The Effect of Cut-out Hole Size on the Formability of Hole Flanging by Multistage Incremental ...

94 Pages·2014·4.08 MB·Turkish

The Effect of Cut-out Hole Size on the Formability of
Hole Flanging by Multistage Incremental Forming

Hatef Valaei

Submitted to the
Institute of Graduate Studies and Research
in partial fulfillment of the requirements for the Degree of

Master of Science
in
Mechanical Engineering

Eastern Mediterranean University
July 2014
Gazimağusa, North Cyprus
Approval of the Institute of Graduate Studies and Research

__________________________
Prof. Dr. Elvan Yılmaz
Director

I certify that this thesis satisfies the requirements as a thesis for the degree of Master
of Science in Mechanical Engineering.

________________________________________
Prof. Dr. Uğur Atikol
Chair, Department of Mechanical Engineering

We certify that we have read this thesis and that in our opinion it is fully adequate in
scope and quality as a thesis for the degree of Master of Science in Mechanical
Engineering.

_______________________________
Asst. Prof. Dr. Ghulam Hussain
Supervisor

Examining Committee

1. Assoc. Prof. Dr. Hasan Hacışevki ___________________________
2. Asst. Prof. Dr. Ghulam Hussain ___________________________
3. Dr. Kiyan Parham ___________________________
2
ABSTRACT
Single point incremental forming is advancing to replace the conventional sheet
forming processes. Multi stage incremental forming is introduced to cover some
shortcomings of this process and extend the complexity of the shapes that cannot be
produced in single stage incremental forming. This method does not require any
special equipment and is very economic.
In this study the effect of varying cut-out hole size on the formability of hole flanging
in multi-stage incremental forming and on the thickness distribution of flange is
investigated. The AA1060 aluminum is taken as the experimental material, and the
formability is measured as the flange depth without sheet fracture. The flanges are
made in 4 stages of 45°, 60°, 75° and 90° at room temperature. Furthermore, the stress
and strain patterns are studied utilizing ABAQUS software in order to understand the
process mechanics.
The results have shown that the hole size has great effect on the flange depth and wall
thickness of the part made by multistage incremental forming. The achieved depth
decreases with increasing the hole size due to lack of material and thinning is less as
the hole diameter gets larger.
The FEA results shows that increasing hole diameter will lead to lower stress and hoop
strain levels due to decreasing the amount of material under load of the tool. Also it
showed that a small amount of work hardening is useful for increasing the formability
of the process.
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Keyword: Multi stage incremental forming, formability, FEA ABAQUS, failure, hole
flanging, hole diameter, stress level, strain level.

iv
ÖZ

Tek nokta artırımlı şekillendirme, konvansiyonel saç şekillendirme prosesinin yerini
alma yönünde ilerlemektedir. Çok aşamalı atışlı şekillendirme metodu tek noktalı
metodun eksikliklerini gidermek ve tek noktalı proses ile üretilemeyen kompleks
parçaları üretmek için tanıtılmıştır. Bu metod herhangi özel bir ekipman gerektirmiyor
ve çok ekonomiktir.
Bu çalışmada çok aşamalı atışlı şekillendirmenin delik ölçüsündeki değişikliklerin,
delik flanş oluşumuna ve flanş kalınlığına etkisi incelenmiştir.
Deneysel malzeme olarak AA1060 aluminyum kullanılmış ve saç kırılması olmadan
şekillendirme ve flanş derinliği ölçülmüştür . Flanşlar oda sıcaklığında 45° ,60°, 75°
ve 90° olmak üzere dort aşamada yapılmıştır.
Prosesin mekaniğini anlamak için mukavemet hesapları ABAQUS yazılımı
kullanılarak yapılmıştır. Çok aşamalı atışlı şekillendirme metodun delik ölçüsünün
flanş derinliği ve et kalınlığı üzerinde büyük etkisi olduğu saptanmıştır. Elde edilen
derinliğin delik ölçüsünün artması ile azaldığı, malzemenin kalınlığının azalması ve
malzemenin kendisi ile alakalı olduğu ve incelmenin delik çapının artması ile azaldığı
saptanmıştır.
Anahtar kelime: Çok aşamalı artışlı şekillendirme, şekillenebilirliği, FEA
ABAQUS, şekillendirme başarısızlığı, flanş, delik çapı, stres düzeyi, gerginlik
seviyesi.

v
DEDICATION

To My Family,
Romina and Findi

vi
ACKNOWLEDGEMENT
I would like to thank Asst. Prof. Dr. Ghulam Hussain for his continuous support and
guidance in the preparation of this study. Without his invaluable supervision, all my
efforts could have been short-sighted.
Prof. Dr. Uğur Atikol, Chairman of the Department of Mechanical Engineering,
Eastern Mediterranean University, helped me with various issues during the thesis
and I am grateful to him. I am also obliged to Dr. Mehdi Shakoori Partovi for his
help during my thesis. Besides, a number of friends had always been around to
support me morally. I would like to thank them as well.
I owe quit a lot to my family who allowed me to travel all the way from Iran to
Cyprus and supported me all throughout my studies. I would like to dedicate this
study to them as an indication of their significance in this study as well as in my life.

vii
TABLE OF CONTENTS
ABSTRACT ................................................................................................................ iii
ÖZ ............................................................................................................................... v
DEDICATION ............................................................................................................ vi
ACKNOWLEDGMENT ........................................................................................... viii
LIST OF TABLES .................................................................................................... xiii
LIST OF FIGURES .................................................................................................. xiv
LIST OF SYMBOLS/ABBREVIATIONS .............................................................. xvii
1 INTRODUCTION .................................................................................................... 1
1.1 Conventional Sheet Metal Processes ................................................................. 1
1.1.1 Hammering ................................................................................................. 1
1.1.2 Spinning ...................................................................................................... 2
1.2 Background ......................................................................................................... 3
1.3 Objective of Thesis ............................................................................................. 5
1.4 Thesis organization ............................................................................................. 5
2 LITERATURE REVIEW ......................................................................................... 6
2.1 Single point incremental forming ....................................................................... 6
2.1.1 Process definition......................................................................................... 6
2.1.2 Significant Parameters ................................................................................. 7
2.1.3 Forming tool ................................................................................................ 7
2.1.4 Forming tool path ........................................................................................ 8
2.1.5 Sheet material .............................................................................................. 9
2.1.6 Forming angle .............................................................................................. 9
2.1.7 Step size ..................................................................................................... 10
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2.1.8 Forming speed ........................................................................................... 11
2.1.9 Lubrication ................................................................................................. 11
2.2 Incremental forming types ................................................................................ 11
2.2.1 Single point incremental forming .............................................................. 12
2.2.2 Two point incremental forming ................................................................. 12
2.3 SPIF Formability .............................................................................................. 14
2.3.1 Strain path .................................................................................................. 15
2.3.2 Through thickness shear ............................................................................ 16
2.3.3 Bending ...................................................................................................... 16
2.3.4 Triaxiality .................................................................................................. 17
2.4 Multi stage incremental forming ...................................................................... 17
2.4.1 On the formability of Hole flanging .......................................................... 20
2.4.1.1 Limiting forming Ratio ........................................................................... 20
2.4.1.2 Multi stage incremental forming strategies ............................................ 21
2.4.1.3 Number of stages .................................................................................... 23
3 ABAQUS FINITE ELEMENT MODELING ......................................................... 25
3.1 General description ........................................................................................... 25
3.1.1 Implicit method .......................................................................................... 25
3.1.2 Explicit method .......................................................................................... 26
3.2 Considerable parameters in FEA method ......................................................... 26
3.2.1 Mass scaling............................................................................................... 26
3.2.2 Time scaling............................................................................................... 27
3.2.3 Finite element type .................................................................................... 28
3.2.4 Yield Criteria and laws .............................................................................. 29
3.2.5 Mesh size sensitivity test ........................................................................... 30
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4 METHODOLOGY ................................................................................................. 33
4.1 Experiments ...................................................................................................... 33
4.1.1 Material properties ..................................................................................... 33
4.1.2 CNC machine............................................................................................. 35
4.1.3 Tooling ....................................................................................................... 36
4.1.4 Fixture system and rig ............................................................................... 36
4.1.5 Measurements ............................................................................................ 38
4.1.6 CAD – CAM .............................................................................................. 38
4.1.7 Chosen parameters for experiments........................................................... 39
4.1.8 Experimental plan ...................................................................................... 40
4.2 Dynamic explicit simulation via ABAQUS ..................................................... 41
4.2.1 Explicit/ Implicit ........................................................................................ 41
4.2.2 Element type .............................................................................................. 41
4.2.3 Meshing type ............................................................................................. 42
4.3 Modeling and boundary conditions .................................................................. 44
4.3.1 Line test ..................................................................................................... 45
4.3.2 Tool path/ Amplitude ................................................................................. 46
4.3.3 Cone test .................................................................................................... 49
4.3.4 Mass scaling............................................................................................... 51
4.3.5 Element selection method for comparison ............................................... 52
5 RESULTS AND DISCUSSION ............................................................................. 53
5.1 Total depth or formability ................................................................................ 53
5.2 Thickness distribution ...................................................................................... 55
5.3 FEA results ....................................................................................................... 64
5.4.1 Stress evolution .......................................................................................... 57
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