes?" Forging Industry Association. Available from 〈http://www.forging.org/facts/faq9.htm〉.

see also Construction Machinery, Hand Tools

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Machine Tools

Machine tools

A machine tool is an electrically powered tool which is used to remove material, usually metal , at a controlled rate to achieve a desired shape or finish. A machine tool typically holds the workpiece and a cutting tool, and moves either the workpiece, tool or both to provide a means of machining the material to the desired shape. Machining, another term for metalcutting, is performed by shaving away the metal in small pieces called chips. An average machining operation can reduce the original workpiece weight by approximately 50%. The modern machine tool is a precision piece of equipment designed to cut metal and produce thousands of parts to an accuracy of millionths of an inch, which is approximately equal to 1/300 of the thickness of a human hair. Machine tools range from very small bench mounted devices to large complex machines weighing hundreds of tons. The major operations performed by machine tools are milling, turning, boring, planing, shaping, drilling, power sawing, and grinding.


Milling machines

Milling machines comprise one of the largest categories of machine tools with many different varieties and configurations available. A milling machine is considered essential equipment in any machine shop because of its wide variety of machining operations and its high metal removal rates. The workpiece, mounted on a movable machine table, is fed against one or more multiple-tooth rotating tools called milling cutters, or mills. The workpiece is usually held in vises, special holding fixtures, or clamped directly to the machine table and fed at right angles to the axis of the milling cutter to produce flat, recessed, or contoured surfaces.


Classifications

Milling machines can generally be classified according to the orientation of the spindle, either vertical or horizontal. Vertical milling machines can also have what is called "multiaxis" capability where the vertical axis can tilt and swivel to enable the machining of closed angles and contoured surfaces. Vertical milling machines are extremely versatile and can machine horizontal surfaces, vertical surfaces, angular surfaces, shoulders, grooves, fillets, keyways, T-slots, dovetails, and precision holes.

Horizontal milling machines are available in plain and universal types. Plain milling machines have tables which are fixed at right angles to the knee. Universal milling machines have a table which can be pivoted in a horizontal plane. This allows the machine table to be swiveled to different angles for milling helical grooves.

The universal milling machine is widely used by maintenance machinists and toolmakers because of its versatility. Computer numerically controlled (CNC) mills or "machining centers" are available in vertical and horizontal configurations and come with automatic tool changers which can store many different tools in "carousels." The major components of a typical milling machine include the following: base, column, knee, elevating screw, saddle, machine table, ram, head, and spindle. The base is the heavy foundation member of the machine which can also be used as a reservoir for coolant or cutting lubricant often used in machining operations. The base is a massive casting which helps to absorb and dampen vibration from the machining process. The column, which is either cast with the base or keyed and bolted on, supports the functioning members of the machine. Horizontal "ways" on top of the column support the ram and head while vertical "ways" on the column front face support the knee, saddle, and machine table. The knee moves along the vertical ways of the column and is the basic work-supporting member. The knee is equipped with ways on top to allow horizontal movement of the saddle to and from the column face. The elevating screw provides additional support for the knee and allows the knee to be raised and lowered. The saddle mounts on the ways of the knee and has horizontal ways at right angles to the knee ways to support the machine table. The machine table moves longitudinally on the ways of the saddle and supports the workpiece. Combined movements of the knee, saddle, and machine table allow for precise positioning and feeding of the workpiece left and right, in and out, and up and down. This is called "3-axis" movement (X = left and right movement, Y = in and out movement, and Z = up and down movement). A rotary table can be added to a 3-axis mill to give it 4-axis capabilities (typically rotation is about the longitudinal or X-axis), while 5-axis mills are able to tilt and swivel about the vertical axis. The ram is mounted on the horizontal ways at the top of the column and supports the head and provides horizontal movement and positioning of the head at varying distances from the column face. The head includes the motor, stepped pulley, belt drive (or in the case of heavier duty mills, the gear drive), and the spindle. The head assembly provides for rotation of the spindle and spindle feeding along the vertical axis using a quill. The spindle contains the tool-holding mount and drives the cutter.


Turning centers or lathes

Lathes are considered to be one of the oldest machine tools in existence. Lathes were typically foot-powered until water and steam power were harnessed. One of the first machines driven by Watt's steam engine was a lathe which is how it came to be known as an "engine lathe." The lathe operates by holding the workpiece in a rotating holder, usually a chuck or collet, and then a single-point cutting tool is fed into the workpiece. If the tool is fed along the axis of rotation of the workpiece, it is considered to be a "turning" operation and any desired cylindrical contour can be made. If the cylindrical contour is produced on the inside of the workpiece, the operation is called "boring." In addition to turning and boring, the lathe is also used for threading, tapping, facing, tapering, drilling, reaming, polishing, and knurling. Some typical parts a lathe may produce are pins, bolts, screws, shafts, discs, pulleys, and gear blanks. Different attachments allow a lathe to perform milling, grinding, and broaching operations. With the right combination of attachments, it is said that the lathe is the only machine tool capable of reproducing itself. The size of a lathe is given in terms of the maximum "swing" and length of bed. The swing refers to the maximum diameter of work which can be rotated in the lathe. The length of the lathe bed refers to the maximum length of the lathe ways, not the maximum distance between centers of the chuck and tailstock. Many different varieties of lathes are available ranging from the small precision lathe used for making watch parts to the extremely large lathes used in producing mill rolls and rocket casings.

Lathes can generally be classified in one of the following five basic groups: engine lathes, speed lathes, turret lathes, vertical lathes, and automatics. The engine lathe, sometimes referred to as a "geared-head" lathe, is the most commonly found lathe model. Speed lathes are used where the workpiece is polished or formed (e.g., spinning) rather than cut. Turret lathes have a "turret" tool changer which rotates to permit a number of different tools to be used in a certain sequence. Vertical lathes have a vertical axis of workpiece rotation rather than horizontal. Automatic lathes consist of high production turning machines such as screw machines and single or multiple spindle chucking and bar fed machines. All of the five basic lathe groups can also be found in a computer numerically controlled version, sometimes called a "turning center." The main components of a typical engine lathe include the following: bed, headstock, feedbox, tailstock, and carriage. The bed is the base of the lathe that supports the other components. The precision ways are the part of the bed on which the carriage travels. The bed is a massive casting in order to absorb and dampen vibration from the machining process. The headstock is mounted rigidly on the bed and houses all the gearing and mechanism for the spindle drive and power takeoff source for the feedbox. Controls for selecting and changing spindle speeds are also part of the headstock. The feedbox, which may be an integral part of the headstock or a separate unit, drives both the feed rod and the lead screw for the feed rate or thread lead required.

A direct mechanical connection with the spindle drive is required to provide the proper relationship for feeding or threading operations. The lead screw is a precision part and is usually only used for threading operations to avoid unnecessary wear.

Most engine lathes incorporate a feed rod which is used to drive the carriage for operations other than threading. The headstock spindle supports a faceplate, chuck, or collet, which in turn holds and drives the workpiece. There are four types of standard spindles, all identified by the type of nose: threaded nose, camlock, taper nose key drive, or flanged nose. The threaded nose spindle is usually only found on smaller and less expensive lathes. The camlock type allows faster changing of faceplates or chucks. The taper nose key drive type provides greater support to the workpiece while the flanged spindle nose permits mounting of special chucks or power operated equipment and can be found on turret lathes and automatics. The tailstock is mounted on the bedways and may be positioned and clamped to support work for turning. It may also use a tool mounted in place of the tailstock center so that boring, drilling, or reaming can be done. The tailstock must be perfectly aligned with the headstock spindle in order to produce good parts. The carriage is the tool platform of the machine and supports and feeds the cutting tool over the work. The carriage consists of the cross slide, which bridges the ways to support the compound and tool post, or toolholder, and the apron. The lead screw and the feed rod pass through the apron and transmit feeding power to the carriage. The main controls for positioning and feeding the tool are also located on the apron.


Boring machines

Boring machines are similar in construction to milling machines except they are generally more massive and built lower to the floor, use different tooling, and feed differently along the axis of the spindle. Boring machines are typically located in very clean, climate controlled environments and are massive for extra rigidity and vibration damping to ensure close tolerance hole sizes and locations, one example being automobile engine piston bores.

Jig boring machines are primarily intended for tool-room use and are used to produce precision dies, jigs, and gages, which are used to ensure the accuracy and interchangeability of high volume production parts. There are three common designs of jig boring machines in use, the open-sided or C-frame, adjustable-rail, and fixed-bridge construction. Variations of the jig boring machine include jig grinders, which are used to realign holes after hardening, and the horizontal jig boring and milling machine, which is utilized for general production operations.

The base of the jig boring machine supports a saddle that moves in and out from the operator to the column. A table moves right or left on the saddle to complement the saddle movement. A massive column supports the spindle housing, which adjusts to the work location by moving up and down the column ways. The spindle moves inside a quill that is supported by the housing or spindlehead.

The quill also moves up and down inside the housing to give a telescoping mechanism which adds rigidity to the spindle. The spindle, quill, and housing are manufactured under very careful and exacting conditions to eliminate any lost motion . The housing is usually made of Invar cast iron to minimize errors due to thermal expansion . Stability of the housing is extremely critical because any expansion would change the tool location relative to the column.

The spindle is hardened, ground, and lapped. Preloaded ball bearings also help to eliminate lost motion of the tool and its driving mechanism. Spindle speeds range from 30-1,500 rpm on an average machine. A digital readout (DRO) system is used to provide a continuous numerical readout of the table position. Jig boring machines may also be computer numerically controlled (CNC). CNC control permits many additional jobs that would be impossible with a manually operated machine. One example would be to produce precise, irregularly curved forms to be generated on cams or master templates without operator involvement.


Planers

Planers remove metal in a series of straight cuts by reciprocating (moving back and forth) the workpiece as the single-point tool feeds. The fixed tool is rigidly supported while the workpiece moves on precision ways for the full length of the cut, thus ensuring maximum accuracy. The rigidity of the tool allows the use of powerful motors, up to 150 hp, which permits higher production speeds and the use of multiple tooling with extremely heavy cuts and feeds. Planers are typically big machines used for handling the largest and heaviest work that can be supported on the machine table, as much as 75 tons
(68 tonnes). Planers may be fitted with hydraulic tracing attachments to enable them to cut curved surfaces.

There are two distinct types of planers, the single-housing, or open-side planer, and the double-housing planer. Double-housing planers are the most widely used and provide the greatest tool support rigidity. The major components of a double-housing planer are the bed, table, housings, arch, cross rail, and heads (side and rail). The bed is the foundation to which the housings are attached. The bed is provided with precision ways over its entire length and supports the reciprocating table.

The table supports the workpiece and reciprocates along the ways of the bed. The table is slightly less than half the length of the bed and its travel determines the dimensional capacity of the machine in length of stroke. The housings are rigid box-type columns placed on each side of the bed and table. They are heavily braced and ribbed to absorb the large cutting forces encountered in planing. The arch joins the housings at the top for greater rigidity of construction and also houses the drive mechanism for tool feeding. The cross rail is a rigid horizontal beam mounted above and across the table on the vertical ways of the columns. It supports the rail heads and provides for horizontal feeding of the cutting tools.

The heads carry the cutting tools and are equipped with "clapper" blocks that lift the tools clear of the work on the return stroke of the table. Single-housing or open-side planers support the cross rail from a single column. This permits wide workpieces to overhang the table on the open side if necessary.

Planers require many strokes of the workpiece to complete a cutting operation. Horizontal and vertical mills are much more efficient at metal removal than planers and have replaced planers for production work.


Shapers

Shapers utilize a reciprocating single-point tool with the workpiece clamped on the machine table. The workpiece position and feeding are controlled to produce the desired shape or surface as the tool passes back and forth along a fixed path taking a series of straight cuts. Horizontal shapers are used for machining flat surfaces, which may be horizontal, vertical, or angular. Vertical shapers or slotters are used for machining slots, keyways, and splines. Shapers may be fitted with hydraulic tracing attachments to enable them to cut curved surfaces. The size of a shaper is designated by the maximum length of stroke or cut it can take.

There are many different types of shapers, but the most common is the horizontal plain shaper, which consists of a bed, column, cross rail, table, ram, and the head. The bed is the rigid base of the machine that supports the column and sometimes an outrigger table support, which is used to increase the rigidity of the workpiece mounting. The column houses the motor and drive mechanisms and is equipped with two sets of precision ways which support the ram and cross rail. The cross rail is a horizontal member that travels vertically on the ways of the column to be adjusted, and clamps in place in the desired position. The cross rail supports the table on precision ways. The table supports the workpiece and feeds along the cross rail. The ram is the tool driving member and reciprocates on precision ways on top of the column. The length of stroke, rate of reciprocation, and overhang at the extreme end of the ram travel are all adjustable. The head, which is mounted on the forward end of the ram, supports the toolholder and provides for vertical feeding or swiveling of the tool 30° either way from vertical.

Shapers require many strokes of the tool to complete a cutting operation. Horizontal and vertical mills are much more efficient at metal removal than shapers and have replaced shapers for production work.


Drilling machines

Drilled holes are required in the manufacture of almost every product and drilling is one of the most common machining operations. Drilling machines are similar in construction to milling machines except they are used exclusively for making holes.

All drilling machines are characterized by a rotating cutting tool which advances along its axis into a stationary workpiece producing a hole. Six common operations which can be performed on a drill press are drilling, reaming, boring, counterboring, countersinking, and tapping. Drilling machine capacity is determined by the size of the largest workpiece over which the spindle can be centered, the maximum clearance under the spindle, and the maximum drill diameter which can be fed at a practical feed rate through mild steel . The five major classifications of drilling machines are uprights, radials, horizontals, turret drills, and multiple-spindle machines. Each classification represents a family of machines which is further subdivided.

Upright drills comprise the largest group and are characterized by a single vertical spindle rotating in a fixed position and supported in a modified C-frame structure. The major components of the upright drill include the base, column, spindle, motor, head, table, feed mechanism, and quill.

Radial drills are designed to accommodate large work. These machines are arranged so that the spindle can be positioned to drill anywhere within reach of the machine by means of movement provided by the head, the arm, and the rotation of the arm about the column. Some types of radials and portable horizontal machines allow the entire machine to be moved to the workpiece.

Horizontal drills are characterized by the position of the spindle. Way-type and spindle-feed horizontals are self-contained units consisting of motor drive, gearing, and spindle which may be mounted at any predetermined drill angle and are used extensively to meet high production needs.

Turret drilling machines provide a number of tools mounted in a turret designed to handle a sequence of operations. The turret drilling machine is also available as a computer numerically controlled machine.

Multiple-spindle drilling machines include those designed with fixed spindles for single-purpose production and those where the spindles are adjustable, either by means of universal joints or by traversing along a worm or spiral drive in a straight line. Multiple-spindle drilling machines are primarily used for high production rate workpieces.


Sawing machines

Sawing machines are primarily used to part material such as rough-cutting excess material away before machining or cutting curved patterns in sheetmetal. Sawing machines substitute mechanical or hydraulic powered motion for arm motion to achieve the speed necessary for production operations. The cutoff operation is usually one of the first requirements in any production process before any machining, welding , or forging is done. The saw blade has individual teeth that "track" through the workpiece, each tooth deepening the cut made by the preceding tooth in the direction of feed. The saw or work may be fed and by controlling the direction of feed, either straight or curved cuts can be made. The width of the cut (also known as "kerf") is approximately equal to the thickness of the saw blade and because of this saw blades are made as thin as possible but with adequate tool strength and rigidity.

There are three common types of sawing machines, reciprocating or hack saws, band saws, and circular saws. These machines all perform the same operation but vary in capability, capacity, and application. Power hacksaws use a reciprocating stroke where on the cutting stroke the saw blade teeth are forced into the metal either by gravity or hydraulic pressure while on the return stroke the pressure is automatically removed to prolong saw blade life. Most of the machines come equipped with a chip tray and a cabinet base which contains the coolant reservoir and its circulating pump. Heavy duty power hacksaws come with automatic bar feeds where the stock is loaded on a carriage which automatically moves forward the necessary distance when the cutting is finished. Hydraulic pressure automatically operates the vise jaws, gauges the material, and raises and lowers the saw blade.

After being set up for cutting material to a specified length, the power hacksaw will operate automatically without need for an operator until all the material loaded on the carriage has been cut. Horizontal band saws are one of the most widely used sawing machines for cutoff operations. These band saws range from small manually operated machines to large, fully automatic production machines. Vertical band saws are also used but are primarily manually controlled machines used in tool rooms and shops for maintenance and low production work.

Band saws have several advantages over other kinds of cutoff machines. The saw blade cutting width or kerf is 1/16 in (0.16 cm) compared to 1/8 in (0.33 cm) for power hacksaws and abrasive disc circular saws, and 1/4 in (0.64 cm) for cold saws. This can represent a sizable savings especially when cutting large or expensive material. The thinner saw blades also require less power to cut through material making them more economical to operate. Because bandsaws have endless blades (band saw blades are welded together to create an endless loop) which cut continuously, the cutting rates are much higher.

Two of the most popular circular saws are the cold saw and the abrasive disc cutoff saw. Cold saws are low rpm circular saws for metal cutting. These saws range in size from hand-operated bench-top models with 8 in (20 cm) blades to fully automatic machines with blades of 3 in (7.6 cm) diameter and larger. Light duty manual or automatic machines are sometimes equipped with a swivel head which enables cuts to be made at different angles. These saws are mostly used for cutting structural shapes such as I-beams, angles, and channel sections because the circular blades can complete their cuts with less travel than straight blades. Heavy duty machines are available with bar feeds and can be used for cutting solid bars up to 10 in (25 cm). Material larger than this size would require excessively large blade diameters, which must be more than double the cutting capacity, which would become too costly along with the machine necessary to drive them. Different speed ranges are provided for cutting metals of different hardness and toughness, and built-in coolant systems help produce better finishes and prolong blade life.

Abrasive cutoff saws utilize an abrasive disc to separate material by using a grinding action. Abrasive cutoff saws are built for either manual operation or with power feeds, with either fixed or oscillating wheel heads. Oscillating wheel heads are used when cutting thick sections of tough materials such as titanium , nickel-based super-alloys, and other high alloy steels. Sizes range from small bench-top machines with 8 in (20 cm) wheels to bigger machines with 20 in (50 cm) or larger wheels. Abrasive cutoff saws are very useful for rapidly cutting small sizes of bar stock, tubing, and structural shapes and also for cutting tough or hardened materials that cannot be cut efficiently with other types of saws.


Grinding machines

There are many different types of grinding machines available which are used to obtain very close tolerances and fine finishes. Grinding machines are used for grinding flat surfaces, external and cylindrical surfaces, tapered surfaces, and irregular surfaces. Production parts are typically ground to tolerances of plus or minus 0.0001 in and special parts for precision instruments are ground to plus or minus 0.000020 in (20 microinches). All grinding machines utilize a rotating abrasive wheel or moving belt in contact with a workpiece to remove metal. Various combinations of wheel feed, either along or normal to the axis of wheel rotation, and also rotary or linear workpiece motion, are provided by the different types of grinding machines. To produce shapes of cylindrical section, workpiece and wheel both rotate on parallel axes while one or the other is fed along its own axis of rotation. Contact between workpiece and wheel is on the outside diameter of the wheel and the work is mounted between centers, chucked, or rotated without centers by a back-up wheel (this is called "centerless" grinding). To produce flat surfaces, the workpiece is mounted on a table and traversed along a line parallel to the surface to be ground or rotated about an axis at right angles to the surface to be ground. The axis of grinding wheel rotation can either be parallel or perpendicular to the surface to be ground, applying either the side or face of the wheel. Complex shapes are routinely ground such as thread forms, cam contours, gear teeth, and cutting tool edges. The same basic devices that control motion between the cutting tool and workpiece in other machine tools are also used in grinding machines such as lead screws, cams, special fixtures and tracer mechanisms. Grinding machines have limitations as to how fast and how much material can be removed but modern manufacturing, with the help of more accurate castings and forgings, is utilizing grinders more and more for both sizing and finishing operations. Some finished parts are produced by grinding only.

The major types of grinding machines available are cylindrical grinders, internal and chucking grinders, universal grinders, centerless grinders, surface grinders, face grinders, disc grinders, and tool and cutter grinders.

See also Industrial Revolution.


Resources

books

Kalpakjian, Serope. Manufacturing Processes for Engineering Materials. New York: Addison-Wesley Publishing Company, 1991.

Neely, John E., and Richard E. Kibbe. Modern Materials and Manufacturing Processes. New York: John Wiley & Sons, 1987.

Repp, Victor E., and Willard J. McCarthy. Machine Tool Technology. Mission Hills, CA: Glencoe Publishing Company, 1984.

Society of Manufacturing Engineers (SME). Tool and Manufacturing Engineers Handbook, Desk Edition. Dearborn, MI: Society of Manufacturing Engineers, 1989.

Vickers, G.W., and R. G. Oetter. Numerically Controlled Machine Tools. Upper Saddle River, NJ: Prentice Hall, 1991.


Glenn G. Whiteside

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Accuracy

—How close measurements are to the true value.

Carousel

—A rotary tool holder used to hold many tools as part of an automatic tool changer on a CNC mill.

Dies

—High precision tooling primarily used in production presses.

Gages

—Extremely accurate tooling used for measuring.

Jigs

—Tooling which is used for locating parts and also for guiding cutting tools such as in a drill jig.

Precision

—How close repeated measurements are to each other.

Quill

—Rotating toolholder.

Spindle

—Assembly which contains a flange mount housing, bearings, and a tapered nose tooling holder.

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