Journal of Minerals and Materials Characterization and Engineering, 2012, 11, 785-789
Published Online August 2012 (http://www.SciRP.org/journal/jmmce)
Drilling of TiO2 and ZnS Filled GFRP Composites
K. V. Arun1*, D. Sujay Kumar2, M. C. Murugesh3
1Department of Mechanical Engineering, Government Engineering College, Haveri, India
2Department of Studies in Industrial and Production Engineering, University B.D.T. College of Engineering, Davangere, India
3Department of Mechanical Engineering, Gowdara Mallikarjunappa Institute of Technology, Davangere, India
Received March 13, 2012; revised April 30, 2012; accepted May 21, 2012
ABSTRACT
In the present work an attempt has been made in order to investigate the drilling behavior of the TiO2 and ZnS filled
glass fabric reinforced polymer matrix composites (GFRP). Th e volume fractions in the matrix were chosen as 1%, 2%
and 3%. Drilling has been con ducted on a rad ial drilling machin e. Speed of drilling and drill tool d iameter were consid-
ered as the varying parameters with three levels. Thrust force has been considered as the output parameter and is been
measured in each combination of parameters chosen. Results reveal that, the addition of filler will increase the thrust
force developed during drilling, also results indicate that, addition of filler will increase thrust force upto 2 vol% of
filler thereafter increase in filler content result in almost constant thrust developed. Also it can be observed that, with
the increase in drill tool diameter the thrust developed also in creases.
Keywords: Fillers; Thrust Force; Drilling; GFRP; Speed
1. Introduction
Polymer matrix composites are increasingly being used
because of their high stiffness, specific strength and wear
resistance. On account of their good combinations of
properties, fiber reinforced polymer composites are used
particularly in the automotive, aircraft industries and the
manufacture of spaceships and sea vehicles [1]. It is gen-
erally known that the epoxy resins with appropriate cur-
ing agents find use as products in protective coatings,
adhesives, structural components because of their good
mechanical properties, excellent chemical resistance,
good wettability and electrical characteristics [2]. Their
use is always indicated where fluids are ineffective or
cannot be tolerated because of the possibility of con-
tamination of the product or the environment, or the lack
of opportunity for maintenance [3].
Many researchers [4-7] were reported that the wear
behavior of polymers was improved by the incorporation
solid particles. The filler materials include organic, inor-
ganic and mechanical particulate materials. The addition
of filler particles to polymer matrices can produce a
number of desirable effects, and this has been widely
been investigated in the past decades. Among polymers,
epoxy resin is widely used in production of glass fiber
composites due to their wetting power and adhesion to
glass fiber, low setting shrinkage, considerable cohesion
strength, adequate dielectric characteristics, and thermal
properties. Epoxies commonly modified by the inclusion
of inorganic-particulate fillers, such as silica, alumina,
mica or talc. Fillers are added to improv e fracture tough-
ness and electrical or heat transfer properties, to increase
resin stiffness, wear resistance, and to reduce the coeffi-
cient of thermal expansion [8].
Drilling of composite materials irresp ective of the area
of application can be considered as a critical operation
owing to their tendency to delaminate when subjected to
mechanical stresses. With regard to the quality of ma-
chined component, the principal drawbacks are related to
surface delamination, fibre/resin pullout and inadequate
surface roughness of the hole wall. Among the defects
caused by drilling, delamination appears to be the most
critical. In order to overcome these difficulties it is nec-
essary to develop procedur es to select appropriate cutting
parameters, due to the fact that an unsuitable choice
could lead to unacceptable work material degradation.
The variation of cutting forces with or without onset
damage during drilling was investigated [9] and con-
cluded that a damage-free drilling process may be ob-
tained by the proper selections of tool geometry and cut-
ting parameters. The influence of trepanning tool on
thrust force and torque when drilling GFRP has been
investigated [10]. The investigation showed that the per-
formance of the trepanning tool was superior to the con-
ventional twist drill, resulting in 50 and 10% of thrust
force and torque, respectively. In order to investigate the
effect of the drill diameter on the thrust force and torqu e,
*Corresponding author.

K. V. ARUN ET AL.
786
researchers [11] employed conventional high speed twist
drills with diameters of 8, 9, 10, 11, 12, and 13 mm to
machine a glass fibre reinforced plastic using a constant
rotational speed of 875 rpm and feed rates of 0.1 - 0.23
and 0.5 mm/rev. The results indicated that thrust force
and torque increased with drill diameter and feed rate,
due to the increase in the shear area. Increasing cutting
speed also resulted in higher thrust force and torque,
however, not to th e same extent as when feed rate is ele-
vated. Effect of drill size and feed on thrust force and
torque has been investigated [12].
From the review of previous works carried out it is
clear that, addition of filler material will improve the
wear properties of the glass fabric reinforced composites
(GFRP). Since large structures of composites cannot be
made out of single mould, composites need to be fas-
tened. Fastening of composites is done by either adhesive
joining or mechanical fastening. To join composites by
mechanical fastening, composites needs to be drilled.
Also it is known that the speed of drilling and drill tool
diameter effects the hole quality to large extent. The
quality of hole generated and delamination is directly
dependent on the Thrust force developed during the
process of drilling. Hence the present work concentrates
on the evaluation of Thrust force generated during drill-
ing, while the speed of drilling and drill tool diameter are
varied. Thrust force gen erated during drilling of unfilled,
TiO2 filled and ZnS filled composites has been recorded.
2. Materials and Experimentation
2.1. Materials
The matrix material used was a medium viscosity epoxy
resin (LAPOX L-12) and a room temperature curing
polyamine hardener (K-6). This matrix was chosen since
it provides good resistance to alkalis and has good adhe-
sive properties. The reinforcement material employed
was 7-mil E-glass fabric. The Titanium dioxide (TiO2)
amorphous powder and Zinc Sulphide (ZnS) amorphous
powder are used as filler materials.
2.2. Composite Combinations
Hand lay-up technique of laminating the composites has
been employed for composite fabrication. Two material
compositions of Glass/Epoxy (G-E) composites were
chosen namely G-TiO2-E and G-ZnS-E. Each material
composition has been fabricated for three different vol-
ume fractions, the details of the percentage volume frac-
tions of epoxy resign, glass fabric and fillers are shown
in Table 1.
2.3. Experimentation
Large plates of composites are made in order to carryout
drilling operation with 10mm thickness. Drilling has
been carried-out in a radial Drilling Machine. The drill-
ing machine is been connected to a Drill Tool Dyna-
mometer which gives the digital reading. Speed of drill-
ing and Drill tool diameters are chosen as input parame-
ters and Thr ust force is con sidered as the outpu t parame-
ter. During conducting tests the maximum Thrust re-
corded is considered as the resultant, and has been re-
corded. The summary of parameters considered for drill-
ing is shown in Table 2.
3. Results and Discussion
Composites can be joined with the help of fasteners,
preferably mechanical fastening, and to do so, it is nec-
essary to drill holes on the composite plates. Hence in the
present work drilling is considered as the machining op-
eration and carried-out on filled and unfilled composites.
Drilling holes in composites can cause failures that are
different from those encountered when drilling metals.
Delamination, fracture, break-out and separation are
some of the most common failures. Delamination (sur-
face and internal) is the major concern during drilling
composite laminates as it reduces the structu ral integrity,
results in poor assembly tolerance, adds a potential for
long term performance deterioration and may occur at
both the entrance and exit plane. Delamination can be
Table 1. Composite combinations.
Sl. No.FillerCombination or volume fractions Representation
01 - Glass Fabric 60% + E poxy 40% GE
02 Glass Fabric 60% + TiO2 1%
+ Epoxy 39% GTE-I
03 Glass Fabric 60% + TiO2 2%
+ Epoxy 38% GTE-II
04
TiO2
Glass Fabric 60% + TiO2 3%
+ Epoxy 37% GTE-III
05 Glass Fabric 60% + ZnS 1%
+ Epoxy 39% GZE-I
06 Glass Fabric 60% + ZnS 2%
+ Epoxy 38% GZE-II
07
ZnS
Glass Fabric 60% + ZnS 3%
+ Epoxy 37% GZE-III
Table 2. Summary of parameters considered for drilling.
Sl. No. Speed in rpm Drill diameter in mm
01 525 3
02 951 6
03 1625 9

K. V. ARUN ET AL. 787
overcome by finding optimal thrust force (minimum
force above which delamination is initiated). Figure 1
shows push out delamination at exit because at a certain
point loading exceeds the interlaminar bond strength and
delamination occurs. Figure 2 shows peel-up delamina-
tion at the entrance, because the drill first abraded the
laminate and then pulled the abraded material away
along the flute causing the material to spiral up before
being machined completely. This type of delamination
decreases as the drilling proceeds since the thickness
resisting the lamina bending becom es greater.
In order to know the effect of filler volume on the
drilling behavior and influence on thrust force the speci-
men are drilled for three different drill sizes and for three
different spindle speeds.
3.1. Effect of Process Parameters on the Drilled
Composite and the Drilling Performance
In order to know the effect of drill size and drilling speed
on the drilling performance, each combination of the
composites is drilled for different drill diameters and
drilling speeds. When speed is varied drill size is kept
constant and in the same way speed is kept constant
when drill size has varied.
Figure 1. Push-out delamination at exit.
Peeling
Action
Figure 2. Peel-in delamina tion at entran ce.
During drilling, a vertical force, that is, a thrust force,
is generated. This thrust force can be considered as the
sum of several components, each one rising either from
the cutting process or from the friction between material
and cutting tool. The cutting process occurs along the
cutting lips and at the chisel edge. The cutting process
along the lips generates a force on each lip that has a
force component parallel to the axis of the drill, that is,
the feed direction. Moreover, the chisel edge generates a
vertical penetration force. The friction forces arise from
two components. The first is related to the friction be-
tween the side surface of the tool and the generated hole
surface, which leads to the vertical force. The second
component is related to the friction between the chip
flow along the helical grooves, which generates the ver-
tical force. Sum-up of all this forces gives the total thrust
force acting on the d rill. Th e thru st force ob served du ring
drilling no t only d epend s on th e geometry of the d rill and
on the type of material and laminate be ing worked upon,
but also on the relation ship between the feed rate and the
cutting speed, as well as on the degree of wear of the
drill.
In the present work Thrust force is considered as the
out-put or resultant of drilling. Thrust force is measured
with the help of a calibrated drill-tool d ynamometer. The
thrust force generated is measured in each case and has
been recorded, the results of which are shown in figures
following.
Figures 3-5 show the thrust force against different
drilling speeds with respect for 3 mm, 6 mm and 9 mm
drill sizes respectively for TiO2 filled composites. From
the figures it can be observed that the Thrust generated
increases with the increase in the speed of drilling. The
common thing that can be observed in all the three cases
is that, the drilling speed is more significan t on the thrust
force, as the spindle speed increases the thrust force gen-
erated also increases. This is because of the reason as the
spindle speed increases the resisting force also increases,
after certain limit the effect of speed becomes less sig-
nificant, this can be observed from block for speed-2 and
THRUST FORCE FO R 3m m DRI LL-TiO
2
0
1
2
3
4
5
6
7
8
9
Speed-1Speed-2 Speed-3
Speed
Thrust force in Kgf
GE
GTE- I
GTE- II
GTE- III
Figure 3. Comparison of thrust force against drilling speeds
for TiO2 filled composite (3 mm).

K. V. ARUN ET AL.
788
THRUST F O RCE F O R 6 m m DRIL L
0
2
4
6
8
10
12
Speed-1Speed-2 Speed-3
Spee d
Thr u st for ce in Kgf
-TiO
2
GE
GTE -I
GTE -II
GTE -III
Figure 4. Comparison of thrust force against drilling speeds
for TiO2 filled composite (6 mm).
THRUST FO RCE FOR 9mm DRIL
0
2
4
6
8
10
12
14
Speed-1 Speed-2 Speed-3
Speed
Thrust force in Kgf
L-TiO
2
GE
GTE-I
GTE-II
GTE- III
Figure 5. Comparison of thrust force against drilling speeds
for TiO2 filled composite (9 mm).
block for Speed-3 in each of the case. The peel-in kind of
delamination can be observed in all the cases, and fiber
pull out is observed at the exit side.
Compared to unfilled and filled composites, thrust de-
veloped during drilling of unfilled composites is com-
paratively lesser with that of filled composites, and wh en
the filler content is under consideration, the effect of
filler content on thrust force is not significan t, this can be
observed from the Figures, in each block the variation in
thrust value is not much differed, this indicates that the
effect of filler is less significant on the drilling perform-
ance. As the drill size varies the thrust force increases
this is because, as the drill diameter increases the force
required by the drill to penetrate the component also in-
creases.
Observations also show that, the Thrust generated in
all the combinations of composites increases with the
increase in drill tool diameter. This is due to reason that,
with the increase in drill tool diameter the shear area
produced by drill too l also in creases, this will leads to th e
increase in Thrust generated.
Figures 6-8 show the thrust force against different
Drilling speeds with respect to 3 mm, 6 mm and 9 mm
drill sizes respectively for ZnS filled composites. From
the figures it is clear that, as the speed of drilling in-
sidering the effect of filler content, the effect of filler
content on the drilling is less significant in case of this
composites, this is because there is no much difference in
thrust force as observed during drilling. As the drill size
increases, the Thrust force required to drill the hole also
increases. The peel-in kind of delamination can be ob-
served in all the cases, and fiber pull out is observed at
the exit side.
As the dri
creases there is an increase in the thrust force also. Con-
lling speed exceeds a certain range, the
Thrust generated remains somewhat constant in all the
cases of composites, this is due to reason that at higher
speeds the heat generated will be more and this heat will
THRUST F ORCE FOR 3 mm DRIL L - ZnS
0
1
2
3
4
5
6
7
8
9
Speed-1 Speed-2 Speed-3
Spee d
Thrust force in Kgf
GE
GZE- I
GZE- II
GZE- III
Figure 6. Comparison of thrust force against drilling speeds
for ZnS filled composite (3 mm).
THRUST FO RCE FO R 6mm DRI LL-ZnS
0
1
2
3
4
5
6
7
8
9
10
Speed-1Speed-2 Speed-3
Speed
Thru st force in Kgf
GE
GZE-I
GZE-II
GZE- III
Figure 7. Comparison of thrust force against drilling speeds
for ZnS filled composite (6 mm).
THRUST F ORCE FOR 9mm DRILL- ZnS
0
2
4
6
8
10
12
Speed-1Speed-2 Speed-3
Spee d
Thrust force in Kgf
GE
GZE- I
GZE- II
GZE - III
Figure 8. Comparison of thrust force against drilling speeds
for ZnS filled composite (9 mm).

K. V. ARUN ET AL.
789
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