Evaluation of additive manufacturing technologies for the manufacturing of prosthetic fingers in ...

162 Pages·2014·4.75 MB·English

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Evaluation of Additive Manufacturing Technologies
for the Manufacturing of Prosthetic Fingers in
Developing Communities
by
T.J. Gerhold

A dissertation submitted to the faculty of Engineering in
fulfilment of the requirements for the degree of

MAGISTER EN INGENERIAE
in
MECHANICAL ENGINEERING
at the
UNIVERSITY OF JOHANNESBURG
Supervisor: DR GA OOSTHUIZEN
Co-Supervisor: DR FF PIETERSE

January 2014
UNIVERSITY OF JOHANNESBURG

FACULTY OF ENGINEERING AND THE BUILT ENVIRONMENT

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declare that the thesis/dissertation/short dissertation, which I hereby submit for the degree DIng/ D
Phil/MIng/ M Phil/ MTech/ DTech at the University of Johannesburg, is the final copy and includes all
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i
Abstract
The high cost of quality aesthetic prostheses and the isolation from trained
prosthetists makes it unfeasible for people in developing communities to obtain
prosthetic devices. There are significant and adverse psychological effects on people
who are missing limbs due to birth defects, disease or amputation. Prosthetic
devices assist in helping people become accepted into every day civilisation by
masking a physical deformity, and enhancing their self-esteem.

Modern 3D digitising techniques and Additive Manufacturing (AM) technologies are
becoming increasingly common in the medical industry. These technologies can also
be used for the production of prostheses. Through the use of 3D Digitising and AM,
the need for a trained prosthetist for producing prostheses is limited. The production
of prostheses by the Base of Pyramid (BoP) might also assist in creating value in
developing communities.

The objective of this study was to establish a process chain to evaluate AM
technologies for the prototyping of prostheses in developing communities.
Technologies considered include Open-Source Fused Deposition Modelling (FDM),
Advanced FDM, 3-Dimensional Printing (3DP), and Stereolithography (SLA).
Parameters which were evaluated include the build time, cost of the build and
material usage. Surface roughness parameters of the parts produced by each of the
AM technologies were also investigated.

The investigation found that a process chain utilising 3D digitising and AM
technologies can be used for the production of prosthetic fingers. Open-source FDM
technologies can be used for the production of prostheses, which produces results
comparable to those obtained from methods used in developing communities. The
advanced FDM, 3DP and SLA technologies produced good quality prosthetic fingers
at a lower cost, in a shorter time and with less material usage than conventional
methods used in developed communities. The aesthetic quality of the prosthetic
ii
fingers obtained from the SLA and 3DP technologies were competitive with modern
conventional methods. Future work can include the implementation of the process
chain to be adopted by the BoP to add value in developing communities.

iii
Acknowledgements

I would like to express my appreciation to the following people:
 The Department of Science and Technology (DST) of the Republic of South
Africa and the tertiary education support program (TESP) of Eskom for
financially supporting this study.
 Dr GA Oosthuizen, for providing me with the opportunity to carry out this
research and for supporting me the whole way.
 Dr FF Pieterse, for assisting me with this study as my co-supervisor.
 Carlos Garcia Pando for sharing his experience in Additive Manufacturing with
me, and for assisting me with the data processing.
 Prof. Dr. Gideon N. Levy for his input and advice.
 Michael Raphael for assisting me with the scan of a finger.
 Jolandi Engelbrecht for sharing her experience in producing prostheses with
me, and assisting me in the manufacture of the prosthetic fingers.
 CAD House for producing the 3DP and Open-Source FDM moulds.
 Johan Els, of the Central University of Technology, for producing the SLA
mould and assisting me with better understanding the practicalities of using
SLA technology.
 Nickey Janse van Rensburg for assisting me with the surface roughness
experiments.
 Mae Heard for encouraging me to complete this research to the best of my
abilities.
 The Lord for blessing me with the opportunities and abilities to study further in
the engineering field.

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Table of Contents

Declaration .................................................................................................................................. i
Abstract ...................................................................................................................................... ii
Acknowledgements ................................................................................................................... iv
Table of Contents ....................................................................................................................... v
List of Figures ........................................................................................................................ viii
List of Tables ............................................................................................................................ xi
Nomenclature ........................................................................................................................... xii
Greek Symbols ......................................................................................................................... xii
Subscripts ................................................................................................................................. xii
Glossary of Terms .................................................................................................................. xiii
CHAPTER 1 – INTRODUCTION ............................................................................................ 1
1.1 Background ................................................................................................................. 1
1.2 Problem Statement ...................................................................................................... 3
1.3 Research Objectives .................................................................................................... 4
1.4 Research Approach ..................................................................................................... 4
CHAPTER 2 – LITERATURE REVIEW ................................................................................. 6
2.1 Prostheses ......................................................................................................................... 6
2.1.1 Manufacture of Prosthetic Fingers ............................................................................ 8
2.1.2 Materials used for Prosthetic Fingers ....................................................................... 9
2.1.3 Conventional Process Chain vs. Advanced Technologies Process Chain for
Prosthetic Fingers............................................................................................................... 9
2.1.4 Research Opportunities in Production of Prosthetic Fingers .................................. 11
2.2 3D Scanning ................................................................................................................... 12
2.2.1 Laser Scanning ........................................................................................................ 12
2.3 Additive Manufacturing ................................................................................................. 14
2.3.1 Classification of AM Technologies ........................................................................ 16
2.3.2 Additive Manufacturing Materials .......................................................................... 24
2.3.3 General Additive Manufacturing Process Chain .................................................... 26
2.3.4 Growth of the AM Industry .................................................................................... 29
2.3.5 SLA Technology ..................................................................................................... 31
2.3.6 Fused Deposition Modelling Technology ............................................................... 36
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2.3.7 3D Printing .............................................................................................................. 43
2.3.8 Design for AM ........................................................................................................ 46
2.3.9 Direct Digital Manufacturing .................................................................................. 47
2.3.10 Cost Estimation ..................................................................................................... 48
2.3.11 Medical Modelling ................................................................................................ 50
2.3.12 Limitations of AM for Medical Applications ....................................................... 50
2.4 Surface Topography ....................................................................................................... 51
2.4.1 Surface Texture Parameter Explained .................................................................... 52
CHAPTER 3 – EXPERIMENTAL SETUP & DESIGN ......................................................... 58
3.1 Experimental Design ...................................................................................................... 58
3.2 Experimental Process ..................................................................................................... 62
3.2.1 3D Digitising ...................................................................................................... 63
3.2.2 Export STL to CAD Package ............................................................................. 64
3.2.3 Boolean Operation to Create Mould .................................................................. 65
3.2.4 Machine Setup ................................................................................................... 72
3.2.5 Fabricate Mould in AM Machine ...................................................................... 78
3.2.6 Post-Processing .................................................................................................. 79
3.2.7 Pouring of RTV Silicon into Mould and Remove Prosthesis ............................ 79
3.2.8 Time, cost of build, and material usage ............................................................. 84
3.2.9 Visual inspection of the respective moulds and fingers..................................... 84
3.2.10 Surface topography ............................................................................................ 85
3.2.11 Removal of fingers from moulds ....................................................................... 88
3.2.12 Aesthetic quality of produced fingers ................................................................ 88
CHAPTER 4 – EXPERIMENTAL RESULTS & DISCUSSION ........................................... 90
4.1 Process chain ............................................................................................................. 90
4.2 Quantitative Results .................................................................................................. 91
4.2.1 Time, cost and material usage ............................................................................ 91
4.3 Surface Topography Measurements .......................................................................... 94
4.3.1 3D Mapping of Surfaces .................................................................................... 94
4.3.2 Average Roughness ........................................................................................... 98
4.3.3 Average Maximum Roughness ........................................................................ 100
4.3.4 Maximum Roughness ...................................................................................... 101
4.3.5 Average Width of Profile Features .................................................................. 103
4.4 Qualitative Results .................................................................................................. 104
4.4.1 Removal of Fingers from Moulds .................................................................... 104
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4.4.2 Aesthetic Quality ............................................................................................. 105
4.4.3 Open-Source FDM Machine – RapMan 3.2 .................................................... 107
4.4.4 FDM Machine – Dimension Elite .................................................................... 111
4.4.5 3DP Machine – ProJet 260 .............................................................................. 114
4.4.6 SLA Machine – Viper ...................................................................................... 117
CHAPTER 5 – CONCLUSION ............................................................................................ 120
CHAPTER 6 – RECOMMENDATIONS .............................................................................. 123
CHAPTER 7 - REFERENCES .............................................................................................. 124
APPENDIX A – MACHINE SPECIFICATION OF THE VIPER SLA MACHINE ........... 130
APPENDIX B – MACHINE SPECIFICATION OF THE RAPMAN 3.2 MACHINE ........ 132
APPENDIX C – MACHINE SPECIFICATION OF THE PROJET 260 MACHINE .......... 134
APPENDIX D – MACHINE SPECIFICATION OF THE DIMENSION ELITE MACHINE
................................................................................................................................................ 136
APPENDIX E – MATERIAL SPECIFICATION OF SI 50 ABS ......................................... 138
APPENDIX F – MATERIAL SPECIFICATION OF ABS .................................................. 140
APPENDIX G – MATERIAL SPECIFICATION OF VISIJET PXL ................................... 142
APPENDIX H – MATERIAL SPECIFICATION OF ABSPLUS ........................................ 144
APPENDIX I – SAIIE 25 CONFERENCE PAPER.............................................................. 146

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List of Figures

Figure 1: Examples of some of the many types of prostheses ................................................... 7
Figure 2: Conventional Prosthetic Production Chain [17] ....................................................... 10
Figure 3: Modern Prosthesis Manufacturing Chain. ................................................................ 11
Figure 4: The laser line scanner uses a laser to obtain a point cloud 3D model of the scanned
object [38] ................................................................................................................................ 13
Figure 5: Additive Manufacturing process classification matrix as Described by Pham
indicating the different AM technologies of various companies [40]. .................................... 16
Figure 6: An illustration of SLA process showing how a part is built [51] ............................. 20
Figure 7: An illustration of the FDM process showing how a part is built [53] ...................... 21
Figure 8: An illustration of the 3D Printing process showing how a part is built [53] ........ 21
Figure 9: An illustration of the SLS process showing how a part is built [41] .................... 22
Figure 10: An illustration of the EBM process showing how a part is built [56] .................... 23
Figure 11: 9 Steps of the AM process adapted from [40] to include 3D digitising ................. 26
Figure 12: Production of castings for hearing aid shells via SLS a) Digital data from wax
imprint. b) SLS Production c) Final Shells [49]. ..................................................................... 29
Figure 13: Evolutionary path of Additive Manufacturing adapted from [35] ......................... 30
Figure 14: Scientific Push and Industrial Pull in Technology Evolution adapted from [49] .. 31
Figure 15: Illustration of vector scan technique showing a part being built [40] .................... 32
Figure 16: Illustration of two photon approach showing part being built [40] ........................ 32
Figure 17: Hierarchy showing subsystems of an SLA machine adapted from [40] ................ 33
Figure 18: The linear, branched and cross-linked polymer types [62] .................................... 35
Figure 19: FDM Extrusion of Material showing the formation of a part through deposition of
filament [41]............................................................................................................................. 36
Figure 20: The RapMan 3.1 is based on Open-Source designs from the RepRap community
and sold by 3D Systems. .......................................................................................................... 37
Figure 21: Illustration showing various subsystems of FDM machines [71] .......................... 39
Figure 22: Extrusion-Based System [40] ................................................................................. 40
Figure 23: Typical extrusion based system fill pattern [72]. ................................................... 41
Figure 24: Extrusion of Materials to Maximize Precision (left) or material strength (right) by
controlling voids [40]. .............................................................................................................. 42
Figure 25: Illustration showing the various subsystems of a DP machine [40] ....................... 44
Figure 26: Basic Setup of DOD System [73]........................................................................... 45
Figure 27: Roughness and Waviness in a Surface [85] ........................................................... 53
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