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Explosive forming is a type of metalworking that can be used to shape very large workpieces. It is typically used in cases where the metal is too large or thick for a traditional press or punch method to be cost effective. The process typically involves placing the metal over a die and then using the concussive force of high explosives to press it into shape. A variety of different materials may be used to create dies, including fiberglass, concrete, and steel. Die materials should typically be stronger than the metal being formed, though that is not always possible.
The most common method for explosive forming typically involves a basin that can be filled with water. A die may be integrated into the bottom of the container, or one may be lowered in. Metal can then be then placed on top of the die and subsequently covered in water. The next step typically involves the detonation of high explosives within the basin. If the procedure is performed correctly, the explosion will propagate through the water and force the metal into the shape of the die.
A benefit of the explosive forming process is that it can be used to create complex components that might otherwise require a multiple step process. It can also be used to form metal that is much larger, heavier, and thicker than can be worked on with more traditional methods. The main drawback is that the process can require extensive setup for each piece, including new explosives and, in some cases, new dies. If the strength of the die is greater than the strength of the metal it may be reusable, though this is not always the case.
The water bath method is commonly used, but is not the only way to accomplish explosive forming. Early methods made use of shaped charge effects, and explosive forming was used to engrave iron in the late 1800s. This method involved placing the explosives directly on the metal, rather than using water or another transmission medium for the concussive force.
Some of the same principles used in explosive forming can also be seen in military applications of shaped charges, such as improvised explosive devices (IEDs). A type of explosive forming can be used in some IEDs, where an effective projectile is actually created by the explosion. This often involves a container with a concave lid that is blown off by an explosion and formed into a shape that may be able to penetrate some conventional armor.