cutter path strategy for machining craniofacial...
TRANSCRIPT
CUTTER PATH STRATEGY FOR MACHINING CRANIOFACIAL MEDICAL IMPLANT PEEK COMPOSITE
MOHAMAD RIDWAN BIN RAMLI
B050910096
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
2013
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
CUTTER PATH STRATEGY FOR MACHINING CRANIOFACIAL
MEDICAL IMPLANT PEEK COMPOSITE
This report submitted in accordance with the requirement of the UniversitiTeknikal
Malaysia Melaka (UTeM) for the Bachelor Degree of Manufacturing Engineering
(Manufacturing Process) (Hons.)
by
MOHAMAD RIDWAN BIN RAMLI
B050910096
861020-29-5569
FACULTY OF MANUFACTURING ENGINEERING
2013
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
BORANG PENGESAHAN STATUS LAPORAN PROJEK SARJANA MUDA
TAJUK: Cutter Path Startegiy For Machining Craniofacial Medical Implant PEEK
Composite
SESI PENGAJIAN: 2012/13 Semester 2
Saya MOHAMAD RIDWAN BIN RAMLI
mengakumembenarkanLaporan PSM inidisimpan di PerpustakaanUniversitiTeknikal Malaysia Melaka (UTeM) dengansyarat-syaratkegunaansepertiberikut:
1. Laporan PSM adalah hak milik Universiti Teknikal Malaysia Melaka dan penulis. 2. Perpustakaan Universiti Teknikal Malaysia Melaka dibenarkan membuat salinan
untuk tujuan pengajian sahaja dengan izin penulis. 3. Perpustakaan dibenarkan membuat salinan laporan PSM ini sebagai bahan
pertukaran antara institusi pengajian tinggi.
4. **Silatandakan (√)
SULIT
TERHAD
TIDAK TERHAD
(Mengandungi maklumat yang berdarjah keselamatan atau kepentingan Malaysiasebagaimana yang termaktub
dalam AKTA RAHSIA RASMI 1972)
(Mengandungi maklumat TERHAD yang telah ditentukan
oleh organisasi/badan di mana penyelidikan dijalankan)
AlamatTetap:
B1-06 Jalan SS6/3 Perumahan
Kastam Wilayah Persekutuan Kuala
Lumpur, 47310 Petaling Jaya
Tarikh: _________________________
Disahkan oleh:
Cop Rasmi:
Tarikh: _______________________
** Jika Laporan PSM ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa/organisasi berkenaan dengan menyatakan sekali sebab dan tempoh laporan PSM ini perlu dikelaskan sebagai SULIT atau TERHAD.
DECLARATION
I hereby, declared this report entitled “Cutter Path Startegiy For Machining
Craniofacial Medical Implant PEEK Composite” is the results of my own research
except as cited in the references.
Signature : ................................................
Author's Name : MOHAMAD RIDWAN BIN RAMLI
Date : 3 June 2013
APPROVAL
This report is submitted to the Faculty of Manufacturing Engineering of UTeM as a
partial fulfillment of the requirements for the degree of Bachelor of Manufacturing
Engineering (Manufacturing Process) (Hons.). The member of the supervisory is as
follows:
...............................................
Dr Raja Izamshah Bin Raja Abdullah
Project Supervisor
i
ABSTRACT
Polyetheretherketones (PEEK) have been increasingly employed as biomaterials for
trauma, orthopedic, and spinal implants. Composites such as polyetheretherketone
(PEEK) used in orthopedic structural components, are generally manufactured by
extrusion, and for this fact, these recent materials need additional machining
operations. One of the major concerns in machining is to reach a good surface
roughness and dimensional precision. However, the experience acquired without
considering the peculiar material response to machining especially to the cutting tool.
Hith tool waer and the need for tight tolerance and good surface finish are some of
the major concerns in machining this material which are directly relate with the
machining cutter path. No significant study has beed carried out so far on the effects
of cutter path on machining PEEK composite. This, this research aims to investigate
the effects of different cutter path strategy on maching performance. Three cutter
path strategies will be investigate namely lead and tilt, normal to dirve surface and
optimized lead on the machining performances namely surface roughness,
dimensional accuracy and machining time. Portions of human craniofacial complex
geometry shape are used as the case study.
ii
ABSTRAK
Polyetheretherketones (PEEK) semakin meningkat kegunaannya sebagai biobahan
untuk trauma, ortopedik, dan implan tulang belakang. komposit seperti
polyetheretherketone (PEEK) yang digunakan dalam komponen struktur ortopedik,
biasanya dibuat oleh penyemperitan, dan untuk fakta ini, bahan-bahan ini
memerlukan operasi pemesinan tambahan. Salah satu daripada permasalahan utama
sewaktu pemesinan adalah untuk mencapai kekasaran permukaan yang baik dan
ketepatan dimensi. Kehausan mata alat yang tinggi dan keperluan untuk toleransi
yang ketat dan kemasan permukaan yang baik adalah sebahagian daripada
permasalahan utama dalam pemesinan bahan ini yang secara langsung berkaitan
dengan laluan pemotong pemesinan. Tiada kajian yang ketara yang telah dijalankan
setakat ini mengenai kesan-kesan laluan pemotong permesinan pada komposit
PEEK. Penyelidikan ini bertujuan untuk menyiasat prestasi permesinan bagi kesan
pemotongan pada laluan pemotongan permesinan yang berbeza. Tiga strategi laluan
pemotong yang di kaji iaitu “Lead And Tilt”, “Normal to Drive Surface”, dan
“Optimized Lead” berdasarkan prestasi permesinan yang telah ditentukan iaitu
kekasaran permukaan. Ketepatan dimensi dan masa permesinan. Tiga strategi jalan
pemotong akan menyiasat iaitu memimpin dan miring, biasa untuk dirve permukaan
dan dioptimumkan membawa kepada prestasi pemesinan iaitu kekasaran permukaan,
ketepatan dimensi dan masa pemesinan. Sebahagian daripada kraniofasial manusian
berbentuk geometri yang komplek digunakan sebagai kajian kes.
iii
DEDICATION
To my beloved parent and family.
iv
ACKNOWLEDGEMENT
Alhamdulillah, Thanks to the entire Almighty from Allah for giving me all the strength
and good health to complete this report without problems and barriers. This report is
finally completed with much assistance of many people.
I would like to express the deepest appreciation to Universiti Teknikal Melaysia Melaka
for providing such a brilliant facility such as equipment and machine for me to fulfil
PSM requirement that‟s need to use while the project is carry on .
Besides that, I am heartily thankful to my supervisor, Dr. Raja Izamshah Bin Raja
Abdullah, whose encouragement, guidance and support from the initial to the final level
enabled me to develop an understanding of the research. I am truly grateful for his the
time spent proofreading and correcting my many mistakes, his tolerance of my mistakes,
and his commitment to my future career.
In addition, I would like to thank all manufacturing engineering department lab staff for
giving me an opportunity to work in a good and productive environment. Their
continuous support and guidance whenever problems occurred while I was performing
new task is really an encouragement in making me to perform at my very best. This has
partly contributed to the success of my research and the completion of this „Projek
Sarjana Muda‟.
Last but not least I would like to thank my friends especially those who help to
contribute the idea and solution while the research is carry on. Thank you.
TABLE OF CONTENT
v
Abstract i
Abstrak ii
Dedication iii
Acknowledgement iv
Table of Content v
List of Tables vii
List of Figures ix
List of Abbreviations, Symbols & Nomenclature xi
CHAPTER 1: INTRODUCTION 1
1.1 Background of Study 1
1.2 Problem Statement 3
1.3 Objective 4
CHAPTER 2: LITERATURE REVIEW 3
2.1 1ntroduction 3
2.2 Orthopedic Machining 6
2.2.1 Work Holding 8
2.2.2 Tooling 9
2.2.3 Material and Machining 9
2.2.4 Traceability 10
2.2.5 Fine Selection 10
2.3 Cutter Path In Milling Machining 11
2.4 Strategy for Surface Milling 13
2.4.1 Direction parallel 13
2.4.2 Contour Parallel 14
2.4.2 ZigZag 15
2.5 Machining performance 16
2.5.1 Surface Roughness 16
2.5.2 Accuracy 17
vi
2.5.3 Machining Time 17
2.6 Consideration in Milling Machining for PEEK Composite 18
2.6.1 Achievable Surface Finish 18
2.6.2 Tolerance 18
2.6.3 Cutting Temperature 19
2.6.4 Material Properties 19
CHAPTER 3: METHODOLOGY 13
3.1 Process Planning (Flow Chart) 13
3.2 Identify Material 14
3.2.1 Material Specification 14
3.3 Software Approach 15
3.3.1 Generate G-Code 15
3.3.2 Simulation 15
3.4 Machining 16
3.4.1 Material Preparation 16
3.4.2 Clamping Position 18
3.5 Result Evaluation 19
3.5.1 Surface Roughness 19
3.5.1.1 Surface Tester Machine 20
3.5.1.2 Surface Tester Machine Calibration 21
3.5.2 Machining Time 21
3.5.3 Dimension Accuracy 21
3.5.3.1 Coordinate Measurement Machine 22
3.5.3.2 CMM calibration 23
3.6 Result Analysis 23
3.7 Summary 23
CHAPTER 4: RESULT AND DISCUSSION
4.1 Machining Parameter 24
4.2 Surface Roughness 25
4.2.1 Surface Roughness Result 26
4.2.2 Surface Roughness Analysis 27
vii
4.3 Dimension Accuracy 28
4.3.1 Product Point Measurement 29
4.3.2 CAD Drawing Measurement 30
4.3.3 Dimension Accuracy Result 32
4.3.4 Dimension Accuracy Analysis 34
4.4 Machining Time Result and Analysis 35
CHAPTER 5: CONCLUSION AND RECOMMENDATION
5.1 Conclusion 37
5.2 Recommendation 38
REFERENCES 39
APPENDICES
A Gantt Chart PSM 1 & 2
viii
LIST OF TABLES
2.1 Main types of 5-axis strategies 12
3.1 Material specifications for biomedical applications 22
4.1 Cutting parameter selection for roughing 37
4.2 lead and tilt surface result 39
4.3 normal to drive surface 39
4.4 optimized lead 40
4.5 lead and tilt dimension compare to drawing 45
4.6 normal to drive surface dimension compare to CAD drawing 46
4.7 optimized lead dimension compare to CAD drawing 47
4.8 Total machining time 48
ix
LIST OF FIGURES
1.1 Example of a PEEK implant fabricated using milling process 1
2.1 Example of stand-alone anterior lumbar fusion cage 5
2.2 Example lumbar interbody fusion cage anterior 6
2.3 Example of Spinal Implant 8
2.4 Degrees of freedom in 5-axis machining 11
2.5 A normal to surface toolpath can usually not directly be machined 13
2.6 Direction Parallel 14
2.7 Contour Parallel 15
3.1 Process Planning (Flow Chart) 21
3.2 CAD Design 23
3.3 Part Operation Setting 24
3.4 Datum Reference Setting 24
3.5 Isoparametric Machining 25
3.6 Tool path strategies selection 26
3.7 Profile and face selection 26
3.8 Tooling setting 27
3.9 Feed rate setting 27
3.10 Macro management 28
3.11 Video simulation using tool path toolbar 28
3.12 simulation 29
3.13 cutting material according to a predetermined size using the bend saw 30
3.14 workpiece after cutting using bend saw 30
3.15 two holes drilled in the bottom surface 31
3.16 workpiece tied on the jig 31
3.17 Jig tied on CNC working table 32
3.18 Portable Surface Roughness Tester Mitutoyo 33
3.19 SurfTest calibrate surface 34
3.20 Coordinate Measuring Machine, WENZEL 3D/ LH 5.6.4 35
4.1 Point area for surface roughness test 38
4.2 Average surface roughness 41
x
4.3 Product back side view 42
4.4 Product front side view 42
4.5 Product upper side view 43
4.6 CAD back side view 43
4.7 CAD front side view 44
4.8 CAD upper Side View 44
4.9 Result for CMM testing 48
4.10 Machining Time for all tool path 49
xi
LIST OF ABBREVIATIONS, SYMBOLS & NOMENCLATURE
CNC - Computer Numerical Control
CAD - Computer Aided Design
CAM - Computer Aided Manufacturing
% - Percentages
1
1.1 Background of study
To meet the demands of the growing orthopaedic market and changing
demographics of patients, implant design solutions are becoming increasingly
sophisticated. Today, device manufactures are leveraging implantable plastics
that process highperformance and customized properties, as they allow for
greater design freedom and ultimately lead to improved applications.
Polyetheretherketones (PEEK) is the most widely used long-tern implatable
plastics in medical application. The increasing use of high performance plastics,
composite materials and compounds can be seen in the development of a wide
range of orthopedic application, including spinal fusion cages and plates,
artificial discs, acetabular cups, femoral stems and arthroscopic bone anchors and
interference screws. In addition to meeting these general implant requirements.
For this reason, only limited number of suitable biomaterials are available for the
development of implantable orthopedic devices, and the emergence of new
biomaterials is rare. Because of their biocompability and high performance,
implatable-grade plastics have emerged as a leading biomaterial in the
developmentof orthopedic applications. These biomaterials are attractive for both
their machenical properties and their associated processing technologies, which
enable device manufacturers to tailor their characteristics to meet certain needs.
The ability to tailor the characteristics of certain implantable-grade plastics
means that device designers can consider factors other than the structural
INTRODUCTION
CHAPTER 1
2
substitution of the natural tissue. Physical characteristics such as the elastic
modulus can be modified to recreate bone modulus. Mechanical properties such
as the strength, wear resistance and impact performance of polymers and
composites can be comparable to metals and offer additional benefits. Since
implantable-grade plastics are not metallic, they do not release metal ions into the
body, which can trigger allergic ractions in certain patients. In addition to
reducing or eliminating allergic reactions, these materials also eliminate artifacs
during post operative examination by traditional techniques such as X-ray, CT
and MRI technology. Non-metallic materials also resist corrosion, leading to a
longer implant life span. Polymers are also less dense than metals, have lower
thermal conductivity and, in areas close to the translucent skin surface, provide
better color aesthetics. In addition, oplymers present the ability to be surface
modified with such coatings as hydroxyapatite or titanium, to aid secondary
fixation or with chemical species as with bone morphogenic proteins (BMPs).
Processing for some plastics can be easily scaled up to meet the increasing
demand for product parts. Incorporating plastic technologies (for example,
injection molding) means that the economics of production are viable on a larger
scale, while complex shapes can be formed as required to aid device fabrication.
However, often for prototype designs or shor production runs, it is not
economically viable to manufacture an injection molding tool. Under such
circumstances, it is common to employ a machining process on the PEEK
polymer materials to form the components.
Figure 1.1 Example of a PEEK implant fabricated using milling process
3
1.2 Problem Statement
Often for prototype designs or short production runs, it is not economically viable to
manufacture an injection molding tool. Under such circumstances, it is common to
machine the PEEK polymer materials to form components. However, because of the
excellent physical properties and wear characteristics of these material can poses a
challenging machining process.
Machining and finishing operation on polymeric materials are prone to
propagating molded-in or residual stresses. Futher stress may be built up
within the material by localized heating at the cutting point during machining
process.
The best way to avoid adverse affects on the material’s biocompability is to
machine dry. However, in many cases coolant is necessary to remove cutting
heat that builds in the workpiece (PEEK doesn’t disspite heat the way metals
do). Pure water serves as the best coolant because it is likely to affect
material biocompability.
As with all medical components, precautions must be taken to prevent
surface contaminant of PEEK workpieces. One precautionary measure is to
dedicate the machine tool, fixturing and tools to machining only that
material. Some shops also insist their employees use gloves when handling
PEEK to keep oils off the part surface.
Most of the machining processes for machining PEEK using a same cutting
tool as machining metal. As the use of PEEK for medical implant devices is
rising, success or failure in machining such an abrasive material depends
largerly on the cutting tools.
Due to the customers’ high quality requirements and the huge price of the
materials, particular care and precision are required during machining.
Traditional manufacturing methods associated with metallic implants are
generally not satisfactory for polymeric materials. Polymers are raltively soft
when compared to implant alloys and this can create manufacturing problems
related to machining, deburring, and cleaning operations.
4
1.3 Objective
Both the difficulties and conventional cutting strategies for machining the
PEEK materials cause to initiate this research. The objectives of this research are :
1. To investigate the effects of cutter path strategy (Lead and tilt,
Noraml to drive surface and Optimized lead) on machining
performance of PEEK material.
2. To propose the optimal cutter path strategy base on machining
performance for effectively machining orthopedic component.
4
2.1 Introduction
Innovation is the driver of industrial growth and doctors, consultants and surgeons,
who are always seeking better treatment for their patients, are driving the orthopaedic
implants market. Alternative material such as biocompatible polyetheretherketone
has been increasingly employed as orthopaedic structural material such as stand-
alone anterior lumbar fusion cage. The benefits of this implant offer include reduced
operating time, better bone fusion, less shrinkage and loss of height, and improved
spinal alignment. The implant can be inserted between vertebrae where it serves as a
substitute for degenerative spinal discs. In first time spinal operations, it can simply
be inserted into place and the grip-like tread on its surface and screws hold it in
place.
LITERATURE REVIEW
CHAPTER 2
5
Figure 2.1 Example of stand-alone anterior lumbar fusion cage
The Young’s Modulus of PEEK is similar to that of cortical bone, therefore, it offers
more elasticity that metal. It can absorb energy, handle the normal weight of the
body and minimise stress on adjacent levels. The material is also radiolucent
(transparent to X-rays) and thereby allows an improved view of the fusion mass that
is taking place. However, to be able to offer X-ray (computer tomography or
magnetic resonance) imaging for optimal positioning and postoperative assessments,
titanium trace wires are press fitted into the implant. Recovery for the patient is faster
in many cases. Some patients need to be operated on from the back. However, the
implant can be inserted through the patient’s stomach where reconstructing the spine
is much less invasive that through the back. Some only need a small incision from
the fron or side, and in these cases recovery can be rapid, requiring only a four or
five day hospital stay followed by a period of recuperation to allow the fusion to knit.
6
2.2 Orthopaedics machining
Fabrication of orthopaedic implants required a combination of multidiscipline fields
especially machining. In the case of machining, the ability to interact with the
concept for new or modified implants is essential.
Figure 2.2 Example lumbar interbody fusion cage anterior
Once the design has been given final approval, the fabrication or machining section
must then be able to produce variable bacthes of complex, high tolerance medical
implants from “exotic” materials. As well as PEEK, these include carbon composite,
manganese alloys and ceramics. A material’s characteristics change during
machining because the process introduces internal stresses into its molecular lattice.
If these stresses are not removed, there is a risk that the implant will fail during its
period of implantation. Post-operation stress relieving (annealing) involves drying
the components for a minimum of 3 hours at 150 deg C. The components are then
7
heated up at 10 deg C per hour until an equilibrium temperature of 250 deg C is
reached. Then the components are allowed to cool at 10 deg C per hour until
reaching below 140 deg C, and subsequently allowed to cool down to room
temperature. In addition, the tight quality control and short lead time’s order of
medical component make it more challenging. The production equipment used in the
manufacturing process of orthopaedic implants involves computer numerical
controlled (CNC) multi-axis machine tools that are able to produce high quality
complex components in a consistent way from raw plastic and titanium material
billets. Novel work holding techniques have been developed for two axis and three
axis CNC machine tools to address the following issues:
The need to keep wastage of high cost materials to an absolute minimum
The complexity of the shapes being machined
The ability to handle components with unsual material characteristics
The need to maintain high accuracy at all times
Specialist applications that required standard machine tool technology to be
adapted
To produce the spinal implants, a CNC vertical machining centre with a fully
integrated fourth-axis capability is required. The main operations are drilling, tapping
and surface contouring components manufactured from titanium and plastic. In
addition, an inclined fixed fifth-axis configuration is required. Combining this with
the CNC machine tool will enable the machining cycle time to be kept to a
minimum. Using CNC programs that contain high levels of parameters programming
capability, it is possible to machine components 8-10 times faster than using manual
machine tool technology. Coordinate measuring (CMM) with bespoke probing
systems and statical process control help ensure accurate and consistent manufacture
of quality products.