Sheet metal is metal formed into thin, flat pieces, usually by an industrial process.

Thicknesses can vary significantly; extremely thin sheets are considered foil or leaf, and pieces thicker than 6 mm (0.25 in) are considered plate, such as plate steel, a class of structural steel.

Sheet metal is available in flat pieces or coiled strips. The coils are formed by running a continuous sheet of metal through a roll slitter.

In most of the world, sheet metal thickness is consistently specified in millimeters. In the US, the thickness of sheet metal is commonly specified by a traditional, non-linear measure known as its gauge. The larger the gauge number, the thinner the metal. Commonly used steel sheet metal ranges from 30 gauge () to about 7 gauge (). Gauge differs between ferrous (iron-based) metals and nonferrous metals such as aluminum or copper. Copper thickness, for example, is traditionally measured in ounces in the US, representing the weight of copper contained in an area of one square foot. Parts manufactured from sheet metal must maintain a uniform thickness for ideal results.

There are many different metals that can be made into sheet metal, such as aluminium, brass, copper, steel, tin, nickel and titanium. For decorative uses, some important sheet metals include silver, gold, and platinum (platinum sheet metal is also utilized as a catalyst). These metal sheets are processed through different processing technologies, mainly including cold rolling and hot rolling. Sometimes hot-dip galvanizing process is adopted as needed to prevent it from rusting due to constant exposure to the outdoors. Sometimes a layer of color coating is applied to the surface of the cold-rolled sheet to obtain a decorative and protective metal sheet, generally called a color-coated metal sheet.

Sheet metal is used in automobile and truck (lorry) bodies, major appliances, airplane fuselages and wings, tinplate for tin cans, roofing for buildings (architecture), and many other applications. Sheet metal of iron and other materials with high magnetic permeability, also known as laminated steel cores, has applications in transformers and electric machines. Historically, an important use of sheet metal was in plate armor worn by cavalry, and sheet metal continues to have many decorative uses, including in horse tack. Sheet metal workers are also known as "tin bashers" (or "tin knockers"), a name derived from the hammering of panel seams when installing tin roofs.

History Hand-hammered metal sheets have been used since ancient times for architectural purposes. Water-powered rolling mills replaced the manual process in the late 17th century. The process of flattening metal sheets required large rotating iron cylinders which pressed metal pieces into sheets. The metals suited for this were lead, copper, zinc, iron and later steel. Tin was often used to coat iron and steel sheets to prevent rust. This tin-coated sheet metal was called "tinplate". Sheet metals appeared in the United States in the 1870s, being used for shingle roofing, stamped ornamental ceilings, and exterior façades. Sheet metal ceilings were only popularly known as "tin ceilings" later as manufacturers of the period did not use the term. The popularity of both shingles and ceilings encouraged widespread production. With further advances of steel sheet metal production in the 1890s, the promise of being cheap, durable, easy to install, lightweight and fireproof gave the middle-class a significant appetite for sheet metal products. It was not until the 1930s and World War Two that metals became scarce and the sheet metal industry began to collapse. However, some American companies, such as the W.F. Norman Corporation, were able to stay in business by making other products until historic preservation projects aided the revival of ornamental sheet metal.

Materials

Steel Low-carbon steel is fabricated as sheet, and often galvanized.

Stainless steel Grade 304 is the most common of the three grades. It offers good corrosion resistance while maintaining formability and weldability. Available finishes are #2B, #3, and #4. Grade 303 is not available in sheet form.

Grade 316 possesses more corrosion resistance and strength at elevated temperatures than 304. It is commonly used for pumps, valves, chemical equipment, and marine applications. Available finishes are #2B, #3, and #4.

Grade 410 is a heat treatable stainless steel, but it has a lower corrosion resistance than the other grades. It is commonly used in cutlery. The only available finish is dull.

Grade 430 is a popular grade, low-cost alternative to series 300's grades. This is used when high corrosion resistance is not a primary criterion. Common grade for appliance products, often with a brushed finish.

Aluminium Aluminium is widely used in sheet metal form due to its flexibility, wide range of options, cost effectiveness, and other properties. The four most common aluminium grades available as sheet metal are 1100-H14, 3003-H14, 5052-H32, and 6061-T6.

Grade 1100-H14 is commercially pure aluminium, highly chemical and weather resistant. It is ductile enough for deep drawing and weldable, but has low strength. It is commonly used in chemical processing equipment, light reflectors, and jewelry.

Grade 3003-H14 is stronger than 1100, while maintaining the same formability and low cost. It is corrosion resistant and weldable. It is often used in stampings, spun and drawn parts, mail boxes, cabinets, tanks, and fan blades.

Grade 5052-H32 is much stronger than 3003 while still maintaining good formability. It maintains high corrosion resistance and weldability. Common applications include electronic chassis, tanks, and pressure vessels.

Grade 6061-T6 is a common heat-treated structural aluminium alloy. It is weldable, corrosion resistant, and stronger than 5052, but not as formable. It loses some of its strength when welded. It is used in modern aircraft structures.All Metal Construction Made Easy

Brass Brass is an alloy of copper, which is widely used as a sheet metal. It has more strength, corrosion resistance and formability when compared to copper while retaining its conductivity.

In sheet hydroforming, variation in incoming sheet coil properties is a common problem for forming process, especially with materials for automotive applications. Even though incoming sheet coil may meet tensile test specifications, high rejection rate is often observed in production due to inconsistent material behavior. Thus there is a strong need for a discriminating method for testing incoming sheet material formability. The hydraulic sheet bulge test emulates biaxial deformation conditions commonly seen in production operations.

For forming limit curves of materials aluminium, mild steel and brass. Theoretical analysis is carried out by deriving governing equations for determining of equivalent stress and equivalent strain based on the bulging to be spherical and Tresca's yield criterion with the associated flow rule. For experimentation circular grid analysis is one of the most effective methods.Baptiste, R., Clark, D.L. and Matin, P., 2017, June. Designing a Strain Measurement System based on Circle Grid Analysis for Sheet Metal Forming Applications. In 2017 ASEE Annual Conference & Exposition. p.3

Gauge

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 pounds per square foot per inch thick,Oberg, p. 2522. equivalent to . The older United States Standard Gauge is based upon 40 pounds 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 (US standard sheet and plate iron and steel decimal inch (mm)) seem somewhat arbitrary. The progression of thicknesses is clear in column 3 (US 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. +Standard sheet metal gauges Gauge US standardOberg, p. 387; . for sheetand plate iron and steel Gaugefor Sheet SteelOberg, p. 2502.inch (mm) Galvanizedsteelinch (mm) Stainlesssteelinch (mm) Steel TubeWallThicknessinch (mm) Aluminiuminch (mm) Zincinch (mm) (mm) (delta) 0000000 32 (−) 000000 30 (−2) 00000 28 (−2) 0000 26 (−2) 000 24 (−2) 00 22 (−2) 0 20 (−2) 1 18 (−2) 2 17 (−1) 3 16 (−1) 4 15 (−1) 5 14 (−1) 6 13 (−1) 7 12 (−1) 8 11 (−1) 9 10 (−1) 10 9 (−1) 11 8 (−1) 12 7 (−1) 13 6 (−1) 14 5 (−1) 15 4.5 (−0.5) 16 4.0 (−0.5) 17 3.6 (−0.4) 18 3.2 (−0.4) 19 2.8 (−0.4) 20 2.4 (−0.4) 21 2.2 (−0.2) 22 2.0 (−0.2) 23 1.8 (−0.2) 24 1.6 (−0.2) 25 1.4 (−0.2) 26 1.2 (−0.2) 27 1.1 (−0.1) 28 1.0 (−0.1) 29 0.9 (−0.1) 30 0.8 (−0.1) 31 0.7 (−0.1) 32 0.65 (−0.05) 33 0.60 (−0.05) 34 0.55 (−0.05) 35 0.50 (−0.05) 36 0.45 (−0.05) 37 0.425 (−0.025) 38 0.400 (−0.025)

Tolerances During the rolling process the rollers bow slightly, which results in the sheets being thinner on the edges. The tolerances in the table and attachments reflect current manufacturing practices and commercial standards and are not representative of the Manufacturer's Standard Gauge, which has no inherent tolerances. +Steel sheet metal tolerances Gauge  Thickness Nominal[in (mm)] Max[in (mm)] Min[in (mm)] 10 11 12 14 16 18 20 22 24 26 28 +Aluminium sheet metal tolerances Thickness[in (mm)] Sheet width [in (mm)] [in (mm)] +Stainless steel sheet metal tolerances Thickness[in (mm)] Sheet width [in (mm)] [in (mm)]

Forming processes

Bending

The equation for estimating the maximum bending force is,

where is a factor taking into account several parameters including friction; is the ultimate tensile strength of the metal; and are the length and thickness of the sheet metal, respectively; and is the open width of a V-die or wiping die.

Curling

The curling process is used to form an edge on a ring. This process is used to remove sharp edges. It also increases the moment of inertia near the curled end. The flare/burr should be turned away from the die. It is used to curl a material of specific thickness. Tool steel is generally used due to the amount of wear done by operation.

Decambering

It is a metal working process of removing camber, the horizontal bend, from a strip shaped material. It may be done to a finite length section or coils. It resembles flattening of leveling process, but on a deformed edge.

Deep drawing

Drawing is a forming process in which the metal is stretched over a form or die.Parker, pp. 20, 85 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.

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