ASTM B832-93(2023)
(Guide)Standard Guide for Electroforming with Nickel and Copper
Standard Guide for Electroforming with Nickel and Copper
SIGNIFICANCE AND USE
4.1 The specialized use of the electroplating process for electroforming results in the manufacture of tools and products that are unique and often impossible to make economically by traditional methods of fabrication. Current applications of nickel electroforming include: textile printing screens; components of rocket thrust chambers, nozzles, and motor cases; molds and dies for making automotive arm-rests and instrument panels; stampers for making phonograph records, video-discs, and audio compact discs; mesh products for making porous battery electrodes, filters, and razor screens; and optical parts, bellows, and radar wave guides (1-3).3
4.2 Copper is extensively used for electroforming thin foil for the printed circuit industry. Copper foil is formed continuously by electrodeposition onto rotating drums. Copper is often used as a backing material for electroformed nickel shells and in other applications where its high thermal and electrical conductivities are required. Other metals including gold are electroformed on a smaller scale.
4.3 Electroforming is used whenever the difficulty and cost of producing the object by mechanical means is unusually high; unusual mechanical and physical properties are required in the finished piece; extremely close dimensional tolerances must be held on internal dimensions and on surfaces of irregular contour; very fine reproduction of detail and complex combinations of surface finish are required; and the part cannot be made by other available methods.
SCOPE
1.1 This guide covers electroforming practice and describes the processing of mandrels, the design of electroformed articles, and the use of copper and nickel electroplating solutions for electroforming.
1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.
1.3 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
General Information
Relations
Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: B832 − 93 (Reapproved 2023)
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 B343 Practice for Preparation of Nickel for Electroplating
with Nickel
1.1 This guide covers electroforming practice and describes
B374 Terminology Relating to Electroplating
the processing of mandrels, the design of electroformed
B489 Practice for Bend Test for Ductility of Electrodepos-
articles, and the use of copper and nickel electroplating
ited and Autocatalytically Deposited Metal Coatings on
solutions for electroforming.
Metals
1.2 This standard does not purport to address all of the
B490 Practice for Micrometer Bend Test for Ductility of
safety concerns, if any, associated with its use. It is the
Electrodeposits
responsibility of the user of this standard to establish appro-
B558 Practice for Preparation of Nickel Alloys for Electro-
priate safety, health, and environmental practices and deter-
plating
mine the applicability of regulatory limitations prior to use.
B571 Practice for Qualitative Adhesion Testing of Metallic
1.3 This international standard was developed in accor-
Coatings
dance with internationally recognized principles on standard-
B578 Test Method for Microindentation Hardness of Elec-
ization established in the Decision on Principles for the
troplated Coatings
Development of International Standards, Guides and Recom-
B636 Test Method for Measurement of Internal Stress of
mendations issued by the World Trade Organization Technical
Plated Metallic Coatings with the Spiral Contractometer
Barriers to Trade (TBT) Committee.
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 [Metric] E0008_E0008M
B242 Guide for Preparation of High-Carbon Steel for Elec- E384 Test Method for Microindentation Hardness of Mate-
troplating rials
B252 Guide for Preparation of Zinc Alloy Die Castings for
3. Summary of Electroforming Practice
Electroplating and Conversion Coatings
B253 Guide for Preparation of Aluminum Alloys for Elec- 3.1 Electroforming is defined (see Terminology B374) as
troplating the production or reproduction of articles by electrodeposition
B254 Practice for Preparation of and Electroplating on upon a mandrel or mold that is subsequently separated from the
Stainless Steel
deposit.
B281 Practice for Preparation of Copper and Copper-Base
3.2 The basic fabrication steps are as follows: a suitable
Alloys for Electroplating and Conversion Coatings
mandrel is fabricated and prepared for electroplating; the
B311 Test Method for Density of Powder Metallurgy (PM)
mandrel is placed in an appropriate electroplating solution and
Materials Containing Less Than Two Percent Porosity
metal is deposited upon the mandrel by electrolysis; when the
required thickness of metal has been applied, the metal-
covered mandrel is removed from the solution; and the mandrel
This guide is under the jurisdiction of ASTM Committee B08 on Metallic and
is separated from the electrodeposited metal. The electroform
Inorganic Coatings and is the direct responsibility of Subcommittee B08.03 on
is a separate, free-standing entity composed entirely of elec-
Engineering Coatings.
trodeposited metal. Electroforming is concerned with the
Current edition approved Nov. 1, 2023. Published November 2023. Originally
fabrication of articles of various kinds.
approved in 1993. Last previous edition approved in 2018 as B832 – 93 (2018).
DOI: 10.1520/B0832-93R23.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or 4. Significance and Use
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
4.1 The specialized use of the electroplating process for
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website. electroforming results in the manufacture of tools and products
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
B832 − 93 (2023)
that are unique and often impossible to make economically by require an additional thin parting film to facilitate separation of
traditional methods of fabrication. Current applications of the electroform from the mandrel (unless the mandrel is
nickel electroforming include: textile printing screens; compo- removed by melting or chemical dissolution).
nents of rocket thrust chambers, nozzles, and motor cases;
5.1.3 Whether or not a permanent or expendable mandrel
molds and dies for making automotive arm-rests and instru-
should be used is largely dependent on the particular article
ment panels; stampers for making phonograph records, video-
that is to be electroformed. If no reentrant shapes or angles are
discs, and audio compact discs; mesh products for making
involved, it is possible to use permanent, rigid mandrels that
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
ously by electrodeposition onto rotating drums. Copper is often
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
conductivities are required. Other metals including gold are 5.1.4 Many solid materials can be used to fabricate man-
electroformed on a smaller scale. drels for electroforming, but the following generalizations may
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-
combinations of surface finish are required; and the part cannot
peratures. In such cases, it may be necessary to use acid copper,
be made by other available methods.
nickel sulfamate, and other electroplating solutions that func-
tion at room temperature.
5. Processing of Mandrels for Electroforming
5.1 General Considerations:
5.2 Mandrel Design:
5.1.1 Mandrels may be classified as conductors or noncon-
5.2.1 The electroforming operation can often be simplified
ductors of electricity, and each of these may be permanent,
by design changes that do not impair the functioning of the
semipermanent, or expendable (Table 1).
piece. Some of the design considerations are summarized in
5.2.2, 5.2.3, 5.2.4, 5.2.5, and 5.2.6. Examples of mandrel
TABLE 1 Types of Mandrel Materials
shapes that may present problems during electroforming are
Types Typical Materials
illustrated in Fig. 1.
Conductors
5.2.2 Exterior (convex) angles should be provided with as
generous a radius as possible to avoid excessive build up and
Expendable Low-melting point alloys; for example,
bismuth-free 92 % tin and 8 % zinc treeing of the deposit during electroforming. Interior (concave)
Aluminum alloys
angles on the mandrel should be provided with a fillet radius of
Zinc alloys
at least 0.05 cm per 5 cm (0.02 in. per 2 in.) of length of a side
Permanent Nickel
Austenitic Stainless
of the angle.
Invar, Kovar
5.2.3 Whenever possible, permanent mandrels should be
Copper and brass
Nickel-plated steel tapered at least 0.08 mm per m (0.001 in. per ft) to facilitate
Nickel/chromium-plated aluminum
removal from the mandrel. (Where this is not permissible, the
mandrel may be made of a material with a high or low
Nonconductors
coefficient of thermal expansion so that separation can be
Expendable Wax
effected by heating or cooling).
Glass
5.2.4 A fine surface finish on the mandrel, achieved by
Permanent (or Semi-Permanent) Rigid and collapsible plastic; for
example, epoxy resins and polyvinyl
lapping or by electropolishing, will generally facilitate separa-
chloride
tion of mandrel and electroform. A finish of 0.05 μm (2 μin.)
Wood
rms is frequently specified.
5.2.5 Flat bottom grooves, sharp angle indentations, blind
holes, fins, v-shaped projections, v-bottom grooves, deep
5.1.2 Whether or not a mandrel is a conductor will deter-
mine the procedures required to prepare it for electroforming. scoops, slots, concave recesses, and rings and ribs can cause
problems with metal distribution during electroforming unless
Conductive mandrels are usually pure metals or alloys of
metals and are prepared by standard procedures but may inside and outside angles and corners are rounded.
5.2.6 An engineering drawing of the mandrel, the electro-
formed article, and auxiliary equipment or fixture for separat-
The boldface numbers in parentheses refer to the list of references at the end of
this standard. ing the electroform from the mandrel should be prepared. The
B832 − 93 (2023)
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
drawing of the mandrel should provide for electrical connec- by spraying the reagent containing the metal ions of choice
tions to be made in nonfunctional areas of the electroform. It simultaneously with a specific reducing agent onto the surface
should provide reference points for and mechanical means of of the mandrel using a double-nozzle spray gun. The chemicals
holding if finish machining is necessary before removal of the react at the surface; the metal is reduced and is deposited on the
mandrel. mandrel surface. Chemical reduction processes are preferred
because dimensional accuracy is not affected, the film has little
5.3 Mandrel Fabrication:
adhesion, and parting is not difficult. If necessary, a silver film
5.3.1 The method of fabrication of the mandrel will depend
can be stripped from a nickel electroform with either nitric
on the type selected, the material chosen, and the object to be
acid, warm sulfuric acid, or a cyanide solution.
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, and to natural or synthetic rubbers that have an affinity for
5.4 Preparing Non-Conducting Mandrels:
graphite, and applying graphite with a binder.
5.4.1 Nonconducting mandrels must be made impervious to
5.4.4 Vapor deposition of silver and other metals is pre-
water and other processing solutions and then rendered con-
ferred for nonconducting mandrels used in the semiconductor
ductive. Porous materials, for example, leather and plastic, may
industry, the optical disc industry, and the manufacture of
be impregnated with wax, shellac, lacquer, or a synthetic resin
holograms. In these cases the mandrel must be made of a
formulation. It is often preferable to use thin films of lacquer to
material that does not outgas in the vacuum chamber. Glass is
seal porous, nonmetallic mandrels.
the preferred substrate for making masters and stampers for
5.4.2 Nonconducting materials may be rendered conductive
optical read-out discs of all kinds.
by applying a chemically reduced film of silver, copper, or
nickel to the surface. In general, these processes are carried out 5.5 Preparing Metallic Mandrels:
B832 − 93 (2023)
FIG. 1 (continued)
5.5.1 Standard procedures should be used whenever adher- alloy with copper and treat it accordingly to prevent attack of
ent electrodeposits are applied to metallic mandrels prior to and the mandrel. See Practice B252.
in preparation for electroforming. See Practices B183, B242, 5.5.7 The low-melting point alloys included in Table 1
B254, B281, and B558, for example. employed to make expendable mandrels that can be melted
5.5.2 With most metallic mandrels an additional chemical away have a tendency to leave a residue of tin on the surface
treatment that forms a parting film on the surface is required to of the electroform. The mandrel can be plated with copper prior
separate the electroform from the mandrel. After removing all to electroforming to prevent this.
traces of grease and oil by means of solvents, various metallic
mandrels are given different treatments for this purpose (see 6. Nickel and Copper Electroforming Solutions
5.5.3, 5.5.4, 5.5.5, 5.5.6, and 5.5.7).
6.1 The choice of metal selected for the electroform will
5.5.3 Stainless steel, nickel, and nickel- or chromium-plated
depend on the mechanical and physical properties required in
steel are cleaned using standard procedures, rinsed, and passi-
the finished article as related to function. The two metals
vated by immersion in a 2 % solution of sodium dichromate for
selected most frequently are nickel and copper. The operation
30 s to 60 s at room temperature. The mandrel must then be
and co
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