Metalworking

Metalworking is the process of working with metals to create individual parts, assemblies, or large scale
structures.

The term covers a wide range of work from large ships and bridges to precise engine parts and
delicate jewelry. It therefore includes a correspondingly wide range of skills, processes, and tools.

General metalworking processes

A combination square used for transferring designs.

A caliper is used to precisely measure a short length.

Metalworking generally is divided into the following categories,

1. forming,

2. cutting, and,

3. joining.

Each of these categories contain various process.

Aluminu Refractor
Process Iron Compatibility
Steel Copper
chart Magnesium
of materials versus Nickel
processes[4] Titanium Zinc
m y metals

Sand casting X X X X Material

X X 0

Permanent mold
X 0 X 0 X 0 0
casting

Die casting X 0 X X

Investment
X X X 0 0
casting
 Closed-die
X 0 0 0 0 0 0
forging

Extrusion 0 X X X 0 0 0

Cold heading X X X 0

Stamping & deep
X X X 0 X 0 0
drawing

Screw machine 0 X X X 0 X 0 0 0

Powder
X X 0 X 0 X 0
metallurgy

Key: X = Routinely performed, 0 = Performed with difficulty, caution, or some sacrifice, blank = Not
recommended

Forming processes
These forming processes modify metal or workpiece by deforming the object, that is, without removing
any material. Forming is done with heat and pressure, or with mechanical force, or both.

Casting
Casting achieves a specific form by pouring
molten metal into a mold and allowing it to cool,
with no mechanical force.

A sand casting mold

Forms of casting include:

 Investment casting (called lost wax casting in art)

 Centrifugal casting
 Die casting
 Sand casting
 Shell casting
 Spin casting

Plastic deforming
Plastic deformation involves using heat
or pressure to make a workpiece more
conductive to mechanical force. Historically, this
and casting were done by blacksmiths, though
today the process has been industrialized.

 Cold sizing
 Extrusion
 Forging
 Hot metal gas forming
 Powder metallurgy
 Friction drilling
A red-hot metal workpiece is inserted into a forging
press.
Sheet metal forming

These types of forming process involve the application of mechanical force at room temperature.

 Bending  Roll bending

 Coining  Repoussé and chasing
 Decambering  Rolling
 Deep drawing  Rubber pad forming
 Drawing  Shearing
 Spinning  Stamping
 Flow turning  Wheeling using an English
 Raising wheel (wheeling machine)
 Roll forming
 A metal spun brass vase

Cutting processes
Cutting is a collection of processes wherein process not machining. There are also
material is brought to a specified geometry by miscellaneous specialty processes such as
removing excess material using various kinds of chemical milling.
tooling to leave a finished part that meets
specifications. The net result of cutting is two
products, the waste or excess material, and the
finished part. If this were a discussion of
woodworking, the waste would be sawdust and
excess wood. In cutting metals the waste is
chips or swarfand excess metal. These
processes can be divided into chip producing
cutting, generally known as machining. Burning
A CNC plasma cutting machining
or cutting with an oxyfuel torch is a welding

Cutting is nearly fully represented by:

 Chip producing processes most commonly known as machining

 Burning, a set of processes which cut by oxidizing a kerf to separate pieces of metal
 Specialty processes.

Drilling a hole in a metal part is the most common example of a chip producing process. Using an oxy-fuel
cutting torchto separate a plate of steel into smaller pieces is an example of burning. Chemical milling is
an example of a specialty process that removes excess material by the use of etching chemicals and
masking chemicals.

There are many technologies available to cut metal, including:

 Manual technologies: saw, chisel, shear or snips
 Machine technologies: turning, milling, drilling, grinding, sawing
 Welding/burning technologies: burning by laser, oxy-fuel burning, and plasma
 Erosion technologies:by water jet or electric discharge.

Cutting fluid or coolant is used where there is significant friction and heat at the cutting interface between
a cutter such as a drill or an end mill and the workpiece. Coolant is generally introduced by a spray across
the face of the tool and workpiece to decrease friction and temperature at the cutting tool/workpiece
interface to prevent excessive tool wear. In practice there are many methods of delivering coolant.

Machining
Milling is the complex shaping of metal or other threading, rabbeting, routing, etc. Two common
materials by removing material to form the final types of mills are the horizontal mill and vertical
shape. It is generally done on a milling machine, mill.
a power-driven machine that in its basic form
consists of a milling cutter that rotates about the
spindle axis (like a drill), and a worktable that
can move in multiple directions (usually two
dimensions [x and y axis] relative to the
workpiece). The spindle usually moves in the z
axis. It is possible to raise the table (where the
workpiece rests). Milling machines may be
operated manually or under computer numerical
control (CNC), and can perform a vast number
of complex operations, such as slot A milling machine in operation, including coolant
cutting, planing, drilling and hoses.

The pieces produced are usually complex 3D objects that are converted into x, y, and z coordinates that
are then fed into the CNC machine and allow it to complete the tasks required. The milling machine can
produce most parts in 3D, but some require the objects to be rotated around the x, y, or z coordinate axis
(depending on the need). Tolerances are usually in the thousandths of an inch (Unit known as Thou),
depending on the specific machine.

In order to keep both the bit and material cool, a high temperature coolant is used. In most cases the
coolant is sprayed from a hose directly onto the bit and material. This coolant can either be machine or
user controlled, depending on the machine.
Materials that can be milled range from aluminum to stainless steel and most everything in between. Each
material requires a different speed on the milling tool and varies in the amount of material that can be
removed in one pass of the tool. Harder materials are usually milled at slower speeds with small amounts
of material removed. Softer materials vary, but usually are milled with a high bit speed.

The use of a milling machine adds costs that are factored into the manufacturing process. Each time the
machine is used coolant is also used, which must be periodically added in order to prevent breaking bits.
A milling bit must also be changed as needed in order to prevent damage to the material. Time is the
biggest factor for costs. Complex parts can require hours to complete, while very simple parts take only
minutes. This in turn varies the production time as well, as each part will require different amounts of time.

Safety is key with these machines. The bits are traveling at high speeds and removing pieces of usually
scalding hot metal. The advantage of having a CNC milling machine is that it protects the machine
operator.

Turning
Turning is a metal cutting process for producing
a cylindrical surface with a single point tool. The
work piece is rotated on a spindle and the
cutting tool is fed into it radially, axially or both.
Producing surfaces perpendicular to the
workpiece axis is called facing. Producing
surfaces using both radial and axial feeds is
called profiling.[5]
A lathe cutting material from a workpiece.

A lathe is a machine tool which spins a block or cylinder of material so that when abrasive, cutting,
or deformation tools are applied to the workpiece, it can be shaped to produce an object which
has rotational symmetry about an axis of rotation. Examples of objects that can be produced on a lathe
include candlestick holders, table legs, bowls, baseball bats, crankshafts,camshafts, and bearing mounts.

Lathes have three main components: the headstock, the carriage, and the tailstock. The
headstock's spindle secures the workpiece with a chuck, whose jaws (usually three or four) are tightened
around the piece. The spindle rotates at high speed, providing the energy to cut the material. While
historic lathes were powered by belts from the ceiling, modern examples uses electric motors. The
workpiece extends out of the spindle along the axis of rotation above the flat bed. The carriage is a
platform that can be moved, precisely and independently, horizontally parallel and perpendicular to the
axis of rotation. A hardened cutting tool is held at the desired height (usually the middle of the workpiece)
by the tool post. The carriage is then moved around the rotating workpiece, and the cutting tool gradually
shaves material from the workpiece. The tailstock can be slid along the axis of rotation and then locked in
place as necessary. It may hold centers to further secure the workpiece, or cutting tools driven into the
end of the workpiece.

Other operation that can be performed with a single point tool on a lathe are:[5]

Chamfering: Cutting an angle on the comer of a cylinder.

Parting: The tool is fed radially into the workpiece to cut off the end of a part.
Threading: A tool is fed along and across the outside or inside surface of rotating parts to produce
external or internalthreads.
Boring: A single-point tool is fed linearly and parallel to the axis of rotation.
Drilling: Feeding the drill into the workpiece axially.
Knurling: Produces a regular cross-hatched pattern in work surfaces intended to be gripped by hand.

Modern computer numerical control (CNC) lathes can do secondary operations like milling by using driven
tools. When driven tools are used the work piece stops rotating and the driven tool executes the
machining operation with a rotating cutting tool. The CNC machines use x, y, and z coordinates in order
to control the turning tools and produce the product. Most modern day CNC lathes are able to produce
most turned objects in 3D.

Materials appropriate for turning used are softer metals, although harder metals can be turned with a bit
more time and effort.

The turning tool material must be harder than the material being turned in order for the process to work.
Production rates for this process depend on the object being turned and the speed at which it can be
done. More complex materials, therefore, will take more time.

Threading
There are many threading processes including:
cutting threads with a tap or die, thread milling,
single-point thread cutting, thread rolling and
forming, and thread grinding. A tap is used to cut
a female thread on the inside surface of a pre-
drilled hole, while a die cuts a male thread on a
preformed cylindrical rod.

Three different types and sizes of taps.

Grinding
Grinding uses an abrasive process to remove
material from the workpiece. A grinding
machine is a machine tool used for producing
very fine finishes, making very light cuts, or high
precision forms using a abrasive wheel as the
cutting device. This wheel can be made up of
various sizes and types of
A surface grinder
stones, diamonds orinorganic materials.

The simplest grinder is a bench grinder or a hand-held angle grinder, for deburring parts or cutting metal
with a zip-disc.

Grinders have increased in size and complexity with advances in time and technology. From the old days
of a manual toolroom grinder sharpening endmills for a production shop, to today's 30000 RPM CNC
auto-loading manufacturing cell producing jet turbines, grinding processes vary greatly.

Grinders need to be very rigid machines to produce the required finish. Some grinders are even used to
produce glass scales for positioning CNC machine axis. The common rule is the machines used to
produce scales be 10 times more accurate than the machines the parts are produced for.

In the past grinders were used for finishing operations only because of limitations of tooling. Modern
grinding wheel materials and the use of industrial diamonds or other man-made coatings (cubic boron
nitride) on wheel forms have allowed grinders to achieve excellent results in production environments
instead of being relegated to the back of the shop.

Modern technology has advanced grinding operations to include CNC controls, high material removal
rates with high precision, lending itself well to aerospace applications and high volume production runs of
precision components.

Filing
Filing is combination of grinding and saw tooth work to fine tolerances and was the hallmark of
cutting using a file. Prior to the development of the craft. Today filing is rarely used as a
modern machining equipment it provided a production technique in industry, though it
relatively accurate means for the production of remains as a common method of deburring.
small parts, especially those with flat surfaces.
The skilled use of a file allowed a machinist to
 A file is an abrasive surface like this one that allows
machinists to remove small, imprecise amounts of
metal.

Other
Broaching is a machining operation used to cut keyways into shafts.Electron beam machining (EBM) is a
machining process where high-velocity electrons are directed toward a work piece, creating heat and
vaporizing the material. Ultrasonic machining usesultrasonic vibrations to machine very hard or brittle
materials.

Joining processes
Welding
Welding is a fabrication process that joins
materials, usually metals orthermoplastics, by
causing coalescence. This is often done
by melting the workpieces and adding a filler
material to form a pool of molten material that
cools to become a strong joint, but sometimes
pressure is used in conjunction with heat, or by
itself, to produce the weld.

Mig welding

Many different energy sources can be used for welding, including a gasflame, an electric arc, a laser,
an electron beam, friction, and ultrasound. While often an industrial process, welding can be done in
many different environments, including open air, underwater and in space. Regardless of location,
however, welding remains dangerous, and precautions must be taken to avoid burns, electric shock,
poisonous fumes, and overexposure to ultraviolet light.
Brazing
Brazing is a joining process in which a filler metal is melted and drawn into a capillary formed by the
assembly of two or more work pieces. The filler metal reacts metallurgically with the workpiece(s) and
solidifies in the capillary, forming a strong joint. Unlike welding, the work piece is not melted. Brazing is
similar to soldering, but occurs at temperatures in excess of 450 °C (842 °F). Brazing has the advantage
of producing less thermal stresses than welding, and brazed assemblies tend to be more ductile than
weldments because alloying elements can not segregate and precipitate.

Brazing techniques include, flame brazing, resistance brazing, furnace brazing, diffusion brazing, and
inductive brazing.

Soldering
Soldering is a joining process that occurs at
temperatures below 450 °C (842 °F). It is similar
to brazing in the fact that a filler is melted and
drawn into a capillary to form a join, although at
a lower temperature. Because of this lower
temperature and different alloys used as fillers,
the metallurgical reaction between filler and
work piece is minimal, resulting in a weaker
joint.

Soldering a printed circuit board.

Riveting
Riveting is one of the most ancient metalwork joining processes. Its use has declined markedly during the
second half of the 20th century, but it still retains important uses in industry and construction into the 21st
century. The earlier use of rivets is being superseded by improvements in welding and
component fabrication techniques.

A rivet is essentially a two-headed and unthreaded bolt which holds two other pieces of metal together.
Holes are drilledor punched through the two pieces of metal to be joined. The holes being aligned, a rivet
is passed through the holes and permanent heads are formed onto the ends of the rivet utilizing hammers
and forming dies (by either coldworking orhotworking). Rivets are commonly purchased with one head
already formed.
When it is necessary to remove rivets, one of the rivet's heads is sheared off with a cold chisel. The rivet
is then driven out with a hammer and punch.

Associated processes

While these processes are not primary metalworking processes, they are often performed before or after
metalworking processes.

Heat treatment
Metals can be heat treated to alter the properties of strength, ductility, toughness, hardness or resistance
to corrosion. Common heat treatment processes include annealing, precipitation
strengthening, quenching, and tempering. Theannealing process softens the metal by allowing recovery
of cold work and grain growth. Quenching can be used to harden alloy steels, or in precipitation
hardenable alloys, to trap dissolved solute atoms in solution. Tempering will cause the dissolved alloying
elements to precipitate, or in the case of quenched steels, improve impact strength and ductile properties.
Often, mechanical and thermal treatments are combined in what is known as thermo-mechanical
treatments for better properties and more efficient processing of materials. These processes are common
to high alloy special steels, super alloys and titanium alloys.

Plating
Electroplating is a common surface-treatment technique. It involves bonding a thin layer of another metal
such as gold,silver, chromium or zinc to the surface of the product. It is used to reduce corrosion as well
as to improve the product's aesthetic appearance.

Thermal spraying
Thermal spraying techniques are another popular finishing option, and often have better high temperature
properties than electroplated coatings.