Metal spinning, a cold-worked metal forming process, uses a combination of force and fast rotational motion to produce seamless, axially symmetric shapes. Rigid tools or rollers shape a metal blank, tube, or pre-form in several stages; until it reaches the desired final geometry specified by the spinning mandrel. Metal spinning produces a large number of products for various applications, including cookware, bells, cans, flowerpots, lampshades, funnels, gas cylinders and trash bins. Although a fast and economical mode of production, metal spinning still has a few drawbacks.
Size and Shape Limitations
Due to the nature of the metal spinning process, its products are limited to those with concentric, axially symmetric shapes. Examples of shapes easily formed through spinning include hemispheres, cones, funnels, flanged covers, parabolas, stepped parts and dished heads. Additionally, the size of the available metal spinning equipment limits the maximum practical diameter of the components produced.
Production Volume Constraints
Metal spinning, whether manual or automated, requires component-specific tools; that is, the manufacturer must purchase or fashion spinning tools exactly suited to the desired geometry. Rollers and spoons -- tools made of hardened steel -- are designed for general use, while mandrels produce specific shapes. From an economic viewpoint, this makes it impractical for a manufacturer to produce low volumes of a component with a unique geometry.
Small Allowance for Errors
Cracks and dents in the component during production are irreparable for all practical purposes. Small irregularities and minor damages to a blank or an unfinished piece means immediate scrapping, as a repair is not a cost-effective solution. During spinning, the metal piece could also undergo an undesirable hardening. It would then have to go through heat treatment before the shaping process can proceed properly.
Manual Spinning Limitations
Manual spinning, though simpler, faster, and cheaper by an order of magnitude than spinning with a computer-numerically-controlled (CNC) lathe, still comes with a few disadvantages. Manual spinning requires that operators have a high level of skill as well as a fair amount of strength, as the process is physically demanding. Also, compared to similar metal-shaping techniques -- such as press forming -- manual metal spinning takes more time before a usable piece is finished.