Manufacturing: Metal Forming

Sheetmetal Forming - Electromagnetic forming

Electromagnetic forming (EM forming or Magneforming) is a high energy rate metal forming process that uses pulsed power techniques to create ultrastrong pulsed magnetic fields to rapidly reshape metal parts.

In practice the metal "work piece" to be fabricated is placed in close proximity to a heavily constructed coil of wire (called the work coil). A huge pulse of current is forced through the work coil by rapidly discharging a high voltage capacitor bank using an ignitron or a spark gap as a switch. This creates a rapidly oscillating, ultrastrong electromagnetic field around the work coil.

The rapidly changing magnetic field induces a circulating electrical current within the work piece through electromagnetic induction, and the induced current creates a corresponding magnetic field around the metal work piece. Because of Lenz's Law, the magnetic fields created within the metal work piece and work coil strongly repel each another. The high work coil current (typically tens or hundreds of thousands of amperes) creates ultrastrong magnetic forces that easily overcome the yield strength of the metal work piece, causing permanent deformation. The metal forming process occurs extremely quickly (typically tens of microseconds). The forming process is most often used to shrink or expand cylindrical tubing, but it can also form sheet metal by repelling the work piece onto a shaped die at a high velocity. Since the forming operation involves high acceleration and decelleration, inertia of the work piece plays a critical role during the forming process. The process works best with good electrical conductors such as copper or aluminum, but it can be adapted to work with poorer conductors such as steel.

Other high energy rate metal forming techniques include electrohydraulic forming and explosive forming. Instead of using powerful magnetic fields, these forming processes use a powerful shock wave created within a fluid, usually water, to perform the operation. The underwater shock wave is generated by either triggering a powerful spark discharge (using a high voltage capacitor bank) or by detonating a high explosive.