Circular cross section machine parts which are symmetrical about the axis of rotation are made by hot

ANS:B - spinning

Spinning is a metal forming process used to create axisymmetric shapes from flat or cylindrical metal blanks. It is particularly suitable for producing parts with circular cross-sections that are symmetrical about their axis of rotation. The process involves the use of a spinning lathe, which consists of a rotating mandrel and spinning tools. Here's how the spinning process works:

1. Preparation of Blank: The process begins with the preparation of a flat or cylindrical metal blank. This blank is usually made from sheet metal or a tube, depending on the desired shape of the final part.
2. Mounting the Blank: The blank is securely mounted onto a rotating mandrel, which serves as the axis of rotation for the spinning process. The mandrel may be driven by a motor to provide the required rotational motion.
3. Starting the Spinning Process: The spinning tool, often called a roller or spinner, is brought into contact with the rotating blank. The tool may have a conical or cylindrical shape, depending on the specific requirements of the part being produced.
4. Forming the Part: As the mandrel and blank rotate, the spinning tool applies pressure to the surface of the blank, causing it to deform plastically. The metal flows and stretches radially outward, gradually taking on the desired shape dictated by the profile of the spinning tool.
5. Controlled Deformation: The operator carefully controls the spinning process to achieve the desired dimensions and wall thickness of the finished part. By adjusting the pressure applied by the spinning tool and the speed of rotation, precise control over the forming process can be maintained.
6. Finishing Operations: Once the desired shape is achieved, any excess material may be trimmed away, and secondary operations such as hole punching or flanging may be performed as needed to complete the part.
7. Heat Treatment (Optional): In some cases, the formed part may undergo heat treatment to relieve residual stresses and improve its mechanical properties.
8. Final Inspection: The finished parts are inspected to ensure they meet the required specifications and quality standards before being released for further processing or assembly.

Overall, spinning is a versatile and cost-effective metal forming process used to produce a wide range of parts, including components for aerospace, automotive, and household appliances, among others. Its ability to create symmetrical, axisymmetric shapes makes it particularly well-suited for applications where precision and consistency are paramount.