The basic concept is that a master pattern is made from some easy to work material, perhaps plastic or aluminum. If non-conductive, then a procedure must be performed to make the pattern, sometimes called a mandrel, conductive. Then, the pattern or mandrel is placed in an electrochemical cell, and metal is plated on. Sometimes, several layers of different metals are plated on in a sequence. In most cases, the pattern or mandrel is later removed. Depending on the configuration and materials involved, the part can be peeled off, the mandrel dissolved chemically, or melted out, like in lost wax casting.
To illustrate, we recently had a part made by electroforming, after exploring the cost of several other technologies. Electroforming was the cheapest way we found to have this part made. It was a metal bellows, about 2" OD, and about 4" long. Two other methods of making these parts were welded stainless steel, which is obviously VERY labor intensive, and hydroforming, which couldn't make a bellows this long. The process used is to CNC machine a mandrel of aluminum, approximately the shape of the ID of the bellows. This is then plated with a very thin layer of copper (or copper alloy). The aluminum mandrel is then dissolved chemically, without harming the copper. Then, the copper is plated with about .003" of nickel, both inside and outside, bringing the wall thickness to about .007".
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