Feasibility and Process Development of Mechanical Micro Drilling for Nickel Based Super Alloys

209 Pages·2010·32.39 MB·English

Feasibility and Process Development of
Mechanical Micro Drilling for Nickel
Based Super Alloys

A thesis submitted to

THE UNIVERSITY OF MANCHESTER

for the degree of

DOCTOR OF PHILOSOPHY

In the Faculty of Engineering and Physical Sciences

2010

Muhammad Imran

School of Mechanical, Aerospace and Civil Engineering
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List of Figures 7
List of Tables 13
List of Nomenclature 14
List of Abbreviations 15
Abstract 17
List of Publications 18
Declaration 19
Copyright Statement 20
Dedication 21
Acknowledgements 22

CHAPTER ONE
Introduction and Research Objectives 23
1.1 Background 23
1.2 Project industrial drivers 24
1.3 Aim and objectives 24
1.4 Thesis organization 25

CHAPTER TWO
Literature Review 28
2.1 Introduction 28
2.2 Twist drill nomenclature 29
2.3 Cutting mechanics 30
2.4 Drill performance evaluation 32
2.5 Twist drill geometry 32
2.5.1 Helix angle 33
2.5.2 Web thickness 34
2.5.3 Point angle 36
2.5.4 Clearance angle 37
2.5.5 Different drill point geometries 38
2.5.6 Drill manufacture and accuracy 41
2.6 Overview of micro machining 42
2.7 Brief introduction to micro drilling 44
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2.7.1 Drill wandering motion in micro drilling 44
2.7.2 Stiffness in micro drills 45
2.7.3 Tool geometry for micro drills 46
2.7.4 Torque and thrust 47
2.7.5 Speeds and feeds in micro drilling 47
2.7.6 Feed to edge radius (f/r ) ratio 48
e
2.8 Introduction to nickel based super alloys 49
2.8.1 Machinability of nickel alloys 50
2.8.2 Surface integrity 50
2.9 Tool wear in machining of nickel alloys 53
2.9.1 Wear mapping 53
2.9.2 Tool wear 54
2.9.3 Tool wear mechanisms 55
2.9.4 Cooling effects 56
2.10 Tool coatings 57
2.11 Summary 63

CHAPTER THREE
Feasibility of Micro Hole Drilling Process 65
3.1 Introduction 65
3.2 Materials and methods 65
3.3 Cutting conditions 69
3.3.1 Speed 69
3.3.2 Feedrate 69
3.3.3 Size effect-feed and tool edge radius relationship 69
3.4 Results and discussions 70
3.4.1 Cutting strategy 70
3.4.2 Cutting conditions 71
3.4.3 Tool wear 74
3.4.4 Sample component results 76
3.4.5 Drilling cycle optimization 77
3.6 Conclusions 80

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CHAPTER FOUR
Evaluation of the Effects of Tool Geometry on Tool Life and Surface 82
Integrity in Micro Drilling Process
4.1 Introduction 82
4.2 Materials and methods 82
4.3 Results and Discussions 86
4.3.1 Effect of geometrical parameters on tool wear 86
4.3.2 Effect of micro drill geometry on burr size 89
4.3.3 Burr formation mechanism 91
4.3.4 Analysis of workpiece subsurface deformations 96
4.4 Conclusions 98

CHAPTER FIVE
Characterization of Surface and Subsurface in Micro Drilling Process 100
5.1 Introduction 100
5.2 Research motivation 101
5.3 Experimental details 101
5.3.1 Materials 101
5.3.2 Micro drilling trials 104
5.3.3 Microstructural observations 106
5.4 Results and discussions 107
5.4.1 Parent microstructure 107
5.4.2 Surface modified layers 108
5.4.3 EBSD studies 116
5.4.4 TEM studies 122
5.4.5 Nano-hardness profile 126
5.4.6 Surface roughness 129
5.5 Micro machining observations 131
5.6 Conclusions 136

CHAPTER SIX
Assessment of Tool Wear and Coatings in the Micro Drilling Process 138
6.1 Introduction 138
6.2 Research motivation 138
6.3 Research methods 139
6.3.1 Workpiece material 139
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6.3.2 Micro drilling tests 139
6.3.3 Coating evaluation 141
6.4 Results and discussions 142
6.4.1 Tool wear phenomena 142
6.4.2 New wear map for micro drilling 146
6.4.3 Tool wear mechanism in wet drilling 148
6.4.4 Tool wear in dry drilling 154
6.4.5 Tool coatings evaluation 161
6.5 Conclusions 165

CHAPTER SEVEN
Evaluation of Surface Integrity in EDM, Laser and Mechanical 167
Micro Drilling Processes
7.1 Introduction 167
7.2 Materials and methods 167
7.3 Results and discussions 169
7.3.1 Scanning electron microscopy study 169
7.3.2 EBSD study 172
7.3.3 Hardness and Young’s modulus 175
7.4 Conclusions 179

CHAPTER EIGHT
Conclusions and Recommendations 181
8.1 Conclusions 181
8.2 Contribution to knowledge 182
8.3 Further work 183

REFERENCES 184

Appendix A 201
List of Equipment Used During This Research
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Figure 2.1 (a) Basic twist drill and (b) Description of drill point 30
Figure 2.2 Variation of helix angle δ, clearance angle α, and feed angle 31
ε, across the main cutting edge of a representative 14.3 mm
diameter drill
Figure 2.3 Description of different point angles 37
Figure 2.4 Conical ground drill geometry 39
Figure 2.5 Spiral point drill geometry 39
Figure 2.6 Circular centre edge geometry 40
Figure 2.7 Web profile ground drill 41
Figure 2.8 Basic coating selection parameters 58
Figure 3.1 Microstructure of single crystal nickel based super alloy 66
CMSX 4
Figure 3.2 Basic geometry of 120° point angle centre drill 67
Figure 3.3 Basic geometry of 150° point angle twist drill 67
Figure 3.4 Dynamometer, workpiece and fixture setup 68
Figure 3.5 Strategy for micro drilling of difficult to cut alloys 71
Figure 3.6 Effect of spindle speed on drill life (at constant feedrate of 5 72
µm/rev)
Figure 3.7 Effect of feedrate on drill life (at 3000 rpm) 73
Figure 3.8 Effect of Peck depth on drill life 74
Figure 3.9 SEM images of tool wear; (a) Drill after 8 holes; (b) Drill 75
after 24 holes and (c) Drill after 80 holes
Figure 3.10 Schematic illustration of abrasion on main cutting edge 75
Figure 3.11 (a) Drilled test-piece and (b) Representative hole definition 76
Figure 3.12 Variation of hole diameter at 3000 RPM & 5µm/rev 77
Figure 3.13 Comparison of thrust forces at various retraction feedrates 78
Figure 3.14 Comparison of tool life at various retraction feedrates 79
Figure 3.15 Thrust Vs time graph at feedrate of 8 µm/rev and speed of 80
3000 rpm during 0.9 mm of cutting (peck depth = 0.1mm)
Figure 4.1 Magnified backscatter electron (BSE) image of material 83
microstructure
Figure 4.2 Tool geometry at various point and helix angles 85
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Figure 4.3 (a) Flank wear main effect plots and (b) Flank wear 88
interaction plots
Figure 4.4 (a) Main effect plots for point and helix angle and 90
(b) Interaction effect plots for point and helix angle
Figure 4.5 Illustration of burr formation mechanism 92
Figure 4.6 Microstructural burr formation mechanism; (a) Cross- 94
section view of cap and workpiece, (b) Microstructural view
of cap and workpiece and (C) BSE microstructure of inlet
burr
Figure 4.7 Effect of drill point geometry on burr cap 95
Figure 4.8 Increase of burr height with cutting length 96
Figure 4.9 Thickness of deformed zone at various point and helix 97
angles (arrows show thickness of deformation zone)
Figure 4.10 Variation of deformation zone at different point and helix 98
angles
Figure 5.1 Frequency of various grain sizes in the parent material 102
Figure 5.2 (a) Taper sectioning technique and (b) SEM micrograph of 104
the samples prepared by using taper sectioning technique

Figure 5.3 Tool geometry for 500 µm diameter twist drill 105
Figure 5.4 TEM sample preparation using FIB 107
Figure 5.5 Microstructure of the parent Inconel 718 plate; (a) a BSE 108
and (b) an inverse pole figure (IPF) colour map overlaid on a
band contrast (BC) map with HAGBs shown in black, twin
boundaries have red lines, low angle misorientations are not
evident (little contrast variation within grains)
Figure 5.6 BSE image showing the surface and subsurface layers upon 109
drilling at 5000rpm with a feedrate of 5µm/rev.The cutting
direction is indicated by the hoop arrow
Figure 5.7 BSE images for radial/hoop sections showing the effect of 111
feedrates on the extent of surface and sub-surface
modifications on the microstructure (cutting direction is
clockwise)
Figure 5.8 (a) Thickness of refined grain layer A at various feedrates at 112
5000 rpm. These values represent an average of
measurements at each quadrant of the hole, (b) Thickness of
deformed layer (B) at various feedrates at 5000 rpm and (c)
Thickness of refined grain layer (A) at various speeds at a
feedrate of 0.5µm/rev
Figure 5.9 Effect of feedrate on thrust force at spindle speed of 3000 113
rpm
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Figure 5.10 Effect of increasing edge radius on extent of deformation 113
zone at feedrate of 5 µm/rev and speed of 3000 rpm
Figure 5.11 Comparison of dry and wet drilling at various feedrates 115
(cutting direction is clockwise)
Figure 5.12 Comparison of thickness of deformation zone in dry and wet 116
drilling
Figure 5.13 Electron backscatter diffraction patterns collected at 117
different distances from the machined surface using an
accelerating voltage of 20kV (a) Refined grain structure
layer (A); (b) Deformed grain structure layer (B); (c) Parent
material (C)
Figure 5.14 (a) Band contrast map (top), (b) IPF colour map overlaid on 118
band contrast map (mid) and (c) misorientation profile along
line L for 5000rpm and 2µm/rev feedrate (wet cutting),
region A appears ‘black’ because of fine grain size
Figure 5.15 (a) Relative frequency of misorientations in parent metal and 119
(b) Relative frequency of misorientations in zone B
Figure 5.16 EBSD maps and relative frequency of misorientations in dry 121
and wet cutting conditions; (a) IPF color map at feedrate of
8 µm/rev and speed of 5000 rpm at wet cutting conditions;
(b) IPF color map at feedrate of 8 µm/rev and speed of 5000
rpm at dry cutting conditions and (C) Relative frequency of
misorientations in dry and wet cutting conditions
Figure 5.17 Transmission electron micrographs a) zone A and b) zone B 123
at feedrate of 5µm/rev and cutting speed of 5000 rpm
Figure 5.18 TEM diffraction patterns from zones; (a) A, (b) B and (c) C 124
at feedrate of 5µm/rev and speed of 5000rpm
Figure 5.19 Transmission electron micrographs at dry and wet cutting 125
conditions at fine grain structure layer; (a) Dry cutting and
(b) Wet cutting
Figure 5.20 TEM diffraction patterns from zone A at dry and wet cutting 126
conditions
Figure 5.21 (a) Position of nano-indentation at various altered layers of 127
the workpiece and (b) Nanoindentation profile across the
three different zones at feedrate of 2 µm/rev and at speed of
3000 rpm
Figure 5.22 (a) Variation of nano-hardness at speed of 1000 rpm and 128
varying feedrates and (b) Variation of nano-hardness at
feedrate of 8 µm/rev and varying speeds
Figure 5.23 Comparison of hardness at various zones in dry and wet 129
cutting conditions
Figure 5.24 (a) SEM micrograph of bottom surface of a hole and (b) 130
Variation of surface roughness at various feeds and speeds
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Figure 5.25 BSE photomicrograph of deformation zones with a negative 132
rake angle tool of -45° at undeformed chip thickness of 5
µm and speed of 3000 rpm
Figure 5.26 Microstructural characterization in zone 1; (a) FIB electron 133
image of fine grain structure layer, A, and deformed grain
structure layer, B; (b) Magnified electron image of layer A
and (c) TEM image of elongated nano size grains in layer A
Figure 5.27 Chip morphology at Freeside 134
Figure 5.28 Microstructural characterization in chip; (a) BSE image of 135
saw-tooth chip form with fracture points and different
microstructures, (b) Magnified FIB image of fully deformed
grains and partially deformed grains and (c) TEM image of
fully deformed and annealed microstructure
Figure 5.29 Nano-hardness profile across different deformation zones 136
Figure 6.1 Cutting geometry for 500 µm diameter twist drill, (a) Top 140
view and (b) Side view
Figure 6.2 Area of interest on drill’s flank wear in FIB microscope 141
Figure 6.3 Twist drill after wear at main cutting edge, secondary 143
cutting edge and drill centre
Figure 6.4 Tool wear progression with increasing number of holes at 144
feedrate of 5 µm/rev and speed of 3000 rpm; (a) Tool wear
progression with increasing number of holes, (b) Tool wear
at stage-1 and (c) Tool wear at stage-2 and Tool wear at
stage-3
Figure 6.5 f/r ratio progression with increasing number of holes at 145
e
feedrate of 5 µm/rev and speed of 3000 rpm
Figure 6.6 Variation of f/r ratio with increasing number of holes at 146
e
various feedrates
Figure 6.7 Tool wear map at the flank face 148
Figure 6.8 Tool wear on flank and rake faces; (a) Tool wear on flank 149
face and chisel edge; (b) Tool wear on rake face
Figure 6.9 Tool wear mechanism on flank face of twist drill; adhesive 149
layer of workpiece material on flank face and micro
chipping near the main cutting edge at cutting conditions of
5000 rpm and 5 µm/rev
Figure 6.10 EDX energy spectrum of different elements on the flank 150
face
Figure 6.11 EDX line scan from the cutting edge towards trailing edge 151
on flank face
Figure 6.12 (a) EDX Line scan for various elements; (b) EDX Line scan 153
for Cr, Fe, Co and Ni elements and (c) Atomic ratios of
various elements with cobalt
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