Analysis Of Springback Problem On Aluminum Sheet.
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
ANALYSIS OF SPRINGBACK PROBLEM ON ALUMINUM
SHEET
This report submitted in accordance with requirement of the Universiti Teknikal
Malaysia Melaka (UTeM) for the Bachelor Degree of Manufacturing Engineering
(Engineering Materials) with Honours
by
LIONG SHUN HSIANG
FACULTY OF MANUFACTURING ENGINEERING
2010
DECLARATION
I hereby, declared this report entitled “ANALYSIS OF SPRINGBACK PROBLEM
ON ALUMINUM SHEET” is the results of my own research except as cited in
references.
Signature
:
………………………………………….
Author‟s Name
:
LIONG SHUN HSIANG
Date
:
9th April 2010
APPROVAL
This report is submitted to the Faculty of Manufacturing Engineering of UTeM
as a partial fulfillment of the requirements for the degree of Bachelor of
Manufacturing Engineering (Engineering Materials) with Honours. The member
of the supervisory committee is as follow:
(Signature of Supervisor)
………………………………
(Official Stamp of Supervisor)
APPROVAL
This report is submitted to the Faculty of Manufacturing Engineering of UTeM
as a partial fulfillment of the requirements for the degree of Bachelor of
Manufacturing Engineering (Engineering Materials) with Honours. The member
of the supervisory committee is as follow:
(Signature of Principal Supervisor)
………………………………
(Official Stamp of Principal Supervisor)
(Signature of Co-Supervisor)
………………………………
(Official Stamp of Co-Supervisor)
ABSTRACT
Springback is an important issue in aluminum sheet forming. Springback defined as
elastic recovery during unloading. It cause by elastic recovery due to bending.
Bending operation is one of the process involves springback. In automobile industry,
it is an issue to predict final shapes of the part after springback and die or bending
tools design to compensate for springback. For this research, an experimental study
carried out to determine the springback of aluminum. Experiment laboratory for
microstructure, bend test and tensile test are carrying out for aluminum sheet 1106.
Varies factor affecting springback problem of aluminum sheet are analyze. The result
determine on how the springback relates to the properties of aluminum sheet.
i
ABSTRAK
“Springback” ialah satu isu penting dalam pembentukan logam. “Springback”
dikenali sebagai pengembalian elastik selepas beban dilepaskan. Ia disebabkan
daripada kekenyalan bahan tersebut selepas pembentukan.. Operasi melenturkan
bahan adalah satu proses melibatkan “Springback”. Dalam industri pembuatan kereta,
ia adalah satu isu untuk meramalkan bentuk terakhir selepas “springback” dan pereka
peralatan untuk mengurangkan springback. Untuk pengajian ini, satu pengajian
dibuat untuk menentukan “springback” aluminum. Eksperimen untuk mikrostructur,
ujian lentur dan ujian tegangan dilakukan. Faktor yang menyebab masalah
“springback” telah dianalisa. Keputusan menentukan bagaimana faktor tersebut
mempengaruhi kadar “springback”.
ii
DEDICATION
For my beloved family.
iii
ACKNOWLEDGEMENT
Initially, I would like to express thousand thanks to Encik Mohamad Haidir bin
Maslan. He is my Project Sarjana Muda supervisor had provided his time to help me
correct my draft report and provide his knowledge and teaching throughout the
problem while going through writing the draft.
Secondly, I would like to express thanks for my course mate and moral support for
junior student for supporting me doing the PSM.
I would also like to thank my family for all of their support throughout my education.
Without their love, I would not have been able to accomplish any of things I have in
my life.
iv
TABLE OF CONTENT
Abstract
i
Abstrak
ii
Dedication
iii
Acknowledgement
iv
Table of content
v
List of figures
ix
List of tables
xi
List of abbreviations, symbols, specialized nomenclature
xii
1
2
INTRODUCTION
1
1.1
Research Title
1
1.2
Background of research
1
1.3
Research Problem
3
1.4
Research Hypothesis
4
1.5
Objective
4
1.6
Research Scope
4
1.7
Thesis Organization
5
1.8
Important of Research
6
LITERATURE REVIEW
7
2.1
Definition of springback
7
2.2
Causes of Springback
9
2.2.1
Thickness
10
2.2.2
Strength of materials
11
2.2.3
Material properties
11
2.2.3.1
Elastic bending below yield stress.
12
2.2.3.2
Elastic bending just exceed yield stress
13
2.2.3.3
Combined stretching and bending.
13
2.2.4
Geometrical factors
13
2.2.5
Conditions of die
14
v
2.2.6
Speed of bending
14
2.2.7
Conditions of the material
15
2.2.8
Other conditions that influence the springback
16
2.3
Ways to compensate springback
2.3.1
Overbending
17
2.3.2
Restriking and overbending
18
2.3.3
Use of special dies
19
2.4
Springback on aluminum alloys
20
2.5
Other Research on Springback
22
2.5.1
Recent Research about dimension and forms tolerances influence
springback
23
2.5.2
Recent Research about springback prediction with FEM/FEA
23
2.5.3
Baushinger Effect on springback materials
24
2.6
Properties of metering on springback
25
2.6.1
Tensile
25
2.6.2
Young modulus
28
2.6.2.1
Linear versus non-linear
29
2.6.2.2
Directional materials
29
2.6.3
3
16
Strain hardening
29
2.7
Guide to conduct the research
31
2.8
Reasons why springback is hard to predict
31
METHODOLOGY
3.1
33
Research Flow Chart
3.1.1
33
3.2
Material used
34
Material Preparation
35
3.2.1
Material preparation for bend test
35
3.2.2
Material preparation for tensile test
37
3.3
Testing Methods
3.3.1
38
Tensile test
38
3.3.1.1
Purpose
38
3.3.1.2
Introduction
38
3.3.1.3
Equipment
39
vi
3.3.1.4
3.3.2
42
3.3.2.1
Purpose
42
3.3.2.2
Introduction
43
3.3.3
Flow chart of bend test experiment
43
3.3.4
Apparatus
44
3.3.5
Parameters used in this experiment/Procedure
Metallographic examinations
45
46
3.3.5.1
Objective
46
3.3.5.2
Introduction
46
3.3.5.3
Equipment used
47
3.3.5.4
Procedures
47
RESULT AND DISCUSSION
49
4.1
Introduction
49
4.2
Tensile test analysis
49
4.2.1
Analysis graph of aluminum sheet in tensile test
49
4.2.2
Comparison of elastic modulus of aluminum sheet
50
4.2.3
Comparison of tensile test of aluminum sheet in various speed
51
4.2.4
Comparison of yield strength for tensile test in different speed
52
4.2.5
Comparison between two thickness of tensile test result
53
4.2.6
Factors affecting the testing result
54
4.3
Bend test analysis
54
4.3.1
Fast bend analysis
54
4.3.2
Slow bend analysis
56
4.3.3
Comparison between fast bend and slow bend test result
57
4.3.4
Comparison between thickness of bend test result
58
4.4
5
40
Bend Test
3.3.4.1
4
Procedure
Effect between speed of tensile test and bend test experiment
CONCLUSION AND RECOMMENDATION
59
61
5.1
Conclusion
61
5.2
Recommendation and Further Research
62
vii
REFERENCES
64
Appendices
68
Appendix A. Gantt Chart PSM 1
68
Appendix B. Gantt Chart PSM 2
69
Appendix C. Tensile test result
70
Appendix D. Bend test result
87
Appendix E. Microstructure result
98
viii
LIST OF FIGURES
2.1 Schematic diagram of stress strain diagram
2.2 Simple diagram of springback
8
10
2.3 Springback of a beam in simple bending. (a), Elastic bending. (b) Elastic
and Plastic Bending, (c) Bending and stretching.
12
2.4 Draw-bend specimens: tracing for various times following forming and
unloading for 6022-T4 aluminum. (Wang et al.)
2.5 Air Bending
15
18
2.6 Setup and sequence of operations for forming a complex shape in a press
brake showing of a restriking operation to reduce springback. (a) Forming
hem in two strokes. (b) Forming of first 90 angle for box section. (c)
Forming channel (d) Closing of box section over a mandrel. Part removed
by sliding off mandrel. (e) Restriking of box section to eliminate
springback.
19
2.7 (a) Forming a U-bend in one stroke (b) Flattening to remove springback
after U-bending. (Semiatin 1996)
20
2.8 Stress strain graph for carbon steel
26
2.9 Stress vs. strain curve of typical aluminum
28
2.10 Stress levels will change if the strain in tool changes
32
3.1 Flowchart of research methodology
34
3.2 Tools used to cut aluminum sheet into pieces
35
3.3 Cutting the aluminum sheet into various sizes
36
3.4 Relative orientation of longitudinal and transverse bend test
36
3.5 Sample Preparation for sheet aluminum
37
3.6 Tensile test flow chart
41
3.7 Bend test parameters
43
3.8 Flow chart of bend test
44
3.9 Part of bend test to investigated
47
4.1 Tensile test of aluminum sheet at1.0mm in speed 1mm/s
49
ix
4.2 Graph of tensile test of 1.0mm aluminum sheet in speed 1.0mm/s, 2.0mm/s
and 3.0mm/s
51
4.3 Comparison between tensile tests with different thickness in speed 1mm/s
53
4.4 Comparison between specimens of fast bend test of springback angle result
55
4.5 Comparison between specimens of slow bend test of springback angle
result
56
4.6 Specimen B springback angle by varies of speed (fast and slow) from bend
test
58
x
LIST OF TABLES
2.1 Springback allowances for 90-degree bend in 2024 and 7075 aluminum
alloy sheet (Semiatin 1996)
21
3.1 Categorized of bend test to determine springback angle
36
3.2 Sample Preparation for Sheet aluminum
37
3.3 List of equipment used in tensile test
39
3.4 Apparatus for bend test
44
3.5 Table of degree of bending versus springback
45
3.6 Equipment used for examining microstructure
47
4.1 Comparison of Modulus of aluminum sheet in different parameters
50
4.2 Comparison of yield strength of aluminum sheet in different speed
52
xi
LIST OF ABBREVIATIONS, SYMBOLS, SPECIALIZED
NOMENCLATURE
-
Degree
%
-
Percentage
2D
-
Two Dimensional
3D
-
Three Dimensional
ASTM
-
American Society for Testing and Materials
E
-
Modulus of elasticity
FEM
-
Finite element method
FEA
-
Finite element analysis
GPa
-
Gigapascals
In.
-
Inch
Ksi
-
Kilo pound force per square inch
Mm/mm
-
Millimeters
MPa
-
Mega Pascal
N/m²
-
Newton per square meter
N/mm²
-
Newton per mili-square meter
kN/mm²
-
Kilo Newton per mili square meter
Pa
-
Pascal
Y
-
Modulus of elasticity
xii
CHAPTER 1
INTRODUCTION
1.1 Research Title
Analysis of Spring Back Problem on Aluminum Sheet
1.2 Background of research
Aluminum has been a popular and widely used material in automobile manufacturing
industries. Aluminum alloy are preferred because of their lightweight and strength
properties. Aluminum alloy has relatively low tensile properties compared to steel.
This project is to identify the springback effect of aluminum and to explain the
causes of springback effect. This project also determines the springback rate of
aluminum. Springback is a phenomenon that happens in every metal sheet forming
industry. Spring back explained by dimensional changes during unloading cause by
elastic forming of the part. Sheet metal forming tools includes L-Shape forming,
Press Brake Forming, etc. Sheet metal formed between tools to obtain desired shape
required. For this reason, springback in sheet metal process involve a major in
automobile industries. The accuracy of dimension remains significant concern in
sheet metal forming process.
Springback problem has become one major and unsolved problem especially for car
manufacturer that the sheets need to bend to complex shape. This study will focus on
springback phenomenon and correlate the material properties to understand the
1
phenomenon. Because most of the materials used for car manufacturer required for
forming operation, there is sometime hard to make a proper forming procedure
required for this operation. This operation consumes time to prepare a proper
forming method to compensate springback problems. Some of the materials has good
formability while others having problems with springback. Effect of process
parameters on springback and strength of the springback has been research by
manufacturing department but the knowledge about the material springback
problems are limited due to many factors affect the springback of the material. There
is numerous factors influence the accuracy of prediction of springback. Certain
calculation involving numerical integration complicates springback prediction. Some
material goes through heat treatment process, tempering process and cold rolling
process that changes the structure of the material influence the springback prediction.
If not correctly predict and compensate for, springback will cause the final part shape
to deviate from design specifications and to create assembly problems. The
springback is the key problems in forming process. A number of numerical technical
methods devised to predict-springback, which enable the forming tool configuration
to modify to meet desired part surface. The purpose of this project is to analysis on
springback problems on aluminum material used for automobile, on the analysis of
experiment tensile test, finite element analysis (FEA) and then the equations to
simulating springback. All the causes of springback problems analyzed. The forming
process analysis using finite element method (FEM) or called finite element analysis
(FEA). Nowadays, these methods considered as an effective way of simulating
bending operations and predicting springback. FEA provides numerical trial and
error procedures, which consumes less time and more economical way of designing
and producing dies. There are some FEA programs providing effective and powerful
tools and environments to model and simulate operations of sheet metal forming.
Aluminum is an expensive material; therefore, design engineers use FEA in design
stages to reduce material and manufacturing costs.
The deep drawing process commonly used to manufacture sheet metal products.
During the process, initially curved or flat blank material clamped between the die
and the blank holder. When the punch pushed into the die cavity, the blank is
plastically deformed and the specific shape of the punch and the die transferred to it.
2
After the tools removed, the elastically driven change of the product shape, or socalled springback, occurs. This phenomenon results into the deviation of the obtained
product shape from the design specification and can be the major cause of assembly
problems. In sheet metal, forming the quality of the final product depends on the
proper tool design, choice of the blank material, blank holder force, lubrication and
some other process parameters. To manufacture a product with the desired shape and
performance an extensive knowledge about the influence of various parameters
needed. In order to establish this knowledge base, experimental try-outs or numerical
simulations are used. Finite element simulation of sheet metal forming is a powerful
tool, which allows test any modifications of the deep drawing process parameters,
prior to the actual tools manufacturing. Calculations made to predict and compensate
for springback and the numerical simulations repeated as often as necessary until the
product with the desired shape produced. Currently the numerical analysis is not able
accurately predict the springback of a formed product. There is always a difference
between the level of springback obtained in simulations and reality, especially for the
products with complicated geometry.
1.3 Research Problem
Springback are major problem to all forming process. To manufacture a product with
the desired shape and performance an extensive knowledge about the influence of
various parameters needed. In order to establish this knowledge base, experimental
try-outs or numerical simulations are used. Finite element simulation of sheet metal
forming is a powerful tool, which allows test any modifications of the deep drawing
process parameters, prior to the actual tools manufacturing. Calculations made to
predict and compensate for springback and the numerical simulations repeated as
often as necessary until the product with the desired shape produced. Currently the
numerical analysis is not able accurately predict the springback of a formed product.
There is always a discrepancy between the level of springback obtained in
simulations and reality, especially for the products with complicated geometry.
Because springback depends on the material properties of the sheet metal, tooling
geometry, friction and many other factors, it is difficult to predict springback of
3
material. Therefore, this compensation is heavily dependent on the designer's
experience and trial and error.
1.4 Research Hypothesis
The springback of aluminum may cause by tensile strength, Young modulus and
elastic modulus of the materials. It may also cause by bending angle, process of
bending and strength of materials. The aluminum sheet may springback more when
the bending radius angle increases. When the thickness of the aluminum sheet is less,
the aluminum may springback more. When the die radius is much bigger, the
aluminum may springback more.
1.5 Objective
The objective of the research is:
(a)
To analyze the springback problem of aluminum sheet
(b)
To analyze springback properties of various factors (bending angle, thickness,
and material properties (tensile) of aluminum
(c)
To analyze springback of aluminum sheet using tensile testing and bend test.
(d)
To analyze relationship between tensile test and bend test.
(e)
To find how the orientation of aluminum sheet influence the springback angle.
1.6 Research Scope
The scope of research including
(a)
Study the springback behavior of the aluminum sheet 1100.
(b)
Conduct experiment of aluminum sheet to investigate springback using
tensile testing, bending test, and microstructure.
4
(c)
Test method covers tension testing of aluminum at room temperature, to
determine yield strength, yield point elongation, tensile strength, elongation,
and reduction of area.
(d)
Study about other research of springback.
1.7 Thesis Organization
Chapter 1 is the introduction to this thesis, and provides a background of this thesis.
The objective and thesis organization are provided in this chapter.
Chapter 2 describes about literature review describe about springback. From here,
causes of springback literature described and other researches about springback are
included. This chapter also provide brief introduction about properties that influence
springback.
Chapter 3 is the methodology of the thesis. It covers the details on how to predict
springback of aluminum and ways to analysis the result. The tests included in this
thesis are tensile testing and bend testing.
Chapter 4 is the result and discussion from the methodology of the thesis. It covers
the details on the springback result cause by bending process and other result
obtained from the tensile test. It also covers result about microstructure of springback
of aluminum as well. In this part, much of the springback problems were discuss as
well. These discussions were discussed based on the result obtained from tensile
testing and bend testing.
Chapter 5 is the conclusion of the project. Conclusion includes recommendation to
improve the result of the experiment and further research needed to do to obtain
more research of the topic.
5
1.8 Important of Research
The important of this research is springback allows reduce the rate of predicting
springback of aluminum sheets. The inaccurate definition of the dependence of
springback on the above parameters can cause products loss due to scrapping or
reworking. Many researches and studies conducted to compensating springback
problems using the actual mechanical and geometrical properties of materials under
deformation. The important of springback prediction and compensation can save
resources and reduce product losses due to scrapping or reworking. Knowledge about
springback enable user to predict springback accurately before the material
undergoes forming operation. Springback is major factors influencing the quality of
the formed sheet metal parts. High springback of sheet metal often results in the
formed component being out of tolerance, introducing problems during assembly or
installation. Therefore, a precise prediction of springback is desirable in sheet metal
forming process because it leads to proper design of the forming tools and material
forming operation. On other hand, it can allow designers to design product using
proper material to compensate springback effect. Predicting springback not only
requires significant try-out time but also increases the cost. In this research,
experiment were carried out the best way springback characteristic of aluminum
sheet metal.
6
CHAPTER 2
LITERATURE REVIEW
The objective of this literature study is to understand the springback phenomenon
and to ascertain the reasons of its inaccurate numerical prediction. One of the reasons
for poor springback prediction is that this phenomenon not accurately represented in
finite element formulations. Various assumptions of material behavior - constant
elastic properties during forming, simplified elastic-plastic anisotropy and work
hardening - introduce the large modeling error. In addition, the accuracy of the
springback prediction affected significantly by the quality of simulation of the
forming operation. Chosen contact algorithms, the method of unloading, the time
integration scheme, the element types and the tooling can be other reasons for
significant deviation of the numerically predicted springback from that observed in
real practice. Furthermore, an analyst plays an important role and inexperienced
users may cause substantial inconsistency of the springback results. Naturally, this
tends to complicate the fabrication process. When a material formed, the stamping
tool bends the metal into certain angle with given bend radius.
2.1 Definition of springback
The springback is a term used to describe as the elastic recovery of metal (metal
return to its original shape) after stressing (to deform a body by a force) (Mandigo &
Crane 1993, p. 1794). Springback is another name of elastic deformation. Dies are
attempt to impart permanent, or plastic deformation into the sheet metal product.
Steel and aluminum, two common stamped materials can exhibit both elastic and
7
ANALYSIS OF SPRINGBACK PROBLEM ON ALUMINUM
SHEET
This report submitted in accordance with requirement of the Universiti Teknikal
Malaysia Melaka (UTeM) for the Bachelor Degree of Manufacturing Engineering
(Engineering Materials) with Honours
by
LIONG SHUN HSIANG
FACULTY OF MANUFACTURING ENGINEERING
2010
DECLARATION
I hereby, declared this report entitled “ANALYSIS OF SPRINGBACK PROBLEM
ON ALUMINUM SHEET” is the results of my own research except as cited in
references.
Signature
:
………………………………………….
Author‟s Name
:
LIONG SHUN HSIANG
Date
:
9th April 2010
APPROVAL
This report is submitted to the Faculty of Manufacturing Engineering of UTeM
as a partial fulfillment of the requirements for the degree of Bachelor of
Manufacturing Engineering (Engineering Materials) with Honours. The member
of the supervisory committee is as follow:
(Signature of Supervisor)
………………………………
(Official Stamp of Supervisor)
APPROVAL
This report is submitted to the Faculty of Manufacturing Engineering of UTeM
as a partial fulfillment of the requirements for the degree of Bachelor of
Manufacturing Engineering (Engineering Materials) with Honours. The member
of the supervisory committee is as follow:
(Signature of Principal Supervisor)
………………………………
(Official Stamp of Principal Supervisor)
(Signature of Co-Supervisor)
………………………………
(Official Stamp of Co-Supervisor)
ABSTRACT
Springback is an important issue in aluminum sheet forming. Springback defined as
elastic recovery during unloading. It cause by elastic recovery due to bending.
Bending operation is one of the process involves springback. In automobile industry,
it is an issue to predict final shapes of the part after springback and die or bending
tools design to compensate for springback. For this research, an experimental study
carried out to determine the springback of aluminum. Experiment laboratory for
microstructure, bend test and tensile test are carrying out for aluminum sheet 1106.
Varies factor affecting springback problem of aluminum sheet are analyze. The result
determine on how the springback relates to the properties of aluminum sheet.
i
ABSTRAK
“Springback” ialah satu isu penting dalam pembentukan logam. “Springback”
dikenali sebagai pengembalian elastik selepas beban dilepaskan. Ia disebabkan
daripada kekenyalan bahan tersebut selepas pembentukan.. Operasi melenturkan
bahan adalah satu proses melibatkan “Springback”. Dalam industri pembuatan kereta,
ia adalah satu isu untuk meramalkan bentuk terakhir selepas “springback” dan pereka
peralatan untuk mengurangkan springback. Untuk pengajian ini, satu pengajian
dibuat untuk menentukan “springback” aluminum. Eksperimen untuk mikrostructur,
ujian lentur dan ujian tegangan dilakukan. Faktor yang menyebab masalah
“springback” telah dianalisa. Keputusan menentukan bagaimana faktor tersebut
mempengaruhi kadar “springback”.
ii
DEDICATION
For my beloved family.
iii
ACKNOWLEDGEMENT
Initially, I would like to express thousand thanks to Encik Mohamad Haidir bin
Maslan. He is my Project Sarjana Muda supervisor had provided his time to help me
correct my draft report and provide his knowledge and teaching throughout the
problem while going through writing the draft.
Secondly, I would like to express thanks for my course mate and moral support for
junior student for supporting me doing the PSM.
I would also like to thank my family for all of their support throughout my education.
Without their love, I would not have been able to accomplish any of things I have in
my life.
iv
TABLE OF CONTENT
Abstract
i
Abstrak
ii
Dedication
iii
Acknowledgement
iv
Table of content
v
List of figures
ix
List of tables
xi
List of abbreviations, symbols, specialized nomenclature
xii
1
2
INTRODUCTION
1
1.1
Research Title
1
1.2
Background of research
1
1.3
Research Problem
3
1.4
Research Hypothesis
4
1.5
Objective
4
1.6
Research Scope
4
1.7
Thesis Organization
5
1.8
Important of Research
6
LITERATURE REVIEW
7
2.1
Definition of springback
7
2.2
Causes of Springback
9
2.2.1
Thickness
10
2.2.2
Strength of materials
11
2.2.3
Material properties
11
2.2.3.1
Elastic bending below yield stress.
12
2.2.3.2
Elastic bending just exceed yield stress
13
2.2.3.3
Combined stretching and bending.
13
2.2.4
Geometrical factors
13
2.2.5
Conditions of die
14
v
2.2.6
Speed of bending
14
2.2.7
Conditions of the material
15
2.2.8
Other conditions that influence the springback
16
2.3
Ways to compensate springback
2.3.1
Overbending
17
2.3.2
Restriking and overbending
18
2.3.3
Use of special dies
19
2.4
Springback on aluminum alloys
20
2.5
Other Research on Springback
22
2.5.1
Recent Research about dimension and forms tolerances influence
springback
23
2.5.2
Recent Research about springback prediction with FEM/FEA
23
2.5.3
Baushinger Effect on springback materials
24
2.6
Properties of metering on springback
25
2.6.1
Tensile
25
2.6.2
Young modulus
28
2.6.2.1
Linear versus non-linear
29
2.6.2.2
Directional materials
29
2.6.3
3
16
Strain hardening
29
2.7
Guide to conduct the research
31
2.8
Reasons why springback is hard to predict
31
METHODOLOGY
3.1
33
Research Flow Chart
3.1.1
33
3.2
Material used
34
Material Preparation
35
3.2.1
Material preparation for bend test
35
3.2.2
Material preparation for tensile test
37
3.3
Testing Methods
3.3.1
38
Tensile test
38
3.3.1.1
Purpose
38
3.3.1.2
Introduction
38
3.3.1.3
Equipment
39
vi
3.3.1.4
3.3.2
42
3.3.2.1
Purpose
42
3.3.2.2
Introduction
43
3.3.3
Flow chart of bend test experiment
43
3.3.4
Apparatus
44
3.3.5
Parameters used in this experiment/Procedure
Metallographic examinations
45
46
3.3.5.1
Objective
46
3.3.5.2
Introduction
46
3.3.5.3
Equipment used
47
3.3.5.4
Procedures
47
RESULT AND DISCUSSION
49
4.1
Introduction
49
4.2
Tensile test analysis
49
4.2.1
Analysis graph of aluminum sheet in tensile test
49
4.2.2
Comparison of elastic modulus of aluminum sheet
50
4.2.3
Comparison of tensile test of aluminum sheet in various speed
51
4.2.4
Comparison of yield strength for tensile test in different speed
52
4.2.5
Comparison between two thickness of tensile test result
53
4.2.6
Factors affecting the testing result
54
4.3
Bend test analysis
54
4.3.1
Fast bend analysis
54
4.3.2
Slow bend analysis
56
4.3.3
Comparison between fast bend and slow bend test result
57
4.3.4
Comparison between thickness of bend test result
58
4.4
5
40
Bend Test
3.3.4.1
4
Procedure
Effect between speed of tensile test and bend test experiment
CONCLUSION AND RECOMMENDATION
59
61
5.1
Conclusion
61
5.2
Recommendation and Further Research
62
vii
REFERENCES
64
Appendices
68
Appendix A. Gantt Chart PSM 1
68
Appendix B. Gantt Chart PSM 2
69
Appendix C. Tensile test result
70
Appendix D. Bend test result
87
Appendix E. Microstructure result
98
viii
LIST OF FIGURES
2.1 Schematic diagram of stress strain diagram
2.2 Simple diagram of springback
8
10
2.3 Springback of a beam in simple bending. (a), Elastic bending. (b) Elastic
and Plastic Bending, (c) Bending and stretching.
12
2.4 Draw-bend specimens: tracing for various times following forming and
unloading for 6022-T4 aluminum. (Wang et al.)
2.5 Air Bending
15
18
2.6 Setup and sequence of operations for forming a complex shape in a press
brake showing of a restriking operation to reduce springback. (a) Forming
hem in two strokes. (b) Forming of first 90 angle for box section. (c)
Forming channel (d) Closing of box section over a mandrel. Part removed
by sliding off mandrel. (e) Restriking of box section to eliminate
springback.
19
2.7 (a) Forming a U-bend in one stroke (b) Flattening to remove springback
after U-bending. (Semiatin 1996)
20
2.8 Stress strain graph for carbon steel
26
2.9 Stress vs. strain curve of typical aluminum
28
2.10 Stress levels will change if the strain in tool changes
32
3.1 Flowchart of research methodology
34
3.2 Tools used to cut aluminum sheet into pieces
35
3.3 Cutting the aluminum sheet into various sizes
36
3.4 Relative orientation of longitudinal and transverse bend test
36
3.5 Sample Preparation for sheet aluminum
37
3.6 Tensile test flow chart
41
3.7 Bend test parameters
43
3.8 Flow chart of bend test
44
3.9 Part of bend test to investigated
47
4.1 Tensile test of aluminum sheet at1.0mm in speed 1mm/s
49
ix
4.2 Graph of tensile test of 1.0mm aluminum sheet in speed 1.0mm/s, 2.0mm/s
and 3.0mm/s
51
4.3 Comparison between tensile tests with different thickness in speed 1mm/s
53
4.4 Comparison between specimens of fast bend test of springback angle result
55
4.5 Comparison between specimens of slow bend test of springback angle
result
56
4.6 Specimen B springback angle by varies of speed (fast and slow) from bend
test
58
x
LIST OF TABLES
2.1 Springback allowances for 90-degree bend in 2024 and 7075 aluminum
alloy sheet (Semiatin 1996)
21
3.1 Categorized of bend test to determine springback angle
36
3.2 Sample Preparation for Sheet aluminum
37
3.3 List of equipment used in tensile test
39
3.4 Apparatus for bend test
44
3.5 Table of degree of bending versus springback
45
3.6 Equipment used for examining microstructure
47
4.1 Comparison of Modulus of aluminum sheet in different parameters
50
4.2 Comparison of yield strength of aluminum sheet in different speed
52
xi
LIST OF ABBREVIATIONS, SYMBOLS, SPECIALIZED
NOMENCLATURE
-
Degree
%
-
Percentage
2D
-
Two Dimensional
3D
-
Three Dimensional
ASTM
-
American Society for Testing and Materials
E
-
Modulus of elasticity
FEM
-
Finite element method
FEA
-
Finite element analysis
GPa
-
Gigapascals
In.
-
Inch
Ksi
-
Kilo pound force per square inch
Mm/mm
-
Millimeters
MPa
-
Mega Pascal
N/m²
-
Newton per square meter
N/mm²
-
Newton per mili-square meter
kN/mm²
-
Kilo Newton per mili square meter
Pa
-
Pascal
Y
-
Modulus of elasticity
xii
CHAPTER 1
INTRODUCTION
1.1 Research Title
Analysis of Spring Back Problem on Aluminum Sheet
1.2 Background of research
Aluminum has been a popular and widely used material in automobile manufacturing
industries. Aluminum alloy are preferred because of their lightweight and strength
properties. Aluminum alloy has relatively low tensile properties compared to steel.
This project is to identify the springback effect of aluminum and to explain the
causes of springback effect. This project also determines the springback rate of
aluminum. Springback is a phenomenon that happens in every metal sheet forming
industry. Spring back explained by dimensional changes during unloading cause by
elastic forming of the part. Sheet metal forming tools includes L-Shape forming,
Press Brake Forming, etc. Sheet metal formed between tools to obtain desired shape
required. For this reason, springback in sheet metal process involve a major in
automobile industries. The accuracy of dimension remains significant concern in
sheet metal forming process.
Springback problem has become one major and unsolved problem especially for car
manufacturer that the sheets need to bend to complex shape. This study will focus on
springback phenomenon and correlate the material properties to understand the
1
phenomenon. Because most of the materials used for car manufacturer required for
forming operation, there is sometime hard to make a proper forming procedure
required for this operation. This operation consumes time to prepare a proper
forming method to compensate springback problems. Some of the materials has good
formability while others having problems with springback. Effect of process
parameters on springback and strength of the springback has been research by
manufacturing department but the knowledge about the material springback
problems are limited due to many factors affect the springback of the material. There
is numerous factors influence the accuracy of prediction of springback. Certain
calculation involving numerical integration complicates springback prediction. Some
material goes through heat treatment process, tempering process and cold rolling
process that changes the structure of the material influence the springback prediction.
If not correctly predict and compensate for, springback will cause the final part shape
to deviate from design specifications and to create assembly problems. The
springback is the key problems in forming process. A number of numerical technical
methods devised to predict-springback, which enable the forming tool configuration
to modify to meet desired part surface. The purpose of this project is to analysis on
springback problems on aluminum material used for automobile, on the analysis of
experiment tensile test, finite element analysis (FEA) and then the equations to
simulating springback. All the causes of springback problems analyzed. The forming
process analysis using finite element method (FEM) or called finite element analysis
(FEA). Nowadays, these methods considered as an effective way of simulating
bending operations and predicting springback. FEA provides numerical trial and
error procedures, which consumes less time and more economical way of designing
and producing dies. There are some FEA programs providing effective and powerful
tools and environments to model and simulate operations of sheet metal forming.
Aluminum is an expensive material; therefore, design engineers use FEA in design
stages to reduce material and manufacturing costs.
The deep drawing process commonly used to manufacture sheet metal products.
During the process, initially curved or flat blank material clamped between the die
and the blank holder. When the punch pushed into the die cavity, the blank is
plastically deformed and the specific shape of the punch and the die transferred to it.
2
After the tools removed, the elastically driven change of the product shape, or socalled springback, occurs. This phenomenon results into the deviation of the obtained
product shape from the design specification and can be the major cause of assembly
problems. In sheet metal, forming the quality of the final product depends on the
proper tool design, choice of the blank material, blank holder force, lubrication and
some other process parameters. To manufacture a product with the desired shape and
performance an extensive knowledge about the influence of various parameters
needed. In order to establish this knowledge base, experimental try-outs or numerical
simulations are used. Finite element simulation of sheet metal forming is a powerful
tool, which allows test any modifications of the deep drawing process parameters,
prior to the actual tools manufacturing. Calculations made to predict and compensate
for springback and the numerical simulations repeated as often as necessary until the
product with the desired shape produced. Currently the numerical analysis is not able
accurately predict the springback of a formed product. There is always a difference
between the level of springback obtained in simulations and reality, especially for the
products with complicated geometry.
1.3 Research Problem
Springback are major problem to all forming process. To manufacture a product with
the desired shape and performance an extensive knowledge about the influence of
various parameters needed. In order to establish this knowledge base, experimental
try-outs or numerical simulations are used. Finite element simulation of sheet metal
forming is a powerful tool, which allows test any modifications of the deep drawing
process parameters, prior to the actual tools manufacturing. Calculations made to
predict and compensate for springback and the numerical simulations repeated as
often as necessary until the product with the desired shape produced. Currently the
numerical analysis is not able accurately predict the springback of a formed product.
There is always a discrepancy between the level of springback obtained in
simulations and reality, especially for the products with complicated geometry.
Because springback depends on the material properties of the sheet metal, tooling
geometry, friction and many other factors, it is difficult to predict springback of
3
material. Therefore, this compensation is heavily dependent on the designer's
experience and trial and error.
1.4 Research Hypothesis
The springback of aluminum may cause by tensile strength, Young modulus and
elastic modulus of the materials. It may also cause by bending angle, process of
bending and strength of materials. The aluminum sheet may springback more when
the bending radius angle increases. When the thickness of the aluminum sheet is less,
the aluminum may springback more. When the die radius is much bigger, the
aluminum may springback more.
1.5 Objective
The objective of the research is:
(a)
To analyze the springback problem of aluminum sheet
(b)
To analyze springback properties of various factors (bending angle, thickness,
and material properties (tensile) of aluminum
(c)
To analyze springback of aluminum sheet using tensile testing and bend test.
(d)
To analyze relationship between tensile test and bend test.
(e)
To find how the orientation of aluminum sheet influence the springback angle.
1.6 Research Scope
The scope of research including
(a)
Study the springback behavior of the aluminum sheet 1100.
(b)
Conduct experiment of aluminum sheet to investigate springback using
tensile testing, bending test, and microstructure.
4
(c)
Test method covers tension testing of aluminum at room temperature, to
determine yield strength, yield point elongation, tensile strength, elongation,
and reduction of area.
(d)
Study about other research of springback.
1.7 Thesis Organization
Chapter 1 is the introduction to this thesis, and provides a background of this thesis.
The objective and thesis organization are provided in this chapter.
Chapter 2 describes about literature review describe about springback. From here,
causes of springback literature described and other researches about springback are
included. This chapter also provide brief introduction about properties that influence
springback.
Chapter 3 is the methodology of the thesis. It covers the details on how to predict
springback of aluminum and ways to analysis the result. The tests included in this
thesis are tensile testing and bend testing.
Chapter 4 is the result and discussion from the methodology of the thesis. It covers
the details on the springback result cause by bending process and other result
obtained from the tensile test. It also covers result about microstructure of springback
of aluminum as well. In this part, much of the springback problems were discuss as
well. These discussions were discussed based on the result obtained from tensile
testing and bend testing.
Chapter 5 is the conclusion of the project. Conclusion includes recommendation to
improve the result of the experiment and further research needed to do to obtain
more research of the topic.
5
1.8 Important of Research
The important of this research is springback allows reduce the rate of predicting
springback of aluminum sheets. The inaccurate definition of the dependence of
springback on the above parameters can cause products loss due to scrapping or
reworking. Many researches and studies conducted to compensating springback
problems using the actual mechanical and geometrical properties of materials under
deformation. The important of springback prediction and compensation can save
resources and reduce product losses due to scrapping or reworking. Knowledge about
springback enable user to predict springback accurately before the material
undergoes forming operation. Springback is major factors influencing the quality of
the formed sheet metal parts. High springback of sheet metal often results in the
formed component being out of tolerance, introducing problems during assembly or
installation. Therefore, a precise prediction of springback is desirable in sheet metal
forming process because it leads to proper design of the forming tools and material
forming operation. On other hand, it can allow designers to design product using
proper material to compensate springback effect. Predicting springback not only
requires significant try-out time but also increases the cost. In this research,
experiment were carried out the best way springback characteristic of aluminum
sheet metal.
6
CHAPTER 2
LITERATURE REVIEW
The objective of this literature study is to understand the springback phenomenon
and to ascertain the reasons of its inaccurate numerical prediction. One of the reasons
for poor springback prediction is that this phenomenon not accurately represented in
finite element formulations. Various assumptions of material behavior - constant
elastic properties during forming, simplified elastic-plastic anisotropy and work
hardening - introduce the large modeling error. In addition, the accuracy of the
springback prediction affected significantly by the quality of simulation of the
forming operation. Chosen contact algorithms, the method of unloading, the time
integration scheme, the element types and the tooling can be other reasons for
significant deviation of the numerically predicted springback from that observed in
real practice. Furthermore, an analyst plays an important role and inexperienced
users may cause substantial inconsistency of the springback results. Naturally, this
tends to complicate the fabrication process. When a material formed, the stamping
tool bends the metal into certain angle with given bend radius.
2.1 Definition of springback
The springback is a term used to describe as the elastic recovery of metal (metal
return to its original shape) after stressing (to deform a body by a force) (Mandigo &
Crane 1993, p. 1794). Springback is another name of elastic deformation. Dies are
attempt to impart permanent, or plastic deformation into the sheet metal product.
Steel and aluminum, two common stamped materials can exhibit both elastic and
7