This document reviews research on drilling fiber reinforced polymers (FRPs), specifically focusing on glass, carbon, and natural fiber reinforced polymers. It discusses key quality aspects of drilling FRPs like thrust force, torque, delamination, and surface roughness. Various studies are summarized that examine how drilling parameters like speed, feed rate, drill geometry, and material properties influence these quality aspects. The document concludes that thrust force, torque, and delamination can be reduced by optimizing drilling parameters, and that parameters like feed rate and drill diameter significantly impact drilling performance.

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https://doi.org/10.1007/s12633-018-9764-9
ORIGINAL PAPER
Review on Machinability of Fiber Reinforced Polymers: A Drilling
Approach
S. Vigneshwaran1 · M. Uthayakumar1 · V. Arumugaprabu1
Received: 18 July 2017 / Accepted: 9 January 2018
© Springer Science+Business Media B.V., part of Springer Nature 2018
Abstract
Performance of conventional materials in diverse engineering application is not satisfactory due to the development in
products design and engineering materials. In this case, fiber reinforced Polymers (FRPs) have attracted the material
engineers with their unique properties and their expansion in various applications. The superior characteristics of the FRPs
emphasized their advancement in machining performance. So it becomes more significant to analyze their machinability
for further improvement in their machining characteristics and applications. The intention of this paper is to review the
machining response of FRPs especially on drilling. Concerning FRPs drilling operation the main aspects were focused on
glass, natural and carbon fiber reinforced polymers. Drilling damages such as delamination of plies, thrust force, and surface
quality in response to various parameter influences were also discussed in detail.
Keywords Drilling · Polymers · Delamination · Thrust force · Surface roughness
1 Introduction
Advance properties of composite material made them supe-
rior in various engineering applications like engineering
structures, aircraft parts, automobiles and in several indus-
trial applications [1]. Glass fiber reinforced polymers are
the more popular composite material and other composite
materials like high performance carbon and Kevlar fiber
reinforced composites and emerging natural fiber reinforced
polymers materials are all having similar fabrication pro-
cess. However, all these polymers differ in their machining
performance because of variation in physical and mechani-
cal properties of the reinforcement and matrix. In polymer
composites machining performance depends on the rein-
forcement characteristics like fiber orientation, fiber amount
and fiber form [2]. While fabricating of polymer compos-
ite it is more complex to form holes and slots without
affecting the reinforcement, in such cases, machining is
the only preferred technique to form complex shapes and
M. Uthayakumar
uthaykumar@gmail.com
1 Faculty of Mechanical Engineering, Kalasalingam University,
Krishnankoil 626 126, India
needed requirements [3]. Composite material because of
their non-homogenous property shows significant variation
on machining when compared to conventional materials
[4]. Further, the cutting mechanism of composite material
greatly varies with conventional material cutting mechanism
[5]. So that it becomes difficult in analyzing their machining
performance. Machining composite material can damage
the material surface due to interlaminar and intralaminar
delamination, fiber exposure, fiber crack and matrix flow
[6]. Since it become uneconomical to machine a composite
material through most of the conventional machining meth-
ods. Performance of fiber reinforced composites may also
get affected by machining conditions which concern the
life and mechanical performance of the polymers compos-
ites [7]. In recent days composite materials uses advanced
machining techniques like electrical discharge machining
[8], ultrasonic machining [9], laser cutting [10], and water
jet and abrasive water jet machining [11]. In the present
work review was done in order to understand the machin-
ing of composites especially on drilling. Further, the paper
illustrates effect of different drilling parameters on surface
roughness and delamination on glass fiber reinforced plas-
tics (GFRP), carbon fiber reinforced plastics (CFRP) and
natural fiber reinforced composite which would help in the
selection of machining parameters to reduce delamination
and trust while drilling of a composite material.

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2 Quality Aspects of Drilling
The highly used and satisfactory machining technique used
for making holes in a composites material is a conventional
drilling operation. In order to facilitate various application
requirements, it has become more essential to drill holes
and other machining operations for the purpose of making
joints. While cutting the composite, the material exhibits
changes in their property, so that it is more important
in considering the material response while machining the
composites. According to Karimi et al. [12], in typical
drilling process, composites tend to damage because of
the separation of reinforcement layers from the matrix
which can occur through matrix cracking, fibers pullout,
fiber breakage and delamination. Delamination and surface
integrity are the two major issues addressed while drilling
composites which are highly influenced by the torque and
trust force.
2.1 Thrust Force and Torque
In a typical drilling process, generally the force produced
is categorized into two major components, i.e., the thrust-
force and torque, which often defines the tool wear and
surface quality of drilled surface respectively [13]. Several
research works addressed that thrust and torque were
the main consideration for the composite delamination
on drilling. Arul et al. [14] observed the increase in
thrust while increasing the feed. Also surface quality
of the drilled holes in a composite material can be
improved by reducing the thrust force [15]. Thrust induces
delamination in the composite material when it exceeds the
interlaminar toughness of the composite layers [16]. The
influence of drilling parameters on the thrust force and
torque developed during traditional drilling operation on
glass fiber reinforced composites were studied by Mohan
et al. [17]. Parameters such as speed, feed rate, drill
size and specimen thickness were found to have higher
influence on thrust. Using Taguchi analysis and analysis
of variance (ANOVA) experiment the operating parameters
were optimized and influence factors were evaluated.
From analysis it was found that spindle speed and drill
size was more significant in affecting the thrust force.
Further specimen thickness and drill size was significant in
affecting the torque. Further the investigation stated that the
composite thickness and drill bit size were the important
parameters influencing the torque on drilling glass fiber
reinforced polyester composite. Zitoune and Collombet
[18] investigated composites structures reinforced with
long fibers for studying the influence of thrust force on
delamination. Using the numerical model the trust force
was calculated and the delamination at exit point was
studied. Influence of feed rate and drill material on torque
was observed while drilling carbon fiber reinforced epoxy
composites [19]. Some researchers witness that the trust,
torque and delamination can be increased by the tool wear
[20–22].
2.2 Delamination
Gaugel et al. [23] defined delamination as the separation or
removal of adjoining composite plies which can be signified
by the development of interlaminar cracks in the material.
Delamination is a major issue which restricts the composite
material use in various applications, since it have an effect
on composites structural integrity, thereby affecting the
assembly tolerance and reducing the performance of the
applications [24]. The strength and the stiffness of the
composites can be decreased by the effect on delamination
which further results in the failure of the material [25].
Drilling in composites becomes a more critical operation
because of the delamination factor. It is recognized as the
crucial problem encountered in composite drilling which
affects the strength and other properties of the material
[26]. Srinivasan et al. [27] studied the delamination in glass
fiber reinforced Polypropylene composites. Delamination
effect on unidirectional carbon fiber reinforced polymer was
examined by Shetty et al. [28], where drilling was done
by two different drills tool made of high speed steel and
titanium nitride coated solid carbide drills. Hocheng and
Tsao [29] analyzed the delamination induced on machining
composites with different drill bits such as saw drill, candle
stick drill, core drill and step drill. On various aspects
delamination developed on composites were reviewed by
Hocheng and Tsao [30]. Using Analysis of Variance
(ANOVA) method drilling parameters were analyzed to find
their influence on delamination of polymers by Gaitonde
et al. [31]. Tsao and Hocheng [32] state that on drilling
a composite, delamination occurs often at both entrance
and exit of the drill. Tsao and Hocheng [33] in another
work presented an analytical model to understand drill tip
and eccentricity characteristics on delamination. Analysis
was done based on machining a composite with two drills
(eccentric twist drill and eccentric candle stick type drills).
For both the drills the thrust force got reduced on enhancing
the point eccentricity. Further Tsao and Hocheng [34]
extended their work on a twist drill, candle stick drill
and saw drill in finding the delamination on drilling a
polymer having 5 mm thick reinforced with carbon fiber.
Machining was executed at various operating conditions.
Significance of feed and drill diameter was found to be more
influencing parameters on overall drilling performance.
Further, the candle-stick and saw drills produced minimum
damage than twist drill, because of the variation in the drills
cutting edges. By variable feed technique Khashaba et al.
[35] machined the cross-winding composites without any

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delamination. Grilo et al. [36] analyzed the delamination
caused on drilled carbon fiber reinforced polymers by using
various drill geometries. Peel-up delamination and push-out
delamination were the two main delamination mechanisms
found in the drilling of fiber reinforced polymer composites
[37]. Peel-up delamination occurs when the drill approaches
the composite surface. As the drill cutting process starts
material in the composite layers get removed and forms
as a spiral up and this region is referred the peel-up
delamination zone. Peel-up delamination can be varied with
tool geometry and friction between the tool and specimen
material. Push-out delamination occurs at the exit point of
the drilled material. The uncut thickness in the material
becomes low when the drill moves toward the end of the
hole so that the resistance to deformation gets reduced. In
that region the interlaminar bonding strength reduced as the
thrust forced maximized. As a result when the tool enters
the exit point an exit delamination region develops [38].
2.3 Surface Roughness
Surface roughness is the major output, which many
applications focused on while machining the materials. In
many applications surface quality determines the precision
of the product. Deviation in surface roughness could
bring the material to fail and sometimes results in
major problem like friction, misalignment, heat production
at hole wall, further increases the cost and time on
reprocess [39]. Fiber reinforced composites exhibits an in
homogeneity property because of the reinforcement and
matrix property, this in-turn show the adverse effect in
surface integrity [40]. Significance of surface roughness is
a highly prominent while concerning mechanical products
and on the production costs [41]. The surface quality
of the drilled hole on a composite can be improved by
studying the drilling parameters [42]. Drilling speed and
feed rate, drill geometry, the material drilled are the major
parameters which highly affect surface quality. Significance
of feed rate and spindle speed decides the surface roughness
of the machined material [43]. Drilling at larger spindle
speed and lower feed give good surface quality on the
drilled holes [44]. Surface topography of a material can
be defined by the optimum experimentation condition of
tool, specimen and their properties [45]. Work-done by
Ismail et al. [46] concentrated on studying the influence of
drilling parameters on the surface roughness of the hemp
fiber-reinforced polycaprolactone composite. According to
Tan et al. [47] feed rate is the highly influencing factor
in determining the surface roughness. Surface roughness
developed on the drilled hole of polyamide composites
was investigated by Rubio et al. [48]. An investigation
was carried out by Angadi et al. [49] to find the drilling
performance (surface roughness and trust) of the cenosphere
filled epoxy composites. Experiment were carried out by
considering parameters such as machining speed, feed rate,
drill diameter and filler proportion. Varying filler proportion
changed the machining performance where 60% of filler
addition reduced the thrust force and surface roughness
considerably. Influence of feed on machining response was
noted, where increase in feed increases trust and decreases
the surface roughness.
3 Drilling on Glass Fiber Reinforced
Composites (GFRP)
In general, drilling on GFRPs was studied by various
researchers where vast amount of studies addressed the
impact of drilling parameters such as tool wear, surface
roughness, delamination, and cutting forces.
Mohan et al. [50] studied the drilling performance of
the glass fiber (GF) reinforced plastics. The work was
mainly focused on the surface integrity developed inside
the drilled hole of GF composite. On three influencing
parameters drilled surface were analyzed. Machining was
done at varying spindle speeds from 90 to 445 rpm and
feed rate at 0.5 mm/rev. The experiment result concludes
the close relationship between the specimen thickness and
the surface quality of the drilled surface. Dhiraj Kumar
et al. [51] investigated the surface roughness developed
as a result of drilling a glass fiber embedded polymer.
With three varying drill geometry (helical flute (HSS) drill,
Carbide tipped straight shank (K20) drill, and Solid carbide
eight-facet drill) drilling was done. Machining on carbide
eight facet drill bit showed a better surface roughness that
other drill bits, where the surface roughness was measured
0.384 to 2.227 μm. Prabhu et al. [52] found the machining
performance of glass fiber reinforced polyester composites
(GRP) and hybrid Nano Clay and Glass Fiber Reinforced
Polyester nano composites (CGRP). With three different
drill bits each of 6 mm diameters (carbide twist drill D
5407060, HSS twist drill BS-328, and HSS end mill) the
experiment was conducted. The experiment condition was
set for three varying spindle speeds (600, 852, and 1260
rpm) and two feed rates (0.045, 0.1 mm/rev). The optimal
operating condition producing minimum delamination was
found by optimizing the machining parameters (feed =
0.1 mm/rev and speed 852 rpm). For the carbide tool
delamination was low when operated at higher feed rate.
Further on the presence of nano clay in the CGRP composite
also cause tool wear.
A hybrid composite was fabricated using glass fiber with
two natural fibers (sisal and jute) as the reinforcement.
Drilling characteristics of the hybrid composite was
analyzed on varying operating parameters (cutting speed,
feed rate and tool diameter). On increasing the feed

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rate and varying the drill diameter the thrust force get
higher, where thrust force was at peak at upper feed rate.
Further lower the spindle speeds higher the torque. Only
at larger feed the composite got more delamination [53].
In the work done by El-Sonbaty et al. [54] the machining
performance of the glass fiber-embedded composites was
revealed. Influence of drill size, feed, cutting velocity,
and fiber content on surface roughness, torque and thrust
force of the machined composite was found. From the
machining performance result it was concluded that the
cutting speed has negative response on thrust force. Further
the feed rate and the spindle speed has no influence on
surface roughness of the composite, also further increase
in the cutting speed increased the surface roughness.
Krishnaraj [55] investigated the glass fiber reinforced
plastic composite drilled by zhirov -point drill, twist
drill, and multifacet drill. Drilling was done by varying
feed rate and spindle speed for examining their effect
on thrust, delamination and surface roughness. Multifacet
drill showed less delamination compared to other drills
which also produced good surface roughness. Comparing
to other tool Zhirov point drilled holes at lower thrust
and showed minimum tool wear. Khan and Kumar [56]
fabricated the glass fiber reinforced polyester composite
and machined using two different alumina ceramic tools
(SiC hair reinforced alumina and TiC/TiN mixed alumina
tools). Machining was done at constant feed rate and varying
spindle speed. SiC hair reinforced alumina cutting apparatus
showed a minimum tool wear than TiC or TiN blended tool.
Verma et al. [57] made a trial to find the optimum
drilling condition of a GFRP composite by using the
fuzzy optimization technique. Material removal rate and
surface roughness developed on machining were analyzed
at varying the cutting conditions. Machining of GFRP
composite was studied by Murthy et al. [58] for finding
the influence of machining variables on thrust power and
torque on drilling with carbide. As a result of design
of experiments (DOE) it was concluded that spindle
speed has significant effect on thrust force and drilling
torque was greatly influenced by drill. Davim et al. [59]
examined the experiment parameters for drilling damage
on drilling carbon fiber reinforced epoxy composite. The
input parameters were analyzed using Taguchi’s experiment
and on the ANOVA analysis. Further work done by Mohd
Ariffin et al. [60] inspected drilling damage effect in the
GFRP composites- sandwich part used on aircrafts by
Boeing Corporation. Two varying drill bits were used for
machining. From the experiment results maximum and
minimum damage length is 0.44 mm and 0.05 produced at
spindle speed of 500 rpm, feed rate of 246.8 mm/rev using
carbide tool and at spindle speed of 3000 rpm, feed rate of
80.2 mm/rev for HSS respectively. Ali et al. [61] examined
the effect of machining on woven laminated GFRP material
by drilling and milling operation. The two cutting process
parameters were analyzed by ANOVA to evaluate the
significance of drilling and milling on composites. Uysal
et al. on drilling a glass fiber polymer observed the
reduction in tool wear when increasing the feed rate [62].
Drilling performance of un-laminated GFRP composite was
investigated by Ramesh et al. [63]. Coated cemented carbide
drill was used to drill the composite at varying process
parameters. Effect of feed rate and machining speed were
analyzed by Taguchi’s method and ANOVA technique to
find their significance on thrust power, torque and damage
factor. Feed rate considerably affects both the thrust and
torque with 88.52% and 92.83% respectively. In addition the
cutting speed showed a negative response on both the thrust
and torque. In case of damage factor at the entrance and exit
point of the workpiece, effect of feed and spindle speed was
trivial.
Khashaba et al. [64] observed machinability of the epoxy
composite with woven glass fiber reinforcement. Increase in
feed and drill diameter enhanced the delamination because
of the raise in thrust increases the undeformed chip size.
Surface roughness of the drilled material increases with
the increase in cutting speed. Further Khashaba et al. [65]
extended his work in analyzing the impact of drill pre-wear
on the drilling variables on processing the same material at
various experimental conditions. Drill pre wear showed a
prominent impact on the thrust force which shows adverse
effect on delaminations and surface roughness. On two
different composite laminates (unidirectional glass fiber
reinforced composite and [(0/90)/0]s glass fiber reinforced)
radial drilling operation was conducted by Dhawan et
al. [66]. The specimen was drilled at three different
feed rate and spindle speed by four kind types of drills
point geometries. Further the experimentation results were
compared with the result formed by the Artificial Neural
Networks (ANN) approach. Capello [67] studied feed rate
significance on the delamination effect produced while
drilling a glass fiber polymer and it was noted that there
was no delamination at low feed rates. Davim and Mata [68]
proposed a drilling study on GFRPs using polycrystalline
diamond (PCD) and cemented carbide cutting tools. Drilling
results exposed that the better performance of PCD cutting
tool when compared to the carbide tool. On the basis
statistical and experimentation result it was concluded that
feed rate was the highly influencing cutting parameter on
surface roughness and specific cutting pressure.
Drilling damage on a laminate having fiber glass
reinforcement was studied by Bhatnagar et al. [69] and
Singh and Bhatnagar [70]. These studies conclude that
there was no close relation between the drilling forces
and the damage for a parabolic point drill. From results
it was found that 8 facet and Jo-drills are more suitable
for drilling composites since they shown lower torque and

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thrust force. Investigations were carried out by Kishore
et al. [71] on the GFRE composites for examining their
machining parameters influence on residual tensile strength
of the machined composite. Parameters feed, speed and
drill geometry were considered and drilling was done by
4 mm diameter carbide drills of three varying geometries (8-
facet drill, 4-facet drill and Jo drill). The optimum drilling
condition for higher residual strength is at machining speed
of 750 rpm and feed rate of 15 mm/min for 8-facet drill. In
addition the result states that selection of drill geometry is
crucial in minimizing the drill damage.
4 Drilling on Natural Fiber Reinforced
Composites (NFRCs)
Over a period of few years, development of natural fiber
reinforced composites (NFRCs) was in remarkable range
due to their biodegradable property, easy availability and
improved mechanical properties. Number of research work
has been carried out on NFRCs, which focused on the
mechanical properties and machining behavior of natural fiber
composites.
Babu et al. [72] stated the natural fiber strengthened
composites as the efficient composites for structural
applications. Machining these materials was not often
easy, so in this study cemented carbide end mill cutter
were used to drill the composite. Further the study
compares the experiment result on GFRP composites
machined by same drills. The machining results prove
the performance of natural composites which is better
than GFRP composites. Further their work extended to
investigate the drilling effect of hemp fiber reinforced
composites [73]. Using optimization techniques the cutting
parameters were analyzed for producing low delamination
and higher tensile strength. On parameter analysis feed
rate and cutting speed were shown higher influence on
delamination. Naveen et al. [74] examined composites with
glass, hemp and sandwich fibers reinforcement for finding
their machine cutting behavior. Fibers were reinforced at
different volume percentage 10%, 20% and 30%Wt. On
machining it was found that damage was higher at high
feed rate. Also noted that while machining at higher feed
fibers was underwent an uneven cutting. Velumani et al.
[75] made a research on sisal and glass fiber reinforced
hybrid composites to explore the drilling performance
using the Response surface methodology (RSM), Multi
layer perceptron neural network (MLPNN), Radial basis
function network (RBFN) and Elman neural network (ENN)
methods. Jayabal et al. [76] work investigated the coir
fiber reinforced polyester composites for understanding
their machining behavior. On optimization of parameters
for finding optimum machining condition, drill diameter at
6 mm and the cutting speed at 600 rpm shown minimum
effect on tool wear, thrust power and torque. Further Jayabal
et al. [77] fabricated the hybrid composite having glass and
coir reinforcement on a polyester matrix to analyze their
machining characteristics. To report the parameter influence
on thrust, torque, and tool wear a regression model has been
developed. Predominate influence of feed rate was noticed
on experimental analysis.
Comparison study on drilling characteristics of glass
and sisal fiber reinforced epoxy composites was made by
Durão et al. [78]. From the experimental work it was
concluded that at higher thrust delamination occurs, because
of the prominent influence of experimental parameters,
tool geometry and material. Sridharana et al. [79] analyzed
polyester composite reinforced with untreated and alkali
treated jute fibers. The fabricated composites were drilled
for evaluating their drilling characteristics. Experimental
results showed the reduction on delamination of treated
fibers but ANOVA results shows that there is no effect on
delamination because of fiber treatment. Further on both
composites delamination increased when raising the feed
rate. Yallew et al. [80] made a drilling study on the woven
jute fiber embedded polypropylene matrix. The outcome
of machining parameters on thrust power and torque was
examined. From the results it was well clear that thrust
force varied greatly with the geometry of drills. And it
was also noted that increase in diameter of drill increase
the trust. Observation on delamination factor shows that
composite has more push-out delamination than the peel-up
delamination which is mainly because of the thrust force.
With the twist drill and trepanning tool made of HSS tool
material drilling was done on the sisal fiber reinforced
polypropylene matrix by Bajpai and Singh [81]. In the
response of drilling variables (cutting speed, feed rate, and
the drill geometry) the green composite was evaluated for
the drilling response especially on thrust, torque and drilling
damage. Results concluded that there was a prominent
influence of the entire three variables on machining.
Notably, drill geometry shown higher influence on drilling
forces and drilling damage. Jute fibers had been used as the
reinforcement material in an epoxy composite and drilling
investigation was carried out on them. The work suggests
the importance of setting optimum drilling condition for
machining the composites. In experimental results drill
size played an prominent role in avoiding delamination
factor [82]. Abilash et al. [83] observed the delamination
on drilling bamboo fiber reinforced composites. A better
surface quality holes were achieved on minimizing the
delamination by using smaller drills and low feed rate.
Drilling damage and surface roughness of a machined
sandwich composite was examined by Vinayagamoorthy
et al. [84]. The sandwich composite has vetiver, jute
and glass reinforcement in a vinyl ester matrix. Natural

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fiber reinforcement improved the drilling performance by
reducing the drilling damage.
5 Drilling on Carbon Fiber Reinforced
Plastics (CFRPs) Composites
Carbon fiber reinforced plastics (CFRPs) are the advanced
composite materials used in various structural applications
because of their low density, high strength, high stiffness,
good toughness, good fatigue, creep, wear, corrosion
resistance, low friction coefficient and good dimensional
stability. It is usual to machine the materials for the purpose
of adjustment of tolerances and to manufacture fitting and
joining surfaces [85]. Many researchers investigated the
CFRPs for their drilling performance. Jia et al. [86] through
his work elaborated the drilling mechanism on machining
CFRP mainly focused on the mechanism involving in
material removal and drilling damage.
Hocheng and Tsao [87] investigated the drilling per-
formance of the composite material having carbon fiber
reinforcement on five varying drill bits (saw drill, candle
stick drill, core drill and step drill) having each 10 mm
diameter. The drilled composites were analyzed by the ultra-
sonic C Scan method to evaluate delamination produced on
machining. The experimental results were compared with
the theoretical predictions of critical thrust force at the
onset of delamination. Each drill bits exhibited variation in
thrust force because of the change in the drill bit geome-
try. The core drill was operated at higher feed rate without
any delamination than other drill bits, where twist drill was
at lower feed rate. Overall for all experimented drill bits
delamination was found to be the minimum at lower thrust
force.
Lachaud et al. [88] studied the drilling damage carbon
reinforced epoxy composite by comparing the experimental
results with the analytical model. Drilling study was
conducted on carbon fiber reinforced plastic composite
by Eshetu et al. [89]. Li et al. [90] tested the multi-
walled carbon nanotubes (MWCNT) reinforced composite
by doing drilling operation. To reduce the delamination and
thermal damage the composite was cured by micro waves
during fabrication. The experiment result was compared
with thermally cured MWCNT reinforced composite.
Drilling was done with the cemented carbide tool having
6 mm diameter, 30◦ helix angle, 140◦ point angle and
chisel edge 0.3 mm. Delamination was greatly decreased
and the interlaminar fracture toughness of the microwave
cooled composite enhanced above 66% than thermal cured
composites. Further drilling temperature was also reduced
to 23 ◦C. Seif et al. [91] carried out a study on carbon
epoxy polymers to examine the delamination caused on
drilling. By using a shadow more laser based imaging
technique the delamination on composites were measured.
Drill having 1.5 mm diameter made of cemented carbide
of different geometry was used by Shyha et al. [92] to
drill the carbon fiber laminate. Life of the tool and trust
were highly dependent on drill type and feed further torque
was influenced by cutting speed and feed. The drilled
hole has maximum damage in the form of internal cracks,
crack in matrix, fibers and matrix run. Phadnis et al. [93]
inspected the significance of machining variables on thrust
power and torque on CFRP composites. Drilling was done
both experimentally and numerically using finite elements
(FE) model in which the difficult due to kinematics at the
drill-workpiece interface analyzed. Experiment and model
results were found to be significant on machining results.
When the feed rate gets increased increase in thrust force,
torque and delamination damage was noted, conversely
gradual reduction is also found while increasing cutting
speed. FE model analysis states that efficient drilling in
CFRP can be executed at lower feed and higher cutting
speed.
Effect of drill geometry on machining CFRPs was
studied by Feito et al. [94]. The study mainly focused on
tool wear and drill point angle since these two variables
highly influence the cutting forces and hole quality. For
a new tool, thrust power has no influence by point angle,
but if the tool wears it has some significance at a notable
level. Variation in delamination at both entry and exit point
was found when the point angle increases. From ANOVA
analysis result wear, point angle and feed rate are the
parameters which shows significance on thrust while there
was insignificant influence by cutting speed. Pérez et al.
[95] performed studies on drilling of CFRP composites
found that the matrix material in the composite shows
the maximum effect for high torque, high thrust and the
machining temperatures. Illiescu et al. [96] evaluated the
drilling parameters (feed rate and tool wear) on drilling
of woven CFRPs. Drilling was done with the coated and
uncoated drills. From the machining result analysis feed
and tool wear were found to be prominent on impacting the
thrust force. The torque has shown minimum influence on
wear when compared to the thrust force. Traditional drilling
was processed in a woven CFRP with the carbide drill by
Mayuet et al. [97]. Delamination at entry and exit of the drill
reached maximum at lower cutting speed and feed.
Drilling experiment was done by Karpat et al. [98] on
the thick fabric woven CFRP laminates. Experiment was
conducted with the uncoated carbide drill and diamond
coated carbide drills of varying geometries. Maximum
drilling damage was observed on the feed influence than
cutting speed. Karnik et al. [99] made a study to find
the delamination in CFRP, the operating parameters speed,
feed and point angle were considered in determining
the delamination factor. The results found that at lower

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feed and point angles the delamination damage can be
reduced. Further for spindle speed, feed rate and point angle
delamination varies and was significantly influenced by
them.
Mata et al. [100] presented the drill characteris-
tics of polyetheretherketone (PEEK) composites. Totally
three kinds of composites were prepared (Unreinforced
polyetheretherketone, polyetheretherketone with 30% of
carbon fibers and 30% of glass fibers. A second order RSM-
mathematical model was designed to study the machining
influence (cutting speed and feed rate) on power and cut-
ting pressure. Machining results showed the reduced thrust
value since the matrix get soften on thermal effect during
drilling. In addition impact of cutting speed shows negligi-
ble effect on thrust. Further the machining performance of
the reinforced PEEK was poor when compared to the PEEK
composite.
Schornı́k et al. [101] and Feito et al. [102] studied the
significance of cutting parameters on drilling CFRP. Further
influence of several drilling parameters on drilling a carbon
fiber reinforced composites were discussed by various
researchers to know the machinability of the composites for
various industrial applications [103–106].
6 Unconventional Drilling Methods
in Polymer Composite Drilling
In recent years number of works investigated the per-
formance of unconventional drilling operation on rein-
forced composites was increased owing to its advantage in
its machining performance. Unconventional methods like
Water jet machining process (WJM), Laser drilling process,
Ultrasonic drilling process and Electric discharge machin-
ing process produce better drilling results on the reinforced
composites when compared with the traditional drilling pro-
cess. Through water-jet machining process it is possible
to produce quality holes on the polymer composites [107].
Vigneshwaran et al. [108] reviewed the Abrasive water-
jet machining performance on fiber reinforced composites.
Phapale et al. [109] machined the CFRP through water jet
machining process and investigated for better hole perfor-
mance. The results suggested that drilling at lower water
pressure, minimum stand-off stand distance produce better
surface finish. To determine the surface roughness pro-
duced on abrasive water jet machining process of polymer
composites Kumaran et al. [110] developed a model and
analyzed using experimental data. Wang and Guo [111]
developed a model for predicting the depth of cut in the
through hole drills of water jet machined process of polymer
composites. Delamination and surface roughness produced
while drilling epoxy polymers were studied by Shanmugam
et al. [112]. The investigation found that machining at
higher water pressure generates higher surface roughness
because of increased kinetic energy. Kumaran et al. [113]
explicated the influence of abrasive water jet machining
parameters on CFPR composites.
Ultrasonic machining process was preferred for drilling
reinforced composites because of its better machining con-
ditions although it is less economical [114]. Dam and
Quist [115] investigation reported that lower machining rate
in ultrasonic drilling process results in improved surface
roughness. Work done by Kurniawan et al. [116] investi-
gated the deburring effect on CFRP composites machined
through ultrasonic assisted dry electrical discharge machin-
ing. Kumaran et al. [117] made drilling operation on CFRP
on rotary ultrasonic machining in a cryogenic environment
and reported that at higher ultrasonic power and feed force
the quality of the drill was better. Other unconventional
drilling techniques like laser drilling [118–120]; drilling in
electric discharge machining [121–123] explaining drilling
effect on reinforced composites were reported by many
researchers.
7 Future Scope in Composite Drilling
Drilling of fiber reinforced composites is a complex
process which requires consideration of various factors
involving in machining. The present work reviewed the
drilling effect on reinforced composites on various aspects.
Although number of investigation discussed the machining
efficiency only few studies investigated the accuracy and
reliability of drilling efficiency through the modeling and
simulation. The efficiency and the rate of influence of
drilling parameters in composite drilling can be further
studied by developing modeling techniques. Since of the
abrasive nature of fibers in composites reduces the tool
life, keen interest should be shown in future on studying
composite machining by advancement in tool design.
8 Conclusions
The paper has presented a literature review on drilling
performance of composite materials. Concerning the
composite material type glass, natural and carbon fiber
reinforced composites have been equally examined for their
drilling performance. On the basis of literature review
some notable observations were summarized which aids in
processing composite drilling.
• In drilling of composites, traditional drilling process
is found to be more convenient and well established
method to drill holes when compared to other
unconventional drilling process.

8. Silicon
• The rate of spindle speed, feed rate, and drill geometry
are found to be most influencing parameters in
machining the composite materials. However the rate
of influence of these parameters varies on varying the
percentage and type of reinforcement.
• For achieving better drilling results it is more necessary
to develop new drill tools, however most of traditional
drilling process uses cemented tungsten carbide drills.
• Although several studies investigated the cutting param-
eters impact on delamination of composite material
during drilling operation, only a few studies stated the
effect of the geometric quality of the hole. Quality of
hole can be improved by machining at controlled feed
rate and speed. Considering delamination damage on
drilling composites, operating parameters feed and drill
geometry had significant influence on delamination.
• Thrust force reduction shows better surface quality on
the drilled holes. Feed rate, drill size, and thickness
are the parameters which influence the thrust force on
drilling polymers. Of all feed rate is more prominent in
affecting the thrust force, it was observed from many
research work that increase in feed increases the thrust
force.
• Surface roughness of the drilled composites can be
improved by drilling at optimum drilling conditions.
In case of surface roughness spindle speed, feed rate,
drill geometry and specimen material are important in
achieving the holes with better surface quality.
• Fiber reinforcement in the polymer composite provides
resistance for drilling which becomes the major reason
for the development of trust force and delamination.
Polymer composites with reinforcement like glass
fibers, natural fibers and carbon fibers should be studied
in regard to the type and amount of reinforcement
for reducing the development of thrust force and
delamination damage.
Acknowledgments The authors would like to express their sincere
thanks to Ministry of environment forest and climatic change (MOEF
CC), Government of India for the financial support (Project No
168/2016/RE (F No 19-20/2012-RE)).
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