ALUMINUM - Materials for Civil and Construction Engineers - page 143

T ABLE 4.1 Casting and Forming Methods for Aluminum Products (Extracted from
Reynolds Infrastructure , 1996)

Casting Methods

Sand Casting Sand with a binder is packed around a pattern. The pattern is

removed and molten aluminum is poured in, reproducing
the shape. Produces a rough texture which can be machined
or otherwise surfaced if desired. Economical for low volume
production and for making very large parts. Also applicable
when an internal void must be formed in the product.

Permanent Molten aluminum is poured into a reusable metal mold.

Mold Casting Economical for large volume production.

Die Casting Molten aluminum is forced into a permanent mold under high

pressure. Suitable for mass production of precisely formed castings.

Forming Methods

Extrusion Aluminum heated to 425 to 540°C (800 to 1000°F) is forced through

a die. Complex cross sections are possible, including incompletely
or completely enclosed voids. A variety of architectural and
structural members are formed by extrusion, including tubes,
pipes, I-beams, and decorative components, such as window and
door frames.

Rolling Rollers compress and elongate heated aluminum ingots, producing

plates (more than 6 mm (0.25 in.) thick), sheets (0.15 to 6 mm
(0.006 to 0.25 in.) thick, and foil (less than 0.15 mm (0.006 in.)).

Roll Forming Shaping of sheet aluminum by passing stock between a series of

special rollers, usually in stages. Used for mass production of
architectural products, such as moldings, gutters, downspouts,
roofing, siding and frames for windows and screens.

Brake Forming Forming of sheet products with a brake press. Uses simpler tooling

than roll forming but production rates are lower and the size of
the product is limited.

Cutting Operations Production of outline shapes by blanking and cutting. In blanking, a

punch with the desired shape is pressed through a matching die.
Used for mass production of flat shapes. Holes through a sheet are
produced by piercing and perforating. Stacks of sheets can be
trimmed or cut to an outline shape by a router or sheared in a
guillotine-action shear.

Embossing Shaping an aluminum sheet by pressing between mated rollers or

dies, producing a raised pattern on one side and its negative
indent on the other side.

Drawing Shaping an aluminum sheet by drawing it through the gap between

two mated dies in a press.

Superplastic Forming An aluminum sheet is heated and forced over or into a mold by air

pressure. Complex and deep contour shapes can be produced but
the process is slow.