ASTM B832-93(2003)
(Guide)Standard Guide for Electroforming with Nickel and Copper
Standard Guide for Electroforming with Nickel and Copper
SIGNIFICANCE AND USE
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).4
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.
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 and health practices and determine the applicability of regulatory limitations prior to use.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation:B832–93 (Reapproved 2003)
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 B 558 Practice for Preparation of NickelAlloys for Electro-
plating
1.1 This guide covers electroforming practice and describes
B 571 Practice for QualitativeAdhesion Testing of Metallic
the processing of mandrels, the design of electroformed ar-
Coatings
ticles, and the use of copper and nickel electroplating solutions
B 578 Test Method for Microhardness of Electroplated
for electroforming.
Coatings
1.2 This standard does not purport to address all of the
B 636 Test Method for Measurement of Internal Stress of
safety concerns, if any, associated with its use. It is the
Plated Metallic Coatings with the Spiral Contractometer
responsibility of the user of this standard to establish appro-
B 659 Guide for Measuring Thickness of Metallic and
priate safety and health practices and determine the applica-
Inorganic Coatings
bility of regulatory limitations prior to use.
B 849 Specification for Pre-Treatments of Iron or Steel for
2. Referenced Documents Reducing Risk of Hydrogen Embrittlement
E 8 Test Methods of Tension Testing of Metallic Materials
2.1 ASTM Standards:
E 384 Test Method for Microhardness of Materials
B 183 Practice for Preparation of Low-Carbon Steel for
Electroplating
3. Summary of Electroforming Practice
B 242 Practice for Preparation of High-Carbon Steel for
3.1 Electroforming is defined (see Terminology B 374) as
Electroplating
the production or reproduction of articles by electrodeposition
B 252 Practice for Preparation of Zinc Alloy Die Castings
uponamandrelormoldthatissubsequentlyseparatedfromthe
for Electroplating and Conversion Coatings
deposit.
B 253 Guide for Preparation of Aluminum Alloys for Elec-
3.2 The basic fabrication steps are as follows: a suitable
troplating
mandrel is fabricated and prepared for electroplating; the
B 254 Practice for Preparation of and Electroplating on
mandrel is placed in an appropriate electroplating solution and
Stainless Steel
metal is deposited upon the mandrel by electrolysis; when the
B 281 Practice for Preparation of Copper and Copper-Base
required thickness of metal has been applied, the metal-
Alloys for Electroplating and Conversion Coatings
coveredmandrelisremovedfromthesolution;andthemandrel
B 311 Test Method for Density Determination for Powder
is separated from the electrodeposited metal. The electroform
Metallurgy (P/M) Materials Containing Less Than Two
2 is a separate, free-standing entity composed entirely of elec-
Percent Porosity
trodeposited metal. Electroforming is concerned with the
B 343 Practice for Preparation of Nickel for Electroplating
2 fabrication of articles of various kinds.
with Nickel
B 374 Terminology Relating to Electroplating
4. Significance and Use
B 489 Practice for Bend Test for Ductility of Electrodepos-
4.1 The specialized use of the electroplating process for
ited and Autocatalytically Deposited Metal Coatings on
electroforming results in the manufacture of tools and products
Metals
that are unique and often impossible to make economically by
B 490 Practice for Micrometer Bend Test for Ductility of
traditional methods of fabrication. Current applications of
Electrodeposits
nickel electroforming include: textile printing screens; compo-
nents of rocket thrust chambers, nozzles, and motor cases;
molds and dies for making automotive arm-rests and instru-
This guide is under the jurisdiction of ASTM Committee B08 on Metallic and
ment panels; stampers for making phonograph records, video-
Inorganic Coatings and is the direct responsibility of Subcommittee B08.08.01on
discs, and audio compact discs; mesh products for making
Engineering Coatings.
Current edition approved Feb. 10, 2003. Published May 2003. Originally
approved in 1993. Last previous edition approved in 1998 as B 832 – 93 (1998).
2 3
Annual Book of ASTM Standards, Vol 02.05. Annual Book of ASTM Standards, Vol 03.01.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
B832–93 (2003)
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
4.2 Copper is extensively used for electroforming thin foil necessary to use mandrel materials that can be removed by
for the printed circuit industry. Copper foil is formed continu- melting or by chemical dissolution, or materials that are
ouslybyelectrodepositionontorotatingdrums.Copperisoften collapsible, such as polyvinyl chloride and other plastics. In
used as a backing material for electroformed nickel shells and some cases, multiple piece mandrels are used that can be
in other applications where its high thermal and electrical removed even with reentrant features.
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
4.3 Electroforming is used whenever the difficulty and cost
help in selecting a suitable material: permanent mandrels are
of producing the object by mechanical means is unusually
preferred for accuracy and for large production runs; expend-
high; unusual mechanical and physical properties are required able mandrels must be used whenever the part is so designed
in the finished piece; extremely close dimensional tolerances
that a permanent mandrel cannot be withdrawn; and it is
must be held on internal dimensions and on surfaces of important that the mandrel retain its dimensional stability in
irregular contour; very fine reproduction of detail and complex
warm plating baths. Wax and most plastics expand when
combinationsofsurfacefinisharerequired;andthepartcannot
exposed to electroplating solutions operated at elevated tem-
be made by other available methods.
peratures.Insuchcases,itmaybenecessarytouseacidcopper,
nickel sulfamate, and other electroplating solutions that func-
5. Processing of Mandrels for Electroforming
tion at room temperature.
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.
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
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
of the angle.
Austenitic Stainless
Invar, Kovar
5.2.3 Whenever possible, permanent mandrels should be
Copper and brass
tapered at least 0.08 mm per m (0.001 in. per ft) to facilitate
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
Nonconductors
coefficient of thermal expansion so that separation can be
effected by heating or cooling).
Expendable Wax
Glass
5.2.4 A fine surface finish on the mandrel, achieved by
Permanent (or Semi-Permanent) Rigid and collapsible plastic; for
lapping or by electropolishing, will generally facilitate separa-
example, epoxy resins and polyvinyl
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-
scoops, slots, concave recesses, and rings and ribs can cause
mine the procedures required to prepare it for electroforming.
problems with metal distribution during electroforming unless
Conductive mandrels are usually pure metals or alloys of
inside and outside angles and corners are rounded.
metals and are prepared by standard procedures but may
5.2.6 An engineering drawing of the mandrel, the electro-
require an additional thin parting film to facilitate separation of
formed article, and auxiliary equipment or fixture for separat-
the electroform from the mandrel (unless the mandrel is
ing the electroform from the mandrel should be prepared. The
removed by melting or chemical dissolution).
drawing of the mandrel should provide for electrical connec-
5.1.3 Whether or not a permanent or expendable mandrel
tions to be made in nonfunctional areas of the electroform. It
should be used is largely dependent on the particular article
should provide reference points for and mechanical means of
that is to be electroformed. If no reentrant shapes or angles are
holding if finish machining is necessary before removal of the
involved, it is possible to use permanent, rigid mandrels that
mandrel.
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 (2003)
NOTE—Examplesofdepositdistributiononcontoursthatrequirespecialconsiderationareshowninanexaggeratedfashion.Thedesignershouldconfer
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
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.Porousmaterials,forexample,leatherandplastic,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.Itisoftenpreferabletousethinfilmsoflacquerto 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 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 B 183, B 242,
ofthemandrelusingadouble-nozzlespraygun.Thechemicals B 254, B 281, and B 558, 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 (2003)
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 inTable 2. Similar
in Guide B 253 to achieve a degree of adhesion that will
information for copper electroforming is given in Table 3.
prevent lifting of the deposit from the mandrel. When low-
s
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.