The process of metal spinning is fairly straightforward; the setup is as follows: First, a formed block is mounted in the drive section of a lathe, which is simply a tool that rotates a workpiece on its axis. Then, a pre-sized blank is clamped against this block with a pressure pad, which is connected to the part of the lathe called the tailstock; the tailstock, also called the foot stock, is used to lend support to the longitudinal rotary axis of the workpiece. Once this is done, the metal spinner can go to work.
Together, the block and workpiece are rotated at high speeds as pressure from the spoons or other work tools cause the workpiece to flow over the block. Spoons, which are standard hand spinning tools, and other tools may be made from hardened steel (best for use with aluminum) or solid brass (best for use with mild steel or stainless steel). Rotating tools, especially those used with CNC spinners, may also be coated with a thin film of ceramic, which protects and prolongs their life.
Once done, workpieces are removed from the block. If the workpiece is complex, it may be formed on a multi-piece block so that it can be removed more easily. In fact, if the shape of a workpiece is highly complex, it may even be spun over an ice form, which will just melt away afterwards.
There are a few variations on the basic metal spinning process, such as reducing or necking and hot spinning.
Reducing is a more involved process that allows for the inclusion of workpieces with reentrant geometries. Using this method, if the form must be exact, the workpiece is spun on an eccentrically mounted mandrel, but if the surface finish and form are not critical, it is instead spun without a mandrel, or “spun on air.”
Hot spinning, as its name implies, incorporates high heat into the spinning process. In this case, the high heat, which is applied to the workpiece, is sourced from a torch. Parts made via hot spinning can be shaped or reduced down to smaller diameters with seamless shoulders using minimal force, because the heated metal distorts as it is shaped.
Also, in many commercial processes, spoons are replaced with rollers attached to the ends of levers. Rollers, which vary in thickness and diameter, can be used to form material down to the mandrel in both CNC and hand metal spinning operations.
Another popular variation on metal spinning is flow forming. This advanced process allows for variation in product wall thickness using two main methods: shear spinning and tube spinning.
Shear spinning produces contoured shapes or cones using rollers over flat blanks on rotating mandrels. Using the shear spinning method, no material is lost and the diameter of a blank does not change, but instead, thickness decreases variably, based on the angle of the mandrel.
Tube forming produces cylinders and tubes by cold-working tubular preforms with rollers and a mandrel. Tube forming may be performed with one of two techniques: forward flow forming, which produces parts with one closed end or reserve flow forming, which produces parts with two open ends. In forward flow forming, the bottom of the preform is positioned on top of the face of the mandrel, while it is moved in the same direction as the rollers. In reverse flow forming, the rollers push against a serrated ring placed at the end of the mandrel. This action compresses and extrudes the metal.
Metal spinners produce products that are used in a variety of industries, such as aerospace, appliances, architecture, defense contracting, food processing, healthcare, interior decorating, music, paper, pharmaceuticals, and more. Specific parts and products created by metal spinners include: rocket nose cones, nozzles, pressure vessels and gas cylinders, filter housings, cartridges, specialty lighting, engine parts, freezers, mixing bowls, funnels, decorative household goods and urns, cookware, brass instrument bells and public waste receptacles.
Metal spinning is a wonderful resource. However, those interested in requesting a metal-spun part or parts must take care to check on a supplier’s output capabilities before placing an order. Some metal spinning manufacturers only offer parts made from a certain type of metal, like aluminum or stainless steel, while others only make products in certain sizes, diameters, and thicknesses. With the proper research and communication, though, customers will be able to find the metal spinning service they need.