References cited in this section

2. A. Squitero, Designing Electroformed Parts, Machine Design, 9 May 1963

3. ASTM B 450, "Standard Practice for Engineering Design of Electroformed Articles," ASTM

4. ASTM B 431, "Standard Practice for Processing of Mandrels for Electroforming," ASTM Electroforming Solutions and Operating Variables

Nickel Electroforming Solutions. Nickel, the most commonly electroformed metal, is plated from Watts, fluoborate, and sulfamate solutions. The last is the most widely used due to lower stresses in the deposits and ease of operation. Nickel is deposited from most baths with moderate to high tensile stress. If uncontrolled, this stress can make removal of the mandrel difficult, can result in distorted parts after mandrel separation, and can even result in deposit cracking. In general, the chloride-free sulfamate bath produces the lowest internal stresses of all the nickel baths. Typical nickel sulfamate electrolyte compositions, operating conditions, and deposit mechanical properties are shown in Table 1. Effects of changes in operating variables on mechanical properties of nickel sulfamate deposits are described in Table 2. Similar information for all commonly used nickel electroforming baths is given in ASTM B 503 (Ref 5).

Table 1 Nickel electroforming solutions and selected properties of the deposits

Parameter

Watts nickel

Nickel sulfamate

Electrolyte composition, g/L (oz/gal)

NiS046H20--225-300 (30-40)

Ni(S03NH2)2--315-450 (42-60)

NiCl26H20--37.5-52.5 (5-7)

H3B03--30-45 (4-6)

H3B03--30-45 (4-6)

NiCl2 6H20--0-22. 5 (0-3)

Operating conditions

Temperature, °C (°F)

44-66 (115-150)

32-60 (90-140)

Agitation

Air or mechanical

Air or mechanical

Cathode current density, A/dm2 (A/ft2)

270-1075 (25-100)

50-3225 (5-300)

Anodes

Soluble nickel

Soluble nickel

pH

3.0-4.2

3.5-4.5

Mechanical properties

Tensile strength, MPa (ksi)

345-482 (50-70)

410-620 (60-90)

Elongation, %

15-25

10-25

Hardness, HV100

130-200

170-230

Internal tensile stress, MPa (ksi)

125-186 (18-27)

0-55 (0-8)

Table 2 Variables affecting mechanical properties of deposits from nickel sulfamate electrolytes

Property

Operational effects

Solution composition effects

Tensile strength

Decreases with increasing temperature to 49 °C, then increases slowly with further temperature increase. Increases with increasing pH. Decreases with increasing current density.

Decreases slightly with increasing nickel content.

Elongation

Decreases as the temperature varies in either direction from 43 °C. Decreases with increasing pH. Increases moderately with increasing current density.

Increases slightly with increasing nickel content. Increases slightly with increasing chloride content.

Hardness

Increases with increasing temperature within operating range suggested. Increases with increasing solution pH.Reaches a minimum at about 13 A/dm2.

Decreases slightly with increasing concentration of nickel ion. Decreases slightly with increasing chloride content.

Internal stress

Decreases with increasing solution temperature. Reaches a minimum at pH 4.0-4.2. Increases with increasing current density.

Relatively independent of variation in nickel ion content within range. Increases significantly with increasing chloride content.

Copper electroforming solutions of significance are the acid sulfate and fluoborate baths. Table 3 lists typical compositions, operating conditions, and mechanical properties for these baths. Changes in operating variables will affect mechanical properties of copper sulfate deposits, as noted in Table 4. Similar information for effects of variable changes on copper fluoborate deposits are found in ASTM B 503 (Ref 5).

Table 3 Copper electroforming solutions and selected properties of deposits

Parameter

Copper sulfate

Copper fluoborate

Electrolyte composition, g/L (oz/gal)

CuS045H20--210-240 (28-32)

Cu(BF4)2--225-450 (30-60)

H2S04--52-75 (7-10)

HBF4--To maintain pH at 0.151.5

Operating conditions

Temperature, °C (°F)

21-32 (70-90)

21-54 (70-129)

Agitation

Air or mechanical

Air or mechanical

Cathode current density, A/dm2 (A/ft2)

1-10 (9.3-93)

8-44 (75-410)

Anodes

Oxygen-free, high-conductivity copper or phosphorized copper

Soluble copper

Mechanical properties

Tensile strength, MPa (ksi)

205-380 (30-55)

140-345 (20-50)

Elongation, %

15-25

5-25

Hardness, HV100

45-70

40-80

Internal tensile stress, MPa (ksi)

0-10 (0-1.45)

0-105 (0-15)

Table 4 Variables affecting mechanical properties of deposits from acid copper sulfate electrolytes

Property

Operational effects

Solution composition effects

Tensile strength

Decreases slightly with increasing solution temperature. Increases significantly with increase in cathode current density.

Relatively independent of changes in copper sulfate concentration within the range suggested. Relatively independent of changes in sulfuric acid concentration within the range suggested.

Elongation

Decreases with increasing solution temperature. Increases slightly with increasing cathode current density.

High acid concentrations, particularly with low copper sulfate concentration, tend to reduce elongation slightly.

Hardness

Decreases slightly with increasing solution temperature. Relatively independent of change in cathode current density.

Relatively independent of copper sulfate concentration. Increases slightly with increasing acid concentration.

Internal stress

Increases with increasing solution temperature. Increases with increasing cathode current density.

Relatively independent of copper sulfate concentration. Decreases very slightly with increasing acid concentration.

Iron Electroforming Solutions. Iron electroforming, while not in major industrial production today, is technically usable if precautions are followed. Three types of electroforming baths exist as slightly acidic systems: sulfate, fluoborate, and sulfamate systems. A fourth system is the highly acidic chloride system, which uses ferrous chloride/calcium chloride operating between 88 and 99 °C (190 and 210 °F). Table 5 presents condensed details of the four baths and primary operating conditions. Except for deposits from the chloride bath, all other baths produce iron deposits brittle in nature and not usable without special thermal treatment, stress-reducing additives, or backup deposits to protect the brittle nature of the iron films. The chloride deposits can be best used with a postplating heat treatment of 260 °C (500 °F) or above to ensure ductility.

Table 5 Iron electroforming solutions and operating conditions

Parameter

Value

Chloride bath

Ferrous chloride (dihydrate), g/L (oz/gal)

300-450 (40-60)

Calcium chloride, g/L (oz/gal)

150-185 (20-25)

Temperature, °C (°F)

90-99 (190-210)

pH (HCl)

0.2-1.8

Current density, A/dm2 (A/ft2)

Without agitation

2-8.5 (20-80)

With agitation

2-21 (20-200)

Sulfate bath

Ferrous sulfate, g/L (oz/gal)

240 (32)

pH

2.8-3.5

Temperature, °C (°F)

32-65 (90-150)

Current density, max, A/dm2 (A/ft2)

at 32 °C (90 °F)

4.3 (40)

at 65 °C (150 °F)

10 (100)

Surface tension, dynes/cm

40

Cathode agitation

Desirable

Fluoborate bath

Iron fluoborate, g/L (oz/gal)

227 (30.3)

Metallic iron, g/L (oz/gal)

55.2 (7.37)

Sodium chloride, g/L (oz/gal)

10.0 (1.34)

Baumé, degrees, at 27 °C (80 °F)

19-21

pH (colorimetric)

3.0-3.4

Temperature, °C (°F)

57-63 (135-145)

Current density (cathode-average), A/dm2 (A/ft2)

2-10 (20-90)

Tank voltage, avg

2-6

Sulfamate bath

Ferrous iron, g/L (oz/gal)

75 (10)

Ammonium sulfamate, g/L (oz/gal)

30-37 (4-5)

Sodium chloride, g/L (oz/gal)

37-45 (5-6)

Temperature, °C (°F)

50-60 (120-140)

Current density, A/dm2 (A/ft2)

5.4 (50)

PH

2.7-3.0

0 0

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