Severe plastic deformation of metallic materials by equal channel angular swaging

173 Pages·2014·7.72 MB·English

Severe plastic deformation of metallic materials by equal channel
angular swaging: Theory, experiment and numerical simulation

Vom Fachbereich Maschinenbau
an der Technischen Universität Darmstadt
zur
Erlangung des Grades eines Doktor-Ingenieurs (Dr.-Ing.)
genehmigte

Dissertation

vorgelegt von

M.Sc. Mehmet Okan Görtan

aus Kocaeli, Türkei

Berichterstatter: Prof. Dr.-Ing. Dipl.-Wirtsch.-Ing. P. Groche
Mitberichterstatter: Prof. Dr.-Ing. C. Müller
Tag der Einreichung: 03.06.2014
Tag der mündlichen Prüfung: 21.07.2014

Darmstadt 2014
D17

Acknowledgements
This work is created during the time I spent as a research assistant
(Wissenschaftlicher Mitarbeiter) in the Institute for Production Engineering and
Forming Machines (PtU) of Technische Universität Darmstadt, under supervision of
Prof. Dr.-Ing. Dipl.-Wirtsch.-Ing. Peter Groche.
Completion of this work would not have been possible without the guidance of my
“Doktorvater”, Prof. Dr.-Ing. Dipl.-Wirtsch.-Ing. Peter Groche. I would like to express
my special thanks to him for his support, tolerance, patience and understanding.
I would also like to extend my thanks to Prof. Dr.-Ing. Clemens Müller for co-
supervising my work and his support during the longstanding project work with him.
Hereby, I would like to state my gratitude to Dr.-Ing. Enrico Bruder for his cooperation
during the project “Production of UFG materials by rotary swaging” upon which my
thesis bases.
I would like to acknowledge all of my coworkers at PtU, the research assistants, our
secretaries and our workshop staff who welcomed me to the institute and to
Germany from the first day on and supported me during the extended “Adaption to
Germany” process.
I would like to thank all my friends who helped me carry this burden through the joy of
their companionship. Among them, Pinar Topal and Ibrahim Topal deserve my
special gratitude for their hospitality in the last phases of my thesis work.
Moreover, I wish to express my gratitude to my family for their encouragement and
support during my doctoral studies.
Finally, I would like to thank my wife, Dr. Fatma Arzu Görtan, with all my heart for her
patience and continuous support. Without her, the completion of this thesis wouldn’t
be possible.

Mehmet Okan Görtan Darmstadt, May 2014

Contents
Symbols and Abbreviations .................................................................................... III
1 Introduction ........................................................................................................ 1
2 State of the Art ................................................................................................... 3
2.1 Severe Plastic Deformation of Metals ............................................................ 4
2.1.1 Major Severe Plastic Deformation Processes .......................................... 4
2.1.2 Secondary Equal Channel Angular Pressing Processes ....................... 15
2.2 Incremental Metal Forming ........................................................................... 22
2.2.1 Classification of Incremental Forming Processes .................................. 24
2.2.2 Rotary Swaging ..................................................................................... 25
2.3 Numerical Simulation and Modeling of Forming Processes ......................... 27
2.3.1 Modeling Material Behaviour by Finite Element Simulations ................. 28
2.3.2 Finite Element Simulation of SPD Processes ........................................ 29
2.3.3 Finite Element Simulation of Incremental Bulk Metal Forming Processes .
............................................................................................................... 32
3 Motivation, Objectives and Approach............................................................ 37
3.1 Motivation ..................................................................................................... 37
3.2 Objectives .................................................................................................... 37
3.3 Approach ...................................................................................................... 38
4 Equal Channel Angular Swaging (ECAS) Process ....................................... 41
5 Properties of Used Materials .......................................................................... 45
5.1 Mechanical Properties .................................................................................. 45
5.2 Tribological Properties .................................................................................. 48
6 Mechanics of Severe Plastic Deformation Processes .................................. 51
6.1 Loads on ECAP-Process .............................................................................. 52
I
Contents
6.2 Loads on ECAS-Process ............................................................................. 61
7 Finite-Element-Simulation of ECAS-Process ............................................... 71
7.1 Determination of Finite Element Simulation Strategy ................................... 71
7.2 Effect of Channel Length ............................................................................. 78
7.3 Effect of Outer Corner Radius...................................................................... 84
8 Experimental Investigations of ECAS-Processes ........................................ 91
8.1 Results of Experiments with Copper Roundbars (Cu-ETP) ......................... 93
8.2 Results of Experiments with Steel Roundbars (C4C) ................................ 104
8.3 Effect of ECAS Processing on Material Properties .................................... 109
8.4 Validity of the Derived Formulas for Higher Channel Angles ..................... 112
8.5 Summary of the Experimental Findings ..................................................... 115
9 Effect of Process Parameters on ECAS ...................................................... 117
9.1 Tribological Parameters ............................................................................. 117
9.2 Temperature .............................................................................................. 122
9.3 Feeding Speed .......................................................................................... 125
9.4 Feeding Type ............................................................................................. 129
9.5 Process Design Suggestions for Future Applications ................................ 133
10 Summary and Outlook .................................................................................. 135
11 References ..................................................................................................... 139
Figure List ............................................................................................................. 151
Table List ............................................................................................................... 155
Appendix ............................................................................................................... 156

II
Symbols and Abbreviations
Symbols, Latin Letters
Symbol Unit Explanation
A mm2 Cross-section area
B MPa Strain hardening effect
C - Strain rate sensitivity
c J/kg K Specific heat
D mm Diameter
E GPa Young's modulus
F mm2 Area of the stationary tool walls
F N Force
F N Axial force
axial
F N Force acting on the lower tool
low
F N Radial force
radial
F N Resulting force
resulting
F N Force acting on the upper tool
up
F N Yielding force
yielding
h W/m2 K Heat transfer coefficient
k MPa Shear yield strength
k W/m K Thermal conductivity
L mm Length of the entry channel
0
L mm Length of the middle channel
1
L mm Length of the exit channel
2
m - Thermal softening exponent
n - Number of severe plastic deformation cycles
n - Strain hardening exponent
P MPa Pressure, punch pressure
P MPa Back pressure
0
P MPa Punch pressure
1
r mm Radius
r mm Inner corner radius
i
III
Symbols and Abbreviations
r mm Outer corner radius
o
r - Total reduction
t
r mm Tool radius
t
r mm Workpiece radius
wp
s - Osculation
t mm Thickness
t s Time
T °C or °K Temperature
t mm Initial thickness
0
T °C Initial temperature
0
T °C Melting temperature
melt
T °C Room temperature
room
V mm/s Speed
w mm Width
w mm Equivalent width
eq
X, Y, Z - Major directions

IV
Symbols and Abbreviations
Symbols, Greek Letters
Symbol Unit Explanation
µ - Friction coefficient
γ - Shear strain
δ - Second parameter to define the position
inside the plastic deformation zone
ε - Strain
ε' 1/s Strain rate
ε - Reference strain
0
ε' 1/s Reference strain rate
0
ε - Von Mises strain
vM
ζ - Deformation heat dissipation factor
d
ζ - Friction heat dissipation factor
f
η ° Angle between slip lines
λ ° Angle of friction
ν - Poisson's ratio
ρ kg/m3 Density
σ MPa Tensile stress
σ MPa Yield strength
y
τ MPa Friction stress
φ ° Half channel angle
φ ° Half arc of curvature
χ - First paramter to define the position inside
the plastic deformation zone
ψ - Shearing fan

V
Symbols and Abbreviations
Abbreviations
2D Two dimensional
3D Three dimensional
ALE Arbitrary Lagrangian-Eulerian
ARB Accumulative roll bonding
C2S2 Continuous confined strip shearing
DMZ Dead metal zone
EBSD Electro backscatter diffraction
ECA Equal channel angular
ECAD Equal channel angular drawing
ECAP Equal channel angular pressing
ECAS Equal channel angular swaging
FEA Finite element analysis
FEM Finite element method
FS Full split
GHG Greenhouse gasses
HAGB High angled grain boundaries
HMP Heinrich Müller Pforzheim
HPT High pressure torsion
IEA International Energy Agency
I-ECAP Incremental ECAP
PDZ Plastic deformation zone
PS Partial split
PtU Institute for Production Engineering and Forming Machines
RD-ECAP Rotary die ECAP
RSE Repetitive side extrusion
SCT Sliding compression test
SEM Scanning electron microscope
SF Shearing fan
SLF Slip-line field
SP Single plane
SPD Severe plastic deformation
TEPS Total equivalent plastic strain
UFG Ultrafine grained
VDI Verein Deutscher Ingenieure
VP Visio-plasticity

VI