Machinery's Handbook, 31st Edition
High-Energy Rate Metal Forming Processes 1441 law). The two antiparallel currents repel each other, supplying energy to the workpiece in the form of kinetic energy, which accelerates in the workpiece up to a certain velocity, such as 650 to 1000 ft/s. This kinetic energy drives the material into the die, causing forming on impact. This method is quite useful for general applications and suitable for any workpiece made from a good conductor, provided the current pulse is of a sufficiently high frequency. There are two very broad ways in which this technique can be employed: Radial forming, in which a round part such as a tube or ring is compressed or expanded. The forming can be done either inward or outward onto a die to give the tube a more com plex shape (Fig. 32). One of the most common applications of electromagnetic forming is the compression crimp sealing and assembly of axis-symmetric components such as automotive oil filter canisters.
Fig. 32. Schematic Illustration of Electromagnetic Radial Forming of Tube Sheet metal forming, in which using the flat coil configuration shown in Fig. 33 forms a sheet metal. The velocity of the workpiece is sufficient to cause its impact against a die to give it a more complex shape. The workpiece material should have an electrical resistance of less than 38 μΩ /in. The die needs to be made of either nonmetallic materials or of poor electric conductors. Advantages of electromagnetic metal forming include: a) reduced number of opera- tions needed; b) narrow tolerances; c) improved strain distribution; d) high repeatability; e) high productivity; f) less reliance on lubricants; and g) lower energy cost.
Fig. 33. Schematic Illustration of Electromagnetic Sheet Metal Forming Electrohydraulic Forming.— Electrohydraulic forming is also known as electric spark forming or electric discharge forming. In this process an electric arc’s discharge is used to convert electrical energy to mechanical energy. Electrical energy is stored in large capacitors, and then a pulse of high current is delivered across two electrodes positioned a short distance apart while submerged in a transfer medium (water or oil). Capacitor banks have typically stored 55 to 58 BTU at a charged voltage of 20 kV. This creates a sudden release of steam, which, along with ionization, causes the development of a high pressure shock wave within the transfer medium. The die cavity containing the blank to be formed
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