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Sheet metal is simply metal formed into thin and flat pieces. It is one of the fundamental forms used in metalworking, and can be cut and bent into a variety of different shapes. Countless everyday objects are constructed of the material. Thicknesses can vary significantly, although extremely thin pieces of sheet metal would be considered to be foil or leaf, and pieces thicker than 1/4 inch or a centimeter can be considered plate.
Sheet metal is generally produced in sheets less than 6 mm. by reducing the thickness of a long work piece by compressive forces applied through a set of rolls. This process is known as rolling and began around 1500 AD. Sheet metals are available as flat pieces or as strip in coils. It is characterized by its thickness or gauge of the metal. The gauge of sheet metal ranges from 30 gauge to about 8 gauge. The higher the gauge, the thinner the metal is. There are many different metals that can be made into sheet metal. Aluminum, brass, copper, cold rolled steel, mild steel, tin, nickel and titanium are just a few examples of metal that can be made into sheet metal. Sheet metal has applications in car bodies, airplane wings, medical tables, roofs for building and many other things.
A main feature of sheet metal is its ability to be formed and shaped by a variety of processes. Each process does something different to the metal giving it a different shape or size.
Stretching is a process where sheet metal is clamped around its edges and stretched over a die or form block. This process is mainly used for the manufacture of aircraft wings, automotive door and window panels.
Drawing forms sheet metal into cylindrical or box shaped parts by using a punch which presses the blank into a die cavity. Drawing process can also be utilised to create arbitrary shapes with the help of soft punch.
Deep Drawing is a type of Drawing process where the depth of the part is more than half its diameter. Deep drawing is used for making automotive fuel tanks, kitchen sinks, 2 piece aluminum cans, etc. Deep drawing is generally done is multiple steps called draw reductions. The greater the depth, the increased number of reductions required. Deep drawing may also be accomplished with fewer reductions by heating the workpiece, used in sink manufacture for example.
In many cases, special material that has been rolled at the steel mill in both directions can aid in the deep drawing process. Material that has been rolled in both directions has a more uniform grain structure and is referred to as "draw quality" material. Draw quality material will often improve deep drawing (limiting tearing).
Cutting sheet metal can be done in various ways from hand tools called tin snips up to very large powered shears. With the advances in technology, sheet metal cutting has turned to computers for precise cutting.
Most modern sheet metal cutting operations are now based either on CNC Lasers 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 or nitrogen or air is fed through the same nozzle from which the laser beam exits. The metal is heated and then burnt by the laser beam, cutting the metal sheet. The quality of the edge can be mirror smooth, and a precision of around 0.1mm can be obtained. Cutting speeds on thin (1.2mm) sheet can be as high as 25m a minute. Most of the laser cutting systems use a CO2 based laser source with a wavelength of around 10um; some more recent systems use a YAG based laser with a wavelength of around 1um.
Punching is performed by moving the sheet of metal between the top and bottom tools of a punch. The top tool (punch) mates with the bottom tool (die), cutting a simple shape (e.g. a square, circle, or hexagon) from the sheet. An area can be cut out by making several hundred small square 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 typical CNC punch has a choice of up to 60 tools in a "turret" that can be rotated to bring any tool to the active punching position. A modern CNC punch can take 600 blows per minute.
A typical component (such as the side of a computer case) can be cut to high precision from a blank sheet in under 30 seconds by either punch or laser.
Bending and Flanging
Bending and flanging imparts stiffness to a sheet metal part or to form various shapes, such as 3 piece aluminum cans. See Bending (metalworking).just form something in a form of a pipe.
Punching and Shearing
During punching or shearing, the sheet metal is cut by using a punch and die. This process can allow many different shapes and patterns, by a computer numerically controlled (cnc) punch machine.
Spinning is used to make axis-symmetric parts by applying a work piece to a rotating mandrel with the help of rollers or rigid tools. Spinning is used to make rocket motor casings and missile nose cones and satellite dishes for example.
This is a form of bending, used for long and thin sheet metal parts. The machine that bends the metal is called a pressbrake. The lower part of the press contains a V shaped groove. This is called the die. The upper part of the press contains a blade that will press the sheet metal down into the v shaped die, causing it to bend. There are several techniques used here, 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 a bending force available 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, 5mm material could be bent in a 40mm 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 1/6th of the V width used in the forming process.
The press usually has some sort of backstop to position the material in the jaws of the machine. The backstop 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.
A continuous bending operation for producing open profiles or welded tubes with long lengths or in large quantities, see Roll forming.