Metal Forming

Bulk Deformation

Rolling Processes

Forging Processes

Extrusion Processes

Wire & Bare Drawing

Bending

METAL FOMING PROCESSMETAL FOMING PROCESSMETAL FOMING PROCESSMETAL FOMING PROCESS

Sheet Metalworking

Bending Operation

Deep or Cup Drawing

Shearing Processes

MiscallenouseProcesses

Bulk

Deformation Deformation

Processes

Bulk-Deformation Processes

PROCESS GENERAL CHARACTERISTICSForging Production of discrete parts with a set of dies; some finishing operations usually

necessary; similar parts can be made by casting and powder-metallurgy techniques;usually performed at elevated temperatures; dies and equipment costs are high;moderate to h igh labor costs; moderate to high operator skill.

RollingFlat Production of flat plate, sheet, and foil at high speeds, and with good surface finish,

especially in cold rolling; requires very high capital investment; low to moderate laborcost.

Shape Production of various structural shapes, such as I-beams and rails, at high speeds;includes thread and ring rolling; requires shaped rolls and expensive equipment; low tomoderate labor cost; moderate operator skill.

Extrusion Production of long lengths of solid or hollow products with constant cross-sections,usually performed at elevated temperatures; product is then cut to desired lengths;

TABLE 6.1 General characteristics of bulk deformation processes.

usually performed at elevated temperatures; product is then cut to desired lengths;can be competitive with roll forming; cold extrusion has similarities to forging and isused to make discrete products; moderate to high die and equipment cost; low tomoderate labor cost; low to moderate operator skill.

Drawing

Swaging

Production of long rod, wire, and tubing, with round or various cross-sections; smallercross-sections than extrusions; good surface finish; low to moderate die, equipmentand labor costs; low to moderate operator skill.Radial forging of discrete or long parts with various internal and external shapes;generally carried out at room temperature; low to moderate operator skill.

[1] Forging Operations

Forging can be carried out as:

a. cold working (T < 0.3Tm)

b. warm working (0.3Tm < T < 0.5Tm )

c. hot working (T > 0.6Tm)

Three basic types:Three basic types:

1. open-die forging (also known as upsetting)

2. Impression die forging

3. Closed-die forging

Ideal (homogeneous) Deformation

FIGURE 6.1 (a) Ideal deformation of a solid cylindrical specimen compressed between flat frictionless dies. This process is frictionless dies. This process is known as upsetting. (b) Deformation in upsetting with friction at the die-workpiece interfaces.

Equations for Open-Die Forging

Reduction in height =

and

%100*0

10

h

hh −

0

101 h

hhe

−=

=

1

01 ln

h

hε

and 01 h

ve −=&

11 h

v−=ε&

Grain Flow Lines

FIGURE 6.2 Grain flow lines in upsetting a solid steel cylinder at elevated temperatures. Note the highly inhomogeneous deformation and barreling. The different shape of the bottom section of the specimen (as compared with the top) results from the hot specimen resting on from the hot specimen resting on the lower, cool die before deformation proceeded. The bottom surface was chilled; thus it exhibits greater strength and hence deforms less than the top surface. Source: J. A. Schey et al., IIT Research Institute.

Impression-Die Forging

FIGURE 6.14 Schematic illustration of stages in impression-die forging. Note the FIGURE 6.14 Schematic illustration of stages in impression-die forging. Note the formation of flash, or excess material that is subsequently trimmed off.

Analysis

Simple shapes, without flashSimple shapes, with flashComplex shapes, with flash

3-55-88-12

F = (Kp)(Yf)(A)

TABLE 6.2 Range of Kp values in Eq. (6.21) for impression-die forging.

Load-Stroke Curve in Closed-Die Forging

FIGURE 6.15 Typical load-stroke curve for closed-die forging. Note the sharp increase in load after the flash begins to form. In hot-forging operations, the flash requires high levels of stress, because it is thin-that is, it stress, because it is thin-that is, it has a small h-and cooler than the bulk of the forging. Source: After T. Altan.

Orbital Forging Process

FIGURE 6.16 Schematic illustration of the orbital-forging process. Note that the die is in contact with only a portion of the workpiece surface. This process is also called rotary forging, swing forging, and rocking-die forging, and rocking-die forging and can be used for forming bevel gears, wheels, and bearing rings.

Heading Piercing Operations

FIGURE 6.17 Forging heads on fasteners such as bolts and rivets. These processes are called heading.

FIGURE 6.18 Examples of piercing operations.

Cogging Operation

FIGURE 6.19 Schematic illustration of a cogging operation on a rectangular bar. With simple tools, the thickness and cross-section of a bar can be reduced by multiple cogging operations. Note the barreling after cogging. Blacksmiths use a similar procedure to reduce the thickness of parts in small increments by heating the workpiece and hammering it numerous times.

Roll Forging Operation

FIGURE 6.20 Schematic illustration of a roll forging (cross-rolling) operation. Tapered leaf springs and knives can be made by this process with specially designed rolls. Source: After J. Holub.

Manufacture of Spherical Blanks

FIGURE 6.21 Production of steel balls for bearings by the skew-rolling process. Balls for bearings can also be made by the forging process shown in Fig. 6.22.

FIGURE 6.22 Production of steel balls by upsetting of a cylindrical blank. Note the formation of flash. The balls are subsequently ground and polished for use as ball bearings and in other mechanical components.

Defects in Forging

1. Surface Cracking: due to excessive stresses and poor die design

2. Internal Cracks: due to oversized billets

3. Cold Shuts: due to small corner radii in the mold

4. Exposed grains: poor material flow and original blank orientation

Forgings are generally anisotropic due to various directions in the metal flow.

Internal Defects In Forging

FIGURE 6.24 Internal defects produced in a forging because of an oversized billet. The die cavities are filled prematurely, and the material at the center of the part flows past the

FIGURE 6.23 Laps formed by buckling of the web during forging.

die cavities are filled prematurely, and the material at the center of the part flows past the filled regions as deformation continues.

Defect Formation In Forging

FIGURE 6.25 Effect of fillet radius on defect formation in forging. Small fillets (right side of drawings) cause the defects. Source: Aluminum Company of America.

Forging A Connecting Rod

FIGURE 6.26 Stages in forging a connecting rod for an internal combustion engine. Note the amount of flash that is necessary to fill the die cavities properly.

Features Of A Forging Die

FIGURE 6.27 Standard terminology for various features of a typical forging die.FIGURE 6.27 Standard terminology for various features of a typical forging die.

Hot-Forging Temperature Ranges

Metal �C �F Metal �C �FAluminum alloysCopper alloysNickel alloys

400-450625-950870-1230

750-8501150-17501600-2250

Alloy steelsTitanium alloysRefractory alloys

925-1260750-795975-1650

1700-23001400-18001800-3000

TABLE 6.3 Hot-forging temperature ranges for various metals.

Presses Used In Metalworking

FIGURE 6.28 Schematic illustration of various types of presses used in metalworking. The choice of the press is an important factor in the overall operation.

[2] Rolling Operations

Rolling is the process of reducing the thickness (flat rolling) or changing the cross-section (shape rolling) of a long workpiece by compressive forces applied through a set of rolls.

Rolling Operationsa. Flat Rollingb. Shape Rolling

Plates: thickness>0.25″Sheets: 0.004″<thickness<0.25″Sheets: 0.004″<thickness<0.25″Foils: thickness<0.004″

Ingot rolling is replaced by continuous casting/rolling with a higher efficiency and lower cost.

Rolling can be performed as hot, warm, or cold forming operations.

Flat-And-Shape-

Rolling Processes

FIGURE 6.29 Schematic outline of various flat-and-shape-rolling processes. Source: American Iron and Steel Institute.

Changes In Grain Structure (HOT)

FIGURE 6.30 Changes in the grain structure of cast or large-grain wrought metals during hot rolling. Hot rolling is an effective way to reduce grain size in metals for improved strength and ductility. Cast structures of ingots or continuous castings are converted to a wrought structure by hot working.

Mechanics of Flat-Rolling

wo and ho : initial width and thickness

wf and hf : final width and thickness

Vo and Vf : entry and exit velocities

Vr : tangential velocity of roll

R: roll radius

FIGURE 6.31 Schematic illustration of the flat-rolling process. A greater volume of metal is formed by rolling than by any other metalworking process.

L: roll gap

Neutral (No-Slip) Point

Vo : entry velocity of the workpiece

Vf : exit velocity of the workpiece

Vr : tangential velocity of roll

α: angle of acceptance

Forward Slip = rf VV −

FIGURE 6.32 Relative velocity distribution between roll and strip surfaces. Note the difference in the direction of frictional forces. The arrows represent the frictional forces acting on the strip.

Forward Slip = r

rf

V

VV −

Notes

At the “no-slip” point: Vr = Vworkpiece

(neutral point)

Before the neutral point: Vr > Vworkpiece

After the neutral point: Vr < Vworkpiece

Pressure Distribution in Rolling (1)

FIGURE 6.34 Pressure distribution in the roll gap as a function of the coefficient of friction. Note that as friction increases, the neutral point shifts toward the entry. Without friction, the rolls slip, and the neutral point shifts completely to the exit.

Pressure Distribution in Rolling (2)

FIGURE 6.35 Pressure distribution in the roll gap as a function of reduction in thickness. Note the increase in the area under the curves with increasing reduction in thickness, thus increasing the roll-separating force.

Effects of Front And Back Tension

FIGURE 6.36 Pressure distribution as a function of front and back tension. Note the shifting of the neutral point and the reduction in the area under the curves with increasing tension.

Forces and Power

Draft = ∆h = ho – hf = µ2 . R µ = tan α (angle of acceptance)

′= YwLF ..

YY 15.1=′

hRL ∆= .

HPFLN

PPower2π==

=

f

o

h

hlnε

n

KY

n

+=

1

.εHPPPower

000,33==

ω/2

.P

LFTTorque ===

Notes on Force Calculations

As friction increases, the draft, forces, power and the damage to surface finish increase.

Roll forces can be reduced by:–reducing friction–Reducing rolls size–Reducing draft–Reducing draft–Applying tension forces (back, front, or both)

Diverse effects of roll forces:–Rolls deflection–Rolls flattening

Problems in Rolling Operations

1. Rolls Deflection: forces bend rolls elastically, this results in thicker parts at the center (CROWN), which can be reduced by:

• Grinding rolls thicker at the center (CAMBER)~0.01“, or

• Bending rolls by applying moments at the end

2. Roll Flattening: results in larger roll radius, and hence larger contact area, which results in larger rolling forces for the same rolling draft.

3. Plastic deformation of rolls (Thermal Camber)

4. Stretch of roll stand (low rigidity)

5. Spreading, especially with high thickness/width ratio. Solution: edger mills.

Roll Deflection and Spreading

FIGURE 6.37 (a) Bending of straight cylindrical rolls (exaggerated) because of the roll force. (b) Bending of rolls, ground with camber, that produce a sheet of uniform thickness during rolling.

FIGURE 6.38 Increase in the width of a strip (spreading) in flat rolling. Spreading can be similarly observed when dough is rolled with a rolling pin.

Workpiece Defects

1. Wavy edges: due to roll bending

2. Surface cracks: due to poor ductility and/or low rolling temeperature

3. Alligatoring: due to defects in the original cast

4. Residual stresses (only when not desired): the type of these stresses are:

• Tensile in the middle/compressive at surface when using small • Tensile in the middle/compressive at surface when using small rolls or draft

• Compressive in the middle and tensile on the surface when using large rolls or draft.

Workpiece Defects In Flat Rolling

FIGURE 6.39 Schematic illustration of typical defects in flat rolling: (a)wavy edges; (b) zipper cracks in the center of strip; (c) edge cracks; (d) alligatoring.

Residual Stresses in Flat Rolling

FIGURE 6.40 The effect of roll radius on the type of residual stresses developed in flat rolling: (a) small rolls, or small reduction in thickness; and (b) large rolls, or large reduction in thickness.

Methods of Roller Leveling

FIGURE 6.41 Schematic illustration of methods of roller leveling. These processes are used to flatten rolled sheets.

Various Roll Arrangements

FIGURE 6.42 Schematic illustration of various roll arrangements: (a) two high; (b) three high; (c) four high; (d) cluster; (e) tandem rolling with three stands; (f) planetary.

Cluster Mill

FIGURE 6.43 Schematic illustration of a cluster (Sendzimir) mill. These mills are very rigid and are used in rolling thin sheets of high-strength materials, with good control of dimensions.

Shape RollingFIGURE 6.44 Stages in shape rolling of an H-section part. Various other structural sections, such as channels and I-beams, are also rolled by this process.

Ring-Rolling

FIGURE 6.45 (a) Schematic illustration of a ring-rolling operation. Reducing the thickness results in an increase in the part’s diameter. (b) Examples of cross-sections that can be formed by ring rolling.

Thread-Rolling Processes

FIGURE 6.46 Thread-rolling processes: (a) flat dies and (b) two-roller dies. These processes are used extensively in making threaded fasteners at high rates of production.

Machined And Rolled Threads

FIGURE 6.47 (a) Schematic illustration of machined or rolled threads. (b) Grain-flow lines in machined and rolled threads. Unlike machined threads, which are cut through the grains of the metal, rolled threads follow the grains and are stronger, because of the cold working involved.

Mannesmann Process

FIGURE 6.48 Cavity formation by secondary tensile stresses in a solid round bar and its use in the rotary-tube-piercing process. This procedure uses the principle of the Mannesmann mill for seamless tube making. The mandrel is held in place by the long rod, although techniques have been developed in which the mandrel remains in place without the rod.

[3] Extrusion Processes

Extrusion Processes1. Direct Extrusion

2. Indirect Extrusion

3. Hydrostatic Extrusion

4. Impact Extrusion4. Impact Extrusion

5. Lateral Extrusion

Types Of Extrusion

FIGURE 6.49 Types of extrusion. (a) direct; (b) indirect; (c) hydrostatic; (d) impact.

Extrusion

FIGURE 6.51 Schematic illustration of three different types of metal flow in direct extrusion.

FIGURE 6.50 Extrusion and examples of products made by sectioning off extrusions. Source: Kaiser Aluminum.

different types of metal flow in direct extrusion.

(a) Ideal: no-friction at the billet-container-die interfaces

(b) Typical: friction at the billet-container-die interfaces

(c) High container wall-billet friction

Extrusion Parameters

1. die angle (α)2. extrusion-ratio (R)3. circumscribing-circle-diameter (CCD): the

diameter of the smallest circle into which the extruded cross-section will fit.

4. shape factor (ratio of the perimeter to the cross-4. shape factor (ratio of the perimeter to the cross-sectional area)

5. billet temperature6. ram speed7. type of lubricant

Extrusion Force/Power Calculations

=

=

=

=

=

1

1

0

.

)ln(lnln

Yu

RL

L

A

A

A

AR

o

f

f

o

f

ε

ε

Extrusion Ratio

Absolute value of the true strain

Energy dissipation per unit volume (for perfectly plastic materials)

+=

==

===

0

27.1.

)ln(.

.....

D

LRYP

RYuP

LApLFuLAWork ooooo

Extrusion pressure (ideal – no friction). For strain-hardening materials, use average flow stress Y

Extrusion pressure (friction between die and billet only)

Work supplied by the ram force (F), which travels a distance Lo

Extrusion Pressure

FIGURE 6.52 Schematic illustration of typical extrusion pressure as a function of ram travel: (a) direct extrusion and (b) indirect extrusion. The pressure in direct extrusion is higher because of frictional resistance in the chamber as the billet moves toward the die.

FIGURE 6.53 Schematic illustration of extrusion force as a function of die angle: (a) total force; (b) ideal force; (c) force required for redundant deformation; (d) force required to overcome friction. Note that there is an optimum die angle where the total extrusion force is a minimum.

Effect of Temperature and Ram Speed

o

o

fo

oo

CY

RD

V

RDD

DV

ln6

lntan6

33

2

==

=

−=

εσ

ε

αε

&

&

& Average true strain rate

Average true strain rate when Do>>Dfand a 45° die angle

Average flow stress

FIGURE 6.54 Schematic illustration of the effect of temperature and ram speed on extrusion pressure. Compare with Fig. 2.11. oAPF

D

LRYP

CY

.

27.1.

0

=

+=

== εσ &Average flow stress considering strain rate

Extrusion Force

Die pressure assuming α=45°

Extrusion Constant

P=Ke*ln(R)

FIGURE 6.55 Extrusion constant, Ke, for various materials as a function of temperature. Source: After P. Loewenstein, ASTME Paper SP63-89.

Cold and Impact Extrusion

FIGURE 6.56 Examples of cold extrusion. Arrows indicate the direction of material flow. These parts may also be considered as forgings.

FIGURE 6.57 (a) Impact extrusion of a collapsible tube (Hooker process).(b) Two examples of products made by impact extrusion, these parts may also be made by casting, forging, and machining, depending on the dimensions and materials involved and the properties desired. Economic considerations are also important in final process selection.

Notes on Extrusion Practices

1. Cold Extrusion has the following advantages over hot extrusion: better mechanical properties (due to work hardening), better dimensional accuracy (little finishing operations) and surface finish (no oxide film), and high production rates at relatively low cost. However cold extrusion requires more expensive tooling (high hardness, strength, toughness, and fatigue strength), complex lubrication and cooling process, and high capacity presses.

2. Hydrostatic extrusion requires much lower forces due to the increased ductility of the material (suitable for brittle materials), and the low friction. Also, it is possible to use low die angles as well as high extrusion ratios.

3. Metal flow in the die influences the qualityand mechanical propertiesof the parts.

4. Extrusion ratio (R) can go up to 400:14. Extrusion ratio (R) can go up to 400:1

5. Coaxial extrusion (cladding) is possible when the strengthand ductilityof both metals are compatible.

6. Hot extrusion: low forces, excessive die wear (can be reduced with preheated dies), non-uniform deformation (can be reduced with preheated dies), oxide film on the billet (reduced by a smaller ram than the container), poor surface finish due to surface oxidation.

7. Dead-metal zones produce extrusions with bright finishes

8. Die materials are generally hot-work die steels, coated with Zicronia to extend the die life.

Defects in Extrusion

Three principal defects in extrusion:

(1) Surface CrackingCause: too high extrusion temperature, friction or speed (intergranular)or at low temperature due to periodic sticking of the extrudate and the die land (knows as bamboo defect) especially during hydrostatic extrusion. Can be reduced by increasing the extrusion speed.

(2) Extrusion defects (pipe, tailpipe, and fishtailing)(2) Extrusion defects (pipe, tailpipe, and fishtailing)Cause: metal flow on the container wall draw surface oxides and impurities towards the center of the billet. Can be reduced by modifying the flow pattern to more homogeneous by reducing friction and minimizing the temperature gradient.

(3) Internal Cracking (chevron cracking or centerburst)Cause: hydrostatic (secondary) tensile stresses at the centerline of the deformation zone.Can be reduced reduced by adjusting the extrusion parameters (die angle, extrusion ratio, friction) so the the deformation zones around the die overlap.

Extrusion Pressure/Extrusion Ratio

FIGURE 6.58 Extrusion pressure as a function of the extrusion ratio for an aluminum alloy. (a) Direct extrusion, α = 90˚. (b) Hydrostatic extrusion, α = 45˚. (c) Hydrostatic extrusion, α = 22.5˚. (d) Ideal homogeneous deformation, 22.5˚. (d) Ideal homogeneous deformation, calculated. Source: After H. Li., D. Pugh, and K. Ashcroft.

Chevron Cracking

FIGURE 6.59 (a) Deformation zone in extrusion, showing rigid and plastic zones. Note that the plastic zones do not meet, leading to chevron cracking. The same observations are also made in drawing round bars through conical dies and drawing flat sheet plate through wedge-shaped dies. Source: After B. Avizur. (b) Chevron cracking in round steel bars during extrusion. Unless the part is inspected properly, such internal detects may remain undetected and possibly cause failure of the part in service.

Extrusion of Seamless Tube

FIGURE 6.60 Extrusion of a seamless tube. The hole in the billet may be prepunched or pierced, or it may be generated during extrusion.;

Extrusion of Complicated Shapes

FIGURE 6.61 (a) An extruded 6063-T6 aluminum ladder lock for aluminum extension ladders. This part is 8 mm (5/16in.) thick and is sawed from the extrusion. (See Fig. 6.50.) (b) Components of various dies for extruding intricate hollow shapes. Source for (b): K. Laue and H. Stenger, Extrusion-Processes, Machinery, Tooling, ASM International, 1981. Used with permission.

[4] Drawing Operations

Drawing is similar to extrusion, except “pulling” through a die is used instead of pushing. It can be used to make wires as small as 0.001″ in diameter.

Process Parameters

Ao , Af initial and final diameters

α = the die angle

FIGURE 6.62 Variables in drawing round rod or wire.

α = the die angle

F = Drawing Force

σd = Drawing Stress

µ = coefficient of friction

Mechanics of Wire Drawing

=

f

od A

AY ln.σ

Ideal deformation: No friction and No redundant work

Y = Yield Stress

fd AF .σ=

(1) Perfectly Plastic materials

(2) Strain Hardening materials

FIGURE 6.63 Variation in strain and flow stress in the deformation zone in drawing. Note that the strain increases rapidly toward the exit. The reason is that when the exit diameter is zero, the true strain reaches infinity. The point Ywirerepresents the yield stress of the wire.

1

ln.

1

+=

=

n

KY

A

AY

n

f

od

ε

σ

(2) Strain Hardening materials

fd AF .σ=

Mechanics of Wire Drawing (continued)

−

+=αµ

µασ

cot

1.tan

1.o

fd A

AY

1

1.tan

1.

1

cot

+=

−

+=

n

KY

A

AY

n

o

fd

ε

µασ

αµ

Ideal deformation with friction (No redundant work)

Y = Yield Stress

(1) Perfectly Plastic materials (2) Strain Hardening materials

1+=

nY

Inhomogeneous Deformation with friction (and redundant work)

+

+=

−+

−

+=

ααµσ

αµ

ασαµ

3

3ln.1.

1

33

41.

tan1. 2

cot

f

od

o

fd

A

AY

r

r

A

AY

Estimation for small die angles only

Die Pressure

nf

f

KY

Yp

ε

σ

.=

−= Die pressure at and point along the die contact length

σ = σd at the die exit

FIGURE 6.65 Variation in the drawing stresses and die contact pressure along the deformation zone. Note that as the drawing stress increases, the die pressure decreases. This condition can be observed from the yield criteria, described in Section 2.11. Note the effect of back tension.

Drawing at elevated temperature (strain

rate effect)

ε&A

A

D

V

f

o

o

o

= ln

6

ε&CY =

Optimum Die Angle

There is an optimum die angle at which the drawing force is a minimum. The optimum die angle increases with %

FIGURE 6.66 The effect of reduction in cross-sectional area on the optimum die angle increases with reduction. Source: After J. G. Wistreich.

angle increases with % reduction in diameter.

Maximum Reduction per pass

The maximum allowed drawing stress is the yield stress of the existing material. Therefore, there is a maximum strain (reduction) per pass.

For a perfectly plastic material, the maximum reduction in cross sectional area is 63% (where ε1=1).reduction in cross sectional area is 63% (where ε1=1).

For a strain hardening material, the maximum reduction in cross sectional area can be calculated as:

( )11 +−−= ne

Tube Drawing

FIGURE 6.67 Various methods of tube drawing.

Defects is Drawing Operations

1. Center cracking is caused by inhomogeneous plastic deformation which increases by increasing the die angle, decreasing the reduction per pass, increasing friction, and the presence of inclusions.

2. Seams, longitudinal scratches/folds in the material which can open up during subsequent forming operations.

3. Residual stresses (transverse, longitudinal, radial) due to inhomogeneous deformation. Very light reductions leaves compressive residual stresses on the workpiece surface which improves fatigue strength.

Residual Stresses

FIGURE 6.68 Residual stresses in cold-drawn AISI 1045 carbon steel round rod: T = transverse directionL = longitudinal direction R = radial direction.

Source: After E. S. Nachtman.

Drawing Dies

FIGURE 6.69 Terminology for a typical die for drawing round rod or wire.

FIGURE 6.70 Schematic illustration of a typical wear pattern in a wire-drawing die.

Rotary Swaging

Also known as Rotary Forging, where a solid rod or a tube is reduced in diameter by the reciprocating radial movement of two or four dies driven by a set of rollers in a cage.

FIGURE 6.71 Schematic illustration of the swaging process: (a) side view and (b) front view. (c) Schematic illustration of roller arrangement, curvature on the four radial hammers (that give motion to the dies), and the radial movement of a hammer as it rotates over the rolls.

in a cage.

Rotary Swaging (continued)

Mandrels are used to control the internal diameter and/or shape (example gun/rifle barrels).

The workpiece diameter is limited to 2 inches, while the length is limited to the length of the mandrel.

Generally performed at room temperature.

FIGURE 6.72 Reduction of outer and inner diameters of tubes by swaging. (a) Free sinking without a mandrel. The ends of solid bars and wire are tapered (pointing) by this process in order to feed the material into the conical die. (b) Sinking on a mandrel. Coaxial tubes of different materials can also be swaged in one operation.

Cross-Sections Produced By Swaging

FIGURE 6.73 (a) Typical cross-sections produced by swaging tube blanks with a constant wall thickness on shaped mandrels. Rifling of small gun barrels can also be made by swaging, using a specially shaped mandrel. The formed tube is then removed by slipping it out of the mandrel. (b) These parts can also be made by swaging.

Die Failures

Failure of dies in metal forming operations results from one or more of the following causes:

1. Improper die design2. Defective die materials3. Improper heat treatment and finishing operations4. Improper installation, assembly, and alignment5. Overheating and heat checking6. Excessive wear7. Overloading, misuse, and improper handling

Dies can fail by cracking, chipping, wear, heat checking (from thermal cycling), or deformation (especially in hot working)

Space Shuttle Launch

FIGURE 6.74 The Space Shuttle Atlantis is launched by two strap-on solid rocket boosters. Source:NASA

Solid Rocket Booster

FIGURE 6.75 Assembly of steel case segments to form a solid rocket booster. Note that nose of the rocket casing is below the platform level. Source: NASA.

Forming Processes For Rocket Casings

FIGURE 6.76 The forming processes involves in the manufacture of solid rocket casings for the U.S. Space Shuttle.