A 100 kJ Pulse Unit for Electromagnetic Forming of Large Area Sheet Metals

Abstract

Magnetoforming of tube or sheet metal parts can significantly extend the range of geometries conceivable with state-of-the-art forming methods. A major advantage is the considerably higher forming speed of the process achievable by using a magnetic piston without inertia. Key for this technology is the development of reliable, long-lifetime, high current pulse power generators able to deliver tens to hundreds of kiloamps of peak current to a mainly inductive load which is highly variable in time during the forming process. A high-current, high energy pulse generator for electromagnetic forming of large area sheet metal has been developed and was taken into operation. Design criteria were reliability and safety for all possible load cases, including short circuits and short-circuiting loads under operation, at nominal peak currents of up to 200 kA and peak pulse energies of up to 100 kJ. In order to comply with the safety requirements, an all-solid-state design has been chosen using high power semiconductor switches for pulse forming instead of ignitrons or spark gaps. Due to constraints concerning space and manageability, the coupling between the load and the pulse forming unit is achieved via a semi-rigid bundle of high voltage cables, allowing an adjustment of the carrier of the forming coil while being electrically connected to each other. We report on the development of a pulse generator for peak currents of 50 kA to up to 200 kA at a pulse width of typically around 100 µs, depending on the load parameters. In order to meet lifetime requirements suitable for industrial applications, the short circuit handling capability of peak currents of up to 450 kA is a major issue in the pulse generator design. A modular 3-branch design of parallel capacitor banks has been adopted to achieve the requirements concerning reliability, lifetime, and short circuit handling. The prototype pulse generator is based upon off-the-shelf devices, including high-current semiconductor switches. First operating results of the commissioning phase of the installation are reported.