Abstract

The Electromagnetic Powder Deposition (EPD) process converts pulsed electrical energy into kinetic and thermal energy to accelerate and heat powder material to conditions suitable for bonding. A high pressure plasma armature is electromagnetically accelerated using a railgun. A supersonic pressure wave is created when the armature accelerates through and "snowplows" the ambient gas ahead of it. The gas column is heated, compressed, and accelerated to the entrainment section of the gun, where some of the thermal and kinetic energy is transferred to an injected stream of powder material. The acceleration burst is repeated rapidly to supply the required deposition rate and to achieve steady thermal conditions. Development of a starter plasma which is reliable at ambient pressure was a major programmatic task. Generation of a low pressure linear arc required to form a planar armature during the pulsed event was investigated. Several geometries (point-to-point breakdown, rail-to-rail breakdown, and confined glow discharge) were explored using different voltage sources (dc, 60 Hz ac, 150 MHz rf, pulsed). Satisfactory operation of the confined glow discharge approach at atmospheric pressure was achieved using rf excitation. Results of testing under the various scenarios are presented and critiqued.

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