ASM Metals HandBook Vol. 14 - Forming and Forging

Подождите немного. Документ загружается.

Fig. 7 French horn fabricated from copper alloys using complex bending and spinning operations.

Fig. 8 Ammunition using a deep-drawn copper alloy cartridge case.

The forming of any part involves the interaction of material, tooling, and lubrication. Tooling and lubrication are

discussed in the article "Presses and Auxiliary Equipment for Forming of Sheet Metal" and "Selection and Use of

Lubricants in Forming of Sheet Metal" in this Volume and are noted in this article only where there are unique or specific

requirements for a copper alloy or a given forming operation. The forming characteristics of copper and copper alloys will

be discussed at length. All of the various major forming operations considered in this article--blanking, bending, stretch

forming, drawing, and coining--depend on some optimal combination of strength, ductility, and work-hardening behavior

of the sheet metal to provide the most cost-effective part. Therefore, much of this article is devoted to understanding the

trade-offs in strength, work-hardening, and ductility available by selection of material composition and temper. Strain rate

sensitivity m is also a factor in some forming operations. However, m is of practical significance only at elevated

temperature. A more comprehensive treatment of the relationships between these materials characteristics and formability

is available in the article "Formability Testing of Sheet Metal" in this Volume and in the article "Sheet Formability

Testing" in Mechanical Testing, Volume 8 of ASM Handbook, formerly 9th Edition Metals Handbook.

Other materials characteristics that reflect formability and can be determined using simple test specimens include the

plastic-strain ratio r, which is a measure of sheet anisotropy; the limiting draw ratio (LDR); bulge height; and minimum

bend-forming radius. These measurements are primarily used to assess drawing and stretching capacity specific to a given

alloy composition, cold-work level, and texture development.

Effects of Composition, Cold Work, and Heat Treatment on Formability

Copper alloys are primarily strengthened by cold work or by alloying additions that solid solution strengthen and enhance

strain hardening. A finely dispersed second phase is sometimes used as a grain refiner to maximize strength/ductility

combinations and/or as a means of ensuring good surface finish after forming.

Precipitation hardening is important to a small but important class of alloys, most notably, the beryllium copper alloys.

Copper-nickel-aluminum and copper-nickel-silicon alloys are also commercially important precipitation-hardenable

alloys. Spinodal and/or precipitation hardening is available in the copper-nickel-tin and copper-nickel-chromium systems.

Hardening by martensite transformation is available in the copper-aluminum system, but is rarely used commercially.

Copper alloys are classified using the Unified Numbering System (UNS). The designations of the Copper Development

Association (CDA) are also used and correspond closely to UNS designations. Wrought copper alloys are divided in the

UNS system into the following groups:

Copper and high-copper alloys

C1xxxx

Zinc brasses

C2xxxx

Zinc-palladium brasses

C3xxxx

Zinc-tin brasses

C4xxxx

Tin bronzes

C5xxxx

Aluminum, manganese, and silicon

C6xxxx

Copper-nickel and copper-nickel-zinc alloys

C7xxxx

Copper alloys are supplied in annealed (soft) and cold-worked (hard) tempers, as defined in Table 1. These designations

are only guidelines; the supplier should be consulted for specific property/temper characteristics. Temper designations for

precipitation-hardened alloys are covered in the section "Precipitation Hardening and Cold Working" in this article.

Table 1 ASTM B 601 temper designations for copper and copper alloys

Temper designation

Temper name or material condition

Annealed tempers

025

Hot rolled and annealed

050

Light annealed

060

Soft annealed

061

Annealed

065

Drawing annealed

068

Deep-drawing annealed

070

Dead soft annealed

080

Annealed to temper-- hard

081

Annealed to temper-- hard

082

Annealed to temper-- hard

OS005

Average grain size 0.005 mm

OS010

Average grain size 0.010 mm

OS015

Average grain size 0.015 mm

OS025

Average grain size 0.025 mm

OS035

Average grain size 0.035 mm

OS050

Average grain size 0.050 mm

OS070

Average grain size 0.070 mm

OS100

Average grain size 0.100 mm

OS120

Average grain size 0.120 mm

OS150

Average grain size 0.150 mm

OS200

Average grain size 0.200 mm

Cold-worked tempers

H00

hard

H01

hard

H02

hard

H03

hard

H04

Hard

H06

Extra hard

H08

Spring

H10

Extra spring

H12

Special spring

H13

Ultra spring

H14

Super spring

Cold-worked and stress-relieved tempers

HR01

H01 and stress relieved

HR02

H02 and stress relieved

HR04

H04 and stress relieved

HR06

H06 and stress relieved

HR08

H08 and stress relieved

HR10

H10 and stress relieved

HR50

Drawn and stress relieved

Cold-worked and order-strengthened tempers

HT04

H04 and order heat treated

HT06

H06 and order heat treated

HT08 H08 and order heat treated

Solid-Solution Strengthening and Cold Working. Solute elements provide a major means of strengthening

copper, and the magnitude of strengthening depends on the type and level of addition. Table 2 lists mechanical properties

resulting from various alloying additions to copper in the annealed condition. Neither tensile elongation (Table 2) nor

reduction in area fully defines usable formability and should not be used to correlate formability; they can, however, offer

some insight into formability. It is clear from Table 2 that strength higher than that of pure copper (Alloy C11000) can be

acquired with limited or no loss of ductility by solid-solution alloying.

Table 2 Mechanical properties of selected solid-solution copper alloys

Grain sizes of all materials listed ranged from 0.010 to 0.025 mm (0.0004 to 0.001 in.).

0.2% offset

yield strength

Tensile

strength

Alloy designation and common name

Nominal

composition, %

MPa ksi MPa

ksi

Elongation,

C11000 (Electrolytic tough-pitch) 99.90 min Cu 83 12 241 35

C21000 (Gilding, 95%) Cu-5Zn 97 14 262 38

C23000 (Red brass, 85%) Cu-15Zn 110 16 290 42

C26000 (Cartridge brass, 70%) Cu-30Zn 179 26 379 55

C50500 (Phosphor bronze, 1.25% E) Cu-1.4Sn 124 18 290 42

C51000 (Phosphor bronze, 5% A) Cu-5Sn 165 24 345 50

C61000

(a)

(. . .) Cu-8Al 207 30 483 70

C70600 (Copper nickel, 10%) Cu-10Ni 124 18 317 46

C71500 (Copper nickel, 30%) Cu-30Ni 172 25 400 58

C75200 (Nickel silver, 65-18) Cu-18Ni-18Zn 179 26 414 60 37

(a)

Available only as tube, but properties are illustrative of copper-

aluminum

alloy strip properties.

Figure 9 shows the work-hardening behavior of copper (C11000) and several copper alloys in terms of strength and

ductility versus cold reduction. The relative work-hardening effects of various alloying elements are evident; the strong

effect of aluminum is contrasted with the weak effect of nickel, with zinc and tin being intermediate. Ductility, as

indicated by tensile elongation, decreases with cold reduction. Again, however, the combination of strength and ductility

is enhanced by solid-solution additives even after cold working.

Fig. 9 Work-hardening behavior of copper and some solid-

solution copper alloys. (a) Effect of cold work by

rolling reduction on ultimate tensile strength

. (b) Effect of cold work on yield strength. (c) Effect of cold work on

elongation.

Precipitation Hardening and Cold Working. Precipitation-hardenable alloys offer the opportunity to form parts in

the maximum-ductility (solution-annealed) condition and then harden the formed part to maximum strength with a

precipitation heat treatment. However, fabrication requirements may preclude this option. Alloys containing 0.15 to 2.0%

Be can be strengthened by solid-state precipitation. For alloys with high beryllium content (1.8 to 2.0%), combinations of

cold work and elevated-temperature aging produce material with tensile strength above 1380 MPa (200 ksi). Lower

beryllium contents are used to sacrifice some strength for better thermal and electrical conductivities. Forming can

precede aging or follow it; the choice is based on property and formability requirements, as well as practicality.

In many cases, volume changes that accompany aging, or other fabricating constraints, preclude aging treatment of the

formed part, and the precipitation-hardened alloys are therefore provided in mill-hardened tempers. Mill-hardened alloys

are either solution annealed or cold rolled before being given an aging treatment at the mill to produce a specific set of

final properties.

Mill-hardened tempers are designed to balance the requirements of strength and formability. They are of particular

importance for intricate parts such as electronic connectors, where elimination of customer heat treatment and cleaning

steps are important to the economics and/or fabrication of the part. Parts that require sharp bends or maximum formability

should be formed from the annealed or rolled tempers before final aging to reach the desired peak strength.

Mill-hardened tempers are much stronger than unaged rolled tempers, but compromise some formability compared to the

rolled tempers in favor of avoiding customer aging and cleaning. The grain size of these alloys is less than 0.03 mm

(0.001 in.) for gages from 0.1 to 1.27 mm (0.004 to 0.050 in.) thick. Temper designations for precipitation-hardening

systems are given in Table 3; mill-hardened temper designations correspond to supplier designations.

Table 3 ASTM B 601 temper designations for precipitation-hardened copper alloys

Temper designation

Temper name or material condition

Solution-treated temper

TB00

Solution heat treated

Solution-treated and cold-worked tempers

TD00

TB00 cold worked to hard

TD01

TB00 cold worked to hard

TD02

TB00 cold worked to hard

TD03

TB00 cold worked to hard

TD04

TB00 cold worked to full hard

Precipitation-hardened temper

TF00

TB00 and precipitation hardened

Cold-worked and precipitation-hardened tempers

TH01

TD01 and precipitation hardened

TH02

TD02 and precipitation hardened

TH03

TD03 and precipitation hardened

TH04

TD04 and precipitation hardened

Precipitation-hardened and cold-worked tempers

TL00

TF00 cold worked to hard

TL01

TF00 cold worked to hard

TL02

TF00 cold worked to hard

TL04

TF00 cold worked to full hard

TL08

TF00 cold worked to spring

TL10

TF00 cold worked to extra spring

TR01

TL01 and stress relieved

TR02

TL02 and stress relieved

TR04

TL04 and stress relieved

Mill-hardened tempers

TM00

TM01

TM02

TM04

TM06

XHM

TM08 XHMS

The mechanical properties of four precipitation-hardenable alloys in the solution-annealed condition are given in Table 4.

The work-hardening behavior of several precipitation-hardening systems in the solution-annealed condition is shown in

Fig. 10. The strong effect of beryllium content on solid-solution strengthening and work hardening is evident in Fig. 10

for Alloy C17200. Table 5 lists the mechanical properties of selected tempers of mill-hardened alloys.

Table 4 Mechanical properties of precipitation-hardenable copper alloys in the annealed condition

0.2% offset yield strength

Tensile strength

UNS

designation

MPa ksi MPa ksi

Elongation, %

C17200 290 42 476 69

C17500 207 30 310 45

C70250 138 20 338 49

Table 5 Mechanical properties of mill-hardened copper alloys

0.2% offset yield strength

Tensile strength UNS designation

Temperature

(a)

MPa ksi MPa ksi

Elongation, %

C17410 TM04 655-862 95-125 758-896 110-130

4-15

C17500 HTR 758-965 110-140 827-1034

120-150

1-4

TM00 552 min 80 min 620 min 88 min

6 min

C70250

TR04 690 min 100 min 731 min 106 min

2 min

TM02 690-862 100-125 827-931 120-135

12-18

C17200

TM04 793-931 115-135 931-1034

135-150

9-15

C72400 TM02 690-827 100-120 876-1000

127-145

10-17

(a)

See Table 3.

Fig. 10 Work-hardening behavior of four precipitation-hardening copper alloys in the solution-

annealed

condition. (a) Effect of cold work by rolling reduction on ultimate tensile strength. (b) Effect of cold work on

yield strength. (c) Effect of cold work on elongation.

Postforming Heat Treatment. Heat treatments, aside from those employed to precipitation harden, are used after

forming to reduce susceptibility to stress corrosion (primarily the brasses) or to increase the stiffness or stress relaxation

resistance of electrical or electronic springs (mainly the brasses, aluminum bronzes, and copper-silicon alloys). These

postforming treatments are performed at low temperatures.

Formability of Copper Alloys Versus Other Metals

In forming a given part, no single materials property completely defines formability. As previously noted, formability can

best be rationalized in terms of the strength, work hardening, and ductility of a copper alloy, but these parameters do not

allow direct correlation with formability. The problem becomes even more difficult when comparing different alloy

systems--for example, ferrous and nonferrous.

Figure 11 shows the annealed ultimate tensile and yield strengths and response to cold rolling for AISI type 304 stainless

steel, 1045 steel, aluminum Alloy 1100, copper Alloy C11000, and some selected copper alloys. The high work-

hardening rate and strength of the austenitic stainless steel are evident. The copper alloys range from above aluminum to

above low-carbon steel in strength and work-hardening rate. A comparison of limiting draw ratio with the plastic-strain

ratio r for ferrous and nonferrous alloys is shown in Fig. 12. Increasing values of r and LDR reflect increasing drawability

(see the section "Drawing and Stretch Forming" in this article).

Fig. 11 Work-hardening behavior of copper alloys versus that of low-

carbon steel, austenitic stainless steel,

and aluminum. (a) Effect of cold work by rolling reduction on ultimate tensile strength.

(b) Effect of cold work

on yield strength.

Fig. 12 Plastic-strain ratio r versus limiting draw ratio for different metals. Source: Ref 1

In general, copper alloys offer better strength/formability combinations than most other alloy systems. The choice of

material system is usually based on economics, including material and other fabrication costs as well as properties.

In general, copper alloys offer better strength/formability combinations than most other alloy systems. The choice of

material system is usually based on economics, including material and other fabrication costs as well as properties.

Reference cited in this section

Sheet Metal Industries--Yearbook, Fuel and Metallurgical Journals Ltd., 1972/1973

Forming of Copper and Copper Alloys

Frank Mandigo and Jack Crane, Olin Corporation

Blanking and Piercing

Nature of the Operation. Blanking, piercing, and related cutting operations (trimming, notching, parting, and so on)

are often used to provide parts that are subsequently formed to final shape by such operations as bending, drawing,

coining, and spinning. Cutting operations are frequently conducted in the same press tooling used to form and shape the

final part geometry. The principal objective of any cutting operation is to produce a workpiece that has the correct

geometric shape, is free of distortion, and possesses sheared edges that are of sufficient quality to allow subsequent

forming, finishing, and/or handling operations.

Materials Considerations. Copper and copper alloys can be readily blanked and pierced. The strip characteristics that

directly affect the quality of the workpiece and/or final part produced by cutting operations are flatness, dimensional

tolerances, (width, thickness, and so on), and shear-to-break ratio. The flatness and dimensional tolerances of copper alloy

strip depend on the equipment and manufacturing expertise. The shear-to-break characteristics of strip depend on strip

composition and temper.

Effects of Alloy Composition and Temper. The quality of blanked edges--shear to break, rollover, breakout angle,

burr height, and so on--is determined by both die clearance and material characteristics. Burr-free and distortion-free parts

can be cut from annealed copper alloy strip at die clearances to about 5% of strip thickness. Unalloyed coppers, such as

C10100 and C10200, require smaller clearances (usually <5%) and less latitude in actual values to produce burr-free

edges, even in rolled tempers. Copper alloys that contain second-phase particles (for example, C19400), that have high

solute additions (such as C26000 or C51000), and/or that are cold rolled more than 50% generally exhibit high-quality

blanked edges at die clearances in the range of 3 to 12%. Low-lead additions to brass and other copper alloys will

decrease burrs and the shear-to-break ratio in blanking operations--but at some cost to formability in almost all types of

forming.

Forming of Copper and Copper Alloys

Frank Mandigo and Jack Crane, Olin Corporation

Bending

Nature of the Operation. Many connectors, terminals, and spring-like components are fabricated by simple bending

operations. Bending is an operation in which a blanked coupon is wrapped, wiped, or formed over a die to a specified

radius and bend angle. Bend formability is usually expressed as minimum bend radius R in terms of strip thickness t (R/t).

Minimum bend radius is defined as the smallest radius around which a specimen can be bent without cracks being

observed on the outer fiber (tension) surface. Bend deformation is highly localized and is confined to the region of the

workpiece in contact with the bending die. Workpiece thickness is not substantially reduced unless the bend radius is less

than 1.0t or the part is coined during bending. A detailed review of bend testing is provided in the Section "Bend Testing"

in Mechanical Testing, Volume 8 of ASM Handbook, formerly 9th Edition Metals Handbook.

Materials Characteristics. Ductility is the principal materials factor that determines bend formability. The ductility

factor of first order importance is the ability of a material to distribute strain in a highly localized region, that is, necking

strain. The necking strain available depends on alloy composition and temper. As strength is increased by cold work, the

ability of an alloy to distribute necking strain decreases. The extent to which bend formability is decreased with

increasing strength is dependent on the alloy composition and the strengthening mechanism. Conventional tensile

elongation cannot be used to predict bend formability, because it does not adequately account for the contribution of

necking strain. However, if the tensile specimen gage length were decreased to define an area of deformation equal to that

deformed during bending, comparable ductility values would be obtained.

Effect of Alloy Composition, Temper, and Orientation. Bend data for a wide range of copper alloys are

summarized in Table 6. Strength-to-bend formability characteristics are dependent on alloy composition, temper, and

orientation. The principal strengthening mechanism is through solute additions to increase the work-hardening rate. For

example, additions of 15 and 30% Zn to copper increase the tensile-strength-to-bend properties by 220 and 290 MPa (32

and 42 ksi), respectively, for 0.25 mm (0.010 in.) thick good-way bends at a bend radius of 0.4 mm ( in.). Precipitation

strengthening is also an important mechanism employed to improve the strength-to-bend performance of copper alloy

strip, particularly if the part is bent in a softer temper and subsequently aged to a higher strength.

Table 6 Maximum strengths required to make the indicated bends in various copper alloys

Maximum strength required to make bend of indicated radius in material of indicated thickness, MPa (ksi)

Good-way bend

Bad-way bend

UNS designation

0.25 (0.010)

(a)

0.50 (0.020)

(a)

0.76 (0.030)

(a)

0.25 (0.010)

(a)

0.50 (0.020)

(a)

0.76 (0.030)

(a)