This document discusses deep drawing, a sheet metal forming process where a punch is used to push a flat sheet into a die cavity. It describes the typical tool setup, components made via deep drawing like cups and conical shapes, and calculations for blank diameter. Stress patterns in different regions during drawing are explained. Factors affecting drawability and defects in formed components like wrinkling and bottom fracture are also summarized. Formulas for total punch force and drawability ratio are provided. Methods to improve drawability like redrawing and controlling texture are outlined.

1. Dr.R.Narayanasamy, B.E.,M.Tech.,M.Engg.,Ph.D.,(D.Sc)
Professor,
Department of Production Engineering ,
National Institute of Technology,
Tiruchirappalli - 620015,
Tamil Nadu,India.
Deep Drawing
By

2. Introduction
Deep drawing is a sheet metal forming
operation.
Punch forces a flat sheet metal into a deep die
cavity
Cylindrical, Conical, Rectangular shaped
components can be manufactured.

3. Typical Tool Setup for Deep Drawing

4. Round sheet metal block is placed over a
circular die opening and held in a place with
blank holder & punch forces down into the die
cavity
If h/d > 0.5, it is called Deep drawing.
If h/d <0.5, it is called Shallow drawing.
Introduction Cont….

5. Components
Cylindrical cups
Utensils
Tube light starter
Square or Rectangular
Fan regulator box
Tube light soak cover
Conical & Hemispherical
Rocket cone nose

6. Calculation of blank diameter
Assumptions: No change in thickness
Where D = Diameter of the blank before
forming
dhdD
dhdD
dhdD
4
4
4/
2
22
22


 

7. Stress Pattern
Metal is subjected to three different types of
deformation in different regions namely
Flange region
Wall region
Punch bottom region.

8. Stress Pattern During Drawing

9. Flange region
 In the radial direction it is subjected to Tensile stress.
 The outer circumferences continuously decreases.
 This means the circumference of the blank is
subjected to Compressive Hoop stress.
 It is a Plane stress deformation.
 Because, only two stresses are acting on the flange
region.
 Thickening takes place in the flange region.

10. Wall region
Here the sheet is subjected to Bi-axial Tensile
stress.
In the wall region the metal is bent and then
straightened

11. Punch Bottom
Here the metal is getting Thinned down, at
the bottom of the punch.
In the punch nose region sheet metal is
subjected to plane strain deformation.

12. Total Punch Force
Total punch force can be divided into three
components.
They are :
Force due to idle deformation (Fideal)
Force due to friction (Ff )
Force due to ironing ( Fironing )

13. Punch Force Continued….
 Force due to idle deformation:
 Increases linearly with increase in stroke.
 Force due to friction:
Frictional force peaks early and decreases with increasing
ram travel.
 Force due to Ironing:
Ironing occurs in the later stage of the drawing process.
Ironing takes place when the clearance between the die
and the punch is not sufficient.

14. Punch force vs. stroke for Deep drawing

15. Clearance
Clearance > Sheet thickness.
Less clearance leads to ironing.

16. Total Punch Force
Punch force = 1st Term +2nd Term + 3rd Term
1st Term : Force due to idle deformation
2nd Term: Force due to friction and blank holder
pressure.
3rd Term: Force required to bend and straighten the
blank.
Be
D
D
H
D
D
hDP
o
p
p
o
op






 2/
)2(ln)1.1( 


17. Notation
P =Total punch load
σo = Average flow stress
Dp = Diameter of punch
Do = Blank diameter
H = Blank hold on pressure
h = Wall thickness
μ =Co-efficient of friction
B = Force required to bend and straighten the
blank
Be
D
D
H
D
D
hDP
o
p
p
o
op 








 2/
)2(ln)1.1( 


18. Fracture at the cup bottom
 Punch load is applied to the bottom of the cup.
 Punch load is transmitted to side wall of the cup.
 Usually failure occurs over the punch nose region
(Bent region of the cup).
 Metal in the wall is subjected to Tensile stress.
 It is plane strain stretching and thinning.
 If drawing stress ≥ tensile strength of the material,
fracture takes place.
 Su=Ultimate tensile strengthhDS pu
3
2
maxP

19. Drawability
It is the ratio of the initial blank diameter to
the diameter of the cup drawn from the blank.
For a given material, there is a limiting draw
ratio(LDR)
LDR = Limiting draw ratio
Do = Blank diameter
LDR = Dp = Diameter of the punch
max








p
o
D
D

20. Factors affecting drawability
 Die radius: should be about 10 times of sheet
thickness
 Punch radius : A sharp radius leads to tearing and
thinning
 Clearance between punch and die: 20 to 40 %
greater than sheet thick ness
 Hold down pressure: about 2 % of average of σys
and σts
 Lubricate die side to reduce friction in drawing

21. Redrawing
Reducing the cup part to smaller diameter and
increasing height is known as Redrawing
Methods of redrawing :
Direct redrawing
Reverse redrawing

22. Direct redrawing
The metal subjected to severe strain
hardening .
This is due to bending and unbending at
punch and die radii.

23. Reverse redrawing
 Cup is turned inside out, So the out side of the drawn cup
becomes the inside surface of the redrawn shell.
 The bending is always in the same direction.
 Less strain hardening of walls.
 Better control over wrinkling.
 Residual stresses are nullified.
 Increased drawability compared to direct redrawing.
 Greater reduction is possible if the metal is annealed in
between re draws.
 Most of the metal permit to a total reduction of 50 – 80 %
before annealing.

24. Methods to improve drawability
Cup nose wall region must be strengthened:
This can be done by using rubber pads in the tool
set up.
Drawability can be increased by roughening the
punch.
With hold the lubrication to the punch improves
drawability.
Heating the flange region may shift the failure.
By controlling the crystallographic texture,
drawability can be increased.

25. Texture
• The correct texture gives the proper
orientation of the slip systems.
• So that the strength in the thick ness direction
is greater than that in the plan of the sheet.
• Resistance to thick ness thinning is measured
by plastic strain ratio (R)
R = = width strain / thickness strain.
)/ln(
)/ln(
tt
WWo
o

26. Defects in formed components
 Bottom fracture
 Wrinkling
 Orange peeling
 Stretcher strain
 Earring

27. Bottom fracture
This is due to thinning near the punch
radius. It can be minimized by :
 Reducing the thinning by using a larger punch
radius
 Decreasing the punch load required for drawing
operations

28. Wrinkling
This is due to high compressive
circumferential stresses.
To prevent this defect, it is necessary to use
sufficient hold down pressure to suppress the
buckling.

29. Orange peeling
This occurs in sheet metal of relatively large
grain size.
The individual grains tend to deform
independently.
This can be minimized by using finer grain size
sheet metal

30. Stretcher strain
 It is commonly found in low carbon steels.
 This defect shows up a flame like pattern of depressions, on
the surfaces.
 As the deformation continues , they spread and join
together to produce uniform rough surface.
 The depressions appear along planes of maximum shear
stress.
 This is non uniform deformation which results from yield
point elongation.
 To avoid this problem , cold reduction of 1-2 % deformation
is given in rolling after annealing operation

31. Earring
It is the formation of a wavy edge on the top
of drawn cup .
This formation is due to directional property
of sheet metal.
Earring can be correlated with the planar
anisotropy( R)
R = (R0 + R90 – 2R45)/2

33. Plot of Blank Holder force Vs Depth of
Shell

34. The Effect of Steel Grade on Depth of
Shell

35. Construction of Tractrix Die

36. TRACTRIX Profile

37. Typical TRACTRIX Die

38. Conical Die

39. Tooling for combined cupping &
Ironing

40. Two Different Punches

103. Reference
Dr.R.Narayanasamy, Ph.D. thesis on
“Drawability of sheet metals”, 1992,
National Institute of Technology,
Tiruchirappalli – 620 015, Tamil Nadu, India.

104. THANK YOU
Dr.R.Narayanasamy, B.E.,M.Tech.,M.Engg.,Ph.D.,(D.Sc)
Professor, Department of Production Engineering ,
National Institute of Technology, Tiruchirappalli - 620015,
Tamil Nadu,India.
Email id’s: narayan@nitt.edu
&
narayan10455@yahoo.co.in