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Metal spinning is a method used to form disks of metal into cylinders, cones, and other shapes that are symmetrical around an axis. Spinning is often used to make parts for industry and manufacturing, but many decorative pieces are also formed by spinning. Spinning may be controlled by hand or by using a computer numerical control (CNC) lathe that is programmed with the desired pattern. Most ductile metals can be worked using the metal spinning process. This method is most often used when a limited number of parts are needed, because small batches can be made more cheaply and efficiently by metal spinning than by other methods.
To begin the metal spinning process, a metal disk, known as a blank, is fitted onto a lathe. The blank must be made out of a metal with high ductility. Ductility is a measure of how easily a solid material can be shaped when exposed to pulling stress. Metals commonly shaped by spinning include aluminum, copper, and even stainless steel alloys. Gold, silver, and brass may be spun to make decorative pieces.
A shaping tool known as a mandrel is also attached to the lathe. The mandrel is the same shape as the inside of the finished product. For example, if a funnel is being formed, the mandrel may be cone shaped. As the mandrel spins against one side of the blank, rollers push against the other side of the blank, causing the metal to form in the shape of the mandrel.
Metal spinning usually forms fairly basic shapes, such as cones, hemispheres, and cylinders. These shapes can then be cut or welded to create more complex products. For example, a funnel may be formed by welding a cone onto the end of a cylinder. A more complex mandrel may also be used to form a complex shape. After spinning, parts may also be pierced, heat treated, or otherwise modified to create the desired shape.
Unlike other methods of shaping metal, metal spinning is usually done when the metal is cold. The process actually increases the tensile strength of the metal being shaped. In the rare cases when heat is used, the process is called hot spinning. Hot spinning creates seamless spun items, such as scuba diving tanks.
Metal spinning is fairly inexpensive when compared to other methods of metalworking. It can be performed quickly, and design changes are easily and inexpensively made. These qualities make metal spinning an ideal choice for artists and for inventors or engineers who are creating prototypes.