1 Preparation of the wooden mandrel.

2 The metal is pushed against the mandrel as both metal and mandrel are spinning.

3 The metal component taking shape over the mandrel.

–  Spinning is a very flexible form of mass-production, which can also lend itself to small-batch production.

–  Low tooling costs.

–  Can generate complex shapes without additional material removal (cutting) or joining processes.

–  Some materials will harden in the spinning process.

–  Spinning often requires post finishing.

–  The process offers limited control over wall thickness because of the way the metal is slightly stretched over the mold.

Volumes of production

From single prototypes to batch production and runs of several thousand.

Unit price vs. capital investment

The tools for pushing and the mandrels are made from wood or metal, depending on the size of the component and the quantity required. For a small number of units it makes sense to use affordable wooden mandrels, but for large production runs metal is a better choice because the former will be subject to greater wear.

Speed

Production cycle times are higher than for press forming (see metal cutting, p.59), but setup times are substantially shorter, making metal spinning suitable for prototyping, one-offs, and short-to medium-batch production.

Surface

A spun surface may need to be polished in order to eliminate the circular witness lines on the external surface of the part.

Types/complexity of shape

This is really only a technique for making symmetrical shapes that start with a sheet of metal. Disks, cones, hemispheres, cylinders, and rings are the typical shapes made using this process. Undercuts and re-entrant angles are achieved by a split mandrel, which comes apart like the segments of an orange in order for the part to be released. Closed shapes such as hollow spheres are made by joining two halves together.

Scale

Spun-metal products can be produced at less than 3/8 inch in diameter, and, at the other end of the scale, Acme Metal Spinning in the US has produced a shape that measures almost 11½ feet across.

Tolerances

Because the metal is stretched around the mandrel, the thickness of a part changes during the spinning process. The flatter the shape, the less the metal will need to stretch.

Relevant materials

Spinning can be applied to a variety of metals, ranging from soft, ductile coppers and aluminum (which are the most common) to hard stainless steels.

Typical products

The kitchen wok is a good example of an item made by spinning—it is even possible to see the evidence of its production in the concentric lines on the outside surface. Other products include bases and lampshades for lighting, cocktail shakers, urns, and a whole mass of industrial components.

Similar methods

Spinning is often combined with other techniques to produce more complex products. For example, pressure-formed parts are often spun to create necks, flanges, and flares. Although far less common than spinning, incremental sheet-metal forming (p.257) is a new process that allows a range of complex forms to be created from sheet metal using a single tool.

Sustainability issues

Metal spinning is one of the most energy-intensive processes available as the part needs to be constantly rotated at a high speed for a long length of time. However, with the formed metal’s high strength, parts have excellent durability which ensures a prolonged life cycle. Additionally, at the end of the product’s lifespan the metal can be melted down and reused.

Further information

www.centurymetalspinning.com

www.acmemetalspinning.com

www.metalforming.com

www.metal-spinners.co.uk

Metal Cutting

including press forming, shearing, blanking, punching, bending, p erforating, nibbling, and stamping

Product	beverage can pull tab
Materials	aluminum
Manufacturer	Rexam
Country	UK
Date	1989

This is an everyday product that has to be super cost-effective, yet must work all the time and must absolutely never cut your lip when you drink from it. Press forming and shearing are just two of the methods used to make this ubiquitous product.

In the metal industry the term “cutting” is hardly ever used, because technically it is such a broad term it has almost no meaning. Cutting processes can be divided into two main categories: chip-forming and non-chip-forming. Press forming, shearing, blanking, punching, bending, perforating, nibbling, and stamping are all terms that in one way or another describe non-chip-forming of metal sheet. Methods such as milling (see machining, p.18) and turning on a lathe (see p.26), on the other hand, are chip-forming techniques.

Punching and blanking are very similar in the sense that they both involve the removal of part of a sheet to form a hole. The processes differ in that punching is used to make sheets with shapes cut out of them, while blanking is a process for making separate shapes, similar to using a cookie cutter to make many cookies from rolled-out dough. The metal disk, which is the starting point for the beverage can tops (pictured), would have been made using blanking.

Nibbling is used to cut a sheet in successive bites from a small punch that pulses up and down in a process similar to that of a sewing-machine. Shearing involves a punch and a die with a tight control over the gap between the two (unlike punching, which doesn’t have a die). The terms “perforating” and “bending” should be fairly self-explanatory.

Metal stamping is a cold forming process that is used to produce shallow components from metal sheet. Although it is a fairly straightforward method of cutting and forming sheet, it includes several variations, all of which combine a punching process together with a forming process, performed either in a sequence or in one action. A single die is needed for each operation, but the component can be removed and placed in another die for additional forming. Progressive dies (like a series of dies) are used in more complex procedures to form multiple actions.

–  Very versatile in terms of producing different shapes.

–  Can be used for any solid metal.

–  High degree of accuracy.

–  Parts may be limited to stock sizes of material.

–  Material utilization can be low due to wastage.