Forming is the broad category of manufacturing processes where a material is shaped through mechanical deformation rather than by removing material (machining) or melting (casting). In a tube mill, forming begins with a flat mult (slit coil) that is progressively bent by a series of rollers into a cylindrical shape. This involves complex multiaxial stress states. The process relies on the material's yield strength; the applied stress must exceed the yield point to achieve permanent shape change but stay below the ultimate tensile strength to avoid fracture.