Sheet metal

Sheet metal is created by shaping metal into thin, flat pieces, typically through industrial methods. It comes either as flat panels or coiled strips, with coils produced by feeding a continuous sheet through a roll slitter. Thickness varies widely: extremely thin sheets are called foil or leaf, while anything thicker than 6 mm qualifies as plate, like plate steel used in construction. Most countries measure sheet metal thickness in millimeters, but the United States uses a non-linear gauge system—higher gauge numbers mean thinner metal. Common steel sheet metal spans from 30 gauge (0.40 mm) to about 7 gauge (4.55 mm). Gauge standards differ between ferrous metals (like steel) and nonferrous ones (like aluminum or copper). For copper, thickness in the US is traditionally given in ounces per square foot. For best results, parts made from sheet metal should have uniform thickness.

Many metals can be turned into sheet metal, including aluminum, brass, copper, steel, tin, nickel, and titanium. Decorative options include silver, gold, and platinum (the latter also serves as a catalyst). Processing methods mainly involve cold rolling or hot rolling. To prevent rust from outdoor exposure, hot-dip galvanizing is sometimes applied. A color coating can also be added to cold-rolled sheets for both protection and decoration, resulting in what’s called a color-coated metal sheet.

Sheet metal appears in car and truck bodies, major appliances, airplane fuselages and wings, tin cans, building roofs, and countless other uses. Iron and other highly magnetic materials, formed into laminated steel cores, are used in transformers and electric machines. Historically, sheet metal was key for cavalry plate armor, and it still serves decorative roles, such as in horse tack. Workers in this trade are sometimes called "tin bashers" or "tin knockers," a term that comes from hammering panel seams during tin roof installation.

**History** Hand-hammered metal sheets have been used for architecture since ancient times. Water-powered rolling mills replaced manual work in the late 17th century, using large rotating iron cylinders to flatten metal into sheets. Suitable metals included lead, copper, zinc, iron, and later steel. Tin was often applied to coat iron and steel sheets to prevent rust, creating "tinplate." Sheet metal arrived in the United States in the 1870s, used for shingle roofing, stamped ornamental ceilings, and exterior façades. These ceilings later became known as "tin ceilings," though manufacturers at the time didn’t use that term. The popularity of shingles and ceilings spurred widespread production. Advances in steel sheet metal production in the 1890s made it cheap, durable, easy to install, lightweight, and fireproof, fueling middle-class demand. The industry declined during the 1930s and World War Two due to metal shortages. Some American companies, like the W.F. Norman Corporation, survived by making other products until historic preservation projects revived ornamental sheet metal.

**Materials**

**Steel** Low-carbon steel is made into sheet and often galvanized.

**Stainless Steel** Grade 304 is the most common, offering good corrosion resistance, formability, and weldability. Available finishes are #2B, #3, and #4. Grade 303 is not sold as sheet. Grade 316 has better corrosion resistance and strength at high temperatures than 304, used for pumps, valves, chemical equipment, and marine applications; finishes are #2B, #3, and #4. Grade 410 is heat treatable but less corrosion-resistant, common in cutlery, and only comes in a dull finish. Grade 430 is a cheaper alternative to the 300 series, used when high corrosion resistance isn’t critical—often for appliances with a brushed finish.

**Aluminum** Aluminum is popular for sheet metal due to its flexibility, variety, cost-effectiveness, and other properties. The four most common grades are 1100-H14, 3003-H14, 5052-H32, and 6061-T6. Grade 1100-H14 is commercially pure, highly weather- and chemical-resistant, ductile for deep drawing, and weldable, but low in strength—used in chemical equipment, light reflectors, and jewelry. Grade 3003-H14 is stronger than 1100, with the same formability and low cost, corrosion-resistant and weldable—found in stampings, spun parts, mailboxes, cabinets, tanks, and fan blades. Grade 5052-H32 is much stronger than 3003 while still formable, with high corrosion resistance and weldability—common for electronic chassis, tanks, and pressure vessels. Grade 6061-T6 is a heat-treated structural alloy, weldable, corrosion-resistant, and stronger than 5052, but less formable and loses some strength when welded—used in modern aircraft structures.