Spinning is a process used to produce an axis-symmetric hollow shape by the application of lateral pressure from a forming tool, to a rapidly revolving circular blank of sheet material, causing it to assume the shape of a former that is rotating with it.
The principles of flow turning
Thicker sheet is plastically deformed by a pressure roller over a former. Metal is thinned.
Series of metal spinning operations
Deformation in metal spinning is a mixture of bending and stretching.
Manufacture:
- Metal spinning involves spinning a flat circular blank of the sheet material on to a special lathe to which a former is attached. This former provides the inside shape and dimensions of the article being produced. Hardwood formers are used. With a lever-like tool the blank is progressively fashioned over the former until it fits like a skin.
- Simple forms like a dish-shaped parabola, for example, can be made in one operation. Two or more formers can be used for more complex shapes.
- A high level of manual skill is involved. Automatic spinning machines with robot assistance are also used to produce higher volume production, e.g. hot-water cylinder bases, with a cycle time of 25 s per component.
- Can be used as a manual batch or prototype process, with low tooling costs.
- Adequate lubrication is required, such as beeswax, tallow or soap.
- The thicker, the harder and the larger the diameter of the blank, the slower the spinning speed will be, e.g. thin copper foil (25 mm in diameter) 2500 rev min – 1. 5 mm thick brass (2m in diameter) 250 rev min-1.
- In the “flow-turning” process, thick gauge material is made to flow plastically by pressure rolling it in the same direction as the roller is travelling, so that a component is produced in which the wall thickness is much less than that of the original blank. This is a more automated process than metal spinning.
Materials:
- The range of metals that can be spun is extensive.
- The properties required for good metal spinning are good ductility and tensile elongation.
- Main materials are aluminium and its alloys, copper, 70-30 brass, mild steel, stainless steel and titanium.
- Mild steel up to 9 mm thick can be spun.
- Stainless steel up to 3 mm thick can also be spun.
Design:
- In general, the larger the component, the more favourable metal spinning becomes.
- Thicknesses between 0.25 and 9 mm can be spun, depending on the material.
- Blank diameters are usually in the range 1.2–1.5 m; blanks up to 2.5 m can be spun if necessary.
- Tolerances can be controlled down to ±0.125 mm.
- Metal spinning is a versatile process able to provide a wide range of component shapes, e.g. bottle-shaped containers, a sphere from two hemispheres, ornaments in copper and brass, musical instruments, cooking utensils in aluminium, stainless steel dairy utensils.
Read more: Metal Spinning / Flow Turning