d

ABSTRACT

The main objective of the project is to prepare a GFRP - Glass Fiber

Reinforced Plastic (composite material) using glass fiber woven with a

binder called bisphenol as a matrix, with the help of a Mechanical Press. The

next step is to perform drilling operation on the composite using different

drill bit materials such as High Speed Steel, Tungsten Carbide and Poly-

Crystalline Diamond. The parameters such as feed of the operation and the

spindle speed of the machine are varied and the test is undertaken.

Simultaneously a dynamometer is attached to the drilling machine to check

the torque and thrust force. The drilled holes are then subjected to a device

called Profile Projector to study the delamination factor of the holes. The last

test is called Flexure test (which is a bending test) in which the strength of

the specimen is tested using the UTM - Universal Testing Machine. After

obtaining all the data, the values are tabulated and graphs are plotted

accordingly.

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APPENDIX 3

TABLE OF CONTENTS

CHAPTER NO. TITLE PAGE NO.

ABSTRACT iii

LIST OF TABLE

LIST OF FIGURES

LIST OF SYMBOLS

xvi

xviii

xxvii

1. INTRODUCTION 1

1.1 GENERAL 1

1.2 . . . . . . . . . . . . . 2

1.2.1 General 5

1.2.2 . . . . . . . . . . . 12

1.2.2.1 General 19

1.2.2.2 . . . . . . . . . . 25

1.2.2.3 . . . . . . . . . . 29

1.2.3 . . . . . . . . . . . . 30

1.3 . . . . . . . . . . .. . . . . . . 45

1.4 . . . . . . . . . . . . . . . . . . 58

2. LITERATURE REVIEW 69

2.1 GENERAL 75

2.2 . . . . . . . . . . 99

2.2 ……………. 100

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1. INTRODUCTION

1.1. INTRODUCTION TO COMPOSITE MATERIALS

Composite materials or Composites are materials made from two or

more constituent materials with significantly different physical or chemical

properties, that when combined, produce a material with characteristics

different from the individual components. The individual components

remain separate and distinct within the finished structure. Composites, unlike

metals are not homogeneous, anisotropic and consist of both unique resins

and fibers. Composites are normally manufactured in near net shape

processes but they require secondary machining operations for assembly.

Hence drilling, cutting and machining composites in any post processing

operations to get to final shape or configuration is different from other

materials.

1.2. HISTORY OF COMPOSITE MATERIALS

The earliest man-made composite materials were straw and mud

combined to form bricks for building construction. This ancient brick-

making process was documented by Egyptian tomb paintings. Wattle and

daub is one of the oldest man-made composite materials, over 6000 years

old. Concrete is also a composite material and is used more than any other

man-made material in the world. As of 2006, about 7.5 billion cubic meters

of concrete are made each year—more than one cubic meter for every person

on Earth.

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1.3. CLASSIFICATION OF COMPOSITE MATERIALS

Composite materials are usually classified by the type of

reinforcement they use. This reinforcement is embedded into a matrix that

holds it together. The reinforcement is used to strengthen the composite. For

example, in a mud brick, the matrix is the mud and the reinforcement is the

straw. Common composite types include random-fiber or short-fiber

reinforcement, continuous-fiber or long-fiber reinforcement, particulate

reinforcement, flake reinforcement, and filler reinforcement.

1.3.1. METAL MATRIX COMPOSITES

A metal matrix composite is a composite material with at least two

constituent parts, one being a metal. The other material may be a different

metal or another metal, such as ceramic or organic compound. When at least

three materials are present, it is called a hybrid composite. A metal matrix

composite is complementary to a cermet. They are made by dispersing a

reinforcing material into a metal matrix. The reinforcement surface can be

coated to prevent a chemical reaction with the matrix.

1.3.2. CERAMIC MATRIX COMPOSITES

Ceramic Matrix Composites are subgroup of composite materials as

well as a subgroup of technical ceramics. They consist of ceramic fibers

embedded in a ceramic matrix, thus forming a ceramic fiber reinforced

ceramic material. The matrix and fibers can consist of any ceramic material,

whereby carbon and carbon fibers can also be considered a ceramic material.

1.3.3. POLYMER MATRIX COMPOSITES

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Polymer Matrix Composite is the material consisting of a polymer

(resin) matrix combined with a fibrous reinforcing dispersed phase. They are

very popular due to their low cost and simple fabrication methods. Use of

non-reinforced polymers as structure materials is limited by low level of

their mechanical properties. The reinforced fibers may be arranged in

unidirectional fibers or roving or chopped strands. They are used for

manufacturing secondary load bearing aerospace structures, boat bodies,

canoes, kayaks, automotive parts, radio controlled vehicles, sport goods,

bullet proof vests and other armor parts, brake and clutch linings

1.4. FIBER REINFORCED COMPOSITES

A fiber-reinforced composite (FRC) is a composite building material

that consists of three components: (i) the fiber as the discontinuous or

dispersed phase, (ii) the matrix as the continuous phase, and (iii) the fine

interphase region, also known as the interface. This is a type of advanced

composite group, which makes use of rice husk, rice hull, and plastic as

ingredients. This technology involves a method of refining, blending, and

compounding natural fibers from cellulosic waste streams to form a high-

strength fiber composite material in a polymer matrix. The designated waste

or base raw materials used in this instance are those of waste thermoplastics

and various categories of cellulosic waste including rice husk and saw dust.

FRC is high-performance fiber composite achieved and made possible

by cross-linking cellulosic fiber molecules with resins in the FRC material

matrix through a proprietary molecular re-engineering process, yielding a

product of exceptional structural properties.

Through this feat of molecular re-engineering selected physical and

structural properties of wood are successfully cloned and vested in the FRC

18

product, in addition to other critical attributes to yield performance

properties superior to contemporary wood.

This material, unlike other composites, can be recycled up to 20 times,

allowing scrap FRC to be reused again and again.

The failure mechanisms in FRC materials include delamination, intra-

laminar matrix cracking, longitudinal matrix splitting, fiber/matrix de-

bonding, fiber pull-out, and fiber fracture.

1.4.1. CARBON FIBER REINFORCED PLASTIC

Carbon fiber reinforced plastic is an extremely strong and light fiber-

reinforced polymer which contains carbon fibers. The polymer is most often

epoxy, but other polymers, such as polyester, vinyl ester or nylon, are

sometimes used. The composite may contain other fibers, such as aramid e.g.

Kevlar, Twaron, aluminum, or glass fibers, as well as carbon fiber. The

strongest and most expensive of these additives, carbon nanotubes, are

contained in some primarily polymer baseball bats, car parts and even golf

clubs where economically viable. Carbon fiber is commonly used in the

transportation industry; normally in cars, boats and trains

Although carbon fiber can be relatively expensive, it has many

applications in aerospace and automotive fields, such as Formula One. The

compound is also used in sailboats, rowing shells, modern bicycles, and

motorcycles, where its high strength-to-weight ratio and very good rigidity is

of importance. Improved manufacturing techniques are reducing the costs

and time to manufacture, making it increasingly common in small consumer

goods as well, such as certain ThinkPad’s since the 600 series, tripods,

fishing rods, hockey sticks, paintball equipment, archery equipment, tent

poles, racquet frames, stringed instrument bodies, drum shells, golf clubs,

helmets used as a paragliding accessory and pool/billiards/snooker cues.

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1.4.2. GLASS FIBER REINFORCED PLASTIC

Glass Fiber Reinforced Plastic is a fiber reinforced polymer made of a

plastic matrix reinforced by fine fibers of glass.

Fiberglass is a lightweight, extremely strong, and robust material.

Although strength properties are somewhat lower than carbon fiber and it is

less stiff, the material is typically far less brittle, and the raw materials are

much less expensive. Its bulk strength and weight properties are also very

favorable when compared to metals, and it can be easily formed using

molding processes.

The plastic matrix may be epoxy, a thermosetting plastic (most often

polyester or vinyl ester) or thermoplastic. Common uses of fiberglass include

high performance aircrafts (gliders), boats, automobiles, baths, hot tubs,

water tanks, roofing, pipes, cladding, casts, Surfboards, and external door

skins. Fiberglass is an immensely versatile material which combines its light

weight with an inherent strength to provide a weather resistant finish, with a

variety of surface textures.

The development of fiber reinforced plastic for commercial use was

being extensively researched in the 1930s. It was particularly of interest to

the aviation industry. Mass production of glass strands was accidentally

discovered in 1932 when a researcher at the Owens-Illinois directed a jet of

compressed air at a stream of molten glass and produced fibers. Owens

joined up with the Corning Company in 1935 and the method was adapted

by Owens Corning to produce its patented "Fiberglas". A suitable resin for

combining the "Fiberglas" with a plastic was developed in 1936 by du Pont.

The first ancestor of modern polyester resins is Cyanamid's of 1942.

Peroxide curing systems were used by then.

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During World War II it was developed as a replacement for the

molded plywood used in aircraft radomes (fiberglass being transparent to

microwaves). Its first main civilian application was for building of boats and

sports car bodies, where it gained acceptance in the 1950s. Its use has

broadened to the automotive and sport equipment sectors as well as aircraft,

although its use there is now partly being taken over by carbon fiber which

weighs less per given volume and is stronger both by volume and by weight.

Fiberglass uses also include hot tubs, pipes for drinking water and sewers,

office plant display containers and flat roof systems.

Fiberglas is also used in the telecommunications industry for

shrouding the visual appearance of antennas, due to its RF permeability and

low signal attenuation properties. It may also be used to shroud the visual

appearance of other equipment where no signal permeability is required,

such as equipment cabinets and steel support structures, due to the ease with

which it can be molded, manufactured and painted to custom designs, to

blend in with existing structures or brickwork. Other uses include sheet form

made electrical insulators and other structural components commonly found

in the power industries.

Because of fiberglass's light weight and durability, it is often used in

protective equipment, such as helmets. Many sports utilize fiberglass

protective gear, such as modern goaltender masks and newer baseball

catcher's masks.

1.5. TYPES OF REINFORCING GLASS FIBERS

Glass-reinforced composites gain their strength from thin glass fibers

set within their resin matrix. These strong, stiff fibers carry the load while

the resin matrix spreads the load imposed on the composites. A wide variety

18

of properties can be achieved by selecting the proper glass type, filament

diameter, sizing chemistry and fiber forms (e.g., roving, fabric, etc.).

Fibers made primarily from silica-based-glass containing several

metal oxides offer excellent thermal and impact resistance, high tensile

strength, good chemical resistance and outstanding insulating properties.

Fibers can also be produced from carbon, boron and aramid. While

these materials offer high tensile strength and are stiffer than glass, they cost

significantly more. For that reason, carbon, boron and aramid are typically

reserved for high-tech application demanding exceptional fiber properties for

which the customer is willing to pay a premium. An alternative is to use

hybrid fiber (combining an expensive fiber with glass fiber), which improves

overall cost yet cost less than using premium fibers alone.

1.5.1. E-GLASS FIBER

E-glass is a popular fiber made primarily of silica oxide, along with

oxides of aluminum, boron, calcium and other compounds. Named for its

good electrical resistance, E-glass is strong yet low in cost, and accounts for

over 90% of all glass fibers reinforcements, especially in aircraft radomes,

antennae and application where radio-signal transparency is desired. E-glass

is also used extensively in computer circuit boards where stiffness and

electrical resistance are required.

In addition to E-glass, several other types of glass can be used for

composite reinforcement. The most popular are high strength glass and

corrosion resistant glass.

1.5.2. HIGH STRENGTH GLASS FIBER

High- strength, carbon or other advanced fibers are used in application

requiring greater strength and lower weight. High-strength glass is generally

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known as S-type in the United States, R-glass Europe and T-glass in Japan.

S-glass was originally developed for military application in the 1960’s and a

lower cost version, S-2 glass, was developed for commercial applications.

High- strength glass has appreciably higher amounts of silica oxide,

aluminum oxide and magnesium oxide than E-glass. S-2 glass is

approximately 40-70% stronger than E-glass.

1.5.3. CORROSION RESISTANT GLASS FIBER

When glass fibers are exposed to water, they become eroded to

leaching. To protect against water erosion, a moisture- resistant coating such

as silane compound is coated on to the fibers during composite formation

provides additional protection. The result is corrosion-resistant glass (called

C-glass)

Some types of glasses perform better than others when exposed to

acids or bases. Both C-glass and S-2 glass offer good corrosion resistance

when exposed to hydrochloric or sulfuric acid. E-glass and S-2 glass resist

sodium carbonate solution better than C-glass.

1.6. MACHINING OF GLASS FIBER REINFORCED COMPOSITES

Machining of GFRPs (Glass fiber reinforced plastics) differs

significantly from machining of conventional metal and alloys. In the former

the material behaviors depend on diverse fiber and matrix properties, fiber

orientation and relative volume of matrix and the fibers. The tool

continuously encounters alternate matrix and fiber material whose response

to machining can vary greatly. For example in a glass/epoxy composite the

tool encounters a low temperature soft epoxy matrix and brittle glass fibers.

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Conventional machining of GFRPs (Glass fiber reinforced plastics) is

difficult due to the presence of comparatively high volume fraction of hard

fibers in the matrix, their orientation and diverse fiber and matrix properties.

The earliest of the literature in FRP (Fiber reinforced plastics)

machining was by Wason. He was of the opinion that the best way to saw

FRP plates was by diamond tipped circular saw with large amount of cutting

fluid. The speed should be high and feed rate slow. Mackrin also stated that

diamond wheel may be used for cutting GFRP. The most significant work in

the machining of GFRP is by Konig, Wulf, Grab and Willerscheid. They

have identified that the major problems associated with different FRPs

namely glass, carbon and Kevlar reinforced ones. They found that type of

fiber used for reinforcement is the major factor which determines the

machinability of the composite.

1.6.1. DRILLING OF FRP

Drilling is far the most important item of machining and it is very

important because it is often a final operation during assembly. Any defects

lead to rejection of the part. In the aircraft industry for example drilling

associated delamination accounts for 60% of all part rejections during the

final assemble of an aircraft. The economic impact of this is significant

considering the value associated with the part when it reaches the assemble

stage.

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2. LITERATURE REVIEW

Glass Fiber Reinforced Plastic refers to a plastic which has been

reinforced with glass fibers. It uses a plastic matrix, which may be an epoxy

resin, a thermosetting or thermoplastic resin to bind the glass fiber together

and improve its mechanical properties. It is far less brittle than carbon fiber

reinforced plastic and less expensive than metals. Its bulk strength and

weight properties are very favorable compared to metals. Morton [1]

discusses about GFRP, how it is fabricated, the advantages of using GFRP

and design considerations to be considered in using equipment are made

from them in his article. Also he discusses the different resins that can be

used for its fabrication. He discusses the thermosetting resins (epoxies,

polyesters, vinyl esters). He discusses the hand layup method of fabrication

that is being used for this project to apply resin on thin glass fiber mats

stacked on top of another till desired dimensions are achieved. This is the

most basic of fabrication techniques. It is also referred to as ‘contact

molding’. The author continues to mention about the strength characteristics

of GFRP and its various properties that make it preferable in various fields

of application like corrosion resistance, weight advantages, high strength,

inexpensiveness and flexibility. A lot of research has been conducted to

achieve efficient drilling of composites materials. Drilling tests were carried

out on GFRPC composites in order to verify the effect of machining

parameters on cut quality. Experiment results showed that, the quality index

was strongly affected by cutting speed to feed ratio (V/s). In particular large

18

damage zones were observed when low V/s values were adopted. However

beyond a limiting value, extend of the damage is no longer influenced by

V /s. A ratio of V/s greater than 150 was suggested in order to obtain best cut

quality in drilling of GFRPC.

The type of drill used has an important influence on the various

process parameters. Here the influence of three drill types of same diameter

is studied. Davim et al. [2] gives details about the study on a straight flute

jobber length type drill and a twist type drill used for composite drilling. The

drills used are of the same diameter (here 5 mm) and varies only in their

type. The “jobber length” drill has a 118 degree point angle. Important

results obtained showed that the Twist drill presents less specific cutting

pressure and thrust force than the Jobber length drill considering the same

cutting parameters (cutting speed and feed rater). The Twist drill produces

less damage on the GFRP composites than the Jobber length drill as well as

has better performances.

Delamination is the cracking of the composites laminate due to the

contact with the drill bit. It is a major problem associated with drilling fiber-

reinforced composite material that, in addition to reducing the structural

integrity of the material, also results in poor assembly tolerance and has the

potential for long performance deterioration. In the machining composites

parts, a finish comparable to metals cannot be achieved because of

inhomogeneity and anisotropy of materials. Tsao et al. [3] mentions that

induced delamination can occur at both entrance and exit planes of work

piece. A rapid increase in feed rate at the end of drilling will cause cracking

around the exit edge of the hole. Tsao et al. [3] mentions that delamination in

drilling have been correlated to thrust force during exit of the drill. A

significant portion of the thrust is due to the chisel edge. Increasing the

chisel edge length, results in the rise of thrust force. The candle stick drill

18

and saw drill have a smaller center than the twist drill; thus, a smaller extent

of the last laminate is subjected to a bending force. Experiments indicate that

there exists s critical thrust force below which no delamination occurs.

Above that level, matrix cracks are generated by interface delamination

growing from the crack tips.

Davim and Reis et al. [2] mentions that the hole surface quality

(surface roughness and dimensional precision) is strongly dependent on

cutting parameters, tool geometry and cutting forces (thrust force and

torque). The author studied the work developed by other authors drew the

conclusion from drilling of glass fiber reinforced plastics manufactured by

hand layup method that the specific cutting pressure decreases with the feed

rate and slightly with the cutting speed, and the thrust force increases with

the feed rate. The feed rate is the cutting parameters which has greater

influence on specific cutting pressure. The damage increases with both

cutting parameters, which means that the composite damage is lesser for

higher cutting speed and for lower feed.

JOURNALS REFERRED

“Effects of special drill bits on drilling-induced delamination of

composite materials”

Introduction

Drilling is the most frequently employed operation of secondary

machining for fiber-reinforced materials owing to the need for joining

structures. Delamination is among the serious concerns during drilling.

Practical experience proves the advantage of using such special drills as saw

drill, candle stick drill, core drill and step drill. The experimental

investigation described in this paper by Hocheng, Tsao et al. [3] examines

the theoretical predictions of critical thrust force at the onset of delamination,

18

and compares the effects of these different drill bits. The results confirm the

analytical findings and are consistent with the industrial experience.

Ultrasonic scanning is used to evaluate the extent of drilling-induced

delamination. The advantage of these special drills is illustrated

mathematically as well as experimentally, that their thrust force is distributed

toward the drill periphery instead of being concentrated at the center. The

allowable feed rate without causing delamination is also increased. The

analysis can be extended to examine the effects of other future innovative

drill bits.

Results

The experimental results of the drilling-induced delamination while

using special drills have been presented. The results are compared with the

theoretical predictions of critical thrust force at the onset of delamination,

and are consistent with the industrial experience as well. Due to the different

drill geometry, these drills show different levels of the drilling thrust force

which varies with the feed rate. The advantage of these special drill bits lies

in their higher threshold feed rate at the onset of delamination. Among the

five drills, the core drill offers the highest critical feed rate followed by the

candle stick drill, saw drill and step drill, while the traditional twist drill

allows for the lowest feed rate. In other words, the core drill, candle stick

drill, saw drill and step drill can be operated at larger feed rate or in shorter

cycle time without delamination damage compared to the twist drill.

“The effect of vibratory drilling on hole quality in polymeric

composites”:-

Introduction

Arul et. al. [4] mentions that anisotropy of fiber-reinforced plastics

(FRP) affects the chip formation and thrust force during drilling.

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Delamination is recognized as one of the major causes of damage during

drilling of fiber reinforced plastics, which not only reduces the structural

integrity, but also has the potential for long-term performance deterioration.

It is difficult to produce good quality holes with high efficiency by

conventional drilling method. This research concerning drilling of polymeric

composites aims to establish a technology that would ensure minimum

defects and longer tool life. Specifically, the authors Arul, Vijayraghavan

Malhotra et al. conceived a new drilling method that imparts a low-

frequency, high amplitude vibration to the work piece in the feed direction

during drilling. Using high-speed steel (HSS) drill, a series of vibratory

drilling and conventional drilling experiments were conducted on glass fiber-

reinforced plastics composites to assess thrust force, flank wear and

delamination factor. In addition, the process-status during vibratory drilling

was also assessed by monitoring acoustic emission from the work piece.

From the drilling experiments, it was found that vibratory drilling method is

a promising machining technique that uses the regeneration effect to produce

axial chatter, facilitating chip breaking and reduction in thrust force.

Results

The results of vibratory drilling studies on woven glass fabric

composite using high speed steel drill were presented. Some of the

observations are:-

The thrust in vibration drilling is smaller than that in the conventional

drilling, which indicates that the vibration drilling method is suitable

for defect constrained drilling of polymeric composites.

The trend of variation of thrust, flank wear, delamination factor, AE

power and AE rms with number of holes for conventional and

vibration drilling are similar.

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Good correlation between thrust and delamination factor indicates that

on-line monitoring of thrust can facilitate defect-constrained drilling.

In conventional drilling, increase of thrust and delamination factor around

30 holes, indicates that 30 is the limiting number of holes to be drilled and in

vibratory drilling 50 is the limiting number of holes to be drilled for defect

tolerance.

“Fiber reinforced composites in aircraft construction”

Introduction

Fibrous composites have found applications in aircraft from the first

flight of the Wright Brothers' Flyer 1, in North Carolina on December 17,

1903, to the plethora of uses now enjoyed by them on both military and civil

aircrafts, in addition to more exotic applications on unmanned aerial vehicles

(UAVs), space launchers and satellites. Their growing use has risen from

their high specific strength and stiffness, when compared to the more

conventional materials, and the ability to shape and tailor their structure to

produce more aerodynamically efficient structural configurations. In this

paper, Soutis et al. [5] gives a review of recent advances using composites

in modern aircraft construction is presented and it is argued that fiber

reinforced polymers, especially carbon fiber reinforced plastics (CFRP) can

and will in the future contribute more than 50% of the structural mass of an

aircraft. However, affordability is the key to survival in aerospace

manufacturing, whether civil or military, and therefore effort should be

devoted to analysis and computational simulation of the manufacturing and

assembly process as well as the simulation of the performance of the

structure, since they are intimately connected.

Results

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The application of carbon fiber has developed from small-scale

technology demonstrators in the 1970s to large structures today. From being

a very expensive exotic material when first developed relatively few years

ago, the price of carbon fiber has dropped to less than £10/kg, which has

increased applications such that the aerospace market accounts for only 20%

of all production. The main advantages provided by CFRP include mass and

part reduction, complex shape manufacture, reduced scrap, improved fatigue

life, design optimization and generally improved corrosion resistance. The

main challenges restricting their use are material and processing costs,

impact damage and damage tolerance, repair and inspection, dimensional

tolerance, size effects on strength and conservatism associated with

uncertainties about relatively new and sometimes variable materials.

Carbon fiber composites are here to stay in terms of future aircraft

construction, since significant weight savings can be achieved. For

secondary structures, weight savings approaching 40% are feasible by using

composites instead of light metal alloys, while for primary structures, such

as wings and fuselages, 20% is more realistic. These figures can always

improve but innovation is the key to making composites more affordable.

“Influence of cutting parameters on thrust force and torque in drilling

of E-glass/polyester composites”

Introduction

Reinforced plastics find wide application in all manufacturing fields

due to their distinct properties such as low weight, high strength and

stiffness. Although components are produced to near net shape, machining is

often needed to fulfill the requirements related to tolerances of assembly

needs. Among all the machining processes, drilling is the most indispensable

method for the fabrication of products with composite panels. The

18

performance of these products is mainly dependent on surface quality and

dimensional accuracy of the drilled hole. Murthy et al [6] studies the effect

of process parameters such as spindle feed, drill diameter and point angle

and material thickness on thrust force and torque generated during drilling of

GFRP composite material using solid carbide drill bit. Full factorial Design

of Experiments (DoE) has been adopted and the results indicate that spindle

speed is the main contributing factor for variation in thrust force and drill

diameter is the main contributing factor for variation for variation in torque.

The optimum combination of process parameters settings has been found out

using the integration on Taguchi method and Response Surface

Methodology.

Results

Thrust force is significantly influenced by spindle speed and they are

inversely proportional. Hence while working on glass fiber reinforced

composites by using solid carbide drills, higher spindle speed are

recommended for process parameter ranges under consideration. Cutting

torque is significantly influenced by drill diameter. Higher the drill diameter,

larger the thrust force and cutting torque required. Thrust force increases

whereas cutting force decreases with the increase in drill point angle. Both

thrust force and cutting torque increase with the increase in feed rate and

material thickness. Integrating taguchi method and RSM can be very

effective in process parameter optimization, as combining of the results of

the two methods can not only optimize the parameters, but also, indicate the

values of response, through which process parameter selection can be refined

and results justified. The results are based on the preselected range of values

of speed, feed, material thickness drill diameter and drill point angle and

hence the inference drawn cannot be completely generalized. The inferences

drawn from this study is of great significance to the practitioners in

18

minimizing tool wear and cutting energy, as solid carbide tool is being

widely used in machining GFRP

3. EXPERIMENTAL DETAILS AND PROCEDURE

3.1. INTRODUCTION

Major constituents in a fiber reinforced composite material are

reinforcing fiber and the matrix which hold the fibers. Fibers are the

principal constituents; they occupy a large volume fraction and the major

portion of load acting on a composite. For this experimental study we select

E type glass fiber and Bisphenol as the reinforcing fiber and the matrix

respectively. In previous studies done in institutions outside, they used epoxy

resins and other resins to hold the fibers. We use Bisphenol to study how it

differs from other resins and the different properties that it imbibes to the

final GFRP that is prepared.

The most common form in which GFRP’s are used in structural

application is called laminated. It is obtained by stacking a number of thin

layers of fibers and matrix and consolidating them to the desired thickness.

The fiber orientation in each layer as well as the stacking sequence of

various layers can be controlled to generate a wide range of physical and

mechanical properties for the composite laminate.

The design of experiment was done by taking three input parameters

namely the drill material, spindle speed and feed rate.

We discuss the details of the experimental procedure and the different

equipment’s and tools used in this study as follows:

3.2. PROCEDURE

Manufacture GFRP using woven glass fiber and Bisphenol as matrix.

Acquire tools, drill bits (HSS, Tungsten Carbide, PCD)

Drill GFRP with the drill bits at varying cutting speed and feed rate

18

Find thrust force and torque by attaching 9257B Kistler Dynamometer

to drilling equipment.

Perform wear test, flexural strength test, hardness test on GFRP

Optimize thrust force, torque and minimize delamination (both entry

and exit) in the holes using Design of Experiments and Response

Table Methodology

Find optimal machining parameters for obtaining best quality drilled

hole.

3.3. MANUFACTURING METHOD FOR GFRP – HAND LAYUP

METHOD

The GFRP is prepared in the laboratory at room temperature using

woven glass fiber mats and using Bisphenol along with promoters and

catalysts to progress the method at room temperature.

Fig.1 Molding process

Mold is treated with a release agent-to prevent sticking.

Gel coat layers are placed on the mold- to give decorative and

protective surface.

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Put the reinforcement (woven roving's or chopped strand mat).

The thermosetting resin is mixed with a curing agent, and applied with

brush or roller on the reinforcement.

The part is allowed to cure and then disassembled from the mold.

Since this process is not typically performed under the influences of

heat and pressure, simple equipment and tooling can be employed.

3.4. TOOLS USED

We use three different drill bits of increasing hardness to test the

effect of drill bit material on the output parameters.

HSS (High Speed Steel), Tungsten Carbide and PCD (Poly Crystalline

Diamond)

Fig.2 HSS

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Fig.3 Tungsten Carbide

Fig. 4 PCD

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Fig. 5 Parts of Twist Drill

We use 5mm diameter twist drill bits.

Nomenclature of drill bit is as follows.

Axis: The imaginary straight line which forms the longitudinal center line of

the drill

Body: The portion of the drill extending from the shank or neck to the outer

corners of the cutting lips

Chisel Edge: The edge at the end of the web that connects the cutting lips

Clearance: The space provided to eliminate undesirable contact between the

drill and the work piece

Clearance Diameter: The diameter over the cut away portion of the drill

lands

Drift: A flat tapered bar for forcing a taper shank out of its socket

Flutes: Helical or straight grooves cut or formed in the body of the drill to

provide cutting lips, to permit removal of chips, and to allow cutting fluid to

reach the cutting lips

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Flute Length: The length from the outer corners of the cutting lips to the

extreme back end of the flutes; it includes the sweep of the tool used to

generate the flutes and, therefore, does not indicate the usable length of the

flutes

Helix Angle: The angle made by the leading edge of the land with a plane

containing the axis of the drill

Land: The peripheral portion of the body between adjacent flutes

Lead: The axial advance of a leading edge of the land in one turn around the

circumference

Lips: The cutting edges of a two flute drill extending from the chisel edge to

the periphery

Margin: The cylindrical portion of the land which is not cut away to provide

clearance

Neck: The section of reduced diameter between the body and the shank of a

drill Oil Grooves: Longitudinal straight or helical grooves in the shank, or

grooves in the lands of a drill to carry cutting fluid to the cutting lips Oil

Holes or Overall Length.

Point: The cutting end of a drill, made up of the ends of the lands and the

web; in form it resembles a cone, but departs from a true cone to furnish

clearance behind the cutting Point Angle: The angle included between the

cutting lips projected upon a plane parallel to the drill axis and parallel to the

two cutting lips

Shank: The part of the drill by which it is held and driven

Tang: The flattened end of a taper shank, intended to fit into a driving slot

in a socket

Taper Drill: A drill with part or all of its cutting flute length ground with a

specific taper to produce tapered holes; they are used for drilling the original

hole or enlarging an existing hole

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Taper Square Shank: A taper shank whose cross section is square

Web: The central portion of the body that joins the lands; the extreme end of

the forms the chisel edge on a two-flute drill.

Point angle =118°

Cutting edge angle = 59°

Helix angle =25°

Clearance angle =6°

Process

Parameters

Spindle

Speed (rpm)

Feed

(mm/rev)

Drill Bit

Level 1 450 0.04 HSS

Level 2 852 0.08TUNGSTEN

CARBIDE

Level 3 1250 0.12 PCD

Table 1: The varying input parameters factor

We use the above sets of spindle speed, feed rate and drill bit to

perform a run test on the GFRP prepared. The spindle speeds and feed rate

values are selected in such a way to keep the settings as low, medium and

high. The previous tests done in other journals influenced us to select the

appropriate values.

The drilling machine was modified so as to measure the thrust and

torque during the drilling cycle. For this a dynamometer was attached to

drilling machine. For proper measurement of the thrust and torque was fixed

in such a way that the axis of the drill bit passes through the center of the

dynamometer.

3.5. EQUIPMENTS USED

The important equipment’s used in experimentation include

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3.5.1. Drilling Machine

The drilling machine used for the experiment is a radial upright type

drilling machine. The machine can be used as an automatic feed machine or

a manual feed machine. The control that allows its use as an automatic feed

machine. The upper lever allows selection of automatic feed in three levels –

0.04mm/rev, 0.08mm/rev and 0.12mm/rev. Once the required level is

selected the lower has to be pulled forward for the machine to start automatic

operation.

The drilling machine can be operated either on a belt drive or a geared

drive. In the case of the belt drive the drive is taken directly from the drive

motor of the drilling machine to it spindle through a belt drive. In the other

case a geared drive also comes into picture. To prevent damage to the

machine change over from belt drive to geared drive or vice versa should be

done only when motor is switch off. Presently the machine is in belt drive;

pull the lever to the blue colored area for the geared drive.

It depends also on the rpm of the drive motor used for the drilling

machine. A 960 rpm or a 1440 rpm motor can be used with this drilling

machine. When using the different drive motor the spindle speeds available

are

960 rpm, Geared drive – 65 rpm, 95 rpm, 140rpm, 205 rpm, 300 rpm

960 rpm, Belt drive- 390 rpm, 570 rpm, 840 rpm, 1230 rpm, 1800 rpm

1440 rpm, Geared drive- 100 rpm, 142 rpm, 210 rpm, 310 rpm, 450 rpm

1440 rpm, Belt drive- 600 rpm, 852 rpm, 1260 rpm, 1860 rpm, 2700 rpm

3.5.2. Dynamometer

A drill tool dynamometer was used to measure the thrust force and

torque occurring during the drilling operation. It is designed to be directly

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mounted on the top of the drilling machine. It is basically a strain gauge

based sensor. This dynamometer consists of 2 strain gauge based sensor; one

measured the thrust force acting on the dill tool, while the other one

measures the twisting force (torque) acting on the drill tool. The

dynamometer has to be mounted in such a way that the drilling machine

passes through the axis of the dynamometer; this will ensure accurate torque

readings. Before starting experiment the instrument has to be put in “ON”

position for about 10min for initial warm-up. Adjust the potentiometer in the

front panel till the display reads “0” for thrust force as well as torque

3.5.3. Profile Projector

The profile projector is used for measuring the drilled holes after

completing the drilling operation. The GFRP piece is mounted on the work

table of the profile projector. The specimen is focused by adjusting the

position of the table to get a clear sharp image. The focusing should be done

properly to ensure that the damage area around the drilled hole is clearly

visible. A magnified image of the GFRP piece is obtained on the screen.

Magnification on the range of 10x, 20x and 50x are possible using the

instrument. Going for a higher magnification allows for easier measurement

of the drilled holes. Both linear and angular measurements can be done

using the profile projector.

3.5.4. Variable Speed and Feed Controller

3.6. DELAMINATION FACTOR

Delamination is a mode of failure for composite materials. It is caused

due to weak bonding of constituents. It reduces the structural integrity of

material and results in poor assembly tolerance and long term performance

deterioration.

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Delamination causes layers of the glass fibers to separate after

repeated cyclic stresses. This makes the material lose the mechanical

toughness.

Delamination factor is determined by the ratio of maximum

diameter (D max) of Delamination and the diameter of the hole (D)

Fd = D max/D

Fig.6 Delamination Factor

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Fig.7 Delamination Entry

Fig.8 Delamination exit

3.7. TESTS PERFORMED ON GFRP

Composite materials emerge as a promising alternative to correct the

deficiencies caused by steel reinforcements in concrete structures. The

advantageous properties of fiber reinforced polymer (FRP) such as high

strength to weight ratio, and corrosion and fatigue resistance create an

interest in engineers.

For wide acceptance and implementation in construction, full

characterizations of the mechanical properties of GFRP specimens are

needed. In particular, it is necessary to define the mean value and

distribution of the tensile strength of GFRP bars for reinforced concrete,

which engineers can use for design purposes and composite manufacturers

for quality control.

3.7.1. FLEXURAL STRENGTH TEST

Flexural strength, also known as modulus of rupture, bend strength or

fracture strength, a mechanical parameter for brittle material, is defined as a

materials ability to resist deformation under load. The transverse bending

test is most frequently employed, in which a rod specimen having either a

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circular or rectangular cross section is bent until fracture using a three point

flexural test technique. The flexural strength represents the highest stress

experienced within the material at its moment of rupture. It is measured in

terms of stress, here given the symbol σ.

Fig.9 Three Point Flexure Test

When an object formed of a single material like a wooden beam or

steel rod, is bent, it experiences a range of stresses across its depth. At the

edge of the object on the inside of the bend, the stress will be at its maximum

compressive stress value. At the outside of the bend, the stress will be at its

maximum tensile value. These inner and outer edges of the beam or rod are

known as ‘extreme fibers’. Most materials fail under tensile stress before

they fail under compressive stress, so the maximum tensile stress value that

can be sustained before the beam or rod fails is its flexural strength.

For a rectangular sample under a load in a three point bending setup

σ = (3FL) / (2bd²)

F is the load (force) at the fracture point (N)

L is the length of the support span (mm)

b is width (mm)

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d is thickness (mm)

4. TABULATION AND GRAPHS

4.1. TABULATION

RESPONSE TABLE FOR DELAMINATION ENTRYDrill Bit Material Speed (rpm) Feed (mm/rev)

Exp. No HSS TC PCD 450 852 1250 0.04 0.08 0.12

1 1.059 1.059 1.059

2 1.068 1.068 1.068

3 1.11 1.11 1.11

4 1.058 1.058 1.058

5 1.09 1.09 1.09

6 1.099 1.099 1.099

7 1.035 1.035 1.035

8 1.068 1.068 1.068

9 1.095 1.095 1.095

10 1.04 1.04 1.04

11 1.065 1.065 1.065

12 1.085 1.085 1.085

13 1.035 1.035 1.035

14 1.062 1.062 1.062

15 1.075 1.075 1.075

16 1.015 1.015 1.015

17 1.043 1.043 1.043

18 1.068 1.068 1.068

19 1.02 1.02 1.02

20 1.026 1.026 1.026

21 1.031 1.031 1.031

22 1.012 1.012 1.012

23 1.015 1.015 1.015

24 1.029 1.029 1.029

25 1.01 1.01 1.01

26 1.016 1.016 1.016

27 1.022 1.022 1.022

TOTAL 9.697 9.488 9.181 9.504 9.475 9.372 9.284 9.453 9.614

AVERAGE 1.077 1.054 1.020 1.056 1.052 1.041 1.031 1.050 1.068

Table 2: Response table for Delamination Entry

RESPONSE TABLE FOR DELAMINATION EXIT

Drill Bit Material Speed (rpm) Feed (mm/rev)

Exp.

NoHSS TC PCD 450 852 1250 0.04 0.08 0.12

1

2

3

4

5

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6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

Table 3: Response table for Delamination Exit

RESPONSE TABLE FOR THRUST FORCE

Drill Bit Material Speed (rpm) Feed (mm/rev)

Exp.

NoHSS TC PCD 450 852 1250 0.04 0.08 0.12

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

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Table 4: Response table for thrust force

RESPONSE TABLE FOR TORQUE

Drill Bit Material Speed (rpm) Feed (mm/rev)

Exp.

NoHSS TC PCD 450 852 1250 0.04 0.08 0.12

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

21

22

23

24

25

26

27

Table 5: Response table for torque

4.2. GRAPHS

DELAMINATION ENTRY GRAPHS

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Fig.10 Speed vs Delamination Entry (HSS)

Fig.11 Feed vs Delamination Entry (HSS)

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Fig. 12 Speed vs Delamination Entry (TC)

Fig.13 Feed vs Delamination Entry (TC)

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Fig.14 Speed vs Delamination Entry (PCD)

Fig.15 Feed vs Delamination Entry (PCD)

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Fig.16 Drill Bit Material vs Delamination Entry

DELAMINATION EXIT GRAPHS

Fig.17 Speed vs Delamination Exit (HSS)

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Fig.18 Feed vs Delamination Exit (HSS)

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Fig.19 Speed vs Delamination Exit (TC)

Fig.20 Feed vs Delamination Exit (TC)

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Fig.21 Speed vs Delamination Exit (PC)

Fig.22 Feed vs Delamination Exit (PCD)

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Fig.23 Drill Bit Material vs Delamination Exit

THRUST FORCE GRAPHS

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Fig.24 Speed vs Thrust Force (HSS)

Fig.25Feed vs Thrust Force (HSS)

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Fig.26 Speed vs Thrust Force (TC)

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Fig.27 Feed vs Thrust Force (TC)

Fig.28 Speed vs Thrust Force (PCD)

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Fig.29 Feed vs Thrust Force (PCD)

Fig.30 Drill Bit Material vs Thrust Force

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TORQUE GRAPHS

Fig.31 Speed vs Torque (HSS)

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Fig.32 Feed vs Torque (HSS)

Fig.33 Speed vs Torque (TC)

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Fig.34 Feed vs Torque (TC)

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Fig.35 Speed vs Torque (PCD)

Fig.36 Feed vs Torque (PCD)

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Fig.37 Drill Bit Material vs Torque

4.3. TEST RESULTS

4.3.1. FLEXURAL STRENGTH

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Fig.38 Flexural Strength Graph

The peak load obtained is 6.8 KN

Flexural strength

σ = (3FL) / (2bd²)

= 3x6800x500/ (2x100x10x10)

= 510 N/mm2

Flexural Strength is found out as 510.00 N/mm2

5. SUMMARY AND CONCLUSION

A brief summary and main conclusion drawn from this study are

presented in this chapter. The main highlight of this work is that this study

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was conducted based on the composites manufacturing and drilling point of

view. The samples for machining were prepared so that the required fiber

orientation 60% by volume could be given. The drilling machine was

modified so that it could measure thrust force and torque value. The

influence of the input parameters on the damage factor and thrust force and

torque is found out and how it is checked to obtain better quality drill hole.

5.1. CONCLUSIONS

From the data received after optimizing the output parameters by

adjusting the input parameters, we come to these following conclusions. The

spindle speed, feed and drill bit material has influence on the final outcome

of the quality of the drilled hole. The drill bit material is most influential

parameter in the output parameters according to study done.

It is observed that the delamination factor or the damage factor, thrust

force and the torque increases as the feed rate is increased while it decreases

with the increase of spindle speed. Also as the hardness of the drill bit

increases, the delamination decreases both at the entry and exit level. It is

also observed that delamination exit is more than the delamination entry. To

achieve minimum delamination, thrust force and torque during drilling

process, we see that we need to reduce the feed rate and increase the spindle

speed. Thus we select the drill bit material as PCD, feed rate as 0.04 mm/rev

and the spindle speed as 1250 rpm to achieve the best quality drilled hole.

REFERENCES

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[1] “Fiber-Glass Reinforced Plastics for Corrosion Resistance” :- Ted R.

Morton, Beetle Plastics, Inc. 1974

[2] “Experimental study of drilling glass fiber reinforced plastics (GFRP)

manufactured by hand lay-up”:-J.Paulo Davim, Pedro Reis - Composites

Science and Technology 64(2004) 289-297

[3] “Effects of special drill bits on drilling-induced delamination of

composite materials” :- H. Hocheng, C.C. Tsao – International Journal of

Machine Tools &Manufacture 46 (2006)

[4] “The effect of vibratory drilling on hole quality in polymeric composites”

:- S. Arul, L. Vijayraghavan, S.K. Malhotra, R. Krishnamurthy –

International Journal of Machine tools & Manufacture 46 (2006) 252-259

[5] “Fibre reinforced composites in aircraft construction”:-C.Soutis –

Progress in Aerospace Sciences 41 (2005) 143-151

[6] “Process Parameters Optimization in GFRP drilling through integration

of Taguchi and Response Surface Methodology” Murthy B.R.N, Lewlyn

L.R. Rodrigues and Anjaiah Devineni – Research journal of Recent Sciences

Vol1 (6) June 2012

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