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

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9 Ironing (wall ironing)

9.1 Definition

Ironing is a bulk forming process where the

deformation force (tensile force) must be ab-

sorbed by the cup wall which is deformed. If

the stress in the formed cup wall exceeds the

tensile strength of the cup material, the base is

torn off.

9.2 Application of the process

For the production of flanged hollow parts

whose base is thicker or thinner than the wall.

With this method, hollow parts with inner

tapering can also be produced.

Figure 9.1 Cup with flange.

Ironing with a ring

9.3 Starting stock

The starting stock is a pre-formed (mainly produced by extrusion), thick-walled cup.

9.4 Principal strain (Figure 9.1)

22 22

00 00

22 22

10 11

ln ln ln

Dd Dd



in mm

ring area before forming

in mm

ring area after forming

in mm external diameter before forming

in mm inside diameter before forming

in mm external diameter after forming

in mm inside diameter after forming (usually d

= d

)

– principal strain

92 9 Ironing (wall ironing)

is provided and the limiting diameter D

is sought where d

= d

= const., then:





During ironing with a die ring (Figure

9.1), the values provided in Table 9.1

are permissible. When ironing with

several die rings arranged one after the

other (Figure 9.2), approx. 20% more

deformation can be allowed (e.g. not

35% but 40%).

Figure 9.2 Multiple ironing. 1 punch, 2 die ring

Table 9.1 Permissible deformations with a die ring

Material

perm

Al 99.8; Al 99.5; Al Mg 1; Al MgSi 1; Al Cu Mg 1

0.35

Cu Zn 37(Ms 63)

0.45

Ck 10 – Ck 15,Cq 22 – Cq 35

0.45

Cq 45; 16 Mn Cr 5; 42 Cr Mo 4

0.35

The number of ironing operations required can be determined from the quotients of actual and

permissible deformation.

Number of ironing operations required:

perm

ln 100

§·



¨¸

©¹

n number of ironing operations required

in mm

cross-sectional area before the first operation

in mm

cross-sectional area after the last (nth) operation

perm

in percent permissible deformation

in percent principal strain.

The actual limiting values, however, result from the ironing force. This must remain lower

than the product of the ring area A

after forming and the strength of the material.

1e 1m

AR AR

esmB

( previously previously ).RR



9.6 Example 93

If F > A

· R

: then a further, undesired deformation occurs.

If F > A

· R

: then the cup tears off near the base.

9.5 Calculation of force and mechanical work

9.5.1 Force

1str





F in kN ironing force

in mm

cross-sectional area after forming

str

in N/mm

mean flow stress

– principal strain

– deformation efficiency

in N/kN conversion factor

9.5.2 Mechanical work

WFhx 

W in kN m mechanical work

in m punch displacement

x – process factor (x = 0.9).

9.6 Example

The aim is to form a thick-walled pre-

formed cup into a cup with reduced wall

thickness (Figure 9.3).

Where: material Cq 45;

= 0.7.

Find:

1. principal strain

2. number of ironing operations

3. smallest possible diameter for the first

operation (

pperm

= 35 %)

4. force for the first operation

Figure 9.3 Ironed workpiece.

a) blank í pre-formed cup,

b) finished part after three operations

94 9 Ironing (wall ironing)

Solution:

Principal strain:

2222

22 22 22

50 mm 30 mm

ln ln 0.82.

40 mm 30 mm



Number of ironing operations required:

perm

82 %

2.34

35 %

n = 3 operations required.

(Repeated soft annealing required after each operation.)

Smallest possible diameter for the first operation:

2222

0.35

50 mm 30 mm

30 mm



 

1min

1600

900 45 mm .

1.419

D 

Force for the first operation:

For

= 35 %: k

str

= 390 N/mm

; k

str

= 860 N/mm

; k

str

= 625 N/mm

During the first operation, D

= 45 mm, d

= d

= 30 mm

1 str p str p

()

10 4 10

Ak D d k

 



2222 2

(45 mm 30 mm ) ʌ 625 N/ mm 0.35

276 kN .

40.710

 



9.7 Exercise on Chapter 9

1. How does ironing differ from forward extrusion?

2. What limits the extent of the deformation?

3. What workpiece shapes is it used for?

10 Wire drawing

10.1 Definition

Wire drawing is a form of drawing using a sliding action (Figure 10.1) where a wire of a larger

size (d

) is pulled through a drawing ring of a smaller size (d

). In this process the wire is

given the shape and the cross-sectional dimensions of the drawing ring. Wire drawing belongs

to the production processes which involve forming by tensile and compressive forces, as a

state of stress develops in the deformation zone due to deformation by both tension and pres-

sure. In wire drawing, a difference is made according to the dimensions of the wire between:

coarse drawing: d = 16 to 4.2 mm

medium drawing: d = 4.2 to 1.6 mm

fine drawing: d = 1.6 to 0.7 mm

ultra-fine drawing: d < 0.7 mm

and according to the machine used, between:

single-draft drawing

tandem drawing.

Figure 10.1 The principle of wire drawing.

1 die, 2 wire

10.2 Application

Wire and rod drawing are used to produce wires and rods with smooth surfaces and low toler-

ances for various fields of application (Table 10.1).

Table 10.1 Fields of application of drawn wires and rods

Material Application

Low-carbon steels, C 10 – C22

Wires, wire meshes, barbed wire, pins, nails, screws and

bolts, rivets

High-carbon steels (up to 1.6% C) Rod material for automatic processing, wire cables

Alloy steels Industrial springs, welding wires

Copper and copper alloys

Wires, wire meshes, screws, bolts and shaped parts, parts

for the electrical industry

Aluminium and Al alloys Screws and bolts, shaped parts, electrical lines, etc.

96 10 Wire drawing

10.3 Starting stock

The starting stock for wire drawing is hot-rolled wires. For rod drawing, rods produced by hot

rolling or extrusion moulding are used as starting stock.

10.4 Principal strain

The principal strain results from the aspect ratio before and after drawing.

in mm

cross-section before drawing

in mm

cross-section after drawing

in mm diameter before drawing

in mm diameter after drawing

e = 2.718 basic number of the natural logarithm

principal strain

10.5 Permissible deformations

The following table contains standard values for the drawing reductions and the permissible

total deformation in tandem drawing.

Table 10.2 Permissible deformations with tandem drawing

Mate-

rial

Intake strength

in N/mm

Intake diameter

in mm

Drawing reduc-

tion between

two draws

perm

(%)

Total deformation

(tandem drawing)

perm

(%)

Number of

drawing sta-

tions

400 4 – 12 18 – 22 380 – 400

1200 4 – 12 18 – 22 380 – 400

Steel wire

1200 0.5 – 2.5 12 – 15 120 – 150

8 – 10 wet draws

40 – 50 350 – 400

materi-

als

Cu (soft)

250

1 – 3.5 18 – 20 200 – 300

12 – 16 wet

draws

20 – 25 250 – 300

Al mate-

rials

Al (soft) and

Al alloy

1 – 3.5 15 – 20 150 – 200

10.7 Drawing speeds 97

In single drawing, the permissible deformations are around:

– Steel wires = 150 – 200 %

– Cu materials = 200 %

(Cu soft)

– Al materials = 200 %

(Al soft).

10.6 Drawing force

According to Siebel, the drawing force can be calculated with the following equation

dr 1 str

FAk

§·



   

¨¸



©¹



The mean coefficient of friction is around

= 0.035 (

= 0.02 to 0.05). The optimum drawing

angle, requiring the least force, is around 2

= 16º. From this it follows for the angle in radi-

ans:

80.13

180 180

q q



If these values are brought into the above equation, then the drawing force during wire draw-

ing can be determined approximately with the simplified equation and the deformation effi-

ciency

= 0.6.

1 str p



in N drawing force

str

in N/mm

mean flow stress

in mm

cross-section of the wire after drawing

– principal strain

– deformation efficiency (

= 0.6).

10.7 Drawing speeds

10.7.1 Single-draft drawing

The drawing speeds for single-draft drawing can be taken from the following table.

98 10 Wire drawing

Table 10.3 drawing speeds

for single-draft draws

Material Intake strength R

in N/mm

max

in m/s

(iron wire)

400

800 15

Steel wire

1300 10

Cu (soft)

250

Brass, bronze

400

Al and Al alloys

80 – 100 25

10.7.2 Tandem drawing

In tandem drawing, the drawing speed differs at every drawing. As the volume is constant, the

speed is higher when the wire cross-section is reduced.

· A



in m/s drawing speed at the first draw

in m/s drawing speed at the 2

draw

in m/s drawing speed at the nth draw

in mm

wire cross-section after the 1

draw

in mm

wire cross-section after the 2nd draw

in mm

wire cross-section after the nth draw

In tables of standard values, the highest speeds, applying to the last drawing, are always listed

for tandem drawing machines.

Table 10.4 Drawing speed

for tandem drawing

Material Intake strength R

in N/mm

in m/s

(iron wire)

400

800 15

Steel wire

1300 10

Cu (soft)

250

Brass, bronze

400

Al (soft), Al alloys

80 – 100

10.8 Drive power 99

The block rotation speed n may then also be calculated from the drawing speed which corre-

sponds to the block peripheral speed involved.

60 s/ min



in m/s drawing speed

d in m block diameter

n in min

–1

block rotation speed

10.8 Drive power

The drive power of the wire drawing machine is determined from the drawing force and the

drawing speed.

10.8.1 Single-draft drawing machine

(Figure 10.2)



P in kW drive power

in kN drawing force

in m/s drawing speed

efficiency of the machine

(

= 0.8).

Figure 10.2 The principle of the single-draft

drawing machine

10.8.2 Tandem drawing machine (Fig-

ure 10.3)

With tandem drawing machines, the total

drive power results from adding together the

power required for each draw.

Figure 10.3 The principle of the tandem drawing machine.

Wire feed:

a) from above with two loops,

b) longitudinally without redirection

100 10 Wire drawing

10.9 Drawing tooling

The drawing die (Figure 10.4) consists o

three zones. These are the cone-shaped intake

with the entry angle 2

and approach angle 2

, the bearing land l

and the cone-shaped

back relief l

with the back relief angle 2

The length of the cylindrical guide bush l

around:

0.15ld 

The approach angle 2

influences the draw-

ing force and the surface finish of the wire.

Table 10.5 shows optimum values.

Figure 10.4 Designations of the angles and

measurements on the drawing die.

Table 10.5 Optimum approach angle 2

depending upon the material, the extent of deformation and the

type of drawing.

Approach angle 2

Material Material

Steel (C < 0.4 %), brass, bronze Steel (C > 0.4 %)

Wet draw Dry draw Wet draw Dry draw

in %

11º 9º 10º 8º 10

16º 14º 15º 12º 22

19º 17º 18º 15º 35

10.9.1 Drawing die materials

Drawing dies are produced from steel, carbide and diamonds.

Steel drawing dies

Table 10.6 Steels and assembly hardnesses for steel drawing dies

Material HRC working

hardness

Fields of application

1.2203

1.2453

1.2080

1.2436

63 – 67

Rod and tube drawing

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

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