|This article needs additional citations for verification. (February 2010)|
Electroforming is a metal forming process that forms thin parts through electrodeposition. The part is produced by coating a conductive layer of liquid metal skin onto a base form, known as a mandrel, which is removed after forming. The conductive layer reverse-plaques to the face of the master electroform, and the mandrel can be parted without the metal coating sticking to it. Ergo, this is the opposite of electroplating. Subsequent electroforming of mothers and sons can be accomplished without reverse-plaques to the new parts because the master and mother can be passivated without precluding conductivity. Passivation precludes adhesion in either direction. This is in contradistinction to electroplating, in which the electrodeposit's adhesion to the mandrel is of utmost concern. This process also differs from electroplating in that the deposit is much thicker than the phases which are plated and can exist as a self-supporting structure when the mandrel is removed.
In recent years, due to its ability to replicate a mandrel surface precisely atom-by-atom with practically no loss of fidelity, electroforming has taken on new importance in the fabrication of micro and nano scale metallic devices and in producing precision injection molds with micro and nano scale feature for production of nonmetallic micromolded objects.
In the basic electroforming process, an electrolytic bath is used to deposit nickel or other electroformable metals onto a conductive patterned surface, such as stainless steel. Once the deposited material has been built up to the desired thickness, the master electroform is parted from the premaster substrate. This process allows high-quality duplication of the premaster and therefore permits quality production—at low unit costs with high repeatability and excellent process control.
If the mandrel is made of a non-conductive material it can be covered with a conductive coating. Technically, it is a process of synthesizing a metal object by controlling the electrodeposition of metal passing through an electrolytic solution onto a metal or metalized form.
The object being electroformed can be a permanent part of the end product or can be temporary (as in the case of wax), and removed later, leaving only the metal form, the “electroform”. New technologies have made it possible for mandrels to be very complex. In order to facilitate the removal of the electroform from the mandrel, a mandrel is often made of aluminum. Because aluminum can easily be chemically dissolved, a complex electroform can be produced with near exactness.
Advantages and disadvantages
The main advantage of electroforming is that it reproduces the external shape of the mandrel within one micrometre. Generally, forming an internal cavity accurately is more difficult than forming an external shape, however the opposite holds true for electroforming because the mandrel's exterior can be accurately machined.
Compared to other basic metal forming processes (casting, forging, stamping, deep drawing, machining and fabricating) electroforming is very effective when requirements call for extreme tolerances, complexity or light weight. The precision and resolution inherent in the photographically produced conductive patterned substrate, allows finer geometries to be produced to tighter tolerances while maintaining superior edge definition with a near optical finish. Electroformed metal is extremely pure, with superior properties over wrought metal due to its refined crystal structure. Multiple layers of electroformed metal can be molecularly bonded together, or to different substrate materials to produce complex structures with "grown-on" flanges and bosses.
A wide variety of shapes and sizes can be made by electroforming, the principal limitation being the need to part the product from the mandrel. Since the fabrication of a product requires only a single pattern or mandrel, low production quantities can be made economically.
Spiro,P. Electroforming: A comprehensive survey of theory, practice and commercial applications, London 1971.