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Explosive hydroforming, also known as HERF (High Energy Rate Forming) or exploform, is a striking alternative to the more traditional process of metal hydroforming. Unlike this older method, which shapes metal using pressurized hydraulic fluid pumped into a forming chamber, HERF techniques utilize an explosive charge to create the necessary pressure. Although the charge is relatively small, it is capable of generating enough force to mold the associated metal into the die.

The explosive charge is typically positioned at a specific distance from the workpiece, and both are immersed in fluid, usually hydraulic fluid or simple water. Certain facilities may also use oil, gelatin, liquid salts, or regular air as the transmission medium. However, water is the most commonly used medium as it is the least expensive, excellent for creating uniform peak pressure, and readily available. Once the charge and workpiece are properly positioned, the charge is detonated, pressing the workpiece into a die. The part is then removed and the process is repeated if necessary.

Explosive Hydroforming Methods
Explosive hydroforming techniques fall into two basic categories. Although both methods function according to the same general principles, they rely on very different placement of the explosive charge within the forming chamber.

Standoff Method: With the Standoff Method, the explosive charge is used in conjunction with an intervening medium. In most hydroforming applications, the intervening material is typically water, oil, or air. The required deformation level dictates how far the explosive charge is placed from the piece of metal to be formed. When the charge detonates, the ensuing force is transmitted through the fluid and pressures the metal into the die. Detonations used in the Standoff Method can often reach several thousand pounds per square inch (psi).

Contact Method: In the Contact Method, an explosive charge is placed in direct contact with the forming metal. This process generates far more pressure than the more conventional Standoff Method. By placing the explosive charge in close proximity to the surface material, the detonation can result in as much as several million psi.

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