i

EFFECT OF PROCESS PARAMETERS ON SURFACE ROUGHNESS

PRODUCED BY TURNING BORING OPERATION

AHMAD DZIA’UDDIN BIN MOHAMED

A project report submitted in partial fulfillment of

the requirements for the award of the degree of Master of

Engineering (Mechanical - Advanced Manufacturing Technology)

Faculty of Mechanical Engineering

Universiti Teknologi Malaysia

MAY 2010

iii

DEDICATION

First of all, all the praises and thanks be to Allah S.W.T for His Love,

This thesis is dedicated to my family,

To my beloved parents,

Mohamed bin Samat, Che Wa bt Yussof

My supportive wife,

Asehara bt. Meor Ahmad

My wonderful brothers and sister,

Wan Abd Ghani Mohamed, Mazzlan Mohamed, Razman Mohamed, Siti Asiah

Mohamed, Badruldin Mohamed, Mohamed Kamal Mohamed

iv

ACKNOWLEDGEMENTS

I would like to thank Allah Almighty for blessing me and giving me strength

to accomplish this thesis. A special thanks and deep gratitude to my supervisor,

Professor Dr. Noordin bin Mohd Yusof who greatly helped in guiding and assisting

me in every way throughout this entire project.

Many thanks to all the technicians and staff from KKTM Balik Pulau, Mr.

Ashamudin Technician in Material Failure Testing and Mr. Mohzani lecturer

Department Mechanical Engineering from USM, Mr. Zulkifli b. Mohamad HOD

Mechanical Engineering and technical staff Alicona lab UiTM Shah Alam for their

cooperation and assisting me in the various laboratory tasks.

I like to express my appreciation to my beloved wife Asehara bt Meor Ahmad

and my three children, Nurulain, Nurul Izzati and Nurul Asyikin for their patience,

support, encouragement, belief and trust. I will forever remain grateful for their

sacrifices.

Finally, thank you to MARA and all the other people who have supported me

during the course of this work. Thank You!

v

ABSTRACT

Critical quality measure and surface roughness (Ra) in mechanical parts

depends on turning parameters during the turning process. Researchers have

predicted and developed various models to determine the optimum turning

parameters for the required surface roughness. The main objective of this study is to

investigate the different cutting tool length parameter effect of surface roughness in

CNC Turning boring operation for an aluminium 6061 workpiece. A fractional

factorial design is use to evaluate the effect of five (5) independent variables (cutting

speed, feed rate, depth of cut, tool length and diameter of boring bar) on the resulting

first cut surface roughness (Ra). Vibration or chatter in internal turning operation is a

frequent problem affecting the result of the machining and in particularly, the surface

finish. This study found that using short tool length always produce a good surface

roughness and that only slight improvement on surface roughness can be achieved by

properly controlling the cutting parameters and/or the diameter size of boring bar.

This study also found that using a long tool length may result in vibration that could

be efficiently controlled by the use of larger diameter size of boring bar. With such a

long tool length, the cutting variables become important factors to control in order to

significantly improve surface roughness result with both diameter sizes of boring

bars. A highly accurate prediction model for surface roughness is proposed for each

types of boring bar.

vi

ABSTRAK

Ukuran kualiti yang kritikal pada kesudahan permukaan (Ra) adalah

bergantung kepada parameter pemesinan semasa proses pemesinan larik dilakukan.

Para penyelidik telah membuat jangkaan dan berbagai model baru dibangunkan bagi

parameter yang optimum untuk kesudahan permukaan yang dikehendaki. Objektif

utama penyelidikan ini adalah untuk menyelidiki tentang perbezaan panjang matalat

boleh memberi kesan kepada kesudahan permukaan di dalam operasi melubang

bahan aloi aluminium 6061 pada mesin CNC larik. Fractional factorial design

digunakan untuk menilai kesan lima (5) parameter bebeza (kadar pemotongan, kadar

hantaran, kedalaman pemotongan, panjang tool dan diameter matalat melubang) ke

atas nilai kesudahan permukaan pada pemotongan yang pertama. Getaran adalah

masalah yang sering berlaku dalam operasi melarik profil dalam dan memberi kesan

pemesinan yang besar pada kesudahan permukaan. Dalam penyelidikan ini didapati

penggunaan matalat yang pendek akan sentiasa memberikan kesudahan permukaan

yang baik dan kesudahan permukaaan akan boleh dipertingkatkan lagi dengan

mengawal keadaan pemotongan dan saiz diameter matalat melubang. Dengan

menggunakan matalat yang panjang, didapati pembolehubah bagi pemotongan

menjadi faktor yang utama untuk dikawal bagi memberikan kesan utama dalam

memperbaiki kesudahan permukaan bagi kedua-dua saiz matalat melubang. Model

jangkaan yang berketepatan tinggi untuk kesudahan permukaan telah dicadangkan

untuk setiap saiz matalat melubang tersebut.

vii

TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENTS iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES x

LIST OF FIGURES xi

LIST OF SYMBOLS xv

LIST OF APPENDICES xvi

1 INTRODUCTION 1

1.1 Background 1

1.2 Problem Statement 3

1.3 Objective of the Study 4

1.4 Significance of the Study 5

1.5 Scope of Study 6

1.6 Overview of the Methodology 7

1.7 Thesis Organization 8

2 LITERATURE REVIEW 9

2.1 Theory of Metal Cutting 9

2.1.1 Orthogonal Cutting 11

2.1.2 Oblique Cutting 12

2.2 Metal Cutting in Turning Operation 12

viii

2.3. Tool Geometry 13

2.4 Turning Cutting Data 15

2.5 Boring Operation 18

2.6 Cutting Forces in Boring Operation 19

2.7 Holding the Boring Bar 21

2.8 Surface Roughness in Turning 25

2.9 Factors Affecting Surface Roughness 27

2.9.1 Nose Radius 26

2.9.2 Feed Rate 28

2.9.3 Depth of Cut 28

2.9.4 Cutting Speed 28

2.9.5 Built-Up Edge 29

2.9.6 Material Side Flow 28

2.9.7 Chip Morphology 30

2.10 Wear Mechanism 30

2.11 Chip Formation 33

2.12 Literature Review on Surface Roughness in 36

Turning Operation

2.13 Summary of Literature Review 44

3 METHODOLOGY 45

3.1 Introduction 45

3.2 Research Methods and Procedure 46

3.3 Machines and Equipment 47

3.4 Measurement Equipment and Setup 49

3.4.1 Surface Roughness Measurement 49

3.4.2 Tool Wear Measurement 51

3.5 Workpiece Material 53

3.6 Tool Cutting Material 55

3.7 Machining Parameters 57

3.8 Cutting Condition 57

3.9 Workpiece Preparation 58

3.10 Measure Surface Roughness 60

3.11 Analyze of Tool Wear 61

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3.12 Analyze of Chips Formation 62

3.13 Experimental Design 62

3.13.1 Test for Significance of the Regression Model 65

3.13.2 Test for Significance on Individual Model 65

Coefficient

3.13.3 Test for Lack-of-Fit 66

4 EXPERIMENTAL RESULTS 68

4.1 Introduction 68

4.2 Experimental Results 70

4.3 ANOVA Analysis 71

4.3.1 Confirmation Run 81

4.3.2 Optimization in Range of Surface Roughness 82

4.4 Tool Wear Mechanism 84

4.5 Chip Formation 88

5 DISCUSSION 94

5.1 Introduction 94

5.2 Surface Roughness in Turning Boring Operation 95

5.3 Tool Wear Mechanism 98

5.4 The Effect of Tool Wear on the Surface Roughness 101

6 CONCLUSION AND RECOMMENDATIONS 102

REFERENCES 105

Appendices A - C 108 - 118

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LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 Summary of finding related to the boring operation 41

and surface roughness

3.1 Typical composition of aluminium alloy 6061 54

3.2 Physical properties of pluminium alloy 6061 54

3.3 Mechanical properties aluminium alloy 6061 54

3.4 Machining parameter 57

3.5 Level of independent variables 58

4.1 Experimental plan for surface roughness by turning 69

boring operation

4.2 Experimental result of surface roughness by turning 70

boring operation

4.3 ANOVA table for surface roughness 71

4.4 Experimental plan for confirmation run 81

4.5 Result of conformation test 81

4.6 Experiment plan for optimization test 83

xi

LIST OF FIGURES

FIGURE NO . TITLE PAGE

2.1 Basic machining operation and important parameter 10

2.2 Cutting process, (a) Orthogonal cutting (b) Oblique cutting 11

2.3 Conventional lathe machine 13

2.4 Turning tool nomenclatures 14

2.5 The main cutting data/tool elements for turning tool

applications

17

2.6 Internal turning operation 19

2.7 Radial and tangential cutting forces deflect the boring bar

during machining, often necessitating cutting edge

compensation and tool damping.

20

2.8 The way a boring bar is clamped is decisive as regards

performance and result

23

2.9 Solid bars overhang

23

2.10 Chip evacuation is a critical factor for successful boring.

24

2.11 Tool wear phenomena

32

2.12 Features of single-point wear in turning. (ISO proposed

standard)

33

2.13 Three basic types of chips

34

2.14 Chips are broken (a) on their own (b) against the tool (c)

against workpiece

35

2.15 Chip formation varies with depth of cut, entering angle,

feed, material and tool geometry

35

3.1 Overall research methodology

46

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3.2 An internal turning setup with a workpiece clamped in a

shuck to the left and a boring bar clamped in a clamping

housing to the right

47

3.3 Machine CNC Turning DMG CTX 310 48

3.4 Surface roughness tester 50

3.5 Measuring setup 50

3.6 Optical Nikon microscope c/w Image analyzing software 51

3.7 Optical 3D measurement Infinite Focus 52

3.8 Solid steel boring bar with cermet insert 55

3.9 Cermet insert Specification 55

3.10 Boring bar specification 56

3.11 U-drill and insert specification 56

3.12 Dimension of workpiece before experiment cut 59

3.13 View of boring operation on a workpiece 59

3.14 Machining the workpiece 60

3.15 Surface roughness measurement of work sample 61

4.1 Normal probability plots of residuals for surface

finish in turning boring operation.

73

4.2 Plots of residuals vs. predicted response for

surface finish in turning boring operation.

74

4.3 Outlier T plot for surface finish in turning boring

operation.

74

4.4 Cutting speed factor influence on Ra in turning

boring operation

76

4.5 Feed rate factor influence on Ra in turning boring

operation

76

4.6 Boring bar length factor influence on Ra in turning

boring operation

76

4.7 Boring bar diameter factor influence on Ra in turning

boring operation

77

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4.8 Influence of interaction machining parameters on Ra

in turning boring operation.

78

4.9 Perturbation graph for Ra in turning boring

operation. (bd = 12 mm)

78

4.10 Perturbation graph for Ra in turning boring operation.

(bd = 16 mm)

79

4.11 Surface and contour plot on Surface finish

80

4.12 Plot for optimum cutting parameter in range.

83

4.13 Initial tool wear for boring bar Ø16 mm with tool

overhang 55 mm.

85

4.14 Initial tool wear for boring bar Ø16 mm with tool

overhang 60 mm.

85

4.15 Initial tool wear for boring bar Ø16 mm with tool

overhang 65mm.

86

4.16 Initial tool wear for boring bar Ø12 mm with tool

overhang 55mm.

86

4.17 Initial tool wear for boring bar Ø12 mm with tool

overhang 65mm.

87

4.18 Initial tool wear for boring bar Ø12 mm with tool

overhang 60mm.

87

4.19 ISO-based chip forms classification

88

4.20 Chips formation using bar diameter 16 mm,

bar length 55 mm.

89

4.21 Chips formation using diameter 16 mm, bar length 65mm. 90

4.22 Chips formation with cutting data Diameter 12 mm,

Bar length 55 mm

91

4.23 Chips formation using Diameter 12, Bar length 65

92

4.24 Chips formation using bar length 60

93

5.1 Surface finish result using cutting data cs=150 m/min,

f=0.1 mm/rev, doc = 0.1 mm, bd=16 mm, bl=55 mm.

97

5.2 Surface finish result using cutting data cs=250 m/min,

f=0.2 mm/rev, doc = 0.25 mm, bd=12 mm, bl=655 mm.

97

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5.3 Material stick on top face insert 99

5.4 Built up edge on rake side 100

5.5 Crater wear on rake side 100

5.6 Marks on surface finish cause of material adhered on to the

tool continuously ploughed on the machined surface

101

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LIST OF SYMBOLS

ANOVA - Analysis of Variance

Al - Aluminium

ECEA - End Cutting Edge Angle

SCEA - Side Cutting Edge Angle

Sqrt - Square root

doc - Depth of Cut

cs - Cutting Speed

f - Feed rate

bd - Bar Diameter

bl - Bar Length

F - Force

Fc - Cutting Force

Ft - Tangential Force

Fr - Radial Force

N - Revolution per Minute

Ra - Surface Roughness

T - Tool Life

V - Cutting Speed

C - Taylor’s constant

n - Taylor’s exponential

α - Rake Angle

Ø - Diameter

ʋ - Cutting Velocity

xvi

LIST OF APPENDICES

APPENDIX TITLE PAGE

A-1 Unmodified ANOVA table for turning boring operation 105

B-1 Box-cox plot for turning boring operation 106

B-2 Initial tool wear for cutting Al 6061, times 6s. 107

B-3(a) Surface finish after turning boring operation sequence

followed experimental plan

108

B-3(b) Surface finish after turning boring operation sequence

followed experimental plan

109

B-4 Result of chip formation 110

C-1 Chip formation chart 111

C-2 Recommendation of tool overhang for internal turning 112

C-3 Factor that effect vibration tendencies positively and

negatively, vibration tendency grow towards the right

113

C-4(a) Table of tool wear 114

C-3(b) Table of tool wear 115

1

CHAPTER 1

INTRODUCTION

1.1 Background

In machining operation, the quality of surface finish is an important

requirement of many bored work pieces and parameter in manufacturing engineering.

It is characteristic that could influence the performance of mechanical parts and the

production cost. Various failure, some time catastrophic, leading to high cost, have

been attribute to the surface finish of the component in question. For these reasons

there have been research developments with the objective of optimizing the cutting

condition to obtain a surface finish.

During an internal turning operation, the cutting tool and the boring bar are

subjected to a prescribed deformation as a result of the relative motion between the

tool and work-piece both in the cutting speed direction and feed direction. As a

response to the prescribed deformation, the tool is subjected to traction and thermal

loads on those faces that have interfacial contact with the work-piece or chip. In the

metal-cutting process, during which chips are formed, the work-piece material is

compressed and subjected to plastic deformation.

2

In internal turning, the metal-cutting process is carried out in pre-drilled holes

or holes in cast, etc. The dimensions of the work-piece hole generally determine the

length and limit the diameter or cross-sectional size of the boring bar. Usually, a

boring bar is long and slender and is thus sensitive to excitation forces introduced by

the material deformation process in the turning operation. The boring bar is generally

the weakest link in the boring bar – clamping system of the lathe. The boring bar

motion may vary with time. This dynamic motion originates from the deformation

process of the work material. The motion or vibration of the boring bar influences the

result of the machining in general, and the surface finish in particular.

With external turning, the tool overhang is not effect by the length of work

piece, and the size of tool holder is selected to withstand the forces and stresses

which arise during the operation. With boring – internal turning, the choice of tool

very much restricted by the component’s hole diameter and length, as the depth of

the hole determines the overhang.

A general rule, which applies to all machining is to always minimize tool

overhang and to select the largest possible tool size in order to obtain the best

possible stability and thereby accuracy. The stability is increased when the larger

boring bar diameter is used, but possibilities are often limited, since the space

allowed by the diameter of the hole in the component must be taken into

consideration for swarf evacuation and any radial movement.

The limitation with regard to stability in boring mean that some extra care

must be taken with production planning and preparation. Selecting the right boring

bar for the operation , applying it correctly and clamping it properly has considerable

effect on keeping tool deflection and vibration to a minimum and consequently the

quality of the hole being machined.

3

Previous studies proved the significant impact of DOC, machining speed, and

rake angles on surface roughness. The few studies that have studied boring bar length

that effect of cutting stability or vibration during boring operation. But very few

researchers have studied the interaction effect of boring bar length and bar diameter.

The combination of both of these factors suggests a significant weight in the

relationship. All the previous studies on predicting surface roughness have not

included boring bar diameter as a major factor that affects surface roughness.

1.2 Problem Statement

The determination of optimal cutting condition for specified surface roughness

and accuracy of product are the key factors in the selection of machining process. In

Turning operations, and especially boring operations, are associated with serious

vibration-related problems. To reduce the problem of vibration and ensure that the

desired shape and tolerance are achieved, extra care must be taken with production

planning and in the preparations for the machining of a work-piece. A through

investigation of the vibrations involved is therefore an important step toward solving

the problem.

Researches have been done to improve cutting tool material, tool geometry and

cutting parameter to optimize the machining process. The diameter and length of

boring bar are the most important factor has to be considering in boring operation,

following the other cutting parameter such as cutting speed, feed rate and depth of

cut. The wrong selection of combination cutting parameter will occurs the bad

cutting condition e.g. vibration that effect the poor surface finish. Different

workpiece material with different property and microstructure give different effect to

the cutting tool performance. In lathe boring operation, we found no adequate

empirical model for prediction of surface roughness.

4

In turning operation, the performances of cutting tools are depending on a few

cutting conditions and parameters. The proper selection of feed rate has direct effect

to the product surface roughness. Turning process by maximizing cutting speed and

depth of cut will optimize the cutting process and minimize the production cost. The

tool life, machined surface integrity and cutting forces are directly dependent on

cutting parameters and will determine the cutting tool performances. The study of

surface roughness form will resolve the characteristic and phenomena happening

during the machining process. The questions to be answered at the end of the study

are how does the boring bar tool length and diameter influence the surface roughness

during internal turning operation?

1.3 Objective of the Study

The study was carried out to evaluate the effects of different cutting tool

length on workpiece for internal cutting profile with turning operation, where the

surface roughness values were statistically comparable and to find out the optimum

cutting condition by analyzing the different cutting tool length to get the lowest

surface roughness in turning an Aluminium alloy 6061 solid bar.

Objective of this study are follow:

• To evaluate the effects of different process parameter on internal turning

operation.

• To develop a mathematical model for predicting surface roughness for

internal turning operation by using design of experiment approach.

• Study the initial tool wear during internal turning operation.

• Study of chip formation to relate the reaction occurring between cutting

condition and chip during cutting.

5

1.4 Significance of the Study

Machining operations tend to leave characteristic evidence on the machined

surface. They usually leave finely spaced micro-irregularities that form a pattern

known as surface finish or surface roughness. The quality of the finished product, on

the other hand, relies on the process parameters; surface roughness is, therefore, a

critical quality measure in many mechanical products.

In the turning operation especially boring operation, chatter or vibration is a

frequent problem affecting the result of the machining, and, in particular, the surface

finish. Tool life is also influenced by vibration. Severe acoustic noise in the working

environment frequently occurs as a result of dynamic motion between the cutting

tool and the workpiece. In order to achieve sufficient process stability, the metal

removal rate is often reduced or the cutting tool changed. But as productivity is

normally a priority in manufacturing, this is the wrong route to go.

Instead the means of eliminating vibration and being able to machine at high

rates should be examined. For these reason there have been research development

with the objective of optimising cutting condition to obtain a surface finish with

making the process more stable. To study the optimum tool length and diameter of

boring bar used during cutting process will reduce the machining cost by reducing of

changing the cutting tool and to increase the metal removal rate.

6

1.5 Scope of the Study

The study has been conducted on the following scopes:

(i) CNC Turning machine will be employed.

(ii) Aluminum alloy solid bar Al 6061 will be used as workpiece material.

(iii) Two different diameters boring bar size 16 .0 mm and 12.0 mm with

carbide cutting tool insert will be used at various tool lengths.

(iv) Cutting speed, feed and depth of cut are the other process factors

investigated.

(v) Performance will be primarily in terms of surface roughness, chip

formation and initial tool wear will also be briefly discussed.

(vi) Design of Experiment technique will be used

7

1.6 Overview of the Methodology

The following methodology has been used as a guide in the study to achieve

the study objectives.

(i) Selecting the proper cutting parameters based on literature reviews and

manufacturer recommendations.

(ii) Plan and design reliable experimental techniques.

(iii) Workpiece preparation

Using CNC Turning and purpose tooling to machine the workpiece.

(iv) Experimental trials consisting of:

Surface finish measurement using stylus instrument.

Chip morphology and tool wear mechanism studies using microscope

(v) Data analysis and validation.

Evaluate the effect of tool length on the surface finish

Evaluate the effect of diameter boring bar on the surface finish

Evaluate the initila tool wear

Evaluate the of chip formed produce by internal turning process

8

1.7 Thesis Organization

The thesis is divided into six chapters. Chapter 1 provides a general overview

of the study. Chapter 2 was organized to summarize the literature reviews of the

related topic to guide the study towards achieving the objective. The experimental set

up and techniques used are explained in Chapter 3. All the experiment data and result

will be presented in Chapter 4. Chapter 5 will discuss the results and comparison will

be made to the work done in previous research. The conclusions of the study and the

recommendations for future work will be given in chapter 6