Elevons
FEATURED ARTICLE 8
ISSUES IN ULTRA-PRECISION
MACHINING (UPM)
OF TITANIUM ALLOYS
R & D ARTICLE 14
Fabric Permeability Computation
with Varying Fiber Distribution
and Packaging
TECHNOLOGY UPDATES 32
Selective Laser Melting (SLM):
Process and Applications
COMBINED EDITION
July 2015 . Newsletter . Volume 5 . Issue 1
contents
Editorial, NCAIR Events and News Updates
1-7
FEATURED ARTICLE
Issues in Ultra-precision Machining (UPM) of Titanium Alloys
– Abhishek Bihari , Prof. Rakesh G. Mote
8
R&D Updates
Fabric Permeability Computation with Varying Fiber
Distribution and Packaging
14
Comparison of various Liquid Composite Moulding (LCM) processes19
Modeling and Simulation of process induced deformations in
fiber reinforced polymer (FRP) matrix composites
24
TECHNOLOGY Updates
Selective Laser Melting (SLM): Process and Applications 32
AEROSPACE NEWS BRIEFS
NASA's 10-engine electric plane completes flight test38
A huge breakthrough in nuclear fusion38
Carbon-fiber epoxy honeycombs mimic the material
performance of balsa wood 38
Composite plane life cycle assessment shows lighter
planes are the future38
Unidirectional carbon fiber prepreg tapes just 15 gsm38
Acknowledgement
We extend our sincere gratitude to the faculty members of IIT-Bombay for their
support.
We are also thankful to the students and staff of NCAIR, for their valu able articles and
other support.
Editors
: Prof. Suhas Joshi and Prof. Asim Tewari
Asst. Editors : Dr. Sarbani Banerjee Belur
Ms. Vani K. Sreedhara
Contact details : admin@ncair.in
Articles that fall under the purview of NCAIR Newsletter are always welcome.
Editorial
Welcome to the present edition of the NCAIR ‘Elevons’ newsletter. This edition of the newsletter
is a combined edition of the December 2014 and March 2015 issues. We regret for the inordinate
delay. We anticipate and expect the year 2015 would be a promising one for NCAIR. We look
forward to NCAIR’s continued growth and achievement of its ambitious goals and milestones.
We welcome you to Volume 5, Issue 1 of the NCAIR newsletter. The important aim of this
newsletter is to keep the readers informed of the ongoing developments, and innovations in
research being a part of NCAIR.
In this issue of the newsletter, we present some interesting contributions related to aerospace
applications and manufacturing processes. The featured article of this issue discusses various
facets of ultra-precision machining (UPM) of titanium alloys.
Research and development is an important aspect of NCAIR. This is reflected in the various R&D
updates, which has articles on fabric permeability computation with varying fiber distribution
and packaging, comparison of various liquid composite moulding processes, modeling and
simulation of process induced deformations in fiber reinforced polymer matrix composites .
The technology update section focuses on recent technological advancements in the arena of
aerospace manufacturing globally. In this issue, we present Selective Laser Melting (SLM): process
and its applications. The newsletter also carries important news briefs in the aerospace domain.
We would like to thank Prof. Rakesh Mote, Ir. Bey Vrancken, Prof. Dr Ir. Jan Van Humbeeck and
Dr. Ir. Akhilesh K. Swarnakar for their contribution to this newsletter. We extend our gratitude,
to the various students and staff of NCAIR, for their articles and contributions. Also we would
like to acknowledge Prof. Mandar Rane, IDC, IIT Bombay and his team for designing ‘Elevons’.
Hope you will find this newsletter interesting. Please feel free to provide us with any feedback,
including things that you would like to see being featured in the forthcoming editions through
email: admin@ncair.in
For an online edition of this newsletter and more news about NCAIR, please visit our website
http://www.ncair.in
Kind regards,
Suhas S. Joshi & Asim Tewari
Editors
1.
NCAIR EVENTS
Technical Communication workshop,
November 1, 2014, IIT Bombay
This was a one-day workshop that focused on reading,
writing and speaking skills. The purpose of the workshop
was to enhance communication skills amongst students
in IIT Bombay. In this workshop, participants engaged in
various exercises, activities and group discussions thus
laid emphasis on their critical analysis and reflective
thinking.
1.1
1.1 - Participants at the Technical Communication workshop,
November 1, 2014.
One-Day Workshop on Advances in Ion and
Electron Beam techniques in Applied Sciences,
November 13, 2014, IIT-Bombay
In our endeavour to provide end-to-end support to Indian
small and medium scale industries to enhance their
ability to participate in aerospace manufacturing, NCAIR
organised a workshop to talk about the advances in ion
and electron beam techniques in applied sciences on
November 13, 2014 at IIT Bombay.
The important highlights of this workshop was talks by
eminent faculty from IIT Bombay, renowned industry
experts from companies like Carl Zeiss and Oxford
instruments and participants having an opportunity
to interact with experts during the panel discussion.
2.1
The workshop was inaugurated by Prof. Subhasis
Chaudhuri, Deputy Director (AIA), IIT Bombay. The chief
guest for the workshop was Mr. Daniel Sims, Managing
Director, Carl Zeiss India. The industry academia
collaboration was presented by Prof. P.M. Mujumdar,
Dean R&D, IIT-Bombay.
2.2
2.1 - Participants of Workshop on Advances in Ion and Electron Beam
Techniques in Applied Sciences, Nov 13, 2014.
2.2 - Mr. Daniel Sims, Managing Director, Carl Zeiss India at the one day
workshop on Advances in Ion and Electron Beam Techniques in
Applied Sciences
2.
One day Composites Convention, February 16,
2015 at VMCC Conference room, IIT Bombay
A one-day composite convention hosted by NCAIR
was held at IIT-Bombay to brainstorm the scenario of
advanced composite manufacturing technologies and
discuss about the implications of it in the current scenario
of the aerospace ecosystem of India.
Dr. P.Mangalagiri, consultant at in the National
Programme on Smart and Micro-Systems at ADA chaired
this convention. Eminent personalities like Dr. Ramesh
Sundaram, Dr. C.M., Manjunatha, Mr. M.K. Sridhar from
NAL, Mr. A. Gnanasekar, Mr. P. Mukhopadhyay from HAL,
Mr. J. Dhanasekaran Mr. BVSR Murthy from ASL, Shri.
A. Rajarajan fromVSSC attended this convention and
gave their opinion on the further need of development
in the field of composites. They were joined by Prof. P.M.
Mujumdar, Dean R&D, Prof. Asim Tewari PIC, NCAIR, Prof.
Naik, Adjunct Professor, Aerospace Department, Prof.
sushil Mishra, Prof. Ramesh Singh, Prof. Anirban Guha
from Mechanical Department, Prof. Sauvik Banerjee from
Civil Department, Prof. Guruprasad and Prof. Mira Mitra
from Aerospace department, Prof. A.R. Bhattacharya,
Prof. Aparna Singh, from Materials and Metallurgical
Department, IIT Bombay to assess the academician view
of the research and development in the area of composite
manufacturing.
3.1 - Participants of the Composite Convention along with NCAIR team
3.2 - Group photo of the participants of the Composite Convention
L-R: Mr. A. Gnanasekhar, HAL, Ms. Swetha Sridhar, NCAIR, Ms. Vani
Sreedhara, NCAIR, Dr. Aparna Singh, IITB, Dr. Sudhho, IITB, Dr. Sushil
Mishra, IITB, Dr. Asim Tewari, IITB, Dr. P.D. Mangalgiri, ADA, Dr. Ramesh
Sundaram, NAL, Mr. M.K. Sridhar, NAL, Mr. A. Rajarajan, VSSC, Dr. C.M.
Manjunatha,CSIR-NAL, Dr. Guruprasad, IITB, Mr. Varun Sharma, Brahmos,
Mr. Taha Khot, NCAIR, Mr. Gautham Salkar, NCAIR, Dr. Sushrut Vaidya,
NCAIR, Mr. P. Mukhopadhyay, HAL.
3.1
3.2
3.
Half day Tech Talk by Mr. Rick Albrecht, Executive
Section Manager for Advanced Mechanical
Design team at GE-Aviation, March 13, 2015, at
VMCC, IIT-Bombay
This talk focused on why innovation is paramount and
its role in positioning any organization as a market
leader. Also, the talk was aimed at various applications
of composites to fan case structure of GEnx engine,
developed high pressure ratio compressors over time,
TAPS combustor & CMC technology to withstand higher
temperatures and produce low emissions.
4.1
4.2 - Mr. Rick Albrecht, Executive Section Manager for Advanced
Mechanical Design team at GE-Aviation.
4.2
4.1 - Participants for the Tech Talk
NCAIR NEWS UPDATES
Continued support from Boeing to NCAIR
• Boeing signed an extension agreement with NCAIR
vouching for their continued support.
• DMC 125 FD duoBLOCK universal milling/turning
machining centre from DMG Mori has been received
at NCAIR, IIT-Bombay.
New Colleagues at
NCAIR
Omanath Pawar
He has his Bachelor of Engineering (B.E.)
degree in 2010 in Mechanical Engineering
from Pune Vidhyarthi Griha’s College
of Engineering and Technology, Pune.
After graduating, he worked as Quality
Assurance Engineer in Elica PB India
Pvt Ltd. For one year. He completed his
M.Tech with specialisation of Materials,
manufacturing and modelling (MMM)
from IIT Bombay in 2014. He has joined
NCAIR as a Research Associate.
Sunil Kumar
He is pursuing his Masters of Technology
and Bachelors of Technology (Dual
4.
Degree) in Aerospace Engineering with
specialization in Structure Optimization
from Indian Institute of Technology
Bombay, Mumbai. He has joined
NCAIR as a Research Associate.
J. Bhagyaraj
He received his PhD degree in Materials
Science and Engineering from Indian
Institute of Technology Kanpur.
He has joined IITB in Mechanical
Engineering department as a PostDoctoral Fellow and will be working
on projects carried out at NCAIR.
Kunal Pralhad Barhate
He has pursued his Master of Technology
degree in Mechanical Engineering
from Nirma University, Ahmedabad
(Gujarat, India). He has joined NCAIR as
a research associate and working on
computational modelling of composite.
Amol More
He is pursuing his Master of
Technology degree in CAD/CAM
from VIT University,Vellore (Tamil
Nadu) India. He has joined NCAIR as
a Project Research Associate.
Nausheen Azam
Gautam Salkar
She has pursued her Computer Engineering
from Mumbai University and has joined
NCAIR as a Research Assistant. Her area of
interest includes programming in different
programming languages. She would be
working as a project staff on NCAIR Project.
He has done his Master of Science
degree in Mechanical Engineering
from North Carolina State University
at Raleigh, NC in USA. He has worked
previously as a Test Engineer at Cummins.
He has joined NCAIR as a Project
Research Associate and is working on
computational modelling of composites.
Sushrut Vaidya
He has his PhD in Civil Engineering, with a
specialization in Applied Mechanics, at the
University of Connecticut, USA. He joined
the Mechanical Engineering Department
of IIT Bombay as a Post-Doctoral Fellow in
March 2015, and will be working with the
Microstructure Modeling Group at NCAIR.
Harshil Shah
He has done his Bachelor of Engineering in
Mechanical Engineering from K.J.Somaiya
College of Engineering, Mumbai. He is a
motorsports and aerospace enthusiast.
He has joined NCAIR as a Research
Assistant and is working mainly on
manufacturing research specifically with
3D modeling and simulation.
Arun Nair
He has done his Bachelor of Engineering
degree in Mechanical Engineering from
University of Pune, Maharashtra (India). He
has joined IIT-B in Mechanical Engineering
department as a Research Assistant
and will be working on 5-Axis DMG Mori
Seiki Machine.and is working mainly
on manufacturing research specifically
with 3D modeling and simulation.
5.
Publications
Papers published
Omanath A. Pawar, Yogesh S. Gaikhe, Asim Tewari, Ramesh Sundaram,
and Suhas S. Joshi; Analysis of hole quality in drilling GLARE fiber
metal laminates, Composite Structures, vol. 123, pp. 350-365, 2015.
http://www.sciencedirect.com/science/article/pii/S0263822314007223
Omanath A. Pawar, Yogesh S. Gaikhe, Asim Tewari and Suhas S. Joshi;
Effect of point angle in single-shot drilling of AA2024/CFRP/Ti6Al4V
stacks, Conference proceedings, MEGRES, 2015, IIT Bombay.
Papers presented in conferences
ISAMPE National Conference on Composites (INCCOM-13) was held on
November 14th and 15th, 2014 at VSSC, Thiruvananthapuram, Kerala.
Following are the papers that were presented:
ƒƒ Effect of Single shot Drilling on Multilayered Metallic-Composite Stack - Yogesh Gaikhe
ƒƒ Fabric Permeability Computation with Varying Fiber Distribution
and Packaging - Kashyap Mohan and Sajan Joshi
ƒƒ Multi-physics Simulation of Process Induced Deformation in Composites Incorporating Effects of Flow Compaction
- Vinayak Khandare
NCAIR exhibited its research work in the recently concluded Sheet
Metal Forming and Research Association Conference 2014 which was
held on 27-28 November, 2014 at Victor Menezes Convention Center,
IIT-Bombay. Posters of ongoing research projects were presented at
the exhibition which was well received by all the participants.
Idea contest at IIT Bombay
Idea contest at IIT Bombay
General Electric (GE) and IIT Bombay organised one day
seminar on Industry Academia Collaboration on Technology,
IACT at IIT Bombay campus.
Jigar Goda, Ashish Saxena and Sagar Telrandhe from NCAIR
has won the winners prize of Rs. 10,000 each.
6.
Visits at NCAIR
Professor Sir Mike Gregory, Head, Institute for
Manufacturing University of Cambridge, UK visited
NCAIR on September 13, 2014.
5.1
5.2
5.1 - Visit to NCAIR office: L-R: Ms. Swetha Manian, Ms. Vani Sreedhara, Mr.
Taha Khot, Prof. Sir Mike Gregory, Prof. Asim Tewari, Mr. Jigar Goda, Mr.
Sumit Katekar.
5.2 - Visit to NCAIR office: L-R: Prof. Rakesh Mote, Prof. Sridhar
Balasubramanian, Prof. Asim Tewari, Prof. Sir Mike Gregory, Prof. Prita Pant,
Prof. Sreedhara Sheshadri, Prof. Sushil Mishra.
Professor Robert Allison, Vice Chancellor and
President Loughborough University, UK visited
NCAIR on November 7, 2014.
Dr. Vahan, VP - Global Sales of X-ray Microscope,
Carl Zeiss visited NCAIR on February 5, 2015.
Dr. Prakash D. Mangalgiri, Consultant, NPMASS,
Aeronautical Development Agency, Bengaluru
visited NCAIR on November 26, 2014.
Mr. Tim Hughes, Development Director, Delcam,
visited NCAIR on March 16, 2015.
Dr. Prasad Potluri, Professor of Robotics and Textile
Composites, The University of Manchester visited
NCAIR on December 24, 2014.
6.1
6.1 - Visit to NCAIR office: L-R: Mr. Taha Khot, Mr. Sumit Katekar, Ms. Swetha
Manian, Dr. Prasad Potluri, Mr. Swarnendu, Prof. Anirban Guha,
Ms. Vani Sreedhara.
7.
Featured Article
Issues in Ultra-precision
Machining (UPM) of
Titanium Alloys
Abhishek Bihari, M.Tech. Student, Department of Mechanical Engineering, IIT Bombay and
Rakesh G. Mote, Assistant Professor, Department of Mechanical Engineering, IIT Bombay. Email: rakesh.mote@iitb.ac.in
Introduction
The high quality surfaces and microstructures have been
widely finding applications in optics, semiconductor, and
biomedical industries. Ultraprecision machining with the
use of diamond tools has been established as the most
preferred method to produce such surfaces. An optical
grade surface finish of the order of 10 nm RMS is generally
obtained through ultra-precision machining processes.
The key to achieve highly accurate surface profile is to
have a machine tool with greater positioning accuracy,
precise control over cutting and feed velocities and the
stiffness. Above all, in order to achieve high degree of
surface characteristics, tooling plays a critical role.
Diamond tools are often used in ultraprecision machining
because of their unmatched properties, including the
highest hardness, quite strong resistance to wear, perfect
chemical stability and satisfactory service life, as well
as the highest sharpness providing the least resistance.
Figure 1 shows a brief comparison of different levels
(operation and surface quality) of machining processes.
Titanium alloys have many excellent properties, for
example, the high specific strength, high strength
at elevated temperature, outstanding cryogenic
property, exceptional resistance to corrosion, good biocompatibility, and so on. Therefore, titanium alloys are
extensively used for aviation, aerospace, biomedical,
marine and automotive applications. The unique
properties of titanium alloys could provide additional
value to optical applications. For example, ultra-precision
components like optical mirrors of satellite, work in
cryogenic environment.
Titanium alloys exhibit poor machinability. This is due to
their high strength and hardness at elevated temperatures,
low thermal conductivity, high strain hardening, and high
chemical reactivity. Due to low thermal conductivity
8.
Fig. 1 Comparison chart for nano-, micro- and macro-machining processes
(based on data in [1]).
Diamond tools are often used
in ultraprecision machining
because of their unmatched
properties, including the highest
hardness, quite strong resistance
to wear, perfect chemical stability
and satisfactory service life,
as well as the highest sharpness
providing the least resistance.
of titanium alloys, heat generated during machining
is not allowed to dissipate from the tool edge causing
tool-tip temperature to be high and hence excess tool
deformation and wear. All such factors lead to high cutting
temperatures, greater specific cutting force, springback
of workpiece material and excessive tool wear and low
material removal rate. Titanium is therefore considered as
difficult to cut material. Hence, machinability of titanium
alloys is always a challenge because of its chemically
reactive nature at high temperature. At high temperature,
they get welded to the tool metals resulting in chipping
off and finally causing failure of the tool. Also, at such
higher temperatures, only a few tools are able to survive.
For machining titanium alloys, conventional tools used
were mainly HSS and carbide tools. Due to problem of
high temperature, these tools can be used only at lower
cutting speeds, otherwise life of the tools will be very
short. In comparison of PCD (polycrystalline diamond),
the performance of conventional tools was very poor.
Also, PCD tools have the lowest wear rate, higher thermal
conductivity, longer tool life at higher cutting speed and
produce better quality surface. Due to all these reasons,
ultra-precision of titanium alloys became necessary.
Machining of Ti Alloys using Diamond Tools
Diamond exhibits the strong covalent bond and the highly
compact lattice structure imparting the highest hardness.
Such unique properties make the diamond a suitable
material for a wide range of engineering applications.
Diamond (naturally occurring and synthetic) and the
derived composites, such as polycrystalline diamond
(PCD) are used in machining of 'difficult-to-machine'
materials. However, the diamond tools are not popular in
machining of ferrous and nickel based alloys due to rapid
graphitization of diamond. The heat during machining
ferrous materials initiates chemical reaction, causing
carbon in diamond to diffuse into iron material at elevated
temperatures during machining. The graphitization
leads to a significant tool wear of diamond tools and
their machining performance degrades. Despite diamond
being used as cutting tool, due to its brittleness, monocrystal diamonds (MCD) need to be used at correct crystal
orientation to prevent fracture and to achieve optimum
performance. To incorporate such properties, MCD have
been substituted by polycrystalline diamond (PCD). For
machining of titanium alloys usually diamond coated
tools and PCD tools are used. In machining of titanium
alloys, PCD tools found to provide significantly extended
tool life over tungsten carbide tools (due to extreme
hardness, PCD tools demonstrate almost 500 times wear
resistance than WC tools) [2]. However, the presence
of titanium can accentuate the onset of oxidization or
graphitization when in contact with diamond at elevated
temperatures [3].
Frequent wear occurs in the tools during machining
of titanium alloys, caused by a combination of high
temperature, high cutting stresses, and the strong
chemical reactivity of titanium. The dominant wear
mechanisms are listed below:
i. Abrasion wear – It is the primary mode of failure
that is produced due to the rubbing action of hard
inclusions in the workpiece material and chips.
ii. Adhesion wear – It always occurs due to chemical
affinity between workpiece and tool material. Due to
the rubbing action of material and tool, adhesive bonds
are formed which lead to adhesion wear of PCD tools.
iii.Attrition – Crater wear is also observed during
machining of titanium alloys due to high chemical
reactivity of titanium alloys which causes chip to
weld to the tool. Welded work material on the cutting
tool gets compressed and removed in the course of
machining. Due to this, cutting tool grains will be
plucked, which is called attrition and takes place on
both of the crater as well as flank surface.
iv. Diffusion – Diffusion is predominant on rake face. It
generates delamination of the coatings and adhesion
wear of the tool material. TiC is formed at the rake
face of tool due to diffusion of carbon particles from
the tool into the titanium layer. This TiC layer is pulled
out due to high cutting force resulting in excessive
crater wear.
v. Notch wear – It happens when excessive local damage
occurs simultaneously at rake face and at flank face.
Ultra-precision Machining of Titanium Alloys
Most of the work on titanium is focused on PCD tools
as discussed in the previous section. However, MCD
structure offers a number of advantages over PCD
(Table 1) as a cutting tool material for extreme precision
machining. The geometry of MCD does not change with
wear and many more things. Mono-crystalline diamond
possesses almost twice the hardness and four times
the thermal conductivity over PCD [4]. Butler et al. [5]
used MCD tool for micro-milling of Ti-6Al-4V and noted
that the performance of MCD tools is sensitive to its
crystallographic orientation in the cutting tool. It was
9.
observed that tools with a rake/flank orientation of
{110}/{100} offered a significantly extended tool life over
the tools having a rake/flank orientation of {100}/{110}.
However, the surface roughness (Ra) was in the range
100 – 270 nm over the cutting length of 25 m.
Table 1: Comparison between mono-crystalline diamonds (MCD) and polycrystalline diamonds (PCD)
MCD
PCD
MCD consist of single grains that have
sharp edges which ensure clean and
efficient cutting action providing high
material removal rates.
PCD consists of micron-sized synthetic
diamond powders bonded together
by sintering at high pressures and
temperatures.
Brittle
Tough
MCD exhibits different properties on
different crystallographic planes in
different crystallographic directions.
PCD is isotropic i.e. exhibiting uniform
properties in all directions.
SCD fractures very easily along certain
cleavage planes.
Crystallites are oriented in random
direction in PCD passing from one
crystallite to another tends to held up.
Hence, they do not fracture easily.
Less uniform particle size distribution
(PSD)
More uniform PSD hence crack
Less homogeneity and packing density.
More homogeneity and packing density
They produce random scratches and
micro-cracking.
They do not produce random scratches
and abrade a workpiece uniformly.
Low wear and sharp cutting edge.
High wear.
Colafemina et al. [6] studied the behaviour of Ti–6Al–4V
and Ti (CP) in MCD in precision face turning experiments
with depth of cut in the range 5-15µm. They noted the
least values of surface roughness (Rz) to be 590 nm
for Ti (CP) and 416 nm for Ti–6Al–4V under the same
machining conditions. Zhang et al. [11] performed turning
experiments on Titanium alloy (TC4) to investigate
tool wear using diamond tools. The experimentation
considered ultrasonic vibration machining method
for machining and then effects on the tool wear were
analyzed. The study revealed that vibration magnitude
and frequency were the most critical factors toward tool
life and wear propagation rate. The surface roughness
(Ra) was noted to be about 260 nm.
As per ultra-precision machining characteristics,
minimum cutting length of 2 km is required to produce
a typical high quality optical component.
10.
Featured Article
Sakamato et al [7] used small depth of cut (1 �m) for
ultra-precision cutting with diamond tool to finish beta
titanium alloy. The surface finish obtained was below
100 nm (Rz) at feed rates below 50 �m/rev (Table 2).
Table 2: Effect of cutting length over surface finish of
Ti-22V-4Al (based on data in ref. [7])
Cutting Length (m)
Ra (nm)
Rz (nm)
100
16
79
6,000
20
97
21,000
30
204
Issues in Ultra Precision Machining of Ti Alloys
Some of the important parameters which are concerned
during ultra-precision machining of titanium alloys are
discussed below:
i. G
raphitization - The major concern during machining
of titanium is poor tool life due to high cutting
temperature and high pressure at the tool-chip
interface which initiates the chemical interaction
between the titanium and the diamond resulting in
the graphitization of the diamond tool.
ii. Excessive tool wear - Zareena et al. [8] used a protective
barrier in the form of a thin Perfluoropolyether
(PFPE) coating for diamond toolsin order to reduce
the tool wear. The PFPE coating aids in minimizing
the initial negative chemical interaction between the
cutting tool and the workpiece and thus delaying the
onset of graphitization of the tool and thus the tool
retains its sharp edge. The surface roughness (Ra)
obtained was of nanometre level sustainable over a
cutting length of about 3 km. Such lubrication will
reduce friction, further reducing cutting force and
power and hence the cutting temperature. In this
way, functional life of the tool and machinability of
Ti alloy is increased. But the thickness of lubricant
layer should be comparable to molecular layer. This is
required to retain the sharpness of the cutting edge,
which is acrucial parameter in UPM to maintain the
surface quality and precision of the part machined.
iii.High specific cutting energy –As the size of chip
decreases, specific cutting energy increases
substantially. This is known as “size effect” and
happens because, load is very high and the contact
Some of the important
parameters which are concerned
during ultra-precision
machining of titanium alloys
are graphitization, excessive
tool wear, high specific cutting
energy and delamination.
11.
area is very small. Such high stresses will again lead to
graphitization and reduce the cutting edge strength.
iv. Delamination - During UPM of Ti alloys, a strain
gradient in workpiece is observed, as compressive
stresses and tension are generated in the surface
layer and in the subsurface layer of the material,
respectively. The strain gradient causes delamination
in the form of the grains of the surface getting detached
itself from the sub surface grains [12].
Table 3 shows summary of ultraprecision machining of
different titanium alloys.
Table 3: Ultraprecision machining of various titanium alloys
BrittleTi Alloy
Process
Tool Material
Surface Roughness
(Ra )
Ti (CP)
SPDT
MCD with PFPE
coating
7 nm [8]
Ti-22V-4Al
SPDT
MCD
100 nm [9]
Ti-22V-4Al
SPDT
MCD
20 nm [7]
Ti-6Al-4V
SPDT
MCD with PFPE
coating
8 nm [8]
Ti-6Al-4V
Micro Milling
MCD
60 nm [10]
Ti-6Al-4V
Ultrasonic vibration
assisted turning
MCD
250 nm [11]
Conclusions and Recommendations
• Titanium alloys have considerable potential in high
precision optical components due to their excellent
strength to weight ratio and corrosion resistance
properties.
• Difficulties in machining of Ti alloys originate mainly
from high cutting temperature, chemical reaction with
tools and low elastic modulus.
• Low thermal conductivit y, high temperature
and pressure at the tool-chip interface results in
graphitization of diamond tool which makes it very
difficult to be machined.
• The smallest values of roughness for Ti alloys made
UPM to be a good option for finishing.
12.
• For ultra-precision machining, MCD tools are proving
Featured Article
to be ideal choice tool material. PCD tools are given
wide consideration in machining of titanium alloys
at macro level.
• For UPM of Ti alloys, tool life has to be functionally
doubled to get a high quality optical component.
• Graphitization of diamond causing excessive tool wear
is one of the major concerns and is being reduced by
having coated tool (e.g. PFPE coatings).
For ultra-precision machining,
MCD tools are proving to be
an ideal choice tool material.
PCD tools are given wide
consideration in machining of
titanium alloys at macro level.
• However, ultra-precision machining of these alloys
with unfriendly machining characteristics require
further understanding of the mechanisms behind the
tool wear rates.
• With these insights, strategies need to be developed in
order to produce high quality surfaces and components.
References
[1] E. Brinksmeier and W. Preuss, “Micro-machining.,” Philos. Trans. A. Math. Phys. Eng. Sci., vol. 370, no. 1973, pp. 3973–92, Aug. 2012.
[10] S. I. Jaffery, N. Driver, and P. T. Mativenga, “Analysis of process [2] J. P. Davim, Ed., Machining of Titanium Alloys, Materials Forming, parameters in the micromachining of Ti-6Al-4V alloy,” in Proceedings of the 36th International MATADOR Conference, 2010, [3] W. Konig and N. Neises, “Turning Ti-6Al-4V with PCD,” Ind. Diam. pp. 239–242.
Rev., vol. 93, no. 2, pp. 85–88, 1993.
[11] Y. Zhang, Z. Zhou, J. Wang, and X. Li, “Diamond tool wear in [4] E. Uhlmann, E. Wörner, and M. Brücher, “More efficient cutting precision turning of titanium alloy,” Mater. Manuf. Process., vol. 28, processes due to the heat-spreading effect of CVD diamond.,” no. 10, pp. 1061–1064, Oct. 2013.
Ind. Diam. Rev., vol. 03, no. 1, pp. 25–29, 2003.
[12] Colafemina, J., Jasinevicius, R. and Duduch, J. 2007. Surface Machining and Tribology. Springer Verlag, Berlin, Germany, 2014.
[5] P. W. Butler-Smith, D. A. Axinte, and V. Limvachirakom, “Preliminary integrity of ultra-precision diamond turned Ti (commercially pure) study of the effects of crystal orientation of a CVD monocrystalline and Ti alloy (Ti-6Al-4V). Proceedings of the Institution of diamond in micromilling of Ti–6Al–4V,” Proc. Inst. Mech. Eng. Part B Mechanical Engineers, Part B: Journal of Engineering Manufacture. J. Eng. Manuf., vol. 224, no. 8, pp. 1305–1312, Aug. 2010.
221, 6 (2007), 999–1006.
[6] J. P. Colafemina, R. G. Jasinevicius, and J. G. Duduch, “Surface integrity of ultra-precision diamond turned Ti (commercially pure) and Ti alloy (Ti-6Al-4V),” Proc. Inst. Mech. Eng. Part B J. Eng. Manuf., vol. 221, no. 6, pp. 999–1006, Jun. 2007.
[7] S. Sakamoto, A. Shinozaki, and H. Yasui, “Possibility of ultra-
precision cutting of titanium alloy with diamond tool,” 2005. [Online]. Available: http://www.aspe.net:16080/publications/
Annual_2005/Posters/6Process/2Mach/1780.PDF. [Accessed: 20-
Nov-2014].
[8] A. R. Zareena and S. C. Veldhuis, “Tool wear mechanisms and tool life enhancement in ultra-precision machining of titanium,” J. Mater. Process. Technol., vol. 212, no. 3, pp. 560–570, Mar. 2012.
[9] H. Yasui, A. Shinozaki, and A. Toyama, “Effect of low cutting speed on ultra-precision cutting of titanium alloy with coated-cemented-
carbide tool,” 2006. [Online]. Available: http://aspe.net/
publications/Annual_2006/Posters/5Process/2Mach/2030.PDF. [Accessed: 20-Nov-2014].
13.
R & D UPDATES
KASHYAP MOHAN
Research Assistant, NCAIR
SAJAN JOSHI
M.Tech 2nd Year, NCAIR
Permeability of a fibrous
medium is a vital parameter
determining the flow behaviour
of a fluid in the medium.
Fabrics are made of fiber tows
stitched or weaved together.
The result of this type of fabric
architecture is that the fabric
behaves as a dual scale porous
media exhibiting both macro
and micro level permeability.
Fabric Permeability Computation
with Varying Fiber Distribution
and Packaging
Introduction
Permeability of a fibrous medium is a vital parameter determining the
flow behaviour of a fluid in the medium. Fabrics are made of fiber tows
stitched or weaved together. The tows are bundles of thousands of untwisted
continuous fiber filaments. The result of this type of fabric architecture is
that the fabric behaves as a dual scale porous media exhibiting both macro
and micro level permeability.
Dual scale permeability characterizes the fluid flow front in the fabric –
both inter tow and intra tow [1]. The global resistance to the fluid flow
is characterized by the bulk or macro level permeability, which is largely
determined by the arrangement of tows. The fluid flow within the tow
depends on the tow level or micro level permeability, which is determined
by fiber arrangement, size and packaging within the tows.
Ongoing and further research aims at developing models which can compute
accurately both macro and micro scale fabric permeability. Such models are
important tools for composite process engineers to optimize resin infusion
processes.
This article is an effort in the direction of permeability modelling. It attempts
to highlight the variation in longitudinal (along fiber direction) saturated
permeability at micro level produced with change in fiber arrangement, size
and distribution within the tows.
Modeling Methodology
Assumptions
To model permeability a homogenous resin porous medium saturated with
resin is assumed. Then a representative volume element (RVE) is considered
for different fiber arrangements. It is assumed that the fluid follows a steady
state laminar flow inside the RVE.
Geometry
• Three different fiber arrangements are considered for the computation
of permeability: Square, Hexagonal and Random, units cells of which are
shown in Fig. 1-4.
• Interspacing between the fibers is varied to vary the volume fraction.
• Simulations are run for two different fiber diameters.
14.
Fabric Permeability Computation with Varying Fiber Distribution and Packaging
Equations and Boundary Conditions
Symmetric conditions are applied at the RVE boundary surface that is there
is no velocity gradient in direction normal to boundary surface. At the fiber
surface, no slip condition exist which indicates that the net velocity is zero
(Fig. 4-5). [2]
Flow behaviour inside the RVE is modelled using Stokes flow equation. The
flow boundary conditions, interface conditions and consistency conditions
(conservation of mass and momentum) are used to solve for velocity and
pressure distribution.
Permeability can be calculated as [3]:
(1)
Fig. 1-3 Schematic showing RVE’s of square,
hexagon and random fiber arrangement.
1
3
2
4
Ki = saturated permeability in i direction
Q = volumetric flow rate
A = cross section area
ΔP = pressure difference across the RVE
L = length of RVE
5
Fig. 4 Fibers arranged in square pattern.
Fig 5 RVE for square arrangement illustrating
the boundary conditions.
15.
Fabric Permeability Computation with Varying Fiber Distribution and Packaging
Meshing and Simulation
3-D RVE’s are modelled in COMSOL multi-physics software package.
Meshing is done using the inbuilt meshing parameters for “FINER” mesh size.
Extruded triangular elements are used to mesh the RVE as shown in Fig. 6.
Pressure difference of 20000 Pa is applied across the RVE. Resin viscosity
is taken to be 1 Pas.
The models are simulated as per the applied boundary conditions to obtain
velocity and pressure distribution in the RVE. (Fig. 7-8). The velocity
distribution is not uniform throughout the RVE. Therefore velocity average
over the outlet surface is calculated. The computed surface average velocity
is substituted in Eq (1) to get the permeability value.
Fig. 6a,b,c Extruded triangular mesh for
square arrangement.
Fig. 7 Velocity distribution after simulation
for square arrangement
Fig 8 Pressure distribution after simulation
for square arrangement.
6a
7
6b
6c
8
Results and Discussion
Packing density is represented by the volume fraction of fibers within the
tows.
In Fig. 9, the variation of longitudinal permeability with fiber volume fraction
is plotted for 15 µm diameter fibers arranged in hexagonal and square
arrangements.
From the graph it is obtained that longitudinal permeability decreases with
an increase in the fiber volume fraction for both ordered arrangements.
In Fig. 10, the variation of longitudinal permeability with fiber volume
fraction is plotted for two different fiber sizes i.e. diameter 10 µm and
20 µm arranged in square pattern.
16.
Fabric Permeability Computation with Varying Fiber Distribution and Packaging
Fig. 9 Variation in longitudinal permeability
with fiber volume fraction for square and
hexagonal arrangements.
Fig. 10 Variation in longitudinal permeability
with fiber fraction for different fiber diameters in
square arrangement
At a given fiber volume fraction, an increase in longitudinal permeability
is observed with an increase in fiber diameter. A similar trend is observed
for hexagonal arrangement.
In Fig.11, longitudinal permeability is plotted for different fiber arrangements
on the same graph.
It is observed that for a given volume fraction and fiber diameter, random
arrangement gives the maximum permeability and hexagonal arrangement
gives the least permeability.
The difference in longitudinal permeability of different fiber arrangements
is more for lower values of fiber volume fractions.
17.
Fabric Permeability Computation with Varying Fiber Distribution and Packaging
Fig. 11 Comparison in longitudinal
permeability of different fiber arrangements.
It is observed that micro level
longitudinal permeability
decreases with an increase in
the volume fraction of fiber.
Longitudinal permeability
shows an increase with an
increase in diameter of fiber.
Also, random arrangement
of fibers shows greater
permeability as compared
to ordered arrangements.
Conclusion and Future Work
This work simulates and analyses the variation in the longitudinal
permeability of a fabric at micro level due to changes in fiber arrangement,
size and distribution. It is observed that micro level longitudinal permeability
decreases with an increase in the volume fraction of fiber. Longitudinal
permeability shows an increase with an increase in diameter of fiber. Also,
random arrangement of fibers shows greater permeability as compared to
ordered arrangements.
It can be concluded that the micro level permeability also depends on many
factors other than volume fraction of fibers. Fabrics can be tailor made
considering the above observations so as to improve resin saturation within
the tows.
The future work entails
• Development of analytical functions to determine the variation micro
level permeability due to fiber arrangement and size related parameters.
• Integration of effects of resin viscosity in the simulation and analytical
models for more accurate results.
REFERENCES
[1] Fuping Zhou, Nina Kuentzer, Pavel Simacek, Suresh G. Advani, Shawn Walsh: Analytic characterization of the permeability of dual-scale fibrous porous media, Composites Science and Technology 66 (2006) 2795-2803
[2] Alexander l. Berdichevsky and ZhongCai: Preform permeability predictions by Self-
Consistent Method and Finite Element Simulation, Polymer Composites, April 1993, Vol. 14, No. 2
[3] N.K. Naik, M. Sirisha, A. Inani : Permeability Characterization Of Polymer Matrix Composites 18.
By RTM/VARTM, Progress in Aerospace Sciences 65 (2014) 22-40
R & D UPDATES
JIGAR P. GODA
Research assistant, NCAIR, IIT Bombay
Industries today are increasingly
converting to Liquid Composite
Moulding (LCM) processes due to
growing demand in composite
industry for quality, economy,
productivity, etc. With the vast
range of processes and the
huge amount of variables to
consider, the selection of perfect
process is very complicated.
Comparison of Liquid Composite
Moulding (LCM) processes
Introduction
Liquid Composite Moulding is a closed mould polymeric composite process in
which the matrix impregnate the dry fabric under the influence of external
pressure. Polymeric composites can be made in many ways, including hand
lay-up and spray-up, prepreg vacuum bagging and autoclave curing, filament
winding, compression moulding of Sheet Moulding Compound (SMC) and Bulk
Moulding Compound (BMC), and Liquid Composite Moulding (LCM). More
industries are converting to Liquid Composite Moulding (LCM) processes due
to growing demand in composite industry for quality, economy, productivity,
etc. With the vast range of processes and the huge amount of variables to
consider, the selection of perfect process is very complicated. This article
gives information on various LCM processes and helps on selection of the
suitable process as per application
There is no single nomenclature for grouping, thus the processes are
differentiated into three types on the basis of the moulds used, type of
clamping as well as pressure maintained. The processes are classified into
these types as represented in the Table 1.
Table 1. Classification of Liquid Composite Moulding processes
TYPES
Type 1
PARAMETERS
PROCESSES
Pressure maintained
Mould used
Type of clamping
Vacuum Pressure
Single sided rigid
Vacuum clamping
only
mould with flexible
only
(0-1 bar abs)
covering
• Vacuum Assisted Resin Transfer Moulding (VARTM)
• Seemann Composite Resin Infusion Moulding Process (SCRIMP)
• Resin Infusion under Flexible Tooling (RIFT)
• Flex Moulding
Type 2
Gauge + vacuum
Rigid or semi-rigid
Vacuum + mechanical
• Vacuum RTM (VRTM)
pressure
both side tooling
clamping
• Resin Transfer Moulding Light (RTM Light)
(0-8 bar abs)
• Resin Transfer Moulding Eco (RTM Eco)
Type 3
Gauge + vacuum
Both sided rigid
Clamping under
• Resin Transfer Moulding pressure
mould
presses
(RTM)
(0-15 bar abs)
• High Pressure Resin Transfer Moulding (HPRTM).
19.
Comparison of Liquid Composite Moulding (LCM) processes
Process description
Type 1
Polymer composite parts are made by placing dry fibre reinforcing fabrics
into a single-part open mould, enclosing the mould with a vacuum bag and
drawing a vacuum in order to ensure a complete preform infiltration with
liquid resin. There is no external pumping pressure applied to the resin.
Vacuum bag with other consumables such as peel ply, flow mesh is utilized
in VARTM / SCRIMP processes. These consumables can be used only once,
thus leading to lot of wastage which is prevented in RIFT/ Flex Moulding by
using reusable silicon bag preformed in the shape of mould. This modification
also helps increase production time by deducing the setup time.
Type 2
These processes utilize both moulds, the base mould being rigid with the
counter mould can be semi rigid to save on cost. Both these moulds are
clamped by high vacuum pressure generated at the periphery of the mould.
Liquid resins impregnate the dry fabric under vacuum. To accelerate the
process resin injection pump may be used.
Type 3
Mechanical clamping is used (hydraulic press, nuts and bolts, toggle clamps
etc.) to hold two rigid moulds in place during resin infusion. Dry reinforcement
is stacked between these moulds and liquid resin is injected under positive
hydraulic pressure with help of injection machine. Vacuum is maintained
inside the mould to improve the part quality and prevent voids. HPRTM is
scaled up version of RTM which is used to manufacture big parts. Here, the
resin is infused at very high pressure (>12 bar) to reduce production time.
Advantages and Limitations of all the processes are summarised in the Table 2.
20.
Comparison of Liquid Composite Moulding (LCM) processes
Table 2. Advantages and Limitation of processes
LIMITATIONS
ADVANTAGES
TYPE 1
- Skilled labour is required.
- Moderate investment due to reduction in tooling cost.
- Risk of leakage leads to voids formation.
- Void free parts can be manufactured.
- Loss of consumables and issue of recycling.
- Sandwich construction.
- Setup time is comparatively high.
- Large possibility of shapes.
- Only one cosmetic surface is possible.
- Variation in part thickness can be achieved from the same mould.
- Easy visual monitoring of resin flow.
TYPE 2
- Vacuum pump and injection machine are required.
- High productivity.
- Reduced labour costs.
- Both male and female moulds are required.
- Cosmetic surfaces on both “A” and “B” side of part.
- Skilled labor required.
- Investment cost is high compared to VARTM process.
- Enhanced dimensional stability.
-Sandwich-construction.
- Improved process control.
- Almost negligible consumables required.
- Long mould life.
- No VOC emissions.
TYPE 3
- Very high rate of production.
- Ideal for parts of high production rate.
- Hydraulic press and lifting facilities
are required
- Ideal for small and medium size parts.
- High pressure injection machine and both side rigid metal moulds are a must.
- Structural parts can be manufactured with consistency and dimensional stability.
- High investment of the equipment.
- Almost negligible consumables required.
- High precision of moulds required.
- Visual monitoring of resin flow is not possible.
21.
Comparison of Liquid Composite Moulding (LCM) processes
Selection of a process
It is dependent on following parameters:
• Part size and layup thickness variability.
• Total number of parts and production rate.
• Integrated specification (strength to weight ratio, cosmetic surfaces,
chemical, fire and thermal resistance, sandwich construction, etc.)
• Investment and Production costs.
All these parameters are compared for all types of processes in the Table 3.
Table 3. Comparison of processes for various parameters
TYPE 1
TYPE 2
TYPE 3
VARTM / SCRIMP / RIFT /
VRTM / RTM Light / RTM
RTM / HPRTM
Flex Moulding
Eco
Part Size
Small, Medium and Large
Small and medium
Small and medium
Layup thickness variability
Can be varied as required
Cannot be varied
Cannot be varied
Number of Parts
500-1000
1000-5000
2000-10000
Production rate / year
200-500
500-2000
2000-5000
Cosmetic Surfaces
Single side only
Both side
Both side
Sandwich composite
Possible
Possible
Not Possible
Strength to weight ratio
High
Medium
High
Chemical, Fire and Thermal
Depends on matrix
Depends on matrix
Depends on matrix
resistance
used.
used.
used.
Investment Cost and
Low
Medium
High
High
Medium
Medium
Specification
maintenance cost
Production Cost
Summary
As Liquid Composite Moulding encompasses a wide variety of composite
manufacturing methods, the sub-processes should be tailor-made for every
part considering the advantages and limitations they offer. The specifications
from a part should be first found and then the correct process should be
moulded accordingly.
22.
Comparison of Liquid Composite Moulding (LCM) processes
BIBLIOGRAPHY / REFERENCES
[1] P. K. Mallick, “FIBRE REINFORCED COMPOSITES, Materials, Manufacturing, and Design “
[2] W.D. Brouwer*, E.C.F.C. van Herpt, M. Labordus, “Vacuum injection moulding for large structural applications,” Composites: Part A 34 (2003) 551–558
[3] http://www.tech.plym.ac.uk/sme/fpcm//fpcm09%5Cpdf/IA2/3.pdf last retrieved on November, 20, 2014
[4] http://www.compositesworld.com/knowledgecenter/closed-moulding/Closed-Mould-
Process/Resin-Transfer-Moulding last retrieved on November, 21, 2014
[5] http://www.composite-integration.co.uk/about-rtm.php last retrieved on November, 16, 2014
23.
R & D UPDATES
VINAYAK KHANDARE
Research Associate, NCAIR, IIT Bombay
Fiber reinforced polymer (FRP)
matrix composites, have proved
themselves to be high in
performance applications like
aerospace application, marine
etc. There are numerous
techniques to manufacture such
composites. They are autoclave
process, resin transfer moulding,
compression moulding, bag
moulding etc, some of which are
simple, while some are complex.
24.
Modeling and simulation of
process induced deformations
in fiber reinforced polymer (FRP)
matrix composites
Introduction
Fiber reinforced polymer (FRP) matrix composites, have proved themselves
to be high in performance applications like aerospace application, marine
etc. There are numerous techniques to manufacture such composites. They
are autoclave process, resin transfer moulding, compression moulding,
bag moulding etc, some of which are simple, while some are complex. For
manufacturing large shapes and high performance components, autoclave
is the most suitable process, despite, its higher cost. In this technique, the
prepreg i.e. the pre-cured resin fiber layups are cut, stacked and laid on an
open mould. This is then placed in the autoclave, where it is subjected to cure
cycle (heating and cooling). The autoclave process generates large residual
stresses which is a major disadvantage leading to part distortion. These
stresses are generated mainly due to anisotropic thermal expansion, shrinkage
of resin at cool-down and tool part interaction. These distortions are named
as process induced deformations (PIDS) namely spring-in, warpage and
shrinkage. Spring-in, is the increase in enclosed angle between two flanges
whereas, warpage is the deviation of the flat surface. The deformations can
be minimized by compensating tool at design level or by controlling the
factors or mechanisms that are responsible for causing such deformations.
FEA simulations were performed to understand the effect of different
parameters on PIDS by using ABAQUS/COMPRO. The constitutive behaviour
of resin is taken into account.
Background
Several researchers have focused on the parameters that contribute to
the PIDS. An overview of some of their works is shown in Table 1. Table 1,
suggests that the tool part CTE, thickness of the component, layup variation
and tool radius has an impact on PIDS. This article illustrates the effect of
these parameters and is further verified with the help of FEA simulations.
Modeling approach
Composites process modeling, usually employs an 'integrated sub-model'
approach. A composites process modeling program COMPRO was developed
on this approach, which is basically a plug-in to 3rd party finite element based
simulation software. It consists of three analysis modules namely ThermoChemical module, Flow-Compaction module and Stress-Deformation module,
which simulates the impact of the evolving material properties on the thermal
and cure history of the part, resin flow within a fully saturated part, and
residual stress and part deformations of the part after tool removal. In this
Modeling and simulation of process induced deformations in fiber reinforced polymer (FRP) matrix composites
Table 1. Summary of literature review
Sr. No.
RESEARCH
REMARKS
1
Carolyne Albert and
To minimize spring-in
Fernlund G. (2002),
• Select tooling material having the coefficient of thermal expansion (CTE) as close as possible to the part CTE
• C-shaped geometry gives more spring-in than L-shaped parts
2
3
Fernlund G., Anoush
• Defined the effect of different cure cycle (single & dual hold) along Poursartip (2003)
with release agent
Cann MT, Adams DO
• The experimental study concluded to find effect of layup on (2001)
deformations. By placing a 90° ply at the tool-part interface, warpage is virtually eliminated
4
Chensong dong (2010)
• FEA study concluded that spring-in increases with the radius–
thickness ratio
5
E. Kappel, D. Stefaniak,
• The specimen flange length should be considered as an essential C. Huhne (2013)
parameter when investigating spring-in of L-profiles
• The effect of different tool materials (Al & Invar) and layup variation is taken into account
study however, the analyses have been performed using only the thermochemical and stress-deformation modules. The results obtained from the
Thermo-chemical module are directly used in the analysis performed using
the Stress-Deformation module.
Thermo-Chemical Module
The Thermo-Chemical module analyzes essentially the heat transfer from
the surrounding air to or from the tool and composite part layup assembly.
Further, the heat generated from within the part due the exothermic chemical
reaction that takes place in the curing resin is also considered. Following is
the governing equation for the thermo-chemical analysis:
(1)
where,
The expression 𝜕𝛼𝜕𝑡 is given by the Scholz equation for cure kinetics as follows:
(2)
and
(3)
25.
Modeling and simulation of process induced deformations in fiber reinforced polymer (FRP) matrix composites
The values for the various terms in the above equation are given in Table 2.
Table 2. Equation parameters and their values
Parameter
Values
Initial fiber volume fraction
Vf = 0.574
ρr = 1.3 × 103 kg/m3
Resin nominal density
HR = 5.4 × 105 J/Kg
Resin heat of reaction
∆E = 66.5KJ/gmole
Activation energy
A = 1.53 × 105s–1
Pre-exponential cure rate coefficient
m = 0.813
First exponential constant
n = 2.740
Second exponential constant
C = 43.1
Diffusion constant
Critical degree of cure at T=0 K
Constant accounting for increase in critical
resin degree of cure with temperature
αC0 = –1.684
αCT = 5.475 × 103 K–1
Stress-Deformation Module
The stress-deformation module analyzes the residual stresses and strains in
the composite part during the cure cycle. As described earlier, the residual
stresses and PID are caused due to the difference in the thermo-mechanical
properties of the resin and the fibers, volumetric shrinkage of the resin during
cure, and tool-part interaction. In COMPRO, the constitutive behaviour of
the resin is modelled as that of a fully visco-elastic material.
The governing equation for a stress-deformation analysis is expressed as a
function for the potential energy for a system as given below:
(1)
where,
U
Ω
ε
σ
D
26.
Internal work
Work done by external forces
Strain tensor
Stress tensor
Material stiffness matrix
(2)
ε0
σ0
u
X
qs
Free/thermal stress tensor
Initial stress tensor
Displacement vector
Body forces
Surface forces
Modeling and simulation of process induced deformations in fiber reinforced polymer (FRP) matrix composites
Present work
The parametric study is done on L-section (two flanges and a 900 corner)
and engine compartment geometry. The L-section geometry is shown in
figure 1. The pre-preg material used in all cases is HEXCEL AS4-8552.
Fig. 1 L-section geometry
Fig. 2 Cure cycle
Fig 1
Fig 2
Effect of Tool radius
In the present study, an attempt has been made to study effect of tool radius
on spring-in for L-section component as shown in Figure 1. The tool radius
of component varied from 3 to 6 mm in step of 1 mm, and at each radius
spring-in, simulation has been performed by keeping all other parameters
constant, and the spring-in is obtained.
The other parameters include; Composite thickness is 4 mm (20 plies) and
Layup orientation is [0, 90] s, Tool material is aluminium, a dual-hold cure
cycle is employed, with a peak hold temperature of 180°C, and a cure cycle
duration of 18300 s as shown in Figure 2.
Fig. 3 Tool radiuses vs. Spring-in
Figure 3 shows the increase in spring-in with respect to increase in tool
radius. The reason for spring-in is the huge amount of stress generation in
27.
Modeling and simulation of process induced deformations in fiber reinforced polymer (FRP) matrix composites
the corner region. Hence, with an increase in tool radius the corner region
gets increased thus with an increase in corner region, stresses also get
increased causing part to distort more to relieve stresses.
Effect of Thickness Variation
The effect of variation of thickness on spring-in during composite processing
has been studied on L-section geometry shown in Figure 1. The thickness of
component varied as 1.6 mm (8 plies), 4.0 mm (20 plies) and 8.0 mm (40 plies)
and at each component thickness spring-in simulation has been performed by
keeping all other parameters constant and spring-in is obtained. The other
parameters includes; Tool radius is 5 mm and Layup orientation is [0, 90] s,
Tool material is aluminium, The cure cycle duration is 18300 s as shown
in Figure 2. It is observed from Figure 4 that the thickness also affects the
spring-in. It is seen that the spring-in decreases as component thickness
increases. Therefore, the results obtained attribute to the fact that the thin
parts relieve stresses better than thicker components, since deformation
obtained in case of thinner part is more. This trend is corroborated by the
observations of the other researchers from the literature.
Fig. 4 Thicknesses vs. Spring-in
Effect of Tooling
In the present study, an attempt has also been made to study effect of tool
material on spring-in, to find out how composite part distorts, when coefficient
of thermal expansion is taken into account.
a) L-Section geometry
Tooling material varied as aluminium and invar (CTE Invar < CTE Aluminium)
and separate simulation is performed for each tooling material. The tooling
material is varied in by keeping other parameters constant; Composite
thickness = 4mm (20 plies) and Layup orientation = [0, 90] s, Tool radius
= 5 mm, the cure cycle is dwell hold as shown in the Figure 2. Spring-in
obtained for L-section geometry is shown with the help of Figure 6. It is
observed from the Figure 5 that aluminium gives higher spring-in than
Invar. The reason for this is, the CTE of invar is less than that of aluminium
28.
Modeling and simulation of process induced deformations in fiber reinforced polymer (FRP) matrix composites
Fig. 5 Tool materials vs. Spring-in (L-section)
Fig. 6 L-section with spring-in
Fig 5
hence the tool and part CTE difference in case of aluminium is higher than
invar. Therefore, difference in expansion rates of tool and part in case of
aluminium is higher, which causes the more stretching of bottom ply (ply in
contact with tool) than invar. Hence, more residual stresses are generated
in the composite part to be produced, which results into more spring-in.
The reduction in spring-in by using invar is 8.5%.
Fig 6
b) Engine - Compartment geometry
The engine compartment geometry with specifications is shown in Figure
7. The engine compartment is expanding in two directions, thus having two
different radii namely, front and back where the back radius is greater in
magnitude than that of the front radius. The composite part is a 4 mm (20
plies) and ply layup considered for this geometry is [0, 90]s.
Fig. 7 Engine Compartment geometry
Tooling material varied as aluminium and composite tooling (CTE Composite
< CTE Aluminium ) and separate simulations are performed for each tooling
material. The spring-in obtained by finite element simulation are recorded
and is as shown in the Figure 8.
It is observed that the spring-in obtained for aluminium tooling for single
29.
Modeling and simulation of process induced deformations in fiber reinforced polymer (FRP) matrix composites
flange on front side is 2.65°, whereas on the backside of compartment springin is 3.8°. Therefore, the total spring-in is the sum of two flanges spring-in.
Hence, it is concluded that as one goes from front-side to back-side, the radius
increases, therefore, the spring-in in the same direction, also increases.
Fig. 8 Tool materials vs. Spring-in
(Engine Compartment)
It is also observed from the graph that, the spring-in obtained for front and
back portion of geometry using composite tooling is very less compared to
aluminium tooling (i.e. by using composite tooling the reduction in springin for front portion is 93.5 % and reduction in spring-in for back portion is
57.36 %). Hence, the effect of tooling as well as radii is seen in this case of
geometry. Therefore, from above result, it is concluded that by using tool
material with CTE as close as to part to be made, less spring-in can be ensured.
These findings also corroborate the trends in the literature.
Tool Compensation
Further in this work, the effect of tool-compensation is studied for the
L-Section. In the case of L-section, the spring-in for one flange is 0.49°. In
order to get the desired dimensions, the tool compensation is required.
Therefore, to compensate the tool, angle of the tool in the corner region is
increased from 90° to 90.49° and new analysis is then performed with the
modified tool geometry, and the composite spring-in in that case is found
to be 0.50°. Therefore the difference between the desired section surface
and the actual surface is 0.01°.
This is a significant change over the previous value of 0.49°. Similarly, the
tool compensation is done on all the geometries to achieve close tolerance
components.
Conclusions
Based on this work the following conclusions are derived.
• The effect of radius variation shows that, with an increase in tool radius
there is an increase in spring-in. This is because the corner portion of the
part is more sensitive to the spring-in.
30.
Modeling and simulation of process induced deformations in fiber reinforced polymer (FRP) matrix composites
• The thickness variation shows that, thicker parts undergo less spring-in
than thinner parts. This can be attributed to the fact that the thinner
sections can relive residual stresses better than the thicker sections, as
they are less stiff in the corner regions.
• Using tooling CTE (coefficient of thermal expansion) as close as possible
to parts CTE, lesser spring-in can be ensured.
• By compensating tool, it is possible to achieve good dimensional accuracy
to avoid fit-up problem during assembling of an aircraft structure.
References
[1] Crolyne A., & Fernlund G. (2002), Spring-in and Warpage of Angled Composite Laminates. Composites Science and Technology, vol. 62 , 1895-1912.
[2] G. Fernlund & Poursarti A. (2003), Residual Stress, Spring-in and Warpage in Autoclaved Parts, ICCM 14 Conference Proceedings, San Diego.
[3] M.T. Cann & DO Adams (2001), Effect of part-tool interaction on cure distortion of flat composite laminates, SAMPE Technical conference, Long Beach.
[4] Dong C. (2010), A parametric study on the process-induced deformation of composite T-stiffener structures, Composites: Part A 41, 515–520.
[5] Kappel E., Sefniak D., & Huhne C. (2013), Process distortions in prepreg manufacturing of an experimental study on CFRP L-profiles, Composite Structures 106 , 615-625.
[6] Johnston A. (1997), An Integrated Model of the Development of Process-Induced Deformation in Autoclave Processing of Composite Structure, University of British Columbia, Vancouver, Ph.D. Thesis.
[7] G. Fernlund, Rahman, N. R.Courdji, Bresslauer M., Poursartip A., Willden K., et al. (2002), Experimental and numerical study of the effect of cure cycle, tool surface, geometry, and lay-up on dimensional fidelity of autoclave-processed composite parts, Composites part-
A 33 , 341-351.
31.
TECHNOLOGY UPDATES
IR. BEY VRANCKEN
Dept. of Materials Engineering (MTM),
KU Leuven, Belgium
Selective Laser Melting (SLM):
Process and Applications
PROF. DR IR. JAN VAN HUMBEECK
Dept. of Materials Engineering (MTM),
KU Leuven, Belgium
DR. IR. AKHILESH K. SWARNAKAR,
Dept. of Materials Engineering (MTM),
KU Leuven, Belgium
Introduction
Additive Manufacturing (AM) is receiving widespread attention as a key
part of the third technological revolution. While the first revolution revolved
around mechanization of labor and the second revolution brought about
mass production, the so-called third industrial revolution encompasses the
digitization of manufacturing and society as a whole. For example, starting
from a virtual CAD model, AM allows the production of this model in a nearnet-shape way by adding material where needed rather than subtracting
from the unnecessary. According to the report published in 2014 by Wohlers
Associates, Inc., the AM industry was worth 3.07 billion US dollars in 2013
and has recorded an increase of 34.9% compared to 2012. This number is
expected to exceed $7 billion by 2016, with a double digit growth percentage
for many years to come[1]. However, the metal AM market comprises only
a small percentage of all AM revenues, but is expected to grow faster than
the AM industry average.
This article gives a brief overview of the main advantages and the most
important parameters that highlight the resulting mechanical properties
and applications in Additive Manufacturing.
Process aspects
Selective Laser Melting (SLM) is an AM technique by which complex shaped,
fully functional metal parts can be produced. A high power laser locally melts
successive layers of powder according to 2D slices extracted from a 3D CAD
model. The highly localized heat input allows full melting of any metal, even
tungsten or tantalum.
SLM and AM in general possess many advantages compared to the traditional
manufacturing techniques such as casting, milling or forging. The layer
wise build up enables designer freedom of shapes and parts. Geometrically
complex designs such as scaffold structures, conformal cooling channels and
internal cavities can lower the weight of products or increase performance,
both of which are factors of major importance in aerospace. Moreover, the
lead time is greatly reduced. While the actual manufacturing of a part is
not particularly fast, the preparation time is reduced by the digital nature
of the SLM process. Lastly, contrary to subtractive techniques where the
eventual part may only comprise of 10% of the material of the block it was
made from, SLM has material use efficiency. Thus any unused powder is
sieved and recycled with minimal amounts of waste, leading to material
usage of 90% and more in SLM technique.
The SLM process is schematically represented in Fig. 1 The feed container
rises to expose fresh powder to the scraper, and the build platform is lowered
32.
Selective Laser Melting (SLM): Process and Applications
by one layer thickness, typically between 20 and 100 µm thick. A layer of
powder is deposited by a roller or scraper and the excess powder is caught
in an overflow container. Using a set of mirrors, the laser is then deflected
onto the powder bed surface. An f-θ lens ensures that the focal point of the
laser is always located on the powder surface. Parts are always attached
to a base plate to fix them during the build process and to minimize any
warping caused by residual stresses.
Fig. 1 Schematic representation
of the SLM process
Several parameters, both adjustable and fixed, affect the quality and properties
of the produced parts. These parameters are summarized in Table 1.
Table 1: Important parameters that can be varied to optimize the quality of SLM parts
Parameter
Symbol
Typical value
Laser Power [W]
P
50-300
Scan Speed [mm/s]
v
100-1500
Scan Spacing [µm]
h
50-100
Layer Thickness [µm]
t
20-100
Scan Strategy
Zigzag,
Island Scanning
Description
Comment
Main adjustable parameters to optimize
the density. These parameters cannot be
adjusted independently without affecting
the quality of the part.
The pattern that
the laser follows
to scan one layer.
Can/Should be
rotated between
layers.
The first goal in successfully processing a material via SLM is to obtain
near full density, above 99.5% of the theoretical density. This is typically
achieved by varying the four main process parameters: laser power
[W], scan speed [mm/s], scan spacing [µm] and the layer thickness [µm].
33.
Selective Laser Melting (SLM): Process and Applications
These parameters are self-explanatory except for the scan spacing, which is
the distance between adjacent scan vectors in one layer (refer Fig. 2). This
distance should be smaller than the width of the melt pool to ensure good
overlap between the tracks and to avoid aligned porosity.
Fig. 2 Different scan strategies.
Top: zig-zag scanning. Bottom: Island scanning,
in which the area is divided into smaller
subsections which are scanned subsequently
The laser power and scan speed determine the energy input per length unit
[J/mm]. This energy input should be large enough to create a melt pool of
sufficient depth, larger than the layer thickness, to fuse the layers together.
SLM machines usually feature a laser of up to 400W, but due to new
developments in laser technology the current trend is to introduce higher
power lasers, up to 1kW. These lasers will facilitate processing materials
that do not absorb the laser power well and/or have a high thermal conductivity,
such as Al alloys and Cu.
Apart from high power lasers, another aspect of recent and future SLM
machines is the increasing amount of quality control. (Infra-red) camera
systems that monitor the melt pool dimensions, temperature and the powder
layer are currently being used to implement online feedback control.
Due to the localized heat input, thermal gradients and cooling rates can be as
high as 106 K/m and 106 K/s. These large gradients lead to thermal stresses,
which in turn create either micro - macro cracks or cause deformation of
the part. Problems with residual stresses, along with availability of suitable
powder and laser absorption issues, are one of the major factors for the
limited amount of materials that are processable via SLM.
Properties
The thermal gradients create unique microstructures unlike any found
after casting or forging or any other manufacturing technique. In Fig. 3a,
the equiaxed microstructure of hot rolled Ti-6Al-4V consists of globular,
light α grains, with about 10% darker β phase at the triple points. This
microstructure is desirable for its adequate strength and ductility and other
mechanical properties. However, the microstructure of Ti6Al4V material
produced by SLM consists of columnar prior β grains that grew more or
less parallel to the building direction (vertical), as shown in Fig.3b. These
grains grow across multiple layers, up to several millimeters long, and have
a width more or less equal to the hatch spacing. The insert shows that the β
phase, stable at high temperature, has fully transformed to a fine plate like
martensite called α’.
Fig. 3 TMicrostructure of Ti6Al4V.
a) Rolled and mill annealed, equiaxed
microstructure, b) SLM produced,
martensitic microstructure
34.
Selective Laser Melting (SLM): Process and Applications
As the microstructure is very fine, the SLM produced material is stronger
than the conventional material. The trade-off for the high strength is a
lower ductility, as is evident from the stress strain curves in Fig.4. Other
materials produced by SLM are at least equally strong and equally ductile
as their conventional counterparts, and can be made superior through the
use of proper heat treatments. For Ti-6Al-4V, a heat treatment is needed to
increase the ductility. To achieve optimal results, the heat treatment needs
to be adjusted because the microstructure of SLM produced material differs
from the conventional microstructure. For example, by applying a solution
heat treatment to AlSi10Mg produced via SLM, the fine microstructure and
high hardness is lost, which cannot be recuperated by aging.
Fig. 4 Stress strain curves for Ti-6Al-4V produced
via SLM compared to curves for conventional
material [2]
Additionally, other properties such as fatigue, fatigue crack growth rate and
fracture toughness of SLM produced Ti-6Al-4V are still a topic of research.
Results thus far have indicated that these properties are either equal or
below those of conventional material. However, applying a HIP treatment
will increase the fatigue limit substantially up to the point where the SLM
material is as good as conventional material.
Applications
Several industrial sectors have shown great interest in AM, for various
reasons. The medical industry seeks to take advantage of the geometrical
freedom to produce patient specific implants. This type of mass customization
is already used for nearly 100% of cochlear implants, and is increasingly
used for dental applications or even complicated hip replacements. In the
latter case, intricate porous structures at the surface of the part can enhance
growth of bones and lead to a better fixation of the implant. Materials of
interest are Ti-6Al-4V, CoCr and various polymers. The oil and gas sector can
also benefit by being able to produce intricate channels inside a functional
part made with a Ni-based super alloy.
Weight reduction is the main reason for the increased interest from the
aerospace and automotive racing industry. By optimizing the design, often
35.
Selective Laser Melting (SLM): Process and Applications
done by using topology optimization software, the weight of parts can be
drastically reduced while leaving the structural performance unchanged.
The weight reduction can be achieved for numerous components of an
aircraft. Once of major step towards using the AM technology in aerospace
sector is replacing the non-critical, polymer parts by AM equivalents. In
this context, Airbus, the major aircraft manufacture in Europe has recently
announced that the new A350 XWB will feature more than 1000 different
3D printed parts. The next step is to replace semi-critical components that
have to bear some structural loads. Hinge brackets are an example of these
kinds of parts. A study by EADS demonstrated that by replacing some of the
hinge brackets in an Airbus A320, a weight reduction of approximately 10
kg could be achieved per aircraft [3].
Fig. 5 A case of typical combustion chamber
(prototype) fabricated by SLM of a compact inspace satellite (220 mm in height and 200 mm
diameter at the base). Image courtesy of
3D Systems –Layer Wise [4]
A third and final class of parts for which production through AM is beneficial
are complex, critically loaded parts. Not only would design optimization lead
to a reduction in weight, but also an improved efficiency. One such example
of a satellite combustion chamber design is shown in Fig. 5, measuring 220
mm in height and 200 mm diameter at the base. The chamber is normally
made with thick walls to accommodate the stresses during launch, but is of
no further use during operation. Using a porous mesh structure (only 12%
density compared to solid material), the structural loads can be absorbed at
a greatly reduced weight. The prototype part shown in Fig. 5 is made out of
Ti-6Al-4V, but the actual part would be made out of a refractory metal such
as tantalum or tungsten to withstand the heat during combustion.
Due to the strict safety demands in the aerospace sector, research is still
ongoing to validate the use of AM for this last class of critical parts. Ultimately,
turbine blades are an ideal candidate of a part to be produced via additive
manufacturing. The intricate shape and internal channels are easily produced
via AM. Moreover, one-off replacement parts could be produced instead of
having to order a whole new set of blades, lowering maintenance cost and
time. An example of a relatively critical part in a jet engine is the fuel nozzle
of the new LEAP engine by GE. Roughly 30.000 nozzles will be produced by
a whole factory of metal AM machines. The AM fuel nozzle not only weighs
25% less, but also increases fuel use efficiency and is five times more durable
[5]. As another example of a part out of the second class with semi-critical
loading, Airbus has decided to use AM to produce titanium brackets in the
future A350 airplane because of the weight reduction but also the possibility
to quickly produce spare parts on demand [3].
Apart from the multitude of components, through which benefits are achieved
by weight savings and better performance, perhaps the greatest added value
of AM for aviation and aerospace is the reduced lead time for component, up
to 80%. Moreover, the number of parts that need to be kept in inventory can
also be reduced. Lastly, Electron Beam Melting is an AM technique similar
to SLM but using an electron beam rather than a laser to melt the powder.
Using EBM, low pressure turbine blades made of γ-titanium aluminide (TiAl)
can be manufactured. However, this is still in the development phase[6].
36.
Selective Laser Melting (SLM): Process and Applications
Conclusion
Selective Laser Melting is part of a rapidly expanding industry, offering
more design freedom, shorter lead times and a reduced need for tooling
because of the near net shape production. Several process parameters
affect the final quality of the part, with properties at least equal to those
of cast material, and in some cases surpassing those of wrought parts. The
possibility to optimize designs and associated increased efficiency and
reduced weight are beneficial for many industrial sectors including aerospace.
References
[1] Wohlers Associates, Inc., Wohlers Report. 2014.
[2] B. Vrancken, L. Thijs, J.P. Kruth, J. Van Humbeeck, Heat treatment of Ti6Al4V produced by Selective Laser Melting: Microstructure and mechanical properties. Journal of Alloys and Compounds, 2012. 541(0): p. 177-185.
[3] Press Release - Printing the future: Airbus expands its applications of the revolutionary additive layer manufacturing process. 2014; Available from: http://www.airbus.com/.
[4] 3D Systems - LayerWise. Available from: http://www.layewise.com.
[5] GE Additive Manufacturing( http://www.ge.com/stories/advanced-manufacturing).
[6] ARCAM, EBM in Aerospace (http://www.arcam.com/solutions/aerospace-ebm/).
37.
AEROSPACE NEWS BRIEFS
NASA's 10-engine electric plane
completes flight test
In one of the recent developments, NASA has developed
the Greased Lightning or GL-10 prototype which is a
battery –powered plane with 10 engines. This aeroplane
can both take off and land like a helicopter as well as
fly efficiently like an aircraft. This plane could be used
for delivery of small packages or vertical takeoff and
landing, long endurance surveillance for agriculture,
mapping and other applications. Research is ongoing
for a scaled up version which would be a good option
for one to four- seater person size personal air vehicle.
The GL-10 is currently in the design and testing phase.
http://www.brahmand.com/news/NASAs-10engine-electric-planecompletes-flight-test/13916/1/18.html
A huge breakthrough in nuclear fusion
A technological breakthrough in alternate energy has
come about in developing a power source based on nuclear
fusion, and the first reactors, small enough to fit on the
back of a truck, could be ready for use in some years from
now. This technology uses the energy released during
nuclear fusion when atoms combine into more stable
forms. The energy created through fusion is 3-4 times
more powerful than the energy released by fission.
This potential energy source is a part of the comprehensive
approach to solving global energy and climate change
problems. The use of this energy would produce far less
waste than coal-powered plants.
http://www.businessinsider.com/andrea-shalal-lockheed-nuclearfusion-breakthrough-2014-10
Carbon-fiber epoxy honeycombs mimic
the material performance of balsa wood
Balsa wood has been used for centuries to have lighter
and stiffer material for producing sandwich panels in
larger structures. However, it is expensive and natural
variation in the grain structure could be impediment to
the required performance. Recently, material scientists
at Harvard and Wyss universities have developed cellular
composite material with superior properties. It mimics
38.
the balsa wood structure where most of the space is
empty and only walls carry the load. Using 3D printing
technology and fiber-reinforced epoxy based ink, they
were able to achieve strength, twice that of the best
printed polymer composite. Key factor in the structure
is the ability to control fiber orientation which allows
better component design and material efficiency.
http://www.seas.harvard.edu/news/2014/06/carbon-fiber-epoxyhoneycombs-mimic-material-performance-of-balsa-wood
Composite plane life cycle assessment
shows lighter planes are the future
Composite plane life cycle assessment has been
carried out for the first time by the Universities of
Sheffield, Cambridge and University College London
and extrapolated the results to the global fleet. This
research was later published in the International Journal
of Life Cycle Assessment and estimated that by the year
2050, composite planes could reduce emissions from the
global fleet by 14-15 % relative to a fleet that maintains
its existing aluminium based configuration. Composite
planes will also help resolve the industry target to halve
carbon dioxide emissions for all aircrafts by 2020.
http://www.sciencedaily.com/releases/2014/12/141216100517.htm
Unidirectional carbon fiber prepreg
tapes just 15 gsm
A group of researchers at North Thin Ply Technology
(NTPT), Penthalaz-Cossonay, Switzerland has developed
possibly the thinnest prepreg tape in the market. This is
an unidirectional prepreg tape with an areal weight of 15
gsm. NTPT achieved this by spreading an intermediate
modulus carbon fiber and adding the high Tg epoxy resin
ThinPreg 120EPHTg – 402. This prepreg can be used
to create lightweight sandwich panels to be used for
ultralight aircrafts, UAVs, other aerospace applications
and rigid wings for racing yachts.
http://www.compositesworld.com/products/unidirectional-carbonfiber-prepreg-tapes-just-15-gsm
39.
40.
41.
ELEVONS are aircraft control surfaces that combine the functions of the elevator
(used for pitch control) and the aileron (used for roll control), hence the name.
All postal/courier
correspondences to NCAIR should
be made on the adjacent postal address:
National Centre for Aerospace Innovation and Research (NCAIR),
2nd Floor, Pre-engineered building, Opp. Power house,
IIT-Bombay, Powai, Mumbai-400076
Disclaimer: The views and opinions expressed in this newsletter are those of the respective authors. The content of this newsletter is solely for the purpose of
dissemination of knowledge and not for any commercial purposes. The articles in this newsletter should not be utilized in real-world analytic products, as they
are based only on very limited and open source information, without the prior consent of the authors.
42.