After reading this article you will learn about:- 1. Meaning of Spinning 2. Process of Spinning 3. Machines 4. Advantages 5. Limitations 6. Applications and Uses 7. Lubrication.
Meaning of Spinning:
Spinning is a sheet metal forming process in which a metal blank is pressed over a rotating chuck or form mandrel with the help pressing tool to obtain axisymmetric hollow shell.
The sheet metal parts that have circular cross-section can be made by this process. Generally, the shapes produced by spinning can also be manufactured by drawing, compressing or flanging.
However, spinning is usually used for forming large parts that require very large drawing process or when various shapes are needed but only a small number of each shape is required.
Process of Spinning:
A Schematic of the spinning operation is shown in Fig. 8.1. The set-up essentially consists of a spinning machine similar to a centre lathe.
The various operation steps are:
(i) The circular blank is properly centred and pushed by the tail stock against the front of the rotating chuck, usually made of wood. A wooden block is used from the tail-stock to support the blank.
(ii) The chuck is rotated by the head-stock of a spinning lathe machine. The spinning speed depends on the blank material, thickness and complexity of the part required. It is varies from a very slow to a high speed of about 3500 r.p.m.
(iii) A hard wood or roller type metallic pressing tool is pushed by the operator onto the external surface of the blank.
(iv) Then the tool is moved gradually on the blank so that is conforms to the shape of the form block or mandrel.
(v) The blank slips under the pressing tool, which causes localized deformation. This deformation of the metal is proceeds by a mixture of bending and stretching.
(vi) To avoid wrinkles, a back-up support is applied to the opposite size of the pressing tool.
(vii) Finally, the blank takes the exact shape of the form mandrel.
A modified version of this method involves replacing the operator by a NC (Numerical Controlled) tool. Better surface quality and more uniform thickness are the advantages of this NC spinning over conventional spinning technique.