The equation for estimating the maximum bending force is,
where k is
a factor taking into account several parameters including
friction. T is
tensile strength of
the metal. L and t are
the length and thickness of the sheet metal, respectively.
The variable W is
the open width of a V-die or wiping die.
Main article: Decambering
Main article: Deep
Drawing is a forming process in which the metal is stretched
over a form. In deep drawing the depth of the part being
made is more than half its diameter. Deep drawing is used
for making automotive fuel tanks, kitchen sinks, two-piece aluminum
cans, etc. Deep drawing is generally done in multiple
steps called draw reductions. The greater the depth the more
reductions are required. Deep drawing may also be
accomplished with fewer reductions by heating the workpiece,
for example in sink manufacture.
In many cases, material is rolled at the mill in both
directions to aid in deep drawing. This leads to a more
uniform grain structure which limits tearing and is referred
to as "draw quality" material.
Expanding is a process of cutting or stamping slits in
alternating pattern much like the stretcher bond in brickwork and
then stretching the sheet open in accordion-like fashion. It
is used in applications where air and water flow are desired
as well as when light weight is desired at cost of a solid
flat surface. A similar process is used in other materials
such as paper to create a low cost packing paper with better
supportive properties than flat paper alone.
Main article: Laser
Sheet metal can be cut in various ways, from hand tools
snips up to
very large powered shears. With the advances in technology,
sheet metal cutting has turned to computers for precise
cutting. Many sheet metal cutting operations are based on
computer numerically controlled (CNC) laser cutting or
multi-tool CNC punch press.
CNC laser involves moving a lens assembly carrying a beam of
laser light over the surface of the metal. Oxygen, nitrogen
or air is fed through the same nozzle from which the laser
beam exits. The metal is heated and burnt by the laser beam,
cutting the metal sheet. The quality of the edge can be
mirror smooth and a precision of around 0.1 mm (0.0039 in)
can be obtained. Cutting speeds on thin 1.2 mm (0.047 in)
sheet can be as high as 25 m (82 ft) a minute. Most of the
laser cutting systems use a CO2 based laser source with a
wavelength of around 10 µm;
some more recent systems use a YAG based laser with a
wavelength of around 1 µm.
Main article: Perforating
Perforating is a cutting process that punches multiple small
holes close together in a flat workpiece. Perforated sheet
metal is used to make a wide variety of surface cutting
tools, such as thesurform.
This is a form of bending used
to produce long, thin sheet metal parts. The machine that
bends the metal is called a press
brake. The lower part of the press contains a V-shaped
groove called the die. The upper part of the press contains
a punch that presses the sheet metal down into the v-shaped
die, causing it to bend. There are several techniques used,
but the most common modern method is "air bending". Here,
the die has a sharper angle than the required bend
(typically 85 degrees for a 90 degree bend) and the upper
tool is precisely controlled in its stroke to push the metal
down the required amount to bend it through 90 degrees.
Typically, a general purpose machine has an available
bending force of around 25 tonnes per metre of length. The
opening width of the lower die is typically 8 to 10 times
the thickness of the metal to be bent (for example, 5 mm
material could be bent in a 40 mm die). The inner radius of
the bend formed in the metal is determined not by the radius
of the upper tool, but by the lower die width. Typically,
the inner radius is equal to 1/6 of the V-width used in the
The press usually has some sort of back
position depth of the bend along the workpiece. The
backgauge can be computer controlled to allow the operator
to make a series of bends in a component to a high degree of
accuracy. Simple machines control only the backstop, more
advanced machines control the position and angle of the
stop, its height and the position of the two reference pegs
used to locate the material. The machine can also record the
exact position and pressure required for each bending
operation to allow the operator to achieve a perfect 90
degree bend across a variety of operations on the part.
Punching is performed by placing the sheet of metal stock
between a punch and a die mounted in a press. The punch and
die are made of hardened steel and are the same shape. The
punch just barely fits into the die. The press pushes the
punch against and into the die with enough force to cut a
hole in the stock. In some cases the punch and die "nest"
together to create a depression in the stock. In progressive
coil of stock is fed into a long die/punch set with many
stages. Multiple simple shaped holes may be produced in one
stage, but complex holes are created in multiple stages. In
the final stage, the part is punched free from the "web".
A typical CNC turret
punch has a
choice of up to 60 tools in a "turret" that can be rotated
to bring any tool to the punching position. A simple shape
(e.g., a square, circle, or hexagon) is cut directly from
the sheet. A complex shape can be cut out by making many
square or rounded cuts around the perimeter. A punch is less
flexible than a laser for cutting compound shapes, but
faster for repetitive shapes (for example, the grille of an
air-conditioning unit). A CNC punch can achieve 600 strokes
A typical component (such as the side of a computer case)
can be cut to high precision from a blank sheet in under 15
seconds by either a press or
a laser CNC machine.
Main article: Roll
A continuous bending operation for producing open profiles
or welded tubes with long lengths or in large quantities.
Main article: Metal
Spinning is used to make tubular(axis-symmetric) parts by
fixing a piece of sheet stock to a rotating form (mandrel).
Rollers or rigid tools press the stock against the form,
stretching it until the stock takes the shape of the form.
Spinning is used to make rocket motor casings, missile nose
cones, satellite dishes and metal kitchen funnels.
Stamping includes a variety of operations such as punching,
blanking, embossing, bending, flanging, and coining; simple
or complex shapes can be formed at high production rates;
tooling and equipment costs can be high, but labor costs are
Alternatively, the related techniques repoussé
and chasing have
low tooling and equipment costs, but high labor costs.
A water jet cutter, also known as a waterjet, is a tool
capable of a controlled erosion into metal or other
materials using a jet of water at high velocity and
pressure, or a mixture of water and an abrasive substance.