5 Deep Drawing

5/26/2018 5 Deep Drawing

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Figure 7.1: Schematic illustration of deep

Experiment (5)

Deep Drawing or Shell DrawingOf Cylindrical Cup

Dr. Mohammad Al-tahat

Department of Industrial Engineering. University of Jordan.

Lab. Of Manufacturing Processes. Course No: 906412 1 Mech. and/Or 096312 IE

1. Objective:For accomplish a deep drawing process and for learn and analyze the general aspects

of the operation, furthermore to determine experimentally the maximum drawing force,

the drawing energy, and to measure the cup height, after that to compare the results with

the approximate theoretical numerical results.

2. Background:For more information about the subject of the experiments, it is recommended for the

student to review section 7.12 of chapter seven of the text.

3. TheoryDeep drawing is one of the most important and widely used metal forming

manufacturing process that is used for Drawing of closed shapes. The depth of such

shapes should be greater than the diameter of the opening (greatest surface dimension).

This process first developed in the 1700s consequently has been studied extensively until

has become an important metalworking process.

3.1 What is Deep DrawingA flat sheet metal blank deeply drawn by means of a punch that presses the blank into the

die cavity. Schematic illustration of deep drawing process is presented in Figure 7.1,

noted how does the stripper ring facilitates the removal of the formed cup from the

punch.


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Fi ure 7.2: A collection of arts roduced b dee

Typical parts produced are Closed Cylindrical shapes as Cans, pots and pans; rectangular

container of all shapes and sizes; sinks, automobile panels, Shells, Cartridge cases; and

many other similar shapes as shown in figure 7.2.

3. 2 Shallow Drawing

Shallow Drawing: - is the process of drawing such products that have a depth less thanthe diameter of the opening (smallest surface dimension).

3. 3 Parameters of Deep DrawingTo study and describe the different interaction of the parameters in deep drawing for

producing a cylindrical cup the following notations have been used.

oD : Diameter of a circular sheet blank.

ot : Thickness of the circular sheet blank.

dR : Corner radius of the die opening.

pD : Punch diameter.

pR : Corner Radius of the punch.

PW : Plastic Work required for deep drawing

oV : Initial volume of blank to be drawn

cV : Volume of drawn cup.

R : Drawing Ratio Do/Dp. : The effective strain.

: Effective stress.

Fi ure 7.3: Variables in dee drawin of a c lindrical cu .


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Figure 7.4: Pure drawing and stretching by draw bead.

High blank holder

force

As shown in figure 7.3 the blank is held in place with a blank holder, or hold-down

ring, with a certain force. The punch moves downward and pushes the blank into the die

cavity to form a cup.

Only the punch force is dependent variable, While significant independent

variables are:1. Properties of the sheet metal2. The ratio of blank diameter to punch diameterR .3. Sheet thickness.4. The clearance between the punch and the die.5. Punch and die corner radii.6. Blank holder force.7. Friction and lubrication at the punch, die, and workplace interfaces.8. Speed of the punch.

3. 4 Pure DrawingPure Drawing: - If the blank holder force is low the blank will flow freely into the diecavity -- as shown in figure 7.4-a -- by reducing the blank diameter as drawing progress.

In this case the deformation of the sheet is mainly in the flange, and the work piece wall

is subjected to longitudinal tensile stress, stresses increase with increasing ratio that can

eventually lead to failure when the cup cannot support the load required to draw in the

flange. Cup wall tends to increase in thickness as it draws into the die cavity because of

the diameter reduction.

3. 5 Stretching DrawingStretching drawing: - With a high blank holder force the blank can be prevented from

flowing freely into the die cavity as in figure 7.4-b. The deformation of the sheet metal

blank takes place mainly under the punch and the sheet begins to stretch. Using of draw

bead can be used also as an alternative for a high blank holder force, eventually resulting

in necking and tearing. Necking could be localized or distributed that depends on; the

mechanical properties of sheet metal and its sensitivity to strain rate; Punch geometry and

design; and finally lubrications.

3. 6 Wrinkl ingWrinkling: - When there is a high clearance -- larger than the metal sheet thickness--

between the punch and the die the length of the unsupported wall is significant in that it

can lead to wrinkling. In figure 7.5 elementAin


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Figure 7.5: Wrinkling in the unsupported region of a sheet indrawin .

Figure 6: Illustration of the ironing

the sheet is being 'Apulled into the die cavity as the punch moves downward to position

,the blank is becoming smaller in diameter and the circumference at the element isalso

becoming smaller. At position the element is being subjected to a circumferential

compressive strain and is unsupported by any tooling. Because the sheet is thin and

cannot withstand compressive strains to any significant extent, it will tend to wrinkle inthe unsupported area.

3. 7 IroningIroning: - Conversely, when the thickness of the sheet metal greater than the clearance

between the punch and the die, the thickness will be reduced. This effect is known as

Ironing and shown in figure 7.6. Because of volume constancy, an ironed cup will be

longer than cup produced with a large clearance. Noted that ironing produced constant

wall thickness and the greater the difference between clearance and sheet thickness the

greater is the ironing.

4. Drawn Cup Height and Plastic Work

The circular blank shown in figure 7.7 has an initial radius of oa and thickness of ot it is

assumed to be drawn into a cup having a uniform cylindrical wall of the same thickness,

mild-wall radiusb and height h . Assuming no change in metal thickness and volume

after drawing then,


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Figure 7.7: Circular cup to be drawn.

r

t

Figure 7.9: Stresses on an element of flange.

( )12

1222

)(21

2

..2....

2

2

222

22

22

22

=

=

===

=

+=

=

Rb

h

ioDrawingRatb

aR

bab

bb

baba

bh

babh

hbttbta

VV

o

ooo

o

oooo

CO

In deep drawing the metal is subjected to a plane radial drawing, and the three principal

stresses are radial stress r , tangential or thickness stress t , and the circumferential or

hoop stress figure 7.9.

For the distortion-energy criterion effective strain expressed as:

( ) ( ) ( )[ ]

0

.3

2

3

2

1

2

12

13

2

32

2

21

==

=

=

++=

t

r

Hoop strain is


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h

xPP

.sinmax

=

hhh

rkh

xhu

hPduu

hPdx

h

xPW

0max

0

max

0

max coscos..sin..

sin

=

===

hPWrk

2.max=

PW

Figure 7.11: approximated Punch load-punch

X

( )

+=

+

===2

1ln

2

12

1

lnln2

2

R

b

Rb

a

bLn

l

l

o

Substituting on the effective strain equation( )

+==

2

1ln

3

1

3

2 2R

the average representative stress .2

fYY+=

The volume of the annulus according to figure 7.7 is ( ) oo tbaV .22 = ,The total plasticwork required is obtained from

=

0

.. dvdWP

Substituting for V,,

and integrating we get

( )( )

++=

++=

2

1ln..1..

32

1

.2

1ln

3

1.

2

222

2

RYYRtbW

VRYY

W

foP

f

P

5. Maximum Punch ForceDrawing load values versus punch travel diagram, something like a sine curve will be

obtained as in figure 7.11, this curve can be described by

The work done by punch is equal to the area under the curve and is

Substituting the value of h in the above equation and equating the result with equation we

obtain,


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( )

++=

2

1ln

32

22

max

RYY

btP f

o

fY

The curve may now be figured indicating the relation between maximum punchforce and R for a given material. by calculating for various values of R and reading off

for this value of strain from the stress-strain curve.

The maximum drawing force is, ( )

++=

2

1ln

32

22

max

RYY

btP f

o . Another simple emprical

equation for calculating the maximum punch force could be express as:

= 7.0)(max

p

o

op

D

DUTStDP

the ideal work of deformation, redundant work,friction work and , when present, the

workrequired for ironing presented in figure 7.10 below:

Figure 7.10: Variation of Punch Force With Stroke in Deep Drawing.

6. Materials:A circular blank of copper is needed to run the experiment

7. Equipments:Universal testing machine equipped with pen recorder the deep drawing punch and die

set and a micrometer.

8. Procedures:1. Calibrate the universal-testing machine.2. Choose the scale in the testing machine.3. Measure the thickness and the diameter of the test specimen.4. Measure the die throat diameter and determine R5. Lubricate the die surface and its throat.6. Place the specimen in position on top of the die and locate the die holder,

and finally place the punch in a proper position.

7. Place the die set between the two platens of the testing machine.


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8. Applied the load gradually until the cup is completely drawn.9. Takes off the die set and get the formed cup.10. Measure the average height of the cup.11. Take off the outographics records of the test.

9. Requirements:

1. Experimentally, Draw the experimental punch load- punch traveldisplacement curve, use that curve to find the energy (area under curve)

and the maximum drawing force (the peak value of the curve).

2. Calculate the theoretical height value of the cup and compare it with theexperimental values, discuss the difference.

3. Calculate the theoretical value of the drawing energy required and compare

that with the experimental value, discuss the difference and explain thedifference relation with lubrication.

4. Calculate the theoretical drawing force value and compare that with theexperimental value.

5. Discuss the following aspects of deep drawing; Pure drawing, Stretchingdrawing; wrinkling; ironing; earing; Tearing.

6. Discuss the effects of lubrication, blank holder force, Draw beads, andClearances on the operation of deep drawing.

10. Questions:1. Explain in details the following:

a. Earing,b. Bell-shaped drawn products,c. Orange peeling;

5 Deep Drawing

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