Volumes of production

This is a semiautomated method, so it can be used for production runs of greatly varying lengths.

Unit price vs. capital investment

This varies greatly, depending on the setup and the volume of production required. Jewelers can use simple tools requiring very little investment. By contrast, millions of pounds would be needed to set up a production process for the whistle (pictured).

Speed

Varies according to setup. The Acme Thunderer featured here takes up to three days to produce.

Surface

Generally, this is dependent on the finish of the sheet material, though polishing and painting are often required.

Types/complexity of shape

The nature of this type of setup allows jigs to be built to accommodate a range of quite complex shapes.

Scale

There is no maximum size for sheet forming.

Tolerances

Can be extremely high. In order to achieve perfect pitch in the whistle, tolerances are ±1/3000 inch.

Relevant materials

Soft metals such as brass, copper, and aluminum are particularly easy to form, but any sheet metal can be used.

Typical products

Sheet-metal forming is used to produce a number of products in a variety of industries—they range from brass musical instruments to computer housings and automobile bodies.

Similar methods

Other processes that give form to flat sheets of metal include metal spinning (p.56), stamping and punching (see metal cutting, p.59), water-jet cutting (p.42), laser cutting (p.46), and CNC folding, a process in which sheet material, usually metal, is folded into different shapes—think of a cookie tin.

Sustainability issues

As this process is largely automated it consumes a fair amount of energy while the numerous stages of production can increase cycle times. However, excess or metal scraps can be recycled back into the process; aluminum is one of the most recycled materials.

Further information

www.acmewhistles.co.uk

Slumping Glass

Product	T oki side table
Designer	Setsu and Shinobu Ito
Materials	float glass
Manufacturer	Fiam Italia
Country	Italy
Date	1995

The full radius of the tabletop curve, and the gentle curves of the feet, offer a suggestion of the simple forms that are possible with glass slumping.

To slump glass is to allow it to sink into shape. Most people know that if a sheet of glass is left alone long enough, its shape will slowly distort. However, glass does need to be heated to a sufficiently high temperature for it to reach an elastic state that enables it to move at an economical rate or, at the very least, faster than the hundreds of years it would take without heat. When a sheet of stiff glass is placed over a refractory mold (a mold made from a heat-resistant material) in a kiln and heated to 1,165ºF, the glass relaxes enough to allow it to sag into a shape that becomes permanent once cooled.

To form the Fiam table (pictured), a blank sheet of ½-inch crystal glass is first cut. The computer-controlled process employs a jet of water, mixed with an abrasive powder, that passes at 3,200 feet per second through a tiny nozzle. This creates a jet strong enough to cut through any material. Once the flat blanks have been cut, the sheet is ready for curving.

The entire sheet and the refractory mold must be brought to the same critical melting temperature—even the smallest temperature variation can result in a broken sheet. At the right temperature, the glass is relaxed enough to sag under its own weight and sink into the mold, with a bit of manual assistance. The apparent simplicity of Fiam’s products conceals the complex heating process, which has to be tightly regulated to keep the glass at exactly the right temperature inside the curving chamber. The pieces may be based on simple ideas and shapes, but this simplicity is only achieved (with a high success rate) by the use of sophisticated modern technology.

–  Allows sheet glass to be formed into a unique three-dimensional shape in as little as a single operation.

–  Slow, and a high degree of skill and experience can be required to trial and error a design.