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Unlike other bulk deformation processes such as extrusion and forging, this process involves workpieces with a high ratio of surface area to thickness. A sheet thicker than 6 mm (1/4 in.) is generally called a plate.

Sheet forming is also called pressworking. It is one of the most important metalworking processes due to its application in a wide range of products.

Sheet metal is produced by a rolling process. It is generally coiled if the sheet is thin. If thick, it is available as flat sheets or plates.

Before a sheet metal is formed, a blank of suitable dimensions is first removed from a large sheet. Removal is usually done by a shearing process. Other methods for cutting sheets also exist. A band saw, which is a chip removal process, is one option. Flame cutting is another common method for thick steel plates. Laser cutting has also become an important process and is used with computer-controlled equipment to cut a variety of shapes consistently.

The basic mechanisms of all sheet-forming processes are stretching and bending. The major factors that influence the overall operation are: elongation, yield-point elongation, anisotropy, grain size, residual stresses, springback, and wrinkling.

Bending

Bending is one of the most common forming operations. In addition to forming parts, such as flanges, seams, and corrugations, bending also impart stiffness to the part by increasing its moment of inertia.

Bending terminology: the bent radius is measured to the inner surface of the bent part.

In bending, the outer fibers of the material are in tension and the inner fibers are in compression. The bend allowance is the length of the neutral axis and is used to determine the blank length for a bent part. The position of the neutral axis depends on the radius and angle of bend. The minimum bend radius for the material is the radius at which a crack appears on the outer surface of the bend. It is usually expressed in terms of the thickness, such as 2T, 3T, 4T, and so on.

Roll Forming

Roll forming is used for bending continuous lengths of sheet metal for large production runs. The metal strip is bent in stages by passing it through a series of rolls. The rolls are generally made of carbon steel or gray iron and may be chromium plated- for better surface finish of the product and wear resisitance of the rolls. Lubricants may be used to improve roll life and surface finish and to cool the rolls and the workpiece.

The roll forming process.