Electroforming,Electroforming,Electroforming,Electroforming,Electroforming
ELECTROFORMING is the process by which articles or shapes can be exactly reproduced by electrodeposition on a
mandrel or form that is later removed, leaving a precise duplicate of the original. In certain applications, the mandrel is
designed to remain as an integral part of the final electroformed object. Electroforms themselves may be used as parents
or masters, usually with special passivating treatments so the secondary electroform can be easily removed. The same or
similar electrodeposition additives as those used for electroplating are required for electroforming to control deposit
stress, grain size, and other resultant mechanical properties in order to produce high-quality electroforms


Early Applications
Electroforming was developed by a Prof. Jacobi of the Academy of Sciences in St. Petersburg, Russia in 1838 while
working with an engraved copper printing plate. While Prof. Jacobi had much difficulty in trying to separate the
replicated layer, he did note that once it was released the copper piece gave a perfect match of the original.
Prof. Boettger of Germany used nickel plating in the 1840s to produce exacting replicates of art objects by the
electroforming process. Electroformed articles, including sculpture, bas-reliefs, and statues from nickel, iron, or copper
were produced prior to 1870. Of special interest were the huge electroformed street lamps found in downtown Paris, the
production of which might be considered an enormous world-record accomplishment for electrodeposition. Iron
electroforming had early applications in the duplication of printing plates for coinage and currency because of its facility
to produce the highest accuracy in copying engraved masters.
Modern Applications
Today, the electroforming industry sees a number of high-tech uses for nickel, copper, iron, and alloy deposits to
electrofabricate exceedingly important components such as the main combustion chamber for the Space Shuttle, heart
pump components, body joint implants (prosthetic devices), high-precision optical scanners and holographic masters (for
credit cards, etc.), and recording masters. Fabrication of duplicating plates such as electrotypes, video disc stampers, and
currency embossing plates is manufacturing technology of today that employs electroforming. High-precision parts such
as molds and dies, where tolerances of internal surfaces are critical, are pieces for which electroforming can be used
advantageously. Optical memory disc mold cavities, including those for compact discs (CD and video discs) rely on the
virtually perfect surface reproduction found with the electroforming process. The average optical disc requires impressions having a mean diameter of about 0.2 μm, which is well within the range of the electroforming processes
practiced today. One of the most widely used applications today is nickel disc mold electroforming.
Examples of electroforming applications are almost limitless, but a few of the more exacting examples are:
· Delicate, thin-wall components such as lightweight heat or cold shields for aerospace applications,
hypodermic needles, foil, fine-mesh screen, and seamless tubing
· Parts that would be difficult to make by any other means, such as electronic waveguides, regeneratively
cooled thrust chambers for rocket engines, musical instruments, Pitot tubes, surface roughness gages,
and complex metal bellows
· Electroform joining (cold welding) of dissimilar metals that are difficult, if not impossible, to join by
thermal means
Electroforming provides unique production advantages for precision operation in the textile, medical, aerospace,
communication, electronics, photocopying, automotive, and computer industries, and a number of other industries and is
used in the manufacturing of items such as textile printing screens, molds and dies, mesh products, bellows, compact disc
stampers, radar wave guides, and optical components.
Electroforming Determinants
Once the conceptual design for a part or component is developed, it is necessary to determine the fabrication process that
best meets the functional requirements of the hardware with least cost impact. The following advantages of
electroforming might be weighed:
· Parts can be mass produced with identical tolerances from one part to the next, provided that mandrels
can be made with adequate replication.
· Fine detail reproduction is unmatched by any other method of mass fabrication. Examples are the
electroforming of microgroove masters and stampers for the record and compact disc industries, surface
roughness standards, and masters and stampers for holographic image reproduction.
· Mechanical properties of electroformed articles can be varied over a wide range by selecting a suitable
plating electrolyte and adjusting operating conditions. In some instances properties can be created in
electroformed metals that are difficult, if not impossible, to duplicate in wrought counterparts.
· Some shapes, particularly those with complex internal surfaces or passages, cannot be made by any
other method without excessive machining costs and scrap losses. These shapes are often easily
electroformed. Examples of such hardware are regeneratively cooled thrust chambers and waveguides
with compound curves.
· Gearing up to high-volume production is relatively easy in many electroforming applications. For
example, a number of first-generation positive replicas can be made from which a large number of
second-generation negatives can be electroformed. Such technology lends itself to many molds,
stamping devices, and optical surfaces requiring volume production.
· The size and thickness of parts electroformed is not limited. Larger size can be accommodated by
increasing the tank volume in which the electrolyte is contained. Thickness may vary from micrometers,
as in foils, to one or more centimeters, as is common in rocket thrust chamber shells.
· Without the use of thermal joining techniques, metal layers can be applied by electroforming to provide
sandwich composites having a variety of functional properties. Waveguides having an inner silver
electroformed layer for high electrical conductivity and an outer electroformed structural layer of
copper, nickel, nickel-cobalt, or other electrodepositable alloys are examples.
There are also some disadvantages of electroforming that must be considered, such as:
· Electroforming is generally an expensive manufacturing method and is chosen when other methods are
more expensive or impractical to produce the desired hardware.

· Thick electroforming is very time-consuming. Some deposits require days, or even weeks, to produce
the desired thickness. However, unlike precision machining, which is also very time-consuming,
electroforming is not labor-intensive once the deposition process is started.
· Design limitations exist in that deep or narrow recesses and sharp angles cause problems. Sudden and
severe change in cross section or wall thickness must be avoided unless subsequent machining can be
permitted.
· Most electrodeposits have some degree of stress in the as-deposited condition that may cause distortion
after the mandrel is separated. Stress relieving and special attention to electrolyte chemistries and
operating parameters can lessen this problem.
· Any degradation in the mandrel surface quality will be reproduced in the electroform made from it.
The Electroforming Process
Electroforming is very similar to conventional electroplating as far as facilities and electrolytes are concerned. However,
the controls are more stringent, because the process consumes much more time and the product must be mechanically
sound and have low internal stress for dimensional acceptance. With long deposition times, high current densities at edges
and surfaces closer to the anodes result in significant buildup, leading to nodules and uncontrolled growth. This results in
further current density variations that can seriously affect the mechanical properties of the deposit.
In electroforming nickel, cobalt, or iron there is significant hydrogen codeposition that, if not removed, causes
pits in the deposit surface. Pumping filtered electrolyte through sprays over the surfaces being electroformed will
minimize the problem and aid in maintaining a smooth deposit. Areas of high current density showing excessive and
rough buildup can be corrected by using nonconducting shields as baffles to improve the current distribution. Where
recessed areas exist, low current density will be experienced. Undesired trace metal impurities will codeposit in such
locales, leading to inferior mechanical properties and surface appearance. Auxiliary or bipolar anodes may be necessary
to overcome the low-current problem.
Electroforming solutions may be used with one or more additives to control stress, brightness, leveling (smoothness), and
microstructure. When mechanical properties (including high ductility) or good electrical or thermal conductivity are
important in the deposit, it is advisable to use nonadditive electrolytes. Because most additives are organic compounds,
they are subject to decomposition if the deposit is subjected to elevated temperatures.
Stress-reducing agents are often used in nickel, iron, and cobalt plating baths to produce neutral or compressive residual
stresses. Such agents are usually grain-refining compounds also. These deposits are generally harder, have higher yield
strength, and exhibit less ductility than conventional deposits of the same metal. Advantages in neutral or compressively
stressed deposits are ease of removal of electroforms from mandrels and inhibition of growth of cracks in deposits should
they occur from impact. A problem with stress reducers in nickel is that sulfur codeposits form when the agent reacts at
the cathode, because most stress reducers contain sulfur. Brazing or welding such deposits causes sulfur to react with
nickel to form a nickel sulfide liquidus in the range of 483 °C (901 °F) to about 650 °C (1200 °F). This leads to the effect
known as "hot shortness" experienced in wrought nickels. Such deposits can be alloyed with as little as 1500 ppm Mg to
counter the problem.
Copper Electroforming. Acid sulfate electrolytes are the industry standard for copper electroforming. Additives are
usually employed for grain refining, leveling, and brightening. The mechanical property improvements achieved are
mostly a result of grain refining. Organic compounds capable of reducing copper oxides at the cathode may also be used
to produce an oxygen-free, high-conductivity copper equivalent (<10 ppm oxygen). Decomposition products from copper
bath additives will codeposit to degrade ductility. Without additives, acid sulfate baths produce copper with grain size
increasing proportionally to deposit thickness. Intergranular voids are created that seriously degrade mechanical
properties. A plating technique known as periodic current reversal will promote deposition of a copper deposit having
uniform grain size and excellent mechanical properties for thicknesses of 0.5 cm (0.2 in.) or greater. This procedure
requires plating in a conventional direction for a given period of time, followed by a reversal of current direction for a
lesser period of time. Although the process results in a slow rate of deposition, the benefits of good mechanical properties,
relatively smooth deposit surfaces, and ability to plate dense, thick deposits make this technique most useful.

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