Machinability Studies of Selective Laser Melted Titanium Alloy Ti-6Al-4V

192 Pages·2017·18.44 MB·English

by  Deakin University

Machinability Studies of Selective Laser Melted Titanium Alloy
Ti-6Al-4V

by

Manikandakumar Shunmugavel
B.E., M.E.,

Submitted in fulfilment of the requirements for the degree of

Doctor of Philosophy

Deakin University

February, 2017

To,
my mom Sivagami, dad Shunmugavel, Sister Sandhya, girlfriend Kowshika and
Professor Guy Littlefair
for their constant support, encouragement and inspiration
Acknowledgements
This work would not have been possible without the help and support of many wonderful
people that I have met in my PhD journey. I offer my sincere thanks and humble appreciation
for all those people who have helped me to successfully complete this work. I also appreciate
and acknowledge the support of two wonderful organizations, Deakin University, Australia
and Bharat Forge, India in successful completion of this project.
Firstly, I would like to thank my Principal Supervisor Prof. Guy Littlefair (Deakin University,
Australia) for his untiring help, support, motivation and inspiration. You made me shine like a
diamond by providing me with all the support and opportunities. Without you, I wouldn’t be
the person I am today. I don’t know how I am going to repay you for all your help and support.
You are a great inspirational leader and my hero in this academic world and I will continue to
follow in your foot steps in the future. Thank you for being the coolest boss!!!!
Secondly, I would like to gratefully thank my external supervisor Dr. Rajkumar Singh (Bharat
Forge, India) for his invaluable help, encouragement and support in completion of this research
project. It is remarkable what a little faith can do, and it is the faith that you have shown in my
abilities which gave me the confidence to complete the research project.
Sincere thanks to associate supervisors Dr Ashwin Polishetty and Dr Moshe Goldberg (Deakin
University, Australia) for their invaluable help, support, guidance and friendship. Your words
of encouragement and appreciation persuaded me to work hard and achieve the project goals.
I also sincerely thank Dr Junior Nomani (Deakin University, Australia) for his constructive
comments and suggestions on the project.
Special thanks to Dr Georgina Kelly (Deakin University, Australia) for her excellent proof
reading of my thesis. I am very privileged to have your help, support and knowledge in
constructing my thesis. Without your help and support, I could not have constructed my thesis
effectively in a timely manner. (Million thanks to you!!!!)
I greatly appreciate the technical help and support of technical officers Damien Elderfield,
Rodney Seiffert, Phil Todd, Rachel Rossau (Deakin University, Australia) and Pravin Mungole
(Bharat Forge, India) in this project.
Sincere thanks to other unmentioned friends and colleagues in Deakin University, Australia
and Bharat Forge, India for their invaluable help and support.
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Finally, I thank my mom Sivagami, dad Shunmugavel and sister Sandhya for their selfless love,
care and affection. I have no words to acknowledge the sacrifices you made and the dreams
you had to let go, just to give me a shot at achieving mine. No matter how bad I failed, I always
knew that you all would treat me like a winner. Thanks for being so supportive. To my loving
girlfriend Kowshika for her love, support, motivation and inspiration. When everything in my
life is going wrong, I call you and you make everything better. You are my greatest strength
and motivation.

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Publications
Journals
Manikandakumar Shunmugavel, Ashwin Polishetty, Junior Nomani, Moshe Goldberg and
Guy Littlefair, “Metallurgical and Machinability Characteristics of Wrought and Selective
Laser Melted Ti-6Al-4V” , Journal of Metallurgy, vol. 2016, Article ID 7407918, 10 pages,
2016. (Published)
Manikandakumar Shunmugavel, Ashwin Polishetty, Moshe Goldberg, Rajkumar Singh
and Guy Littlefair, “Tool Wear and Surface Integrity Analysis of Machined Heat Treated
Selective Laser Melted Ti-6Al-4V”, International Journal of Materials Forming and
Machining Processes, Volume 3, Issue 2, Pages 50-63. (Published)
Manikandakumar Shunmugavel, Ashwin Polishetty, Moshe Goldberg, Rajkumar Singh
and Guy Littlefair, “A Comparative Study of Mechanical Properties and Machinability of
Wrought and Additive Manufactured (Selective Laser Melting) Titanium Alloy-Ti-6Al-4V”,
Rapid Prototyping Journal, Emerald Insight, 2017. (Accepted – 11-Nov-2016)
Manikandakumar Shunmugavel, Moshe Goldberg, Junior Nomani, Shoujin Sun, Raj
Kumar Prasad Singh and Guy Littlefair, “Chip Formation Characteristics of Wrought and
Selective Laser Melted Ti-6Al-4V”, Australian Journal of Mechanical Engineering,
Engineers Australia Technical Journal, 2017. (Submitted)
Conferences
Ashwin Polishetty, Manikandakumar Shunmugavel, Moshe Goldberg, Guy Littlefair and
Rajkumar Singh, “Cutting Forces and Surface Finish Analysis of Machining Additive
Manufactured Titanium Alloy, Ti-6Al-4V”, International Conference on Sustainable
Materials Processing and Manufacturing, SMPM 2016, Kruger National Park, Procedia
Manufacturing 7 (2016) 284-289. (Published)
Manikandakumar Shunmugavel, Ashwin Polishetty and Guy Littlefair, “Microstructure
and Mechanical Properties of Wrought and Additive Manufactured Ti-6Al-4V Cylindrical
Bars”, Proceedings of the 1st International Design Technology Conference, DesTech2015,
Procedia Technology 20(2015) 231-236. (Presented and published)

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Manikandakumar Shunmugavel, Ashwin Polishetty, Moshe Goldberg, Rajkumar Singh
and Guy Littlefair, “An Overview of Machinability of Additive Manufactured Ti-6Al-4V”,
High Performance Cutting 2016, Chemnitz, Germany. (Presented)
Manikandakumar Shunmugavel, Ashwin Polishetty, Moshe Goldberg,Junior Nomani,
Rajkumar Singh and Guy Littlefair, “Influence of Build Orientation on Machinability of
Selective Laser Melted Titanium alloy-Ti-6Al-4V”, ICMMM 2017: 19th International
Conference on Machining and Machinability of Materials, Venice, Italy. (Accepted)

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Abstract
Selective Laser Melting (SLM), a promising Additive Manufacturing (AM) technology, has
huge potential in fabrication of Ti-6Al-4V near-net shape components. However, the poor
surface finish of the components fabricated from this technology means that machining is
required to achieve the desired accuracy and tolerances. Therefore, a systematic understanding
of material and machinability characteristics of SLM fabricated Ti-6Al-4V alloy is paramount
to improve productivity and surface quality. Considering this, the present study investigates
the mechanical properties, machinability characteristics and chip formation nature of SLM
fabricated Ti-6Al-4V alloy.
Mechanical properties of SLM fabricated Ti-6Al-4V alloy in “As Built” (A.B) and “Heat
Treated” (H.T) condition was evaluated and compared with conventionally produced wrought
Ti-6Al-4V alloy. It was found that SLM Ti-6Al-4V (A.B/H.T) alloy had higher strength and
hardness, but poor ductility compared to wrought Ti-6Al-4V alloy. This was attributed to the
martensitic (α’)/lamellar (α+β) microstructure of the SLM materials. The applied heat
treatment of SLM Ti-6Al-4V slightly improved its ductility by conversion of acicular α’
microstructure to a lamellar α+β microstructure.
Machining tests at different speeds were used to characterise tool wear, cutting forces, surface
roughness and sub-surface microstructure to gain understanding of machining behaviour of
SLM fabricated Ti-6Al-4V materials. These tests revealed that the overall machinability of
SLM Ti-6Al-4V (A.B/H.T) alloy is poor compared to conventionally produced wrought Ti-
6Al-4V. Machining of SLM Ti-6Al-4V alloy demonstrated poor machinability characteristics
at high cutting speeds. However, at low cutting speeds, superior machined surface quality
compared to wrought Ti-6Al-4V alloy was observed in machining of SLM Ti-6Al-4V due to
reduced plastic flow during machining. Tool wear was a major issue in machining of the SLM
Ti-6Al-4V with coating delamination, adhesion, attrition, diffusion-dissolution and chipping
as the major tool wear mechanisms operating. The applied heat treatment and conversion of
α’→α+β microstructure did not significantly improve the machinability of SLM Ti-6Al-4V
alloy.
Chip formation has a strong influence on tool wear and machined surface quality, so studies
were undertaken to understand and explore the influence of material characteristics on
machinability and chip formation. These studies revealed that the tendency to form segmented
or “sawtooth” chips was higher in SLM Ti-6Al-4V materials as compared to conventionally
produced wrought Ti-6Al-4V.
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Further analysis revealed that cracks were a common feature in the primary and secondary
deformation zones of SLM Ti-6Al-4V chip samples, illustrating that periodic crack initiation
was the root cause of “sawtooth” formation during machining. Furthermore, the tendency to
form build up edge during machining was less in SLM Ti-6Al-4V materials compared to
wrought Ti-6Al-4V, offering better surface finish of SLM Ti-6Al-4V materials at low cutting
speeds.
Finally, by performing slow orthogonal cutting tests, the influence of build orientation (or prior
β grain orientation) on machinability characteristics of SLM fabricated Ti-6Al-4V titanium
alloy was studied. Significant variations in cutting forces, chip curling, chip roughness ratio
and machined surface quality were observed during orthogonal cutting along different prior β
grain orientations. This indicated the influence of prior β grain orientation on shear deformation
during machining of SLM Ti-6Al-4V. However, microstructural alteration and work hardening
characteristics of SLM Ti-6Al-4V were not influenced by the machining strategy /prior β grain
orientation. The results obtained from the slow speed orthogonal cutting tests are similar to the
results obtained from turning tests in this thesis, highlighting the practical importance of
microstructure, build orientation on cutting forces, chip formation and surface finish of SLM
Ti-6Al-4V, and wrought Ti-6Al-4V alloy.

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