Metal Spinning, the principle of metal spinning

As an example, a blank metal disc or pre-form produced by deep drawing (process in which a sheet metal blank is radially drawn into a forming die by the mechanical action of a punch ) is clamped in a concentric manner against the metal spinning chuck. This rotates via the main spindle. The metal spinners roller is driven in planes X-Z and progressively forms the blank until the spun metal lies internally on the spinning chuck and a workable zone local to the roller contact point is achieved. In this zone, compressive stresses placed at tangents are introduced radially, keeping the wall thickness constant. At the same time, the final spun metal form is completed and the surface smoothed.

Using these techniques, shapes such as tank ends, reflectors, wheel rims, gas bottles, centrifuges, lighting reflectors, brake cylinders can be spun and formed.

Metals used include light and regular gauge sheet steels as well as plate, non-alloyed carbon steels, heat-resistant and stainless steels, non-ferrous heavy metals and light alloys. With some materials, an intermediate annealing operation is required (a heat treatment that alters the microstructure of a material causing changes in properties such as strength and hardness). In some cases, metals may be formed by partial heating. Metal thickness may range from 0.5 to 30 mm and a spun metal part may have diameter from 10 to 5000 mm. The accuracy achieved during spinning negates the need for further working, meaning that spun metal parts are in the majority of cases “ready for use”.

Wall thickness tolerances are in the region of +- 0.1 mm for spun metal up to 500 mm diameter. Above this diameter, tolerances are in the order of a few tenths of a millimetre (e.g cylinder ends in 10 mm boiler plate, dia. 3000 mm, wall thickness tolerance +-0.4mm).

In the same set-up, it is popular to carry out a number of secondary operations, such as the edge of the spun metal being turned and then beaded. Frequently, the edge is trimmed or the base parted off.

For these metal spinning and metal forming operations, a diverse variety of metal forming rollers, metal trimming wheels, or metal turning tools are required, all of which operate by moving in and out along a straight line. The secondary tooling for this is fixed to convenient tool posts operating independently of the main unit. If the required profile cannot be achieved with the fixed tool post, then the main spinning slide is used. This is free to move within its plane of operation and will usually select the appropriate tool from an automatic magazine.

Conventional metal spinning is achieved with a single spinning roller. In special cases this is not enough. When metal spinning heavy-gauge or high-strength material with only one roller, a high side load is created, which tries to lever the blank out of the clamped position, and also pushes the chuck off central position. In these cases, a machine with two opposed cross slides is used to balance the loads. This has a secondary effect of two diametrically opposed workable (plasticised) zones being created which has the benefit of equalising distribution of stresses in the spun metal, reducing the risk of material failure.