Metal spinning is also called chipless forming. It involves sheet metal which is cut into a circle, centered and clamped between an inside form mandrel and a live center on a specially designed lathe, then rolled down on the outside of the form. Typically it is an economical method of making a metal shell with close inside tolerances matching the form.
Spinning can replace 1) using billet (solid block) and extensively machining inside and out, 2) sheet metals roll formed with a welded seam eliminating welding and excessive blending or 3) draw formed parts on a press with very expensive tooling and 4) they can also replace castings.
The process is used extensively in many industries for prototype, short run and many times long runs depending on criteria. Some familiar spun parts would be bomb nose cones, cooking pots and pans, wheels, circular metal lamp shades, metal funnels to name a few. Although the material typically used is thin, the forming process increases the strength tremendously by work hardening the material giving a stronger, lighter, less costly part: many times increasing value. Spun parts can be made to very close tolerances or machined to an exact tolerance when a tight tolerance is necessary.