ASTM B832-93(2008)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
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Designation: B832 − 93(Reapproved 2008)
Standard Guide for
Electroforming with Nickel and Copper
This standard is issued under the fixed designation B832; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope B490 Practice for Micrometer Bend Test for Ductility of
Electrodeposits
1.1 This guide covers electroforming practice and describes
B558 Practice for Preparation of Nickel Alloys for Electro-
the processing of mandrels, the design of electroformed
plating
articles, and the use of copper and nickel electroplating
B571 Practice for Qualitative Adhesion Testing of Metallic
solutions for electroforming.
Coatings
1.2 This standard does not purport to address all of the
B578 Test Method for Microhardness of Electroplated Coat-
safety concerns, if any, associated with its use. It is the
ings
responsibility of the user of this standard to establish appro-
B636 Test Method for Measurement of Internal Stress of
priate safety and health practices and determine the applica-
Plated Metallic Coatings with the Spiral Contractometer
bility of regulatory limitations prior to use.
B659 Guide for Measuring Thickness of Metallic and Inor-
ganic Coatings
2. Referenced Documents
B849 Specification for Pre-Treatments of Iron or Steel for
2.1 ASTM Standards: Reducing Risk of Hydrogen Embrittlement
B183 Practice for Preparation of Low-Carbon Steel for
E8 Test Methods for Tension Testing of Metallic Materials
Electroplating E384 Test Method for Knoop and Vickers Hardness of
B242 Guide for Preparation of High-Carbon Steel for Elec-
Materials
troplating
3. Summary of Electroforming Practice
B252 Guide for Preparation of Zinc Alloy Die Castings for
Electroplating and Conversion Coatings 3.1 Electroforming is defined (see Terminology B374)as
B253 Guide for Preparation of Aluminum Alloys for Elec- the production or reproduction of articles by electrodeposition
troplating uponamandrelormoldthatissubsequentlyseparatedfromthe
B254 Practice for Preparation of and Electroplating on deposit.
Stainless Steel
3.2 The basic fabrication steps are as follows: a suitable
B281 Practice for Preparation of Copper and Copper-Base
mandrel is fabricated and prepared for electroplating; the
Alloys for Electroplating and Conversion Coatings
mandrel is placed in an appropriate electroplating solution and
B311 Test Method for Density of Powder Metallurgy (PM)
metal is deposited upon the mandrel by electrolysis; when the
Materials Containing Less Than Two Percent Porosity
required thickness of metal has been applied, the metal-
B343 Practice for Preparation of Nickel for Electroplating
coveredmandrelisremovedfromthesolution;andthemandrel
with Nickel
is separated from the electrodeposited metal. The electroform
B374 Terminology Relating to Electroplating
is a separate, free-standing entity composed entirely of elec-
B489 Practice for Bend Test for Ductility of Electrodepos-
trodeposited metal. Electroforming is concerned with the
ited and Autocatalytically Deposited Metal Coatings on
fabrication of articles of various kinds.
Metals
4. Significance and Use
4.1 The specialized use of the electroplating process for
This guide is under the jurisdiction of ASTM Committee B08 on Metallic and
electroforming results in the manufacture of tools and products
Inorganic Coatings and is the direct responsibility of Subcommittee B08.03 on
that are unique and often impossible to make economically by
Engineering Coatings.
traditional methods of fabrication. Current applications of
Current edition approved Aug. 1, 2008. Published September 2008. Originally
nickel electroforming include: textile printing screens; compo-
approved in 1993. Last previous edition approved in 2003 as B832 – 93 (2003).
DOI: 10.1520/B0832-93R08.
nents of rocket thrust chambers, nozzles, and motor cases;
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
molds and dies for making automotive arm-rests and instru-
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
ment panels; stampers for making phonograph records, video-
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. discs, and audio compact discs; mesh products for making
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B832 − 93 (2008)
porous battery electrodes, filters, and razor screens; and optical can be separated from the finished electroform mechanically
parts, bellows, and radar wave guides (1-3). and reused. If reentrant angles and shapes are involved, it is
necessary to use mandrel materials that can be removed by
4.2 Copper is extensively used for electroforming thin foil
melting or by chemical dissolution, or materials that are
for the printed circuit industry. Copper foil is formed continu-
collapsible, such as polyvinyl chloride and other plastics. In
ouslybyelectrodepositionontorotatingdrums.Copperisoften
some cases, multiple piece mandrels are used that can be
used as a backing material for electroformed nickel shells and
removed even with reentrant features.
in other applications where its high thermal and electrical
5.1.4 Many solid materials can be used to fabricate man-
conductivities are required. Other metals including gold are
drels for electroforming, but the following generalizations may
electroformed on a smaller scale.
help in selecting a suitable material: permanent mandrels are
4.3 Electroforming is used whenever the difficulty and cost
preferred for accuracy and for large production runs; expend-
of producing the object by mechanical means is unusually
able mandrels must be used whenever the part is so designed
high; unusual mechanical and physical properties are required
that a permanent mandrel cannot be withdrawn; and it is
in the finished piece; extremely close dimensional tolerances
important that the mandrel retain its dimensional stability in
must be held on internal dimensions and on surfaces of
warm plating baths. Wax and most plastics expand when
irregular contour; very fine reproduction of detail and complex
exposed to electroplating solutions operated at elevated tem-
combinationsofsurfacefinisharerequired;andthepartcannot
peratures.Insuchcases,itmaybenecessarytouseacidcopper,
be made by other available methods.
nickel sulfamate, and other electroplating solutions that func-
tion at room temperature.
5. Processing of Mandrels for Electroforming
5.2 Mandrel Design:
5.1 General Considerations:
5.2.1 The electroforming operation can often be simplified
5.1.1 Mandrels may be classified as conductors or noncon-
by design changes that do not impair the functioning of the
ductors of electricity, and each of these may be permanent,
piece. Some of the design considerations are summarized in
semipermanent, or expendable (Table 1).
5.2.2, 5.2.3, 5.2.4, 5.2.5, and 5.2.6. Examples of mandrel
shapes that may present problems during electroforming are
TABLE 1 Types of Mandrel Materials
illustrated in Fig. 1.
Types Typical Materials
5.2.2 Exterior (convex) angles should be provided with as
Conductors
generous a radius as possible to avoid excessive build up and
Expendable Low-melting point alloys; for example, treeing of the deposit during electroforming. Interior (concave)
bismuth-free 92 % tin and 8 % zinc
anglesonthemandrelshouldbeprovidedwithafilletradiusof
Aluminum alloys
at least 0.05 cm per 5 cm (0.02 in. per 2 in.) of length of a side
Zinc alloys
Permanent Nickel
of the angle.
Austenitic Stainless
5.2.3 Whenever possible, permanent mandrels should be
Invar, Kovar
tapered at least 0.08 mm per m (0.001 in. per ft) to facilitate
Copper and brass
Nickel-plated steel removal from the mandrel. (Where this is not permissible, the
Nickel/chromium-plated aluminum
mandrel may be made of a material with a high or low
coefficient of thermal expansion so that separation can be
Nonconductors
effected by heating or cooling).
Expendable Wax
5.2.4 A fine surface finish on the mandrel, achieved by
Glass
lapping or by electropolishing, will generally facilitate separa-
Permanent (or Semi-Permanent) Rigid and collapsible plastic; for
example, epoxy resins and polyvinyl
tion of mandrel and electroform. A finish of 0.05 µm (2 µin.)
chloride
rms is frequently specified.
Wood
5.2.5 Flat bottom grooves, sharp angle indentations, blind
holes, fins, v-shaped projections, v-bottom grooves, deep
scoops, slots, concave recesses, and rings and ribs can cause
5.1.2 Whether or not a mandrel is a conductor will deter-
problems with metal distribution during electroforming unless
mine the procedures required to prepare it for electroforming.
inside and outside angles and corners are rounded.
Conductive mandrels are usually pure metals or alloys of
5.2.6 An engineering drawing of the mandrel, the electro-
metals and are prepared by standard procedures but may
formed article, and auxiliary equipment or fixture for separat-
require an additional thin parting film to facilitate separation of
ing the electroform from the mandrel should be prepared. The
the electroform from the mandrel (unless the mandrel is
drawing of the mandrel should provide for electrical connec-
removed by melting or chemical dissolution).
tions to be made in nonfunctional areas of the electroform. It
5.1.3 Whether or not a permanent or expendable mandrel
should provide reference points for and mechanical means of
should be used is largely dependent on the particular article
holding if finish machining is necessary before removal of the
that is to be electroformed. If no reentrant shapes or angles are
mandrel.
involved, it is possible to use permanent, rigid mandrels that
5.3 Mandrel Fabrication:
5.3.1 The method of fabrication of the mandrel will depend
The boldface numbers in parentheses refer to the list of references at the end of
this standard. on the type selected, the material chosen, and the object to be
B832 − 93 (2008)
NOTE 1—Examples of deposit distribution on contours that require special consideration are shown in an exaggerated fashion. The designer should
confer with the electroformer before designing an electroform having any of these contours. An experienced electroformer can minimize some of the
exaggeration shown.
FIG. 1 Examples of Deposit Distribution on Electroforms
electroformed. Mandrels may be manufactured by casting, 5.4.3 Other ways of making non-conducting materials con-
machining, electroforming, and other techniques. Permanent ductive include: using finely divided metal powders dispersed
mandrels can be made by any of the conventional pattern- in binders (“bronzing”), applying finely divided graphite to
making processes. wax,andtonaturalorsyntheticrubbersthathaveanaffinityfor
graphite, and applying graphite with a binder.
5.4 Preparing Non-Conducting Mandrels:
5.4.4 Vapor deposition of silver and other metals is pre-
5.4.1 Nonconducting mandrels must be made impervious to
ferred for nonconducting mandrels used in the semiconductor
water and other processing solutions and then rendered con-
industry, the optical disc industry, and the manufacture of
ductive.Porousmaterials,forexample,leatherandplastic,may
holograms. In these cases the mandrel must be made of a
be impregnated with wax, shellac, lacquer, or a synthetic resin
material that does not outgas in the vacuum chamber. Glass is
formulation.Itisoftenpreferabletousethinfilmsoflacquerto
the preferred substrate for making masters and stampers for
seal porous, nonmetallic mandrels.
optical read-out discs of all kinds.
5.4.2 Nonconducting materials may be rendered conductive
by applying a chemically reduced film of silver, copper, or 5.5 Preparing Metallic Mandrels:
nickel to the surface. In general, these processes are carried out 5.5.1 Standard procedures should be used whenever adher-
by spraying the reagent containing the metal ions of choice entelectrodepositsareappliedtometallicmandrelspriortoand
simultaneously with a specific reducing agent onto the surface in preparation for electroforming. See Practices B183, B242,
ofthemandrelusingadouble-nozzlespraygun.Thechemicals B254, B281, and B558, for example.
reactatthesurface;themetalisreducedandisdepositedonthe 5.5.2 With most metallic mandrels an additional chemical
mandrel surface. Chemical reduction processes are preferred treatment that forms a parting film on the surface is required to
because dimensional accuracy is not affected, the film has little separate the electroform from the mandrel. After removing all
adhesion, and parting is not difficult. If necessary, a silver film traces of grease and oil by means of solvents, various metallic
can be stripped from a nickel electroform with either nitric mandrels are given different treatments for this purpose (see
acid, warm sulfuric acid, or a cyanide solution. 5.5.3, 5.5.4, 5.5.5, 5.5.6, and 5.5.7).
B832 − 93 (2008)
FIG. 1 (continued)
5.5.3 Stainless steel, nickel, and nickel- or chromium-plated the finished article as related to function. The two metals
steel are cleaned using standard procedures, rinsed, and passi- selected most frequently are nickel and copper. The operation
vatedbyimmersionina2 %solutionofsodiumdichromatefor
and control of nickel and copper electroforming solutions are
30 to 60 s at room temperature. The mandrel must then be described in this section.
rinsed to remove all traces of the dichromate solution.
6.2 The nickel electroplating solutions commonly used for
5.5.4 Copper and brass mandrels that have been nickel
electroforming are Watts and nickel sulfamate with and with-
and/orchromium-platedmaybetreatedasdescribedin5.5.3.If
out addition agents. The advantages of nickel electroforming
not electroplated, the surface can be made passive by immer-
from sulfamate solutions are the low internal stress of the
sion in a solution containing 8 g/L sodium sulfide.
deposits and the high rates of deposition that are possible. The
5.5.5 Aluminum alloys may require special treatments even
important copper electroforming solutions are copper sulfate
when they are used as expendable mandrels to be separated by
and copper fluoborate.The formulations of nickel electroform-
chemical dissolution. If the deposits are highly stressed, it may
ing solutions, typical operating conditions, and typical me-
be necessary to use the zincate or stannate treatments included
chanical properties of the deposits are given inTable2.Similar
inGuideB253toachieveadegreeofadhesionthat
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