Use of gauge numbers to designate sheet metal thickness is discouraged by numerous international standards organizations. For example, ASTM states in specification ASTM A480-10a: "The use of gauge number is discouraged as being an archaic term of limited usefulness not having general agreement on meaning." Manufacturers' Standard Gauge for Sheet Steel is based on an average density of 41.82 lb per square foot per inch thick, equivalent to . The older United States Standard Gauge is based upon 40 lb per square foot per inch thick. Gauge is defined differently for ferrous (iron-based) and non-ferrous metals (e.g. aluminium and brass). The gauge thicknesses shown in column 2 (U.S. standard sheet and plate iron and steel decimal inch (mm)) seem somewhat arbitrary. The progression of thicknesses is clear in column 3 (U.S. standard for sheet and plate iron and steel 64ths inch (delta)). The thicknesses vary first by inch in higher thicknesses and then step down to increments of inch, then inch, with the final increments at decimal fractions of inch. Some steel tubes are manufactured by folding a single steel sheet into a square/circle and welding the seam together. Their wall thickness has a similar (but distinct) gauge to the thickness of steel sheets.
Tolerances During the
rolling process the rollers bow slightly, which results in the sheets being thinner on the edges. 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 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.
Hemming and seaming Hemming is a process of folding the edge of sheet metal onto itself to reinforce that edge. Seaming is a process of folding two sheets of metal together to form a joint.
Hydroforming Hydroforming is a process that is analogous to deep drawing, in that the part is formed by stretching the
blank over a stationary
die. The force required is generated by the direct application of extremely high
hydrostatic pressure to the workpiece or to a bladder that is in contact with the workpiece, rather than by the movable part of a die in a mechanical or hydraulic press. Unlike deep drawing, hydroforming usually does not involve draw reductions—the piece is formed in a single step.
Incremental sheet forming Incremental sheet forming or ISF forming process is basically sheet metal working or sheet metal forming process. In this case, sheet is formed into final shape by a series of processes in which small incremental deformation can be done in each series.
Ironing Ironing is a sheet metal working or sheet metal forming process. It uniformly thins the workpiece in a specific area. This is a very useful process. It is used to produce a uniform wall thickness part with a high height-to-diameter ratio. It is used in making aluminium beverage cans.
Laser cutting Sheet metal can be cut 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. 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 can be obtained. Cutting speeds on thin sheet can be as high as per minute. Most laser cutting systems use a 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.
Photochemical machining Photochemical machining, also known as photo etching, is a tightly controlled corrosion process which is used to produce complex metal parts from sheet metal with very fine detail. The photo etching process involves photo sensitive polymer being applied to a raw metal sheet. Using CAD designed photo-tools as stencils, the metal is exposed to UV light to leave a design pattern, which is developed and etched from the metal sheet.
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 the
surform.
Press brake forming 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 tons per meter 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 forming process. The press usually has some sort of
back gauge to 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 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 is sized to be a very close fit in 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 stamping, a 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 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 15 seconds by either a
press or a laser CNC machine.
Roll forming A continuous bending operation for producing open profiles or welded tubes with long lengths or in large quantities.
Rolling Rolling is metal working or metal forming process. In this method, stock passes through one or more pair of rolls to reduce thickness. It is used to make thickness uniform. It is classified according to its temperature of rolling: • Hot rolling: in this temperature is above recrystallisation temperature. • Cold rolling: In this temperature is below recrystallisation temperature. • Warm rolling: In this temperature is used is in between hot rolling and cold rolling.
Spinning 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 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 low. Alternatively, the related techniques
repoussé and chasing have low tooling and equipment costs, but high labor costs.
Water jet cutting 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.
Wheeling The process of using an English wheel is called wheeling. It is basically a metal working or metal forming process. An English wheel is used by a craftsperson to form compound curves from a flat sheet of metal of aluminium or steel. It is costly, as highly skilled labour is required. It can produce different panels by the same method. A stamping press is used for high numbers in production. == Sheet metal fabrication ==