Upload
others
View
5
Download
0
Embed Size (px)
Citation preview
Application and Optimization of Friction Stir Welding
on Electrical Transformers Components
João Filipe Gomes Duarte Prior
Thesis to obtain the Master of Science Degree in
Materials Engineering
Supervisor: Professora Luísa Coutinho
Examination Committee
Chairperson: Professora Mª Fátima Vaz
Supervisor: Professora Luísa Coutinho
Members: Professora Rosa Miranda
Professor Rogério Colaço
Engenheiro Joel Mendes
March 2015
A toda a minha família e à Susana,
Por todo o apoio e paciência.
i
I. Abstract
This work intends to assist the industrial implementation of Friction Stir Welding (FSW)
process in components of electric power transformers. A methodology based on Taguchi method was
used to estimate the optimal parameters of butt welds in thin sheets of commercially pure aluminum,
AA1070, 1.6mm thick and 1.1mm thick, C11000, copper alloy. For this study three levels of the
parameters were considered: Axial Force (Fz), Travel Speed (Vx), and Probe Length (Lpin). The
optimum parameters were obtained through an analysis of variance (ANOVA) on three factors of
overall efficiency. GET, GEB and HARD coefficients were reached based on the results of tensile,
bending and hardness, respectively. Were also tested solutions for dissimilar welds with visually
satisfactory results. A preliminary feasibility study was made for the implementation of the process,
which shows a payback period of less than five years. Thus, it was concluded that the FSW process is
perfectly suited to the reality of SIEMENS FS because it allows significant improvements when
compared to the current process, Tungsten Inert Gas (TIG). This will lead to improvements on weld
quality, cost reduction and improved working environment.
II. Key-Words
FSW, Taguchi, Aluminum, Copper, Dissimilar Welding and Feasibility Study.
ii
III. Resumo
O presente trabalho foi desenvolvido com o intuito da aplicação industrial do processo de
soldadura por fricção linear (SFL) em componentes de transformadores eléctricos de potência. Assim,
de forma a estimar os parâmetros óptimos de soldaduras topo-a-topo em chapas finas de alumínio
(AA1070) e cobre (C11000) de 1.6mm e 1.1mm de espessura respectivamente, foi desenvolvido um
estudo com base no método de Taguchi. Para este estudo foram escolhidos três níveis diferentes
para os parâmetros de soldadura: força axial (Fz), velocidade de avanço (Vx) e comprimento do pino
(Lpin). Os parâmetros óptimos foram obtidos através da análise de variância (ANOVA) de três
factores de eficiência global, GET, GEB e HARD, desenvolvidos com base em resultados de tracção,
flexão e dureza respectivamente. Investigou-se ainda a ligação de materiais e geometrias
dissimilares, tendo sido realizadas soldaduras com características visualmente satisfatórias. Por
último foi realizado um estudo preliminar de viabilidade económica para a implementação do
processo, cujo período de retorno seria inferior a cinco anos. Conclui-se portanto que a SFL é um
processo perfeitamente adequado para a realidade da fábrica SIEMENS, pois permite melhorias
significativas em relação ao processo actual (TIG), nomeadamente na qualidade das soldaduras, no
custo unitário por soldadura e nas condições de segurança de trabalho dos operadores.
IV. Palavras-Chave
SFL, Taguchi, Aluminio, Cobre, Soldadura Dissimilar e Viabilidade Económica.
iii
V. Acknowledgements
I would like to express my deep gratitude to my supervisor, Professor Luísa Coutinho for all
commitment and personal interest in this dissertation.
A sincerely thank you to Professor Pedro Vilaça for inviting me to join SIEMENStir, such a
challenging and promising project. Thanks for all the trust and total freedom to develop my work and
all the technical support given.
Big thanks to my co-supervisor, Engineer Joel Mendes, for all the help, effort and interest. I
acknowledge the warm welcome within SIEMENS-FS and all the time spent for monitoring and
supervising the work.
My thanks to SIEMENS-FS for the confidence placed in me throughout the work. The material
and the funds invested in the project. I have to express my gratitude to Engineers António Silva and
Eugénio Santis.
I thank Professor Beatriz Silva for the help and time spent in the performance and
interpretation of the uniaxial tensile tests.
My thanks to Professor Rosa Miranda for the help and equipment provided to the hardness
tests, as well as to Professor Telmo Santos for supporting the conductivity tests.
I would like to thank Doctors João Gandra and Filipe Nascimento for the fellowship and
friendship, the training and help they always gave to me. I will never forget all the advices they gave to
me, in the many times I went desperate in their office. Thanks to Master André Oliveira for the
company and friendship in long hours writing and testing.
A special thanks to Mr. Daniel Pomiel and Mr. Carlos Farinha for all the assistance and
knowledge transmitted.
I also express my grateful to Mr. João Luís by the excellent work in the production of work
tools and other components designed, as well as to Mr. Lopes for machining of test specimens.
To my colleagues Nuno Ferreira, Daniel Pimentel, Mirela Lourenço, Tiago Gomes, Filipa
Baltazar, Francisco Sá, Bernardo Dias Miguel, Lucas Niven, João Nicolau, Teresa Gouveia e Tiago
Soares among many others, I express my deep regard for the strong friendship that has developed
throughout the course and systematic support during this work. Special thanks to Jacob Francisco for
reviewing and correcting the English.
iv
VI. Agradecimentos
Venho por este meio expressar a minha profunda gratidão à minha orientadora, Professora
Luísa Coutinho por todo o seu apoio e interesse na concepção desta dissertação.
Um sincero obrigado ao Professor Pedro Vilaça por me ter convidado para integrar um
projecto tão desafiante e promissor como o SIEMENStir, por toda a confiança que depositou em mim,
conferindo-me total liberdade para desenvolver o meu trabalho e por todo o apoio técnico dado.
Um enorme agradecimento ao meu co-orientador, Engenheiro Joel Mendes, por toda a sua
ajuda, empenho e interesse. Não posso deixar de agradecer a forma como me recebeu e me integrou
na SIEMENS-FS e por todo o tempo despendido para o acompanhamento e orientação do trabalho.
O meu muito obrigado à SIEMENS-FS pela confiança em mim depositada durante todo o
trabalho, pelo material cedido e pelos fundos investidos no projecto. Não posso deixar expressar a
minha gratidão aos Engenheiros António Silva e Eugénio Santis.
Agradeço à Professora Beatriz Silva pela ajuda e tempo despendido na realização e
interpretação dos ensaios de tracção uniaxial.
O meu muito obrigado à Professora Rosa Miranda pela ajuda e equipamento cedido para a
realização dos ensaios de dureza, assim como ao Professor Telmo Santos pelo apoio aos ensaios de
condutividade.
Gostaria de agradecer aos Doutores Filipe Nascimento e João Gandra pela camaradagem e
amizade com que sempre me trataram, pela formação e ajuda que me deram. Nunca esquecerei os
conselhos que me dirigiram nos muitos momentos em que entrei desesperado no gabinete deles. Ao
Mestre André Oliveira pela companhia e amizade em longas horas de escrita e ensaios.
Aos Srs. Daniel Pomiel e Carlos Farinha um especial obrigado por toda a assistência e
conhecimentos transmitidos.
Expresso também o meu apreço pelo Sr. João Luís por um excelente trabalho de produção
das ferramentas e de outros componentes projectados, assim como ao Sr. Lopes pela maquinação
de provetes.
Aos meus colegas Nuno Ferreira, Daniel Pimentel, Mirela Lourenço, Tiago Gomes, Filipa
Baltazar, Francisco Sá, Bernardo Dias Miguel, Lucas Niven, João Nicolau, Teresa Gouveia e Tiago
Soares entre muitos outros, expresso a minha profunda consideração pela forte amizade que se
desenvolveu ao longo do curso e todo o apoio sistemático durante a realização deste trabalho. Um
agradecimento especial ao Francisco Jacob pela revisão e correcção do Inglês.
v
VII. Contents
I. Abstract ..................................................................................................................................i
II. Key-Words .............................................................................................................................i
III. Resumo ................................................................................................................................ ii
IV. Palavras-Chave .................................................................................................................... ii
V. Acknowledgements ............................................................................................................. iii
VI. Agradecimentos ................................................................................................................... iv
VII. Contents ...............................................................................................................................v
VIII. List of Tables ..................................................................................................................... viii
IX. List of Figures .................................................................................................................... viii
X. List of Equations .................................................................................................................. ix
XI. Nomenclature .......................................................................................................................x
XII. List of Symbols .................................................................................................................... xi
1. Introduction .......................................................................................................................... 1
1.1. Scope ........................................................................................................................... 1
1.2. Problem Statement and Research Questions ............................................................. 1
1.3. Objectives .................................................................................................................... 2
1.4. Dissertation Structure .................................................................................................. 2
2. State of the Art ..................................................................................................................... 3
2.1. Introduction to Electrical Transformers ........................................................................ 3
2.1.1. Aluminum-Copper Comparison ............................................................................... 5
2.2. FSW ............................................................................................................................. 6
2.2.1. Basic concepts of the FSW process ....................................................................... 6
2.2.2. Parameters of the process ...................................................................................... 7
2.2.3. Microstructure obtained ........................................................................................... 8
2.2.4. Advantages and limitations of FSW ........................................................................ 9
2.3. Aluminum and its alloys ............................................................................................. 10
2.3.1. Properties and applications ................................................................................... 10
2.3.2. Alloys and temper designation .............................................................................. 10
2.3.3. Aluminum weldability ............................................................................................. 12
2.4. Copper and its Alloys ................................................................................................. 13
2.4.1. Properties and applications ................................................................................... 13
2.4.2. Alloys designation ................................................................................................. 13
2.4.3. Copper weldability ................................................................................................. 14
2.5. Statistic Method – Taguchi Method ........................................................................... 15
2.5.1. Methodology .......................................................................................................... 15
2.5.2. ANOVA .................................................................................................................. 17
2.6. Friction Stir Welding development on the study area ................................................ 18
2.6.1. FSW on thin sheets .............................................................................................. 18
2.6.2. Dissimilar Al/Cu welds .......................................................................................... 19
2.6.3. Taguchi on FSW ................................................................................................... 19
3. Equipment Characterization .............................................................................................. 21
3.1. Esab LegioTM
FSW 3U ............................................................................................... 21
3.2. FSW Tools ................................................................................................................. 23
4. Tests Characterization ....................................................................................................... 25
4.1. Tensile Test ............................................................................................................... 25
4.2. Bending Test .............................................................................................................. 27
vi
4.3. Micro-hardness .......................................................................................................... 29
5. Base Material Characterization ......................................................................................... 31
5.1. Aluminum Foil Characterization ................................................................................. 31
5.2. Copper Foil Characterization ..................................................................................... 33
6. Characterization of Taguchi on FSW................................................................................. 35
6.1. Evaluation Factors ..................................................................................................... 35
6.2. Control Parameters and their Levels ......................................................................... 36
6.3. Design of Experiments (DOE) ................................................................................... 36
7. Experimental Study Cases ................................................................................................ 37
7.1. Aluminum Butt Welding ............................................................................................. 37
7.1.1. Experimental Setup ............................................................................................... 37
7.1.2. Tool Geometry....................................................................................................... 37
7.1.3. Parameters ............................................................................................................ 38
7.1.4. Tensile Tests Results ............................................................................................ 40
7.1.5. Bending Tests Results .......................................................................................... 41
7.1.6. Hardness Tests Results ........................................................................................ 42
7.1.7. Analysis of Variance (ANOVA).............................................................................. 43
7.1.8. Optimum parameters identification ....................................................................... 44
7.1.9. Aluminum Butt Welding Results ............................................................................ 44
7.2. Copper Butt Welding ................................................................................................. 46
7.2.1. Experimental Setup ............................................................................................... 46
7.2.2. Tool Geometry....................................................................................................... 46
7.2.3. Parameters ............................................................................................................ 46
7.2.4. Tensile Tests Results ............................................................................................ 48
7.2.5. Bending Tests Results .......................................................................................... 49
7.2.6. Hardness Tests Results ........................................................................................ 50
7.2.7. Analysis of Variance .............................................................................................. 50
7.2.8. Optimum parameters identification ....................................................................... 51
7.2.9. Copper Butt Welding Results ................................................................................ 52
7.3. Overlap Foil-Bar weld ................................................................................................ 53
7.3.1. Aluminum Foil – Aluminum Bar Weld .................................................................. 54
7.3.2. Copper Foil – Copper Bar Weld ............................................................................ 54
7.3.3. Aluminum Foil – Copper Bar weld......................................................................... 55
7.3.4. Summary of Results .............................................................................................. 56
7.4. Other Geometries ...................................................................................................... 57
7.4.1. Aluminum-Copper Butt welding............................................................................. 57
7.4.2. Aluminum-Copper overlap welding ....................................................................... 57
7.4.3. Thin Copper-Copper butt weld ............................................................................. 57
8. Preliminary Feasibility Study ............................................................................................. 59
8.1. The Client Needs ....................................................................................................... 59
8.2. Operating costs.......................................................................................................... 60
8.3. Initial Investment and Payback .................................................................................. 60
8.4. Quality ........................................................................................................................ 62
8.5. Conclusions on Feasibility Study ............................................................................... 62
9. Conclusions ....................................................................................................................... 63
10. Future Work ....................................................................................................................... 65
10.1. Dissimilar butt welding ........................................................................................... 65
10.2. Foil-Bar Quality Tests ............................................................................................ 65
vii
10.3. Static Shoulder/Pinless Tool .................................................................................. 65
XIII. References ........................................................................................................................ 67
XIV. Annexes ............................................................................................................................... a
A. Experimental Procedures ................................................................................................ b
A1. Friction Stir Welding Procedures. ............................................................................ b
A2. Procedures for Metallographic Analysis. ..................................................................c
A3. Hardness Tests Procedures. ................................................................................... d
A4. Tensile Tests Procedures ........................................................................................ d
A5. Procedures for three point Bending Test. ................................................................ e
B. Results .............................................................................................................................. f
B1. Aluminum butt welds................................................................................................. f
B2. Copper Butt Welds ................................................................................................... h
C. Specimen Design...............................................................................................................j
C1. Tensile test specimen design ....................................................................................j
C2. Bending test specimen design ...................................................................................j
D. Bending structure...........................................................................................................j
E. Technical Sheets ..............................................................................................................k
E1. Support Table ............................................................................................................l
E2. Work Table ............................................................................................................. m
E3. Tool Body ................................................................................................................. n
E4. Probe – 4J3 ............................................................................................................. o
E5. Probe – 4I3 .............................................................................................................. o
E6. Shoulder 4P3 ........................................................................................................... p
E7. Shoulder 4O3 ........................................................................................................... q
F. Feasibility Study Calculation ............................................................................................. r
F1. TIG Cost ................................................................................................................... r
F2. FSW Cost .................................................................................................................s
G. Confidential Experiment Tables ................................... Error! Bookmark not defined.
G1. Aluminum Butt Welding ........................................... Error! Bookmark not defined.
G2. Copper Butt Welding................................................ Error! Bookmark not defined.
H. Confidential optimum parameters identification .......... Error! Bookmark not defined.
H1. Aluminum optimum parameters ............................... Error! Bookmark not defined.
H2. Copper optimum parameters ................................... Error! Bookmark not defined.
viii
VIII. List of Tables
Table 2.1 – Composition of the different series of wrought aluminum alloys. .......................... 11
Table 2.2 – Composition cast aluminum alloys series. ............................................................ 11
Table 2.3 – Specification for Cold Work alloys. ........................................................................ 12
Table 2.4 – Heat Treatment designation. ................................................................................. 12
Table 2.5 – Composition of the different families of wrought copper alloys. ............................ 14
Table 5.1 – Tensile tests results for 3 specimens of Aluminum Base Material. ....................... 32
Table 5.2 – Bending tests results for 3 specimens of Aluminum Base Material. ..................... 32
Table 5.3 – Tensile tests results for 2 specimens of Copper Base Material. ........................... 33
Table 5.4 – Bending tests results for 3 specimens of Copper Base Material. .......................... 33
Table 6.1 – GET weight for each property of tensile test. ........................................................ 35
Table 6.2 – GEB weight for each property of bending test. ...................................................... 36
Table 6.3 – Control Parameters and their Levels. .................................................................... 36
Table 6.4 – Taguchi L9 Orthogonal Array with 3 columns. ...................................................... 36
Table 7.1 – Visual analysis of aluminum welds. ....................................................................... 39
Table 7.2 – Summary of results for tensile tests of aluminum.................................................. 40
Table 7.3 – Summary of results for bending tests of aluminum. .............................................. 41
Table 7.4 – Summary of results for hardness tests of aluminum. ............................................ 42
Table 7.5 – Results of variance analysis for the three evaluation parameters for aluminum. .. 43
Table 7.6 – Visual analysis of copper welds. ........................................................................... 47
Table 7.7 – Summary of results for tensile tests of copper. ..................................................... 48
Table 7.8 – Summary of results for bending tests of copper .................................................... 49
Table 7.9 – Summary of results for hardness tests of copper .................................................. 50
Table 7.10 – Results of variance analysis for the three evaluation parameters for copper. .... 51
Table 7.11 – Aluminum Foil-Bar ............................................................................................... 54
Table 7.12 – Copper Foil-Bar weld ........................................................................................... 55
Table 7.13 – Cu-Al-Cu Sandwich like weld parameters range. ................................................ 56
Table 8.1 – Production variables for the winding manufacturing. ............................................ 59
Table 8.2 – Estimated costs per weld for both processes. ....................................................... 60
Table 8.3 – Estimated costs for the project. ............................................................................. 61
Table 8.4 – Comparison of non-quantifiable variables of both processes. .............................. 62
IX. List of Figures Figure 2.1 – Transformer principle basic scheme. Adapted from [5]. ........................................ 3
Figure 2.2 – Ideal Transformer equivalent circuit. ...................................................................... 4
Figure 2.3 – Different Winding assembly processes .................................................................. 4
Figure 2.4 – FSW Process Scheme adapted from Vilaça et al. [17]. ......................................... 6
Figure 2.5 – FSW hot and cold condition classification [15]. ...................................................... 8
Figure 2.6 – Typical macrograph scheme of a section transversal to the FSW direction [19]. .. 8
Figure 2.7 – Taguchi Method Flow Chart ................................................................................. 16
Figure 3.1 – Welding equipment LEGIOTM
FSW 3U of ESAB. ................................................. 21
Figure 3.2 – Representation of the different constituents of the equipment. ............................ 21
Figure 3.3 – Work table and fixing system used. ..................................................................... 22
Figure 3.4 – 3-D view of the iSTIRtool_v3 assembly. .............................................................. 23
Figure 3.5 – Different M4 shoulder geometries. ....................................................................... 24
Figure 3.6 – M4 Probes ............................................................................................................ 24
Figure 4.1 – Representation of the cuts made on butt welded sheets ..................................... 25
Figure 4.2 – Tensile testing machine, Instrom 4507, overall view at left, testing zone at right. 25
ix
Figure 4.3 – Magnification of Tensile test results of AA1070, BM1 trial, near elastic regime. . 26
Figure 4.4 – Tensile test results of AA1070, BM1 trial. ............................................................ 27
Figure 4.5 –Three Point Bending example of aluminum weld specimen. ................................ 27
Figure 4.6 – Representation of bending test setup for aluminum. ........................................... 28
Figure 4.7 – Bending test result for copper C11000. ................................................................ 28
Figure 4.8 – Mitutoyo HM-112 Vickers micro-hardness testing machine ................................. 29
Figure 5.1 – Aluminum foil, as received. .................................................................................. 31
Figure 5.2 – AA1070 composition certification. ........................................................................ 32
Figure 5.3 – Aluminum mechanical properties certification. ..................................................... 32
Figure 5.4 – Copper Foil, as received. ..................................................................................... 33
Figure 5.5 – Chemical composition certification for C11000. ................................................... 33
Figure 7.1 – Experimental setup for aluminum welds. ............................................................. 37
Figure 7.2 – Probe 4J3 and shoulder geometry 4P3 used in aluminum butt weld. .................. 37
Figure 7.3 – Overall look of the face and root sides of the nine trials of aluminum. ................ 38
Figure 7.4 – GET results for each trial (left) and parameter level (right). ................................. 40
Figure 7.5 – GEB results for each trial (left) and parameters level (right). ............................... 41
Figure 7.6 – Hardness coefficient results for each trial (left) and parameters level (right). ...... 42
Figure 7.7 – Average values of the nine hardness profiles of Aluminum welds. ...................... 43
Figure 7.8 – Contribution of each parameter for the three evaluation parameters. ................. 44
Figure 7.9 – Metallographic analysis of the confirmatory trial. ................................................. 45
Figure 7.10 – Eddy current conductivity test performed, at 250 kHz, ...................................... 45
Figure 7.11 – Probe 4J3 and shoulder 4O3 used in copper butt weld. .................................... 46
Figure 7.12 – Overall look of the face (left) and root (right) sides of the nine trials of copper. 47
Figure 7.13 – GET results for each trial (left) and parameters level (right). ............................. 48
Figure 7.14 – GEB results for each trial (left) and parameters level (right). ............................. 49
Figure 7.15 – Hardness Coefficient results for each trial (left) and parameters level (right). ... 50
Figure 7.16 – Contribution of each parameter for the three evaluation parameters. ............... 51
Figure 7.17 – Eddy current conductivity test performed, .......................................................... 52
Figure 7.18 – TIG Foil-Bar weld in aluminum at left, and in copper at right. ............................ 53
Figure 7.19 – Aluminum Foil-Bar weld example. ...................................................................... 54
Figure 7.20 – Copper Foil-Bar weld example. .......................................................................... 55
Figure 7.21 – Aluminum foil – copper bar weld instabilities. .................................................... 55
Figure 7.22 – Cu-Al-Cu Sandwich like weld example. ............................................................. 56
Figure 7.23 – Aluminum-Copper butt weld instabilities. ........................................................... 57
Figure 7.24 – Aluminum-Copper overlap weld example. ......................................................... 57
Figure 7.25 – Examples of thin copper trials. ........................................................................... 57
Figure 8.1 – Costs division for TIG and FSW weld. ................................................................. 60
Figure 8.2 – Estimated Payback Period. .................................................................................. 61
X. List of Equations (2.1) ............................................................................................................................................. 4
(2.2) ............................................................................................................................................. 5
(2.3) ............................................................................................................................................. 5
(2.4) ............................................................................................................................................. 5
(2.5) ............................................................................................................................................. 5
(2.6) ............................................................................................................................................. 5
(2.7) ............................................................................................................................................. 7
(2.8) ........................................................................................................................................... 17
(2.9) ........................................................................................................................................... 17
x
(2.10)......................................................................................................................................... 17
(2.11)......................................................................................................................................... 17
(2.12)......................................................................................................................................... 17
(4.1) ........................................................................................................................................... 26
(4.2) ........................................................................................................................................... 26
(6.1) ........................................................................................................................................... 35
(6.2) ........................................................................................................................................... 35
(6.3) ........................................................................................................................................... 36
(7.1) ........................................................................................................................................... 44
(7.2) ........................................................................................................................................... 44
(7.3) ........................................................................................................................................... 51
(7.4) ........................................................................................................................................... 51
XI. Nomenclature AA Aluminum Alloy
AC Alternating Current
ANOVA Analysis of Variance
BM Base Material
DC Direct Current
DOF Degrees Of Freedom
EN European Standard
FS Friction Surfacing
FSSW Friction Stir Spot Welding
FSW Friction Stir Welding
GEB Global Efficiency on Bending
GET Global Efficiency on Tensile
GOES Grain Oriented Electrical Steel
HARD Hardness Coefficient
HAZ Heat Affected Zone
HV Vickers Pyramid Number
IADS International Alloy Designation System
IDMEC Institute of Mechanical Engineering
IST Instituto Superior Técnico
iStir Friction Stir Investigation Group from IDMEC-IST
J Joule
kN kilo Newton
kV kilo Volt
LDT Large Distribution Transformer
LOP Lack Of complete Penetration of the weld seam in the weld joint thickness
MIG Metal Inert Gas
min Minutes
mm millimeters
OA Orthogonal Array
Pa Pascal
Qty Quantity
SIEMENS-FS SIEMENS Transformers Factory of Sabugo
SIEMENStir Investigation project between SIEMENS-FS and iStir
TMAZ Thermo-mechanically Affected Zone
TWI The Welding Institute
UNS Unified Numbering System
UTL Universidade Técnica de Lisboa
xi
XII. List of Symbols
𝛼 Tilt angle
𝛽 Side tilt angle
𝜀 Elongation
𝜌 Resistivity
𝜌𝑖(𝑗) Influence of parameter i on factor j
0.2 Offset yield strength
𝑚𝑎𝑥 Ultimate tensile strength
𝛺 Rotational speed or ohm
Ag Silver
Al Aluminum
Cr Chromium
Cu Copper
d Displacement
Dt Dwell time
DT Distribution Transformer
E Young’s modulus
En Energy
F Load
Fe Iron
Fi(j) F-test of parameter i on factor j
Fz Axial force
HCl Hydrogen chloride
HF Hydrogen fluoride
HNO3 Nitric acid
I Current
Li Lithium
Lpin Probe length
Mg Magnesium
Mn Manganese
MT Tenacity modulus
Ni Nickel
P Phosphorus
Pb Lead
Ps Plunge speed
PT Power Transformer
R Electric resistance
Si Silicon
Sn Tin
SSi(j) Sum of Squares of parameter i on factor j
SST(j) Total Sum of Squares on factor j
V Potential difference
Vi(j) Variance of parameter i on factor j
Vx Travel speed
Wp Weld position
Zn Zinc
xii
1
1. Introduction
1.1. Scope
SIEMENStir is a project between SIEMENS Transformers Factory, specialized in oil immersed
transformers, and iStir, a research group from IDMEC in IST. A first study was developed focusing on
the weldability of aluminum foil for electrical purposes [1]. This project aimed the joining of foil coils, a
raw component for LDT transformer windings. In this first study it was acknowledged that Friction Stir
Welding (FSW) could be a significant addition and leverage for the Factory (SIEMENS-FS) as an
upgrade of welding possibilities, for joining thin Aluminum sheets in butt welds. The higher quality of
FSW welding comparatively to the current arc welding process is also a significant improvement, from
the mechanical and electrical point of view.
The present work attempts to extend and strengthen the knowledge of friction stir welding
technique for electrical applications, using the core of the first SIEMENStir project as starting point.
Even though FSW welding technique is well known by iStir, the present application places new
challenges, conductors’ materials, such as thin sheets of pure Al and pure Cu, which were never tried
before in the group, and place particular constrains to the use of the process.
Recent demands for replacing the technically pure copper as conductive materials by new
materials, e.g. aluminium, introduced new manufacturing conditions that need feasible and reliable
new technological solutions focusing joining of components. The new solutions should allow an easy
integration in the existing production system and envisage higher productivity. Also dedicated non-
destructive testing techniques and solutions should be developed. Existing joining processes applied
in the manufacturing of the electrical transformers are based on fusion arc welding processes, mainly
GTAW. This results frequently in defective weld beads with porosity and hot cracking. The residual
deformations should also be reduced.
The Factory is also interested in evaluating the applicability of FSW from the technological and
economical point of view. Bearing in mind those goals, FSW was tested in several arrangements and
different materials, of aluminum and copper alloys. And a comparative preliminary feasibility study
between the current process and the FSW process was performed envisioning its possible
implementation.
1.2. Problem Statement and Research Questions
The search for new markets and opportunities require the use of the best possible solutions
alongside with innovative alternatives to develop products that stand out in the current market. The
current welding process, Tungsten Inert Gas (TIG), does not have this potential. TIG welding cannot
butt weld neither aluminum nor copper sheets because of their reduced thicknesses. The overlap
solution, used only for copper sheet, leads to both an increase in the size of the transformer and in the
2
consumption of material. TIG’s inability to weld dissimilar materials, due to the significant differences
of their chemical properties, is also a big disadvantage.
FSW seems the perfect replacing process for this application, if is found answer for some
questions. First of all, there is the need to prove that it’s possible to butt weld such pure alloys in such
thin sheets as the used 1.6mm thick AA1070 and 1.1mm thick C11000. Dissimilar aluminum-copper
butt weld has been done before, but, in order to enable the flow of the same current in both materials,
to avoid hotspots and material waste, the thickness of the two materials is different. Which make this a
very difficult and doubtful solution of thin sheet butt weld of dissimilar materials with dissimilar
thicknesses. The foil-end bar weld also raised some doubts, due to the slight discrepancy of
mechanical properties between the end-bar and foil, and it was uncertain if the former would support
the load necessary for a satisfactory weld.
1.3. Objectives
Evaluation of the FSW weldability on different materials and geometries to increase the ranges
of SIEMENS-FS applications and opportunities. Study the possibility of welding dissimilar foil butt
joints and foil-end bar overlapped joints. Finding the optimal parameters, through a Taguchi study, for
butt welding of Al and Cu thin sheets, in order to achieve and transfer the correct know-how and
technology to the factory. Analyzing the financial impact of the acquisition and implementation of FSW
equipment for SIEMENS FS based on a preliminary feasibility study.
1.4. Dissertation Structure
This section explains the structure of this essay, by addressing the main contents of each
chapter and their sections: The State of the Art, Chapter 2, is divided into six sections: 1) Introduction
to Electrical Transformers; which gives a quick overall view of transformers principals and their
features. 2) FSW; it explains the fundaments behind the process, such as its parameters,
microstructure obtained and the advantages and limitations. Sections 3) and 4) intend to be a general
guide of the materials used during the procedures, reviewing the main properties and applications.
They also refer to the alloy designations and weldability. 5) Statistic Method; which explains the
methodology used to the experimental study of butt welds. Finally, section 6) refers scientific work
developed in similar materials, technology and trials. Chapter 3 introduces the FSW equipment used
during the experimental work. Chapter 4 explains the mechanical tests performed. Chapter 5 presents
the base material characterization, in which are presented the geometry, microstructure and
mechanical properties of the material as received. Chapter 6 explain the methodology adopted for butt
weld tests. The evaluation factors, the control parameters and the design of experiments. Chapter 7
includes the experimental study case and it’s divided in four sections: Sections 1) and 2) address the
experimental work, results and variance analysis of both aluminum and copper butt welds. Section 3)
and 4) show foil-bar and dissimilar joints and the set of parameters used. Chapter 8 focuses on the
feasibility study to implement the process. Chapter 9 discusses the major results obtained in the thesis
and Chapter 10 describes the future work proposal.
3
2. State of the Art
The State of the Art addresses the main elements of this work, and the different approaches
done by several authors to the themes.
2.1. Introduction to Electrical Transformers
Transformers are important devices for the electric energy transmission and distribution
through the grid. These devices transfer energy from one circuit to another by a common magnetic
field [2]. Electric power transmission at long distances cannot be made at low voltage, because it has
great losses. On the other hand, the power generation and consumption can’t happen at high voltages
since they need pronounced insulation. For that reason step-up transformers are needed to raise the
voltage after the generation for transmission and then step-down transformers, named Distribution
Transformers (DT), take the voltage to an appropriate distribution level. The power generation is
usually obtained in a range from 11 to 33kV, then it is supplied to the transport network at 150, 220 or
400 kV[3]. At last, the consumption occurs at 230/420V as mono or tri phase voltage respectively.
The two principles in which the transformers rely on are electromagnetism and
electromagnetic induction. This is the capability of an electric current to produce a magnetic field, and
the varying magnetic field within a coil that induces a voltage across the extremities of that coil. This
induction only occurs in Alternating Current (AC) resulting from the reversal of electric flow.
Therefore, a transformer works in the following principle, an AC current is applied by an
energy source to the primary winding that induces the current to the secondary winding that will supply
the energy to the user [4]. Figure 2.1 shows a simple arrangement of this principle, the majority of the
transformers work in three-phase, so they have 3 sets of 2 bobbins each that are lagged 120º from
each other.
Figure 2.1 – Transformer principle basic scheme. Adapted from [5].
4
The relationship between the number of turns (n), the current intensity (I) and the voltage (V)
of primary (p) and secondary coils (s) in an ideal transformer is shown in Figure 2.2 and is given by
equation (2.1):
𝒏𝒑
𝒏𝒔=𝐈𝒔𝑰𝒑=𝐕𝒑
𝐕𝒔 (2.1)
In order to sustain the magnetic flux inside the coils high permeability silicon steel and/or grain
oriented electrical steel (GOES) is used as core. There are two main phenomena that reduce the
magnetic flux, and those are eddy current losses and hysteresis-losses, these are reduced by the
geometry of the core, generally, laminated steel of small thickness with insulated layers of
magnesium-silicate phosphate.
Generally HV windings are made of resin insulated wire, as shown in Figure 2.3 a). In
Distribution Transformers LV windings are usually assembled by concentric foils one above the other
and insulated by paper, Figure 2.3b). The joint between Foil windings and the connection bars is one
of the aims of this work.
Figure 2.2 – Ideal Transformer equivalent circuit.
Figure 2.3 – Different Winding assembly processes
a) wired winding made in copper b) foil winding in aluminum c) final assembly of an aluminum bobbin.
5
2.1.1. Aluminum-Copper Comparison
In the past years, aluminum has emerged in the electric conductors industry. The main reason
is the obvious economic factor because aluminum is between two to three times cheaper than copper.
However electric conductivity of aluminum is smaller, so to maintain the current density and voltage
drop the equivalent aluminum wire needs to be dimensioned.
Ohm’s Law states that in an electric circuit [5], the current (𝐼) through a conductor between
two points is directly proportional to the potential difference (𝑉) across the two points, and the constant
of proportionality is the electric resistance (𝑅), equation (2.2):
𝑰 =𝑽
𝑹 (2.2)
As the current and the potential difference is the same to both conductors, assumption can be
made that the copper resistance must be equal to aluminum resistance. Resistance can be written,
equation (2.3), in function of conductor material resistivity (𝜌), length (𝐿) and section (𝑆).
𝝆𝑪𝒖𝑳
𝑺𝑪𝒖=𝝆𝑨𝒍𝑳
𝑺𝑨𝒍 (2.3)
The relatively higher resistivity of commercial pure Aluminum (2.82x10-8
Ω.m) comparing to
annealed Copper (1.72x10-8
Ω.m) leads to a 1.64 times higher section for the same conductor length.
Then, for the same current density and voltage drop at a given length, copper wiring provides a
smaller nominal section leading to smaller conductor, which can be an advantage for certain
applications.
However for the majority of applications the weight factor is more significant. Assuming that
each wire has the shape of a perfect cylinder with cross section equal to 𝑆𝐶𝑢 and 𝑆𝐴𝑙, respectively for
Copper and Aluminum, the relationship between both is given by the equation (2.4).
𝑽𝑨𝒍 = 𝑺𝑨𝒍. 𝑳 = 𝟏. 𝟔𝟒𝑺𝒄𝒖. 𝑳 = 𝟏. 𝟔𝟒𝑽𝑪𝒖 (2.4)
Equation (2.5) expresses the relationship between the mass of both materials in function of
their density and respective volume:
𝒎𝑨𝒍
𝒎𝑪𝒖=𝒅𝒆𝒏𝒔𝑨𝒍
𝒅𝒆𝒏𝒔𝑪𝒖×𝑽𝑨𝒍
𝑽𝑪𝒖 (2.5)
Finally, using the known values of density for copper (8.89g/cm3) and for aluminum
(2.7g/cm3) the relation of mass is obtained.
𝑚𝐴𝑙 = 1.64 2.7
8.89= 0.498 𝑚𝐶𝑢 (2.6)
To sum up, for the same current and potential difference at a certain length, although
aluminum conductors exhibit bigger section and volume (164%), its mass and consequently its weight
is halved (49.8%) when compared to copper conductors, as shown in equation (2.6). Even considering
the lower resistance of aluminium to thermal, chemical and mechanical loadings, and all the issues
related with joining with terminals based on copper components. Aluminium is nowadays a significant
trend in the production of windings for transformers for power systems[6], [7] and opens the possibility
of developing new products and new processes.
6
2.2. FSW
2.2.1. Basic concepts of the FSW process
The Friction Stir Welding (FSW) process was firstly patented in 1991 by Wayne Thomas of
The Welding Institute (TWI) [8] and it might be the most important breakthrough of the last decade of
the XX century, regarding joining components’ technology. It has been through a rapid growth in
research, development and application since the early 2000s as shown in the 230 organizations
licensed by TWI whom submitted more than 3000 patent applications [9], in the numerous technic-
scientific published items and also in the several friction stir based technologies that are being
discovered and developed (Friction Stir Processing [10], Spot Weld [11], Channeling [12]). The FSW
technology has been subjected to the most demanding quality standard requirements and used in
challenging industrial applications over a wide range of structural and non-structural components
mainly in light alloys for transport industries. Such examples are naval [13], aerospace [14], railway
[15] and automotive [16] industries.
The FSW is a solid state joining process, which uses a non-consumable tool, made of a
material harder than the material being welded. Both the shoulder and the probe of the tool can be
designed depending on the thickness and type of material to be welded. The principles and the used
nomenclature of the process are shown in Figure 2.4.
Figure 2.4 – FSW Process Scheme adapted from Vilaça et al. [17].
The rotating tool is inserted (plunged) into the joint of two materials at a constant speed (Ps)
until it reaches the desired position (Wp), this position is critical to avoid root defects or thickness
reduction. After obtaining the appropriate thermal conditions by maintaining the rotation in the Wp
during the dwell time (Dt) the tool is animated of the linear movement (Vx). The weld control can
switch from the position control, which forces the tool to preserve the same height, to force control that
conserves the same axial force (Fz). At the end of the weld, the linear movement stops when the tool
reaches the final position and the tool is slowly removed, leaving a keyhole in the work piece. This is
one of the main drawbacks of the classic FSW process but, today, it can be avoided with a special
designed retreating probe [18].
7
The FSW process requires a tight constrain and this is obtained by the system, shoulder and
anvil, at top and bottom and by the cold base material at the sides. This is the well-known “third body
region”. The interfacial friction caused by the rotation and the axial force of the shoulder at the surface
of the material, origins an internal friction in a sub-superficial region inside the material, which is the
driving force of the process, the heat generated thermo mechanically softens the material and the tool
movement produces an extruded, forged and stirred weld. The material transportation is accomplished
because the probe splits the incoming flow of visco-plastic material that is then forge welded together
at the trailing edge of the probe. This process occurs continuously during the passage of the shoulder.
As generally happens in solid state weld processes the efficiency of FSW is high, because the
mechanical energy is converted in heat inside the work piece, as stated above, by the interaction
between the tool and the material. This heat is responsible for the reduction of material’s mechanical
resistance allowing this to flow around the pin.
2.2.2. Parameters of the process
The main FSW process parameters must be chosen according to the joint type, the materials
to weld and their geometry. Below, we found a brief description of the main parameters [19], followed
by their abbreviations (abr.) and currently used units [unit]:
• Tool geometry includes the probe and shoulder geometry, being the major concerns the
use of the adequate diameter and length accordingly to the thickness of the material;
• Plunge speed (Ps) [mm/s], the optimization of this parameter avoids increasingly the
appearance of defects in the starting phase of the process;
• Tool rotational speed (Ω) [rpm] and direction, rotational direction depends on the probe
geometry, left-handed screw must lead to a clockwise rotation and vice versa. Rotational speed is
generally associated with travel speed, together they define the hot-to-cold conditions that are
explained in the weld pitch ratio topic;
• Travel Speed (Vx) [mm/min] must be adjusted according to the superficial friction on the
material with the purpose of avoiding stick and slide movements;
• Axial force (Fz) [Kg] insufficient load result in poor weld conditions but excess axial force
increases the flash leading to a depression below the shoulder passage path;
• Dwell time (Dt) [s] is important to obtain the appropriate thermal conditions;
• Clamping system, material must be stiff enough to support, especially, the torsion forces
felt by the plates. It’s important that the system enables an easy extraction of the work piece;
• Tilt (α) and side tilt (β) angles, the first is very important to allow a good entrance of the
material below the shoulder and the second must be used in case of different thicknesses of the side
plates.
𝒘𝒆𝒍𝒅 𝒑𝒊𝒕𝒄𝒉 𝒓𝒂𝒕𝒊𝒐 [𝒓𝒆𝒗 𝒎𝒎⁄ ] = 𝜴 [𝒓𝒑𝒎]
𝒗[𝒎𝒎 𝒎𝒊𝒏]⁄ (2.7)
8
• Weld pitch ratio is a combination of two other parameters, see equation (2.7). Varying the
weld pitch ratio changes the heat input from the frictional internal and interfacial energy, being some
effects in the weld region behavior easily predicted. For aluminum alloys it is usual to consider the
value of weld pitch ratio = 4 as intermediate condition. For weld pitch ratio higher than 4 there is a hot
condition and for weld pitch ratio smaller than 4 there is a cold condition.[20] Concerning the influence
of the hot-to-cold conditions in the metallurgical features of a FSW weld joint, the classification is
established in Figure 2.5.
2.2.3. Microstructure obtained
During the FSW process the work piece material suffers intense plastic deformation resulting,
generally, on smaller and rounder grain size than in the base material. This result from the thermo-
mechanical cycle, a feature of the FSW, in which the solid state heat leads to a stired cooling that
consists essentially in forging. This fine microstructure produces good mechanical properties in friction
stir welds. Better quality joints are associated with intense three-dimensional material flow.
The main zones in a FSW joint, showed in Figure 2.6, with distinct metallurgical properties are:
i) the thermo-mechanically affected central zone (TMAZ) that includes the dynamically recrystallized
zone ii) the nugget; iii) the heat affected zone (HAZ) and iv) the unaffected base material (BM).These
different zones result from the combined application of mechanical energy and heat energy from
frictional dissipation.
The typical characteristics of each of these zones for aluminum alloys are the following [21]:
i. The TMAZ grain preserves the characteristics of the HAZ however the grain presents
increased deformation, as they get closer to the interface with the nugget. This fact
results from the influence of the material flow prescribed by the movement of the tool
and the relatively high maximum temperature reached in this zone;
Figure 2.5 – FSW hot and cold condition classification [15].
Figure 2.6 – Typical macrograph scheme of a section transversal to the FSW direction [19].
9
ii. The nugget is the region of the TMAZ undergoing dynamic recrystallization with grain
size refined and homogenized. The TMAZ/nugget interface enhances the significant
difference between the structure of initial grain and the equiaxial grain resultant of the
dynamical recrystallization process, with fine dispersion of the precipitates in the solid
solution. The asymmetric geometry of the nugget region is due to the difference in
generated heat between the advance and retreating sides, resulting of the direct
superposition of rotational speed, and travel speed;
iii. The HAZ is only affected by the heat energy and typically presents some slight
coalescence of grain relatively to the original grain size but is subjected to internal
point and linear defects rearrangements. Thus, for the heat treatable wrought
aluminum alloys the HAZ may present some reduction in the distribution of
precipitates at grain boundaries;
iv. The BM is the region that was unaffected by the FSW process.
2.2.4. Advantages and limitations of FSW
The advantages claimed for the process result essentially of being a solid-state process that
allows similar metallurgical characteristics and wear and static mechanical resistance to the base
material. This avoids the degradation of material proprieties due to the low heat input of the process,
resulting also in lower distortion and smaller residual stress levels. It’s very environmental and human
friendly, as it does not need welding consumables, operates with the absence of welding fumes or UV
emissions and the noise it produces is almost non-existent. The training of the machine operator isn’t
so complex when compared to fusion weld, which probably results in a decrease of training expenses.
Being the FSW easily reproduced, it’s very suitable for automation repeatability, leaving a good
surface appearance right after the processing. This avoids subsequent surface treatment processes. It
can weld virtually any thicknesses with only one path (depending only on the machine capacity), in all
positions and in continuous mode (unlimited length, again depending on the machine configuration).
It’s not influenced by magnetic forces neither the environmental conditions.
The current limitations of the FSW process are the need of a backing anvil (except in bobbin-
tool). It also leaves a keyhole at the end of each weld, except when a run-off tab is introduced or when
is used a FSW tool with a retractable probe. Other limitation is the inability to start the weld joint from
the edges of the plates to be welded, except when using a run-on tab. The work piece requires rigid
clamping. The cost and size of the equipment are also a major drawback, as it has significant initial
investment and its size prevents it from being easily transported.
10
2.3. Aluminum and its alloys
Aluminum is the most abundant metal in the crust of the Earth, however it is always combined
with other elements, such as iron, oxygen or silicon [22]. After the development of the reduction Hall-
Héroult electrolytic process, in 1886, aluminum became an economic competitor in engineering
applications [23].
2.3.1. Properties and applications
Aluminum is already used in several industries and their use is expected to increase mostly
because of the following proprieties:
-Low density, 2,68g/cm3, about 1/3 of the density of steel or copper, giving it a good ratio
mass/volume that ensures a better carriage in relation to others metals that may be used to make
packages. The low density allied with its mechanical strength makes it a material to be considered in
aerospace and automotive industry because it provides good performance and low fuel consumption.
-Good electric and thermal conductivity, which is very desirable in the Transmission of Power
Industry and useful for heat exchangers.
-Nice formability that allows an easy conformation and deformation and enables its usage on
several production processes.
-Good corrosion resistance, when passived by an oxide layer, being used in civil engineering
ensuring preservation and easy maintenance. It also allows the manufacturing of hygienic and
contamination free packages.
-High variety of finishing, which allows anodization and painting, enabling another layer of
protection and corrosion barrier.
-Recyclable, grants a reduction of cost not only in production but also to the environment as it
can be reused, recovering part of the production costs and reduces the use of raw materials. The
recycling costs are much smaller than the production costs, as it can be done several times without
the loss of properties.
2.3.2. Alloys and temper designation
Aluminum alloys can be separated in wrought and cast aluminum, being the first class
responsible for 85% of the world’s production. The two classes use different identification systems.
Wrought aluminum is identified based on a four-digit number, assigned by the International Alloy
Designation System (IADS), in which the first digit identifies the alloying elements as shown in Table
2.1. The second digit is related with the modifications to the alloy, with the original alloy having this
digit equals to 0. The last two digits stand for the purity of the alloy in the case of the series 1xxx, for
example the alloy 1050 having 99.50% aluminum, and the alloy 1199 having 99.99%. For the others
series these two digits are just used to identify different alloys. When the alloy is in research it is used
the prefix X for its identification [22].
11
Table 2.1 – Composition of the different series of wrought aluminum alloys.
Series Main alloying element Others elements
1xxx Pure Aluminum -
2xxx Cu Mg, Li
3xxx Mn Mg
4xxx Si -
5xxx Mg -
6xxx Mg and Si -
7xxx Zn Cu, Mg, Cr, Zr
8xxx Li, Sn, Fe, Cu, e Mn -
9xxx -
The Aluminum Association (AA) has adopted a nomenclature for cast alloys similar to that of
wrought alloys. In the AA system, the second two digits reveal the minimum percentage of aluminum.
The digit after the decimal point takes a value of 0 or 1, denoting casting and ingot respectively. The
main alloying elements in the AA system are those shown in Table 2.2:
Table 2.2 – Composition cast aluminum alloys series.
Series Main alloying element
1xx.x Pure Aluminum
2xx.x Cu
3xx.x Si, Cu, Mg
4xx.x Si
5xx.x Mg
7xx.x Zn
8xx.x Li
Aluminum alloys can also be divided in two groups according to the ability to be heat treated,
alloys from the series 2xxx, 6xxx, and 7xxx are generally heat treatable and those from series 1xxx,
3xxx, 4xxx and 5xxx are considered non-heat treatable. The temper designation [23] follows the cast
or wrought designation number with a dash, a letter, and potentially a one to three digits number, e.g.
6061-T6. When the alloy does not suffer any temper process it receives the letter F (as fabricated),
when it was annealed for softening the letter O, and when it as the letter W it means that it suffered
only natural solution heat treatment. The letter H is used to cold work treatments and is usually
followed by two digits, the first is related to the treatment used and the second to the thickness
reduction leading to a variation in the hardness. Those two digit specifications are summarized in the
Table 2.3.
12
Table 2.3 – Specification for Cold Work alloys.
1st
Digit Cold Work 2nd
Digit Degree of Hardness
H1x Strain hardened without
thermal treatment Hx2 ¼ Hard
H2x Strain hardened and partially annealed
Hx4 ½ Hard
H3x Strain hardened and stabilized
by low temperature heating
Hx6 ¾ Hard
Hx8 Full Hard
Hx9 Extra Hard
Finally there are the alloys that receive heat treatments to enhance their properties, and which
are classified by the letter T followed by one or more digits. The temper designation of the first digit is
shown in Table 2.4, the second and following digits can be related to a thickness reduction by cold
work, with the type of stress relief or following heat treatments.
Table 2.4 – Heat Treatment designation.
Type Heat treatment
T1 Cooled from hot working and naturally aged (at room temperature)
T2 Cooled from hot working, cold-worked, and naturally aged
T3 Solution heat treated and cold worked
T4 Solution heat treated and naturally aged
T5 Cooled from hot working and artificially aged (at elevated temperature)
T6 Solution heat treated and artificially aged
T7 Solution heat treated and stabilized
T8 Solution heat treated, cold worked, and artificially aged
T9 Solution heat treated, artificially aged, and cold worked
T10 Cooled from hot working, cold-worked, and artificially aged
2.3.3. Aluminum weldability
In the 40’s aluminum was seen as unable to weld, but since then the evolution of the fusion
weld processes changed that belief. With the appearance of the Tungsten Inert Gas (TIG) and Metal
Inert Gas (MIG) it was possible to do good weld beads, with fine mechanical properties and industrially
competitive.
The weldability of aluminum alloys varies significantly, depending on the chemical composition
of the alloy used. Aluminum alloys must also be cleaned prior to welding, with the goal of removing all
oxides, oils, and loose particles from the surface to be welded. This is especially important because of
aluminum weld’s susceptibility to porosity due to hydrogen and dross due to oxygen [24].
Aluminum alloys are susceptible of hot cracking, and to address the problem, welders
increase the welding speed to lower the heat input. Preheating reduces the temperature gradient
across the weld zone and thus helps reduce hot cracking, but it can reduce the mechanical properties
of the base material and should not be used when the base material is restrained. The design of the
joint can be changed as well, and a more compatible filler alloy can be selected to decrease the odds
for hot cracking occurring.
13
The emergence of Friction Stir Welding resulted in an aluminum weld with high efficiency
without the need of consumable material, neither harmful noise and fumes, and avoiding the
undesired porosity and distortion caused by fusion techniques. To sum up, FSW can obtain excellent
and clean weld beads with high repeatability, boosting the aluminum alloys in the Metalworking
Industry.
2.4. Copper and its Alloys
Copper and its alloys have been used for thousands of years, as it can be found in native form
copper being the first metal to be extracted by the men. Copper smelting led to the second Era of the
human prehistory, the Bronze Age. During Bronze Age besides bronze (copper and tin alloy) the
ancients used native copper or brass (copper and zinc alloy) to produce their tools and weapons or as
a currency in their transactions[25].
2.4.1. Properties and applications
Pure copper is soft and malleable, its surface has a reddish-orange color when freshly
exposed, and after natural aging it forms a natural green patina very much appreciated in architecture
and design. Its high oxidation resistance to a wide variety of aqueous agents made it perfectly suited
for plumbing, and when it price was low its use became widespread. Nowadays, due to the price
increase it’s being replaced for cheaper materials such as polymers. This chemical resistance
combined with a good thermal conductivity led to a general use in heat exchangers and heating
systems.
Copper’s electric conductivity is one and a half times the aluminum conductivity and because
of that the major application of copper, about half of world’s production, is electrical wires; from power
generation, transmission and distribution to telecommunications and electronic circuits. The rest of
copper applications are mainly roofing and plumbing and industrial machinery, a small part is yet
combined with other elements to form an alloy such as cupronickel, used in low-denomination coins,
brass and bronze.
2.4.2. Alloys designation
Copper and copper alloys can be grouped in families [25]. Coppers with a minimum copper
content of 99.3%. High copper alloys, with at least 96% copper for wrought alloys and a minimum of
94% for cast alloys. Brasses, as stated above, are alloys that contain zinc as the principal alloying
element. Bronzes, originally described as alloys with tin as its only or principal alloying element are
now more accurately defined as copper alloys in which the major alloying element is not zinc or nickel.
Copper-nickels are, as implied, alloys with nickel as the principal alloying element, with or without
other designated alloying elements. Copper-nickel-Zinc alloys, commonly known as "nickel silvers",
are alloys that contain zinc and nickel as the principal and secondary alloying elements. Leaded
coppers, which comprise a series of cast alloys of copper with 20% or more lead, sometimes with a
small amount of silver, but without tin or zinc. And finally, those whose chemical compositions do not
fit into any of the above categories are combined in a group called "special alloys”.
14
In the Unified Numbering System (UNS), numbers from C10000 through C79999 denote
wrought alloys. Cast alloys are numbered from C80000 through C99999. In the Table 2.5 are
summarized the different families of wrought copper alloys, their groups and the UNS numbers
assigned to each one [26].
Table 2.5 – Composition of the different families of wrought copper alloys.
Family Main alloying
element Group
Secondary alloying elements
UNS Number
Copper - Coppers - C10100-C15999
High Copper Alloys - C16000-C19999
Brass Zinc (Zn)
Yellow Brasses - C2xxxx
Leaded Brasses Lead (Pb) C3xxxx
Tin Brasses Tin (Sn) C4xxxx
Bronzes
Tin (Sn) Phosphor Bronze Phosphorus (P) C50000-C52999
Leaded Phosphor Bronzes Lead (Pb), Phosphorus (P) C53000-C54999
- Brazing Alloys
Phosphorus (P), Silver (Ag)
C55000-C55299
Copper-Silver-Zinc-Alloys Silver (Ag), Zinc (Zn) C55300-C60799
Aluminum (Al) Aluminum Bronzes - C60800-C64699
Silicon (Si) Silicon Bronzes - C64700-C66199
Zinc (Zn) Copper-Zinc Alloys - C66200-C69999
Copper Nickel Nickel (Ni)- Copper Nickel - C70000-C73499
Nickel Silvers Zinc (Zn) Copper-Nickel-Zinc Alloys Nickel (Ni) C73500-C79999
2.4.3. Copper weldability
Copper weld is very susceptible to cracking during solidification and porosity. When welding
copper it is very important to take in consideration the oxygen content because it can lead to porosity
and/or discontinuities to the weld bead. Because of those problems, fusion processes do not easily
weld copper alloys. Therefore, FSW presents as a very suitable process and because the thermal
delivery is smaller, minimizing the HAZ, the problems with distortion and buckling are avoided [27].
FSW of copper is more difficult as compared to FSW of aluminum as copper has it has a significantly
higher melting point, thermal conductivity and flow stress.
An important aspect of linear friction welding of copper is the need of tool cooling, preventing
overheating and, therefore, the increase of temperature in the underlying base material. This can lead
to degradation of the quality of the welds due to penetration of sharp tool and burr formation.
Excessive heating of the base material may also cause grain growth in the heat affected zone, with
negative consequences for the mechanical properties of the joint. Despite the possibility of incidence
of these problems, it should however be noted that the cooling of the tool, if excessive, can also lead
to the formation of welding defects characteristic of execution of the process at low temperature [28].
15
2.5. Statistic Method – Taguchi Method
Genichi Taguchi developed a technique for designing and performing experiments in order to
investigate processes where the output depends on many factors, this methodology is called Taguchi
Method [29]. By systematically choosing certain combinations of variables it is possible to separate
their individual effects, and avoid the need of perform all possible combinations of values of those
variables.
Although similar to the design of experiments (DOE1), the Taguchi method only considers
balanced experimental combinations (orthogonal), which makes it even more effective than a
fractional factorial planning, which runs only a fraction of the total number of combinations of variables
process input. Using the Taguchi Method allows industries to significantly reduce the cycle time for
product development in the design and production, thereby reducing costs and increasing profits.
Taguchi had three main theories for quality management [30]:
1- Quality should be designed into a product, not inspected into it. Quality is designed into a
process through system design, parameter design, and tolerance design. Quality "inspected into" a
product means that the product is produced at random quality levels and those too far from the mean
are simply thrown out.
2- Quality is best achieved by minimizing the deviation from a target. The product should be
designed so that it is immune to uncontrollable environmental factors. In other words, the signal
(product quality) to noise (uncontrollable factors) ratio should be high.
3- The cost of quality should be measured as a function of deviation from the standard and the
losses should be measured system wide. This is the concept of the loss function, or the overall loss,
incurred upon the customer and society from a product of poor quality. Because the producer is also a
member of society and because customer dissatisfaction will discourage future patronage, this cost to
customer and society will come back to the producer.
2.5.1. Methodology
Application of Taguchi Method, Figure 2.7, begins with the definition of the problem or the
objective of the study to be performed. This means determining what performance to be optimized.
This may be a flow rate, temperature, weight, cost, roughness, thickness, and so on. With the choice
of the object is also necessary to choose which quality characteristic best suits the chosen object of
study. There are three types of quality feature: Larger the better (for example tensile strength), Smaller
the better (e.g. carbon emissions) or On-target with minimum variation (e.g. size).
The next step is to identify the operating parameters that have significant effects on the
process. Control parameters are those whose values will be controlled and changed. The number of
levels, their associated values for each test parameter defines the tests to be performed. Increasing
the number of levels to vary a parameter increases the number of experiments to be conducted, and
reducing the number of levels could lead to a non-conclusive test. Robust parameter designs consider
16
controllable and uncontrollable noise variables; they seek to exploit relationships and optimize settings
that minimize the effects of the noise variables.
After this process, it’s time to choose the Orthogonal Array (OA) for the parameter design
indicating the number and conditions for each experiment. The selection of OA is based on the
number of parameters and the levels of variation for each parameter.
Subsequently, the experiments indicated in the OA are conducted and the results are
collected. Here can be performed only one trial for each parametric combination or more repetitions
depending on the number of noise parameters.
After the tests performed, it is determined the optimal set of parameters. This optimum
condition is not necessarily provided in one of the tests performed during the trial, that is, may not
match any of the rows of the matrix of orthogonal vectors applied.
Once identified the optimum condition, follows the application of the analysis of variance. This
is a statistical tool used to interpret experimental results. Analysis of variance allows knowing the
influence of each parameter variation in the quality of the piece obtained, i.e. the importance of small
variations in the input parameters to the variance of output parameters.
Finally, after having found the optimal parametric adjustment and the subsequent response to
that adjustment, it’s advisable to conduct a confirmatory test. If the result of this test is satisfactory and
verifies an improvement in the process, the application of Taguchi method ends. Otherwise, it’s
necessary to repeat the method changing the experimental plan or use the same plan but reducing the
range of values of the levels of each parameter.
If n
ot
sati
sfa
cto
ry
Performance to be optimized
Objective
Matrix Selection
Conduct Experiments
Identify Optimum Condition
Confirmatory TRIAL
Number of parameters that will be changed
Number of levels of changes
Control Parameters
Figure 2.7 – Taguchi Method Flow Chart
17
2.5.2. ANOVA
In ANalysis Of VAriance (ANOVA) the variance in the response measurements is partitioned
into the components that correspond to different sources of variation. Those sources are the control
parameters, the interactions between parameters and a random variation (error) [31]. For a study of k
control parameters, varied for n levels, with no interactions between those parameters, the partition of
the Total Sum of Squares, 𝑆𝑆𝑇, is given by equation (2.8):
𝑺𝑺𝑻 = ∑𝑺𝑺𝒊
𝒊=𝒌
𝒊=𝟏
+ 𝑺𝑺𝒆𝒓𝒓𝒐𝒓 (2.8)
Where:
𝑆𝑆𝑇 = ∑ ∑ (𝑌𝑖𝑗 − )2𝑖=𝑘
𝑖=1𝑗=𝑛𝑗=1 , is the Sum of Squares of the deviation of all individual responses,
Y, and their average, ;
𝑆𝑆𝑖 = ∑ 𝑛(𝑌𝑖𝑗 − 𝑖)2𝑗=𝑛
𝑗=1 , is the Sum of squares of control parameter i:
In analogy, it’s possible to summarize the number of system degrees of freedom (DOF) [32] as
shown in equation (2.9):
𝑫𝑶𝑭𝑻 = ∑𝑫𝑶𝑭𝒊
𝒊=𝒌
𝒊=𝟏
+ 𝑫𝑶𝑭𝒆𝒓𝒓𝒐𝒓 (2.9)
Where:
𝐷𝑂𝐹𝑇 = (𝑛 × 𝑘) − 1
𝐷𝑂𝐹𝑖 = 𝑛 − 1
The Mean Square, MS, variation of each parameter or error is given by equation (2.10):
𝑴𝑺𝒊 =𝑺𝑺𝒊𝑫𝑶𝑭𝒊
(2.10)
F-test is used to check the null hypothesis, H0, that there is no deviation on the mean values of
each factor level. In order to accept or reject H0 it’s need to compare 𝐹𝑖 = 𝑀𝑆𝑖/𝑀𝑆𝑒𝑟𝑟𝑜𝑟 , with Fc.,
equation (2.11).
𝑭𝒊 > (𝑭𝒄 = 𝑭(𝜶,𝑫𝑶𝑭𝒊, 𝑫𝑶𝑭𝑻) (2.11)
The null hypothesis is rejected with a significance level of α when the above equation is
satisfied. This means that the factor is relevant to the final output. F-test is tabled for significance
levels of 1%, 5% and 10%, and generally the level used is the intermediate.
Finally it is used ρi, equation (2.12), to express the relative influence of each parameter and
error, to the total output of the study.
𝜌𝑖 = 𝑆𝑆𝑖/𝑆𝑆𝑇 (2.12)
18
2.6. Friction Stir Welding development on the study area
It was acknowledge that FSW is a high quality process in fast development, especially in the
transportation industry. Is perfectly suitable for transformers manufacture and can be a significant add
to this industry. SIEMENStir presents as an innovative and pioneer project in FSW to electrical
components. The versatility and easy reproducibility of the process, adding to, the improvement on the
weld quality and mechanical properties of the final joint make this an important study to SIEMENS-FS.
Several studies have been performed on aluminum FSW, but none has been done using such soft
alloy as the used AA1070 thin sheet. Electrolytic Though Pitch Copper FSWeldability is also relatively
unknown. This is why this is a challenging work and a possible breakthrough to the sector.
2.6.1. FSW on thin sheets
The FSW process diminishes some of the weldability problems usually associated with fusion
welding processes, due to its low heat input [33]. However, FSW process has limitations in butt-joining
thin sheets. The thickness reduction resulting from the forging effect of the shoulder can significantly
reduce the mechanical resistance in thin plates. The presence of micro defects, usually acceptable in
thick welds, also create serious problems in thin plate sheet welds [34]. FSW is primarily studied for
aluminum, after all those are the main applications of the process. However, typical thicknesses are
superior to 3mm and usual alloys are from heat treatable 2XXX, 6XXX or 7XXX series that were once
considered “unweldable”. Few studies have been found regarding the joint of thin sheets even for the
stated alloys and none of them used an annealed alloy.
Leitão et al. [35] used 1mm thick sheets of AA5182-H111 and AA6016-T4, with base
hardness’s of 71 and 66HV02, respectively, to study the mechanical behavior of similar and dissimilar
welds. Afterwards Leal et al. [36] studied the material flow in those dissimilar welds. And finally
Rodrigues et al. [37] used the same 1mm thick sheets of 6016-T4, to investigate the influence of tool
geometry and welding parameters on the material flow path during welding. Thin sheets of commercial
pure aluminum have been successfully join by FSW, although the used alloy, AA1050-T4, had
significant high hardness due to solution heat treatment. Topic et al. [38] studied the grain size
variations of accumulative roll bonding (ARB) sheets submitted to FSW. FSW is especially suitable to
weld ultra-fine grains produced by ARB because the softening of this alloys is reduced compared to
other joining processes [39].
In the first stage of this project [1] was shown that it is technologically feasible to weld the
aluminum sheet in study. It was also concluded that the maximum load capacity of the welded zone
even matches the base material properties for the tensile tests and overmatches in about 20% the
bending tests. Nevertheless the ductility of the weld zone is reduced.
Although copper’s mechanical resistance fits better in FSW needs, also few studies have been
found on thin copper sheets welded by FSW. Galvão et al. [40] studied the influence of shoulder
geometry on properties of FSW in 1mm sheet of copper-DHP (base hardness of 92HV). The welds
were produced using three different shoulder geometries: flat, conical and scrolled, and varying the
rotation (400, 750 and 1000 rpm) and travel speeds of the tool (160 and 250mm/min). It was
19
acknowledged that both scrolled and conical shoulders can be used to obtain defect free welds, but
both needed a minimum rotational speed to avoid internal defects, 1000rpm for conical shoulder and
750rpm for scrolled one. The same copper-DHP sheets have been successfully weld by Leal et al.[41]
using tools with different shoulder cavities. The study was done based on mechanical and
metallographic tests. It was concluded that the torque, the microstructure and hardness and the
formation of defects in the welds are influenced mainly by tool rotation speed and, to a lesser extent,
by the traverse speed and shoulder cavity.
2.6.2. Dissimilar Al/Cu welds
Copper and Aluminum are widely used in the electric power industry. However, it is difficult to
join them using fusion welding methods due to their large differences in physical and chemical
properties and tendency to form brittle intermetallic compounds [42].
Akinlabi [43] studied the effect of shoulder size on butt weld properties of AA5754 and C11000
dissimilar FSW of 3.175mm thick plates. Using 15, 18 and 25 mm shoulder diameter it was concluded
that 15 and 18 mm diameters were more suitable than 25mm shoulder. Galvão et al. [44] studied
copper over aluminum lap welding by FSW. Using 6mm thick plates of a heat-treatable (AA6082) and
a non-heat-treatable (AA5083) aluminum alloys and 1mm copper sheet, being stated that welds using
AA5083 resulted on excellent surface finishing but highly defective Al/Cu interfaces. It was also
registered an impressive hardness increase due to the formation of ultra-refined microstructure of
aluminum. Firouzdor and Kou [45] studied FSW of 6061 Al to commercially pure Cu. Conventional lap
FSW was modified by butt welding a small piece of Al to the top of Cu, with a slight pin penetration
into the bottom of Al. At travel speeds up to 127 mm/min the modified welds were about twice the joint
strength and five to nine times the ductility of the conventional lap welds.
2.6.3. Taguchi on FSW
Since it emerged, the Taguchi Method has been used in several areas of study, publications
can be found from medicine to robotics passing by food science or zoology. In the present work, it will
be addressed only works on Friction Stir related processes on metals [46]–[48], and other materials
[49]–[51].
Koilraj [46] used a Taguchi study for optimization of FSW process parameters to a dissimilar
aluminum alloys weld. Varying rotational speed, travel speed, tool geometry and ratio between tool
shoulder diameter and pin diameter. The optimum process parameters were determined with
reference to tensile strength of the joint and then confirmed by a last trial with the optimum
parameters. Vidal [47] optimized fatigue behavior of aerospace alloy AA2024-T351, based on tensile,
bending and hardness characterization. Heidarzadeh [48] used a larger DOE to study the tensile
behavior of friction stir welded 6061-T4. Bagheri [49] studied the effect of rotational speed, travel
speed and temperature to FSW of ABS. Bozkurt [50] developed the same study for FSW of
polyethylene varying rotational speed, travel speed and machine tilt angle. Dashatan et al. [51] used
similar approaches for optimized dwell time, plunge speed and rotational speed of FSSW of dissimilar
PMMA and ABS.
20
2.7. Summary of State of the Art
In the past years, aluminum has emerged in the electric conductors industry. The main reason
is the obvious economic factor because aluminum is between two to three times cheaper than copper.
Although aluminum conductors exhibit bigger section and volume, it’s mass and consequently its
weight is halved when compared to copper conductors. This leads to a significant trend in the
production of windings for transformers for power systems, and opens the possibility of developing
new products and new processes. One of the challenges of this change is the relatively low weldability
of aluminum sheets with conventional welding processes.
The Friction Stir Welding (FSW) process is a breakthrough on joining components’ technology
and has been through a rapid growth in research, development and application since the early 2000s.
It has been subjected to the most demanding quality standard requirements and used in challenging
industrial applications over a wide range of structural and non-structural components mainly in light
alloys for transport industries. But few tests have been found on electrical components.
The Taguchi Method is a technique for designing and performing experiments in order to
investigate processes where the output depends on many factors. By systematically choosing certain
combinations of variables it is possible to separate their individual effects, and avoid the need of
perform all possible combinations of values of those variables.
Several studies have been performed on aluminum FSW, but none has been done using such
soft alloy as the used AA1070 thin sheet. Electrolytic Though Pitch Copper FSWeldability is also
relatively unknown. So it’s important to develop process parameters and tools for such applications.
This is why this is a challenging work and a possible breakthrough to the sector.
21
3. Equipment Characterization
3.1. Esab LegioTM FSW 3U
All friction stir welds in this work have been made with LEGIOTM
FSW 3U manufactured by
ESAB (Figure 3.1), this is a FSW driven laboratorial equipment with computer numerical control that
can perform welds either in vertical position control or in forging force control. This machine enables
besides the force control, parameters monitoring and tool cooling system. Those are the main
advantages to conventional milling equipment also used to perform FSW.
Figure 3.1 – Welding equipment LEGIOTM
FSW 3U of ESAB.
The equipment has four degrees of freedom: one of head rotation (C-axis) and three linear
axis: (1) x-axis (1200 mm max. extent) granted by a rack and pinion system; (2) y-axis (amplitude 400
mm) by an endless screw; (3) z-axis (approx. 340 mm extent) done by a hydraulic cylinder with start
and end limit sensors.
Figure 3.2 – Representation of the different constituents of the equipment.
Caption 1. Welding Head 2. Welding Head Support 3. Overall Support Structure 4. Motor for X-axis Movement 5. Motor for rotation (C-axis) 6. Hydraulic Cylinder 7. Hydraulic Unit 8. Control Booth 9. Numerical Control Panel 10. Cooling System
22
In Figure 3.2 are represented the various components of the machinery. The support for the
welding head can be rotated ±5º in XZ plan to introduce tilt angle. When a side tilt angle is needed
there are two possible solutions. The first one is to slope the work table (rotation in X-axis), the second
solution is to weld in YY direction although this solution is inadvisable as it can damage the endless
screw transmission. More detailed information about the equipment and the parameters that can be
controlled can be found in the user guide.
Figure 3.3 – Work table and fixing system used.
The FSW machine is coupled to a support table (Annex E1) that has been designed to sustain
the load applied during the welding process. This table can be used directly as a work table, but since
most of the welds of this study needed strict restraining systems a second work table has been used.
The design of the work table can be seen in Annex E2, the table has been planned to allow the proper
fixing to the weld sheets, in an edge-to-edge setup. Figure 3.3 exhibits the fixing system used. This
work table presents a removable center piece, in the weld path, which can be replaced whenever it
gets so damaged that it could spoil the weld. This allows experimenting longer probe lengths or bigger
loads without concerns.
23
3.2. FSW Tools
FSW Tool geometry is one of the most important parameters in the process. Therefore, it is
essential not only the geometry of the shoulder and probe, that are in contact with the parts to be
welded, but also how the tool body resists to the mechanical efforts applied and dissipates the heat
generated during the process. The third version of the modular tool developed at IST, called
iSTIRtool_v3 [52], was used in the present work (Figure 3.4). This tool consists of three modules
(body, shoulder and probe) which are integrated to compose the final geometry, adjustable to the type
and thickness of the materials to be welded.
The body of the tool was built in Steel Ck45, shoulder and probe were made of tool steel, whit
a specification in accordance with the European Standard (EN) is X40CrMoV5-1, H13 in AISI
designation. This material was machined to its final form, annealed and subsequently subjected to
heat treatments of quenching and tempering under vacuum at a temperature of 400ºC, which gave it
an average hardness of 533HV. This hardness assures high resistance resulting in a rigid behavior
and non-consumable when in contact to the materials to weld. In order to increase the life of the tool
all the components were cleaned with glass beads, for surface oxides removal. Subsequently, it was
subjected to thermochemical treatment for surface hardening by nitriding to a depth of around 30
micrometers. In order to reduce the phenomenon of adherence of material to the shoulder and probe
was also promoted the oxidation treatment with steam at 500 ºC to a depth of about 3 micrometer.
Those modules, probe and shoulder are easily replaceable and matchable, allowing a wide
range of solutions. This tool allows the use of an internal forced cooling and incremental changes in
the length of the pin 1/12 mm without the need to dismantle or remove the tool from the machine.
Figure 3.4 – 3-D view of the iSTIRtool_v3 assembly. 1) Tool body; 2) Shoulder; 3) Probe; 4) Fixing Shoulder Screws; 5) Fixing Probe Screw.
24
For this work five different M4 shoulders and two M4 probes have been designed, combining
for 10 different tool geometries. Aluminum butt weld was the first study case of the project [1], and
after the first stage it was acknowledged that the 5mm diameter probe used, was probably too big,
causing problems with the material flow, and the 3mm diameter probe also tested was too small,
causing problems in the joint itself. To overcome this problem intermediate shoulders and probes with
4mm were designed as shown in Figure 3.5 and in Figure 3.6, respectively, the corresponding
drawings can be seen in Annex E. For each type of weld addressed in this report the chosen tool
combination is explained and justified in the beginning of the topic.
Figure 3.5 – Different M4 shoulder geometries. a) Concave Smooth; Flat scrolled with: b) one striate normal pace c) two striates double pace d) two striates
normal pace e) one striate double pace.
Figure 3.6 – M4 Probes a) with conical tips, final diameter 3mm, b) with cylindrical tips, 6 mm length.
25
4. Tests Characterization
In order to acknowledge the mechanical response of aluminum and copper butt welds, they
were submitted to tensile, bending and hardness tests. Figure 4.1 represents the cuts that were made
in the welded sheets to make the appropriated specimens for those tests. Each section has been
numbered, from X.0 to X.7, to indicate the position on the weld sheet. Tensile (T) and bending (B)
specimens were cut, according to standards, with 20mm width and try to represent, in both tests, all
the welding length. Specimens X.0 and X.7 (M) have been used for metallographic analysis and were
used to test the hardness profile of the transversal section of the weld. X character represents the trial
number of the Taguchi study that will be introduced further on.
4.1. Tensile Test
Tensile testing was performed using an Instrom 4507 equipment, Figure 4.2, in Secção de
Tecnologia Mecânica, Instituto Superior Técnico, Universidade Técnica de Lisboa with a 200kN load
cell and bi-axial extensometers of high resolution and following the experimental procedure in annex
A4.
Figure 4.2 – Tensile testing machine, Instrom 4507, overall view at left, testing zone at right.
Figure 4.1 – Representation of the cuts made on butt welded sheets of aluminum and copper for taguchi study.
26
Three tensile specimens in accordance to the NP-EN895:2002 standard [53] were machined
with the dimensions shown in annex C1, from each base material and experimental welding trial.
Tensile test results, load (𝐹) and respective displacement (𝑙), were properly treated in order to obtain
the Engineering Stress (σ) and Strain (ε) curve according to equation (4.1):
𝜺 =𝒍 − 𝒍𝟎𝒍𝟎
=𝒍
𝒍𝟎− 𝟏
𝝈 =𝑭
𝑨𝟎
(4.1)
After, they are transformed in the True Stress (𝜎) versus True Strain (𝜀) curve through the
equation (4.2):
𝒅 =𝒅𝒍
𝒍⇔ = 𝒍𝒏
𝒍
𝒍𝟎= 𝐥𝐧 (𝜺 + 𝟏)
=𝑭
𝑨=
𝑭 × 𝒍
𝑨𝟎 × 𝒍𝟎= 𝝈(𝜺 + 𝟏)
(4.2)
Values of five mechanical properties were found, Young’s modulus (𝐸), offset yield tensile
strength at 0.2% (𝜎0.2), ultimate tensile strength (𝜎𝑚𝑎𝑥), tenacity modulus (𝑀𝑇) and finally the maximum
elongation before rupture (𝜀) [54]. The Young’s modulus is obtained by the slope of the elastic regime
linear trendline based on Hooke’s law. The offset yield tensile strength is the tensile value that
generates a 0.2% elongation, after elastic recuperation, see Figure 4.3. The ultimate tensile strength is
found by corresponding the maximum engineering tensile with their true tensile value. Maximum
elongations before rupture is self-explained, and the tenacity modulus is the area below the curve until
rupture, see Figure 4.4.
Figure 4.3 – Magnification of Tensile test results of AA1070, BM1 trial, near elastic regime.
Schematic representation of 𝑬 and 𝟎.𝟐.
27
Figure 4.4 – Tensile test results of AA1070, BM1 trial.
Schematic representation of the properties 𝒎𝒂𝒙, 𝑴𝑻 and .
4.2. Bending Test
Three bending specimens in accordance to the NP EN 910:1996(E) standard [55] were
obtained from each trial and base material with dimensions of annex C2. These specimens were
tested in the ESAB LEGIOTM
FSW 3U machine using a 0.1mm/s Plunge Speed. The complete
experimental procedure can be seen in annex A5. Figure 4.5 shows the test apparatus using the
structure of annex D.
Figure 4.5 –Three Point Bending example of aluminum weld specimen.
28
The three point bending setup for aluminum was done with a mandrel of 9.5mm diameter (D)
and two 5mm rollers (R) spaced of 14mm (L) as shown in Figure 4.6. For copper the thickness (a) is
only of 1.1mm and the distance between the rollers (L) has been reduced to 13.0mm.
Bending test results represent the behavior of the material when submitted to a constant
descendent speed in a curve Load (F) vs displacement (d). From the bending results have been
found values of three mechanical properties, maximum force (Fmax), displacement at maximum force
(𝑑𝐹𝑚𝑎𝑥) and absorbed energy (En) as shown in the Figure 4.7.
Note that ESAB LEGIO reads data at each tenth of a second but the hydraulic cylinder that
generates the downward movement is not so sensitive and the decreasing speed is very slow,
0.1mm/s. This means that for each displacement there is, most of the times, more than one load read
as seen above. This graphical displacement can be corrected either by averaging the respective load
values or increasing the decreasing speed. Both solutions can be tricky leading to smaller
discrepancies in the results in the former case and to masked peaks in the latter.
Figure 4.6 – Representation of bending test setup for aluminum.
Figure 4.7 – Bending test result for copper C11000.
Schematic representation of Fmax, dFmax and En.
29
4.3. Micro-hardness
Vickers hardness testing was performed using a Mitutoyo HM-112 Micro-Vickers Hardness
Testing Machine available at Departamento de Engenharia Mecânica e Industrial, Faculdade de
Ciências e Tecnologia, Universidade Nova de Lisboa (Figure 4.8). Micro-hardness indentations have
been performed under a load of 200 g spaced 1.0 mm from each other according to the ISO 6507-
1:1997(E) standard [56]. Hardness profiles were taken at the average thickness of the transversal plan
to the welding direction. At least ten indentations have been made for each side of the sample, starting
from the center of the nugget region.
Figure 4.8 – Mitutoyo HM-112 Vickers micro-hardness testing machine a) Overall view of the equipment, control display at right, and data recording monitor at left b) View of the 50x lens
used to measure the hardness c) View of the indenter used to perform the test.
30
31
5. Base Material Characterization
The present chapter studies the base material used in this work, the material selection was
done together with SIEMENS FS and aims to represent not only the principal geometries used in
Sabugo´s products but also the more challenging combinations for the work. Having said that, foil
thicknesses slightly smaller than those that are usually studied were chosen, also, as one of the goals
of this work is dissimilar foil welding, and as shows in Chapter 2.1.1, aluminum thickness should be
around 1.64 times the copper thickness. The Aluminum foil had 1.6mm, and copper had 1.1mm of
thickness.
Foil characterization was done through metallographic analysis, and mechanical resistance
tests (micro-hardness, tensile and bending), to verify the supplier certification, when applicable. The
results were also compared and verified in the corresponding Standards for aluminum [57] and copper
[58] for electrical purposes.
5.1. Aluminum Foil Characterization
AA1070 aluminum foil was received from SIEMENS FS, in sheets with 1.6mm thick and
dimensions of 1100x800mm. Those sheets have been cut accordingly to the applications, for butt
welding samples with 200x100mm were used with the bigger dimension being cut perpendicular to
rolling direction. For foil-bar welding, the samples used were adjusted to the bar dimensions.
Figure 5.1 – Aluminum foil, as received.
Figure 5.1 shows the AA1070 cold hardened and partially annealed foil as received. This
sample has been prepared according to the procedure described in Annex A2, and etched to reveal
grain boundaries with Poulton reagent.
Figure 5.2 was obtained of a supplier certification document and indicates, in the first line, the
composition of the specified material of the client, SIEMENS FS, and the composition of two different
lots shipped to the factory. There is no guarantee that the material used came from any of those lots. It
was assumed that the material follows the client certification, so that aluminum foils have, at least
99.70% aluminum and, as it was explained in section 2.3.2, this can be classified as AA1070.
32
Figure 5.2 – AA1070 composition certification.
Figure 5.3 – Aluminum mechanical properties certification.
The table of Figure 5.3 was also obtained from the supplier technical sheet, and it was used to
verify the results of tensile tests done to base material. Those tests have been made in 3 specimens
extracted along the rolling direction with dimensions that can be seen in Annex C1. The results are
summarized in Table 5.1. The comparable values are the offset yield strength (at 0.2%), the ultimate
tensile strength, 𝜎𝑚𝑎𝑥, and elongation. All values seem to be correct and in accordance with the
standards that specify 𝜎𝑚𝑎𝑥 of 65-95 MPa, 𝜎0.2 of at least 20 MPa and minimum elongation of 33%
[57].
Table 5.1 – Tensile tests results for 3 specimens of Aluminum Base Material.
E [GPa] 𝟎.𝟐 [MPa] 𝒎𝒂𝒙 [MPa] 𝑴𝑻 [J/mm3] [%]
BM1 81.19 34.77 77.74 20.25 36.00
BM2 71.17 34.53 76.01 19.90 36.00
BM3 69.80 35.42 79.54 19.01 34.00
Average 74.05 34.91 77.76 19.72 35.33
Bending tests results are summarized in
Table 5.2, again, they were obtained by testing 3 specimens and the average value of the 3
tests was considered the standard for the following work.
Table 5.2 – Bending tests results for 3 specimens of Aluminum Base Material.
Fmax [kN] dFmax [mm] 𝑬𝒏 [J]
BM1 1.03 6.19 530.07
BM2 1.07 5.96 518.50
BM3 1.03 6.04 513.94
Average 1.04 6.06 520.84
Finally the Base Material was tested for measurement of it hardness, 2 sets of 9 points were
measured, and the average was 27.9HV.
33
5.2. Copper Foil Characterization
C11000 fully annealed copper sheet was received in a 101Kg winding, with 1.1mm thick and
690mm width. The metallographic analysis of copper, Figure 5.4, revealed a matrix-lamellae
microstructure with anisotropic arrangement of the grains. Figure 5.5 shows the supplier chemical
composition certificate.
Figure 5.4 – Copper Foil, as received.
The same approach used to characterize aluminum, was used here. Three specimens were
produced for tensile testing and three for bending. A sample was used to analyze microstructure and
test the hardness. The hardness test revealed a value of 65.1HV. The results of the tensile and
bending tests are shown in Table 5.3 and Table 5.4, respectively. All these results are very similar and
are in accordance to those found in the Standards [58] for the same alloy and manufacture process.
The Standards recommend a 𝜎𝑚𝑎𝑥 of at least 250 MPa, an yield strength with a maximum of 120MPa,
an elongation of 25-35% and an Hardness of 40-65HV.
Table 5.3 – Tensile tests results for 2 specimens of Copper Base Material.
E [GPa] 𝟎.𝟐 [MPa] 𝒎𝒂𝒙 [MPa] 𝑴𝑻 [J/mm3] [%]
BM1 175.48 76.62 306.34 64.15 35.00
BM2 103.53 73.93 305.60 64.76 36.00
Average 139.50 75.28 305.97 64.45 35.50
Note: There was a problem with the extensometer in the third trial, so the values were discarded.
Table 5.4 – Bending tests results for 3 specimens of Copper Base Material.
Fmax [kN] dFmax [mm] 𝑬𝒏 [J]
BM1 1.16 6.53 645.99
BM2 1.16 6.62 997.89
BM3 1.17 7.73 996.38
Average 1.16 6.96 880.09
Figure 5.5 – Chemical composition certification for C11000.
34
35
6. Characterization of Taguchi on FSW
In this work, two Taguchi studies were made, one for aluminum and the other for copper butt-
welding. In both studies the evaluation and control parameters, as well as the orthogonal array
applied, were the same. The nominal values of those parameters were obviously adjusted to each
condition. The concepts and theory explained in this section are general and will be used in each of
the sections corresponding to both tests, for aluminum and copper, in section 7.1 and 7.2 respectively.
6.1. Evaluation Factors
Three factors were used to evaluate the overall quality of the different trials, based in the
mechanical response of the welds. The first of those global analysis factors, Global Efficiency on
Tensile (GET) has been developed by Vilaça, P. [59]. Representing in percentage the performance of
the trial, according to the base material values weighted by the importance between the various
properties obtained. Equation (6.1)defines GET factor:
𝑮𝑬𝑻 = 𝑪𝑬 ×𝑬𝒊𝑬𝑩𝑴
+ 𝑪𝟎,𝟐 ×𝟎.𝟐𝒊𝟎.𝟐𝑩𝑴
+ 𝑪𝒎𝒂𝒙 ×𝒎𝒂𝒙𝒊𝒎𝒂𝒙𝑩𝑴
+ 𝑪𝑴𝑻×
𝑴𝑻𝒊
𝑴𝑻𝑩𝑴
+ 𝑪 ×𝒊𝑩𝑴
(6.1)
Where:
𝐸𝑖 ; 𝜎0.2𝑖 ; 𝜎𝑚𝑎𝑥𝑖 ; 𝑀𝑇𝑖 ; 𝜀 – represent the properties measured in tensile test of trial, 𝑖 ;
𝐸𝐵𝑀 ; 𝜎0.2𝐵𝑀 ; 𝜎𝑚𝑎𝑥𝐵𝑀 ; 𝑀𝑇𝐵𝑀 ; 𝜀𝑀 – these are the properties measured in tensile test
of base material used in trial, 𝑖 ; 𝐶𝐸 ; 𝐶0.2 ; 𝐶𝑚𝑎𝑥 ; 𝐶𝑀𝑇 ; 𝐶 – indicate the weight factors for each property of GET
factor. Those are specified in Table 6.1.
GET weight factors of the five properties measured in tensile test were chosen based on the
know-how and experience of the author, although lacking any scientific support. For this application,
the main objective is maintaining the elastic behavior. Therefore, the most important parameter is the
offset yield strength (𝜎0.2) as Young’s Modulus (𝐸) variance is generally small or related to the trial
initial instability. Maximum elongation (𝜀) is also an important factor to allow higher deformations,
Ultimate tensile strength (𝜎𝑚𝑎𝑥) has average importance and Tenacity Modulus (𝑀𝑇) is not relevant
due to the absence of impact loads.
Table 6.1 – GET weight for each property of tensile test.
𝑪𝑬 𝑪𝟎.𝟐 𝑪𝒎𝒂𝒙 𝑪𝑴𝑻 𝑪
10% 30% 20% 15% 25%
In analogy to GET, Vidal et al. [47] developed Global Efficiency on Bending (GEB), shown in
equation (6.2), and the Hardness Coefficient (HARD) that appears in equation (6.3). These summarize
the response of the welds to bending and hardness tests, respectively.
𝑮𝑬𝑩 = 𝑪𝑭 ×𝑭𝒊𝑭𝑩𝑴
+ 𝑪𝒅 ×𝒅𝒊𝒅𝑩𝑴
+ 𝑪𝑬𝒏 ×𝑬𝒏𝒊𝑬𝒏𝑩𝑴
(6.2)
Where:
𝐹𝑖 ; 𝑑𝑖 ; 𝐸𝑛𝑖 – represent the properties measured in bending test of trial, 𝑖 ; 𝐹𝐵𝑀 ; 𝑑𝐵𝑀 ; 𝐸𝑛𝐵𝑀 – are the properties measured in bending test of base material used
in trial, 𝑖 ; 𝐶𝐹 ; 𝐶𝑑 ; 𝐶𝐸𝑛 – indicate the weight factors for each property of GEB factor. Those are
specified in Table 6.2.
36
The GEB weight factors were, once again, just like in the GET case, chosen without scientific
support but representing an effort to establish a global criterion based on authors experience and in
the product application.
Table 6.2 – GEB weight for each property of bending test.
𝑪F 𝑪d 𝑪En
50% 25% 25%
𝑯𝑨𝑹𝑫 = 𝒎𝒊𝒏𝒊𝒎𝒖𝒎 𝒉𝒂𝒓𝒅𝒏𝒆𝒔𝒔
𝒃𝒂𝒔𝒆 𝒎𝒂𝒕𝒆𝒓𝒊𝒂𝒍 𝒉𝒂𝒓𝒅𝒏𝒆𝒔𝒔 (6.3)
Where the numerator is the smaller value of hardness read at half thickness of weld cross
section and the denominator the average hardness measured at half thickness of the base material.
6.2. Control Parameters and their Levels
The control parameters have been chosen from the FSW operation parameters (Section 2.2.2)
based on expertise and previous works [47]. The selected control parameters were Axial Force, Travel
Speed and Probe Length as they characterize all welding possibilities and avoid or introduce LOP
defects. Three levels have been selected for each of the three control parameters.
Table 6.3 – Control Parameters and their Levels.
Control Parameters Level 1 Level 2 Level 3
Vertical Force (Fz) F1 F2 F3
Travel Speed (Vx) V1 V2 V3
Probe Length (Lpin) L1 L2 L3
Table 6.3 represents the different parameter levels that are nominal values, in Kg, mm/min
and mm for Fz, Vx and Lpin parameters, respectively, equally spaced from the level before. As the
goal is to study the influence of the control parameters on the quality of the join, the remaining
parameters were kept fixed in all trials. Those parameters and respective values will be addressed
later.
6.3. Design of Experiments (DOE)
As the aim is to find the best set of parameters for three different control parameters (F, V and
L) over a window of three defined values (Level 1,2 and 3) it is used the Taguchi L9 orthogonal array
(OA), with just three columns, shown in Table 6.4. This OA has a total of 8 DOF (number of trials - 1).
So it’s possible with this OA to test up to four different parameters, with no interactions, or two
parameters, with interaction. For this study each factor will have 2 DOF (number of levels – 1)
summing a total of 6 DOF. This leaves 2 free degrees for error.
Table 6.4 – Taguchi L9 Orthogonal Array with 3 columns.
Trials Vertical Force (Fz) Travel speed (Vx) Probe Length (Lpin) 1 F1 V1 L1 2 F1 V2 L2 3 F1 V3 L3 4 F2 V1 L2 5 F2 V2 L3 6 F2 V3 L1 7 F3 V1 L3 8 F3 V2 L1 9 F3 V3 L2
37
7. Experimental Study Cases
7.1. Aluminum Butt Welding
7.1.1. Experimental Setup
The experimental setup is one of the most important factors when studying the interference of
parameters to the quality of the welds, because if the experimental conditions are different from trial to
trial it is not possible to establish a relation between results and those trials.
To avoid adhesion of the weld specimen to the worktable a copper bar with 10mm thick was
used, below the sheets to weld. As shown in Figure 7.1, the copper plate was placed above the steel
worktable, and fixed by four clamps. The aluminum sheets are then placed above and fixed by a
secondary and more local restrictive fixing system: a five screw portico in each side.
Figure 7.1 – Experimental setup for aluminum welds.
7.1.2. Tool Geometry
Figure 7.2 – Probe 4I3 and shoulder geometry 4P3 used in aluminum butt weld.
After testing different combinations of shoulders and probes, based on experience [1], visual
analyses of the resulting welds and the cleaning of the tool after the weld, the 4I3 probes (Annex E7)
were chosen with the 4P3 shoulder (Annex E4) to this aluminum butt welds (Figure 7.2). A cylindrical
probe was required because of the small thickness of the welding sheets, avoiding the accumulation
of material in the gap between probe and shoulder. The one-striate shoulder was used because in
38
double scrolled ones, aluminum adheres to the surface, similarly to what happens with the concave
shoulder. This phenomenon causes instabilities through the weld path, causing the need to clean the
shoulder and the probe after each weld and consequently decreasing the productivity, especially when
the aim is to create a more efficient industrial solution.
7.1.3. Parameters
Once the experimental setup and the tools were defined, the following step was to choose the
fixed and the control parameters of the study. The following parameters were fixed, using the know-
how of a previous work [1]:
Ω = 800 rpm
Wp: 0.1 mm
α = 0.5º
Dt = 3s
Ps = 0.1mm/s
Tool Rotation Speed (Ω) was fixed according to preliminary trials, Welding Position (Wp) was
measured from the anvil copper plate, tilt angle (α) was chosen in compliance with the tool geometry
and Dwell Time (Dt) and Plunge Speed (Ps) were settled based on the thermal response of the
material.
Axial Force, Travel Speed and Probe Length have been chosen as the control parameters, as
explained in Section 6.2. The three levels of Vertical Force have been chosen so that they cover the
most of the welding spectrum of aluminum, from almost underrated to almost overrated force, Travel
speed levels aimed to represent both cold and hot welds and finally the Probe Length levels try to
represent undersized and oversized lengths. Table G.1 of the confidential annex G shows the Taguchi
matrix of trials with the nominal values of the control parameters.
Figure 7.3 shows both face and root sides of the nine trials performed on aluminum. In Annex
B1 can be seen a closer look of each weld.
Figure 7.3 – Overall look of the face and root sides of the nine trials of aluminum.
39
Table 7.1 summarizes the visual analysis of such welds. The amount of burr was not
significant in none of the welds although it was present in some. The Weld Bead Hollow in face side
and the Depression on root side seem to be directly related to the Axial Force of the Tool. Doubtful
Bond was found in more than half the welds.
Table 7.1 – Visual analysis of aluminum welds.
Trial
Burr Weld Bead (face) Weld Bead (root)
Quantity Type Width Striate Hollow Depression Bond
None
Few
A lo
t
Contin
uous
Gra
nula
r
Regu
lar
Varia
ble
Regu
lar
Varia
ble
None
Sm
ooth
None
Sm
ooth
Pro
no
unced
Yes
Doubtfu
l
1 X NA NA X X X X X
2 X X X X X X X
3 X NA NA X X X X X
4 X X X X X X X
5 X NA NA X X X X X
6 X NA NA X X X X X
7 X NA NA X X X X X
8 X NA NA X X X X X
9 X NA NA X X X X X
40
7.1.4. Tensile Tests Results
The results for aluminum welds are summarized in Table 7.2, and are weighted to the same
properties of base material. Finally the GET factor was calculated as explained in Section 6.1. The
results can be seen graphically in Figure 7.4.
Table 7.2 – Summary of results for tensile tests of aluminum.
Base Material
𝑬𝑩𝑴 [GPa] 𝟎.𝟐𝑩𝑴[MPa] 𝒎𝒂𝒙𝑩𝑴[MPa] 𝑴𝑻𝑩𝑴
[J/mm3]
𝑩𝑴 (%) 𝑮𝑬𝑻𝑴𝑩
74.05 34.91 77.76 19.72 35.33 1.00
Trials 𝑬𝒊 𝑬𝒊𝑬𝑩𝑴
𝟎.𝟐𝒊 𝟎.𝟐𝒊𝟎.𝟐𝑩𝑴
𝒎𝒂𝒙𝒊 𝒎𝒂𝒙𝒊𝒎𝒂𝒙𝑩𝑴
𝑴𝑻𝒊
𝑴𝑻𝒊
𝑴𝑻𝑩𝑴
𝒊 𝒊𝑩𝑴
𝑮𝑬𝑻𝒊
1 61.78 0.83 34.70 0.99 65.73 0.85 8.79 0.45 17.50 0.50 0.74
2 67.43 0.91 35.03 1.00 68.55 0.88 10.44 0.53 20.00 0.57 0.79
3 61.21 0.83 34.89 1.00 61.66 0.79 5.85 0.30 12.00 0.34 0.67
4 63.71 0.86 36.00 1.03 69.80 0.90 14.29 0.72 27.00 0.76 0.87
5 55.19 0.75 35.75 1.02 57.90 0.74 4.22 0.21 9.00 0.25 0.63
6 73.21 0.99 36.75 1.05 69.51 0.89 14.35 0.73 27.00 0.76 0.89
7 56.21 0.76 35.25 1.04 54.27 0.70 3.51 0.18 7.75 0.22 0.61
8 54.27 0.73 35.51 1.02 63.91 0.82 8.20 0.42 16.50 0.47 0.72
9 70.37 0.95 36.76 1.05 70.50 0.91 17.70 0.90 33.00 0.93 0.96
In the first graph of Figure 7.4 it’s possible to see that Trials 4, 6 and 9 have factors of more
than 0.8, which means that those parameters are well adjusted to this material. Trials 3, 5 and 7, the
trials with smaller GET factor, have the longest probe length. This means that this probe length was
too long and induced instabilities on the movement, such as scratching the base plate. To evaluate the
influence of the parameters in GET factor, the mean values of each level were calculated and plotted
in the right graph of Figure 7.4. This means that, for example, value V1 corresponds to the average of
trials 1, 4 and 7 GET value. From the analysis of the graph it is possible to conclude that the optimum
values for GET factor of the axial force, the travel speed and the probe length are F2, V3 and L2,
respectively. The value of the Level 3 of probe length is the smallest as expected from the previous
analysis of the individual trial results. All three values of Axial Force are very similar, which indicates
that variations in this parameter do not affect significantly this factor.
0.74 0.79
0.67
0.87
0.63
0.89
0.61
0.72
0.96
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
1 2 3 4 5 6 7 8 9
Trial
GET - Trials
0.73 0.80 0.76 0.74 0.71
0.84 0.79
0.87
0.64
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
F1 F2 F3 V1 V2 V3 L1 L2 L3
Parameter Level
GET - Parameters
Figure 7.4 – GET results for each trial (left) and parameter level (right).
41
7.1.5. Bending Tests Results
From the bending results, values of three mechanical properties were found, being those the
maximum load (𝐹), displacement (𝑑) and absorbed energy (En). Table 7.3 summarizes the values
obtained by the average of two valid results, from the three performed. Those results, as for tensile,
have been weighted with those of base material, and the global efficiency factor has been calculated
and plotted in the left graph of Figure 7.5.
Table 7.3 – Summary of results for bending tests of aluminum.
Base Material 𝑭𝑩𝑴 [kN] 𝒅𝑩𝑴[mm] 𝑬𝒏𝑩𝑴[J] 𝑮𝑬𝑩𝑴𝑩
1.04 6.08 520.84 1.00
Trials 𝑭𝒊 𝑭𝒊𝑭𝑩𝑴
𝒅𝒊 𝒅𝒊𝒅𝑩𝑴
𝑬𝒏𝒊 𝑬𝒏𝒊𝑬𝒏𝑩𝑴
𝑮𝑬𝑩𝒊
1 0.84 0.81 4.50 0.74 322.19 0.62 0.75
2 0.89 0.85 5.66 0.93 410.10 0.79 0.86
3 0.91 0.88 5.93 0.98 458.42 0.88 0.90
4 0.92 0.89 4.75 0.78 365.03 0.70 0.81
5 0.89 0.86 5.02 0.83 375.45 0.72 0.82
6 0.87 0.84 5.35 0.88 381.77 0.73 0.82
7 0.89 0.85 4.78 0.79 355.36 0.68 0.79
8 0.91 0.88 3.78 0.62 275.60 0.53 0.73
9 0.89 0.86 3.69 0.61 269.80 0.52 0.71
Figure 7.5 illustrates the GEB factor trials for aluminum welding, showing a good overall result
for all trials. Global Efficiency on Bending illustrate very consistent results for almost all trials, being
the exception trials 8 and 9 which have a reduced value, probably due to excessive force. Trials 2 and
3 have above average results, which would indicate better parameters selection. The parameters’
influence in GEB is shown in the right figure and demonstrate that this factor is very well behaved, with
increase of force and decrease of speed and probe length, the GEB factor increases. So the optimum
levels for this factor are F1, V3 and L3. Speed levels look very similar, indicating that this parameter
has little influence; however the force shows a big amplitude.
0.75
0.86 0.90
0.81 0.82 0.82 0.79 0.73 0.71
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
1 2 3 4 5 6 7 8 9
Trial
GEB - Trials
0.84 0.82 0.74 0.76 0.79
0.84 0.78 0.80 0.81
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
F1 F2 F3 V1 V2 V3 L1 L2 L3
Parameter Level
GEB - Parameters
Figure 7.5 – GEB results for each trial (left) and parameters level (right).
42
7.1.6. Hardness Tests Results
Table 7.4 summarizes the results of hardness tests. For each trial, a profile of at least 21
points was done. Those were summarized into three comparable values, minimum, average and
maximum hardness values. According to (6.3), the Hardness coefficient (Hard) for each trial was
calculated.
Table 7.4 – Summary of results for hardness tests of aluminum.
Base Material
𝑴𝒊𝒏 [HV] 𝑨𝒗𝒈[HV] 𝑴𝒂𝒙[HV] 𝑯𝒂𝒓𝒅𝑴𝑩
21.9 27.9 34.0 1.00
Trials 𝑴𝒊𝒏𝒊 𝑨𝒗𝒈𝒊 𝑴𝒂𝒙𝒊 𝑯𝒂𝒓𝒅𝒊
1 27.8 32.9 44.7 1.00
2 26.7 30.7 37.7 0.96
3 21.8 28.6 40.3 0.78
4 28.2 32.2 35.5 1.01
5 27.9 33.8 43.6 1.00
6 24.9 32.7 41.5 0.89
7 31.2 35.5 39.3 1.12
8 27.2 33.5 43.3 0.97
9 26.1 31.2 38.1 0.94
From the analysis of the average values it’s obvious that FSW strengthens aluminum in the
nugget region, being this event predictable. The doubt was if it would weaken the joint near the
transition between TMAZ and HAZ. Apparently this does not occur, as the hardness coefficients are
very close to the unit, for almost all trials, except for trials 3 and 6.
Figure 7.6 – Hardness coefficient results for each trial (left) and parameters level (right).
The hardness coefficient seems significantly much influenced by the parameter levels,
increasing when force and probe length increases and decreasing when the speed decreases.
However, it’s more dependent on Speed and Force that on probe length. The optimum parameters are
F3, V1 and L3 for axial force, travel speed and probe length.
1.00 0.96
0.78
1.01 1.00 0.89
1.12
0.97 0.94
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1 2 3 4 5 6 7 8 9
Trial
HARD - Trials
0.95 0.97 0.97 1.04
0.98
0.87 0.91
0.97 1.01
0.00
0.20
0.40
0.60
0.80
1.00
1.20
F1 F2 F3 V1 V2 V3 L1 L2 L3
Parameter Level
HARD - Parameters
43
Figure 7.7 – Average values of the nine hardness profiles of Aluminum welds.
From advancing side at left, to retreating side at right.
Figure 7.7 shows the average hardness of all nine trials by position, in order to emphasize the
increase of hardness resulting from the FSW. Due to the grain refinement of the process, it’s more
intense in the region between the TMAZ and the nugget, about 3 mm to the advancing side.
7.1.7. Analysis of Variance (ANOVA)
ANOVA has been used to quantify the contribution (ρ) of each parameter to each factor.
Table 7.5 summarizes the results, identifying the degrees of freedom (DOF), the sum of
squared deviations (SS), variance (V) and F-test (F) for each parameter of each evaluation factor. As
this test was made without replication isn’t possible to assign error contribution to random errors or
lack-of-fit errors.
Table 7.5 – Results of variance analysis for the three evaluation parameters for aluminum.
Parameter
DO
F SS V F ρ(%)
GET GEB Hard GET GEB Hard GET GEB Hard GET GEB Hard
Fz 2 0.0063 0.0141 0.0142 0.0031 0.0070 0.0071 9.9570 1.7698 1.7859 5.11 50.58 45.00
Vx 2 0.0274 0.0012 0.0452 0.0137 0.0006 0.0226 43.6702 0.1465 5.7003 22.43 3.10 3.72
Lpin 2 0.0880 0.0081 0.0004 0.0440 0.0040 0.0002 140.0725 1.0170 0.0479 71.94 24.36 25.86
Error 2 0.0006 0.0079 0.0079 0.0003 0.0040 0.0040 - - - 0.51 21.96 25.42
Total 8 0.1224 0.0313 0.0677 - - - - - - 100 100 100
As shown in Figure 7.8 the contribution of each parameter is especially important to each one
of the factors. Being the probe length the main contributor to the GET variance, as well as the travel
speed for Hardness coefficient and the axial force for GEB. Error contribution is small for each factor,
which indicates that neither pure errors nor lack-of-fit errors are big contributors to this test.
Consequently, one could argue that this design of experiments was appropriated.
20
25
30
35
40
-10 -8 -6 -4 -2 0 2 4 6 8 10
Ha
rdn
es
s (
HV
)
Distance to center (mm)
Average Hardness
Average Base Material
44
7.1.8. Optimum parameters identification
To fulfill the main objective of improvement of the mechanical behavior of friction stir welded
aluminum butt welds, it was used an algorithm that would encompass the results of Taguchi method to
obtain the most robust set of parameters to improve globally the properties of welded joints [47].
Using the optimum values for the evaluation factors, described in sections 7.1.4 to 7.1.6, the
first matrix of equation (7.1) was build. The second matrix was made by weighting the contribution of
each parameter from section 7.1.7. Identity of former product matrixes represents the optimum values
for each parameter, considering the same weight for the three test factors.
[
𝑭𝑮𝑬𝑻 𝑭𝑮𝑬𝑩 𝑭𝑯𝒂𝒓𝒅𝑽𝑮𝑬𝑻 𝑽𝑮𝑬𝑩 𝑽𝑯𝒂𝒓𝒅𝑳𝑮𝑬𝑻 𝑳𝑮𝑬𝑩 𝑳𝑯𝒂𝒓𝒅
]
[ 𝝆𝑭(𝑮𝑬𝑻)
𝝆𝑭(𝑻)
𝝆𝑽(𝑮𝑬𝑻)
𝝆𝑽(𝑻)
𝝆𝑳(𝑮𝑬𝑻)
𝝆𝑳(𝑻)𝝆𝑭(𝑮𝑬𝑩)
𝝆𝑭(𝑻)
𝝆𝑽(𝑮𝑬𝑩)
𝝆𝑽(𝑻)
𝝆𝑳(𝑮𝑬𝑩)
𝝆𝑳(𝑻)𝝆𝑭(𝑯𝒂𝒓𝒅)
𝝆𝑭(𝑻)
𝝆𝑽(𝑯𝒂𝒓𝒅)
𝝆𝑽(𝑻)
𝝆𝑳(𝑯𝒂𝒓𝒅)
𝝆𝑳(𝑻) ]
= [𝑳𝒐𝒂𝒅 𝒙 𝒙𝒙 𝑽𝒆𝒍𝒐𝒄𝒊𝒕𝒚 𝒙𝒙 𝒙 𝑷𝒓𝒐𝒃𝒆
] (7.1)
Equation (7.2) represents the results:
[𝑭𝟐 𝑭𝟏 𝑭𝟑𝑽𝟑 𝑽𝟑 𝑽𝟏𝑳𝟐 𝑳𝟑 𝑳𝟐
] [𝟎. 𝟎𝟕 𝟎. 𝟐𝟒 𝟎. 𝟕𝟓𝟎. 𝟔𝟑 𝟎. 𝟎𝟒 𝟎. 𝟐𝟔𝟎. 𝟐𝟗 𝟎. 𝟕𝟐 𝟎. 𝟎𝟏
] ≅ [𝑭𝟏. 𝟓 𝒙 𝒙𝒙 𝑽𝟏. 𝟓 𝒙𝒙 𝒙 𝑳𝟐
] (7.2)
The nominal values of the parameters can be found in the confidential annex H.
7.1.9. Summary of Aluminum Butt Welding Results
The application of Taguchi method to the aluminum butt weld was developed defining three
levels for the three main parameters and performing nine trials according to Taguchi L9 orthogonal
array. Given the small contribution of Error for the variation of the results (GET 0.47%, GEB 21.96%
and HARD 11.72%), it’s possible to assume that the design of experiments was correctly defined and
that inherent errors had a small influence.
5.11%
22.43%
71.94%
0.51%
45.00%
3.72%
25.86%
25.42%
20.93%
66.79%
0.56%
11.72%
Force
Speed
Probe
Error
Hardness
GEB
GET
Figure 7.8 – Contribution of each parameter for the three evaluation parameters.
45
Tensile results revealed that the optimum set of parameters for Global Efficiency on Tensile
were F2, V3 and L2, with the probe length being the most influencing parameter and Axial Force the
less significant. The Three Point Bending results showed a large dependence on force and little
relation to travel speed. The optimum parameters were F1, V3 and L3. The Hardness coefficient was
mainly dependent on travel speed variation and indifferent to probe length. The best results were
obtained with F3, V1 and L3 parameters levels. This study concluded that the optimum set of
parameters equally weighted by the three factors were the mean value between F1 and F2 for Axial
Force, the mean value of V1 and V2 for travel speed and L2 for probe length.
Confirmatory trials have been made using the optimum parameters and submitted to
mechanical, metallographic and electrical conductivity characterization tests. The mechanical results
on the aluminum confirmatory trials were 0.79 GET, 0.80 GEB and 0.99 HARD, which gives a
reduction of only 14% from the base material. Those results confirmed the legitimacy of this statistic
model and proving that this analysis can be used to define welding parameters. The metallographic
analysis, Figure 7.9, evidences the transition, Heat Affected Zone, between the Base Material and
Thermo-Mechanical Affected Zone in which the Nugget can be found.
Electrical conductivity results, Figure7.1, express the very low impact of the FSW weld beads
on conductivity of commercial pure aluminum. The decay from the base material electrical conductivity
is about 4%. This reduction is due to the substantial reduction of the grain size inside the TMAZ of the
weld bead, shown in Figure 7.9 and as concluded by Santos et al. [60].
Figure 7.10 – Eddy current conductivity test performed, at 250 kHz,
in three arbitrary paths (L1, L2, L3) of aluminum’s confirmatory trial.
BM
HAZ
TMAZ
Nugget BM
Figure 7.9 – Metallographic analysis of the confirmatory trial.
46
7.2. Copper Butt Welding
7.2.1. Experimental Setup
For copper’s butt welding was used the work table and the fixing system that were addressed
in Chapter 3.1. Again, it is important to mention that the system constrains are very important in the
FSW process. Without the proper constraint, conditions are not fulfilled for correct welding. Bigger
support plates with 250mm were produced. This allowed the use of all 3 screws of the portico, causing
better fitting and constraining. Another very important detail of a correct setup is the alignment and
flattening of the foil edges. To achieve this the foils were flatten, using a milling machine, the edges
parallel to the welding direction.
7.2.2. Tool Geometry
Probe 4I3 and Shoulder 4O3 were used in copper welding, based on preparatory trials and
expertise. Figure 7.11 shows the mentioned tools and their drawings can be seen in Annex E4 and
E7, respectively. Shoulder cavity has about 3º but has little influence in final weld quality as stated by
Leal [41]. The use of the concave shoulder lead to a tilt angle of two and an half degrees to promote
the correct material feed. Due to the small thickness of the foil a cylindrical probe was used once the
vertical flow of the material is not very useful.
7.2.3. Parameters
For copper welding the following parameters were used, according to the material properties,
the tool geometry and based on the expertise and preliminary trials:
Ω = 1000 rpm
Wp = 0.1 mm
α = 2.5º
Dt = 5s
Ps = 0.1mm/s
Tool Rotation Speed (Ω) was fixed according to preliminary trials and based on the study of
Galvão [40]. Welding Position (Wp) was measured from the back-anvil plate, tilt angle (α) was chosen
in compliance with the tool geometry and Dwell Time (Dt) and Plunge Speed (Ps) were settled based
on the thermal response of the material.
Figure 7.11 – Probe 4I3 and shoulder 4O3 used in copper butt weld.
47
Axial Force, Travel Speed and Probe Length have been chosen as the control parameters, as
explained in Section 6.2. The three levels of Vertical Force have been chosen so that they cover the
most of the welding spectrum of copper, from almost underrated to almost overrated force, Travel
speed levels aimed to represent both cold and hot welds and finally the Probe Length levels try to
represent undersized and oversized lengths. Nominal values can be found in Table G.2 of the
confidential annex G.
Figure 7.12 shows both face and root sides of the nine trials performed on copper. In Annex
B2 can be seen a closer look of each weld. Table 7.6 summarizes the visual analysis of such welds.
Table 7.6 – Visual analysis of copper welds.
Trial
Burr Weld Bead (face) Weld Bead (root)
Quantity Type Width Striate Hollow Depression Bond
None
Few
A lo
t
Contin
uous
Gra
nula
r
Regu
lar
Varia
ble
Regu
lar
Varia
ble
None
Sm
ooth
None
Sm
ooth
Pro
no
unced
Yes
Doubtfu
l
1 X X X X X X X
2 X X X X X X X
3 X X X X X X X
4 X X X X X X X
5 X X X X X X X
6 X X X X X X X
7 X X X X X X X
8 X X X X X X X
9 X X X X X X X
Figure 7.12 – Overall look of the face (left) and root (right) sides of the nine trials of copper.
48
7.2.4. Tensile Tests Results
Copper’s tensile test results were handled similarly to what was explained in section 4. The
five physical properties’ values as well as their weighing of base material have been compiled into
Table 7.7. In the last column it is shown the corresponding values of the GET factor plotted in the left
chart of Figure 7.13.
Table 7.7 – Summary of results for tensile tests of copper.
Base Material 𝑬𝑩𝑴 [GPa] 𝟎.𝟐𝑩𝑴[MPa] 𝒎𝒂𝒙𝑩𝑴[MPa] 𝑴𝑻𝑩𝑴 [J/mm
3] 𝑩𝑴 (%) 𝑮𝑬𝑻𝑴𝑩
139.50 75.28 305.97 64.45 35.50 1.00
Trials 𝑬𝒊 𝑬𝒊𝑬𝑩𝑴
𝟎.𝟐𝒊 𝟎.𝟐𝒊𝟎.𝟐𝑩𝑴
𝒎𝒂𝒙𝒊 𝒎𝒂𝒙𝒊𝒎𝒂𝒙𝑩𝑴
𝑴𝑻𝒊 𝑴𝑻𝒊
𝑴𝑻𝑩𝑴
𝒊 𝒊𝑩𝑴
𝑮𝑬𝑻𝒊
1 108.40 0.78 95.77 1.27 262.26 0.86 60.39 0.94 34.00 0.96 1.01
2 104.87 0.75 90.29 1.20 272.07 0.89 67.03 1.04 37.50 1.06 1.03
3 84.62 0.61 94.51 1.26 148.92 0.49 8.22 0.13 6.75 0.19 0.60
4 107.88 0.77 95.83 1.27 270.44 0.88 67.49 1.05 37.25 1.05 1.06
5 128.76 0.92 90.26 1.20 100.04 0.33 3.35 0.05 3.50 0.10 0.55
6 115.08 0.82 94.33 1.25 257.33 0.84 50.07 0.78 28.50 0.80 0.94
7 126.38 0.91 92.29 1.23 265.59 0.87 67.14 1.04 38.00 1.07 1.06
8 105.34 0.76 92.77 1.23 216.95 0.71 25.60 0.40 16.50 0.46 0.76
9 109.65 0.79 93.23 1.24 171.52 0.56 12.59 0.20 9.50 0.27 0.66
The right chart of Figure 7.13 displays the GET factor per parameter level (right chart). From
its analysis it is clear that Force has little influence in the tensile results of copper weld. However it is
possible to identify some relations from the other two parameters. It seems that only the first level of
travel speed is able to perform consistent welds, because the remaining leads to cold conditions
welds. Level V3 leads to unstable welds probably because of anvil scratching. The optimum
parameters for maximizing GET factor are F1, V1 and L2. This factor demonstrates an inverse
proportionality with the axial force, travel speed and the second and third values of probe length.
1.01 1.03
0.60
1.06
0.55
0.94 1.06
0.76 0.66
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1 2 3 4 5 6 7 8 9Trial
GET - Trials
0.88 0.85 0.83
1.04
0.78 0.73
0.91 0.92
0.74
0.00
0.20
0.40
0.60
0.80
1.00
1.20
F1 F2 F3 V1 V2 V3 L1 L2 L3
Parameter Level
GET - Parameters
Figure 7.13 – GET results for each trial (left) and parameters level (right).
49
7.2.5. Bending Tests Results
The three points bending results for copper where summarized in Table 7.8 and they reveal
very close results, when compared with the base material, with maximum load achieved in almost all
trials. The displacement values also show good results, being higher than 0.79 for eight of the nine
trials executed.
Table 7.8 – Summary of results for bending tests of copper
Base Material
𝑭𝑩𝑴 [kN] 𝒅𝑩𝑴[mm] 𝑬𝒏𝑩𝑴[J] 𝑮𝑬𝑩𝑴𝑩
1.16 6.96 880.09 1.00
Trials 𝑭𝒊 𝑭𝒊𝑭𝑩𝑴
𝒅𝒊 𝒅𝒊𝒅𝑩𝑴
𝑬𝒏𝒊 𝑬𝒏𝒊𝑬𝒏𝑩𝑴
𝑮𝑬𝑩𝒊
1 1.20 1.03 6.02 0.84 594.05 0.60 0.87
2 1.16 1.00 5.93 0.83 589.61 0.59 0.85
3 0.94 0.81 3.93 0.55 385.92 0.39 0.64
4 1.09 0.94 5.79 0.81 527.46 0.53 0.80
5 1.10 0.95 5.98 0.83 556.88 0.56 0.82
6 1.16 1.00 6.43 0.90 673.53 0.68 0.89
7 1.15 0.99 6.08 0.85 625.85 0.63 0.86
8 1.09 0.94 5.45 0.76 513.05 0.51 0.79
9 1.23 1.06 6.84 0.95 689.55 0.69 0.94
The GEB values per trial (left chart of Figure 7.14) show a very good consistency, except for
trial 3. Optimum parameters for this evaluation factor are the maximum values of each parameter
contribution in the right chart of Figure 7.14 to be precise F3, V1 and L2. In all parameters and levels
the results are very similar, varying only from 0.78 to 0.87. However it is possible to notice the
proportionality of the GEB to the axial force, and again the poor resistance of L3.
0.87 0.85
0.64
0.80 0.82 0.89 0.86
0.79
0.94
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
1 2 3 4 5 6 7 8 9Trial
GEB - Trials
0.79 0.84 0.86 0.85 0.87
0.78 0.85 0.82 0.82
0.000.100.200.300.400.500.600.700.800.901.00
F1 F2 F3 V1 V2 V3 L1 L2 L3
Parameter Level
GEB - Parameters
Figure 7.14 – GEB results for each trial (left) and parameters level (right).
50
7.2.6. Hardness Tests Results
Hardness Tests of copper butt welds are summarized in Table 7.9 and plotted in the left chart
of Figure 7.15 and reveal unexpected values for trial 1 in which all comparative values were much
smaller than the remaining ones. The remaining trials resulted in very homogeneous hardness
coefficients, varying just from 0.97 to 1.05 of base material. However, the influence of each parameter
level on the hardness coefficient showed a very good behavior being proportional to each level,
resulting in F3, V3 and L3 optimum values, as shown in the right chart of Figure 7.15.
Table 7.9 – Summary of results for hardness tests of copper
Base Material 𝑴𝒊𝒏 [HV] 𝑨𝒗𝒈[HV] 𝑴𝒂𝒙[HV] 𝑯𝒂𝒓𝒅𝑴𝑩
93.2 103.6 110.6 1.00
Trials 𝑴𝒊𝒏𝒊 𝑨𝒗𝒈𝒊 𝑴𝒂𝒙𝒊 𝑯𝒂𝒓𝒅𝒊
1 76.3 87.7 95.3 0.85
2 97.4 104.7 114.5 1.01
3 97.8 105.7 113.9 1.02
4 98.5 105.5 111.3 1.02
5 94.0 100.3 109.4 0.97
6 102.5 107.5 115.1 1.04
7 103.1 109.2 119.7 1.05
8 99.9 104.6 110.2 1.01
9 94.0 100.5 107.7 0.97
7.2.7. Analysis of Variance
From the results of the three mechanical tests performed and which have been addressed
previously, it was expected that the variance analysis would result in large values for error, due
especially to unexpected values of trial 3 on bending, and trial 1 on hardness. Table 7.10 shows the
degrees of freedom (DOF), the sum of squared deviations (SS), the means square variance (MS) and
the F-test (F) for each evaluation factor and contribution (ρ) of each process parameter to the final
outcome of each test.
0.85
1.01 1.02 1.02 0.97
1.04 1.05 1.01 0.97
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1 2 3 4 5 6 7 8 9
Trial
Hardness - Trials
0.96 1.00 1.01 0.97 1.00 1.01 0.96 1.01 1.01
0
0.2
0.4
0.6
0.8
1
1.2
F1 F2 F3 V1 V2 V3 L1 L2 L3
Parameter Level
Hardness - Parameters
Figure 7.15 – Hardness Coefficient results for each trial (left) and parameters level (right).
51
1.36%
46.71%
17.60%
34.33%
15.00%
2.09%
24.30%
58.60%
16.91%
6.66%
12.86%
63.56%
Force
Speed
Probe
Error
Hardness
GEB
GET
Table 7.10 – Results of variance analysis for the three evaluation parameters for copper.
Parameter D
OF
SS V F ρ(%)
GET GEB Hard GET GEB Hard GET GEB Hard GET GEB Hard
Fz 2 0.0047 0.0088 0.0051 0.0024 0.0044 0.0026 0.0395 0.2560 0.2661 1.36 15.00 16.91
Vx 2 0.1629 0.0012 0.0020 0.0815 0.0006 0.0010 1.3604 0.0357 0.1049 46.71 2.09 6.66
Lpin 2 0.0614 0.0142 0.0039 0.0307 0.0071 0.0019 0.5127 0.4147 0.2024 17.60 24.30 12.86
Error 2 0.1198 0.0343 0.0192 0.0599 0.0171 0.0096 - - - 34.3 58.60 63.56
Total 8 0.3488 0.0585 0.0302 - - - - - - 100 100 100
The contribution of each parameter for the evaluation parameters is shown in Figure 7.16. As
expected the contribution of Error is higher than the contribution of the process parameters both for
GEB and for Hardness Coefficient. For the GET factor, despite the fact that travel speed has a higher
contribution with 46.71%, the error still has a very significant contribution with 34.33% exceeding both
probe length and force together.
7.2.8. Optimum parameters identification
As in aluminum, in order to obtain the set of parameters that maximize the mechanical
response of the three evaluating parameters it was used the algorithm of equation (7.3). With the
weighing factors and the optimum values for each parameter calculated in the previous sections.
[
𝑭𝑮𝑬𝑻 𝑭𝑮𝑬𝑩 𝑭𝑯𝒂𝒓𝒅𝑽𝑮𝑬𝑻 𝑽𝑮𝑬𝑩 𝑽𝑯𝒂𝒓𝒅𝑳𝑮𝑬𝑻 𝑳𝑮𝑬𝑩 𝑳𝑯𝒂𝒓𝒅
]
[ 𝝆𝑭(𝑮𝑬𝑻)
𝝆𝑭(𝑻)
𝝆𝑽(𝑮𝑬𝑻)
𝝆𝑽(𝑻)
𝝆𝑳(𝑮𝑬𝑻)
𝝆𝑳(𝑻)𝝆𝑭(𝑮𝑬𝑩)
𝝆𝑭(𝑻)
𝝆𝑽(𝑮𝑬𝑩)
𝝆𝑽(𝑻)
𝝆𝑳(𝑮𝑬𝑩)
𝝆𝑳(𝑻)𝝆𝑭(𝑯𝒂𝒓𝒅)
𝝆𝑭(𝑻)
𝝆𝑽(𝑯𝒂𝒓𝒅)
𝝆𝑽(𝑻)
𝝆𝑳(𝑯𝒂𝒓𝒅)
𝝆𝑳(𝑻) ]
= [𝑳𝒐𝒂𝒅 𝒙 𝒙𝒙 𝑽𝒆𝒍𝒐𝒄𝒊𝒕𝒚 𝒙𝒙 𝒙 𝑷𝒓𝒐𝒃𝒆
] (7.3)
Equation (7.4) expresses the results:
[𝑭𝟏 𝑭𝟑 𝑭𝟑𝑽𝟏 𝑽𝟏 𝑽𝟑𝑳𝟐 𝑳𝟐 𝑳𝟑
] [𝟎. 𝟎𝟒 𝟎. 𝟖𝟒 𝟎. 𝟑𝟐𝟎. 𝟒𝟓 𝟎. 𝟎𝟒 𝟎. 𝟒𝟒𝟎. 𝟓𝟏 𝟎. 𝟏𝟐 𝟎. 𝟐𝟑
] ≅ [𝑭𝟑 𝒙 𝒙𝒙 𝑽𝟏 𝒙𝒙 𝒙 𝑳𝟐
] (7.4)
The nominal values of the parameters can be found in the confidential annex H.
Figure 7.16 – Contribution of each parameter for the three evaluation parameters.
52
7.2.9. Summary of Copper Butt Welding Results
The optimum set of values for each evaluation factor was defined, the Global Efficiency on
Tensile, the Global Efficiency on Bending and the Hardness Coefficient and the set of values that
maximize the global response to all those factors. Since the inherent error to this results looks too
high, so it is mandatory to conduct a confirmatory trial.
Tensile results revealed that the optimum set of parameters for Global Efficiency on Tensile
were F1, V1 and L2. With the travel speed being the most important parameter followed by error. The
three Point Bending results showed a much larger dependence of error than from the tested
parameters, the optimum parameters were F3, V1 and L2. The hardness coefficient had, again, an
error value superior than for the remaining factors the axial force, the travel speed and the probe
length. Anyway the best results were obtained with F3, V3 and L3 parameters levels.
This study concluded that the optimum set of parameters equally weighted by the three factors
were Axial Force level F3, V1 of travel speed and a probe length with L2.
Confirmatory trials have been made using the optimum parameters and submitted to
mechanical and electrical conductivity characterization tests. The mechanical results on copper
confirmatory trials were 0.67 GET, 0.77 GEB and 0.97 HARD, which gives a reduction of about 20%
from the base material. Copper’s conductivity test, Figure 7.17, revealed a slight increment of 0.5%
IACS in the region between TMAZ and HAZ in the advancing side of the weld. This increase can be
explained by a possible growth of the grain size in this region.
Figure 7.17 – Eddy current conductivity test performed,
in two arbitrary paths (L1, L2),at 250 kHz, of copper’s confirmatory trial.
53
7.3. Overlap Foil-Bar weld
Foil-Bar welding was another geometry required from the client, those welds are essential and
irreplaceable in the present foil winding manufacture. For each foil winding, two mandatory foil-bar
welds are performed, to the entrance bar and end-bar.
Figure 7.18 shows both macro and micrographic photos of the two similar welds presently
performed in SIEMENS-FS in TIG weld. As shown in macro, the HAZ is very large. It can also be seen
that big differences exist in the microstructure with larger grain size in the affected zone. Both welds
evidence initial cracking sites that were highlighted.
Preliminary trials were done to find an adequate range of parameters for these welds. As
stated in Section 2.1 those components are not subjected to high mechanical stresses. So there was
no necessity to perform any optimization, neither any characterization test. As the objective of this
preliminary study was only to achieve a range of parameters that could perform acceptable welds. The
geometry used was overlapped. In theory this weld could also be done in a corner joint in order to
save material, using a side tilt angle.
Figure 7.18 – TIG Foil-Bar weld in aluminum at left, and in copper at right.
Full macros at the top and micrographic photo of initial cracking sites, at bottom.
54
7.3.1. Aluminum Foil – Aluminum Bar Weld
Table 7.11 – Aluminum Foil-Bar
weld parameters range.
Several tool geometries were tested, such as double and single scrolled or smooth concave
shoulders, with conical and cylindrical probes. Tilt angles have been varied from 0º with scrolled
shoulders to a maximum of 2.5º with smooth concave. Different probe lengths and diameters were
also tested. Substantial probe lengths were used with almost the double of the foil thickness (3mm
probe length to a 1.6mm thickness). Because of this generous length M3 probes were automatically
discarded, both M4 and M5 probes were tested.
Finally a range of welding parameters was obtained as summarized in Table 7.11. Those
parameters were obtained for a conical M5 probe that proved to be steadier than cylindrical or M4
ones. The shoulder used was a double scrolled with 0.5 pace. A 0º tilt angle was used, Dt was set to
3s and the Ps to 0.2 mm/s. Figure 7.19 shows a weld performed with those parameters.
7.3.2. Copper Foil – Copper Bar Weld
After experiencing no technical difficulties with the smooth concave shoulder and a tilt angle of
2.0º in copper’s butt welding, copper’s Foil-Bar weld was also made with this geometry, using the
same cylindrical probe. Again as for aluminum, the goal was to achieve material mixture in the joint, so
a probe length with almost the double of the foil thickness (2mm probe length for 1.1mm thick) was
used. The M4 probe was used with suitable results. Table 7.12 shows the parameter window that led
to acceptable outcomes from the visual point of view. An example of such welds is shown in Figure
7.20.
Parameter Min Max
Fz (Kg) 200 300
Vx (mm/min) 150 300
Ω (rpm) 1000 1200
Figure 7.19 – Aluminum Foil-Bar weld example.
55
Table 7.12 – Copper Foil-Bar weld
parameters range.
7.3.3. Aluminum Foil – Copper Bar weld
The aluminum foil – copper bar weld was by far the more challenging combination of all foil-
bar welds performed. The softness of aluminum foil is too high to support the load needed to weld
copper, regardless of the constraining system tightness, the load applied or the heat generated. Figure
7.21 evidence some of those superficial defects. No satisfactory trials were performed although it
seems that it can be done with a more intensive study, with different tool geometries. Increasing
shoulder diameter to avoid aluminum blow-off or shorter pin lengths to prevent vertical instabilities can
be tested for solve this problem.
Figure 7.22 demonstrate the approach used to achieve satisfactory welds to this joint. This
approach involved overlap a copper foil over the aluminum, and then weld together both foils and bar
in a sandwich like form. The parameters of Table 7.13 and a Tool with M5 conical probe (3.5mm
length) and a smooth concave shoulder were used to achieve some good welds from the visual point
of view. A tilt angle with two degrees was used alongside with a 5s dwell time.
Parameter Min Max
Fz (Kg) 700 1000
Vx (mm/min) 150 250
Ω (rpm) 800 1200
Figure 7.21 – Aluminum foil – copper bar weld instabilities.
Figure 7.20 – Copper Foil-Bar weld example.
56
Table 7.13 – Cu-Al-Cu Sandwich like weld parameters range.
7.3.4. Summary of Results
The overlap Foil-Bar weld was performed in similar and dissimilar materials with satisfactory
results, despite the significant differences between physical properties of foil and bars. Several tool
geometries and welding parameters have been tested and defined.
It was acknowledged that M5 cylindrical probe with a double scrolled shoulder is the most
suitable of the available geometries for Aluminum Foil – Aluminum Bar weld. For Copper Foil –
Copper Bar weld was used a smooth concave shoulder with a M4 cylindrical probe. And finally for
dissimilar materials was used a M5 conical probe and a smooth concave shoulder.
The main difficulties of those welds lay on the significant differences in the hardness values
between foil and bars. Those differences are even more pronounced in the aluminum foil – copper bar
joint. A sandwich like setup was used to constrain aluminum foil and enable a good weld.
A deeper study must be done on Foil-Bar welds, in order to quantify the quality of the
performed welds. Mechanical tests need to be adjusted to the geometry of the samples and
conductivity tests must be run.
Parameter Min Max
Fz (Kg) 450 600
Vx (mm/min) 180 210
Ω (rpm) 800 1000
Figure 7.22 – Cu-Al-Cu Sandwich like weld example.
57
7.4. Other Geometries
7.4.1. Aluminum-Copper Butt welding
As explained in section 2.6.2 this geometry, aluminum-copper butt weld with such thin foils
and especially with dissimilar thicknesses could not be found in bibliography. Theoretically it’s possible
to perform this weld. The problems rely on the difference in the two materials which prevents a good
mixture and the thickness difference that avoids a good constraining to the system (Figure 7.23). The
latter problem can be solved with a correct side tilt angle. However the existing work table is not able
to perform small angle variations. Some new designs have been studied and can be seen in Annex Z,
yet none have been produced, needing further study on feasibility.
According to expertise and
bibliography the harder material should be
placed in the advancing side of the weld.
During this study side tilt angles of 2.5º, 3º and
3.7º were tested and the best results seem to
be found in the latter case. It’s also possible to
confine the weldable parameters in the ranges
of 200-450 Kg, 150-250 mm/min and 800-1200
rpm respectively for axial force, travel speed
and rotational speed.
7.4.2. Aluminum-Copper overlap welding
After experiencing the technical
difficulties inherent to aluminum-copper butt
welding, another possibility was tested.
Aluminum-Copper overlap welding was
performed with relative success. Placing
copper on top of aluminum allowed a better
constraining of aluminum, Figure 7.24.
7.4.3. Thin Copper-Copper butt weld
A thinner copper foil with just 0.4mm thick was also tested. With 0.5mm the shoulder scrolls
were thicker than the foil himself. Besides that, due to the small section any small instability could lead
to a disruption. Small loads and speeds were tested, hot and cold conditions also. However, the
outcome was always the same, Figure 7.25, unavoidable breakdown and not once proper welding
conditions were achieved.
Figure 7.24 – Aluminum-Copper overlap weld example.
Figure 7.25 – Examples of thin copper trials.
Figure 7.23 – Aluminum-Copper butt weld instabilities.
58
59
8. Preliminary Feasibility Study
This study is divided in 4 separated parts. In the first part, the production needs of SIEMENS-
FS are listed. The second part explains the operating costs of both processes (TIG and FSW). The
third part shows the initial investment to purchase, optimize and implement the FSW machine. The
fourth part enumerates the non-quantifiable variables related to the Quality of the process.
8.1. The Client Needs
In this section are shown the actual needs of the client, SIEMENS-FS, in Table 8.1. The
number of weld paths has been estimated from the expected number of transformers. For an
estimated annual production of 500 transformers a total of 3000 weld paths are mandatory. This
because there are two welds per bobbin and each transformer has three bobbins.
The weld length and the thickness vary from about 850 mm and 1.1 mm thick for copper welds
to 1100 mm and 1.6 mm thick for aluminum welds. The current production of aluminum coil
transformer in SIEMENS-FS is small but with the increase of copper’s price and the improvement of
aluminum products it is expected that aluminum demand will exceed copper’s. It was used a ratio of 1
aluminum transformer for each 5 produced.
Table 8.1 – Production variables for the winding manufacturing.
Needs Qty units
Transformers/year 500 unit
Unit/year 1500 unit
Welds/year 3000 unit
Weld length variable m
Thickness of base sheets variable mm
Number of weld passes 1 unit
Ratio aluminum/copper weld 0.20 -
60
8.2. Operating costs
In order to estimate the operating costs, the models introduced by Tipaji [61] to calculation and
comparison of FSW and TIG costs. All calculations and assumptions used in this work can be
consulted in the annex F.
Table 8.2 – Estimated costs per weld for both processes.
Operating Cost TIG FSW
Labor cost 9.23 € 5.07 €
Machine cost 0.33 € 5.00 €
Tool cost 0.20 € 0.44 €
Gas cost 8.40 € 0.00 €
Power cost 1.67 € 0.27 €
Total cost 19.83 € 10.78 €
As it can be seen in the summary Table 8.2 TIG operating costs per weld is almost double the
cost of FSW. This is due to the high cost of the shielding gas and a slight reduction on weld time. Pie
diagrams in Figure 8.1 show the comparative costs of the current solution and the FSW process. Each
process has two big contributors, Gas and Labor costs for TIG and Machine and Labor costs for FSW.
Figure 8.1 – Costs division for TIG and FSW weld.
8.3. Initial Investment and Payback
The initial investment, Table 8.3, is the area of this study that lacks more confirmation, due to
all the values being estimated by excess. The first phase is already in motion. SIEMENStir is a
partnership between SIEMENS-FS and IDMEC-IST and involves two Master Degree proposers, so
the money invested for this preliminary study is acknowledged as sunk cost and it’s assumed to be nil.
Design and Development was envisioned to support the wage and travel expenses of someone to
follow all the Design and Development of the project, for a minimum of 12 months. Machinery costs
and Locksmith costs are self-explained, and are the biggest part of the investment. This particular
investment cannot be neglected since this is a precision process.
Labor cost 47%
Machine cost 2%
Tool cost 1%
Gas cost 42%
Power cost 8%
TIG
Labor cost 47%
Machine cost 46%
Tool cost 4%
Power cost 3%
FSW
61
Table 8.3 – Estimated costs for the project.
Initial Investment
Study 0 €
Design and Development 18,000.00 €
Machine cost 150,000.00 €
Locksmith cost 25,000.00 €
Tests 5,000.00 €
Staff training 7,000.00 €
Total cost 205,000.00 €
The Payback period, Figure 8.2, was estimated to about four and an half years. It was used
the simplest approach to obtain this estimation. The cost of each process was multiplied by the
production and added the initial investment. The intersection of both curves is considered the payback
period, that means the moment FSW cost equals the cost of TIG.
This study only takes into account the welds that the present process is able to do. If it’s taken
in consideration the amount of welds that FSW can add to production, and all the versatility that it
gives, it’s clear that the real payback period is smaller. Also with good use of financial mathematics it
is possible to decrease even more this period.
Figure 8.2 – Estimated Payback Period.
0
100000
200000
300000
400000
500000
600000
700000
0 1 2 3 4 5 6 7 8 9
Co
st
(€)
Years
Payback Period
TIG FSW
62
8.4. Quality
In this final section have been exposed some proprieties that couldn’t be quantifiable. The
purpose of Table 8.4 is to help the display of the real advantages that FSW will bring, when compared
with the current process. Some properties are related to the environment and safety, others show the
versatility of the process and last but not least there are the mechanical properties, which have been
previously reported.
Table 8.4 – Comparison of non-quantifiable variables of both processes.
Property TIG FSW
Environment risk High Low
smoke /toxic gas Very High Very Low
UV emissions Very High X
Noise High Low
Fire hazard √ X
Protection Gear √ X
Operator Training High Low
2D work-plain CAD-CAM Available Implicit
Different geometries X √
Welding of dissimilar alloys X √
Repeatability High Very High
Date log X √
Porosity High Low
Distortion High Low
Contamination of joints High Low
Mechanical Proprieties of joints Base Mat. Stronger
Energy consumption High Low
Recycle possibility Low High
Heating - Achieved temp. Very High Low
Al welding thin sheets X √
Initial investment Low High
Constrains precision Low High
8.5. Conclusions on Feasibility Study
In this preliminary study, it was analyzed the payback of the investment needed and the fixed
costs of each solution, the standard being the TIG Welding and proposed solution, the use of FSW.
It’s clear that from the quality, energy consumption and work condition aspects, the FSW
process is much better than the standard process used nowadays. The initial investment is high, albeit
this opens the opportunity to improve the quality of the process and creates the possibility of welding
dissimilar materials together, as Al and Cu.
63
9. Conclusions
This essay intended to extend knowledge about friction stir welding of electrical components in
pure aluminum and copper, by analyzing different geometries and optimizing their process
parameters. This was accomplished through the Taguchi analysis of butt welds in aluminum and
copper thin sheets, of 1.6 and 1.1mm thick, respectively. Parameters and tools geometry have also
been investigated for Foil-Bar welds and Al/Cu dissimilar weld.
The Taguchi Method has been used for butt welding supported by mechanical tests results of
tensile, three point bending and hardness. Using the evaluation factors GET, GEB and Hardness and
a variance analysis it was possible to conclude the optimum parameters to weld each material.
Confirmatory trials in Aluminum Butt welds revealed a slight decrease of mechanical properties from
the base material of 14% and a decrease in conductivity of 4%, the model fitted perfectly with small
error influence. Copper Butt welds revealed a decrease in mechanical properties of 20% and a slight
increase in conductivity. Also copper welds were much more influenced by external errors.
Overlapped Foil-Bar welds have been performed with satisfactory results, tool geometry and
welding parameters have been defined with success. Similar welds have been achieved without any
particular challenge. On the other hand, dissimilar weld of aluminum foil to copper bar was hard to
achieve due to the components hardness’ difference, a sandwich like weld has been attempted with
success. Dissimilar butt welds have been also study and a similar approach has been used to avoid
the discontinuity in the weld bead. This discontinuity is mainly due to the different thicknesses of the
two materials.
A preliminary feasibility study was built based on the actual needs of the client to estimate the
operating cost of TIG and FSW. It was acknowledged that the main contributors to the TIG cost per
weld were the gas and labor cost. In the case of FSW, machine cost and labor cost represent the
bigger part of a cost that still represents only half of copper’s. Based on the cost per weld of both
processes and using the estimate production (per year) of the factory, it was also calculated the
payback period of a project, for implementation of FSW solution. The estimated time of payback was
of about four and an half years.
The final conclusion is that the implementation of the FSW is perfectly suitable for the
SIEMENS FS status quo, because FSW can perform the same amount of welds currently done using
the TIG with the surplus of enabling the production of more profitable joints, with no loss of reliability
and quality standards.
64
65
10. Future Work
During the development of this work, several ideas occurred from the need to adjust the
technical approach and move towards the best solution, mainly due to the complex and unknown field
of FSW application on conductive materials. Most of them were could not be performed along this
work, however were documented in this report as hints and described in this chapter.
10.1. Dissimilar butt welding
As described on Chapter 7.4.1 the tests have shown that the welding of dissimilar materials
was difficult. This is due mainly to the soft aluminum that cannot receive the same load as Copper.
Additionally, the different and small thickness increase the complexity of the welding. Several
procedures were tried to reach a reasonable weld bead, with different tools geometries and several tilt
angles tested. One possibility was left out due to the equipment limitation of using tilt and side tilt
angles simultaneously. To solve this problem it was created a concept for an oscillating table that
needs to guarantee its stability and stiffness during the welding process.
An alternative solution was tested to enable the connection of these different materials, an
overlapped arrangement where the copper was placed above, supporting most of the load and
restricting the aluminum below. This is a technical approach that must be studied and tested in detail.
10.2. Foil-Bar Quality Tests
The weld quality is generally proven by mechanical tests, such as Tensile and Bending, as
done in this work for butt welds. However for Foil-Bar geometry, standard tests could not be used. In
this case, the significant differences between the thickness of the components leads to asymmetry,
which means that the axial strength test will be challenging, and there will be a distortion and constrain
difficulty. For instance it could be applied a Taguchi study adapted to tests that can be performed such
as hardness, conductivity or fatigue for example.
10.3. Static Shoulder/Pinless Tool
Because of the reduced thickness of the foils used, especially those with 0.4mm in copper,
some more exoteric and new solutions can be tested. A static shoulder could enhance the joint quality
of similar butt welds and a pinless tool with a shallower striate shoulder could potentiate the welding of
thinner foils.
66
67
XIII. References
[1] P. Vilaca, J. Mendes, E. Santis, J. Prior, and L. Quintino, “Application of FSW to join aluminium foil windings for electrical transformers,” presented at the 6th IIW Annual Assembly, Dusseldorf, Germany, 2013, p. 18.
[2] D. Allen and H. Moore, “Theory and Principles,” in Electric Power Transformer Engineering, CRC Press, 2004, p. 10.
[3] REN - Rede Eléctrica Nacional S.A., “Technical Report on Electricity 2012.” 02-Apr-2013.
[4] DOE, DOE Fundamentals Handbook - Electrical Science, vol. Volume 4. Washington, 1992.
[5] J. A. B. Faria, Electromagnetic Foundations of Electrical Engineering. John Wiley & Sons, 2008.
[6] C. R. Sullivan, “Aluminum Windings and Other Strategies forHigh-Frequency Magnetics Design in anEra of High Copper and Energy Costs,” IEEE Transactions on Power Electronics, vol. 23, no. 4, pp. 2044–2051, 2008.
[7] P. Paul, M. Sacotte, and F. Walter, “Large aluminium distribution transformer,” in 2012 1st International Conference on Power and Energy in NERIST (ICPEN), 2012, pp. 1–5.
[8] W. M. Thomas, E. D. Nicholas, J. C. Needham, M. G. Murch, and C. J. Temple-Smith, “Improvements relating to friction stir welding,” US Patent N
o.54603171991.
[9] TWI, “List of FSW patents & applications - Intellectual Property Rights,” 2013. [Online]. Available: http://www.twi.co.uk/services/intellectual-property-licensing/friction-stir-welding/intellectual-property-rights/. [Accessed: 13-Aug-2013].
[10] M. P. Scott, A. F. Richard, J. S. Russell, E. R. Monte, and E. T. Brian, “Solid State Processing of Materials Through Friction Stir Processing and Friction Stir Mixing.,” WO Patent N
o.
0945412005.
[11] J. Bersaas, A. Oosterkamp, and L. Oosterkamp, “Friction Stir Spot Welding Method and Apparatus,” WO0128732 (A1)26-Apr-2001.
[12] R. S. Mishra, “Integral channels in metal components and fabrication thereof,” US Patent N
o.69233622005.
[13] S. W. Kallee, “Application of friction stir welding in the shipbuilding industry,” presented at the Lightweight Construction - Latest Developments, London, UK, 2000.
[14] S. W. Kallee, E. D. Nicholas, and W. M. Thomas, “Industrialisation of friction stir welding for aerospace structures,” presented at the Structures and Technologies - Challenges for Future Launchers Third European Conference, Strasbourg France, 2001.
[15] S. W. Kallee, J. Davenport, and E. D. Nicholas, “Railway rolling stock manufacturers implement friction stir welding,” Welding Journal, Oct-2002.
[16] W. M. Thomas, S. W. Kallee, D. G. Staines, and P J Oakley, “Friction Stir Welding - Process variants and developments in the automotive industry,” presented at the 2006 SAE World Congress, Cobo Center, Detroit, Michigan, USA., 2006.
[17] P. Vilaca, J. Gandra, and C. Vidal, “Linear Friction Based Processing Technologies for Aluminum Alloys: Surfacing, Stir Welding and Stir Channeling,” in Aluminium Alloys - New Trends in Fabrication and Applications, Z. Ahmad, Ed. InTech, 2012.
[18] C. B. Fuller, “Friction Stir Tooling: Tool Materials and Designs,” in Friction Stir Welding and Processing, R. S. Mishra and M. W. Mahoney, Eds. ASM International, 2007, pp. 7–35.
[19] P. Vilaca and W. Thomas, “Friction Stir Welding Technology,” in Structural Connections for Lightweight Metallic Structures, Springer, 2012.
[20] P. Vilaca, L. Quintino, and J. dos Santos, “iSTIR - Analytical thermal model for friction stir welding,” Journal of Materials Processing Technology, vol. 169, no. 3, pp. 452–465, 2005.
[21] R. S. Mishra and M. W. Mahoney, “Introduction,” in Friction Stir Welding and Processing, ASM International, 2007, pp. 1–5.
68
[22] W. F. Smith, “Ligas Metálicas de Engenharia,” in Princípios de ciência e engenharia de materiais, 3rd ed., McGraw-Hill, 1998.
[23] J. R. Davis, Aluminum and Aluminum Alloys. ASM International, 1993.
[24] AWS, “Aluminum and Aluminum Alloys,” in Welding Handbook, Volume 3 - Materials and Applications, Part 1, 8th ed., 1996, pp. 1–120.
[25] J. R. Davis, Copper and Copper Alloys. ASM International, 2001.
[26] “UNS Standard Designation for Wrought and Cast Copper.” [Online]. Available: http://www.copper.org/resources/properties/standard-designations/introduction.html. [Accessed: 21-May-2013].
[27] AWS, “Copper and Copper Alloys,” in Welding Handbook, Volume 3 - Materials and Applications, Part 1, 8th ed., 1996, pp. 163–216.
[28] R. M. Leal, “Soldadura por fricção linear de elementos de baixa espessura - ligações homogéneas e heterogéneas,” Coimbra, 2010.
[29] G. Taguchi, Taguchi methods, research and development. American Supplier Institute, 1992.
[30] R. K. Roy, Design of Experiments Using The Taguchi Approach. John Wiley & Sons, 2001.
[31] J. Nahas, “Statistics and Design of Experiments,” presented at the Short Course Fall 2012, University of Notre Dame, 2012.
[32] D. C. Montgomery, Design and analysis of experiments. Hoboken, NJ: John Wiley & Sons, Inc., 2013.
[33] W. M. Thomas and E. D. Nicholas, “Friction stir welding for the transportation industries,” Materials & Design, vol. 18, no. 4, pp. 269–273, 1997.
[34] A. Scialpi, M. De Giorgi, L. A. C. De Filippis, R. Nobile, and F. W. Panella, “Mechanical analysis of ultra-thin friction stir welding joined sheets with dissimilar and similar materials,” Materials & Design, vol. 29, no. 5, pp. 928–936, 2008.
[35] C. Leitao, R. M. Leal, D. M. Rodrigues, A. Loureiro, and P. Vilaça, “Mechanical behaviour of similar and dissimilar AA5182-H111 and AA6016-T4 thin friction stir welds,” Materials & Design, vol. 30, no. 1, pp. 101–108, Jan. 2009.
[36] R. M. Leal, C. Leitao, A. Loureiro, D. M. Rodrigues, and P. Vilaca, “Material flow in heterogeneous friction stir welding of thin aluminium sheets: Effect of shoulder geometry,” Materials Science and Engineering a-Structural Materials Properties Microstructure and Processing, vol. 498, no. 1–2, pp. 384–391, 2008.
[37] D. M. Rodrigues, A. Loureiro, C. Leitao, R. M. Leal, B. M. Chaparro, and P. Vilaca, “Influence of friction stir welding parameters on the microstructural and mechanical properties of AA 6016-T4 thin welds,” Materials & Design, vol. 30, no. 6, pp. 1913–1921, 2009.
[38] I. Topic, H. W. Höppel, and M. Göken, “Friction stir welding of accumulative roll-bonded commercial-purity aluminium AA1050 and aluminium alloy AA6016,” Materials Science and Engineering: A, vol. 503, no. 1–2, pp. 163–166, Mar. 2009.
[39] Y. S. Sato, Y. Kurihara, S. H. C. Park, H. Kokawa, and N. Tsuji, “Friction stir welding of ultrafine grained Al alloy 1100 produced by accumulative roll-bonding,” Scripta Materialia, vol. 50, no. 1, pp. 57–60, Jan. 2004.
[40] I. Galvão, R. M. Leal, D. M. Rodrigues, and A. Loureiro, “Influence of tool shoulder geometry on properties of friction stir welds in thin copper sheets,” Journal of Materials Processing Technology, vol. 213, no. 2, pp. 129–135, Feb. 2013.
[41] R. M. Leal, N. Sakharova, P. Vilaca, D. M. Rodrigues, and A. Loureiro, “Effect of shoulder cavity and welding parameters on friction stir welding of thin copper sheets,” Science and Technology of Welding & Joining, vol. 16, no. 2, pp. 146–152, 2011.
[42] K. Savolainen, “Friction Stir Welding of Copper and Microstructure and Properties of the Welds,” PhD, Aalto, 2012.
69
[43] E. T. Akinlabi, “Effect of Shoulder Size on Weld Properties of Dissimilar Metal Friction Stir Welds,” JOURNAL OF MATERIALS ENGINEERING AND PERFORMANCE, vol. 21, no. 7, pp. 1514–1519, Jul. 2012.
[44] I. Galvão, D. Verdera, D. Gesto, A. Loureiro, and D. M. Rodrigues, “Influence of aluminium alloy type on dissimilar friction stir lap welding of aluminium to copper,” Journal of Materials Processing Technology, vol. 213, no. 11, pp. 1920–1928, Nov. 2013.
[45] V. Firouzdor and S. Kou, “Al-to-Cu Friction Stir Lap Welding,” Metall and Mat Trans A, vol. 43, no. 1, pp. 303–315, Jan. 2012.
[46] M. Koilraj, V. Sundareswaran, S. Vijayan, and S. R. Koteswara Rao, “Friction stir welding of dissimilar aluminum alloys AA2219 to AA5083 – Optimization of process parameters using Taguchi technique,” Materials & Design, vol. 42, pp. 1–7, Dec. 2012.
[47] C. Vidal, V. Infante, and P. Vilaca, “Assessment of Improvement Techniques Effect on Fatigue Behaviour of Friction Stir Welded Aerospace Aluminium Alloys,” Fatigue 2010, vol. 2, no. 1, pp. 1605–1616, 2010.
[48] A. Heidarzadeh, H. Khodaverdizadeh, A. Mahmoudi, and E. Nazari, “Tensile behavior of friction stir welded AA 6061-T4 aluminum alloy joints,” Materials & Design, vol. 37, pp. 166–173, May 2012.
[49] A. Bagheri, T. Azdast, and A. Doniavi, “An experimental study on mechanical properties of friction stir welded ABS sheets,” Materials & Design, vol. 43, pp. 402–409, Jan. 2013.
[50] Y. Bozkurt, “The optimization of friction stir welding process parameters to achieve maximum tensile strength in polyethylene sheets,” Materials & Design, vol. 35, pp. 440–445, Mar. 2012.
[51] S. H. Dashatan, T. Azdast, S. R. Ahmadi, and A. Bagheri, “Friction stir spot welding of dissimilar polymethyl methacrylate and acrylonitrile butadiene styrene sheets,” Materials & Design, vol. 45, pp. 135–141, Mar. 2013.
[52] P. Vilaca and T. G. Santos, “Ferramenta não Consumível Modular Ajustável e Refrigerável para Soldadura e Processamento por Fricção Linear,” PT Patent N
o.1040722008.
[53] NP EN 895, “NP EN 895:2002 - Ensaios destrutivos de soldaduras em materiais metálicos Ensaio de tracção transversal.” ISQ, 2002.
[54] W. F. Smith, “Propriedades Mecânicas dos Materiais Metálicos,” in Princípios de ciência e engenharia de materiais, 3rd ed., McGraw-Hill, 1998.
[55] DIN 40501-1, “DIN 40501-1:1985-06 - Aluminium for electrical purposes - E-Al plate, sheet and strip - Technical delivery conditions.” Deutsches Institut für Normung, 1985.
[56] ISO 6507-1, “ISO 6507-1:2005 - Metallic materials - Vickers hardness test - Part 1: Test method.” International Organization for Standardization, 2005.
[57] ISO 6361-2, “ISO 6361-2:2011 - Wrought aluminium and aluminium alloys - Sheets, strips and plates - Part 2: Mechanical properties.” International Organization for Standardization, 2011.
[58] BS EN 13601, “BS EN 13601:2002 - Copper and copper alloys - Copper rod, bar and wire for general electrical purposes.” British Standards, 2002.
[59] P. Vilaca, “Fundamentos do Processo de Soldadura por Fricção Linear: Análise Experimental e Modelação Analítica,” IST, 2003.
[60] T. G. Santos, R. M. Miranda, P. Vilaca, and J. P. Teixeira, “Modification of electrical conductivity by friction stir processing of aluminum alloys,” International Journal of Advanced Manufacturing Technology, vol. 57, no. 5–8, pp. 511–519, 2011.
[61] P. K. Tipaji, “E-design tools for friction stir welding: cost estimation tool,” 2007.
70
a
XIV. Annexes
b
A. Experimental Procedures
A1. Friction Stir Welding Procedures.
In this section the procedure adopted for the laboratory testing of friction stir welding is
described. These tests require an initial phase of preparation to the experimental work that will follow:
i. Acquire the material to test in sufficient quantity and at the same time.
ii. Cutting the foils to obtain sheets with the predetermined final dimensions, for the
welds described in Cap. 4 were used sheets with 200x100mm.
iii. Machining at least one side of the sheet to ensure complete perpendicularity between
the sides in order to perfect adjustment of the sheets, either between themselves or in
relation to the base plate of the fastening system. Followed by a slight grinding of
those surfaces to remove excess material.
iv. Clean equipment, including support desk where will be placed the fixing system.
v. Turn on and check the connectivity of both FSW machine and the computer of data
acquisition.
Performed the preparatory work described, follows the test procedure adopted:
1. Cleaning modular tool components, in particular the base and the pin that will be
used. Coating the bolts thread portions with Teflon, mount the tool and adjust the
length of the pin.
2. Fit and tight the tool in the equipment.
3. Start the cooling system and check its correct functioning.
4. Set the reference point in the z-axis.
5. Clean the sheets to be welded with acetone to degrease and remove any particles.
6. Place the sheets in the fixing system, ensuring the perfect fit with each other and
orienting joint line in accordance with the linear forward movement of the tool.
7. Tightening the clamping system to ensure the constraining of all movements of the
sheets.
8. Insert the parameters in the software of tool control.
9. Set the coordinates (x, y) of the start and end points of the weld path.
10. Start the software of data acquisition.
11. Perform the weld, by starting the tool movement.
12. Follow the weld process to ensure that everything is ok. Respect a secure distance to
the set until all movement cease.
13. Check the data read by the software and save it to further consultation
14. Extract the weld plate, mark and book it, with used parameters and observations of
defects. Classify the specimen and photograph them.
15. If this was not the last trial, repeat the procedure with a new pair of sheets.
c
A2. Procedures for Metallographic Analysis.
The experimental procedure followed for mounting metallographic samples were:
1. Cut and machine a sample from the welded plate with suitable, pre-determined
dimensions.
2. Grind sample edges to remove the burr.
3. Identifying each sample.
4. Mount samples in molds with a diameter appropriate to the size of the sample, with
cold forming resin.
5. Grind the samples with Sandpaper with following particle size: 600, 1000, 2400 and
4000 lubricated with water.
Notes: Advance in sandpaper after homogenizes the entire sample surface. Don't
reuse sandpaper of grinding harder materials. After each sandpaper, rinse the
sample, pass through alcohol and dry it.
6. Apply the samples to ultrasound, immersed in alcohol for a period of 5 minutes to
remove surface impurities.
7. Continue polishing the samples with cloths impregnated lubricant and diamond
powder with a grain size of 3 micrometer and 1 micrometer, for 5 minutes.
Notes: Whenever there is contamination of the cloth wash and brush it with detergent.
The time stated above must be seen as an approximated value, we must homogenize
the sample before move forward.
8. Repeat step 6.
9. Finish polishing, in a cloth impregnated with an OP-S solution for 1 minute.
10. Repeat step 6.
11. Contrasting the samples the appropriated reagent previously prepared. Note: For the
same reagent the time of contrasting is lesser for micrograph than for macrograph
analysis.
12. Use an optical microscope to capture several photomicrographs, with different
magnifications to illustrate the relevant aspects of each sample.
Reagents used:
For aluminum: 60% HCl + 30%HNO3 + 5% HF + 5% H2O (Poulton)
For copper: 50% HNO3 + 50% H2O (no specified name)
d
A3. Hardness Tests Procedures.
The test procedures adopted in the measurement of the hardness profile were as follows:
1. Adjust the sample dimensions to the sample holder of the equipment.
2. Flatten the sample through polishing its base.
3. Prepare the sample as defined in section B.2 until point 5.
4. Connect the equipment and check if it is calibrated.
5. Determine the minimum distance between indentation centers, according to ISO
6507-2.
6. Establish a plan of indentations.
7. Select, in the control panel of the equipment the option for the type of Vickers
hardness. Choose the appropriated load and indentation time for the material to test.
8. Identify and mark the center of the nugget. Choose a testing direction.
9. Focus the middle vertical distance of the surface with a 40x lens.
10. Change the lens to the indenter, and proceed with the indentation.
11. Shift the sample to the side in the direction chosen in point 8, at least the minimum
distance determined in point 5.
12. Repeat points 9 to 11, until all samples is traveled, since the nugget through the
processed zone until base material.
13. If only one direction as been cover, go back to point 8 shifting direction. If not, skip this
point.
14. Switch to the 40X objective and measure the two diagonals of each indentation.
15. Record the hardness values obtained.
16. If it is the last sample, remove sample and turn-off the equipment. If not, re-start the
procedure.
A4. Tensile Tests Procedures
There were tested three specimens for each condition of welding and three for the base
material analysis. The procedure used was the follow:
1. Cut and machine the specimens with dimensions according to the ISO 6892-1.
2. Grind the edges to remove the burr, but avoid reducing the thickness.
3. Use a marker to define the initial length of the specimens.
4. Introduce the geometric parameters of the specimen in the equipment control
software.
5. Place and grip the specimen to the testing machine. Adjust the extensometer, with a
starting distance of 50mm to the specimen gauge section.
6. Start the tensile test.
7. Wait until the rupture of the specimen.
8. Record the data acquired for further processing and analysis.
9. Measure the final extension.
10. Return to point 5 if there are more specimens to test.
e
A5. Procedures for three point Bending Test.
The test procedure used for the testing of three point bending was as follows:
1. Cut and machine all the specimens from the welded sheets, with dimensions specified
in the standard.
2. Grind the edges to remove the burr.
3. Determine and prepare the support with the distance indicated by the standard.
4. Place the specimen on the supports, centering the weld with the line of action of the
mandrel.
5. Start data acquisition software.
6. Start the test at a constant speed of advancement of the mandrel, Plunge Speed.
7. Keep testing until the specimens bow to an angle of about 90 degrees.
8. Record the data acquired for further processing and analysis.
9. Remove and photograph the sample and visually check the final state.
10. Back to the point 5 if there are more specimens to be tested.
f
B. Results
B1. Aluminum butt welds
g
h
B2. Copper Butt Welds
i
j
C. Specimen Design
C1. Tensile test specimen design
C2. Bending test specimen design
D. Bending structure
k
E. Technical Sheets
l
E1. Support Table
m
E2. Work Table
n
E3. Tool Body
o
E4. Probe – 4J3
E5. Probe – 4I3
p
E6. Shoulder 4P3
q
E7. Shoulder 4O3
r
F. Feasibility Study Calculation
F1. TIG Cost
s
F2. FSW Cos
t