International Journal on Mechanical Engineering and Robotics (IJMER)
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Optimization of Process Parameters of Drilling in Ti-Tib Composites
using Taguchi Technique
Tamilselvan, Raguraj
Dr.Mahalingam College of Engineering and Technology, Pollachi, Tamilnadu, India
Email: Selvan2012@gmail.com,ragurajmech@gmail.com,
Abstract: Titanium and its alloys exhibit excellent
combination of mechanical and thermal properties, which
have made them material of choice in various aerospace,
defence and corrosion, resistant application. The Ti
composite is processed through powder metallurgy route
namely by Spark Plasma Sintering, Hot Isostatic Pressing
and Vacuum Sintering process. Two different targets
volume percentages of TiB(20vol%&40vol%) have been
prepared. The present work focuses on finding the drilling
characteristics of the Ti-TiB composite produced by the
above three process. The drilling tool dynamometer are to
be used for finding the thrust force, overcut, taper and
circularity of the composites. The Taguchi’s experimental
design and Analysis of Variance (ANOVA) techniques have
been implemented to understand the effects, contribution,
significance and optimal machine settings of process
parameters, namely, spindle speed, feed rate, process, and
drilling material. The performance characteristics of the
drilling were evaluated through thrust force, overcut,
circularity and taper. The outcome of this project revealed
that spindle speed and feed rate have the most significant
impact on the dimensional accuracy of the hole, spindle
speed and feed rate controls the thrust force. Drilling
material, process influences less contribution on drilling of
Ti-TiB composites.
Keywords:Ti-TiB composites, drilling, Taguchi method,
Anova, Optimization
I. INTRODUCTION
Titanium is a chemical element with the symbol Ti and
atomic number 22. It has a low density and is a strong,
lustrous, corrosion-resistant (including sea water, aqua
regia and chlorine) transition metal with a silver colour.
Titanium can be alloyed with iron, aluminum,
vanadium, molybdenum, among other elements Ti
produce strong lightweight alloys for aerospace (jet
engines, missiles, space craft), military , industrial
process (chemicals and petro chemicals, desalination
plants, pulp and paper), automotive . agri-food, medical
prostheses, orthopedic implants ,dental and endodontic
instruments and files, dental implants, sporting goods
and jewelers, mobile phones and other applications.
ratio of any metal. In this unalloyed condition, titanium
is as strong as some steels, but 45% lighter. There are
two allotropic forms and five naturally occurring
isotopes of this element, 46Ti through 50 Ti, with 48Ti
being the most abundant (73.8%). Titanium’s properties
are chemically and physically similar to zirconium, as
both of them have the same number of valence electrons
and are in the same group in the periodic table.
1.2 TITANIUM COMPOSITES
Titanium and an alloy comprising mainly of titanium
have inherent excellent properties such as lightweight
property, high strength (high specific strength) and
corrosion resistance, titanium materials are used in
various fields for application not only as industrialized
materials such as fuselage materials and component
materials for aircraft , materials for heat exchangers and
electrode materials, but also as building materials such
as roof materials and wall materials, and materials for
goods of livelihood such as materials for decoration
articles, sporting goods and equipment for leisure time
amusement.
However, titanium materials are expensive compared
with other materials for use (e.g. about 10 times higher
in cost than stainless steel generally used as a corrosion
resistant materials) and are poor in process ability. For
these drawbacks, titanium materials are not replacing
other materials and unlikely to be used in increasing
amounts despite their excellent properties as described
above. To reduce the costs of expensive titanium
materials, an attempt was made to provide a “composite
material” which comprises an inexpensive material
covered with a thin sheet of titanium material by means
of a metallurgical or mechanical process. The attempt
was partly realized for commercial products.
1.3 TITANIUM DIBORIDE
TiB2 is the most stable of several titanium boron
compounds. The material does not occur in nature but
may be synthesized by carbothermal reduction if TiO2
and B2O3.
The two most useful properties of the metal form are
corrosion resistance and the highest strength-to-weight
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International Journal on Mechanical Engineering and Robotics (IJMER)
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As with other largely covalent bonded materials, TiB2 is
resistant to sintering and is usually densified by hot
pressing or hot isostatic pressing. Pressure less than
sintering of TiB2 can achieve high densities but liquid
forming sintering aids such as iron, chromium and
carbon are required.
packing arrangement of Ti and TiB2 Particles in the
starting mixture were suggested for formation of varied
morphologies in different composites.
TiB2 is resistant to oxidation in air up to 1000oc. It is
also resistant to HCl and HF but reacts with HNO3. It is
readily attacked by alkalis. Hot pressing of TiB2 ( with
small additions of metallic or carbide sintering aids) is
carried out at 1800-1900oc and achieves close to
theoretical density. Pressure less sintering requires
higher levels of sintering aids and sintering temperatures
in excess of 2000oc
III. SELECTION OF COMPOSITIES:
1.4 Ferro Molybdenum
It is a beta-stabilizing agent. It has been added to the
titanium composites in order to improve the ductility of
the product.
The volume fraction which we used was 15% .
II. RELATED WORKS:
Many reviews were done to know more about titanium
composites. The journals and the content were as
follows
J. Prasannaet al. [1] concluded that thrust force
decreased with the increase in feed rate. The spindle
speed and the feed rate had almost equal contribution
towards minimizing the thrust force for Ti–6Al–4V plate
of thickness 0.4 mm.Even though lowfeed rate produced
good circularity, it impaired overcut and produced
higher thrust force. The increase in feed rate plays a
predominate role in the drastic reduction of overcut.
Higher spindle speed engendered to lesser thrust force
and produced holes with good circularity and lesser
taper angle.
The first step was to select the suitable titanium
composite. The suitable titanium composition selected
was Ti(70%), FeMo (15%), TiB2(15%) .
The next step was to mix the titanium powders and the
composites with the help of ball milling. This process
will take around 20 hrs for the perfect binding. The steel
balls are used for mixing the powders. The blended
titanium was then fabricated into titanium specimens by
means of sintering. Ferro Molybdenum is a betastabilizing agent. It has been added to the titanium
composites in order to improve the ductility of the
product.
The next process is to fabricate the titanium by means of
Hot Isostatic Pressing, Spark Plasma Sintering and
Vacuum Sintering. After fabricating, the titanium pieces
are subjected to wire cut EDM to get the required shape.
Ti+TiB2
2TiB
Compositions Selected
Ti
(Wt%)
70
FeMo
(Wt%)
15
TiB2
(Wt%)
15
Target Volume of
TiB(Wt%)
40
Wire Cut EDM process was conducted at New G.M.
Automations, Coimbatore. Ti-TiB Composites produced
by the three processes were cut into coin shape to a
thickness 1.5mm and diameter 9mm. Fig .1 shows the
work piece before and after wire cut EDM process.
Researchers have proved Taguchi’s experimental design
and ANOVA techniques as an effective tool in
analyzing the effect of process parameters in drilling
[13,14].This literature survey of project works in drilling
has highlighted the dearth of information available to
understand the effect of process parameters on the
performance of drilling ( 3mm) in Ti–TiB composites
by conventional dry drilling process.
K.S.Ravichandran and S.S.Sahay [15] fabricated Ti-TiB
Composites with different volume fractions of TiB by
hot pressing Ti-powders. In all the composites, TiB was
the predominant boride phase. The composites with
relatively high TiB content also revealed the presence of
an un reacted phase T the measured x-ray integrated
intensities of various planes of Ti,TiB2 phases agreed
reasonably well with the computed data. The volume
fraction of TiB phase in
the composites were
determined from the integrated intensities by the direct
comparison method. A mechanism on the basis of
crystallography of TiB preferential diffusion of TiB in
the axial direction of TiB whiskers and the bimodal
Fig :1 Work piece before and after wire cut EDM
process
IV. DESIGN OF EXPERIMENTS
Taguchi Method
Taguchi has envisaged a new method of conducting the
design of experiments which are based on well-defined
guidelines. This method uses a special set of arrays
called orthogonal arrays. These standard arrays stipulate
the way of conducting the minimal number of
experiments which could give the full information of all
the factors that affect the performance parameter. The
crux of the orthogonal arrays method lies in choosing
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ISSN (Print) : 2321-5747, Volume-2, Issue-4,2014
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International Journal on Mechanical Engineering and Robotics (IJMER)
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the level combinations of the input design variables for
each experiment.
4.1 Orthogonal array
While there are many standard orthogonal arrays
available, each of the arrays is meant for a specific
number of independent design variables and levels . For
example, if one wants to conduct an experiment to
understand the influence of 4 different independent
variables with each variable having 3 set values ( level
values), then an L9 orthogonal array might be the right
choice. The L9 orthogonal array is meant for
understanding the effect of 4 independent factors each
having 3 factor level values. This array assumes that
there is no interaction between any two factors. While in
many cases, no interaction model assumption is valid,
there are some cases where there is a clear evidence of
interaction.
The Table.1 shows an L9 orthogonal array layout using
Minitab software. There are totally 9 experiments to be
conducted and each experiment is based on the
combination of level values as shown in the table. For
example, the third experiment is conducted by keeping
the independent design variable 1 at level 1, variable 2 at
level 3, variable 3 at level 3, and variable 4 at level 3.
Table :1 L9 Orthogonal array layout using Minitab
software
5.1 EXPERIMENTAL SETUP
The input and output parameters for the drilling of TiTiB composites are given below.
5.2 Input Parameters
•
Speed
•
Feed
•
Process
•
Drilling material
5.3 Output Parameters
•
Thrust force
•
Overcut
•
Taper
•
Circularity
Table :2 Experimental parameters and their levels
Input
parameters
Feed
rate(mm/rev)
Speed(rpm)
Minimum
Mean
Maximum
0.05
0.07
0.08
600
800
1000
5.4MACHINING SETUP
The drilling experiments were conducted on a three axis
Computer Numerical Control (CNC) vertical machining
centre. Fig:2 shows the CNC machine during drilling
process. The thrust force measurements were made
using a Kistler dynamometer and simultaneously the
values were sent to Kistler charge amplifier and stored
in a personal computer. The hole quality assessment was
done by Video Measuring Device.
Fig:2CNC Machine during drilling process
5.5 MEASUREMENT PROCEDURE
5.5.1 Overcut
V. .EXPERIMENTAL DETAILS
In this experiment, small holes of diameter 3 mm were
drilled on Ti-TiB composites of thickness 1.5 mm under
varying combinations of cutting process parameters
which include spindle speed, feed rate and process and
drilling material. The drill bit used was solid carbide
tool, diamond coated HSS and cobalt coated HSS. The
accuracy of the drilled holes was analyzed in terms of
overcut, circularity and taper angle. As thrust force
significantly affects the machining dynamics, it forms an
indispensable parameter to determine and analyze
during a machining process.
Overcut is the difference between the radius of the
machined hole and the drill bit radius. Since the
periphery of the machined hole may not be a perfect
circle, the average radius of the machined hole was
considered for calculating the overcut. As the entry hole
radius was found to be the larger compared to the exit
hole radius, the entry hole was considered for the
overcut measurements. Using VMS, twelve points were
located on the circumference of the hole to obtain the
average radius of the entry hole.
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International Journal on Mechanical Engineering and Robotics (IJMER)
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5.5.2 Circularity
The roundness error of the machined hole is proposed in
terms of circularity. The error of circularity is defined as
the distance between the minimum circumscribing circle
diameter and the maximum inscribing circle diameter.
The circularity error exists both at the entrance and the
exit of the machined hole, their maximum value was
used for evaluating the circularity of the machined hole.
5.5.3 Taper
contribution of each process parameter on the
performance characteristics were found out using
ANOVA method. The objective of this project was to
determine the process parameters required to achieve
minimum thrust force, overcut, circularity and taper.
Therefore, the quality characteristic of ’smaller is better’
for all performance characteristics were engaged in this
study. The ANOVA results were developed by using the
statistical software MINITAB. Work pieces after drilling
is shown Fig.5,
Taper angle between the entry and exit surface was
calculated by using the formula given below
Tanθ = D-d/2L
Where D is the average diameter of the entry surface, d
is the average diameter in exit surface. L is the depth of
cut.
5.6 OPTIMIZATION AND MODELING
The experiments were conducted using Taguchi L9
design approach. The optimal parameters were
determined by using S/N graphs. The significance and
Fig:5 Work piece after drilling (SPS process)
3.Experimental results of L9 array of drilling of Ti-TiB composites with CNC kistler dynamometer.
Feed (mm/
Speed
Process
Drilling material
Thrust
Overcut Taper
Rev)
(rpm)
force (N)
(µm)
(deg)
0.05
600
SPS
Solid carbide
58.65
66.01
3.22
0.07
600
HIP
Diamond coated HSS 52.88
62.89
1.11
0.08
600
Vacuum
Cobalt coated HSS
45.14
55.13
0.89
sintering
0.05
800
HIP
Cobalt coated HSS
41.45
44.08
2.33
0.07
800
Vacuum
Solid carbide
39.09
41.91
1.09
sintering
0.08
800
SPS
Diamond coated HSS 38.34
40.17
0.98
0.05
1000
Vacuum
Diamond coated HSS 25.56
35.77
1.51
sintering
0.07
1000
SPS
Cobalt coated HSS
22.77
36.11
1.01
0.08
1000
HIP
Solid carbide
21.41
30.44
0.77
S.
No.
1
2
3
4
5
6
7
8
9
VI.RESULTS AND DISCUSSIONS
6.1 ANOVA FOR THRUST FORCE
Analysis of Variance Thrust force (N) with respect to
Spindle speed
Source
D
F
Seq SS
Adj SS
Adj MS
F
Speed
(rpm)
2
1266.63
1266.63
633.31
35.81
Error
6
106.13
106.13
17.69
Total
8
1372.75
%
of
contributio
n
92.27%
Analysis of Variance for Thrust force (N) with respect to
Feed rate
Source
DF
Seq SS
Adj SS
Adj MS
F
Feed
(mm/rev)
2
64.3
64.3
32.1
0.1
5
%
of
contributio
n
4.68%
Error
Total
6
8
1308.5
1372.8
1308.5
Circulari
ty (µm)
55
49.22
40.87
33.43
31.76
29.65
43.44
37.32
33.14
218.1
Analysis of Variance for Thrust force (N) with respect to
Drilling material
Source
DF
Seq SS
Adj SS
Adj
MS
F
Drilling
material
2
27.5
27.5
13.8
0.06
Error
6
1345.3
1345.3
224.2
Total
8
1372.8
%
of
contributio
n
2.00%
Analysis of Variance for Thrust force (N) with respect to
process
Source
DF
Seq SS
Adj SS
Adj MS
F
Process
Error
Total
2
6
8
14.4
1358.4
1372.8
14.4
1358.4
7.2
226.4
0.03
% of
contribu
tion
1.05%
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ISSN (Print) : 2321-5747, Volume-2, Issue-4,2014
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International Journal on Mechanical Engineering and Robotics (IJMER)
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VII. CONCLUSIONS
Ti-TiB composites (1.5mm thickness) are drilled by
3mm diameter of drilling tool such as solid carbide,
diamond coated high speed steel, cobalt coated high
speed steel and the hole quality was analyzed in terms of
overcut, circularity and taper angle for various settings
of feed rate, spindle speed, process and drilling material.
The following conclusions were made
1.
Thrust force decreased with the increase in spindle
speed.
2.
The increase in spindle speed plays a predominate
role in the drastic reduction of overcut.
3.
Higher feed rate engendered to lesser taper angle.
4.
Spindle speed had the predominant contribution
towards improving circularity when compared to
the other three process parameters.
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