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Table of Contents
                            Declaration of license
Acknowledgments
Abstract
1. Introduction
2. Titanium and its alloys
	2.1. Crystal structure
	2.2. The alloying behavior of titanium
	2.3. Titanium alloys families
	2.4. Phase transformations
	2.5. The Ti-6Al-4V alloy
3. The forging process
	3.1. Forging and forming mechanism of materials
	3.2. Classification of bulk forming processes
	3.3. Cold and hot forging
	3.4. Flow behavior and stress state during a forging process
	3.5. Open and close die forging
	3.6. Forging materials
	3.7. Die materials
	3.8. Advantages and disadvantages of forging processes
	3.9. Application fields of forging processes
4. Literature review
	4.1. On the flow stress properties of titanium alloys
		4.1.1. Developed constitutive models
	4.2. On the phase transformation and microstructural evolution
		4.2.1. Phase transformation kinetic models
		4.2.2. Transformation plasticity phenomena
	4.3. Numerical applications in forging processes design of titanium alloys
5. Numerical characterization of Ti-6Al-4V alloy
	5.1. Themo physical properties
	5.2. Elastic behavior
	5.3. Plastic behavior
	5.4. Phase transformation behavior
6. Data validation
	6.1. The TitaForm project
	6.2. Flow stress data validation
	6.3. Numerical experiments on the transformation plasticity
	6.4. Project forging work package
	6.5. Die geometry determination
	6.6. Simulation campaign output
		6.6.1. Forging load prediction
		6.6.2. Temperature prediction
		6.6.3. Effective strain prediction
		6.6.4. Effective strain rate prediction
		6.6.5. Phase transformation prediction
	6.7. Comparison with experimental data
		6.7.1. Flow instability and forging defects analysis
		6.7.2. Metallographic analysis of forgings and comparison with numerical phase prediction and distribution
7. Self-consistent modeling
	7.1. Phasic flow stress curve SCM determination
	7.2. Johnson-Cook SCM modelization
		7.2.1. A-parameter determination
		7.2.2. B-parameter determination
		7.2.3. Strain hardening exponent determination
		7.2.4. Strain rate sensitivity modulus determination
		7.2.5. Reference strain rate determination
		7.2.6. Strain rate sensitivity exponent determination
		7.2.7. Thermal modulus, exponential modulus and exponent determination
		7.2.8. Thermal softening modulus and reference temperatures determination
		7.2.9. Thermal softening exponent determination
		7.2.10. Model results and discussions
8. Conclusions and further developments
9. Appendixes
	9.1. Figures
	9.2. Tables
10. References
                        
Document Text Contents
Page 1





Ducato Antonino

[
Computer aided engi
neering for thermo
-
mechanical
-
metallurgical
analysis of forging operations of titanium alloys
]





PHD IN MANUFACTURING

ENGINEERING

0





































































Page 2





Ducato Antonino

[
Computer aided engi
neering for thermo
-
mechanical
-
metallurgical
analysis of forging operations of titanium alloys
]





PHD IN MANUFACTURING

ENGINEERING

I



Palermo

22/06/1983

Declaration

of license


TUTTI I CONTENUTI DEL REPOSITORY ISTITUZIONALE AD ACCESSO


APPLICAZIONE DELLA LEGGE 22 APRILE 1941, N. 633 E SU
CCESSIVE
INTEGRAZIONI E MODIFICAZIONI.

Con la presente licenza, l'Università degli Studi di Palermo richiede, a tutti coloro che

Ricerca, le seguenti dichiarazioni e
autorizzazioni.

Il/La sottoscritto/a
Dott.

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DICHIARA,


sotto sua esclusiva responsabilità,

-



tesi di
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intitolata





documenti

documenti (files);

-

che si tratta di un suo lavoro originale e non contrasta, per quanto a sua conoscenza,
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che detta tesi e i documenti a
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-


la facoltà di autorizzare la riproduzione e la
comunicazione al pubblico di detti materiali per finalità non commerciali nel Repository
Antonino Ducato

15/01/2015

Computer aided engineering for

thermo
-
mecha
nical
-
metallurgical analysis of


forging operations

of titanium alloys


Dottorato di Ricerca in Ingegneria Chimica, Gest
ionale, Informatica e
Meccanica,
Indirizzo
-

Ingegneria dell
a Produzione

25/02/2015

1




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Ducato Antonino

[
Computer aided engineering for thermo
-
me
chanical
-
metallurgical
analysis of forging operations of titanium alloys
]




PHD IN MANUFACTURING

ENGINEERING

119


Hsu et al.
[
168
]

proposed
a col
d forging process design method based on the induction
of analytical kno
wledge, using a
finite
-
element
-
based
software

to analyze various multi
-
stage cold forging processes based on pre
-
defined

process condition parameters and
tooling geometry.
Two industri
al cases have been studied to demonstrate how to use the
analytical knowledge for process design, accomplished with two different approaches:
one is the forward manner seeks what the product will be, based on the pre
-
defined
process conditions; and the oth
er is the backward manner, which optimizes the process
condition parameters based on the required product information.
According to the
simulation results, a knowledge
-
acquisition procedure
was instituted and a neural
network model,
in which the multi
-
laye
r network and the back
-
propagation algorithm are

utilized to learn the training examples from the simulation results
, was developed
.
Moreover
, an industrial case study for the

multi
-
stage cold forging process design of a
low
-
carbon steel speaker tip
was

st
udied and the
optimal process condition parameters,

such as the preform punch geometry and the preform punch stroke
were found
, based on
the requirement of homogeneous plastic

deformation of the cold
-
forged product.
This

method
resulted

useful to decide th
e cold forging process

parameters for producing a
part
within the required minimum quantity of the die set.

Altan et al.
[
169
]

investigated

real applications of forged parts with particular focus on

suck
-
in type extrusion defect
s
, forging of bevel gears, stress analysis of forging

tooling,
design of multi
-
stage cold
-
forging ope
rations, design of a net
-
shape cold
-
forging
operation for pipe fittings and

development of a new test to evalua
te lubrication in cold
forging.

Badawy et al.
[
170
]

described a computer
-

designing the forming sequence for multistage

forging of round parts.
This CAE software

can handle only sol
id
round parts without protrusions

and
can be

expanded to design
forming steps for hollow parts and parts with internal protrusions that are forged without
flash in

upsetters, automatic forging machines, and vertical presses
.


Di Lorenzo et al.
[
171
]

studied the

finishing
forging
in order

to

obtain the desired
product without shape defects such as underfilling or folding and with a m
inimum
material loss into

the flash in closed die forging.
It was applied an

inverse approach to the
pre
form shape optimization problem

using

a response

function which links the set of
parameters defining the preform shape with the fulfillment of the produ
ct design




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Ducato Antonino

[
Computer aided engineering for thermo
-
mechanical
-
metallurgical
analysis of forging operations of titanium alloys
]




PHD IN MANUFACTURING

ENGINEERING

120


specifications.
This approach was applied

to a closed die forging process aimed to the
production of a

C
-
shape component, and has allowed to determine the optimal preform
geometry which ensures the complete filling of

die cavity .

Tomov et al.
[
172
]

provided a

description of some die
forging operations selected as
representative steps for the near
-
net
-
shape forging of spur gears. The main r
esults are

obtained on the basis of quasi
-
static model material experiments that have been applied
to collect data needed for

statistical processing or to verify some analytical solution and
computer simulations.
A combined approach of using model

material

experiments
and
statistical p
rocessing of the data collected
together with

some analytical solutions and
FEM simulations
has been applied to cov
er certain consecutive steps of
the near
-
net
-
shape forging of cylindrical spur gears.

Simple
regression

equati
o
ns were derived for
calculating
both the shape chang
es and the force conditions for
some preparat
ory open
-
die forging operations and an
improved pre
-
forging shape
for preform
design in the
close
d
-
die forging of H
-
shaped parts was proposed. These results co
uld be helpful in
engineering practice for simple calculations in process planning design.

Liou at al.
[
173
]

presented a study on the optimization of forged parts by means a

robust design methodology
and FE analysis

to identify the
controlling process parameters
which have great effects on the formation of residual stre
sses in the radial forging process.

The
experimental
plan, in which

frictional coefficient, length of die land, reduction
percentage, inlet angle and corner fillet were taken into account,
was performed by using
the orthogonal array and concept of the sign
al
-
tonoise

ratio. The
ANOVA analysis
showed that the inlet angle,
friction coefficient and length
of die land have the most
significant effects on the optimum residual stresses.

Either
,

parametric FE simulations were carried
out in

order to
o
ptimize

the de
sign
parameters of the manufactured

products and the manufacturing
processes.

The selected controlling process parameters of the forging operation influencing the
residual stress distribution in products were: length of die land (L); inlet angle (a); fric
tion
coefficient (F); reduction percentage of cross
-
section (R); corner fillet (C).

Results
(
Figure
71
)
showed

that
the

inlet angle (a) was the dominant
process parameter
in deciding the residual stresses in the f
orged products. The smaller the

inlet angle, the
smaller the residual stresses. The comer

fillet (C) showed a negligible
effect on the forged
residual stresses
, while

the longer die land (L) ha
d

a better surface finish, but from the



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Ducato Antonino

[
Computer aided engineering for thermo
-
mechanical
-
metallurgical
analysis of forging operations of titanium alloys
]




PHD IN MANUFACTURING

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244


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metallurgical analysis in hot forging processes.
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[199] Astarita A, Ducato A, Fratini L, Paradiso V, Scherillo F, Squillace A, et al.
Beta
Forging of Ti
-
6Al
-
4V: microstructure evolution and mechanical properties. Key
Eng
Mater. 2013;554
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557:359
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71.

[200] Buffa G, Ducato A, Fratini L. Dissimilar material lap joints by Friction Stir Welding
of Steel and Titanium Sheets: Process Modeling. Aip Conf Proc. 2013;1532:491
-
8.

[201] Buffa G, Ducato A, Fratini L. Numerical proced
ure for residual stresses prediction
in friction stir welding. Finite Elem Anal Des. 2011;47:470
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6.

[202] Avrami M. Kinetics of phase change. I General theory. The Journal of Chemical
Physics. 2004;7:1103
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12.

[203] Seshacharyulu T, Medeiros SC, Frazier WG,

Prasad YVRK. Hot working of
commercial Ti
-
6Al
-
4V with an equiaxed alpha
-
beta microstructure: materials modeling
considerations.
Mat Sci Eng a
-
Struct. 2000;284:184
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94.

[204] Bruschi S, Poggio S, Quadrini F, Tata ME.
Workability of Ti

6Al

4V alloy at high
t
emperatures and strain rates. Materials Letters. 2004;58:3622

9.

[205] Hollomon JH. Tensile deformation. AIME TRANS. 1945;12:1
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22.

[206] Lee W
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S, Lin C
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F. Plastic deformation and fracture behaviour of Ti

6Al

4V alloy
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ous temperatures. Materials Science and
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[207] Lee W
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S, Lin C
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F. High
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temperature deformation behaviour of Ti6Al4V alloy
evaluated by high strain
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rate compression tests. J Mater Process Tech. 1998;75:127
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36.

[208] Kay G. Fail
ure modeling of titanium
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61
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4 V and 2024
-
T3 aluminum with the
Johnson
-
Cook material model. Technical Rep, Lawrence Livermore National Laboratory,
Livermore. 2002.

[209] Motyka M, Kubiak K, Sieniawski J, Ziaja W. Hot Plasticity of Alpha Beta Alloys.
2012.

[
210] Lee D, Backofen W. An experimental determination of the yield locus for titanium
and titanium
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alloy sheet. AIME MET SOC TRANS. 1966;236:1077
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flow stress in
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[
Computer aided engineering for thermo
-
me
chanical
-
metallurgical
analysis of forging operations of titanium alloys
]




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ENGINEERING

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orthogonal metal cutting toward the identification of the constitutive equation.
International Journal of Machine To
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cutting speeds

study of tool/work material interaction. CIRP Annals
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element simulation of conventional and high speed machining
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