While many different metals are suitable for metal expansion, copper is chosen particularly for this process when being employed by certain companies, such as those in the electrical, heating and cooling, refrigeration, construction, ornamental and architectural industries.
A non-ferrous transition material, copper has excellent thermal and electrical conductivity combined with good corrosion resistance and strength. The expanding metals process improves the strength, rigidity and weight to strength ratio of a metal such as copper. Expanded metal sheets made of copper and its alloys are therefore suitable as heat sinks, radiators and enclosures. The reddish brown appearance of copper makes it a popular choice for decorative mesh as well as decorative ornaments, filters, walkways and grates.
Copper expanded metal allows for varying amounts of light, water, air, sound and debris to pass through it, improving visibility, safety and ventilation. While other manufacturing processes can achieve these same benefits, metal expansion is more cost effective than punching and perforation techniques because there is no material wasted as there is with these other techniques. The solid construction also means that there are no seams, welds or joints to wear and work loose over time, making copper expanded metal a more stable and long lasting alternative to the use of welders or fasteners.
Copper expansion begins with flat plates or sheets of the metal that are produced by roll forming the raw mineral. These stock shapes are then fed into an automated expansion machine. It is important to consider that the thickness will be significantly reduced and the length increased in order to select the most appropriate sheet metal for a given application. The process of expansion can increase the length of a sheet of copper up to ten times that of the original.
In the expansion machine, a series of knife-like dies slit the metal hundreds and sometimes thousands of times in an alternating offset pattern. At the same time, the sheet is being drawn through rollers. This heat and pressing technique stretches the metal causing the pre-cut holes to swell. The once solid sheet of metal is then extruded from the machine as an open latticework of solid construction. While it is possible to expand metal manually, computerized equipment shows significant gains on speed and precision.
Most often the apertures are diamond shaped, although hexagonal and custom shaped openings are also available with the use of different dies. Not only the shape, but the percentage of open area should be carefully considered with regards to the finished product or any secondary operations. Malleable and ductile, copper is easily formed and processed both before and after metal expansion.