MICRO-GROOVING ON ELECTROLESS NICKEL
PLATED DIE MATERIALS
ALTABUL QUDDUS BIDDUT (B. Sc. Eng., BUET)
A THESIS SUBMITTED
FOR THE DEGREE OF MASTER OF ENGINEERING
DEPARTMENT OF MECHANICAL ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE
2005
Acknowledgements
Acknowledgements
The author would like to express his deepest and heartfelt gratitude and
appreciation to Professor Mustafizur Rahman, Department of Mechanical Engineering,
National University of Singapore (NUS), for his non-stop guidance, support, advice
and inspiration as academic supervisor throughout the entire research work. His
initiative, encouragements, patience and invaluable suggestions are gratefully
acknowledged. The author also would like to convey his sincere thanks to Assoc.
Professor A. Senthil Kumar, Department of Mechanical Engineering, NUS, for
providing his invaluable assistances, encouragements and ideas during the research
work.
The author wishes to express his appreciation to Mr. Neo Ken Soon,
Professional officer, AML, for his technical supports and suggestions. The author also
extends his gratitude equally to the following staffs for their help without which this
project would not be successfully completed; Mr. Nelson Yeo Eng Huat, Mr. Tan
Choon Huat, and Mr. Lim Soon Cheong from Advanced Manufacturing Lab (AML),
who provided technical assistance and support in performing the experimental works
in the study.
A lot of encouraging supports delivered by the author’s many friends and peers
at various stages of this research work is heartily acknowledged with so much cordial
thanks.
Finally, the author would like to acknowledge the Mechanical Engineering
Department, National University of Singapore for their financial support.
i
Table of Contents
Table of Contents
Acknowledgements
i
Table of Contents
ii
Summary
vi
List of Figures
viii
List of Tables
xiii
List of Symbols
xiv
Chapter 1 Introduction
1
1.1 Overview
1
1.2 Objectives
3
1.3 Organization of Thesis 3
Chapter 2 Literature Review
5
2.1 Introduction
5
2.2 Properties of Electroless Nickel
6
2.2.1 Microstructure of Electroless Nicke
6
2.2.2 Hardness
7
2.2.2.1 Effect of Phosphorus Content
7
2.2.2.2 Effect of Heat Treatment
8
2.2.3 Corrosion Resistance 9
2.2.3 Wear Resistance
9
ii
Table of Contents
2.3 Ductile Mode Cutting of Electroless Nickel
10
2.4 Machining of Electroless Nickel with Diamond Tools
13
2.4.1 History
13
2.4.2 Tool Wear
16
2.4.3 Scope of Work 19 Chapter 3 Aspects of Micromachining
20
3.1 Introduction
20
3.2 Chip Formation 20
3.3 Tool Geometry - Minimum Cutting Thickness
21
3.4 Cutting Force and Energy
25
3.5 Cutting Temperature
25
3.6 The Action of Cutting Fluid on Machining 26 Chapter 4 Experimental Details
27
4.1 Experimental Set-up
27
4.1.1 Toshiba Ultra-precision Machine
28
4.1.2 Diamond Tools
28
4.1.3 Workpiece
30
4.1.4 Force Data Acquisition System
31
4.1.5 Vacuum Suction System
32
4.1.6 Chip Collection System
32
4.2 Measuring Equipments Used
32
4.2.1 Mitutoyo Formtracer CS-5000
32
iii
Table of Contents
4.2.2 Nomarski Optical Microcope
33
4.2.3 JOEL JSM-5500 Scanning Electron Microscope & Energy Dispersive X-ray (EDX) Machine
34
4.2.4 Keyence VHX Digital Optical Microcope
35
4.3 Measurement and Analysis
36
4.3.1 Surface roughness Measurement
36
4.3.2 Micro-cutting Force Measurement
36
4.3.3 Tool Wear Observation
37
4.3.4 Machined Surface Observation
37
4.4 Experimental Procedure
37
4.4.1 Effect of Cutting Parameters
39
4.4.2 Optimal Cutting Condition
39
4.4.3 Tool Wear Observation Procedure 40
Chapter 5 Results and Discussion
41
5.1 Introduction
41
5.2 Cutting Parameters
42
5.2.1 Effect of Cutting Speed
42
5.2.1.1 Effect on Surface Roughness
43
5.2.1.2 Effect on Cutting Forces
45
5.2.2 Effect of Infeed Rate
47
5.2.2.1 Effect on Surface Roughness
47
5.2.5.2 Effect on Cutting Forces
50
5.3 Determination of Optimal Cutting Conditions
51
iv
Table of Contents
5.4 Effect of Phosphorus Content on Hardness of Wokrpieces 52
5.5 Diamond Tool Wear Characteristics 53
5.5.1 Diamond Tool Wear Patterns
53
5.5.1.1 Diamond Tool with the +50 Rake Angle
53
5.5.1.2 Diamond Tool with the 00 Rake Angle
57
5.5.1.3 Diamond Tool with the-+50 Rake Angle
59
5.5.2 Diamond Tool Wear Mechanisms
61
5.6 Performance of Diamond tools 65
5.6.1 Wear Resistance and Tool Life
65
5.6.2 Cutting Forces
68
5.6.2 Machined Electroless Nickel Surface Characteristics
70
5.7 Chip Observation 74 Chapter 6 Conclusions and Recommendations for Future Work
76
6.1 Introduction 76
6.2 Conclusions 76
6.3 Recommendations for Future Work
78
Bibliography 80
List of Publications 86
v
Summary
Summary
In recent years, ultra-precision machining with diamond turning has been rapidly
growing for manufacturing high precision machined parts of advanced industrial
applications .Outstanding hardness and crystalline structure of diamond make it
possible to fabricate diamond cutter with very sharp cutting edges which are necessary
for ultra-precision machining. Components with sub micron form accuracy and surface
roughness in the nanometer range can be machined cost effectively using single point
diamond tool due to its extreme hardness and high resistance to wear. Thus the
technology has established itself to produce components with high degree of surface
finish and dimensional accuracy. However, it is limited by the number of materials that
can be produced by diamond turning, especially in the fabrication of molds for optical
components. Electroless nickel is one of such machinable materials which exhibit
excellent properties such as hardness, corrosion resistance; more importantly diamond
machine electroless nickel effectively. Therefore, diamond turning of this material is a
viable option for producing high quality optical surfaces without any post machining
process. The feature makes the technique economical and advantageous by reducing
the overall production time of machining compared to other techniques such as
grinding.
Diamond turning of micro-grooves on non-ferrous metals such as electroless
nickel plated molding dies is one important application areas for the production of high
precision prismatic light guide for CD/DVD pickup lenses. Many studies had already
been carried out on machining of electroless nickel as well as on other materials with
diamond tool of different crystal orientations and infrared absorption quality for
various cutting distances. However, there is no known reported study on the evaluation
of the cutting performance of the diamond tools with different rake angles during
vi
Summary
micro- grooving on electroless nickel plated die materials. The aims of this study is to
compare and investigate the cutting performance of three single crystal diamond tools
with different rake angles (00, +50 and -50) during micro grooving on electroless nickel
plated die material. The machining performances are evaluated in terms of tool wear,
cutting forces, and surface roughness of the machined workpieces. The wear
progression characteristics and the wear mechanisms of diamond tools with different
rake angles are presented and illustrated. The effects of machining parameters such as
spindle speed and infeed rate are also investigated in this study.
It was found that diamond tools with the 00 rake angle have superior performance
compared to those with +50 and -50 with respect to tool wear, cutting forces, and
machined surface roughness. Tool wears on the flank and rake faces of the +50 rake
and the -50 rake tool were found to increase with cutting distance with corresponding
increase in forces. On the other hand, the 00 rake tool machined satisfactorily up to the
same cutting distance (11.689 km) without any sign of tool wear. However, the
increase in wear on tools with +50 and -50 rake angles, and cutting forces on the
diamond tools with all these three different rake angles did not significantly affect the
surface roughness. Surface quality of up to 3nm Ra was achievable during micro-
grooving of electroless nickel.
vii
List of Figures
List of Figures
Figure 2.1 Influence of Phosphorus Content and Heat Treatment Condition on Structure
7
Figure 2.2 Influence of Phosphorus Content on Hardness
8
Figure 2.3 Influence of Phosphorus Content and Heat Treatment Condition on Hardness
9
Figure 2.4 A Chip Removal Model for Cutting Brittle Material when the Depth of Cut is (a) Smaller and (b) Larger
11
Figure 2.5 Influence of Phosphorus Content and Heat Treatment Condition on Diamond Tool Wear
18
Figure 3.1 Geometry of Orthogonal Cutting
21
Figure 3.2 A Model of Micro Cutting
22
Figure 3.3 Cutting Force in the Elastic Region
22
Figure 3.4 Force Model in Cutting Region
23
Figure 3.5 Stress on the Neutral Point
24
Figure 4.1 Photographic View of Experimental Setup
27
Figure 4.2 View of the Toshiba ULG-100C Ultra-precision Machine
28
Figure 4.3(a) Single Point Diamond Tool (00 rake)
29
Figure 4.3(b) Single Point Diamond Tool (+50 rake)
29
Figure 4.3(c) Single Point Diamond Tool (-50 rake)
29
Figure 4.4 Electroless Nickel Plated Workpiece
30
Figure 4.5 Schematic View of the Machined Workpiece and Details of Groove X- Section
31
Figure 4.6 Schematic Diagram of Micro-cutting Force Data Acquisition System
32
Figure 4.7 Photographic View of Mitutoyo FORTRACER
33
Figure 4.8 Nomarski Optical Microscope (Olympus STM-6)
34
viii
List of Figures
Figure 4.9 Scanning Electron Microscope (SEM) Associated with Energy Dispersive X-ray (EDX) Machine
35
Figure 4.10 Photograph of Keyence VHX Digital Optical Microscope
36
Figure 5.1 Cutting Force Directions on Tool
43
Figure 5.2 Variation of Surface Roughness with Spindle Speed for Different Tools with Different Rake Angles
44
Figure 5.3(a) Photograph of the Machined Surface and Corresponding R Profile at 100 rpm with 00 Rake Tool
44
Figure 5.3(b) Photograph of the Machined Surface and Corresponding R Profile at 250 rpm with 0o Rake Tool
44
Figure 5.3(c) Photograph of the Machined Surface and Corresponding R Profile at 500 rpm with 00 Rake Tool
45
Figure 5.3(d) Photograph of the Machined surface and Corresponding R Profile at 750 rpm with -50 Rake Tool
45
Figure 5.3(e) Photograph of the Machined Surface and Corresponding R Profile at 1000 rpm with 00 Rake Tool
45
Figure 5.4(a) Effect of Spindle Speeds on Cutting Forces for the Tools with Three Different Rake Angles
46
Figure 5.4(b) Effect of Spindle Speeds on Thrust Forces for the Tools with Three Different Rake Angles
47
Figure 5.5 Variation of Surface Roughness with Infeed Rate for Different Tools with Different Rake Angles
48
Figure 5.6(a) Photograph of The Machined Surface and Corresponding R Profile at 0.1µm/rev with 0 deg. Rake Tool.
48
Figure 5.6(b) Photograph of the Machined Surface and Corresponding R Profile at 0.5µm/rev with 0 deg. Rake Tool
49
Figure 5.6(c) Photograph of the Machined Surface and Corresponding R Profile at 1µm/rev with -5 deg. Rake Tool.
49
Figure 5.6(d) Photograph of the Machined Surface and Corresponding R Profile at 2 µm/rev with +5 deg. Rake Tool.
49
Figure 5.6(e) Photograph of the Machined Surface and Corresponding R Profile at 3 µm/rev with 0 deg. Rake Tool
50
ix
List of Figures
Figure 5.7(a) Effect of Infeed Rates on Cutting Forces for the Tools with Three Different Rake Angles
50
Figure 5.7(b) Effect of Infeed Rates on Thrust Forces for the Tools with Three Different Rake Angles
51
Figure 5.8 Effect of Phosphorus Content on Hardness of Workpieces
52
Figure 5.9(a) Nomarski Microscope Photograph of Flank Wear Region of Diamond Tool with +50 Rake Angle after Cutting 2.347 km
54
Figure 5.9(b) Nomarski Microscope Photograph of Flank Wear Region of Diamond Tool with +50 Rake Angle after Cutting 6.03 km
54
Figure 5.9(c)
Nomarski Microscope Photograph of Flank Wear Region of Diamond Tool with +50 Rake Angle after Cutting 7.26 km
54
Figure 5.9(d) SEM Photograph of Micro-grooves on Flank Wear Region of Diamond Tool with +50 Rake Angle after Cutting 7.26 km
55
Figure 5.9(e) SEM Photograph of Flank Wear Region of Diamond Tool with +50 Rake Angle after Cutting 10.5 km
55
Figure 5.9(f) SEM Photograph of Micro-grooves on Flank Wear Region of Diamond Tool with +50 Rake Angle after Cutting 10.5 km
55
Figure 5.10(a) Nomarski Microscope Photograph of Rake Face of Diamond Tool with +50 Rake Angle after Cutting 4.9 km
56
Figure 5.10(b) SEM Photograph of Rake Face of Diamond Tool with +50 Rake Angle after Cutting 8.5 km
56
Figure 5.10(c) SEM Photograph of Rake Face of Diamond Tool with +50 Rake Angle after Cutting 10.5 km
57
Figure 5.11(a) VHX digital Microscope Photograph of Flank Face of Diamond Tool with 00 Rake Angle after Cutting 7.53 km
57
Figure 5.11(b) VHX digital Microscope Photograph of Flank Face of Diamond Tool with 00 Rake Angle after Cutting 11.69 km
58
Figure 5.12(a) VHX digital Microscope Photograph of Rake Face of Diamond Tool with 00 Rake Angle after cutting 7.53km
58
Figure 5.12(b) VHX digital Microscope Photograph of Rake Face of Diamond Tool with 00 Rake Angle after Cutting 11.69 km
58
Figure 5.13(a) VHX Digital Microscope Photograph of Flank Face of Diamond Tool with -50 Rake Angle after Cutting 3.76 km
59
x
List of Figures
Figure 5.13(b) VHX Digital Microscope Photograph of Flank Face of Diamond Tool with -50 Rake Angle after Cutting 9.42 km
60
Figure 5.14(a) VHX Digital Microscope Photograph of Rake Face of Diamond Tool with -50 Rake Angle after Cutting 1.88 km
60
Figure 5.14(b) VHX Digital Microscope Photograph of Rake Face of Diamond Tool with -50 Rake Angle after Cutting 5.65 km
60
Figure 5.14(c) VHX Digital Microscope Photograph of Rake Face of Diamond Tool with -50 Rake Angle after Cutting 9.42 km
61
Figure 5.14(d) VHX Digital Microscope Photograph of Rake Face of Diamond Tool with -50 Rake Angle after Cutting 9.42 km
61
Figure 5.15 Schematic Diagram of Chip Flow Mechanism
63
Figure 5.16(a) Keyence VHX Optical Microscope Photography of Flank Face of -50 Rake Angle tool with Adhered Layer of Electroless Nickel.
64
Figure 5.16(b) Keyence VHX Optical Microscope Photography of Flank Face of 00 Rake Angle tool with Adhered Layer of Electroless Nickel.
64
Figure 5.17 EDX (Energy Dispersive X-ray) Analysis of the Adhered Layer on the -50 Rake Angle Tool.
64
Figure 5.18 Flank Wear with Cutting Distance for the Tools with Different Rake Angles
66
Figure 5.19(a) Rake Face of the -50 Rake Angle Tool after Cutting 11.69km
67
Figure 5.19(b) Rake Face of the +50 Rake Angle Tool after Cutting 11.69km
67
Figure 5.20(a) Effect of Cutting Distance on Thrust Forces for Diamond Tools with Different Rake Angles
69
Figure 5.20(b) Effect of Cutting Distance on Cutting Forces for Diamond Tools with Different Rake Angles
70
Figure 5.21(a) Effect of Cutting Distance on Surface Roughness, Ra
71
Figure 5.21(b) Effect of Cutting Distance on Surface Roughness, Ry
71
Figure 5.22(a) Roughness Profile of Electroless Nickel for tool with the 00
rake angle after cutting 11.69km
72
Figure 5.22(b) Roughness Profile of Electroless Nickel for tool with the -50
rake angle after cutting 11.69km. 72
xi
List of Figures
Figure 5.22(c) Roughness Profile of Electroless Nickel for tool with the +50
rake angle after cutting 11.69km.
73
Figure 5.23(a) Photograph of Machined Micro-grooves after cutting 11.69 km with the 00 rake angle
73
Figure 5.23(b) Photograph of Machined Micro-grooves after cutting 11.69 km with the -50 rake angle
74
Figure 5.23(c) Photograph of Machined Micro-grooves after cutting 11.69 km with the +50 rake angle
74
Figure 5.24(a) Machined Electroless Nickel Chip Produced by 00 Rake Angle Tool
75
Figure 5.24(b) Machined Electroless Nickel Chip Produced by -50 Rake Angle Tool
75
Figure 5.24(c) Machined Electroless Nickel Chip Produced by +50 Rake Angle Tool
75
xii
List of Tables
List of Tables
Table 4.1 The Geometries of Diamond Tools
29
Table 4.2 Matrix of Cutting Parameter 39
Table 4.3 Cutting Conditions during Performance Test
40
xiii
List of Symbols
List of Symbols Bc Minimum cutting thickness
Fc Cutting force
Ft Thrust force
Lc Tool chip contact length
f Feed rate
pe Normal stress on the round tool edge in elastic region
r The tool edge radius
tm Minimum cutting thickness
t1 Uncut chip thickness
t2 Chip thickness
w Width of the tool
α Tool rake angle
αe Effective tool rake angle
ϕ Shear angle
β Mean friction angle between the chip and the tool
µ Friction coefficient
βe Friction angle in elastic region
βp Friction angle in plastic region
τS Shear strength
γ Clearance angle
xiv
Chapter 1: Introduction Chapter 1
Introduction
1.1 Overview
Ultra precision metal cutting is one of the most successful developments within
last fifty years. Generally, this can be defined as a cutting technique which enables us
to produce components with micrometer or sub micrometer form accuracy and surface
roughness within a few tens nanometer. From 1960’s, its development started as a
promising method for fabricating dedicated optical, mechanical, or electronic parts
essential for different particular advanced applications. The technique was applied for
the production of a variety of optical components through the 1970’s for its high
precision, versatility and lower overall manufacturing cost. In the 1980’s the technique
has resulted in extended industrial use for manufacturing of aluminum scanner mirrors,
and aluminum substrates for computer memory disks; where very fine surface finish
was highly desirable. Along with these industrial applications, more recently the
technique has been also used for the manufacturing of highly sophisticated optical
parts with extremely high geometrical accuracy and surface finish [Ikawa et al., 1991].
By Continuous improvement, not only of machine parts (spindles, slides etc.)
machine constructions, electronic control, measuring techniques, but also of cutting
tool quality are now common practice [Oomen and Eisses, 1992].Outstanding hardness
and crystalline structure of diamond holds the possibilities to fabricate diamond tools
with very sharp cutting edges which are necessary for ultra precision machining.
Components with sub micron form accuracy and surface roughness in the nanometer
range can be machined cost effectively using single point diamond tools due to their
Micro-grooving on Elcetroless Nickel Plated Die Materials 1
Chapter 1: Introduction extreme hardness, high resistance to wear, and good thermal conductivity for heat
removal during machining [Rahman et al., 2004].
Technology has established itself already to produce components with high
degree of surface finish and dimensional accuracy. However, it is limited by the
number of materials that can be produced by diamond turning, especially in the
fabrication of molds for optical components. Electroless nickel is one of such materials
which exhibit excellent properties such as hardness, corrosion resistance; more
importantly diamond machines electroless nickel very efficiently. Therefore, the
diamond turning of this material becomes a viable option for producing high quality
optical surfaces without any post machining process. The feature makes the technique
economical and advantageous by reducing the overall production time of machining
compared to other techniques such as grinding and lapping [Casstevens, 1978].
The studies were already carried out for turning of electroless nickel as well as
other materials with diamond tools of different crystal orientations and infrared
absorption quality for various cutting distance. However, machining performance of
diamond tools with different rake angles is not well investigated. Besides, micro-
grooving on electroless nickel plated die materials with diamond tools are also
essential to study for its increasing applications for producing very high resolution and
highly accurate prismatic light guide for CD/ DVD pickup lenses. The example of
unique capability of micro-grooving on an electroplated copper disk with diamond
tools is done already for mastering of new optical memory disk application.[Ikawa,
1991]. Therefore, this study has attempted to machine micro-grooves with diamond
tools with different rake angles on electroless nickel plated die materials. The aims of
research work are to compare and investigate the performance of three single point
diamond tools with different rake angles (00, +50 and -50). The machining performance
Micro-grooving on Elcetroless Nickel Plated Die Materials 2
Chapter 1: Introduction was evaluated in terms of tool wear, cutting forces and surface roughness of the
machined workpieces. The characteristics of wear pattern of the tools and it’s
mechanisms with different rake angles are carried out. Moreover, effects of machining
parameters, infeed rate and cutting speed, are also carried out to find a suitable optical
cutting condition within this study.
1.2 Objectives
The objectives of this study are described below.
• To investigate the effects of different machining parameters of single crystal
diamond tools with three different rake angles during micro grooving on
electroless nickel-plated materials.
• To investigate wear patterns and wear mechanisms of diamond tools with
respect to cutting distance for diamond tools with three different rake angles.
• To investigate the machining performance of diamond tools with three different
rake angles with respect to tool wear, machined surface roughness, and micro-
cutting forces.
• To investigate the machined electroless nickel surface and the chips produced
while cutting with diamond tools with three different rake angles.
1.3 Organization of Thesis
In Chapter 2, the brief history of electroless nickel deposits and it’s machining with
diamond tool are discussed. Investigations on theoretical aspect of micro-grooving on
brittle materials and factors affecting the technique are discussed in Chapter 3. Chapter
4 describes the experimental setup and procedure, the details about workpieces, cutting
tools, machining parameters, surface measurement system, cutting forces data
Micro-grooving on Elcetroless Nickel Plated Die Materials 3
Chapter 1: Introduction acquisition system and taking pictures of surfaces and cutting edges. Details
discussions of the experimental findings are presented in Chapter 5. The conclusions
drawn from this study are presented in Chapter 6, along with a brief discussion on the
future directions of the work.
Micro-grooving on Elcetroless Nickel Plated Die Materials 4
Chapter 2: Literature Review
Chapter 2
Literature Review
2.1 Introduction
Electroless nickel coatings have been used increasingly in various industries
since the early 1980’s. Some of the outstanding characteristics of these coatings are
excellent corrosion and wear resistance, exceptional uniformity, wide range of
thickness as well as mechanical and physical properties, good solderability, and
surface lubricity [Baudrand, 1978]. They are widely used either as protective or
decorative coatings in many industries, including optics, electronics, computer,
nuclear, chemical, petroleum, and aerospace [Parker, 1972]. In addition, compared to
conventional electroplating methods, elcetroless nickel coatings can be applied on
different substrates, either conductive or nonconductive, since no external current is
applied to the component. The process is termed “autocatalytic” where nickel acts as
catalyst in the reaction [Casstevens and Daugherty, 1978].
Although electroless nickel coatings are fairly new, the discovery of the fact
that nickel could be deposited on a surface from an aqueous solution of its salt by
reduction with hypophosphite was proposed by Waltz in 1844 [Reidel, 1991]. Due to
the poor quality of the reducing agents that leads to rough deposits with inferior
properties, Waltz’s idea was not developed for a whole century. In 1944, the first
laboratory experiment reported on electroless nickel was completed by Brenner and
Riddel, who were later given credit for introducing the electroless nickel method to the
world. The process discovered was patented in 1950. The process was further
developed by General American Transportation Corporation and marketed under name
“Kanigen” [Casstevens and Daugherty, 1978]. The years 1978 to 1982 marked a
Micro-grooving on Elcetroless Nickel Plated Die Materials 5
Chapter 2: Literature Review
further advance in the technology, insofar as phosphorous-rich electroless nickel
coatings were developed. These deposits are normally laid down without the use of
heavy metal or sulphur-coating stabilizers and form a glassy, amorphous structure.
Where problems due to corrosion or wear arise, such electroless nickel coatings-
known as “third-generation”- are finding increasing applications [Reidel, 1991].
Nowadays, electroless nickel is no longer a single type of coating but an entire
family of coatings. Thus, they are available from many companies for commercial and
experimental use. However, electroless nickel with high phosphorus content (>13%) is
difficult to achieve and more importantly, costly. In addition, the other problem is to
get high thickness of coating which results in defective surface [Pramanik, 2004].
2.2 Properties of Electroless Nickel
2.2.1 Microstructure of Electroless Nickel
The properties of electroless nickel coatings are directly attributed to their
micro structural characteristics. The phosphorus content of electroless nickel deposits
controls their microstructure and properties [Park and Lee, 1988]. Electroless nickel
deposit is not well understood in their details structure but as plated electroless nickel
coatings have been reported to be either crystalline, amorphous, or a co-existence of
both. The general trend in the understanding of electroless nickel deposits is that as-
plated electroless coatings containing 1-5% phosphorus are crystalline; those
containing 6-9% phosphorus consist of mixed crystalline and amorphous
microstructures; whereas those containing 10-13% phosphorus are amorphous and
crystallize on heat treatment to nickel and various forms of nickel phosphides.
However, since the diffraction pattern of the high-alloy electroless nickel deposits are
very similar to those of materials that are rapidly cooled from the liquid state and that
Micro-grooving on Elcetroless Nickel Plated Die Materials 6
Chapter 2: Literature Review
are considered to be glasses, electroless nickel can justifiably be considered amorphous
[Mallory and Haju, 1990]. Figure 2.1 shows the structure of as-plated electroless
nickel coatings with variation of phosphorus content and heat treatment temperatures.
Figure 2.1: Influence of Phosphorus Content and Heat Treatment Condition on Structure [Syn and Dini, 1985]
2.2.2 Hardness
Huge amount of works regarding the hardness of electroless nickel were done
and therefore, hardness is the most widely studied property of electroless nickel
deposits [Riedel, 1991]. Hardness, which plays a significantly important role in
selecting the cutting tool materials and values of cutting parameters, is mainly
controlled by the phosphorus content and heat treatment, this fact makes elcetroless
nickel more attractive in machining world.
2.2.2.1 Effect of Phosphorus Content
The hardness of electroless nickel deposits, as with other properties, is directly
affected by the phosphorus content. As Figure 2.2 shows, increasing the phosphorus
content of the deposits lowers the hardness of the coating. At the maximum hardness
the phosphorus content is minimum where the microstructure consists of single
Micro-grooving on Elcetroless Nickel Plated Die Materials 7
Chapter 2: Literature Review
crystallize β phase. As the phosphorus content increase, β phase in microstructure
decreases while amorphous γ phase increases; which leads to reduce the hardness of
the elcetroless nickel coating as the γ phase is a softer compared to the β phase. The
minimum value of hardness is reached when the amount of phosphorus content is high
(11%P) with completely γ phase in microstructure [Duncan, 1983].
Figure 2.2: Influence of Phosphorus Content on Hardness [Duncan, 1983]. 2.2.2.2 Effect of Heat Treatment
One of the outstanding characteristics of electroless nickel coatings is the
possibility of obtaining very high hardness values through an appropriate heat
treatment process, thus post heat treatment process is a significant impact on the
hardness of electroless nickel coatings. Heat treatment of electroless nickel deposits
provides a unique wear and erosion resistance. Figure 2.3 shows the effect of heat
treatment temperature on electroless nickel coatings hardness. The maximum hardness
was obtained after a heat treatment at 400oC for one hour whish is also reported from
many other studies [Baudrand, 1978 and Reidel, 1997].
Micro-grooving on Elcetroless Nickel Plated Die Materials 8
Chapter 2: Literature Review
Figure 2.3: Influences of Phosphorus Content and Heat Treatment Condition on Hardness [Syn et al., 1985]
2.2.3 Corrosion Resistance
Excellent corrosion resistance is another unique property of electroless nickel
coatings in different industrial environments. This corrosion resistance is attributed by
their phosphorus content. However, the concept that high phosphorus coatings are
more corrosion resistant than low phosphorus coatings cannot be generalized for all
industrial environments. However, coatings having high phosphorus content have
amorphous microstructures, which provides a better corrosion resistance due to the
absence of grain boundaries. There are several other factors affecting the corrosion
properties of electroless nickel coatings which include coating thickness, porosity, type
of heat treatment [Duncan, 1983].
2.2.4 Wear Resistance
One of the unique characteristics of electroless nickel deposition is the superior
wear resistance of the coatings. The wear resistance of electroless nickel deposits
depends on both phosphorus content and the type of post heat treatment applied.
However, there are numerous parameters such as the nature of the applied stress which
affect wear properties. It was explained previously that the hardness reaches its highest
Micro-grooving on Elcetroless Nickel Plated Die Materials 9
Chapter 2: Literature Review
value at approximately 4 % phosphorus content - the γ phase first forms- whereas it
reaches its lowest value when the last remaining β phase disappears. The same
conclusion is true for explaining the wear resistance properties of electroless nickel
coatings.
2.3 Ductile Mode Cutting of Electroless Nickel
As described in the previous sections, electroless nickel, having many
advanced physical and mechanical properties, is now used extensively in optical
industry and infra-red optics. Microscopically, electroless nickel is considered to be an
extremely brittle and hard material that exhibits little ductility during actual machining.
Therefore, in order to generate surfaces of high optical quality on brittle materials such
as electroless nickel, it is important that the material must be machined in ductile
mode. It is to be noted again that recently ultra-precision diamond turning has enabled
fabrication of mirror-like surface of brittle materials by controlling the cutting mode to
be ductile [Ikawa et al., 1991].
Over the years, researchers have attempted to understand the ductile
machining of brittle materials. The research work among the studies on ductile
machining of brittle materials involves mainly ductile grinding and ductile cutting, and
especially, ductile turning of brittle materials. In this section, however, the focus will
be on literature reviews on ductile cutting of brittle materials.
In 1986, Toh and McPherson noticed that plastically deformed chips can be
formed in the machining of ceramic materials when the scale of machining is small (<
1 µm depth of cut), which indicates that ductile mode cutting of brittle materials could
be achieved if the depth of cut is in mesoscale. Similar ductile chip formation has also
Micro-grooving on Elcetroless Nickel Plated Die Materials 10
Chapter 2: Literature Review
been observed in fine scale machining of debris from a wide range of ceramics,
glasses, semiconductor materials and crystals [Blackley and Scattergood, 1994; Fang
and Venkatesh, 1998; Moriwaki et al., 1992]. It has been well demonstrated that
during machining of brittle materials, there is a transition from brittle mode to ductile
mode when the depth of cut decreases to very small (usually < 10 µm). Shimada et al.
[1995] proposed a generalized hypothesis for brittle-to-ductile transition in micro-
machining and micro-indentation of brittle materials. According to them, the mode of
materials removal, brittle or ductile, may depend upon the dominance of two criteria:
the resolved tensile stress on a cleavage plane or the shear stress on a slip plane
exceeds a certain critical value for each stress level under particular machining
conditions.
An interpretation of ductile transition phenomena is based on cleavage fracture
due to the presence of defects [Nakasuji et al., 1990]. The critical values of a cleavage
and plastic deformation are affected by the density of defects/dislocations in the work
material. Since the density of defects is not so large in brittle materials, the critical
value of a fracture depends on the size of the stress field. Figure 2.4 shows a model of
Too
ChiChi
Tool
Cracks
Defect Critical Stress
(a) (b)
Figure 2.4: A Chip Removal Model for Cutting Brittle Material when the Depth of Cut is (a) Smaller and (b) Larger [Nakasuji et al., 1990]
Micro-grooving on Elcetroless Nickel Plated Die Materials 11
Chapter 2: Literature Review
chip removal with size effects. When the uncut chip thickness is small, the size of the
critical stress field is small, thus avoiding cleavage. Consequently, the transition chip
removal process from brittle to ductile depends on the uncut chip thickness.
In addition to the cutting parameters such as depth of cut and feed rate, the
cutting edge of the tool plays an important role in ductile mode cutting of brittle
materials such as silicon. There is a strong relationship between the cutting edge of the
tool and the undeformed chip thickness, which is instrumental in achieving ductile
mode cutting of brittle materials. Asai and Kobayashi (1990) reported that during ultra-
precision machining, to get a mirror-like surface, the thickness of undeformed chip
must be equal to or smaller than the cutting edge radius of a tool. Usually a common
single crystal diamond tool contains a cutting edge radius of some tens of nanometers
or larger. However, an extremely small undeformed chip thickness approaches the
same order of or smaller than the cutting edge radius of the tool. In this case, the
cutting edge effects include at least two aspects [Yan et al., 2002; Patten and Gao,
2001]. Firstly, edge roundness decreases the stress concentration and yields a relatively
uniform stress field in the cutting region. Secondly, the effective rake angle induced by
the edge radius becomes a large negative value, and as a result, material in front of the
cutting edge is suppressed downward and the compressive stress (hydrostatic stress
field) becomes predominant.
According to the theory of plasticity, the magnitude of hydrostatic stress
determines the extent of plastic deformation prior to fracture, which in turn determines
material ductility or brittleness. Therefore, with the sufficient hydrostatic pressure
generated by the tool edge at the cutting region, plastic deformation is more likely to
occur than crack generation even at a lower temperature and therefore, ductile mode
Micro-grooving on Elcetroless Nickel Plated Die Materials 12
Chapter 2: Literature Review
cutting of brittle materials can be achieved [Castaing et al., 1981]. Hence this is
considered to be the origin of the brittle-to-ductile transition in diamond turning.
2.4 Machining of Electroless Nickel with Diamond Tools
2.4.1 History
First study of diamond turning on electroless nickel was reported in 1978 by
Casstevens and Daughherty (1978). In this preliminary work on electroless nickel, an
explanation of the electroless nickel plating process is given and important
metallurgical and mechanical properties of the plating were discussed. Extensive tests
on machinability were conducted with variations in types of plating, thickness of
plating, types of substrates, and heat treatment of the plating. In addition, results of the
testing program were presented. Experiments were conducted on electroless nickel
plated disk of 102 mm diameter at Oak Ridge Y-12 Plant following the conditions:
spindle speed of 350 to 1000 rpm, and tool feeds from 14.5 to 2.54 µm/rev. The tools
with different round-nose radius (0.53, 1.60, 3.18 and 25.4 mm) were employed during
machining. The calculated surface finish at typical diamond turning parameters had not
been reached. Moreover, the effect of tool radius upon surface finish was not
completely clear during the work. The conclusion was that the tool radius did not
greatly affect the measured surface roughness of electroless nickel if the tool advance
was matched to the tool radius to give the same theoretical finish. When machining
electroless nickel, tool life was about the same as when machining such softer fcc
metals as copper and aluminum. Surface finishes of diamond machined electroless
nickel had quite a different appearance than those of fcc metals, such as copper, when
both materials were machined at the same speed and tool advance. Electroless nickel
was characterized by very uniform and distinct tool marks, much in contrast with the
Micro-grooving on Elcetroless Nickel Plated Die Materials 13
Chapter 2: Literature Review
smoother appearance of copper surfaces. Heat treatment of diamond-turned nickel in a
vacuum furnace appeared to roughen the surface slightly, giving it an orange-peel
appearance when viewed under a surface-finish microscope. Tool life, when
machining hardened electroless nickel, might be shortened somewhat, although very
good finishes had been machined on heat-treated electroless nickel.
Dini (1981) studied electroless nickel coating as a coating that offered
significant advantages for diamond turning applications. He reported the best diamond
turning results, he achieved, on electroless nickel with the deposits produced in acid
solutions containing hypophosphite as the reducing agent. Irregular results were seen
with the deposits produced in alkaline electroless nickel solutions where some were
turnable but others broken down the tool edge immediately. Concluded reason he
reported was the deposits produced in alkaline solution had less corrosion resistance
compared to those deposits produced in acid solutions. Arnold (1970) observed
comparatively fast tool wear on in house Y-12 electroless nickel coatings while much
less tool wear was seen on coating provided by the outside vendor even the phosphorus
content was almost same. Micro hardness test showed that the sample surfaces that had
given the best diamond turning results were relatively hard compared to the surfaces
that were poorly machined. Arnold concluded that this difference in hardness was
probably due to a difference in structure obtained as a result of heat treatment.
Later in 1982, Sanger and Dini reported the importance of quality and
reliability of the electroless nickel coatings. They stated that with a good quality
coating, e.g. the absence of surface pits, porosity, nodules, stress and inclusions large
enough to damage the diamond tool or adversely affect conventional polishing process.
Any material that can be adherently coated with elcetroless nickel can be finished by
Micro-grooving on Elcetroless Nickel Plated Die Materials 14
Chapter 2: Literature Review
conventional polishing or diamond turning techniques, thus greatly expanding design
strategies and supporting manufacturing capability for optical surfaces.
Dini (1985) studied again with Syn the machinability of electroless nickel with
respect to tool life. They reported that machinability was a function of phosphorus
content, age of the solution, additives in the solution, heat treatment conditions, etc.
Hence, their study included machinability studies on electroless nickel deposits
varying in phosphorus content (1.8%-13%) at different heat treatment temperature
(200, 400, and 600oC). The conclusion that can be drawn from this study was that
electroless nickel should have contained at least 11% phosphorus to control the tool
wear during cutting with single crystal diamond tool. A stress relief treatment at 2000C
for two hours appeared to even further enhance the cutting characteristics of deposits
containing greater than 11% phosphorus was noted also. However, it was difficult to
develop a correlation between surface finish and hardness. The only conclusion that
could be extracted from this preliminary analysis was that for a good finish, samples
should contain substantial amount of phosphorus content and could be heat treated to
various hardness levels.
In the same year 1985, Taylor et al. worked on surface finish measurements of
diamond turned electroless nickel-plated mirrors. They had presented surface
roughness data with samples having different phosphorous contents (1.8% to 13%) and
heat treatments. The cuttings were performed with the Precision Engineering Research
Lathe (PERL) with single crystal diamond tools. Commercial optical and stylus
profilometers (Wyko and Talystep) were used to measure the roughness
measurements. The results obtained from this study showed that the lowest surface
roughness was achieved with 13% Phosphorous and 200° C heat treatment
Micro-grooving on Elcetroless Nickel Plated Die Materials 15
Chapter 2: Literature Review
temperature. The composition and heat treatment combinations yielding the lowest
surface roughness were closely correlated to an amorphous electroless nickel structure.
2.4.2 Tool Wear
From 1978, it is reported that electroless nickel was machined and studied
extensively by many researchers. Studies on phosphorus content of electroless nickel
and heat treatment, and machinability of electroless nickel were mostly done. Besides,
few works on short and long distance diamond machining were done. Within this
research works, very few works were reported to predict the performance of different
diamond tools with different rake angles with respect to tool wear, cutting forces and
machined surface.
Casstevens and Daugherty (1978) studied the tool life during machining
electroless nickel and softer fcc metals such as copper and aluminum. When machining
with electroless nickel, it was reported that tool life was same as when machining
softer materials. It was noted that diamond tool showed only very slight wear under
microscopic observation. On the other hand, during machining with softer materials,
tool damage mostly often results from accidental crushing of ultra sharp edge rather
than from wear.
Syn et. al. (1986) performed a study on diamond tool wear for machining of
heat treated (at 2000C for two hours) electroless-nickel with phosphorus content
(13%w/w) where cutting distance was 21.336km. This reported work was on the
performance of two single crystal natural diamond cutters with different infrared
absorption characteristics with respect to surface roughness and tool wear, where the
absorption characteristics depend on diamond impurity and hardness. It was noted that
up to 1st 0.3 km cutting distance, the surface roughness increased rapidly; after that it
Micro-grooving on Elcetroless Nickel Plated Die Materials 16
Chapter 2: Literature Review
increased gradually up to 21.34km. The round-nosed tool tip was flattened due to tool
wear and in some cases, burnishing was happened rather than cutting. This study
explained the reasons of wear that both micro-fracture and chemical reaction and/or
dissolution contribute to the wear of diamond tool edge causing groves at flank face.
Of the two tools, the one predicted by infrared absorption measurements to have a
higher hardness and lower fracture toughness was found to wear at a lower rate for the
first 15.24km and to exhibit somewhat more evidence of edge micro fracture. Cause of
scratches at rake face was lower phosphorus content in the deposits.
Syn et al. (1985) studied tool wear using diamond tools of 0° rake and 7°
clearance angle with electroless nickel having phosphorous content of 1.8 to 13
percent. The reported wear on the rake face of the cutting edge was graded from 0 to
15 depending on the extent of wear zone. The rake face wear was plotted in solid line
contours on the matrix of heat treatment temperature and phosphorous content as
shown in Figure 2.5.It is evident, shown in Figure 2.4, that the increasing trend of rake
face wear is correlated to decreasing phosphorous content. As phosphorous content
decreases, nickel content as crystalline nickel increases, especially when the samples
are heat treated and crystalline nickel is known to wear and damage diamond tools
very rapidly. It is not known why the wear of diamond tools is reduced when nickel
contains phosphorous. One speculation is that the reduced wear may be due to the
formation of a protective layer of phosphorous on the diamond. Another fact is that as
the phosphorous content decreases the tendency for inhomogeneous distribution of
nickel and phosphorous increases. This increases the frequency of crystalline nickel
islands available to degrade the diamond tool. Another possibility relates to the fact
that the behavior of nickel is noticeably changed by the presence of phosphorous.
Micro-grooving on Elcetroless Nickel Plated Die Materials 17
Chapter 2: Literature Review
Oomen et al. (1992) reported the wear behavior of diamond tools, both natural
and synthetic, considering tool wear and cutting forces as a function of tool life. The
electroless nickel having 9% phosphorus content was machined with several others
materials during this study. During cutting with electroless nickel, a wear pattern
consisting of several grooves on the rake face which mostly known as crater wear was
noticed along with slightly chipping off at the cutting edge. No significant difference
was observed at the tool edge chipping for different types of diamond used. Moreover,
almost identical wear behavior of the synthetic diamonds was reported.
Figure 2.5: Influence of Phosphorus Content and Heat Treatment Condition on Diamond Tool Wear [ Syn et al.,1986]
Pramanik et al. (2003) studied extensively the cutting performance of synthetic
diamond tools on electroless nickel during ultra precision turning with respect to
cutting parameter, machined surface roughness, phosphorus content, and tool wear. It
was reported that the surface roughness decreased with the increase of phosphorus
content. Besides, no variation of surface roughness was seen with the variation of
Micro-grooving on Elcetroless Nickel Plated Die Materials 18
Chapter 2: Literature Review
depth of cut. However, surface roughness increased with the increase of feed rate.
Flank wear land was observed after cutting about 15.6 km distance with some grooves
spread at 10 µm across the flank wear zone. At the end of the cutting test, 202.8 km,
the amount of flank wear was about 4 µm even producing a mirror finish surface
appearance. A critical value of spindle speed for obtaining the best surface finish was
also remarkable. The cutting and the thrust forces were increased with depth of cut,
spindle speed, and feed rate, but decreased with the increase of phosphorus content.
2.4.3 Scope of Work
The diamond turning of this material is a possible option for producing high
quality optical surfaces without any post machining process. However, it is
surprisingly reported that there is no study conducted yet on the performances of
different diamond tools with different rake angles during machining of micro grooves
on electroless nickel plated die materials. Therefore, the aims of this study are to
compare and investigate the performance of different single point diamond tools with
different rake angles during micro grooving on electroless nickel plated die materials.
The machining performance was evaluated in terms of tool wear, cutting forces and
surface roughness of the machined workpieces. The characteristics of wear pattern of
the tools of having different rake angles are carried out.
Micro-grooving on Elcetroless Nickel Plated Die Materials 19
Chapter 3: Aspects of Micromachining
Chapter 3
Aspects of Micromachining
3.1 Introduction
Ultra precision metal cutting has satisfied many of the present industrial needs
in the manufacturing of optical, electrical and mechanical parts for advanced
technology. Currently, scientific analysis of micromachining phenomena is under
development over the world and has been contributing substantially to establishing
predictable performance parameters. However, it is still a challenge to machine brittle
and hard materials which are difficult to cut in ductile mode. For nano finish of optical
surface it is essentially important to machine in ductile regime which ensures the crake
free surface. In addition, machined surface in ductile mode has higher strength than
that of machined in brittle mode. This chapter highlights on some of the theoretical and
physical aspects of micromachining such as chip formation, minimum cutting
thickness, effect of cutting fluid etc.
3.2 Chip Formation
The chip formation is a process of deformation mostly in plastic range where
forces are subjected by cutting tool upon the work material as shown in Figure 3.1. It is
known that no permanent effect is produced by stresses within the elastic range. In
contrast, stress in the plastic range may cause large deformation. In this range,
deformation is no longer a simple separation of atoms, irrecoverable structural changes
occur. When a cutting tool removes a layer from the workpiece, the uncut layer is first
elastically deformed followed by plastic deformation separation taking place near the
cutting edge of the tool. However, it is difficult to postulate that the deformation is
Micro-grooving on Elcetroless Nickel Plated Die Materials 20
Chapter 3: Aspects of Micromachining
concentrated at one point or one line. On the contrary, plastic deformation takes place
in a certain region entrapped between the undeformed material on one side and the
cutting tool on the other [Bhattacharyya, 1996].
Figure 3.1: Geometry of Orthogonal Cutting [Sutter, 2005]
3.3 Tool Geometry - Minimum Cutting Thickness
Geometry of cutter has a significant effect on the cutting mode. More
importantly, diamond tool sharpness is a primary factor affecting the cutting process
and quality of machined surface. Therefore, the cutting edge radius is the most
important parameter among all cutting parameters which affects the brittle-to-ductile
transition, hence limits the minimum cutting thickness [Li et al., 2003].
In micro diamond cutting, the minimum cutting thickness depends on the tool
edge radius and the physical relationship between a tool and a workpiece. Figure 3.2
shows the material behavior of a sub-micrometers precision diamond cutting. In the
case of a relatively small cutting depth compared to the tool edge radius, some material
may be deformed, uncut, underneath the tool. This is called plowing, and the force
associated with this is defined as the plowing force. This force is irrelevant in macro
cutting, but it becomes an important factor in micro cutting.
Micro-grooving on Elcetroless Nickel Plated Die Materials 21
Chapter 3: Aspects of Micromachining
Figure 3.2: A Model of Micro Cutting [Son et al., 2005]
Figure 3.3: Cutting Force in the Elastic Region [Son et al., 2005]
Son et al. [2004] has assumed that the workpiece material is divided into
perfectly plastic and perfectly elastic regions according to the minimum cutting
thickness (Bc) as shown in Figure 3.2. Figure 3.3 shows the force relationship at a
depth of cut of less than the minimum cutting thickness. The workpiece is fully
recovered after contact with a tool, and so the differential normal force and the
differential tangential force are expressed as the following equations,
θθµθθθθµθθ
sincoscossin
rdprdpdFrdprdpdF
eeez
eeex
−=+=
(3.1)
where, pe is the normal stress on the rounded tool edge in the elastic region, r is the
tool edge radius, and µ is the friction coefficient. The ration of dFex/dFez is given by
( ) ( )( ) ( )
( e
ee
ee
ez
ex
rdp
rdpdFdF
βθβθµθ
βθµθ+=
++
++= tan
cos1
sin12
2
) (3.2)
Micro-grooving on Elcetroless Nickel Plated Die Materials 22
Chapter 3: Aspects of Micromachining
Where, βe is the friction angle in a perfectly elastic region.
When the cutting depth is more than perfectly elastic depth, associated force
model is shown in Figure 3.4. The principle force using Merchant’s force expression is
given by
( )( )dt
wdF
p
pspx θβφφ
αβτ++
−=
cossincos
(3.3)
Where, τs is the shear strength, w is the width of the tool, βp is the friction angle in a
perfectly plastic region, and a is the rake angle, and by dt= rsinθdθ, where r is the tool
edge radius. Hence, principle and thrust forces can be written as:
( )( ) θ
θβφφθβθτ
dw
dFp
pspx ++
+−=
sinsinsinsin
(3.4)
( )
( ) θθβφφθβθτ
dw
dFp
pspz ++
+−=
sinsincossin
(3.5)
From these two Equations, the forces ration can be written as:
( θβ += pez
ex
dFdF
tan ) (3.6)
Figure 3.4: Force Model in Cutting Region [Son et al., 2005]
Micro-grooving on Elcetroless Nickel Plated Die Materials 23
Chapter 3: Aspects of Micromachining
Figure 3.5: Stress on the Neutral Point[Son et al., 2005]
Figure 3.5 shows all the stress on a differential element under the minimum
depth of cut. From the equilibrium of forces, with the shear angle Ф being assumed to
be almost equal to stagnation angle or neutral angle:
,1sin/cos/
=cez
cex
rdddFrdddF
θθτθθτ
tan(βe+θc)=cotθc (3.7.a)
or
,1sin/cos/
=cez
cex
rdddFrdddF
θθτθθτ
tan(βp+θc)=cotθc (3.7.b)
Therefore, the minimum cutting thickness is
mt = ⎟⎟⎠
⎞⎜⎜⎝
⎛⎟⎠⎞
⎜⎝⎛ −−
24cos1 βπr (3.8)
Where tm= minimum cutting thickness
r = cutting edge radius of cutting tool
β = either the friction angle between a tool and an un-cut workpiece passed
under the tool or the friction angle between a tool and a continuous chip.
It has been observed by many researches that the tendency for subsurface micro
cracks to develop in the brittle materials decreases with decrease in the undeformed
chip thickness and to almost disappear below a critical value of cut depth. This has
Micro-grooving on Elcetroless Nickel Plated Die Materials 24
Chapter 3: Aspects of Micromachining
been thought to be due to the material being less brittle below a certain value and has
therefore been termed ‘ductile’ mode cutting. If the depth of cut is less than the cutting
edge radius in Equation 3.8, the material is removed with the radius of the tool and not
by the rake face. The material under these conditions behaves in an elastic-plastic
manner without fracture. Alternately, it has been argued that at very shallow depths of
cut with a blunt tool, the energy required to propagate cracks may be larger than the
energy required for plastic yielding, so plasticity may become the dominant material
removal mechanism [Komanduri et al., 1998]
3.4 Cutting Force and Energy
In principle, cutting force of micromachining processes is usually at sub-
Newton lever or less and equivalent to that on a single abrasive grain in grinding.
Usually these micro forces are very difficult to measure accurately due to its very
small magnitudes compared to its noise, both mechanical and electrical. However, it is
well established, the cutting forces reflect clearly the chip removal process and is an
important physical parameter for understanding cutting phenomena.
3.5 Cutting Temperature
Cutting temperature in micro cutting could be quite low compared to that in
conventional cutting, due to low cutting energy as well as the high thermal
conductivity of diamond [Ikwa et al., 1987]. However, very small temperature rise of
the order of 10 K in a tool may cause a deterioration of the machining accuracy. In
addition, the cutting temperature is considered to govern the rate of wear of a diamond
tool in which even damage of micron size could increase the surface roughness
extensively [Ikawa et al., 1991]. In many cases, temperature plays a significant role for
Micro-grooving on Elcetroless Nickel Plated Die Materials 25
Chapter 3: Aspects of Micromachining
chemical damage on diamond tool. On the other hand, during cutting brittle materials,
temperature maily affects on modulus of rigidity, effective surface energy and
resistance of lattice to dislocation movement where with the increase of temperature
hardness of materials decrease which leads to ductile mode machining. Therefore, it is
also very important to conduct research on the cutting temperature and its effect on
diamond tool wear.
3.6 The Action of Cutting Fluid on Machining
During the micro cutting operation, the cutting fluids play a vial role in the
cutting zone side. For improving the cutting processes, cutting fluids, usually in the
form of a liquid, are applied to the chip-formation zone. Effective cutting fluid reduces
friction on the face of the tool which results in a decease in the cutting forces and
cutting temperature. However, improvements can take place in several forms,
depending on the tool and work materials, the cutting fluid, and to a large extend on
the cutting conditions. The most two important ways in which a cutting fluid can act
are coolant and lubricant. During acting a coolant, it increases the tool life significantly
reducing the cutting temperature [Boothroyd, 1975]. During ultra precision cutting of
ductile materials, the temperature rise and machining error are reduced by spreading
kerosene over the workpiece surface prior to cutting and they are further reduced by
spraying the mist of kerosene to the cutting point zone [Moriwaki et al., 1990].
However, although the coolant is usually successful in doing its job in continuous
cutting operations, there is a possibility that in intermittent cutting the tool will be
subjected to thermal shock which in turn may lead to breakage of the tool [Mills &
Redford, 1983].
Micro-grooving on Elcetroless Nickel Plated Die Materials 26
Chapter 4: Experimental Details
Chapter 4
Experimental Details
4.1 Experimental Setup
The experiments were carried out using the Toshiba ULG-100C ultra-precision
machine. A photographic view of experimental setup is shown in the Figure 4.1, which
shows the position of mist spray nozzle, workpiece, cutting tool, chip suction nozzle
and force dynamometer clearly.
3-D force Dynamometer
Chip Suction Nozzle
Vacuum chuck
Workpiece Mist Spray Line
Diamond Insert
Ft
Fc
Figure 4.1: Photographic View of Experimental Setup
Experimental setup mainly composed of the following components.
1. Toshiba Utra-precision machine
2. Single crystal diamond cutting tool
3. Electroless Nickel Plated workpiece
4. Kisler piezoelectric 3 component dynamometer and data acquisition
system
5. vacuum suction system for chip removal
Micro-grooving on Elcetroless Nickel Plated Die Materials 27
Chapter 4: Experimental Details
6. kerosene based oil mist spray system
4.1.1 Toshiba`Ultra-precision Machine
In this study, a TOSHIBA ultra-precision lathe machine (ULG – 100C)
composed of an air bearing spindle and an air slide with a capacity of 1 nm positioning
accuracy was used for the experiments. Figure 4.2 is a photographic view of the ultra-
precision CNC lathe machine which shows its two major units; the control unit and the
machining unit. This CNC machine has 4-axis simultaneous control system where the
motion of the machine is controlled by the FANUC series 15 MB controller.The
foundation of the machine contains an active damper of air suspension to isolate the
machine from the vibration of external sources.
Control Unit
Machine Unit
Figure 4.2: View of the Toshiba ULG-100C Ultra-precision Machine
4.1.2 Diamond Tools
The artificial diamond tools were supplied by the Osaka Diamond. These were
a preformed single point diamond tool to generate grooves. The tool geometry and tool
photograph are shown in Table 4.1 and Figure 4.3 respectively.
Micro-grooving on Elcetroless Nickel Plated Die Materials 28
Chapter 4: Experimental Details
Table 4.1: The Geometries of Diamond Tools Rake Angle Crystal Orientation
Rake Face Clearance
Angle Plan Angle
+50 {1 1 0} 80 90°01´ 00 {1 1 0} 80 89°30´ -50 {1 1 0} 80 89°40´
Cutting edge
PLAN VIEW
Figure 4.3(a): Single Point Diamond Tool (00 rake)
PLAN VIEW
Cutting Edge
Figure 4.3(b): Single Point Diamond Tool (+50 rake)
PLAN VIEW
Cutting Edge
Figure 4.3(c): Single Point Diamond Tool (-50 rake)
Micro-grooving on Elcetroless Nickel Plated Die Materials 29
Chapter 4: Experimental Details
4.1.3 Workpiece
Electroless nickel plated workpiece in their as deposited condition were used
for the experiments. The thickness of the plating was 100 µm on Starvax pieces of 100
mm diameter and 20 mm thickness with a concentric recess of 5 mm diameter at the
center, as shown in Figure 4.4. The pieces were coated by outside vendors and
trimmed off before the experiments to get a perfectly flat surface. About 10 µm thick
layers were trimmed off to get the workpieces ready for machining. The phosphorous
content of the workpieces were about 9-12 %( w/w).
Figure 4.4: Electroless Nickel Plated Workpiece
The detail of the machined workpieces is shown in Figure 4.5. The depth of each micro
groove was 6 µm. The number of micro-grooves produced on each workpieces was
176. The groove profiles were cut with the preformed of the tools.
Micro-grooving on Elcetroless Nickel Plated Die Materials 30
Chapter 4: Experimental Details
x =1°15’ and y = 89°30’ for 0° rake tool x = 1°30’ and y = 90°01’ for +5° rake tool x = 1°10’ and y = 89°40’ for -5° rake tool
6 x y
Figure 4.5: Schematic View of the Machined Workpiece and Details of Groove X- Section
4.1.4 Force Data Acquisition System
Figure 4.6 shows the schematic diagram of the micro-cutting force data
acquisition system. A KISTLER mini 3-Component dynamometer (Model-9256A1)
was used for measuring the micro-cutting forces. The two components of micro-
cutting force such as thrust force Ft, and cutting force Fc were first sensed by the
dynamometer. The signals of these forces were subsequently amplified by a KISTLER
charge amplifier. In the mean time, a SONY digital data recorder records the cutting
force signals into a Sony data cartridge of 2 GB capacity, in which the variation of
force data was set within 5 Newton. The digital force data stored in the cartridge was
later processed with the aid of PC Scan MKII data acquisition software, which
measures the maximum, minimum, average or peak-valley cutting force in Newton.
±
Micro-grooving on Elcetroless Nickel Plated Die Materials 31
Chapter 4: Experimental Details
Machining Unit
KISTLER Dynamometer
Figure 4.6 Schematic Diagram of Micro-cutting Force Data Acquisition System [Uddin, 2004]
4.1.5 Vacuum Suction System
The vacuum suction system included a compressor, suction nozzle and pipe.
This unit was used to facilitate the removal of chip from the tool workpiece interface.
4.1.6 Chip collection System
The chips were collected to facilitate clean cutting and prevent and chip
deposition on cutting tool or grooved workpiece surfaces. This system consists of a
compressor, suction pipe and nozzle.
4.2 Measuring Equipments Used
4.2.1 Mitutoyo FORTRACER (CS-5000)
A Mitutoyo FORTRACER (CS-5000), operated with a cone type stylus (F-
421895), was used to measure the surface roughness of the machined silicon work
material. The photograph of the machine is shown in Figure 4.7. The height, radius and
KISTLER Charge Amplifier
SONY Digital Instrumentation
Data Recorder
Ft Fc
Ft Fc
Computer Monitor
Micro-grooving on Elcetroless Nickel Plated Die Materials 32
Chapter 4: Experimental Details
angle of the stylus are 14.08 mm, 2 µm and 60° respectively. The resolutions of the
machine in X and Z directions are 0.00625 µm and 0.002 µm respectively. The data
analysis software Formtracepak is used to measure and analyze both contour and
surface roughness. The machine was used to evaluate surface roughness of the
workpiece and evaluate both Primary and Roughness profiles for the machined
workpieces surfaces. The condition used for evaluating the profile and roughness of
the machined workpieces are as follows:
Measured length: 5mm Measurement Pitch: 0.0020mm
Cutt off: 0.025 Roughness Pitch: 0.0005mm
Measuring speed: 0.2 mm/sec Kind of filter Gaussian
Figure 4.7 Photographic View of Mitutoyo FORTRACER
4.2.2 Nomarski Optical Microscope
A Nomarski optical microscope (OLYMPUS STM-6) (Figure 4.8) was used to
observe the physical condition of the tools at various intervals of cutting distance. The
machine was also used to observe the machined workpieces surface. The flank wear
and the rake wear region of the tools were preliminary examined by this microscope.
Two magnifications of 100X and 500X were used during the observations. The
Micro-grooving on Elcetroless Nickel Plated Die Materials 33
Chapter 4: Experimental Details
microscope is connected to a monitor and a digital camera which are used to capture
the photographs of the surfaces.
Figure 4.8 Nomarski Optical Microscope (Olympus STM-6)
4.2.3 JOEL JSM-5500 Scanning Electron Microscope & Energy Dispersive X-ray
A Scanning electron microscope (SEM) (JSM-5500, JEOL Ltd.), as shown in
Figure 4.9, was used to examine tool cutting edge, flank and rake wear region, and
chips produced. The microscope with one electron beam can be operated with a
resolution of 4 nm. The maximum values of magnification and accelerating voltage
which can be attained by the microscope, are 50,000X and 30 KV, respectively. The
probe current ranges from 10-12 to 10-6A. An Energy Dispersive X-ray (EDX) machine
associated with the SEM was also used to investigate any diffusion or dissolution
between tool materials and work materials or chips.
Micro-grooving on Elcetroless Nickel Plated Die Materials 34
Chapter 4: Experimental Details
Figure 4.9 : Scanning Electron Microscope (SEM) Associated with Energy Dispersive X-ray (EDX) Machine
4.2.4 Keyence VHX Digital Optical Microscope
A Keyence VHX Digital Optical Microscope, shown in Figure 4.10, was used
to observe the physical condition of the tools, flank and rake wear region, at various
intervals of cutting distance. The machine was extensively used to observe the
machined workpieces surface. The flank wear and the rake wear region of the tools
were mostly observed and further examined by this microscope. The highest
magnification of this machine was 3000X. The microscope is highly efficient for
observations of diamond tools compared to SEM and Normarski microscope quickly.
The machine consist of two units; one is digital photo taker with a optical microscope,
and another one is a monitor for captured digital data editing with a preinstall windows
support softer.
Micro-grooving on Elcetroless Nickel Plated Die Materials 35
Chapter 4: Experimental Details
Figure 4.10: Photograph of Keyence VHX Digital Optical Microscope
4.3 Measurement and Analysis
4.3.1 Surface Roughness Measurement
The roughness of the machined electroless nickel workpiece was measured
using a Mitutoyo FORTRACER (CS-5000) (Figure 4.7). Measurement is done along
the radial direction of the workpieces. After each experiment, the readings were taken
from three region of the workpiece where each data consisted 5 mm measuring length
of the workpieces. The surface finish quality of machined electroless nickel was
measured in terms of average roughness (Ra), and peak to valley roughness (Ry).
4.3.2 Micro-Cutting Force Measurement
The micro-cutting forces, cutting and thrust force, profile as well as data
recorded during the machining were retrieved from the data cartridge using the Sony
digital data recorder, interfacing and the PC Scan II software installed in a computer.
Retrieved data was further used to observe the force in real time and to analyze. Data
Micro-grooving on Elcetroless Nickel Plated Die Materials 36
Chapter 4: Experimental Details
were taken from the three different selected zones for each experiment. Those exported
force data were further saved as ASCII tab files, which were later retrieved into
Microsoft Excel format. The average value of the three sections was calculated as the
final value of the cutting and thrust force data for the each experiment. The micro-
cutting force measurements were done for machining with diamond tools of different
rake angles.
4.3.3 Tool Wear Observation
At various intervals of cutting distance, the tool wear region was examined
using Nomarski optical microscope, SEM, and Keyence VHX Digital Optical
Microscope. The tool rake and flank faces were observed after each five experiments
and microphotographs of the tool faces were taken using the attached photo taking
system for further analysis.
4.3.4 Machined Surface Observation
After each experiment, machined surface was analyzed using Nomarski optical
microscope, and Keyence VHX Digital Optical Microscope. Microphotographs of the
machined surface were taken using the attached photo taking system for further
analysis.
4.4 Experimental Procedure
The experimental setup is shown in Figure 4.1, which was used to perform all
the experiments. The workpiece was attached to the spindle with the vacuum chuck
and was balanced with a of a dial indicator. The diamond tools were mounted on the
tool holder of the machine and the holder was screwed under the dynamometer as
Micro-grooving on Elcetroless Nickel Plated Die Materials 37
Chapter 4: Experimental Details
show in Figure 4.1. The machining process can be divided in to three major
observations and determinations and these are;
1. Determination of optimal cutting condition
2. Observation of wears characteristic during the machining
3. Observation of machined surface
For all the experiments, measurements and observations made included:
a) Optical observations of the cutting tool with the JOEL JSM-5500 Scanning
Electron Microscope, Nomarski microscope and Keyence VHX Digital Optical
Microscope.
b) Optical observations of the machined electroless Nickel surfaces with
Nomarski Microscope and Keyence VHX Digital Optical Microscope.
c) Observation of the surface roughness (Ra and Ry) of machined grooves with
Mitutoyo Formtracer CS-5000 after each pass.
d) Measurement of cutting and thrust forces during machining with a Kistler
piezoelectric three-component dynamometer in conjunction with a Kistler
three-channel charge amplifier and a recorder to record the forces.
e) Hardness of workpieces with Mitutoyo AVK-C2 hardness tester
At the beginning, the new workpiecrs were trimmed off to get a perfectly flat
surface. After that, each grooved workpiece was trimmed off again for further use in
next experiment. During the very first trimming of new workpieces, the chips were
collected to check the phosphorus content and trimmed of workpieces were
simultaneously tested for hardness with Mitutoyo AVK-C2 hardness tester.
Micro-grooving on Elcetroless Nickel Plated Die Materials 38
Chapter 4: Experimental Details
4.4.1 Effects of Cutting Parameters
The two variables were considered to determine the effects of those variables
on the surface roughness of the machined workpieces. The variables were used were
spindle speed (rpm), and infeed rate (µm/rev). The effects of the cutting parameters on
machined surfaces and forces were studied following the parameter matrix shown in
Table 4.2.
Table 4.2: Matrix of Cutting Parameter
Expt No. Spindle speed (rpm) Infeed rate (µm/rev) Depth of cut (µm) 1
2
3
4
5
6
7
8
9
1000
1000
1000
1000
1000
750
500
250
100
3
2
1
0.5
0.1
0.5
0.5
0.5
0.5
6
4.4.2 Optimal Cutting Conditions
The optimal cutting parameters were chosen based on machined surface
roughness and cutting forces. The surface roughness and cutting forces were plotted
with respect to different cutting conditions. A set of optimal cutting condition was
evaluated from those plots. Further during the performance test of the different
diamond tools, experiments were carried out following this set of optimal cutting
condition shown in the Table 4.3.
Micro-grooving on Elcetroless Nickel Plated Die Materials 39
Chapter 4: Experimental Details
Table 4.3: Cutting Conditions during Performance Test
Groove depth of cut (µm) 6
Infeed rate (µm/rev) 0.5
Spindle speed (rpm) 1000
4.4.3 Tool Wears Observation Procedure
Machining of micro grooves on the work piece was done by plunge cut method
traveling the tool from periphery to the center .All the experiments were carried out
using spindle speed of 1000 rpm and infeed rate of 0.5 µm/rev. During the experiment,
the infeed was used to plunge into the work materials.
After each few experiments tool was checked under Nomarski Microscope,
Keyence VHX Digital Optical Microscope, and SEM. For each tool, same procedures
were followed to observe the tool wears. During presences of any unexpected material
on the tool, the tools were examined using EDX whether there were any base material
depositions or not. Progressions of tool wears were calculated based on the
microphotograph taken during optical observation of diamond tools.
Micro-grooving on Elcetroless Nickel Plated Die Materials 40
Chapter 5: Results and Discussion
Chapter 5
Results and Discussion
5.1 Introduction
Ultra precision diamond cutting is an efficient manufacturing method of
precision parts in various fields of the high-tech industry such as electronics,
information and communication technology, biotechnology, precision machinery, and
others. Being one of the most modern manufacturing processes, there has been
substantial interest in investigation on ultra precision cutting. However, the cutting
process is not governed solely by cutting tools but also critically by the work materials.
At present, typical materials that can be successfully machined are Cu alloys, Al
alloys, silver, gold, electroless nickel, PMMA plastic and some of the “infrared
materials” [Ikawa et al., 1991]. Among these, Electroless nickel is one of such
materials which exhibits excellent properties such as hardness, corrosion resistance;
more importantly diamond machines electroless nickel very effectively. In addition,
electroless nickel is generally used for molding dies of plastic, optical parts such as
LCD projection TV, magnetic memory drives, laser equipments, electrostatic copier,
printing machine, and high resolution and high accuracy light guide for CD /DVD
pickup lenses. However, high costs of diamond cutters and the associated machine
make it necessary to evaluate the performance of the diamond cutters during cutting
with electroless nickel to achieve a nano finish. The intent of this chapter is to present
the results and to discuss the followings:
• The effect of different cutting parameters on the machined surface roughness
and cutting forces.
• Evaluation of the optimal cutting conditions and their importance.
Micro-grooving on Elcetroless Nickel Plated Die Materials 41
Chapter 5: Results and Discussion
• Effect of phosphorus content on hardness of the workpiece.
• The wear characteristics of diamond tools with different rake angles during
micro-grooving and their mechanisms.
• Evaluation of the performance of diamond tools with respect to tool wear,
micro-cutting forces and machined surface roughness for tools with different
rake angles for long distance cutting of micro-grooves on electroless nickel
plated die materials.
5.2 Cutting Parameters
The cutting speed and the infeed rate are the two most important parameters
which can be adjusted to achieve optimal cutting conditions during micro-grooving.
An optimal set of cutting conditions is an essential pre-requisite for any machining
process. Therefore, two cutting parameters, spindle speed and infeed rate were
investigated with respect to machined surface roughness and cutting forces for all the
three tools. After investigation, one set of cutting parameters were selected to carry out
the performance test for three different tools with three different rake angles.
5.2.1 Effect of Cutting Speed
In precision machining, the arithmetic surface roughness usually decreases with
increasing spindle speed. With the increase of spindle speed, the width of shear zone
decreases, which leads to a better machined surface at higher spindle speed. The effect
of cutting speed on cutting forces was also observed. That is why, two force
components, cutting and thrust forces, was measured during the experiments. The
cutting force, Fc, acts in the direction to the cutting tool face and the thrust force, Ft,
normal to the workpiece surface as shown in Figure 5.1.
Micro-grooving on Elcetroless Nickel Plated Die Materials 42
Chapter 5: Results and Discussion
Fc
Ft
Tool
Workpiece
Figure 5.1: Cutting Force Directions on Tool
5.2.1.1 Effect on Surface Roughness
The variation of surface roughness, Ra, with spindle speed for the tools of three
different rake angles is shown in Figure 5.2. It has been observed from the figure that
the variation of the surface roughness with spindle speed is not very much significant.
The photographs of the machined surfaces of the workpices under Nomarski
microscope are shown in Figure 5.3 (a, b, c, d and e) for the best surface roughness
achieved during the particular spindle speed with respect to surface topography and
roughness values ( Ra and Ry). Since the surface roughnesses achieved were in the
nanometric level, the variation in surface appearance does not vary much from these
photographs.
Micro-grooving on Elcetroless Nickel Plated Die Materials 43
Chapter 5: Results and Discussion
0
1
2
3
4
5
6
7
0 200 400 600 800 1000 1200
Spindle Speed(rpm)
Sur
face
Rou
ghne
ss(n
m)
0 deg. Rake +5 deg. Rake -5 deg. Rake
Figure 5.2: Variation of Surface Roughness with Spindle Speed for Different Tools with Different Rake Angles.
` Figure 5.3(a) Photograph of the Machined Surface and Corresponding R Profile at 100
rpm with 00 Rake Tool.
Figure 5.3(b): Photograph of the Machined Surface and Corresponding R Profile at 250 rpm with 0o Rake Tool.
Micro-grooving on Elcetroless Nickel Plated Die Materials 44
Chapter 5: Results and Discussion
Figure 5.3(c): Photograph of the Machined Surface and Corresponding R Profile at 500 rpm with 00 Rake Tool
Figure 5.3(d): Photograph of the Machined surface and Corresponding R Profile at 750
rpm with -50 Rake Tool
Figure 5.3(e): Photograph of the Machined Surface and Corresponding R Profile at 1000 rpm with 00 Rake Tool
5.2.1.2 Effect on Cutting Forces
Figure 5.4(a) and Figure 5.4(b) show the influence of spindle speed on cutting
forces and thrust force respectively. It was observed that cutting and thrust forces
Micro-grooving on Elcetroless Nickel Plated Die Materials 45
Chapter 5: Results and Discussion
increased proportionately with spindle speed. Results indicate that all the diamond
tools with different rake angles show almost similar trend of force increment with
increasing spindle speed. With the increase of spindle speed, both the cutting speed
and rate of material removal increases which might increase the forces [Pramanik et
al., 2003]. It was also observed by researchers that with increasing cutting speed there
is an increase in the acceleration of chip removal, which is a probable cause of the
increment in forces [Jared et al., 20004]. Another explanation of this phenomenon is
that with increasing cutting speed, there is an increased strain rate on the workpiece
material causing an increase in the yield strength of the material through strain
hardening. This increment in the yield strength may cause the increment in the thrust
and cutting forces [Trent and Wright, 2000].
0
0.1
0.2
0.3
0.4
0.5
0.6
0 200 400 600 800 1000 1200
Spindle Speed(rpm)
Cutti
ng F
orce
(N)
0 deg. Rake +5 deg. Rake -5 deg. Rake
Figure 5.4(a): Effect of Spindle Speeds on Cutting Forces for the Tools with Three Different Rake Angles
Micro-grooving on Elcetroless Nickel Plated Die Materials 46
Chapter 5: Results and Discussion
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 200 400 600 800 1000 1200
Spindle Speed(rpm)
Thru
st F
orce
(N)
0 deg. Rake +5 deg. Rake -5 deg. Rake
Figure 5.4(b): Effect of Spindle Speeds on Thrust Forces for the Tools with Three Different Rake Angles
5.2.2 Effect of Infeed Rate
Surface roughness and cutting forces were observed with the variation of infeed
rate. These infeed rates were given to the workpieces toward the thrust forces
direction. During micro-grooving, the cutting tool is advanced in the direction of thrust
force gradually to cut grooves up to a desired depth. Therefore, effect of infeed rate is
an another important parameter that could influence the process in terms of cutting
forces, machined surface roughness and machining time.
5.2.2.1 Effect on Surface Roughness
The influences of infeed rate on machined surface for diamond tools with three
different rake angles are shown in Figure 5.5. Variation of the machined surface
roughness that can be seen from the figure is not very significant. It could be assumed
that the infeed rate does not play any significant role on machined surface roughness in
this range of cutting. Figure 5.6(a, b, c, d and e) shows the photographs of the best
machined surface and corresponding R profile of the measured roughness for different
Micro-grooving on Elcetroless Nickel Plated Die Materials 47
Chapter 5: Results and Discussion
tools under Nomarski microscope. From these figures, no brittle fracture was observed
for any experiments.
0
1
2
3
4
5
6
0 0.5 1 1.5 2 2.5 3 3.5
Infeed Rate(µm/rev)
Sur
face
Rou
ghne
ss(n
m)
0 deg. Rake +5 deg. Rake -5 deg. Rake
Figure 5.5: Variation of Surface Roughness with Infeed Rate for Different Tools with Different Rake Angles
Figure 5.6(a) Photograph of The Machined Surface and Corresponding R Profile at 0.1µm/rev with 0 deg. Rake Tool
Micro-grooving on Elcetroless Nickel Plated Die Materials 48
Chapter 5: Results and Discussion
Figure 5.6(b) Photograph of the Machined Surface and Corresponding R Profile at 0.5µm/rev with 0 deg. Rake Tool
Figure 5.6(c) Photograph of the Machined Surface and Corresponding R Profile at 1µm/rev with -5 deg. Rake Tool
Figure 5.6(d) Photograph of the Machined Surface and Corresponding R Profile at 2 µm/rev with +5 deg. Rake Tool
Micro-grooving on Elcetroless Nickel Plated Die Materials 49
Chapter 5: Results and Discussion
Figure 5.6(e) Photograph of the Machined Surface and Corresponding R Profile at 3 µm/rev with 0 deg. Rake Tool
5.2.2.2 Effect on Cutting Forces
The effects of infeed rate on the machining forces, thrust and cutting, are
shown in Figure 5.7(a & b). The results indicate that both the cutting and the thrust
forces increased with infeed rate. The increase in infeed rate resulted in more stresses
concentration on the tool face thus increasing the forces. With the increase in infeed
rate more material are removed from the workpiece in each revolution, imposing
higher forces on the cutting tool [Pramanik et al., 2003].
00.10.20.30.40.50.60.70.80.9
1
0 0.5 1 1.5 2 2.5 3 3.5
Infeed Rate(µm/rev)
Cut
ting
Forc
e(N
)
0 deg. Rake +5 deg. Rake -5 deg. Rake
Figure 5.7(a): Effect of Infeed Rates on Cutting Forces for the Tools with Three
Different Rake Angles
Micro-grooving on Elcetroless Nickel Plated Die Materials 50
Chapter 5: Results and Discussion
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 0.5 1 1.5 2 2.5 3 3.5
Infeed Rate(µm/rev)
Thru
st F
orce
(N)
0 deg. Rake +5 deg. Rake -5 deg. Rake
Figure 5.7(b): Effect of Infeed Rates on Thrust Forces for the Tools with Three Different Rake Angles
5.3 Determination of Optimal Cutting Conditions
It is essentially important to find out optimal cutting conditions for
investigating the cutting performance of different tools with cutting distance.
Obviously, there could be an optimal cutting condition for each tool. However, during
the performance test with different tools, one single set of optimal cutting condition is
important to compare the performance of tools with respect to cutting forces, surface
roughness, and tool wears. During observing the effect of spindle speed, among all sets
of measured surface roughness, roughness achieved by using 1000 rpm were found to
be best based on mathematical average of the roughness measured with three different
tools. During observing the effect of infeed rate on machined surface roughness, it can
be seen from the Figure 5.5 that the best mathematical average surface roughness was
achieved at two conditions; one was at 0.5 µm/rev and another one was at 3 µm/rev. It
can be noted that 3 µm/rev is useful to accelerate the cutting process with a
considerably high cutting and thrust forces. On the other hand, with respect to cutting
distance for a single experiment, any tools with infeed rate of 0.5 µm/rev travels more
Micro-grooving on Elcetroless Nickel Plated Die Materials 51
Chapter 5: Results and Discussion
than six times compared to any tools with infeed rate of 3 µm/rev. In addition, the
cutting and the thrust forces measured during cutting with infeed rate of 0.5 µm/rev
were considerably low which further enhances the tool life. Therefore, after observing
the effect of two different cutting parameters on the machined surface and on the
machining forces, it was decided to use 1000 rpm and 0.5 µm/rev as spindle speed and
infeed rate respectively for further experiments.
5.4 Effect of Phosphorus Content on Hardness of Wokrpieces
The material removal process is not governed solely by cutting tool but also
critically by the work material. Work materials must be chosen which give an
acceptable machinability on which nanometric surface finish can be achieved [Ikawa et
al., 1991]. For electroless nickel, phosphorous content has a great influence on both
hardness and structure. It was also observed that the diamond machines a workpiece
well with a higher phosphorous content [Syn et al., 1985]. Before starting the
performance test experiments, the workpieces from different lots were randomly
chosen to test the phosphorous content and hardness. It has been observed that the
532
534
536
538
540
542
544
8 9 10 11 12 13
Phosphorous Content(%w/w)
Har
dnes
s(H
V)
Figure 5.8: Effect of Phosphorus Content on Hardness of Workpieces
Micro-grooving on Elcetroless Nickel Plated Die Materials 52
Chapter 5: Results and Discussion
hardness of workpieces decrease with increasing phosphorous content. The results of
the hardness tests are shown graphically in Figure 5.8, which are in agreement with the
results found by Pramanik et al. [2003].
5.5 Diamond Tool Wear Characteristics
At various interval of cutting distance, wear region and the cutting edge of the
diamond tools with different rake angles, were monitored and examined under the
SEM, Nomarski optical microscope, and VHX digital optical microscope.
5.5.1 Diamond Tool Wear Patterns 5.5.1.1 Diamond Tool with the +50 Rake Angle
Figure 5.9(a) is a Nomarski photograph of the flank face of the diamond tool
after cutting 2.347 km. A very small scale wear on the flank region was observed at the
leading edge of the cutting tool. Figure 5.9(b) shows that after cutting 6.03 km, the
wear region exhibits gradual flank wear as well as spreads up to about 0.2515 mm on
the flank face. Figure 5.9(c) shows the diamond tool wear region after cutting for about
7.26 km. From this figure, it was seen that a gradually flank wear dominated along the
effective cutting edge length of the tool which was 0.25 mm with micro-grooves on
flank face as shown in Figure 5.9(d).
It can be seen from Figure 5.9(e) that wear zone on the flank face increased in
height along the effective cutting edge with no further information of micro-grooves
on flank wear land as shown in Figure 5.9(f)). SEM observation of flank wear region
of diamond tool in large magnification indicates that wear on the flank face was
traditional flank wear and gradually increased in height, whereas the height of the wear
Micro-grooving on Elcetroless Nickel Plated Die Materials 53
Chapter 5: Results and Discussion
land as well as micro-grooves was large at the leading cutting edge and gradually
decreases along the cutting edge.
Nomarski Microscope 500X Cutting Dist: 2.347 km
Wear Zone
Figure 5.9(a): Nomarski Microscope Photograph of Flank Wear Region of Diamond Tool with +50 Rake Angle after Cutting 2.347 km
Nomarski Microscope 500X Cutting Dist: 6.03 km
Wear Zone
Figure 5.9(b): Nomarski Microscope Photograph of Flank Wear Region of Diamond Tool with +50 Rake Angle after Cutting 6.03 km
Wear Zone
Nomarski Microscope 500X Cutting Dist: 7.26
Figure 5.9(c): Nomarski Microscope Photograph of Flank Wear Region of Diamond Tool with +50 Rake Angle after Cutting 7.26 km
Micro-grooving on Elcetroless Nickel Plated Die Materials 54
Chapter 5: Results and Discussion
Micro-grooves
Figure 5.9(d): SEM Photograph of Micro-grooves on Flank Wear Region of Diamond Tool with +50 Rake Angle after Cutting 7.26 km
Wear Zone
Figure 5.9(e): SEM Photograph of Flank Wear Region of Diamond Tool with +50
Rake Angle after Cutting 10.5 km
Flank face with traces of lots of micro-grooves
Cutting Direction
Figure 5.9(f): SEM Photograph of Micro-grooves on Flank Wear Region of Diamond Tool with +50 Rake Angle after Cutting 10.5 km
Micro-grooving on Elcetroless Nickel Plated Die Materials 55
Chapter 5: Results and Discussion
Figure 5.10(a) shows the photograph of the rake face of the diamond tool just
after cutting 4.9 km. No evidence of wear on rake face was noticed until cutting 4.9
km. Figure 5.10(b) shows that after cutting 8.5 km, a number of micro-grooves were
appeared on rake face without any regular shapes. It can be seen from Figure 5.10(c)
that with the increase of cutting distances, both the number and height of the grooves
increased and extended along with the effective cutting edge. It was observed that after
cutting 10.5 km, the micro-groove formation on the rake face was only dominant factor
for this tool.
Nomarski microscope 500X Cutting Dist: 4.9km
Figure 5.10(a): Nomarski Microscope Photograph of Rake Face of Diamond Tool with +50 Rake Angle after Cutting 4.9 km
Micro-grooves
Figure 5.10(b): SEM Photograph of Rake Face of Diamond Tool with +50 Rake Angle
after Cutting 8.5 km
Micro-grooving on Elcetroless Nickel Plated Die Materials 56
Chapter 5: Results and Discussion
Micro-groove
Figure 5.10(c): SEM Photograph of Rake Face of Diamond Tool with +50 Rake Angle
after Cutting 10.5 km
5.5.1.2 Diamond Tool with the 00 Rake Angle
Figure 5.11(a) and Figure 5.11(b) show the flank face of diamond tool after
cutting 7.53 km and 11.69 km respectively. From these figures, it can be noticed that
no wear on flank face at the edge of the diamond tool was observed during cutting. No
sign of chippings or micro-grooves were observed also until cutting 11.69 km.
Similarly, rake face of the diamond tool was observed in the same manner as
the flank face was. There was no sign of any wear on rake face until cutting 11.69 km.
The photographs of the rake face of the diamond tool are shown in the Figure 5.12(a)
and Figure 5.12(b) at different cutting distance where no evidence of rake face wear
was noticed.
Flank Face X450 Cutting Dist: 7.53
Figure 5.11(a): VHX digital Microscope Photograph of Flank Face of Diamond Tool with 00 Rake Angle after Cutting 7.53 km
Micro-grooving on Elcetroless Nickel Plated Die Materials 57
Chapter 5: Results and Discussion
with 0 Rake Angle after Cutting 11.69 km
Figure 5.12(a): VHX digital Microscope Photograph of Rake Face of Diamond Tool with 00 Rake Angle after cutting 7.53km
Figure 5.11(b): VHX digital Microscope Photograph of Flank Face of Diamond Tool 0
Figure 5.12(b): VHX digital Microscope Photograph of Rake Face of Diamond Tool with 00 Rake Angle after Cutting 11.69 km
Rake Face X450 Cutting Dist: 7.53
Flank Face X450 Cutting Dist: 11.69
Rake Face X450 Cutting Dist: 11.69
Micro-grooving on Elcetroless Nickel Plated Die Materials 58
Chapter 5: Results and Discussion
5.5.1.3 Diamond Tool with the -50 Rake Angle
angle at various interval of cutting
distanc
e face of the diamond tool with -50 rake angle after
cutting
ond Tool with -5 Rake Angle after Cutting 3.76 km
Using the diamond tool with -50 rake
e, wear region of tool was monitored and examined. Figure 5.13(a) illustrates
the flank wear surface of the tool after cutting 3.76 km. A narrow flank wear land was
identified at the cutting edge region without any details of this wear. Figure 5.13(b)
shows that when cutting up to 9.42 km, the width of the wear region increased slightly
up to entire effective cutting edge.
Figure 5.14(a) shows the rak
1.88 km. It was observed from this figure that a numbers of micro-grooves
were appeared after cutting 1.88 km. No regular shapes of those grooves were noticed
during further experiments. Initially the maximum groove length measured was about
16 µm and located in the middle of the effective cutting region (Figure 5.14(d)). Figure
5.14(b) and Figure 5.14(c) show the rake face photographs after cutting 5.65 km and
9.42 km respectively. It can be illustrated from these figures that the number of micro-
grooves increased with cutting distance with the increase of micro-groove length
which was measured 32 µm. At the higher cutting distance of 9.42 km, gradual wear
on the rake face was dominated over almost whole effective cutting edge length, as
depicted in Figure 5.14(d).
Figure 5.13(a): VHX Digital Microscope Photograph of Flank Face of Diam0
Flank Face X1000 Cutting Dist: 3.76 km
Flank Wear Region
Micro-grooving on Elcetroless Nickel Plated Die Materials 59
Chapter 5: Results and Discussion
ond Tool
Figure 5.13(b): VHX Digital Microscope Photograph of Flank Face of Diamwith -50 Rake Angle after Cutting 9.42 km
Flank Face X10 : 9.42 km
Flank Wear Region
00 Cutting Dist
Figure 5.14(a): VHX Digital Microscope Photograph of Rake Face of Diamond Tool with -50 Rake Angle after Cutting 1.88 km
Figure 5.14(b): VHX Digital Microscope Photograph of Rake Face of Diamond Tool with -50 Rake Angle after Cutting 5.65 km
Micro-grooving on Elcetroless Nickel Plated Die Materials 60
Chapter 5: Results and Discussion
Figure 5.14(c): VHX Digital Microscope Photograph of Rake Face of Diamond Tool
Figure 5.14(d): VHX Digital Microscope Photograph of Rake Face of Diamond Tool
.5.2 Diamond Tool Wear Mechanisms
The wear of diamond tools in ultra-precision machining has been the subject of
controversial studies [Oomen and Eisses, 1992; Wada et al., 1980]. Phenomena of the
wear mechanisms are not well understood yet. It is common belief that different
mechanisms such as mechanical, thermo chemical and possible electrical effects can
contribute to diamond tool wear where some of which may be involved only under
certain circumstances [Uddin et al., 2004].
As described in the previous section, the wear patterns and region of diamond
tool with the +50 and the -50 rake angles exhibited traces of micro-grooves on the rake
with -50 Rake Angle after Cutting 9.42 km
eyence Microscope 450X Cutting Dist: 9.42 km
Gradual Rake Wear
K
with -50 Rake Angle after Cutting 9.42 km
5
Micro-grooving on Elcetroless Nickel Plated Die Materials 61
Chapter 5: Results and Discussion
faces w
can be
due to
re formed on the tool flank face, indicating a typical abrasive flank
wear as
a sliding contact between the following chip and tool rake face.
hich increase both in number and length with cutting distance. Traditional
gradual flank wear were dominant for both of these tools with trace of micro-grooves
in +50 rake angle. Beside wears on these two tools, the diamond tool with 00 rake angle
did not reveal any type of wear either in flank or rake face. In this section, the
following paragraphs will discuss possible wear mechanism of these two tools.
During micro-grooving or cutting at a very small undeformed chip thickness of
less than a micro-meter, the basic tool wear could be a gradual process. This
the actions of mechanical abrasion wear, and in some cases due to the action of
adhesion wear.
Examination of flank face of the tool with +50 rake angle revealed that some
micro-groves we
shown in Figure 5.9(f) where the micro-grooves were formed along the cutting
direction. At the beginning of cutting, since the tool edge is very sharp. Therefore,
stress acting on the tool cutting edge is extremely severe, resulting micro-ruggedness
on the cutting edge. Besides, when the hard particles present in electroless nickel come
in contact with the inhomogeneities along the cutting edge these may increase the
mechanically weak spots at the edge of the tool [Trent and Wright, 2002 and Oomen
and Eissses, 1992]. Hard particles may also results from the breaking down if heavily
work-hardened, unstable built-up edge. This can lead to micro-grooves on the flank
region along with increasing in length and number. On the other hand, wear on flank
face of -50 rake angle tool is reasonably low compared to +50 rake angle tool.
Therefore, details of this flank wear could not be found out except gradual increase
with cutting distance.
During high speed machining, formation of chip by shearing action at the shear
plane always involves
Micro-grooving on Elcetroless Nickel Plated Die Materials 62
Chapter 5: Results and Discussion
Thus a
of Chip Flow Mechanism
Besides, a +50 rake
angles, adhered layer on the cutting edges of -50 and 00 rake angle tools were noticed
during
brasion wear can take place in this region in the form of groves [Mills and
Redford, 1983]. Flow of chips along the rake face of -50 and +50 rake angles tool might
cause the micro-grooves on these rake faces of the tools. High pressure on the rake
face and chips or micro-grains of electroless nickel acted as abrasive powder flowing
over the rake face [Oomen, 2003]. The numbers of micro-grooves on the tool with -50
rake angle were reasonably high compared to +50 rake angle tool. This can happene
due to efficient chip flow mechanism of positive rake tools which facilitate better chip
flow [Bhattacharyya, 1984] as shown in Figure 5.15.
+ve rake -ve rake
Figure 5.15: Schematic Diagram
brasion on flank and rake face of the tools with -50 and
cutting. Figures 5.16(a) and 5.16(b) show that a layer of materials deposited on
the cutting edge and flank face. As shown in Figure 5.17, the materials were identified
as elceltroless nickel deposit after EDX test. During cutting, eliminating friction
completely at the cutting edge is almost impossible even in the presence of lubricant.
Moreover, temperature at the cutting region is extremely high. Therefore, at high
temperature, some electroless nickel particles can be melted and adhered on the tool
surface. Besides, rate of adhesion may depend on the efficiency of lubrication system
as well as chip removal system.
Micro-grooving on Elcetroless Nickel Plated Die Materials 63
Chapter 5: Results and Discussion
Figure 5.16(a): Keyence VHX Optical Microscope Photography of Flank Face of -50 Rake Angle tool with Adhered Layer of Electroless Nickel.
Figure 5.16(b): Keyence VHX Optical Microscope Photography of Flank Face of 00 Rake Angle tool with Adhered Layer of Electroless Nickel.
Figure 5.17: EDX (Energy Dispersive X-ray) Analysis of the Adhered Layer on the -50 Rake Angle Tool.
Adhered layer of Electroless Nickel
Adhered layer of Electroless Nickel
Micro-grooving on Elcetroless Nickel Plated Die Materials 64
Chapter 5: Results and Discussion
5.6 erformance of Diamond tools
this study, experiments were carried out on the ultra-precision lathe using
t rake angles to evaluate the tools
perform
nd Tool Life
ultra-precision machining, the effect of tool wear on machined surface finish
rtant. Hence, it is necessary to evaluate the
trend
icro-area of flank wear
zones w
P
In
single crystal diamond tools with differen
ance. During the experiments, micro grooving operations were performed on
electroless nickel plated die materials, where the mechanism of chip formation in the
cutting region was dominated by plastic deformation rather than fracture propagation
in the work material. During the experiments, tools were employed to machine up to
11.69 km to analyze the cutting performance. This section reports extensive
experimental results from this study. Tool wears patterns with respect to cutting
distance and its mechanisms were already discussed for diamond tools with different
rake angles in the previous section. In this section, machining performance in terms of
wear resistance, micro-cutting forces and surface roughness are described and
compared for these tools.
5.6.1 Wear Resistance a
In
as well as surface integrity is very impo
of tool wear progression with respect to cutting distance. In addition,
performance of diamond tools varies with the different rake angles. In view of this,
under the same experimental conditions (Table 4.3), cutting experiments using
diamond tools having different rake angles were performed.
In was seen in previous section 5.5, that both the flank and the rake wears were
dominant during experiments. For all the diamond tools, m
ere measured by VHX digital optical microscope directly using the software
attached in this system. Besides, the rake wears were measured graphically with the aid
Micro-grooving on Elcetroless Nickel Plated Die Materials 65
Chapter 5: Results and Discussion
of picture taken by Nomarski microscope, VHX digital optical microscope and SEM at
various cutting distance.
Figure 5.18 shows the flank wear characteristics with respect to cutting
distance for diamond tools with three different rake angles. From this figure, a gradual
increase of flank wear with respect to cutting distance was observed for the +50 and the
-50 rake angle tools. After cutting 11.69 km, the characteristic of the rake wear for the
+50 and the -50 rake angle tools can been seen from the figures 5.19(a) and
5.19(b).However, no flank and rake wear on diamond tool with the 00 rake angle was
observed up to this cutting distance, which was discussed in the previous section also.
Therefore, it can be said that diamond tool with the 00 rake angle has higher wear
resistance compared to those with other rake angles.
11.69 8.29 7.16 6.03 1.88
-5 deg. rake0 deg. rake
+5 deg. rRake0
100
200
300
400
500
600
700
800
Flan
k W
ear(
µm2 )
Cutting Distance(km)
-5 deg. rake 0 deg. rake +5 deg. rRake
Figure 5.18: Flank Wear with Cutting Distance for the Tools with Different Rake
Angles
Similarly, results on flank wear patterns and mechanisms indicate that, during
micro scale machining of brittle mate tting edge recession, micro-grooving
formati
rials, cu
on and gradual flank wear due to mainly the mechanical abrasion, and adhesion
wear were predominant for diamond tools with the -50 and the +50 rake angles.
Besides, during cutting with the -50 and the +50 rake angle tools, rake wear pattern
Micro-grooving on Elcetroless Nickel Plated Die Materials 66
Chapter 5: Results and Discussion
shows the gradual increase in number of grooves on the rake face due to abrasion
wear. It is interestingly seen that flank wear resistance for tool with the -50 rake angle
is higher than the +50 rake angle tool. On the other hand, the rake wear resistance for
tool with the +50 rake angle is higher than the -50 rake angle tool where the numbers of
grooves appeared after cutting 11.69 km were comparatively high on the -50 rake angle
tool compared to the +50 rake angle tool.
During high speed machining of non-ferrous metals, practice shows that a
positive rake tool facilitates efficient chip flow over the rake face compared to negative
rake to
Figure 5.19(b): Rake Face of the +50 Rake Angle Tool after Cutting 11.69km
ol. On the other hand, positive rake weakens the cutting edge, hence reduce the
tool life due to poor heat dissipation from the cutting edge. A negative rake improves
the tool life by strengthening the wedge angle which improves the heat conduction
from the cutting edge to the tool shank [Bhattacharyya, 1984].
Figure 5.19(a): Rake Face of the -50 Rake Angle Tool after Cutting 11.69km
Effective Cutting Edge length, 0.25mm
Effective Cutting Edge length, 0.25mm
Micro-grooving on Elcetroless Nickel Plated Die Materials 67
Chapter 5: Results and Discussion
Hence from our results on wear resistance for diamond tools, it can be said that
diamond tools with positive rake angles have lower resistance to flank wear. Flank
wear resistance increases with decrease of rake angle and then starts to decrease after a
certain rake angle. On the other hand, diamond tools with negative rake angles have
lower resistance to rake wear. Further increases of rake angles increase the resistance
to ra ese
experim
0 0
mely, thrust force, Ft and cutting
force, F acting on the diamond tools tip during the actual machining was depicted in
of this chapter.
, the cutting forces, both thrust and
cutting
0
ke wear which decreases again after a certain value of rake angle. During th
ents, diamond tool with the 00 rake angle shown the best resistance to both
flank and rake wears. Further increase or decrease of rake angles, i.e. +5 and the -5
rake angle respectively, lower the wear resistances.
5.6.2 Cutting Forces
In this study, along with the tool wear characteristics, two major components of
micro-cutting forces wear observed and measured to investigate the cutting
performance during micro-grooving with the diamond tools with different rake angles.
A schematic diagram of the force components na
c
the Figure 5.1 beginning
Figures 5.20(a) and 5.20(b) show the relationships between cutting forces with
respect to cutting distance for the diamond tools with three different rake angles. The
error bars in the graph were in between 21%. During the whole cutting distance, both
the cutting and thrust forces increased with cutting distance. The thrust and cutting
forces on the 00 rake tool were significantly lower compared to those with different
rake angles throughout the experiments. Initially
, were higher on the -50 rake tool compared to the +50 rake tool. However, after
cutting about 2 km, the thrust forces on the +5 rake tool were found to be higher.
Micro-grooving on Elcetroless Nickel Plated Die Materials 68
Chapter 5: Results and Discussion
Similarly, the cutting forces on the +50 rake tool became higher after about 5 km
cutting. It is also found that the cutting forces characteristics for diamond tools with
these three different rake angles show a very similar trend with cutting distance.
In traditional cutting, with the increase in cutting distance, which is
proportional to machining time, the tool flank wear increases, and hence, there is a
natural and gradual increase in micro-cutting forces [ Mills and Redford, 1983]. From
our experimental results on micro-cutting forces, it can be said that predominantly
higher tool wear resistance for the diamond tool with the 00 rake tool could be the
reason for lower forces. On the other hand, the higher forces for the diamond tools
with other two different rake angles may correspond to lower flank wear resistance. In
addition, it could be noticed from the Figure 5.18 that the flank wear on +50 rake tool
was higher than the -50 rake tool throughout the experiments, thus the +50 rake angle
tool shows high cutting forces compared to the -50 rake tool. During micro-grooving,
the axial thrust force is always higher than the cutting force component. Thus during
these experiments, it is clear from the figures 5.20(a) and 5.20(b) that the thrust forces
is greater than the cutting forces for all the experiments.
0
0.5
1
2
2.5
3
ust
ce)
1.5
0 2 4 6 8 10 12 14
Cutting Distace(km)
Thr
For
(N
0 deg. Rake +5 deg. Rake-5 deg. Rake Linear (0 deg. Rake)Linear (+5 deg. Rake) Linear (-5 deg. Rake)
Figure 5.20(a): Effect of Cutting Distance on Thrust Forces for Diamond Tools with
Different Rake Angles
Micro-grooving on Elcetroless Nickel Plated Die Materials 69
Chapter 5: Results and Discussion
0
0.2
0.4
0.6
0.8
1
0 2 4 6 8 10 12 14
Cutting Distance(km)
Cut
ting
Forc
e(N
)
0 deg. Rake +5 deg. Rake-5 deg. Rake Linear (0 deg. Rake)Linear (+5 deg. Rake) Linear (-5 deg. Rake)
g Distance on Cutting FFigure 5.20(b): Effect of Cuttin orces for Diamond Tools with Different Rake Angles
5.6.3 Machined Electroless Nickel Surface Characteristics
Generally the machined surface roughness depends on many factors such as
tool wear, work material hardness, and machining conditions. For instance, the tool
wear is very much dependent on cutting distance assuming other factors are held
constant. In this study, at 0.377 km interval of cutting distance, surface finish of the
machines electroless nickel was was measured using Mutitoyo Formtracer.
The influence of the cutting distance on the surface roughness of electroless
n
5.21(b). From these figures, it can be seen that the roughness parameters Ra (Average)
ted randomly within a
very na
dition, it is
ickel for diamond tools with different rake angles is presented in Figures 5.21(a) and
and Ry (Peak-valley) of machined electroless nickel are distribu
rrow range and their variations lie between 3 nm to 5 nm, and between 14 nm
to 35 nm respectively. This result indicates that with the increase in cutting distance
and hence, in tool wear on +50 and -50 tools, and the increase in cutting forces on all
the diamond tools, there is no significant variation in surface roughness (Ra and Ry) of
the machined workpiece during micro-grooving of electroless nickel. In ad
Micro-grooving on Elcetroless Nickel Plated Die Materials 70
Chapter 5: Results and Discussion
clear that the 00 rake tool performed well compared to other two inserts. The likely
cause of this reason is wear on cutting edge of the +50 and the -50 rake inserts which
further increases the machined surface roughness slightly compared to the 00 rake
insert. However, this kind of reasonably consistent surface roughness characteristics
for the +50 and the -50 rake tools obtained from the experiment could be the result of
the smooth surface structure of gradual tool flank wear land.
0
1
3
4
6
7
Cutting Distance(km)
Sfa
cou
gne
ss R
a(µ
)
2
5
0 2 4 6 8 10 12 14
ure
Rh
,m
0 deg. Rake +5 deg. Rake -5 deg. Rake
Figure 5.21(a): Effect of Cutting Distance on Surface Roughness, Ra
0
5
10
1520
25
30
35
40
0 2 4 6 8 10 12 14
Cutting Distance(km)
Sur
face
Rou
ghne
ss,R
y(nm
)
0 deg. Rake +5 deg. Rake -5 deg. Rake
Figure 5.21(b): Effect of Cutting Distance on Surface Roughness, Ry
Micro-grooving on Elcetroless Nickel Plated Die Materials 71
Chapter 5: Results and Discussion
In addition to the trend of surface roughness characteristics for all diamond
tools, the roughness profile of machined electroless nickel can indicate the actual
asperities on the surface after machining. Figures 5.22(a)-5.22(c) illustrate the surface
roughness profile of machined electroless nickel for the diamond tools with different
rake angles after cutting 11.69 km. From these figures, it is found that the variations in
roughness parameters for all tools were less, but diamond tool with the 00 rake angle
shows lower surface roughness values compared to those with other rake angles at the
end of same cutting distance. Fang and Venkatesh (1998) noticed that the use of
diamond tools with the 00 rake angle results in better surfaces finish than tools with the
other rake angles at same cutting conditions.
Figure 5.22(a): Roughness Profile of Electroless Nickel for tool with the 00 rake angle
after cutting 11.69km.
Figure 5.22(b): Roughness Profile of Electroless Nickel for tool with the -50 rake angle after cutting 11.69km.
Micro-grooving on Elcetroless Nickel Plated Die Materials 72
Chapter 5: Results and Discussion
Figure 5.22(c): Roughness Profile of Electroless Nickel for tool with the +50 rake angle after cutting 11.69km.
The machined surface roughness of the electroless nickel was also observed
under Nomarski microscope and VHX digital optical microscope at 0.377 km interval
of cutting distance. Figures 5.23(a)-5.23(c) show the machined surface finish of micro-
grooves after cutting 11.69 km for the diamond tools with different rake angles under
Nomarski microscope. All the machined grooves surfaces reveal smooth appearance
without any visible crakes generated in the surfaces. It can be concluded that during
cutting micro-grooves with d e angles, the chip formation
was occurred in plastic deformation of electroless nickel material at shear zone.
the 0 rake angle.
iamond tools of different rak
Figure 5.23(a): Photograph of Machined Micro-grooves after cutting 11.69 km with 0
Nomarski Photograph X100 Cutting Dist: 11.69 km
Micro-grooving on Elcetroless Nickel Plated Die Materials 73
Chapter 5: Results and Discussion
Figure 5.23(b): Photograph of M oves after cutting 11.69 km with the -50 rake angle.
Figure 5.23(c): Photograph of M ves after cutting 11.69 km with the +50 rake angle.
.7
Chips produced during micro-grooving, were observed and examined under
EM. Figures 5.24(a)-5.24(c) show SEM photographs of the machined electroless
ickel after cutting 11.69 km. These figures are evidences of continuous chip
formation for all the tools with different rak angles. It reveals that plastic deformation
w
achined Micro-gro
Nomarski Photograph X100 Cutting Dist: 11.69 km
Nomarski Photograph X100 Cutting Dist: 11.69 km
achined Micro-groo
5 Chip Observation
S
n
e
as achieved during the experiment until the end.
Micro-grooving on Elcetroless Nickel Plated Die Materials 74
Chapter 5: Results and Discussion
Figure 5.24(a): Machined Electroless Nickel Chip Produced by 00 Rake Angle Tool
Figure 5.24(b): Machined Electroless Nickel Chip Produced by -50 Rake Angle Tool
Figure 5.24(c): Machined Electroless Nickel Chip Produced by +50 Rake Angle Tool
Micro-grooving on Elcetroless Nickel Plated Die Materials 75
Chapter 6: Conclusions and Recommendations for Future Work
Chapter 6
Conclusions and Recommendations for Future Work
6.1 Introduction
This chapter illustrates some significant conclusions that can be drawn from the
experimental results and a comprehensive discussion on them in Chapter 6. In
addition, considering the limitations and prospects of this work, some
recommendations have also been made in this chapter for its future work.
6.2 Conclusions
From analysis of experimental results, the following conclusions can be drawn:
• During cutting with the tools having three different rake angles, no significant
variation on machined surface roughness was observed with change in spindle
speed and infeed rate.
• Micro-cutting forces, both thrust and cutting, increased with increase in spindle
speed and infeed rate for all the tools during the experiments. The interaction
between tool face and workpiece and stress on the cutting tool increase with
increase in infeed rate which might be a cause of an increment of forces. On the
other hand, increase in spindle speed material removal rate increases which
further increase the forces.
• Experimental results on hardness on electroless nickel shows that hardness of
the workpieces decreased with increase in phosphorus content.
• No significant wear is observed on the 00 rake angle tool. However, wear on
other two tools are noticeable.
Micro-grooving on Elcetroless Nickel Plated Die Materials 76
Chapter 6: Conclusions and Recommendations for Future Work
• The SEM, digital optical microscope and Nomarski optical microscope
observations on flank face indicates flank wear on tools with the -50 and the
+50 rake angles where the wear rate increases with cutting distance. Flank wear
on of the +50 rake angle tool is found to be groove types. However, details of
the flank wear on the -50 rake tool are not understood since the wear rate is low.
• Similarly, microscopic observations on rake face shows grooves on the tools
with -50 and +50 rake angles where the grooves increases in number and length
with cutting distance. The numbers of grooves observed on -50 rake angle tool
are larger compared to +50 rake angle tool.
• Investigation of tool wear patterns and mechanism reveals that mechanical
abrasion is dominant for gradual wears on the flank and rake faces with -50 and
+50 rake angles tools.
• Investigation of tool surfaces shows some adhered layer appeared on the
cutting edge which is identified electroless nickel later. At high temperature,
electroless nickel possibly melted and adhered on the tool surface.
• Considering the micro-cutting force characteristics for all diamond tools, it is
noted that diamond tool with the 00 rake angle shows lower thrust force
compared to those with other rake angles. Such micro-cutting forces
characteristics for this tool can be attributed to their lower wear rate with
cutting distance.
• The trend of micro-cutting forces, both thrust and cutting, were increasing trend
with similar characteristics with cutting distance.
• It was also noticed that thrust force is always greater than the cutting force
because of the special plunge cut technical where axial force component is
higher than the cutting force component.
Micro-grooving on Elcetroless Nickel Plated Die Materials 77
Chapter 6: Conclusions and Recommendations for Future Work
• There is no significant variation in surface roughness parameters such as Ra
(average) and Ry (Peak-Valley) with respect to cutting distance. The increase in
wear on +50 and -50 rake angle tools and cutting forces on all three tools does
not significantly affect the surface roughness. The surface quality of up to 3nm
Ra was achieved under optimal cutting conditions.
• The 00 rake angle tool performs better than other two tools within same cutting
conditions with respect to tool wear, surface roughness, and micro-cutting
forces. Tool wear and micro-cutting forces increase with further increase or
decrease in rake angels compared to the 00 rake angle tool.
6.3 Recommendations for Future Work
Bearing in mind the possible limitations in this study, the following suggestions
for further exploring the diamond tool wear characteristics as well as their performance
during micro-cutting on electroless nickel plated die materials.
• The trimming off the workpieces should be perfectly carried out to get a
perfectly flat surface. During trimming off, the manual inspections of
workpieces were taken into consideration for measuring the flatness. If the
surface is not exactly flat the depth of grooves can not be controlled. In
additions, during cutting in micro rage, micro-cutting forces vary significantly
with depth of cut. Therefore, every workpieces should be checked carefully
before the experiments using surface flatness measuring instruments to ensure a
perfectly flat surface.
• Another technical factor is to balance the workpieces properly once it is
chucked. Precise dial indicator for balancing should be used to avoid any
accidental failure of the tools.
Micro-grooving on Elcetroless Nickel Plated Die Materials 78
Chapter 6: Conclusions and Recommendations for Future Work
• Proper direction of mist spray nozzle is important to avoid undesired surface
roughness. Therefore, it should be recommended to check the direction of mist
spray nozzle before each experiment.
• SEM observation of the machined micro-groove is significant in term of sub
surface damages. During this experiment, it was not possible to observe the
machined micro-groove due to weight and size limitation of workpieces.
Therefore, workpiece can be cut in small pieces to exam under SEM.
• During micro-grooving, a theoretical analysis of wear resistance of diamond
tools with different rake angles could be made to predict wear resistance of
diamond tools with different rake angles in actual cutting.
• Thermo-chemical effect is thought to be one of the wear mechanisms of
diamond tools. It would be interesting to investigate the temperature
characteristics of the cutting process, which could turn out to be a significant
factor affecting tool wear in micro scale machining.
Micro-grooving on Elcetroless Nickel Plated Die Materials 79
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List of Publications
List of Publications
Conference Papers “Effect of Rake Angle of Diamond Tools on Micro Grooving”, A.Q. Biddut,
M.Rahman, Neo Ken Soon.
5th international conference and 7th annual general meeting of the European Society
for Precision engineering and Nanotechnology, May 8th - May 11th 2005, Montpellier,
France.
“Cutting Performance of Single Crystal Diamond Tools during Micro Grooving on
Electroless Nickel Plated Die Materials”, A.Q. Biddut, Neo Ken Soon, M.Rahman.
4th International Mechanical Engineering Conference, 29th -31th December 2004,
Dhaka, Bangladesh.
Journal Paper “Performance of Single Crystal Diamond Tools with Different Rake Angles during
Micro-grooving on Electroless Nickel plated Die Materials”, A. Q. Biddut, M. Rahman,
K. S. Neo, K M Rezaur Rahman, M. Sawa, Y. Maeda.
Submitted to International Journal of Advanced Manufacturing Technology.
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