Machining is a process in which a material (often metal) is cut to a desired final shape and size by a controlled material-removal process. The processes that have this common theme are collectively called subtractive manufacturing, which utilizes
machine tools
A machine tool is a machine for handling or machining metal or other rigid materials, usually by cutting, boring, grinding, shearing, or other forms of deformations. Machine tools employ some sort of tool that does the cutting or shaping. All m ...
, in contrast to ''
additive manufacturing
3D printing or additive manufacturing is the construction of a three-dimensional object from a CAD model or a digital 3D model. It can be done in a variety of processes in which material is deposited, joined or solidified under computer co ...
'' (3D printing), which uses controlled addition of material.
Machining is a part of the
manufacture
Manufacturing is the creation or production of goods with the help of equipment, labor, machines, tools, and chemical or biological processing or formulation. It is the essence of secondary sector of the economy. The term may refer to a rang ...
of many
metal
A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...
products, but it can also be used on other materials such as
wood
Wood is a porous and fibrous structural tissue found in the stems and roots of trees and other woody plants. It is an organic materiala natural composite of cellulose fibers that are strong in tension and embedded in a matrix of lignin th ...
,
plastic
Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptab ...
,
ceramic
A ceramic is any of the various hard, brittle, heat-resistant and corrosion-resistant materials made by shaping and then firing an inorganic, nonmetallic material, such as clay, at a high temperature. Common examples are earthenware, porcelain ...
, and
composite material
A composite material (also called a composition material or shortened to composite, which is the common name) is a material which is produced from two or more constituent materials. These constituent materials have notably dissimilar chemical or ...
. A person who specializes in machining is called a
machinist
A machinist is a tradesperson or trained professional who not only operates machine tools, but also has the knowledge of tooling and materials required to create set ups on machine tools such as milling machines, grinders, lathes, and drilling ...
. A room, building, or company where machining is done is called a
machine shop
A machine shop or engineering workshop (UK) is a room, building, or company where machining, a form of subtractive manufacturing, is done. In a machine shop, machinists use machine tools and cutting tools to make parts, usually of metal or plast ...
. Much of modern-day machining is carried out by
computer numerical control
Numerical control (also computer numerical control, and commonly called CNC) is the automated control of machining tools (such as drills, lathes, mills, grinders, routers and 3D printers) by means of a computer. A CNC machine processes a pie ...
(CNC), in which computers are used to control the movement and operation of the mills, lathes, and other cutting machines. This increases efficiency, as the CNC machine runs unmanned therefore reducing labour costs for machine shops.
History and terminology
The precise meaning of the term ''machining'' has evolved over the past one and a half centuries as technology has advanced. In the 18th century, the word ''
machinist
A machinist is a tradesperson or trained professional who not only operates machine tools, but also has the knowledge of tooling and materials required to create set ups on machine tools such as milling machines, grinders, lathes, and drilling ...
'' simply meant a person who built or repaired
machine
A machine is a physical system using Power (physics), power to apply Force, forces and control Motion, movement to perform an action. The term is commonly applied to artificial devices, such as those employing engines or motors, but also to na ...
s. This person's work was done mostly by hand, using processes such as the
carving of wood and the hand-
forging
Forging is a manufacturing process involving the shaping of metal using localized compressive forces. The blows are delivered with a hammer (often a power hammer) or a die. Forging is often classified according to the temperature at which i ...
and hand-
filing of metal. At the time,
millwright
A millwright is a craftsperson or skilled tradesperson who installs, dismantles, maintains, repairs, reassembles, and moves machinery in factories, power plants, and construction sites.
The term ''millwright'' (also known as ''industrial mecha ...
s and builders of new kinds of ''engines'' (meaning, more or less, machines of any kind), such as
James Watt
James Watt (; 30 January 1736 (19 January 1736 OS) – 25 August 1819) was a Scottish inventor, mechanical engineer, and chemist who improved on Thomas Newcomen's 1712 Newcomen steam engine with his Watt steam engine in 1776, which was fun ...
or
John Wilkinson, would fit the definition. The noun ''
machine tool
A machine tool is a machine for handling or machining metal or other rigid materials, usually by cutting, boring, grinding, shearing, or other forms of deformations. Machine tools employ some sort of tool that does the cutting or shaping. All m ...
'' and the verb ''to machine'' (''machined, machining'') did not yet exist.
Around the middle of the 20th century, the latter words were coined as the concepts that they described evolved into widespread existence. Therefore, during the
Machine Age
The Machine Age is an era that includes the early-to-mid 20th century, sometimes also including the late 19th century. An approximate dating would be about 1880 to 1945. Considered to be at its peak in the time between the first and second wo ...
, ''machining'' referred to (what we today might call) the "traditional" machining processes, such as
turning
Turning is a machining process in which a cutting tool, typically a non-rotary tool bit, describes a helix toolpath by moving more or less linearly while the workpiece rotates.
Usually the term "turning" is reserved for the generation of ...
,
boring,
drilling
Drilling is a cutting process where a drill bit is spun to cut a hole of circular cross-section in solid materials. The drill bit is usually a rotary cutting tool, often multi-point. The bit is pressed against the work-piece and rotated at ra ...
,
milling,
broaching
The BROACH warhead is a Tandem-charge, multi-stage warhead developed by Team BROACH; BAE Systems Global Combat Systems Munitions, Thales Missile Electronics and QinetiQ. BROACH stands for ''Bomb Royal Ordnance Augmented CHarge''.
Development of ...
,
sawing
A saw is a tool consisting of a tough blade, wire, or chain with a hard toothed edge. It is used to cut through material, very often wood, though sometimes metal or stone. The cut is made by placing the toothed edge against the material and mov ...
,
shaping,
planing,
abrasive cutting,
reaming
A reamer is a type of rotary cutting tool used in metalworking. Precision reamers are designed to enlarge the size of a previously formed hole by a small amount but with a high degree of accuracy to leave smooth sides. There are also non-precisio ...
, and
tapping
Tapping is a playing technique that can be used on any stringed instrument, but which is most commonly used on guitar. The technique involves a string being fretted and set into vibration as part of a single motion. This is in contrast to stand ...
. In these "traditional" or "conventional" machining processes,
machine tool
A machine tool is a machine for handling or machining metal or other rigid materials, usually by cutting, boring, grinding, shearing, or other forms of deformations. Machine tools employ some sort of tool that does the cutting or shaping. All m ...
s, such as
lathes
A lathe () is a machine tool that rotates a workpiece about an axis of rotation to perform various operations such as cutting, sanding, knurling, drilling, deformation, facing, and turning, with tools that are applied to the workpiece to cre ...
,
milling machine
Milling is the process of machining using rotary cutters to remove material by advancing a cutter into a workpiece. This may be done by varying direction on one or several axes, cutter head speed, and pressure. Milling covers a wide variety of d ...
s,
drill press
A drill is a tool used for making round holes or driving fasteners. It is fitted with a bit, either a drill or driverchuck. Hand-operated types are dramatically decreasing in popularity and cordless battery-powered ones proliferating due to i ...
es, or others, are used with a sharp
cutting tool
In the context of machining, a cutting tool or cutter is typically a hardened metal tool that is used to cut, shape, and remove material from a workpiece by means of machining tools as well as abrasive tools by way of shear deformation. The major ...
to remove material to achieve a desired geometry.
Since the advent of new technologies in the post–World War II era, such as
electrical discharge machining
Electrical discharge machining (EDM), also known as spark machining, spark eroding, die sinking, wire burning or wire erosion, is a metal
fabrication process whereby a desired shape is obtained by using electrical discharges (sparks). Material i ...
,
electrochemical machining,
electron beam machining
Electron-beam machining (EBM) is a process where high-velocity electrons concentrated into a narrow beam that are directed towards the work piece, creating heat and vaporizing the material. EBM can be used for very precise cutting or boring of a w ...
,
photochemical machining
Photochemical machining (PCM), also known as photochemical milling or photo etching, is a chemical milling process used to fabricate sheet metal components using a photoresist and etchants to corrosively machine away selected areas. This process ...
, and
ultrasonic machining, the
retronym
A retronym is a newer name for an existing thing that helps differentiate the original form/version from a more recent one. It is thus a word or phrase created to avoid confusion between older and newer types, whereas previously (before there were ...
"conventional machining" can be used to differentiate those classic technologies from the newer ones. In current usage, the term "machining" without qualification usually implies the traditional machining processes.
In the decades of the 2000s and 2010s, as
additive manufacturing
3D printing or additive manufacturing is the construction of a three-dimensional object from a CAD model or a digital 3D model. It can be done in a variety of processes in which material is deposited, joined or solidified under computer co ...
(AM) evolved beyond its earlier laboratory and rapid prototyping contexts and began to become common throughout all phases of manufacturing, the term ''subtractive manufacturing'' became common
retronym
A retronym is a newer name for an existing thing that helps differentiate the original form/version from a more recent one. It is thus a word or phrase created to avoid confusion between older and newer types, whereas previously (before there were ...
ously in logical contrast with AM, covering essentially any removal processes also previously covered by the term ''machining''. The two terms are effectively
synonym
A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are all ...
ous, although the long-established usage of the term ''machining'' continues. This is comparable to the idea that
the verb sense of ''contact'' evolved because of the proliferation of ways to contact someone (telephone, email, IM, SMS, and so on) but did not entirely replace the earlier terms such as ''call'', ''talk to'', or ''write to''.
Machining operations
The three principal machining processes are classified as
turning
Turning is a machining process in which a cutting tool, typically a non-rotary tool bit, describes a helix toolpath by moving more or less linearly while the workpiece rotates.
Usually the term "turning" is reserved for the generation of ...
,
drilling
Drilling is a cutting process where a drill bit is spun to cut a hole of circular cross-section in solid materials. The drill bit is usually a rotary cutting tool, often multi-point. The bit is pressed against the work-piece and rotated at ra ...
and
milling. Other operations falling into miscellaneous categories include shaping, planing, boring,
broaching
The BROACH warhead is a Tandem-charge, multi-stage warhead developed by Team BROACH; BAE Systems Global Combat Systems Munitions, Thales Missile Electronics and QinetiQ. BROACH stands for ''Bomb Royal Ordnance Augmented CHarge''.
Development of ...
and sawing.
*Turning operations are operations that rotate the
workpiece
A workpiece is a piece, often made of a single material, that is being processed into another desired shape (such as building blocks).
The workpiece is usually a piece of relatively rigid material such as wood, metal, plastic, or stone. After a ...
as the primary method of moving metal against the cutting tool. Lathes are the principal machine tool used in turning.
*Milling operations are operations in which the cutting tool rotates to bring cutting edges to bear against the workpiece. Milling machines are the principal machine tool used in milling.
*Drilling operations are operations in which holes are produced or refined by bringing a rotating cutter with cutting edges at the lower extremity into contact with the workpiece. Drilling operations are done primarily in drill presses but sometimes on lathes or mills.
*Miscellaneous operations are operations that strictly speaking may not be machining operations in that they may not be
swarf producing operations but these operations are performed at a typical machine tool.
Burnishing is an example of a miscellaneous operation. Burnishing produces no swarf but can be performed at a lathe, mill, or drill press.
An unfinished workpiece requiring machining will need to have some material cut away to create a finished product. A finished product would be a workpiece that meets the specifications set out for that workpiece by
engineering drawings
An engineering drawing is a type of technical drawing that is used to convey information about an object. A common use is to specify the geometry necessary for the construction of a component and is called a detail drawing. Usually, a number o ...
or
blueprints
A blueprint is a reproduction of a technical drawing or engineering drawing using a contact print process on light-sensitive sheets. Introduced by Sir John Herschel in 1842, the process allowed rapid and accurate production of an unlimited numb ...
. For example, a workpiece may be required to have a specific outside diameter. A lathe is a machine tool that can be used to create that diameter by rotating a metal workpiece, so that a cutting tool can cut metal away, creating a smooth, round surface matching the required diameter and surface finish. A drill can be used to remove metal in the shape of a cylindrical hole. Other tools that may be used for various types of metal removal are milling machines, saws, and
grinding machine
A grinding machine, often shortened to grinder, is a power tool (or machine tool) used for grinding. It is a type of machining using an abrasive wheel as the cutting tool. Each grain of abrasive on the wheel's surface cuts a small chip from the ...
s. Many of these same techniques are used in
woodworking
Woodworking is the skill of making items from wood, and includes cabinet making (cabinetry and furniture), wood carving, woodworking joints, joinery, carpentry, and woodturning.
History
Along with Rock (geology), stone, clay and animal parts, ...
.
As a commercial venture, machining is generally performed in a
machine shop
A machine shop or engineering workshop (UK) is a room, building, or company where machining, a form of subtractive manufacturing, is done. In a machine shop, machinists use machine tools and cutting tools to make parts, usually of metal or plast ...
, which consists of one or more workrooms containing major machine tools. Although a machine shop can be a stand-alone operation, many businesses maintain internal machine shops which support specialized needs of the business.
Machining requires attention to many details for a workpiece to meet the specifications set out in the engineering drawings or blueprints. Beside the obvious problems related to correct dimensions, there is the problem of achieving the correct finish or surface smoothness on the workpiece. The inferior finish found on the machined surface of a workpiece may be caused by incorrect
clamping
A wheel clamp, also known as wheel boot, parking boot, or Denver boot, is a device that is designed to prevent motor vehicles from being moved. In its most common form, it consists of a clamp that surrounds a vehicle wheel, designed to preven ...
, a dull tool, or inappropriate presentation of a tool. Frequently, this poor surface finish, known as chatter, is evident by an undulating or irregular finish, and the appearance of waves on the machined surfaces of the workpiece.
Overview of machining technology
Machining is any process in which a cutting tool is used to remove small chips of material from the workpiece (the workpiece is often called the "work"). To perform the operation, relative motion is required between the tool and the work. This relative motion is achieved in most machining operation by means of a primary motion, called "cutting speed" and a secondary motion called "feed". The shape of the tool and its penetration into the work surface, combined with these motions, produce the desired shape of the resulting work surface.
Machining operations
There are many kinds of machining operations, each of which is capable of generating a certain part geometry and surface texture.
In
turning
Turning is a machining process in which a cutting tool, typically a non-rotary tool bit, describes a helix toolpath by moving more or less linearly while the workpiece rotates.
Usually the term "turning" is reserved for the generation of ...
, a cutting tool with a single cutting edge is used to remove material from a rotating workpiece to generate a cylindrical shape. The primary motion is provided by rotating the workpiece, and the feed motion is achieved by moving the cutting tool slowly in a direction parallel to the axis of rotation of the workpiece.
Drilling
Drilling is a cutting process where a drill bit is spun to cut a hole of circular cross-section in solid materials. The drill bit is usually a rotary cutting tool, often multi-point. The bit is pressed against the work-piece and rotated at ra ...
is used to create a round hole. It is accomplished by a rotating tool that typically has two or four helical cutting edges. The tool is fed in a direction parallel to its axis of rotation into the workpiece to form the round hole.
In
boring, a tool with a single bent pointed tip is advanced into a roughly made hole in a spinning workpiece to slightly enlarge the hole and improve its accuracy. It is a fine finishing operation used in the final stages of product manufacture.
Reaming
A reamer is a type of rotary cutting tool used in metalworking. Precision reamers are designed to enlarge the size of a previously formed hole by a small amount but with a high degree of accuracy to leave smooth sides. There are also non-precisio ...
is one of the sizing operations that removes a small amount of metal from a hole already drilled.
In
milling, a rotating tool with multiple cutting edges is moved slowly relative to the material to generate a plane or straight surface. The direction of the feed motion is perpendicular to the tool's axis of rotation. The speed motion is provided by the rotating milling cutter. The two basic forms of milling are:
* Peripheral milling
* Face milling.
Other conventional machining operations include shaping, planing, broaching and sawing. Also, grinding and similar abrasive operations are often included within the category of machining.
Cutting tool
A cutting tool has one or more sharp cutting edges and is made of a material that is harder than the work material. The cutting edge serves to separate chip from the parent work material. Connected to the cutting edge are the two surfaces of the tool:
* The rake face; and
* The flank.
The rake face which directs the flow of newly formed chip, is oriented at a certain angle is called the rake angle "α". It is measured relative to the plane perpendicular to the work surface. The rake angle can be positive or negative. The flank of the tool provides a clearance between the tool and the newly formed work surface, thus protecting the surface from abrasion, which would degrade the finish. This angle between the work surface and the flank surface is called the relief angle. There are two basic types of cutting tools:
* Single point tool; and
* Multiple-cutting-edge tool
A single point tool has one cutting edge and is used for turning, boring and planing. During machining, the point of the tool penetrates below the original work surface of the workpart. The point is sometimes rounded to a certain radius, called the nose radius.
Multiple-cutting-edge tools have more than one cutting edge and usually achieve their motion relative to the workpart by rotating. Drilling and milling use rotating multiple-cutting-edge tools. Although the shapes of these tools are different from a single-point tool, many elements of tool geometry are similar.
Cutting conditions
Relative motion is required between the tool and work to perform a machining operation. The primary motion is accomplished at a certain
cutting speed
The phrase speeds and feeds or feeds and speeds refers to two separate velocities in machine tool practice, cutting speed and feed rate. They are often considered as a pair because of their combined effect on the cutting process. Each, however, ...
. In addition, the tool must be moved laterally across the work. This is a much slower motion, called the feed. The remaining dimension of the cut is the penetration of the cutting tool below the original work surface, called the depth of cut. Collectively, speed, feed, and depth of cut are called the cutting conditions. They form the three dimensions of the machining process, and for certain operations, their product can be used to obtain the
material removal rate
Material removal rate (MRR) is the amount of material removed per time unit (usually per minute) when performing machining operations such as using a lathe or milling machine. The more material removed per minute, the higher the material remova ...
for the process:
:
where
*
– the material removal rate in ''mm
3/s'', (''in
3/s''),
*
– the cutting speed in ''mm/s'', (''in/min''),
*
– the feed in ''mm'', (''in''),
*
– the depth of cut in ''mm'', (''in'').
:Note: All units must be converted to the corresponding decimal (or
USCU) units.
Stages in metal cutting
Machining operations usually divide into two categories, distinguished by purpose and
cutting conditions:
* Roughing cuts
* Finishing cuts
Roughing cuts are used to remove large amount of material from the starting workpart as rapidly as possible, i.e. with a large Material Removal Rate (MRR), in order to produce a shape close to the desired form, but leaving some material on the piece for a subsequent finishing operation.
Finishing cuts are used to complete the part and achieve the final dimension,
tolerances, and surface finish. In production machining jobs, one or more roughing cuts are usually performed on the work, followed by one or two finishing cuts. Roughing operations are done at high feeds and depths – feeds of 0.4–1.25 mm/rev (0.015–0.050 in/rev) and depths of 2.5–20 mm (0.100–0.750 in) are typical, but actual values depend on the workpiece materials. Finishing operations are carried out at low feeds and depths – feeds of 0.0125–0.04 mm/rev (0.0005–0.0015 in/rev) and depths of 0.75–2.0 mm (0.030–0.075 in) are typical. Cutting speeds are lower in roughing than in finishing.
A
cutting fluid
Cutting fluid is a type of coolant and lubricant designed specifically for metalworking processes, such as machining and stamping. There are various kinds of cutting fluids, which include oils, oil-water emulsions, pastes, gels, aerosols (mists) ...
is often applied to the machining operation to cool and lubricate the cutting tool. Determining whether a cutting fluid should be used, and, if so, choosing the proper cutting fluid, is usually included within the scope of cutting condition.
Today other forms of metal cutting are becoming increasingly popular. An example of this is water jet cutting. Water jet cutting involves pressurized water in excess of 620 MPa (90 000 psi) and is able to cut metal and have a finished product. This process is called cold cutting, which eliminates the damage caused by a heat affected zone, as opposed to laser and
plasma cutting
Plasma cutting is a process that cuts through electrically conductive materials by means of an accelerated jet of hot plasma. Typical materials cut with a plasma torch include steel, stainless steel, aluminum, brass and copper, although other con ...
.
Relationship of subtractive and additive techniques
With the recent proliferation of
additive manufacturing
3D printing or additive manufacturing is the construction of a three-dimensional object from a CAD model or a digital 3D model. It can be done in a variety of processes in which material is deposited, joined or solidified under computer co ...
technologies, conventional machining has been
retronym
A retronym is a newer name for an existing thing that helps differentiate the original form/version from a more recent one. It is thus a word or phrase created to avoid confusion between older and newer types, whereas previously (before there were ...
ously classified, in thought and language, as a
subtractive manufacturing
Machining is a process in which a material (often metal) is cut to a desired final shape and size by a controlled material-removal process. The processes that have this common theme are collectively called subtractive manufacturing, which utilizes ...
method. In narrow contexts, additive and subtractive methods may compete with each other. In the broad context of entire industries, their relationship is complementary. Each method has its own advantages over the other. While additive manufacturing methods can produce very intricate prototype designs impossible to replicate by machining, strength and material selection may be limited.
ADDITIVE/SUBTRACTIVE MANUFACTURING RESEARCH
/ref>
See also
*Abrasive flow machining Abrasive flow machining (AFM), also known as abrasive flow deburring or extrude honing, is an interior surface finishing process characterized by flowing an abrasive-laden fluid through a workpiece. This fluid is typically very viscous, having th ...
* Abrasive jet machining
* Biomachining
*Cutting
Cutting is the separation or opening of a physical object, into two or more portions, through the application of an acutely directed force.
Implements commonly used for wikt:cut, cutting are the knife and saw, or in medicine and science the scal ...
*Design for manufacturability for CNC machining
Design for manufacturability (also sometimes known as design for manufacturing or DFM) is the general engineering practice of product design, designing products in such a way that they are easy to manufacture. The concept exists in almost all engi ...
*Chip formation Chip formation is part of the process of cutting materials by mechanical means, using tools such as saws, lathes and milling machine, milling cutters.
The formal study of chip formation was encouraged around World War II and shortly afterwards, wit ...
*Machinability Machinability is the ease with which a metal can be cut (machined) permitting the removal of the material with a satisfactory finish at low cost.Degarmo, p. 542. Materials with good machinability (free machining materials) require little power to c ...
*Machine tools
A machine tool is a machine for handling or machining metal or other rigid materials, usually by cutting, boring, grinding, shearing, or other forms of deformations. Machine tools employ some sort of tool that does the cutting or shaping. All m ...
*Machine shop
A machine shop or engineering workshop (UK) is a room, building, or company where machining, a form of subtractive manufacturing, is done. In a machine shop, machinists use machine tools and cutting tools to make parts, usually of metal or plast ...
*Machining vibrations
Machining vibrations, also called chatter, are the relative movement between the workpiece and the cutting tool. The vibrations result in waves on the machined surface. This affects typical machining processes, such as turning, milling and drilli ...
*Tool management
Tool management is needed in Manufacturing, metalworking so that the information regarding the tools on hand can be uniformly organized and integrated. The information is stored in a database and is registered and applied using tool management. T ...
References
Bibliography
*
Further reading
*
*
* "Machine Tool Practices", 6th edition, by R.R.; Kibbe, J.E.; Neely, R.O.; Meyer & W.T.; White, , 2nd printing, copyright 1999, 1995, 1991, 1987, 1982 and 1979 by Prentice Hall.
External links
www.nmri.go.jp/eng, Elementary knowledge of metalworking
Videos about machining
published by Institut für den Wissenschaftlichen Film. Available in the AV-Portal of the German National Library of Science and Technology
The German National Library of Science and Technology (german: Technische Informationsbibliothek), abbreviated TIB, is the national library of the Federal Republic of Germany for all fields of engineering, technology, and the natural sciences. I ...
.
Crankshaft Machining
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