Effectiveness of Minimum Quantity Lubrication in Hard Milling of AISI H13

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國 立 高 雄 應 用 科 技 大 學

機械工程系

博士論文

AISI H13 硬銑削最少量潤滑有效性之研究

Effectiveness of Minimum Quantity Lubrication in Hard

Milling of AISI H13

Student: Do The Vinh (杜勢 榮)

Advisor: Dr. Quang-Cherng Hsu (許光城 教授)

中華民國 106 年 6 月

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AISI H13 硬銑削最少量潤滑有效性之研究

Effectiveness of Minimum Quantity Lubrication in Hard Milling of

AISI H13

研究生: 杜 勢 榮

指導教授: 許光城 教授

國立高雄應用科技大學

機械工程系

博士論文

A Dissertation Submitted to Institute of Mechanical Engineering

National Kaohsiung University of Applied Sciences

In Partial Fulfillment of the Requirements

For the Degree of Doctor of Philosophy

In Mechanical Engineering

June 2017

Kaohsiung, Taiwan, Republic of China

中華民國 106 年 6 月

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中文摘要

最小量潤滑(MQL)可有效取代濕切及乾切製程，其應用於硬銑削可改善

表面光度、降低刀具磨耗、增加刀具壽命及降低切削溫度等優點。

本研究分為兩部分：第一部分以降低表面粗度值為品質目標利用田口

方法找出 AISI H13 於硬銑削下之最佳切削參數。本研究以槽銑加工進行

研究，採用 L9 直交表進行實驗配置並以訊噪比(S/N)及變異數分析(ANOVA)

分析最小量潤滑參數(切消液種類、壓力及流量)對表面光度的影響。結果

顯示其最佳參數為流量 50 ml/h 且壓力 3 kg/cm2 之水溶性切削液，其流量

與壓力貢獻度經變異數分析後依序為 68.13%及 30.19%。

在第二部分之研究主要基於表面粗糙度及切削力來驗證最小量潤滑之

效率，以乾切與最小量潤滑之切削力及表面粗糙度做比較，選用 L27 直交表

進行實驗規劃，運用反應曲面法及變異數分析來分析切削參數對切削力及

表面粗糙度的影響。結果顯示在乾切與最小潤滑的條件下進給率及切深皆

對表面粗糙度影響最大。切削力分量主要受切削深度影響其次為進給速率。

當切削條件為高切速、低進給與低切深且低硬度之材料即可獲得較良好的

表面粗糙度和最小的切削力。而最小量潤滑切削可提供較好的表面粗糙度

及降低刀具磨耗。以統計模型建立出預測模型用以預測乾切與最小量潤滑

條件下之切削力和表面粗糙度，其結果顯示最小量潤滑相較於乾切條件下

更具有顯著的效果。

關鍵字：最小量潤滑、優化、切削力、表面粗糙度、刀具磨耗、硬銑削、

田口方法、反應曲面法

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Effectiveness of Minimum Quantity Lubrication in Hard Milling of

AISI H13

Student：Do The Vinh Advisors: Prof. Quang-Cherng Hsu

Institute of Mechanical Engineering

National Kaohsiung University of Applied Sciences

ABSTRACT

As a successful alternative to flood coolant processing and dry cutting, the

minimum quantity lubricant (MQL) has already been applied to hard milling for

improvement of surface finish, reduction of tool wear, an increase of tool life,

reduction of cutting temperature, etc.

This research was divided into two parts. In the first part, Taguchi method

was used to find the optimal values of MQL condition in the hard milling of AISI

H13 with consideration of improved surface roughness. Slot milling was selected

for the investigation as an operation that is commonly applied for machining of

the closed slots or pockets and grooves, etc. Taguchi’s L9 array was used to

design the experiments. The signal-to-noise (S/N) ratio and analysis of variance

(ANOVA) were utilized to analyze the influence of the performance

characteristics of MQL parameters (i.e., cutting fluid type, pressure, and fluid

flow) on surface finish. In the results section, the water-soluble oil lubricant, the

50 ml/h fluid flow and the 3 kg/cm2 pressures provided the best results for

surface roughness in hard-milling of AISI H13. Lubricant and pressure of MQL

condition are determined to be the most influential factors giving a statistically

significant effect on machined surfaces. The pressure factor contributed 68.13 %

and the lubricant factor contributed 30.19 % of the total effect. The effect of them

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carried statistical significance. The three parameters of MQL conditions

explained 99.76 % of the variability in surface roughness.

In the second part, the research objective is to demonstrate the efficiency of

MQL based on certain process parameters such as surface roughness and cutting

force. A comparative analysis was done to prove the effectiveness of MQL

versus dry cutting. The characteristics of the cutting force and the surface

roughness obtained under dry cutting and MQL condition were experimentally

investigated. The experiments were conducted using the L27 orthogonal array of

Taguchi’s experimental design technique. The response surface methodology

(RSM) and analysis of variance (ANOVA) were employed for analysis the

influence of cutting parameters (i.e., cutting speed, feed rate, depth-of-cut and

hardness of work-piece) on the cutting force and the surface roughness. As the

result, under both cutting conditions (MQL and dry), feed rate and depth of cut

are the most influential variables regarding surface roughness. The cutting force

components get affected mostly by depth of cut followed by feed rate. Higher

cutting speed, lower feed rate, lower depth of cut and lower work-piece hardness

applied lead to good surface roughness and minimum cutting force. MQL cutting

provided better surface roughness and reduced tool wear. The difference of

values of cutting force components under two cutting conditions (MQL and dry)

is negligible in short machining time. The statistical models to predict cutting

force and surface roughness under dry cutting and MQL condition were

established. The results of the research showed the outstanding effectiveness of

MQL compared to dry cutting.

Keywords: Minimum quantity lubricant, optimization, cutting force, surface

roughness, tool wear, hard milling, Taguchi method, response surface

methodology.

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ACKNOWLEDGMENTS

The fulfillment of over four years of study at National Kaohsiung University

of Applied Sciences (KUAS) has brought me into closer relations with many

enthusiastic people who wholeheartedly devoted their time, energy, and support

to help me during my studies. Therefore, this is my opportunity to acknowledge

my great debt of thanks to them.

I wish to express my thanks and gratitude to my academic supervisor, Prof.

Dr. Quang-Cherng Hsu, for his continuous guidance, valuable advice, and

helpful supports during my studies. He has always been supportive of my

research work and gave me the freedom to fully explore the different research

areas related with MQL hard milling.

I would also like to thank Prof. Yung-Chou Kao, my first supervisor, for his

help and advice during my first study time at KUAS.

I wish to acknowledge my deepest thanks to President of KUAS and Office

of International Affairs for giving me a great opportunity, necessary scholarships

to study at KUAS and many enthusiastic helps during my time in KUAS. I am

also particularly grateful to Thai Nguyen University provided me unflagging

encouragement, continuous helps and support to complete this course.

My gratitude also goes to all of the teachers, Dean and staffs of Department

of Mechanical Engineering for their devoted teaching, great helping and

thoughtful serving during my study in ME.

I would also like to express my sincere gratitude to all of my colleagues at

the Precision and Nano Engineering Laboratory, Department of Mechanical

Engineering, KUAS. I would specially like to thank Mr. Ye Jhan Hong, Mr. Li

Wen Hsiung and Mr. Wei Lin for their great helps in my experimental process.

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I want to express my sincere thanks to all my Vietnamese friends in

KUAS for their helpful sharing and precious helping me over the past time.

I also wish to express my gratitude to all those who directly or indirectly

helped me during my study in KUAS.

Finally, my special thanks to my dad Đỗ Văn Kiểu and my mom Nguyễn Thị

Hà, to my brother Đỗ Minh Khoa, to my adorable wife Nguyễn Thị Nguyên, to

lovely little daughter Đỗ Khánh Linh, who is the most motivation for me over

years in Taiwan.

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CONTENTS

中文摘要.........................................................................................................iv

ABSTRACT.....................................................................................................v

ACKNOWLEDGMENTS .............................................................................vii

CONTENTS....................................................................................................ix

LIST OF FIGURES ......................................................................................xiii

LIST OF TABLES........................................................................................xvi

NOMENCLATURE ....................................................................................xvii

Chapter 1 INTRODUCTION...........................................................................1

1.1 Motivation of the research .......................................................................1

1.2 Objective of the research .........................................................................4

1.3 Scopes of the research..............................................................................5

1.4 Organization of the Dissertation..............................................................6

Chapter 2 BACKGROUND.............................................................................8

2.1 Hard machining........................................................................................8

2.1.1 Overview ..........................................................................................8

2.1.1.1 Concepts of hard machining.....................................................8

2.1.1.2 Advantages and disadvantages.................................................8

2.1.2 Basic operations in hard machining .................................................9

2.1.2.1 Hard turning .............................................................................9

2.1.2.2 Hard milling ...........................................................................10

2.1.2.3 Other operations.....................................................................11

2.1.3 The characterization of hard machining.........................................13

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2.1.3.1 Cutting temperature................................................................13

2.1.3.2 Surface roughness...................................................................14

2.1.3.3 Cutting force...........................................................................15

2.1.3.4 Tool wear................................................................................17

2.2 Cooling and lubrication in metal cutting ...............................................19

2.2.1 Functions of cutting fluid ...............................................................19

2.2.1.1 Cooling ...................................................................................20

2.2.1.2 Lubrication .............................................................................22

2.2.2 Types of cutting fluid .....................................................................22

2.2.2.1 Neat cutting oil .......................................................................23

2.2.2.2 Soluble oil...............................................................................24

2.2.2.3 Semisynthetic .........................................................................25

2.2.2.4 Synthetic .................................................................................26

2.2.3 Cooling/lubrication methods..........................................................26

2.2.3.1 Wet machining method ..........................................................26

2.2.3.2 Dry machining method...........................................................28

2.2.3.3 Minimum quantity lubrication method ..................................28

2.3 Minimum quantity lubrication...............................................................29

2.3.1 Introduction ....................................................................................29

2.3.2 Principles of MQL system..............................................................30

2.3.3 The MQL systems..........................................................................32

2.3.4 The lubricant feeding forms in MQL .............................................33

2.3.4.1 Internal feeding form..............................................................33

2.3.4.2 External feeding form.............................................................34

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2.3.5 Cutting fluids and parameters for MQL.........................................34

2.3.5.1 Fluid types for MQL...............................................................34

2.3.5.2 Wetting of fluids.....................................................................35

2.3.5.3 Viscosity of fluids ..................................................................35

2.3.5.4 Position of external nozzle .....................................................35

2.3.5.5 Fluid flow and air pressure.....................................................37

2.3.6 Benefits and limitations of MQL ...................................................37

2.3.6.1 Benefits...................................................................................37

2.3.6.2 Limitations..............................................................................38

2.4 Literature review....................................................................................38

Chapter 3 RESEARCH METHODS..............................................................46

3.1 Taguchi method .....................................................................................46

3.2 Response surface methodology .............................................................50

3.3 Analysis of variance...............................................................................52

Chapter 4 OPTIMIZATION OF MQL PARAMETERS...............................53

4.1 Design of experiment.............................................................................53

4.2 Experimental procedure.........................................................................56

4.3 Results and Discussions.........................................................................59

4.4 Summary................................................................................................62

Chapter 5 EFFECTIVENESS OF MQL IN HARD MILLING ....................63

5.1 Design of experiment.............................................................................63

5.2 Experimental procedure.........................................................................64

5.3 Results and Discussions.........................................................................66

5.3.1 The analysis of variance and the mathematical model of surface

roughness and cutting force under MQL conditions. ....................68

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5.3.2 The analysis of variance and the mathematical model of surface

roughness and cutting force under dry conditions.........................74

5.3.3 The comparative analysis. ..............................................................81

5.4 User interface of calculation of response characteristics in hard milling

of AISI H13 ...........................................................................................99

5.5 Summary..............................................................................................100

Chapter 6 CONCLUSION AND FUTURE WORKS .................................102

6.1 Conclusion ...........................................................................................102

6.1.1 Optimization of MQL parameters................................................102

6.1.2 Comparison between MQL and dry condition.............................103

6.2 Future works........................................................................................104

LIST OF PUBLICATIONS .........................................................................106

SCIE papers ...............................................................................................106

EI papers ....................................................................................................106

International conferences...........................................................................106

APPENDICES .............................................................................................108

I. Technical Drawing .................................................................................108

II. Settings for machining program............................................................108

III. NC program .........................................................................................109

IV. Code for the calculation of response characteristics ...........................111

REFERENCE...............................................................................................119

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LIST OF FIGURES

Figure 1- 1 Research procedure..............................................................................6

Figure 2- 1 Hard turning process [33]....................................................................9

Figure 2- 2 Hard milling process [35]..................................................................10

Figure 2- 3 Hard boring operation [39]................................................................11

Figure 2- 4 Hard hobbing operation [41] .............................................................12

Figure 2- 5 Dissipation of heat through chips during cutting process [43]..........13

Figure 2-6 Influences of cutting speed and work material on cutting

temperature[44]...............................................................................14

Figure 2- 7 Influence of cutting parameters on surface roughness[43]................15

Figure 2- 8 The relationship between cutting force and hardness[4]...................16

Figure 2- 9 Relationship of cutting speed and cutting force components[50] .....16

Figure 2- 10 The influence of feed-rate and depth-of-cut on cutting force[43]...17

Figure 2- 11 Two basic wear types (a) crater wear, (b) flank wear [53]..............18

Figure 2- 12 Wear of end milling tool..................................................................19

Figure 2- 13 The distribution of the heat sources in cutting [57].........................20

Figure 2- 14 Built-up edge [58]............................................................................22

Figure 2- 15 Classification of cutting fluids in metal cutting [58].......................23

Figure 2- 16 Machining with wet cutting method [67] ........................................27

Figure 2- 17 Benefits of dry cutting [15]..............................................................28

Figure 2- 18 Metal-working fluid costs in metal machining [12]........................30

Figure 2- 19 The ideal concept of MQL[72]........................................................31

Figure 2- 20 Model of a simple MQL atomizer [70] ...........................................31

Figure 2- 21 External and internal MQL system..................................................32

Figure 2- 22 External and internal lubrication feeding forms [73] ......................33

Figure 2- 23 The special drill tool with internal feed[71]....................................34

Figure 2- 24 Levels of wetting of fluids[71] ........................................................35

Figure 2- 25 Optimal position of external MQL nozzle for end milling [71]......36

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Figure 2- 26 The dead zone in feeding by external MQL nozzle [71].................36

Figure 2- 27 The optimal angle of MQL nozzle [71]...........................................37

Figure 3- 1 The general Design Of Experiments process [87].............................47

Figure 4- 1 Peanut oil ...........................................................................................55

Figure 4- 2 Test - tube ..........................................................................................55

Figure 4- 3 TiAlN coated-carbide end mill tool...................................................55

Figure 4- 4 Experimental set-up ...........................................................................57

Figure 4- 5 Measurement of surface roughness by SJ-400 Mitutoyo surf-test

instrument........................................................................................58

Figure 4- 6 Noga MC 1700 cooling system .........................................................58

Figure 4- 7 Statistical analysis by Minitab software ............................................59

Figure 4- 8 Effect of MQL parameters on surface roughness..............................60

Figure 5- 1 Experimental setup. ...........................................................................65

Figure 5- 2 Using Minitab for statistical analysis ................................................66

Figure 5- 3 Optimization plot of surface roughness: a) Optimization for Ra-mql;

and, b) Optimization for Ra-dry......................................................82

Figure 5- 4 Plot of response surface for Ra-mql (other factors are held at middle

value)...............................................................................................83

Figure 5- 5 Plot of response surface for Ra-dry (other factors are held at middle

value)...............................................................................................84

Figure 5- 6 Optimization plot of cutting-force components: a) Optimization for

cutting force components of MQL conditions; and, b) Optimization

for cutting force components of dry conditions..............................86

Figure 5- 7 Plot of response surface for Fx-mql (other factors are held at middle

value)...............................................................................................87

Figure 5- 8 Plot of response surface for Fy-mql (other factors are held at middle

value)...............................................................................................88

Figure 5- 9 Plot of response surface for Fz-mql (other factors are held at middle

value)...............................................................................................89