Electroforming is a metal forming process in which parts are fabricated through electrodeposition on a model, known in the industry as a mandrel.
The process involves passing direct current through an electrolyte containing salts of the metal being electroformed.
The process continues atom by atom until the required electroform thickness is achieved.
Electroforming is very effective when requirements call for complex parts (burr and stress free holes, accurate hole size and sharp edges) extreme tolerances and light weight.
With courtesy: https://en.wikipedia.org/wiki/Electroforming