Tsch?tsch H., Koth A. Metal Forming Practise: Processes - Machines

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12.4 The extrusion process 111

Figure 12.4 The principle of indirect extrusion. 1 pressure plate, 2 punch, 3 die holder (tool con-

tainer), 4 die, 5 container, 6 plunger, 7 slide, 8 profile, 9 billet, 10 dummy block

12.4.3 Solid and hollow extrusion

Producing solid profiles is known as solid extrusion, and producing hollow profiles is known

as hollow extrusion. Table 12.1 shows an overview of the processes.

Table 12.1 Extrusion processes

Basic schematic diagram Process Application

Direct extrusion: the die and con-

tainer are fixed against one an-

other. The punch moves and

presses the billet through the die.

Solid profiles, rods

and strips made

from solid billets

Indirect extrusion: the die, with a

dummy block, is on a stationary,

hollow punch. Movement is made

by the container with blank,

closed at one end. The container is

moved against the stationary die.

Wires and profiles

made from solid

billets

112 12 Extrusion

Table 12.1 The extrusion process (continued)

Basic schematic diagram Process Application

Direct hydrostatic extrusion: the

billet is formed by means of a

high-pressured liquid (12,000 bar)

The pressure is created by the

forwards movement of the punch.

Small, simple pro-

files made of ma-

terials which are

hard to extrude,

which can not be

extruded by other

processes.

Direct tube extrusion over a sta-

tionary mandrel: the blank is a

hollow billet. The stationary man-

drel and the die form the annular

gap. The hollow punch makes the

extrusion movement.

Tubes and hollow

profiles made from

hollow billets.

Indirect tube extrusion with sta-

tionary mandrel: the closed con-

tainer makes the extrusion move-

ment. The die is located on the

front of the stationary punch.

Tubes and solid

profiles made from

hollow billets or

solid billets which

are pierced in the

press.

1 Product, 2 die, 3 billet, 4 dummy block, 5 container, 6 punch, 7 dummy block with die, 8 plug, 9 seal-

ant, 10 extrusion liquid, 11 mandrel

Table 12.2 Advantages and disadvantages of extrusion processes

Process Advantages Disadvantages

Forward extru-

sion

Ease of operation, good product surface,

easy cooling of extrusion

High frictional heat between dummy

block and container, change in material

properties due to raised temperature,

lower extrusion speeds

Backward ex-

trusion

Higher extrusion speeds, lower deformation

resistance, lower residual materials as flow

patterns are optimal all the way into final

zone, lower wear in container

Extrusion diameter limited as passed

through the hollow punch.

Cooling down harder, requires good

dummy block surface (generally ma-

chined surface)

Hydrostatic

extrusion

Forming purely by pressure, ideal flow pat-

tern, brittle materials can also be formed,

highest degrees of deformation up to

= 900 % e.g. with Al materials

Problems with sealing due to high

working pressure necessary (up to

20,000 bar)

12.6 Strain rates during extrusion 113

12.5 Principal strain

– principal strain

in mm

cross section before deformation

in mm

cross section after deformation

– degree of extrusion



Figure 12.5 Parameters for calculation of force and mechanical work in solid extrusion

12.6 Strain rates during extrusion



Because of the complicated flow of material in the deformation zone (Figure 12.6) the strain

rate during extrusion is determined approximately with the following formulae:



in s

–1

strain rate

in mm/s punch speed

D in mm container diameter, principal

strain

ext

in m/min exit speed of the extrusion

in mm

cross-section before deforma-

tion

in mm

cross-section after deformation

in mm billet diameter

in mm extrusion diameter

mm/m conversion factor for m into

60 s/min conversion factor for min into s











Figure 12.6

Flow pattern during

forward solid extrusion

with

= 90°

114 12 Extrusion

Table 12.3 Permissible deformation, extrusion temperatures, speeds and extrudability for steel, copper

and Al materials

Speed Extrudability

(formability)

Extrusion Punch

Material Extrusion tem-

perature in °C

(mean value)

Max.

flash

max



perm

ext

m/min

in m/s

for

max

good

medium

bad

Al 99.5

AlMg 1

AlMgSi 1

AlCuMg 1

430

440

460

430

1000

150

250

6.9

5.0

5.5

3.8

50 – 100

30 – 75

5 – 30

1.5 – 3

1.6

8.3

2.0

1.1

E-Cu

CuZn 10 (Ms 90)

CuZn 28 (Ms 72)

CuZn 37 (Ms 63)

CuSn 8

850

800

775

800

400

100

250

6.0

3.9

4.6

5.5

4.4

300

50 – 100

150 – 200

12.5

16.6

13.3

6.2

C15

C35

C45

C60

1200 90 4.5 360 66 u

100 Cr 6

50 CrMo 4

1200

1250

3.9

360

120

Ti TiA 15 Sn 2.5

950 100 4.6 360 60 u

12.7 Extrusion force

12.7.1 Forward solid extrusion

F = F

def

+ F

str

0wstr

FDlk





= 0.4 – 0.6

= 0.15 – 0.2 with good lubrication

12.7 Extrusion force 115

12.7.2 Backward solid extrusion

Here, the frictional force in the container does not apply as the billet does not move in the con-

tainer.

0str p



F in N total extrusion force

def

in N deformation force

in N frictional force in the container

in mm

billet cross-sectional area

in mm billet diameter



– principal strain

F

– deformation efficiency



– coefficient of friction for the wall friction in

the container

str

in N/mm

yield strength

In hot forming, the yield strength, k

str

, depends upon:

í the deformation temperature

í the strain rate.

The k

str

values for the optimum deformation temperatures can be taken from Table 12.4 for a

strain rate of



= 1 s

–1

The k

str

value when the actual strain rate is taken into consideration can be calculated using the

following equation:

str str

.kk

§·

¨¸

©¹



= 1 is given the value s

–1

(basic value in Table 12.4) the equation can be simplified:

str str





str

in N/mm

yield strength with optimum deformation temperature and the actual

strain rate



in s

–1

actual strain rate

st p

6 v



§·

¨¸

©¹



in s

–1

basic speed



= 1 s

–1

str

in N/mm

yield strength with optimum deformation temperature and basic speed



= 1 s

–1

m – material exponent

str

and m can be taken from Table 12.4.

116 12 Extrusion

12.8 Mechanical work

In extrusion, as in other processes, the deformation work can be determined using Siebel’s

fundamental equation.

pstr





W in kNm deformation work

V in mm

volume involved in the deformation

str

in N/mm

yield strength

conversion factor from Nmm to kNm

The force-displacement diagram (Figure 12.7) shows the flow of force during direct extrusion.

The total work (area below the curve) is divided into

upsetting by the dummy block

setting flow into action

actual deformation (shear, frictional and

sliding resistance in the deformation

zone)

friction between the surface of the

dummy block and the container bore.

Figure 12.7 Force-displacement diagram

12.8 Mechanical work 117

Table 12.4 Basic k

str

values for



= 1 s

–1

with the deformation temperatures provided and material

exponent m to calculate k

str

= f (



)

Material m k

str1

where



= 1 s

–1

(N/mm

)

(°C)

C 15

0.154 99/ 84

C 35

0.144 89/ 72

C 45

0.163 90/ 70

C 60

0.167 85/ 68

1100/1200

X 10 Cr 13

0.091 105/ 88

X 5 CrNi 18 9

0.094 137/116

X 10 CrNiTi l8 9

0.176 100/ 74

1100/1250

E-Cu

0.127 56 800

CuZn 28

0.212 51 800

CuZn 37

0.201 44 750

CuZn 40 Pb 2

0.218 35 650

CuZn 20 Al

0.180 70 800

CuZn 28 Sn

0.162 68 800

CuAl 5

0.163 102 800

Al 99.5

0.159 24 450

AlMn

0.135 36 480

AlCuMg 1

0.122 72 450

AlCuMg 2

0.131 77 450

AlMgSi 1

0.108 48 450

AlMgMn

0.194 70 480

AlMg 3

0.091 80 450

AlMg 5

0.110 102 450

AlZnMgCu 1.5

0.134 81 450

str

.kk

§·

¨¸

©¹



For



= 1 s

–1

then

str





118 12 Extrusion

12.9 Tooling

Extrusion assemblies are under high mechanical and thermal stress. Figure 12.8 shows an

assembly for direct extrusion split into its separate parts; Figure 12.9 shows an assembly for

the indirect extrusion of tubes over a moving mandrel.

Figure 12.8 Direct extrusion of tubes. 1 pressure plate, 2 bolster, 3 holder for bolster, 4 die, 5 man-

drel, 6 die holder, 7 extrusion punch, 8 dummy block, 9 mandrel, 10 container

Figure 12.9 Assembly for the indirect extrusion of tubes over a moving mandrel

12.9 Tooling 119

Figure 12.10

The component parts of the container (Part 10 in Figure 12.8)

a) outer ring,

b) middle ring,

c) inner ring

The container (part 10 in Figure 12.8) is reinforced and generally consists of three parts, as

shown in Figure 12.10.

In extrusion, care has to be taken that lubrication is optimal, as well as that the assembly ele-

ments have the correct dimensions. Glass, graphite, oil and MoS

are most often used as lubri-

cants.

Table 12.5 below shows tooling materials for extrusion tooling.

Table 12.5 Tooling materials for extrusion tooling (Figures 12.8 and 12.10)

Al alloys Cu alloys Steel and steel alloys Tooling components

Material HRC as-

sembly

hardness

Material HRC as-

sembly

hardness

Material HRC as-

sembly

hardness

Container (Figure

12.10) inner ring c

middle ring b

outer ring a

1.2343

1.2323

1.2312

40 – 45

32 – 40

30 – 32

1.2367

1.2323

40 – 45

32 – 40

30 – 32

1.2344

1.2323

1.2343

40 – 45

32 – 40

30 – 32

Punch head 7

1.2344 45 – 52 1.2365 45 – 52 1.2365 45 – 52

Dummy block 8

1.2343 42 – 48 1.2344 42 – 48 1.2365 42 – 48

Bottom die 4

1.2343 42 – 48 1.2367 42 – 48 1.2344 42 – 48

Bottom die holder 3

1.2714 40 – 45 1.2714 40 – 45 1.2714 40 – 45

120 12 Extrusion

12.10 Extrusion presses

With extrusion presses, a difference is made between

the extrusion of solid and tubular shapes.

A standard extrusion press (Figure 12.11) is mainly used to produce solid profiles, e.g. rods,

strips and wires.

Figure 12.11 Diagrammatic view of a forward extrusion press for solid profiles, rods, strips and wires.

1 platen, 2 die slide or die turner, 3 shear blade, 4 billet container, 5 platen ring, 6 punch, 7

cylinder platen 8 oil receptacle with drive and controls. (Illustration from the SMS Hasen-

clever Maschinenfabrik works, Düsseldorf, Germany)

Tube extrusion presses (Figure 12.12) are commonly used for the production of tubes and

hollow profiles.

Figure 12.12 Diagrammatic view of a forward rod and tube extrusion press. 1 platen, 2 die slide or die

turner, 3 shear blade, 4 billet container, 5 platen ring, 6 punch, 7 mandrel, 8 piercer, 8 cylin-

der platen, 10 oil receptacle with drive and controls. (Illustration from the SMS Hasenclever

Maschinenfabrik works, Düsseldorf, Germany)

The tube extrusion press, unlike the standard extrusion press, has a mandrel which can move

independently to the punch. This means both hollow and solid billets can be formed into tubes

or hollow profiles on this machine. For hollow billets a mandrel pusher (low force) suffices;

for solid billets a stronger piercer (part 8 in Figure 12.12) is needed to pierce the billet.

Extrusion presses are driven by oil or water hydraulics.

Tsch?tsch H., Koth A. Metal Forming Practise: Processes - Machines - Tools

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