How are electroforming moulds made and what are they used for?

Electroforming moulds are special processing methods that use the principle of electrolytic deposition of metals to precisely reproduce certain complex or specially shaped workpieces. It is a special application of electroplating. Electroforming was invented in 1837 by the Russian scholar B.С. Jacobi.

Electroforming metal usually has copper, nickel and iron 3 kinds, sometimes also use gold, silver, platinum nickel - cobalt, cobalt - tungsten and other alloys, but to nickel electroforming is the most widely used. Electroforming layer thickness is generally 0.02 ~ 6 mm, there are also up to 25 mm thick. The size error between electroforming and the original mould is only a few microns.

The main use of electroforming is the precise reproduction of micro-fine, complex and some difficult to use other methods of processing the special shape of the workpiece, such as the production of banknotes and stamps printing plate, record pressure mold, lead lettering mold, metal artwork reproduction pieces, reflective mirror, surface roughness sample block, micro-hole filter, dial, EDM processing with electrodes, high-precision diamond grinding wheel substrate, etc..

The original mould, made in advance to the required shape, is used as the cathode and the electroforming material is used as the anode, which is placed together in the same metal salt solution as the anode material and energised with direct current. Under the action of electrolysis, a metal electroforming layer is gradually deposited on the surface of the original mould, and after reaching the required thickness, it is removed from the solution and the electroforming layer is separated from the original mould to obtain a metal replica corresponding to the shape of the original mould.

Electroforming equipment consists of electroforming tank, DC power supply (generally 12 volts, several hundred to several thousand amps) and electroforming solution of constant temperature, stirring, circulation and filtering devices. The electroforming solution is an aqueous solution containing sulphate, aminosulphonate, fluoroborate and chloride of electroformed metal ions. The main disadvantage of electroforming is the low efficiency, generally the thickness of the electroformed metal layer per hour is 0.02 to 0.05 mm. The use of high concentration electroforming solution, and appropriate to improve the solution temperature and strengthen the stirring and other measures, can improve the current density, shorten the electroforming time, thus can improve the electroforming efficiency. This method has been applied in the electroforming of nickel.