Metal Spinning

Metal spinning, also called conventional spinning or just spinning, is the forming of an axis-symmetric part over a rotating mandrel. Force is delivered by a tool with a rounded end or a roller. A flat, or possibly preformed, work piece is held between a mandrel and tail stock. As the apparatus rotates, the tool applies localized pressure to the work while it gradually moves up the mandrel. This causes the sheet metal work to be wrapped over the mandrel, thus taking its shape. Metal spinning is commonly performed cold, but in some cases parts may be subject to warm or hot spinning. Spinning is capable of producing large parts with diameters as high as 20 feet.

The tooling in a metal spinning operation is generally made from tool steel. The mandrel in some cases may be made of wood. Containers with bottle or tapered necks can be manufactured on collapsible mandrels, that are disassembled and removed from the formed parts. Set up costs for metal spinning are usually low. Conducting a spinning operation is relatively expensive on a per unit basis. Deep drawing is usually the main alternative manufacturing method to metal spinning, for producing parts. In contrast, deep drawing often requires a high initial investment for set up, while the cost of production per part is low. For these reasons, deep drawing is more useful for mass production of parts. Spinning is employed for small numbers of parts, unique, curved, or varied parts and large parts. Operator skill is important in metal spinning. CNC machinery is now replacing the operator in many cases. CNC spinning gives a high quality consistent product.

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Spinning Of Sheet Metal

Shear Spinning

Shear spinning is a process related to conventional spinning and is also known as flow turning or spin forging. In a conventional spinning operation the work is essentially formed by bending. There is usually not much change in the thickness of the sheet metal. The diameter of the work in conventional spinning must be large enough to account for the size of the final part. Shear spinning involves forming the work over the mandrel, causing metal flow within the work. This metal flow will act to reduce the thickness of the work as it is formed. The initial diameter of the work can be smaller in shear spinning. Limits to the amount of reduction of work thickness exist in order to prevent fracture. Coolants are normally used in shear spinning, since this manufacturing process can generate a lot of heat. One or two rollers, (tools), may be used, two will provide a better balance of forces during the operation. Shear spinning of some materials will be conducted at elevated temperatures.

Figure:312
Shear Spinning

Tube Spinning

Tube spinning is performed on cylindrical parts. Tube spinning is similar to shear spinning in that metal flow occurs within the work. This metal flow acts to reduce the thickness of the metal. While using tube spinning to reduce the thickness of the tube, the tube's length will be increased. This manufacturing process can be performed externally with the tube over a mandrel or internally with the tube enclosed by a die. The tool can also in some cases be moved during the operation, in order to create contours or features on the inside or outside of the tube.

Figure:313
Tube Spinning

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