ASTM B832-93(1998)
(Guide)Standard Guide for Electroforming with Nickel and Copper
Standard Guide for Electroforming with Nickel and Copper
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 problems, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
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Designation: B 832 – 93 (Reapproved 1998)
Standard Guide for
Electroforming with Nickel and Copper
This standard is issued under the fixed designation B 832; 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 (e) indicates an editorial change since the last revision or reapproval.
1. Scope Plated Metallic Coatings with the Spiral Contractometer
B 659 Guide for Measuring Thickness of Metallic and
1.1 This guide covers electroforming practice and describes
Inorganic Coatings
the processing of mandrels, the design of electroformed ar-
E 8 Test Methods of Tension Testing of Metallic Materials
ticles, and the use of copper and nickel electroplating solutions
E 384 Test Method for Microhardness of Materials
for electroforming.
1.2 This standard does not purport to address all of the
3. Summary of Electroforming Practice
safety concerns, if any, associated with its use. It is the
3.1 Electroforming is defined (see Terminology B 374) as
responsibility of the user of this standard to establish appro-
the production or reproduction of articles by electrodeposition
priate safety and health practices and determine the applica-
upon a mandrel or mold that is subsequently separated from the
bility of regulatory limitations prior to use.
deposit.
2. Referenced Documents 3.2 The basic fabrication steps are as follows: a suitable
mandrel is fabricated and prepared for electroplating; the
2.1 ASTM Standards:
mandrel is placed in an appropriate electroplating solution and
B 183 Practice for Preparation of Low-Carbon Steel for
metal is deposited upon the mandrel by electrolysis; when the
Electroplating
required thickness of metal has been applied, the metal-
B 242 Practice for Preparation of High-Carbon Steel for
covered mandrel is removed from the solution; and the mandrel
Electroplating
is separated from the electrodeposited metal. The electroform
B 252 Practice for Preparation of Zinc Alloy Die Castings
is a separate, free-standing entity composed entirely of elec-
for Electroplating and Conversion Coatings
trodeposited metal. Electroforming is concerned with the
B 253 Guide for Preparation of Aluminum Alloys for Elec-
fabrication of articles of various kinds.
troplating
B 254 Practice for Preparation of and Electroplating on
4. Significance and Use
Stainless Steel
4.1 The specialized use of the electroplating process for
B 281 Practice for Preparation of Copper and Copper-Base
2 electroforming results in the manufacture of tools and products
Alloys for Electroplating and Conversion Coatings
that are unique and often impossible to make economically by
B 311 Test Method for Density of Cemented Carbides
traditional methods of fabrication. Current applications of
B 343 Practice for Preparation of Nickel for Electroplating
nickel electroforming include: textile printing screens; compo-
with Nickel
2 nents of rocket thrust chambers, nozzles, and motor cases;
B 374 Terminology Relating to Electroplating
molds and dies for making automotive arm-rests and instru-
B 489 Practice for Bend Test for Ductility of Electrodepos-
ment panels; stampers for making phonograph records, video-
ited and Autocatalytically Deposited Metal Coatings on
2 discs, and audio compact discs; mesh products for making
Metals
porous battery electrodes, filters, and razor screens; and optical
B 490 Practice for Micrometer Bend Test for Ductility of
2 parts, bellows, and radar wave guides (1-3).
Electrodeposits
4.2 Copper is extensively used for electroforming thin foil
B 558 Practice for Preparation of Nickel Alloys for Electro-
2 for the printed circuit industry. Copper foil is formed continu-
plating
2 ously by electrodeposition onto rotating drums. Copper is often
B 571 Test Methods for Adhesion of Metallic Coatings
used as a backing material for electroformed nickel shells and
B 578 Test Method for Microhardness of Electroplated
2 in other applications where its high thermal and electrical
Coatings
conductivities are required. Other metals including gold are
4B 636 Test Method for Measurement of Internal Stress of
electroformed on a smaller scale.
4.3 Electroforming is used whenever the difficulty and cost
This guide is under the jurisdiction of ASTM Committee B08 on Metallic and
Inorganic Coatings and is the direct responsibility of Subcommittee B08.08.01on
Engineering Coatings. Annual Book of ASTM Standards, Vol 03.01.
Current edition approved Jan. 15, 1993. Published March 1993. The boldface numbers in parentheses refer to the list of references at the end of
Annual Book of ASTM Standards, Vol 02.05. this standard.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superceded and replaced by a new version or discontinued. NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
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B 832
of producing the object by mechanical means is unusually exposed to electroplating solutions operated at elevated tem-
high; unusual mechanical and physical properties are required peratures. In such cases, it may be necessary to use acid copper,
in the finished piece; extremely close dimensional tolerances nickel sulfamate, and other electroplating solutions that func-
must be held on internal dimensions and on surfaces of tion at room temperature.
irregular contour; very fine reproduction of detail and complex
5.2 Mandrel Design:
combinations of surface finish are required; and the part cannot
5.2.1 The electroforming operation can often be simplified
be made by other available methods.
by design changes that do not impair the functioning of the
piece. Some of the design considerations are summarized in
5. Processing of Mandrels for Electroforming
5.2.2, 5.2.3, 5.2.4, 5.2.5, and 5.2.6. Examples of mandrel
5.1 General Considerations:
shapes that may present problems during electroforming are
5.1.1 Mandrels may be classified as conductors or noncon-
illustrated inFig. 1.
ductors of electricity, and each of these may be permanent,
5.2.2 Exterior (convex) angles should be provided with as
semipermanent, or expendable (Table 1).
generous a radius as possible to avoid excessive build up and
5.1.2 Whether or not a mandrel is a conductor will deter-
treeing of the deposit during electroforming. Interior (concave)
mine the procedures required to prepare it for electroforming.
angles on the mandrel should be provided with a fillet radius of
Conductive mandrels are usually pure metals or alloys of
at least 0.05 cm per 5 cm (0.02 in. per 2 in.) of length of a side
metals and are prepared by standard procedures but may
of the angle.
require an additional thin parting film to facilitate separation of
5.2.3 Whenever possible, permanent mandrels should be
the electroform from the mandrel (unless the mandrel is
tapered at least 0.08 mm per m (0.001 in. per ft) to facilitate
removed by melting or chemical dissolution).
removal from the mandrel. (Where this is not permissible, the
5.1.3 Whether or not a permanent or expendable mandrel
mandrel may be made of a material with a high or low
should be used is largely dependent on the particular article
coefficient of thermal expansion so that separation can be
that is to be electroformed. If no reentrant shapes or angles are
effected by heating or cooling).
involved, it is possible to use permanent, rigid mandrels that
5.2.4 A fine surface finish on the mandrel, achieved by
can be separated from the finished electroform mechanically
lapping or by electropolishing, will generally facilitate separa-
and reused. If reentrant angles and shapes are involved, it is
tion of mandrel and electroform. A finish of 0.05 μm (2 μin.)
necessary to use mandrel materials that can be removed by
rms is frequently specified.
melting or by chemical dissolution, or materials that are
5.2.5 Flat bottom grooves, sharp angle indentations, blind
collapsible, such as polyvinyl chloride and other plastics. In
holes, fins, v-shaped projections, v-bottom grooves, deep
some cases, multiple piece mandrels are used that can be
scoops, slots, concave recesses, and rings and ribs can cause
removed even with reentrant features.
problems with metal distribution during electroforming unless
5.1.4 Many solid materials can be used to fabricate man-
inside and outside angles and corners are rounded.
drels for electroforming, but the following generalizations may
5.2.6 An engineering drawing of the mandrel, the electro-
help in selecting a suitable material: permanent mandrels are
formed article, and auxiliary equipment or fixture for separat-
preferred for accuracy and for large production runs; expend-
ing the electroform from the mandrel should be prepared. The
able mandrels must be used whenever the part is so designed
drawing of the mandrel should provide for electrical connec-
that a permanent mandrel cannot be withdrawn; and it is
tions to be made in nonfunctional areas of the electroform. It
important that the mandrel retain its dimensional stability in
should provide reference points for and mechanical means of
warm plating baths. Wax and most plastics expand when
holding if finish machining is necessary before removal of the
mandrel.
TABLE 1 Types of Mandrel Materials
5.3 Mandrel Fabrication:
Types Typical Materials
5.3.1 The method of fabrication of the mandrel will depend
Conductors
on the type selected, the material chosen, and the object to be
Expendable Low-melting point alloys; for example, electroformed. Mandrels may be manufactured by casting,
bismuth-free 92 % tin and 8 % zinc
machining, electroforming, and other techniques. Permanent
Aluminum alloys
mandrels can be made by any of the conventional pattern-
Zinc alloys
Permanent Nickel making processes.
Austenitic Stainless
5.4 Preparing Non-Conducting Mandrels:
Invar, Kovar
5.4.1 Nonconducting mandrels must be made impervious to
Copper and brass
Nickel-plated steel
water and other processing solutions and then rendered con-
Nickel/chromium-plated aluminum
ductive. Porous materials, for example, leather and plastic, may
be impregnated with wax, shellac, lacquer, or a synthetic resin
Nonconductors
formulation. It is often preferable to use thin films of lacquer to
Expendable Wax
seal porous, nonmetallic mandrels.
Glass
5.4.2 Nonconducting materials may be rendered conductive
Permanent (or Semi-Permanent) Rigid and collapsible plastic; for
example, epoxy resins and polyvinyl
by applying a chemically reduced film of silver, copper, or
chloride
nickel to the surface. In general, these processes are carried out
Wood
by spraying the reagent containing the metal ions of choice
NOTICE: This standard has either been superceded and replaced by a new version or discontinued. NOTICE: This standard has either been superceded and replaced by a new version or discontinued.
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B 832
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
simultaneously with a specific reducing agent onto the surface in preparation for electroforming. See Practices B 183, B 242,
of the mandrel using a double-nozzle spray gun. The chemicals B 254, B 281, and B 558, for example.
react at the surface; the metal is reduced and is deposited on the
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).
5.4.3 Other ways of making non-conducting materials con-
5.5.3 Stainless steel, nickel, and nickel- or chromium-plated
ductive include: using finely divided metal powders dispersed
steel are cleaned using standard procedures, rinsed, and passi-
in binders (“bronzing”), applying finely divided graphite to
vated by immersion in a 2 % solution of sodium dichromate for
wax, and to natural or synthetic rubbers that have an affinity for
30 to 60 s at room temperature. The mandrel must then be
graphite, and applying graphite with a binder.
rinsed to remove all traces of the dichromate solution.
5.4.4 Vapor deposition of silver and other metals is pre-
5.5.4 Copper and brass mandrels that have been nickel
ferred for nonconducting mandrels used in the semiconductor
and/or chromium-plated may be treated as described in 5.5.3. If
industry, the optical disc industry, and the manufacture of
not electroplated, the surface can be made passive by immer-
holograms. In these cases the mandrel must be made of a
sion in a solution containing 8 g/L sodium sulfide.
material that does not outgas in the vacuum chamber. Glass is
5.5.5 Aluminum alloys may require special treatments even
the preferred substrate for making masters and stampers for
optical read-out discs of all kinds. when they are used as expendable mandrels to be separated by
5.5 Preparing Metallic Mandrels: chemical dissolution. If the deposits are highly stressed, it may
5.5.1 Standard procedures should be used whenever adher- be necessary to use the zincate or stannate treatments included
ent electrodeposits are applied to metallic mandrels prior to and in Guide B 253 to achieve a degree of adhesion that will
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