ASM Metals HandBook Vol. 14 - Forming and Forging

Подождите немного. Документ загружается.

Fig. 2 Minimum bending limits for press-

brake versus slower (hydraulic) bending of beryllium sheet in

transverse and longitudinal directions. r, bend radius; t, sheet thickness

In a laboratory, a radius of 2 t was bent in beryllium sheet at the rate of 50 mm/min (2 in./min), and a radius of 5 t at

305 mm/min (12 in./min). Forming temperature in both cases was 745 °C (1375 °F).

Effect of Fabrication History. Beryllium products consolidated by vacuum hot pressing have low ductility, even at a

theoretical density of 100%. The ductility of hot pressed beryllium can be increased by hot mechanical working.

Forming of Beryllium

Revised by Larry A. Grant, Electrofusion Corporation

Equipment and Tooling

Presses operated by air or hydraulic systems are usually used for forming beryllium, because of the slow speeds required.

Standard mechanical presses or other fast forming presses are not suitable.

Critical components of the equipment must be protected against damage by the heat of forming. This protection usually is

achieved by means of simple insulation.

Tooling. Because the tools used for forming beryllium will be heated, allowances must be made for thermal expansion,

high-temperature strength, and oxidation when selecting tool material and designing tools. Tooling requirements for

forming beryllium are similar to those for hot forming titanium (see the article "Forming of Titanium and Titanium

Alloys" in this Volume). When only a few pieces are required, mild steel is usually used for dies. However, mild steel

oxidizes rapidly at elevated temperatures, and when more than a few identical pieces are to be formed, the best practice is

to make dies from hot work die steels, stainless steel, or one of the nickel-base or cobalt-base heat-resistant alloys.

Forming of Beryllium

Revised by Larry A. Grant, Electrofusion Corporation

Heating Dies and Workpieces

In most forming applications, both the die and the workpiece must be preheated. Dies are specially constructed to permit

heating; heat may be supplied by either electrical elements or gas burners. Although sometimes torches are satisfactory

for heating the work (as when heating sheet for spinning), usually a furnace is preferred. No specially prepared

atmosphere is needed.

At the maximum temperature used for forming beryllium, surface oxidation is usually negligible. However, if desired, to

prevent surface discoloration (hard oxide layer), the workpiece can be coated with a film of commercial heat-resistant oil.

After forming, the film of oil can be removed by wet blasting, or by degreasing with an agent such as trichloroethylene.

In the forming of thin sheet (less than ~1 mm, or 0.040 in., thick), cooling of the work between the furnace and the

forming equipment is often a problem. Overheating to compensate for this heat loss is not recommended. One satisfactory

solution is to "sandwich" thin sheets of beryllium between two sheets of low-carbon steel. This sandwich is retained

throughout heating and forming.

Forming of Beryllium

Revised by Larry A. Grant, Electrofusion Corporation

Stress Relieving

Stress relieving between stages of forming, or after forming is completed, is needed only in the forming of relatively thick

sheet or in severe forming. For some finish-formed parts, stress relieving has proved an effective means of counteracting

"oil canning" or excessive warpage. When stress relieving is used, regardless of whether it is an intermediate step or a

final operation, holding at 705 to 760 °C (1300 to 1400 °F) for 30 min is recommended. No specially prepared

atmosphere is needed.

Forming of Beryllium

Revised by Larry A. Grant, Electrofusion Corporation

Lubrication

Lubrication or coating of some type is needed in most beryllium forming operations. For less severe operations, such as

bending, powdered mica has been used.

For operations such as joggling, forming in matched dies, or deep drawing, colloidal graphite in oil is commonly used.

The role of lubrication is especially critical in deep drawing, and is discussed in more detail in the section "Deep

Drawing" in this article.

Forming of Beryllium

Revised by Larry A. Grant, Electrofusion Corporation

Safety Practice

No special precautions or safety measures are required in forming of beryllium because no fines or oxide dust is created

in forming; and the maximum temperature (815 °C, or 1500 °F) used for preheating causes the formation of only a thin

film of hard oxide, which under normal operating conditions will not harm personnel. Extreme caution should be used,

however, and safety equipment should be available in the event of a furnace overrun.

However, if parts require cleaning after forming and if grit blasting is used, the wet method is recommended. Wet blasting

minimizes the possibility that beryllium oxide dust will contaminate the surrounding atmosphere. Adequate ventilation

must be provided if parts are processed by chemical etching after forming.

The usual precautions observed in working with beryllium must be taken. Details on protection can be obtained from the

publication "Health Protection in Beryllium Facilities," which is available from the U.S. Atomic Energy Commission.

Also, a video tape, "Beryllium: Safe Handling," is available through Brush Wellman Inc.

Forming of Beryllium

Revised by Larry A. Grant, Electrofusion Corporation

Deep Drawing (Ref 1)

Deep drawing is the forming of deeply recessed (cuplike) parts by means of plastic flow of the material (see the article

"Deep Drawing" in this Volume). Tooling consists of a punch and a suitable die or draw ring. Normally, the deformation

in deep drawing is actually a combination of deep drawing and stretching.

There are two parameters that must be under control during any successful deep-drawing operation: friction and hold-

down pressure. Both can be controlled by proper die design and lubricant selection, as discussed below.

Lubrication is required to prevent galling between the beryllium workpiece and the die. A lubricant film must be

maintained over that portion of the blank surface making contact with the drawing surfaces of the die throughout the

entire draw. Because elevated temperatures (595 to 675 °C, or 1100 to 1250 °F, for the workpiece; 400 to 500 °C, or 750

to 930 °F, for the dies) are required to deep draw beryllium, conventional lubricants applied directly to the blank and die

will burn off, causing galling between workpiece and die at high-pressure areas such as the draw ring. The solution to this

problem is best achieved by using die materials that are self-lubricating, such as graphite or an overlay of colloidal

suspension of graphite on an asbestos paper carrier.

The technique of using consolidated graphite as a self-lubricating die material was initially developed for forming small,

thin-walled parts to finished size. This technique has evolved to the point that very deep drawing of 6.35 mm (0.25 in.)

thick blanks over a graphite draw ring is routine. The disadvantage is that such draw rings have short service life.

Organic emulsified suspensions of powdered graphite, aluminum, and copper have all been used successfully to lubricate

punches to facilitate part stripping. These materials can also be applied to the draw ring to improve lubricity of the

drawing surface under the graphite-impregnated paper.

Blank development for deep drawing of beryllium generally follows the same rules as for other metals. Blanks too

thin to support themselves during the early stages of drawing will buckle or wrinkle. A restraining force is required to

prevent this.

There are numerous factors involved in determining whether blank restraint is required during any drawing operation. The

two most important are the ratio of blank diameter d to blank thickness t and the percentage of reduction from one draw to

the next.

The relationship between reduction R and d/t is shown in Fig. 3 for cylindrical parts, whether they are flat bottomed or

hemispherical cups. The areas under the curves were determined experimentally, with the curves themselves being the

normal limit of formability for a given reduction at a given d/t ratio.

Fig. 3 Percent reduction in deep-drawing versus diameter-to-thickness (d/t

) ratio for deep drawing of

cylindrical beryllium shells. X and O, experimental observations used to derive the curve limits; d,

blank

diameter; t, blank thickness; shaded areas, marginal. Source: Ref 1.

The curves in Fig. 3 describe formability limits; therefore, some consideration should be given during design to avoid

borderline cases. Reductions of more than 50% are possible but will require partial drawing followed by several anneals,

usually with a high failure rate. Several stages of tooling requiring smaller reductions is a more practical approach.

Tool Design. There are many different tool designs for deep drawing sheet metal parts. Two general types will be

described here. One type does not apply blank restraint to prevent wrinkling and is referred to as single action. The other

type does apply blank restraint and is referred to as double action.

Single-action tooling should be used to form parts that fall in the no-restraint section of Fig. 3. Double-action tooling, or

tooling which applies blank restraint to avoid wrinkling, was developed in two forms. In one system, the lower cushion

ram in a hydraulic press is used as the second action for blank restraint (Fig. 4). The other type of double-action tooling

used to deep draw beryllium are described in detail in Ref 1.

Fig. 4 A double-

action tool for deep drawing of beryllium that uses the action of the lower press action for

blank restraint. Lubrication with

this type of tooling is best achieved using asbestos paper impregnated with

colloidal graphite (see inset). Source: Ref 2.

Materials used for beryllium deep-drawing tooling need not be exotic. Gray cast iron is satisfactory for most punch and

die applications. Drawing surfaces are usually made from a free-machining tool steel or, in the case of very large dies,

low-carbon steel that has been carburized after machining.

Strain rates during deep drawing of beryllium may vary widely, depending on the severity of the draw. For deep

drawing simple hemispherical shells, punch speeds of 760 to 1270 mm/min (30 to 50 in./min) are commonly used. With

optimal die clearance and lubrication, strain rates in excess of 2500 mm/min (100 in./min) have been observed in

successful deep draws.

Applications. Numerous shapes have been deep drawn from beryllium. Considerable material savings may be achieved

by deep drawing rather than machining thin-walled parts. The process lends itself to cup-shaped parts that have a slightly

thicker wall at the equator than at the pole because of thickening in this area during forming.

References cited in this section

J.J. Blakeslee, chapter 7, Metalworking IV: Forming, in Beryllium Science and Technology,

Vol 2, D.R.

Floyd and J.N. Lowe, Ed., Plenum Press, 1979, p 107-124

J.L. Frankeny and D.R. Floyd, "Ingot Sheet Beryllium Fabrication," RFP-910, Rock

y Flats Division, Dow

Chemical Company, Feb 1968

Forming of Beryllium

Revised by Larry A. Grant, Electrofusion Corporation

Three-Roll Bending (Ref 1)

Three-roll bending is a process for shaping smoothly contoured, large-radius parts by applying three-point bending forces

progressively along the part surface (see the article "Three-Roll Forming" in this Volume). Usually one or more of the

forming rolls is driven. The process has been used to form curved panel sections and full cylinders from beryllium. As in

all forming operations for beryllium, it is necessary to heat the blank to achieve the necessary ductility to avoid cracking.

Applications. Three-roll bending has been used to form precision beryllium cylinders. The cylinders were joined by an

electron beam fusion weld and are round within 0.5 mm (0.02 in.) total indicator reading on the diameter.

Panels for the Agena spacecraft also have been formed to a 762 mm (30 in.) radius of curvature. There were two sizes of

panels formed, 635 × 635 mm (25 × 25 in.) and 559 × 355 mm (22 × 14 in.), at thicknesses of 1.4 and 1.88 mm (0.055

and 0.074 in.), respectively, from cross-rolled beryllium powder sheet. The flat beryllium sheet was heated to about 427

°C (800 °F), placed on a stainless steel sheet somewhat longer than the beryllium, and manually rolled to contour. The

stainless steel sheet was used to "lead-in" the beryllium and reduce the flat end inherent to roll forming. The rolled panels

were stress-relieved at 732 °C (1350 °F) for 20 min.

Reference cited in this section

J.J. Blakeslee, chapter 7, Metalworking IV: Forming, in Beryllium Science and Technology,

Vol 2, D.R.

Floyd and J.N. Lowe, Ed., Plenum Press, 1979, p 107-124

Forming of Beryllium

Revised by Larry A. Grant, Electrofusion Corporation

Stretch Forming (Ref 1)

Stretch forming is the shaping of a sheet or part, usually of uniform cross section, by first applying suitable tension or

stretch, then wrapping it around a die of desired shape (see the article "Stretch Forming" in this Volume). When applying

this technique to beryllium, the wrapping operation usually takes place quite slowly.

Tooling. Two commonly used types of tooling used to stretch form beryllium are generally described as open-die and

closed-die tooling. Open die, the most common, consists of a male die with the desired contour and some means of

forcing the blank to assume that contour. Tension is not normally required for beryllium because the high modulus resists

buckling and wrinkling.

Closed die tooling has male and female counterparts. The male die is used to force the blank into the female die, thereby

causing the blank to assume the contour of the male die. This type of tooling lends itself well to beryllium forming

because both portions of the die may be heated to facilitate maintenance of the heat necessary in the blank to avoid

cracking. Friction forces on the female die can help to restrain the part and cause stretching.

Reference cited in this section

J.J. Blakeslee, chapter 7, Metalworking IV: Forming, in Beryllium Science and Technology,

Vol 2, D.R.

Floyd and J.N. Lowe, Ed., Plenum Press, 1979, p 107-124

Forming of Beryllium

Revised by Larry A. Grant, Electrofusion Corporation

Spinning

Beryllium sheets up to 5.1 mm (0.200 in.) thick have been successfully formed by spinning. For sheets less than about 1

mm (0.040 in.) thick, a common practice is to sandwich the beryllium between two 1.5 mm (0.060 in.) sheets of low-

carbon steel and heat the sandwich to 620 °C (1150 °F) for spinning. The steel sheets not only help to maintain

temperature, but also help to prevent buckling. Beryllium sheets more than about 1 mm (0.040 in.) thick usually are not

sandwiched between steel sheets for spinning, and are heated to 730 to 815 °C (1350 to 1500 °F).

Hemispherical shapes have been spun in as many as nine stages with no adverse effect on the properties of the beryllium.

The part and mandrel often are torch-heated during spinning.

Lubrication is especially important in spinning. Colloidal graphite or glass is usually used. Wet blasting is the

recommended means of cleaning the workpiece after spinning.

Figure 5 plots combinations of conditions under which parts of a variety of shapes have been successfully produced by

spinning cross-rolled beryllium powder sheet. The points plotted, however, represent only limited data, and many more

points would have to be established before it would be safe to designate dimensional limitations for spinning specific

shapes. More information on the spinning process is available in the article "Spinning" in this Volume.

Fig. 5 Dimensional combinations for the successful spinning of beryllium sheet. d

, blank diameter; d

diameter of spun part; t, blank thickness; h, height of spun part

Forming of Beryllium

Revised by Larry A. Grant, Electrofusion Corporation

References

J.J. Blakeslee, chapter 7, Metalworking IV: Forming, in Beryllium Science and Technology,

Vol 2, D.R.

Floyd and J.N. Lowe, Ed., Plenum Press, 1979, p 107-124

J.L. Frankeny and D.R. Floyd, "Ingot Sheet Beryllium Fabrication," RFP-

910, Rocky Flats Division, Dow

Chemical Company, Feb 1968

Forming of Copper and Copper Alloys

Frank Mandigo and Jack Crane, Olin Corporation

Introduction

COPPER AND MOST COPPER ALLOYS are readily formed at all sheet gages. The copper alloys commonly formed are

characterized by strength and work-hardening rates between those of steel and aluminum alloys. This article will review

the general characteristics of copper and copper alloys and how these characteristics affect the behavior of strip in

different types of forming operations. The attempt is to provide an understanding of copper alloy formability coupled with

illustrative data rather than to offer a complete single-source alloy data reference.

Acknowledgements

The authors would like to acknowledge the significant contributions to this article from John Breedis, Olin Corporation,

and John Turn, Brush Wellman Inc. Without their assistance, completion of this document would not have been possible.

Forming of Copper and Copper Alloys

Frank Mandigo and Jack Crane, Olin Corporation

General Considerations

The combination of moderate-to-high strength, high electrical and thermal conductivity, modest cost, good corrosion and

stress-corrosion resistance, and ease of joining, coupled with good formability, accounts for the use of copper and copper

alloys in a wide range of applications. The list of typical applications given below reveals the diversity of forming

operations used:

Application

Forming operations

Electrical terminals and connectors

Bending, stretch forming, blanking, coining, drawing

Electronic lead frames

Bending, coining, blanking

Hollow ware, flatware

Roll forming, blanking

Builder's hardware

Shallow and deep drawing, and stretch forming operations

Heat exchangers

Roll forming, bending, sinking, blanking

Coinage

Blanking, coining, embossing

Bellows, flexible hose

Cupping, deep drawing, bending

Musical instruments

Blanking, drawing, coining, bending, spinning

Ammunition Blanking, deep drawing

These applications are illustrated in Fig. 1, 2, 3, 4, 5, 6, 7, and 8.

Fig. 1 Electrical and electronic applications for formed copper alloy pa

rts. (a) Connectors used in home

appliances and automotive electrical systems. (b) Copper alloy leadframe for a semiconductor device.

Fig. 2 Typical household flatware utensils formed from copper alloys.

Fig. 3 Builder's hardware formed from copper alloys. (a) Doorknob fabricated by deep drawing.

(b) Recessed

fixture for kitchen and bathroom accessories.

Fig. 4 Automotive radiator fabricated from several formed copper alloy components, including a deep-

drawn

water tank, roll-formed cooling tubes, and formed cooling fins.

Fig. 5 Copper alloy U.S. currency with heavy coining and embossing.

Fig. 6 Deep-drawn and corrugated copper alloy bellows.