“The Quarter Shrinker uses a technique called high velocity electromagnetic metal forming, or “Magneforming”. This technique was originally developed by the aerospace industry in conjunction with NASA, and has been popularized by Aerovox, Grumman, and Maxwell. It involves quickly discharging a high energy capacitor bank through a work coil to generate a very powerful and rapidly changing electromagnetic field which then “forms” the metal to be fabricated. While it works best with metals of relatively high electrical conductivity such as copper or aluminum alloys, it will work to a more limited extent with many poorer conducting metals and alloys such as steel or nickel.” Thanks Derek! Link.