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What is Electroforming

Electroforming is a highly specialized process for fabricating metal parts by electrodeposition in a plating bath over a base form called a mandrel, which is subsequently removed leaving just the electrodeposited metal.  The mandrel is fabricated by conventional means and then electroplated.  Once the desired thickness is achieved, anywhere between .001″ (.025 mm) up to over a half inch (12.7 mm), the mandrel is extracted or dissolved.

 

 

 

This diagram shows the positively charged electroforming metal source (anode) at the left being broken down by DC electric current causing each surface atom to lose two electrons (ionized) in the copper or nickel electrolyte solution, which are then attracted to the negatively charged mandrel (cathode) where they get their electrons back and become metal again.  Build up is achieved at an approximate rate of .001″ (.025 mm) per hour.

The advantage of this process is that metal is deposited against the mandrel surface on a molecular level at room temperature, as it is formed atom by atom.  This faithfully reproduces the form or mandrel exactly, to within less than a micron, without the shrinkage or distortion associated with other metal forming techniques such as casting, stamping or drawing.  And since the mandrel is an outside surface, complex features, close dimensional tolerances and surface finishes can be created on inside surfaces that are impossible to obtain by any other method known.

Electroforming should be thought of as a basic manufacturing process when considering alternatives best suited for making any particular item.  Other basic metal forming processes, including casting, forging, stamping, deep drawing, machining, EDM and rapid prototyping may serve well for most applications, but can be pressed beyond their limits when requirements call for extreme tolerances, complexity or light weight.  Electroforming is a real problem solver in these instances; it is the most accurate way on earth of establishing internal dimensions and reproducing surface detail.

Why do that?

Because the metal is formed on a molecular level over a surface replicating the image needed in reverse, really deep and complicated features can be made as a structure with outside features which simply cannot be produced as internal features.  Since the metal goes on at room temperature, there is no shrinkage or distortion, leaving internal dimensions of a complex structure having exactly the same finish, detail and dimensions that were established on the Mandrel, which was made as an outside structure.  This is the most accurate way in the world to make internal cavities, or reproduce surface detail.  This picture shows a complex featured microwave waveguide next to a mandrel like the one it was made on, and a reflector next to its mandrel.

 

 

What metals can we electroform?

We can make parts of copper or nickel, 4 types of copper, our OFC, Type 1A, Type II and Type IIA, plus 2 types of nickel, our Type 1 and Type II per the enclosed chart.  We can also make parts of a nickel / cobalt alloy.  We can alter the grain structure and thus the physical properties of the metals by using grain refining additives in the plating baths, resulting in copper parts ranging from pure soft OFC up to type IIA having 120,000 lbs. / sq. inch tensile strength, and nickel from pure soft up to Type II having 200,000 lbs. / sq. inch tensile strength with a hardness of Rockwell C-50.  Multiple layers of the same or different electroformed metals can be molecularly bonded together, or to different substrate metals to produce complex structures with other “grown on items” such as flanges, baffles, bosses and inserts.

 

 

 

What are mandrels made of?

Mandrels can be made of a wide variety of materials including stainless steel, aluminum, rubber, epoxy, plastic, plaster, wax, glass and stereo lithography to name a few.  Mandrels that are not conductive can be coated with thin layer of conductive material first, such as silver reduction.  Reusable mandrels are made of stainless steel or rubber (RTV).  Reusable mandrels are only good for parts with no undercuts, otherwise the mandrels need to be disposable, of which the most common material is aluminum. This can be machined to really accurate tolerances and after electroforming be totally dissolved away in sodium hydroxide, which does not etch copper or nickel at all.