Most architects don’t like to think of explosions in relation to their designs. The word “explosion” alone reminds people of terrorism and collapsing buildings. However, explosions can be useful!
Explosion forming can be used to produce complex and twin-curve shapes with relatively simple means. Almost all types of metal like aluminum, steel and stainless steel, but also nickel and titanium, can be shaped by means of explosion forming.The technology to shape metal by means of explosion forming dates from 1888. It was first used to engrave/punch iron sheets. This type of explosion forming put the explosives in direct contact with the iron sheet. The thickness of the sheet determined the depth of the relief. Early last century explosion forming was used mainly in the armaments industry. After WWII explosion forming was applied in the aerospace industry to make complex twin-curve components like the head of the Saturn V rocket, but also fuel filters, corrugated panels and asymmetric exhaust nozzles for the first jet planes.
Compared to other metal shaping technologies, explosion forming has several benefits. Large size objects up to ten meters can be manufactured in one go, and up to six centimeters thick stainless steel sheets can be shaped. Plus, the process involves fewer steps putting less strain on the metal. Also pre-anodized and coated metal sheets can be shaped. Consequently, total costs may prove lower than for other technologies, such as via a deep-drawing die, a press, et cetera. Explosion forming is especially suitable for making prototypes and small series, but also big series can easily be manufactured by shaping several sheets concurrently.
Today explosion forming is not only applied in the aerospace industry but also in the energy sector and the construction industry. This technology proved preeminently useful in making twin-curve panels and putting relief in flat panels. For instance, the twin-curve corners of the ING Head Office building in Amsterdam, designed by Exploform in Rijswijk and produced by Mayer & Van Schooten, were made via explosion forming. Another example concerns the twin-curve panels for the roof of the Haarlemmermeer Pavilion by Asymptote Architects, or the “Desert Storm” aluminum facade panels, with a relief designed by Dirk Jan Postel for the above described Castellum Theater in Alphen a/d Rijn.
There are two different types of explosion forming: direct (contact) explosion forming and indirect explosion forming. In direct explosion forming the explosive charge is placed directly on the sheet to be shaped. The explosion pushes the sheet into a mold where it is shaped. This technology involves a lot of force and a high risk of production errors. It was therefore discontinued. Indirect explosion forming occurs inside a liquid. The sheet under production is placed in a mold and the cavity between mold and sheet is vacuum extracted. Then the whole thing is placed in a bath of liquid. An explosive charge is placed over the sheet in the liquid and detonated, making the sheet press at high velocity into the mold where it assumes the intended shape. Indirect explosion forming is generally done in a container filled with water, but other liquids may be used. Explosives generally used are TNT and RDX (an explosive material used today in many military weapons, but in 1890 still prescribed as medication).Moreover, explosion forming uses one single mold, no counter mold. The mold must obviously be explosion proof, but for the rest the choice of material is subject mainly to the material (manipulation) costs. Materials commonly used are steel and aluminum, and there are instances where MDF and concrete are used.