Laser Machining Of Medical Grade Zirconia Ceramic For Dental
Reconstruction Applications
Fraser Craig Dear
Submitted for the degree of Doctor of Philosophy
Heriot-Watt University
School Of Engineering and Physical Sciences
May 2008
This copy of the thesis has been supplied on condition that anyone who consults it is
understood to recognise that the copyright rests with its author and that no quotation
from the thesis and no information derived from it may be published without the prior
written consent of the author or of the University (as may be appropriate).
i
ABSTRACT
The aim of this project is to provide a fundamental understanding of the processes
involved in economically manufacturing complex component parts from medical grade
Yttria Stabilised Zirconia. Such material is an attractive choice for many engineering
applications, primarily due to its stiffness, hardness and wear resistance. Due to the
hardness of the material however, conventional mechanical machining - especially at
small micrometer scales - is difficult. As an alternative fabrication route this project
investigated the precision limits of machining such ceramics using high power, pulsed
lasers operating in millisecond, and nanosecond regimes and at wavelengths of
1075 nm, 1064 nm, 532 nm and 10.6 m. In order to establish the suitability of
machined parts for biomedical implant, the use of a Raman Spectrometer was vital to
establish the phases present in the final machined parts. The work focuses heavily on
the use of Yttrium Oxide (Y2O3) Partially Stabilized Zirconia (PSZ) as it is the prime
material used in dental reconstructions to date however a comparison with Alumina is
carried out. In depth investigation of the processing parameters used in millisecond
Nd:YAG and nanosecond Nd:YVO4 laser sources was conducted providing maximum
material removal rates of 13 mm3/s and 2.1 mm3/min respectively. Successful CO2
laser processing was conducted on 8 mm thick samples however, when processing
complex components, bulk failures were observed. An un-calibrated infrared camera
was used in this process, highlighting potential thermal gradients responsible for bulk
fracture. The particularly difficult process of blind hole drilling using a mechanical
method has been investigated using a laser to pre-drill a suitable hole before mechanical
machining takes place. This investigation has resulted in a 97% reduction in processing
time using the developed laser process over the mechanical method used currently.
Additionally, a dual laser process is examined in order to provide a two phase
machining method utilising the speed and precision of two different lasers respectively.
A novel high beam quality laser process is presented which offers a technique to section
14 mm thick samples of the material via a crack propagation method. Future research
opportunities have been identified and discussed, focussing on ways to resolve these
key issues and other possibilities in laser processing.
ii
DEDICATION
This thesis is dedicated to
my mother, late father and sister,
Sheila, Norman & Emma.
iii
ACKNOWLEDGEMENTS
Having studied my undergraduate degree and conducted my postgraduate research at
Heriot-Watt University, I have made many friends and colleagues. I thank everyone
whom I have worked with though out my time here; let’s hope I get to work with as
good a team in my future career.
Special thanks must go to Professor Duncan Hand for his supervision and guidance
through out the course of the project. Dr Jon Shephard for his help from the moment I
started right up to completion – a breath of fresh air and the ‘odd’ dodgy joke! Further
thanks must go to all the members of the Applied Optics Group at Heriot Watt
University for the support provided on too many occasions to mention. Special thanks
must also go to the entire team at Renishaw Plc with a special mention to Nick Jones,
Nick Weston and Alan Brooker. The technical staff at Heriot-Watt with special thanks
to the EPS stores & Physics clerical team – they know the help they have given,
technical and supportive – priceless! The recognition of the work put into this thesis
from the Association of Industrial Laser Users, awarding me the “Young UK Laser
Engineer Prize 2008” must be acknowledged with heartfelt gratitude and thanks!
Finally my family and friends for their continual support – Jacqui, Lena, Catherine &
Suzi….. couldn’t have done it without you!
iv
ACADEMIC REGISTRY
Research Thesis Submission
Name:
FRASER DEAR
School/PGI:
School of Engineering and Physical Sciences
Version:
Final
(i.e. First,
Resubmission, Final)
Degree Sought:
Doctor of Philosophy
Declaration
In accordance with the appropriate regulations I hereby submit my thesis and I declare that:
1)
2)
3)
4)
5)
*
the thesis embodies the results of my own work and has been composed by myself
where appropriate, I have made acknowledgement of the work of others and have made
reference to work carried out in collaboration with other persons
the thesis is the correct version of the thesis for submission and is the same version as
any electronic versions submitted*.
my thesis for the award referred to, deposited in the Heriot-Watt University Library, should
be made available for loan or photocopying and be available via the Institutional
Repository, subject to such conditions as the Librarian may require
I understand that as a student of the University I am required to abide by the Regulations
of the University and to conform to its discipline.
Please note that it is the responsibility of the candidate to ensure that the correct version
of the thesis is submitted.
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Candidate:
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v
TABLE OF CONTENTS
Abstract ......................................................................................................................ii
Dedications .................................................................................................................iii
Acknowledgements ....................................................................................................iv
Declaration .................................................................................................................v
Table of Contents .......................................................................................................vi
List of Tables..............................................................................................................xi
List of Figures ............................................................................................................xii
List of Publications ....................................................................................................xix
List of Awards ............................................................................................................xx
Chapter 1 – Introduction .........................................................................................1
1.1. – Rationale ..............................................................................................1
1.2. – Summary Of Chapters ..........................................................................1
Chapter 2 – Background and Review of Literature .............................................3
2.1. – Materials ...............................................................................................3
2.1.1. – Zirconia .................................................................................3
2.1.2. – Alumina .................................................................................7
2.2. – Properties of Laser Light ......................................................................7
2.2.1. – Pulsing a Laser ......................................................................9
2.2.2. – Pulse Duration .......................................................................9
2.2.3. – Pulse Energy and Power ......................................................10
2.2.4. – Quality and Focussing of Beams...........................................11
2.2.5. – Wavelength and Optical Absorption .....................................13
2.3. – Specific Lasers Used ............................................................................14
vi
2.3.1. – Nd:YAG Lumonics JK705 Laser ..........................................14
2.3.2. – Spectra-Physics Inazuma Laser.............................................16
2.3.3. – Trumpf TruFlow 2700 CO2 Laser ........................................17
2.3.4. – IPG YLR1000 Fibre Laser ....................................................17
2.3.5. – Beam Delivery ......................................................................18
2.3.6. – Laser/Material Interactions ...................................................20
2.4. – Manufacturing Methods For Ceramics ................................................21
2.4.1. – Diamond Grinding ................................................................21
2.4.2. – Assisted Machining (TAM PAM & LAM) ...........................22
2.4.3. – Laser Machining of Ceramics ...............................................24
2.4.4. – Other Forming Methods ........................................................28
2.5. – Raman Spectroscopy ...........................................................................29
2.5.1. – Raman Theory .......................................................................30
2.5.2. – Specific Apparatus ................................................................31
2.5.3. – Raman Analysis and Zirconia ...............................................32
2.6. – References ............................................................................................34
Chapter 3. – Experiments on Millisecond Pulse Length Laser Machining of Y-TZP
....................................................................................................................................46
3.1. – Process Optimisation............................................................................46
3.1.1. – Experimental Setup ...............................................................47
3.1.2. – Pulse Length Optimisation ....................................................48
3.1.3. – Assist Gas Optimisation ........................................................49
3.1.4. – Power Optimisation...............................................................53
3.2. – HAZ & Recast Layer Structures .........................................................54
3.2.1. – Absorption of 1064nm In Zirconia Bulk ...............................54
vii
3.2.2. – Surface Cracking of Re-Solidified Material .........................57
3.2.3. – Pores at Material Interaction .................................................59
3.2.4. – Re-crystallisation Due to Heat ..............................................62
3.3. – Drilling and Cutting .............................................................................64
3.3.1. – General Drilling ....................................................................65
3.3.2. – Cutting ...................................................................................68
3.4. – Effects & Measurements ......................................................................70
3.4.1. – Plasma Generation ................................................................70
3.4.2. – Molten Ejected Material ........................................................71
3.4.3. – Beam Quality Measurements ................................................72
3.4.4. – Extended Focus Arrangement ...............................................74
3.4.5. – Surface Raman Analysis of Processed Material ..................75
3.5. – Laser Pre-Heating ...............................................................................76
3.6. – SPI Fibre Laser Process ......................................................................78
3.7. – References ............................................................................................80
Chapter 4. – Experiments on Nanosecond Pulse Length Laser Machining of YTZP ............................................................................................................................84
4.1. – Nd:YVO4 Inazuma ...............................................................................84
4.1.1. – Experimental Setup ...............................................................85
4.1.2. – Initial Feasibility ...................................................................86
4.1.3. – Scanning System ...................................................................88
4.2. – Powerlase Starlase AO2 ......................................................................93
4.2.1. – Y-TZP ...................................................................................94
4.2.2. – Alumina .................................................................................94
4.3. – Bend Testing of Samples .....................................................................95
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4.4. – Controlled Crack Propagation ..............................................................97
4.4.1. – Experimental Setup ...............................................................98
4.4.2. – Results ...................................................................................99
4.5. – References ............................................................................................101
Chapter 5. – Experimental High Average Power Machining ..............................103
5.1. – TRUMPF ™ CO2 System ....................................................................103
5.1.1. – CO2 Laser Machining............................................................103
5.1.2. – Initial Parameters ..................................................................104
5.1.3. – Process Development ............................................................105
5.1.4. – IR Profiling ...........................................................................108
5.1.5. – CO2 Laser Machining with IR Observation ..........................114
5.1.6. – Conclusion ............................................................................119
5.2. – IPG ™ Fibre Laser ..............................................................................120
5.2.1. – Laser Machining Results .......................................................120
5.2.2. – Raman Spectroscopy Analysis ..............................................126
5.2.3. – Conclusion ............................................................................134
5.3. – References ............................................................................................135
Chapter 6. – Engineering Challenges Using Experimental Multi Tooled Systems
....................................................................................................................................138
6.1. – Surface Optimisation Using A Millisecond And Nanosecond Laser ..139
6.2. – Manufacturing Blind Holes Using A Millisecond Laser And
Mechanical Processes...........................................................................144
6.2.1. – Mechanical Only Process ......................................................144
6.2.2. – Creating A Laser Process ......................................................146
ix
6.2.3. – Integrating Laser & Mechanical Processes ...........................151
6.3. – Fibre Laser & Mechanical ....................................................................158
6.4. – References ............................................................................................164
Chapter 7. – Summary Of Work ............................................................................165
7.1 – Summary & Conclusions .....................................................................165
7.1.1. – Millisecond Nd:YAG Laser Processing ................................166
7.1.2. – Nanosecond Laser Processing ...............................................166
7.1.3. – CO2 Laser Processing............................................................166
7.1.4. – Fibre Laser Processing ..........................................................167
7.1.5. – Engineering Challenges ........................................................167
7.2. – Future Work ........................................................................................167
7.2.1. – CO2 Laser Processing............................................................168
7.2.2. – Fibre Laser ............................................................................168
7.2.3. – Other Laser Sources ..............................................................168
7.2.4. – Process Monitoring & Digitisation .......................................169
APPENDICES ..........................................................................................................170
A. – Material Properties .................................................................................170
B. – High Speed Photography of a Millisecond Laser Pulse .........................172
C. – Beam Quality Measurements of JK507..................................................173
D. – Image Processing Program (MATLAB) ................................................179
A.D.1 – Program for Image Processing & Output of Single Images .179
A.D.2 – Program for Image Processing Outputting a Video .............180
E. – IR Imagining of CO2 Laser Processing ..................................................182
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LISTS OF TABLES AND FIGURES
TABLES
Table 2.1 :
Utilised Laser Properties ....................................................................14
Table 2.2 :
Optical cavities available with the JK705 (based on information from
GSI Lumonics ) ..................................................................................15
Table 2.3 :
Main Raman band positions for cubic Zirconia and 3% mol Y-TZP,
monoclinic and tetragonal polymorphs. .............................................32
Table 3.1 :
The effect of tilt angle of assist gas nozzle on cut quality..................53
Table 3.2 :
Plasma generation ~200 s into 1ms laser pulse for varying fluencies
............................................................................................................71
Table 5.1 :
A comparison between published material parameters and successful
experimental parameters. ....................................................................106
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FIGURES
Figure 2.1 :
Schematic showing the atomic structure of the zirconia polymorphs with
Bravis lattice . (Zr – Large purple spheres, O – Smaller green spheres)
............................................................................................................4
Figure 2.2 :
Phase changes and temperatures in YTZP .........................................5
Figure 2.3 :
Zirconia-Yttria phase diagram showing the region with high Zirconia
(low Yttria) content – Shaded region shows Y-TZP region. ..............6
Figure 2.4 :
Schematic showing basic laser components and setup.......................8
Figure 2.5 :
Graphs showing the differences between peak and average power in
various pulse setups – A: CW Operation, B: Mechanical Chopper
Operation, C: Long Pulse Operation, D: Short Pulse Operation. .......10
Figure 2.6 :
Schematic of laser interaction with single element lens. ....................12
Figure 2.7 :
Optical beam path for the JK-705 Lumonics Laser (based on information
from GSI Lumonics )..........................................................................15
Figure 2.8 :
Schematic for an optical scanner .......................................................19
Figure 2.9 :
Schematic showing the differences between standard and F-Theta
corrected optics ..................................................................................19
Figure 2.10 : Setup for Laser Assisted Machining (LAM) ......................................23
Figure 2.11 : Schematic of ‘Hot Tooling’ Setup ......................................................25
Figure 2.12 : Specimen Placement Scheme for ‘Hot Tooling’ ................................26
Figure 2.13:
Various interactions between light and a molecule showing Stokes and
Anti-Stokes Scattering. The lowest energy is the ground state ‘m’ with
energy increasing up from there. The illustration is not to scale.......30
Figure 2.14 : Raman results showing data from dental grade 3% mol Y-TZP ........33
Figure 3.1 :
Schematic for JK 705 Millisecond Laser Processing With High Pressure
Gas Assist Nozzle and XYZ High Precision Stages ..........................47
Figure 3.2 :
Graph showing how the volume of material removed varies with pulse
length. .................................................................................................49
Figure 3.3 :
Laser cut channels in Zirconia showing different levels of blackening on
the channel and surrounding area. A – Helium, B – Oxygen, C –
Compressed Air ..................................................................................50
Figure 3.4 :
Laser Processing of Y-TZP using different gas. Sample tilted to show
the back wall of laser machined tracks. A – Helium, B – Oxygen, C –
Compressed Air ..................................................................................52
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Figure 3.5 :
Schematic for Optimisation of Nozzle Standoff and Angle Using the JK
705 Millisecond Laser Processing System .........................................52
Figure 3.6 :
Schematic showing different beam quality propagation within materials
during laser machining. ......................................................................54
Figure 3.7 :
Sample setup for scattering experiment .............................................55
Figure 3.8 :
Schematic for scattering measurement ...............................................55
Figure 3.9 :
Normalised scattering measurement of Y-TZP at 1064 nm ...............56
Figure 3.10 : Measurement of Y-TZP at 1064 nm showing drop in intensity due to
scattering effect ..................................................................................57
Figure 3.11 : Cracking observed on the re-solidified interior wall of a blind hole ..58
Figure 3.12 : Schematic showing where re-solidified cracking has caused secondary
cracking into the bulk of the material .................................................59
Figure 3.13 : Propagation of air bubbles in molten material described by Triantafyllidis
............................................................................................................60
Figure 3.14 : Bubbles at material boundary .............................................................60
Figure 3.15 : Pores observed mid-columnar structure .............................................61
Figure 3.16 : Re-crystallisation through thermal gradient.; A-C : Stacked Columnar
Structures, D : Intergranular Fracture Region, E : Transgranular Fracture
Region ................................................................................................62
Figure 3.17 : Laser processed area showing direction of the thermal gradient with
respect to incident beam. ....................................................................63
Figure 3.18 : Re-crystallisation through thermal gradient. A-C : Stacked Columnar
Structures. D : Intergranular Fracture Region. E : Transgranular
Fracture Region ..................................................................................63
Figure 3.19 : Re-crystallisation through thermal gradient. A : Stacked Columnar
Structures. B : Intergranular Fracture Region. C : Transgranular
Fracture Region ..................................................................................64
Figure 3.20 : (a) An angled cross section of a laser drilled through hole, (b) cross
section of blind hole (end section) showing recast. ............................65
Figure 3.21 : Different samples with different pulse energies showing 124 m and 126
m penetration ....................................................................................66
Figure 3.22 : Graphs showing (a) the material removal (volume) and (b) depth of
material removal with laser fluence using a 1ms pulse ......................67
Figure 3.23 : Multi-pulse (8 pulses) drilled holes in Y-TZP for a)18.5 J pulse energy
with the sample 4mm below focus, b) 18.5 J pulse energy with the
xiii
sample 2 mm below focus, c) 18.5 J pulse energy with the sample on
focus, d) 8.5 J pulse energy with the sample on focus and, e) 3 J pulse
energy with the sample on focus. The lower images show the differences
in the surface structure of the recast layer. .........................................68
Figure 3.24 : (a) Demonstration part – scale ½ mm, (b) demonstration bulk, (c)
microscope image of cross section of sample showing 87 m of crack
material, (d) microscope image of cross section of bulk showing 59 m
of cracking. .........................................................................................69
Figure 3.25 : Reference showing location of nozzle with respect to sample ...........70
Figure 3.26 : High speed photography showing two discrete stages in material
removal; a) plasma and high speed, small particle removal, b) low speed,
large volume material blown with assist gas ......................................72
Figure 3.27 : Setup for measurement of M2 in three resonator modes ....................73
Figure 3.28 : Y-TZP billet with square machined from its bulk. ............................74
Figure 3.29 : Raman spectrum from a control bulk sample (black) and Raman
spectrum taken from the re-solidified (red) ........................................76
Figure 3.30 : Setup for heat trials on zirconia ..........................................................77
Figure 3.31 : Y-TZP undergoing laser heating showing spike at 650 ºC ................77
Figure 3.32 : Drawing of holder designed for fibre laser collimator .......................79
Figure 3.33 : Schematic of SPI Laser setup .............................................................79
Figure 4.1 :
Schematic showing Inazuma laser setup ............................................85
Figure 4.2 :
Glassy material on the surface showing thermal stress relaxation through
fracture ................................................................................................86
Figure 4.3 :
Glassy material on the surface showing thermal stress relaxation through
fracture and sub micron patterning .....................................................87
Figure 4.4 :
Glassy material on the surface showing increasing stage speed and
subsequent periodic structure due to pulse separation .......................88
Figure 4.5 :
Schematic showing the Inazuma laser setup with scanning head ......89
Figure 4.6:
Graph showing three different processing regimes comparing fluence
with ablation depth .............................................................................90
Figure 4.7 :
Examples of nanosecond laser processing where a) the parameters and
pulse overlap were incorrect b) optimised parameters were applied. 91
Figure 4.8:
Nanosecond laser machining showing no cracking existing in the bulk
............................................................................................................91
xiv
Figure 4.9 :
Sample part machined in Y-TZP using the Inazuma nanosecond system
............................................................................................................92
Figure 4.10 : Sample part machined in alumina using the Inazuma nanosecond system
............................................................................................................92
Figure 4.11 : Schematic showing Powerlase laser setup with scanner ....................93
Figure 4.12 : Y-TZP processed using Powerlase AO2 ............................................94
Figure 4.13 : Alumina processed using Powerlase AO2, depth increasing from right to
left. ......................................................................................................95
Figure 4.14 : Schematic of the ‘4-point’ bend test arrangement ..............................96
Figure 4.15 : Bend test results on Y-TZP exposed to Nd:YVO4 processing ..........97
Figure 4.16 : 2mm thick Y-TZP showing Nd:YVO4 laser track and associated crack
............................................................................................................99
Figure 4.17 : Examples of different successful parameters; a) 15kHz @ 10mm/s, b)
30kHz @ 15mm/s ...............................................................................99
Figure 4.18 : 1.6mm sample of Y-TZP with channel machined at 15kHz (20mm/s)
then heated with a defocused beam at 15kHz (25mm/s) ....................100
Figure 5.1 :
Schematic for CO2 Laser Processing Using High Pressure Gas Assist
Nozzle and XY Precision Stages ........................................................104
Figure 5.2 :
A sample CO2 machined billet showing a basic 2D profile with recast
material attached to the bulk and laser beam path employed. ............107
Figure 5.3 :
Geometrical 2D shape required for the manufacture of a dental bridge.
............................................................................................................108
Figure 5.4 :
The intensity profile and wavelength peaks for Zirconia at a range of
temperatures. ......................................................................................109
Figure 5.5 :
The transmittance of Sapphire filter ...................................................110
Figure 5.6 :
Wavelength selection of the black body curve considered ................110
Figure 5.7 :
Theoretical intensity output of the heated Y-TZP system .................111
Figure 5.8 :
Experimental setup of IR camera and tube furnace calibration .........112
Figure 5.9 :
An image from the IR Camera (false colour applied through LabViewTM)
............................................................................................................112
Figure 5.10 : Experimental result of the IR camera detecting over 600 K-1600 K.
............................................................................................................113
Figure 5.11 : Normalised intensity readings of the IR cameras spectral response and
the theoretical emission from the Y-TZP sample ..............................113
Figure 5.12 : Schematic of the CO2 system & IR camera .......................................114
xv
Figure 5.13 : Schematic and image interpretation of the IR camera........................115
Figure 5.14 : IR Image showing the ‘counts’ converted into temperature (K) .......116
Figure 5.15 : Three IR images of the point at which the CO2 process fails. Scale on
images is in ‘counts’ not temperature. ...............................................117
Figure 5.16 : Molten material re-solidified on a) a bridge profile b) an example of a resolidified structure c) an example of a re-solidified structure. ...........118
Figure 5.17 : Images showing surface finish and bridge profile on Y-TZP ............119
Figure 5.18 : Schematic for IPG Fibre Laser Processing With High Pressure Gas Assist
Nozzle and XYZ Stages .....................................................................120
Figure 5.19 : Schematic of single pulsed hole .........................................................121
Figure 5.20a) : A schematic of the drilled holes ........................................................123
Figure 5.20b) : A sectioned single hole showing the cracked surface to the right and left
of the HAZ ring ..................................................................................123
Figure 5.21 : Two images showing the same sample of Y-TZP after fibre laser
processing and crack propagation at different scales. ........................124
Figure 5.22 : Fibre laser machined Y-TZP showing angled separation result .........126
Figure 5.23 : Raman Spectroscopy analysis sites; 1-Bulk material on back surface of
sample, 2-Material between drilled holes on the fractured surface, 3Recast layer surrounding hole , 4-Material on the back surface of the
drilled hole, 5-Material on the top surface of the sample, 6-Bulk material
on the top surface of the sample. ........................................................127
Figure 5.24 : Images directly from the Raman Analysis machine of the actual sites
measured .............................................................................................128
Figure 5.25 : Raman analysis of the bulk control sample 1 showing the standard peaks
for Tetragonal (T) material .................................................................129
Figure 5.26 : Raman analysis of the propagated surface between drilled holes on YTZP .....................................................................................................130
Figure 5.27 : Raman analysis of the back wall of the drill holes on the fibre processed
samples of Y-TZP...............................................................................131
Figure 5.28 : Raman analysis of the recast layer around the drilled hole (light) .....132
Figure 5.29 : Raman analysis of the recast layer around the drilled hole (dark) .....133
Figure 5.30 : Raman analysis of the upper surface of the recast layer around the drilled
holes ....................................................................................................134
Figure 6.1 :
Sample edge cross section with no processing ...................................138
xvi
Figure 6.2 :
Millisecond laser prepared surface (A) with secondary nanosecond laser
processing (B). Highlighted regions show nanosecond laser deposits
............................................................................................................139
Figure 6.3 :
Schematic showing A) sample prepared with millisecond laser showing
large recast and cracking layers, B) proposed secondary processing with
incident nanosecond laser removing the recast layer, C) actual result
showing removal of initial recast and cracking region but a new cracking
region exists. .......................................................................................140
Figure 6.4 :
Beam path diagram for the nanosecond removal of recast layer in ‘U’
shape ...................................................................................................141
Figure 6.5 :
Nanosecond laser removal of recast material showing small beam width
and high accuracy ...............................................................................142
Figure 6.6 :
Images showing the millisecond primary surface and nanosecond
secondary surface a) top view, b) cross section ................................143
Figure 6.7 :
Cross-section of a dental crown showing the position of the blind hole
required. ..............................................................................................144
Figure 6.8 :
Cross-section of mechanically drilled blind holes in Y-TZP. Images
focused on back and front of drilled holes respectively. (green area is
mounting material) .............................................................................145
Figure 6.9 :
Mechanically prepared surfaces showing no cracking into the bulk ..146
Figure 6.10 : Problems when utilising a multi-drilled component. A)molten material
back flow into adjacent hole, B) central spigot remain between adjacent
drill holes. ...........................................................................................147
Figure 6.11 : Recast material shown on the right image (white) which has recovered
machined material. Central spigot stump clearly visible...................147
Figure 6.12 : Hole diameter, depth and volume during single pulse blind hole drilling
............................................................................................................148
Figure 6.13 : Multi-pulse material removal varying pulse energy. ..........................149
Figure 6.14 : Cross section of laser drilled hole 1mm from the surface in Y-TZP..150
Figure 6.15 : A section of the base of the laser drilled hole showing a large collection
of recast material ................................................................................150
Figure 6.16 : Raman spectrum of the black recast layer generated by millisecond
processing showing disorder in the crystalline structure ....................151
Figure 6.17 : Two stage preparation (laser with subsequent mechanical machining) of
the hole showing no cracking into the bulk or recast layer ................152
xvii
Figure 6.18 : Images showing the two stage preparation (laser with subsequent
mechanical machining) process. Images focus on back and front of
drilled holes respectively ....................................................................152
Figure 6.19 : Diamond encrusted tool used for a single secondary mechanical process.
............................................................................................................153
Figure 6.20 : Angled image to show the differences in the remaining sample structure
............................................................................................................154
Figure 6.21 : Raman spectra from the laser machined area .....................................154
Figure 6.22 : Raman spectra from the two stage preparation (laser with subsequent
mechanical machining) process. .........................................................155
Figure 6.23 : Inter-granular Region .........................................................................156
Figure 6.24 : Intergranular Region (Higher Orders). ...............................................156
Figure 6.25 : Raman spectra from the white recast layer showing exposure to heat.
............................................................................................................157
Figure 6.26 : Schematic of terraces machined into the fiber laser machined sample.
............................................................................................................159
Figure 6.27 : Image showing terraces mechanically machined into fiber processed
sample .................................................................................................160
Figure 6.28 : SEM images showing the mechanical cross-section of the fibre processed
area. (left x23, right x95 – markers show rotation of part in increased
magnification).....................................................................................161
Figure 6.29 : Raman spectra from between 0 m and 80 m from the upper laser
machined surface ................................................................................161
Figure 6.30 : Raman spectra from between 100 m and 200 m from the upper laser
machined surface ...............................................................................162
Figure 6.31 : SEM image of fibre laser prepared surface with fine mechanical grinding
perpendicular to the fibre drilled holes. ..............................................163
Figure 6.32 : Raman spectra comparing the cross sectional data with ‘on-surface’ data
............................................................................................................163
xviii
LISTS OF PUBLICATIONS & AWARDS
PUBLICATIONS
Laser machining in ceramics manufacture (invited paper) Paper #105, Proceedings of
the 3rd Pacific International Conference on Application of Lasers and Optics (2008)
Duncan Hand, Fraser Dear, Jonathan Parry, Jonathan Shephard, Krzysztof Nowak,
Howard Baker, Denis Hall
Pulsed laser micro-machining of Y-TZP dental ceramic for manufacturing, International
Journal of Applied Ceramic Technology, 5 [2] 188–197 (2008) Fraser C. Dear,
Jonathan D. Shephard, Xin Wang, Julian D. C. Jones, and Duncan P. Hand
Nanosecond-Laser Post-Processing of Millisecond-Laser-Machined Zirconia (Y-TZP)
Surfaces, International Journal of Applied Ceramic Technology. doi: 10.1111/j.17447402.2008.02222.x (2008) Jonathan P. Parry, Jonathan D. Shephard, Fraser C. Dear,
Nick Jones, Nick Weston, and Duncan P. Hand
Optimised nanosecond pulsed laser micro-machining of Y-TZP ceramics, Journal of
The American Ceramic Society, 91 [2] 391–397 (2008) Xin Wang, Jonathan D.
Shephard, Fraser C. Dear, and Duncan P. Hand
Techniques and limits in processing of bio-implantable Zirconia Ceramics
using millisecond pulsed lasers. Technical Digest of LAMP2006, (2006) Fraser C.
Dear, Jonathan D. Shephard, Xin Wang, Julian D. C. Jones, and Duncan P. Hand
Micromachining PSZ ceramics using pulsed nanosecond lasers. Technical Digest of
LAMP2006, (2006) Xin Wang, Jonathan D. Shephard, Fraser C. Dear, and Duncan P.
Hand
Single-pulsed femtosecond laser machining of glass. Journal of Optics A : Pure and
Applied Optics, 7 [4] 162-168 (2005) S. Campbell, F. C. Dear, D. P. Hand and D. T.
Reid
xix
AWARDS
Young UK Laser Engineer’s Prize 2008
“Fraser Dear is AILU's 2008 Young Laser Engineer in recognition of his successful
development of fine laser machining techniques in zirconia for the manufacture of tooth
crowns and bridges for dental restorations.” – AILU Website (www.ailu.co.uk)
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