THESIS FOR MAIL

DESIGN AND DEVELOPMENT OF ADJUSTABLE
PLASTIC PYLON FOR LOWER LIMB
PROSTHESIS
By
AABRAHAM SAMRAJ PONMANI S
MUNIYAPPAN M
NATARAJAN A G S
KARTHICK.S.M
A PROJECT REPORT
Submitted to the
FACULTY OF TECHNOLOGY
In partial fulfillment of the requirements
for the award of the degree
of
BACHELOR OF TECHNOLOGY
IN
PLASTICS TECHNOLOGY
CENTRAL INSTITUTE OF PLASTICS ENGINEERING AND TECHNOLOGY
GUINDY, CHENNAI – 600 032
ANNA UNIVERSITY
CHENNAI 600 025
APIRL 2014
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ANNA UNIVERSITY: CHENNAI 600 025
BONAFIDE CERTIFICATE
Certified that this project report “DESIGN AND
DEVELOPMENT OF ADJUSTABLE PLASTIC PYLON
FOR LOWER LIMB PROSTHESIS” is the bonafide work of
“AABRAHAM SAMRAJ PONMANI S (32110220001)
MUNIYAPPAN M (32110220024), NATARAJAN A G S
(32110220025), and KARTHICK.S.M (32110220309)” who
carried out the project work under my supervision.
Dr. M.ABDUL KADER MR. Y HIDAYATHULLAH,
HEAD OF THE DEPARTMENT SUPERVISOR
DEPT. OF PLASTICS TECHNOLOGY STO, ARSTPS
CIPET CHENNAI CIPET CHENNAI
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DESIGN AND DEVELOPMENT OF ADJUSTABLE
PLASTIC PYLON FOR LOWER LIMB
PROSTHESIS
AABRAHAM SAMRAJ PONMANI S ( REG.NO.32110220001)
MUNIYAPPAN M (REG.NO.32110220024)
NATARAJAN A G S (REG.NO.32110220025)
KARTHICK.S.M (REG .NO.32110220309)
PROJECT WORK
VIVA-VOCE EXAMIANTION
The viva-voce examination of this project work done as a part of
Bachelor of Technology held on __________________
INTERNAL EXAMINER EXTERNAL EXAMINER
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ABSTRACT
DESIGN AND DEVELOPMENT OF ADJUSTABLE PLASTIC PYLON
FOR LOWER LIMB PROSTHESIS
In medicine, a prosthesis, is an artificial device that replaces a missing
body part lost through trauma, disease, or congenital conditions. Lower Limb
prosthesis are used by the amputees who have their lower knee cut off mostly
due to accidents, disease and by surgery. The lower limb prosthesis usually
consists of a metal rod called pylon which acts as the skeleton for the prosthesis
by bearing the load and connecting the socket and the foot. The metal pylon
made up of steel is of fixed height, adjustment in height needs a replacement.
The dimensions, properties, and the load acting on the steel pylon is to be
studied and the suitable plastic material is to be chosen considering all the
requirements. The feasibility study of the adjusting mechanism is to be made, and
a suitable mechanism is to be chosen for designing the pylon. The adjustable
plastic pylon is to be designed and the design is to be optimised. The finalised
design is to be analysed for its processability and the same is to be prototyped for
design confirmation.
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ACKNOWLEDGEMENT
It has been a great privilege, and good learning experience for us to be a part of
CIPET-Chennai while doing B.Tech in Plastics technology. It’s a matter of great pride to
acknowledge with gratefulness and appreciation to all those who have guided, inspired,
motivated and extended their cooperation throughout the period of our project. We are
especially grateful to Prof. Dr. S. K. Nayak, Director General CIPET, for his inspiring
advice and constant encouragement throughout the tenure of the project work. We would
like to convey my deep regards and gratitude to Dr. K.Palanivelu, Principal associating
us to various sections of the concern for facilities and foregoing guidance for completing
this project
Our sincere thanks to Mr. R. Joseph Bensingh, Scientist, ARSTPS, Chennai for
motivating us to do this project. Our deepest thanks to Mr.Y.Hidayatullah, STO,
ARSTPS, Chennai and the guide of the project for guiding us with most attention and care.
We also thank Mr. S Ethayakkannan, ARSTPS for helping us throughout this work.
We would also like to convey our deep regards and gratitude to Dr. M. Abdul
Kader, Head of the Department and Dr. Syed Amanulla, Training In-Charge, for
associating us to various sections of the concern for facilities and foregoing guidance for
completing this project. We also thank all our teaching and non-teaching faculty, friends
and family for supporting us throughout the course.
- AABRAHAM SAMRAJ PONMANI S
MUNIYAPPAN M
NATARAJAN A G S
KARTHICK S M
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TABLE OF CONTENTS
CHAPTER NO. TITLE PAGE NO.
ABSTRACT i
ACKNOWLEDGEMENT ii
LIST OF TABLES iii
LIST OF FIGURES iv
LIST OF ABBREVIATION v
1 INTRODUCTION 01
1.1 Plastics 01
1.2 Prosthetics 03
1.2.1 Pylon 04
1.2.2 Materials for Metal Pylons 04
1.2.3 Manufacturing of Metal Pylons 06
1.2.4 Description of Metal Pylons 08
1.3 Research Objective and scope 09
1.3.1 Objective 09
1.3.2 Scope 10
1.4 Research Methodology 10
1.5 Design Considerations 11
2 LITERATURE REVIEW 12
2.1 Plastics 12
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2.1.1 Classification of Plastics 13
2.1.2 Poly Butylene Terephalate 15
2.1.3 Polacetal (PolyOxyMethlene) 16
2.2 Plastics product design 18
2.3 Factor of Safety 21
2.4 Computer Aided Design 22
2.4.1 Unigraphics 22
2.4.2 Application Overview 22
2.5 Computer Aides Engineering 27
2.5.1 Finite Element Method 27
2.5.2 Ansys Software 29
2.5.3 Fundamental FEA Concepts 30
2.5.4 Steps in analysis of product using ANAYS 31
2.6 Introduction to Moldflow 33
2.6.1 Steps involved in Moldflow 33
2.6.2 Types of mesh used in Moldflow 33
2.6.3 Types of analysis used in Moldflow 34
2.7 Conversion of Metal to Plastics 34
2.8 Guidelines for Metals Replacement 37
2.9 Choosing the Right Plastic 38
2.10 Prototyping 40
2.11 Rapid Prototyping 40
2.11.1 Benefits or advantages of Rapid
Prototying 41
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2.11.2 Basic Process steps in Rapid Prototyping 41
2.11.3 Rapid Prototyping Materials 41
2.11.4 Rapid Prototyping Applications 41
2.11.5 Feature development in Rapid Prototyping 42
2.12 Rapid Prototyping Techniques 42
2.12.1 Stereolithography 43
2.13 Highlights of Stereolithogarphy 43
3 MATERIAL SELECTION FOR PYLON 46
3.1 Pylon requirement 46
3.2 Plastics for Pylon 46
3.3 Plastics material selection for Pylon 47
3.3.1 Comparsion of various important properties 48
3.3.2 Characteristics of Polyacetal (POM) 49
3.3.3 Characteristics of Polybutylene terephthalate 50
3.3.4 Selection of Delrin® 570 NC000 50
3.3.5 Selection of VALOX® 830 52
4 DESIGN OF ADJUSTABLE PLASTICS PYLON 54
4.1 Existing Design Of Metal Pylon. 54
4.1.1 Existing drawing of Pylon 54
4.1.2 CAD Model ot the Existing Pylon Assembly56
4.2 Analysis of Metal Pylon 57
4.2.1 Dimensions and Units 57
4.2.2 Software used 57
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4.2.3 Material chosen for simulation 58
4.2.4 Finite element model 58
4.2.5 Boundary and Loading Condition 59
4.2.6 Structural Analysis Results 59
4.3 Proposed Pylon 61
4.3.1 CAD model and Design 61
4.3.2 Detailed Image of Top part 62
4.3.3 Detailed Image of Adjusting ring 62
4.3.4 Detailed Image of Bottom part 63
4.4 Structural Analysis using ANSYS 63
4.4.2 Material Chosen for simulation 64
4.4.3 Calculation of Weight 65
4.4.4 Finite Element model 65
4.4.5 Boundary and Loading Condition 65
4.4.6 Structural Analysis Results for DELRIN
570 NC 65
4.4.7 Structural Analysis Results for
VALOX 830 U 67
4.4.8 Calculation of factor of safety 68
4.5 Processability study in the Adjustable Pylon 69
4.5.2 Material chosen for simulation 70
4.6 Flow Simulation 71
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4.6.1 Molding window analysis 71
4.6.2 Fill time 73
4.6.3 Pressure at V/P Switch over point 74
4.6.4 Weld lines 75
4.6.5 Orientation of Fiber 77
4.6.6 Shear Stress at Wall 78
4.6.7 Air Traps 80
5 PROTOTYPING OF ADJUSTABLE PYLON 81
5.1 Object Eden 350 81
5.2 Prototype of adjustable pylon 83
CONCLUSION 84
REFERENCE 85
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LIST OF TABLES
TABLE NO. DESCRIPTION PAGE NO.
2.1 Software used 30
3.1 Comparison of various properties of material 45
3.2 Polyacetal Data sheet 48
4.1 Calculation of weight of metal pylon 51
4.2 Dimensions and units 53
4.3 Software used for metal pylon analysis 53
4.4 Mesh statics for metal pylon analysis 54
4.5 Software used for adjustable plastic pylon analysis 59
4.6 Material table for adjustable plastic pylon 59
4.7 Mesh statics for adjustable pylon analysis 60
4.8 Software used 65
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LIST OF FIGURES
FIGURE NO. DESCRIPTION PAGE NO.
1.1 Prosthetic lower limb 3
1.2 Pylon 4
2.1 Polybutylene Terephthalate 15
2.2 Polyacetal 16
2.3 Conversion road Map 35
2.4 Stereolithography 45
4.1 Upper fixture detailed view 54
4.2 Pylon detailed view 55
4.3 Lower fixture detailed view 55
4.4 Upper fixture 56
4.5 Pylon 56
4.6 Lower fixture 56
4.7 Assembly view of metal pylon 56
4.8 Exploded view of metal pylon 56
4.9 Finite Element method for metal pylon 58
4.10 Boundary conditions for metal pylon 59
4.11 Von Mises stress plot for metal pylon 60
4.12 Deformation of metal pylon 60
4.13 CAD model for adjustable plastic pylon 61
4.14 Top part detailed view of adjustable plastic pylon 61
4.15 Adjusting ring of adjustable plastic pylon 62
4.16 Bottom part of adjustable plastic pylon 62
4.17 Finite Element method for adjustable plastic pylon 64
4.18 Boundary conditions for adjustable plastic pylon 65
4.19 Von Mises stress plot for adjustable plastic pylon (POM) 66
4.20 Deformation for adjustable plastic pylon (POM) 66
4.21 Von Mises stress plot for adjustable plastic pylon (PBT) 67
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4.22 Deformation for adjustable plastic pylon (PBT) 67
4.23 Quality plot of Adjusting ring 72
4.24 Zone plot of Adjusting ring 72
4.25 Quality plot of Bottom part 72
4.26 Zone plot of Bottom part 72
4.27 Quality plot of Top part 73
4.28 Zone plot of Top part 73
4.29 Fill time –Adjusting ring 73
4.30 Fill time –Bottom part 74
4.31 Fill time –Top part 74
4.32 Press at switch over –Top part 75
4.33 Press at switch over –Bottom part 75
4.34 Press at switch over – Adjusting ring 75
4.35 Weld lines - Bottom part 76
4.36 Weld lines – Adjusting ring 76
4.37 Weld lines – Top Part 77
4.38 Fiber orientation –Adjusting ring 77
4.39 Fiber orientation –Bottom part 78
4.40 Fiber orientation – Top part 78
4.41 Shear stress at wall –Top part 78
4.42 Shear stress at wall –Bottom part 79
4.43 Shear stress at wall –Adjusting ring 79
4.44 Air Traps 80
5.1 Object Eden 350v 81
5.2 Individual parts 83
5.3 Prototype in opened and closed position 83
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ABBREVIATIONS:
CAD : Computer Aided Design
CAM : Computer Aided Manufacturing
CAE : Computer Aided Engineering
FEA : Finite Element Analysis
FEM : Finite Element Modelling
ANSYS : Analysis System
UG : UNIGRAPHICS
CATIA : Computer Aided Three Dimensional Interactive
Application
POM : Poly Oxy Metylene
PBT : Poly Butylene Terephthalate
APDL : Ansys Parametric Design language
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1
CHAPTER 1
INTRODUCTION
1.1 PLASTICS
Over the years plastics replacing other materials like, metals, glass, wood,
etc. because of its impressive advantages over others such as light weight, faster
production, low cost, non-corrosiveness, wide range of colour possibilities with
great design freedom to achieve aesthetic appearance and wide range of material
availability to suit the functional requirements. In addition to the above
advantages plastics has great advantage of moulding many smaller parts into
one single part to reduce assembly time and to improve part strength.
There are two main types of plastics: thermoplastics and thermosetting
polymers. Thermoplastics are the plastics that do not undergo chemical change
in their composition when heated and can be moulded again and again.
Thermosets can melt and take shape once; after they have solidified, they stay
solid. In the thermosetting process, a chemical reaction occurs that is
irreversible.
Varieties of processing techniques are used to transform raw plastics into
the objects that we use. Some of the plastics processing techniques includes;
Injection moulding, Blow moulding, Extrusion, Compression moulding,
Transfer moulding, Rotational moulding, Thermo forming, etc. Injection
Moulding process is ideally suited to manufacture mass produced plastic parts
of complex shapes requiring precise dimensions with wide range of material to
use. In this process, hot polymer melt is forced into a cold empty cavity of a
desired shape and is then allowed to solidify under a high holding pressure. The
mould is then opened and the part is ejected. The complete injection moulding
cycle includes, mould filling, cooling, and ejection.
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Injection mould is an assembly of parts containing within it an impression
into which plastic material is injected and cooled. Impression is the part of
mould which imparts shape to the moulding. The impression is formed by two
mould members namely core and cavity. The mould is made of two halves
namely fixed half and moving half. Fixed half is the injection side and the
moving half is the ejection side. Mould normally contains the mould elements,
ejection systems, feed systems and cooling systems. Type of mould is decided
according to the part geometry. The mould is designed to suit a specific
Moulding machine.
Computer Aided Engineering (CAE) plays a vital role in validating the
design and optimizing the process conditions. Software such as Moldflow and
Moldex3D are well known in Injection moulded part validation. It helps to
improve the part quality, to increase the production rate and to reduce the part
cost by optimizing the processing parameters such as fill time, injection
pressure, mould and melt temperatures, etc. This software uses various
computer simulation techniques to analyze and execute the results. The result
interpretation requires sound knowledge of the plastic material, its process,
mould design and machining. Even though the results are not 100% accurate, it
is acceptable one. The accuracy varies because of various factors such as,
selection of unsuitable elements, deficiencies in individual elements, poor
assessment of output data, masking of important features, lack of
standardisation between system codes, etc.
Rapid Prototyping is an important tool in design verification and
optimization to qualify the form / fit / function of individual part and
assemblies. It is also used as a concept visualization tool to verify design
details. It acts as a communication tool for internal design reviews, for design
reviews with the customer and for dry fit installation checks. It builds the
models directly from 3D CAD data based on layer by layer construction.
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SOCKET
PYLON
FOOT
Important factors deciding the parts quality is its speed, build size capacity and
layer thickness with accuracy and surface finish.
1.2 PROSTHETICS:
In medicine, prosthesis is an artificial device that replaces a missing body
part lost through trauma, disease, or congenital conditions. In developing
countries like Indonesia and India the lack of basic public hygiene, infection
lack of nutrition causes amputation. In war-torn countries such as Cambodia,
Iran, and Afghanistan, 80 to 85 percent of amputees are land mine survivors.
Other factors are Accidents, Terror Attacks etc. The lower limb prosthetics
replace the amputated lower limb in affected persons.
Fig 1.1 Prosthetic Lower Limb.
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1.2.1 Pylon
The pylon is a simple tube or shell attaches the socket to the terminal
device (foot). Pylon can be Exoskeleton which is rigid exterior, hard to make
adjustments, simulates appearance of leg, Or an Endoskeleton which is easier to
adjust; central pylon is similar to bones w/ foam covering as flesh.
Pylon is generally made up of Steel, Aluminium, Titanium, most recently
using Carbon fibre. The pylon is the internal frame or skeleton of the prosthetic
limb. Its main function is to bear the body’s weight. The Low cost Pylon also
uses materials like PVC Pipes, HDPE Tubes, Bamboos, and Wood etc. Heavier
prosthesis to the daily lives of people with disabilities does not bring a lot of
cases instead they are highly inconvenient, the higher the cost and increase the
economic burden of the user.
1.2.2 Materials for Metal Pylons
 Aluminium
Aluminium is a silvery white metal and it is not used in its pure form due to
it’s inherit weakness. It is used mostly in alloy form. The typical alloying
elements of Aluminium include copper, magnesium, manganese, and silicon,
Zinc, Lead and Bismuth. Alloy material possesses better properties than the
original material because the alloying is done according to the functional
requirement
Fig 1.2 Pylon
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Aluminium has the following general properties;
 Light weight
 Good strength to weight ratio
 Good corrosion resistance
 Impermeable
 Good electrical conductivity
 Odourless
 Low melting point
 Good ductility
 High resistance to chemicals and weathering.
 100% recyclable
 Good reflector of visible light
 Titanium:
Titanium is a high performance, Light weight Material. A hard, lustrous
metal that is as strong as steel but much less dense.
 Titanium is a lustrous transition metal with a silver colour.
 They are light in weight.
 Theyhave ability to withstand extreme temperatures.
 Titanium is classified as a transitional metal.
 It has excellent corrosion resistance.
 Titanium is as strong as steel but 45 percent lighter. It is 60
percent heavier than aluminium, but twice as strong.
 Low Density
 High Strength
 Highly Resistant to corrosion in sea water, aqua regia and
chlorine
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 Steel
Steel is an alloy of iron and a small amount of carbon. It is a shiny metal
with attractive finish.
 It conducts heat and electricity
 It can be rolled into thin sheets rods, bar or beams.
 It can be forged into different shapes.
 It can be stretched and drawn out into thin wires.
 It is very strong and resistant to fracture.
 Steel is highly Durable
 It can be easily alloyed with other metals.
 Steel can be easily coated with metals like zinc, chromium,
Plastics or Paint.
1.2.3 Manufacturing of metal pylons:
The metal pylon are generally manufactured by die casting. Die casting is
a metal casting process that is characterized by forcing molten metal under high
pressure into a mould cavity. The mould cavity is created using two hardened
tool steel dies which have been machined into shape and work similarly to an
injection mould during the process. Most die castings are made from non-
ferrous metals, specifically zinc, copper, aluminium, magnesium, lead, pewter
and tin based alloys. Depending on the type of metal being cast, a hot- or cold-
chamber machine is used.
The casting equipment and the metal dies represent large capital costs and this
tends to limit the process to high volume production. Manufacture of parts using
die casting is relatively simple, involving only four main steps, which keeps the
incremental cost per item low. It is especially suited for a large quantity of small
to medium sized castings, which is why die casting produces more castings than
any other casting process. Die castings are characterized by a very good surface
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finish (by casting standards) and dimensional consistency. There are two basic
types of die casting machines: hot-chamber machines and cold-chamber
machines.
The following are the four steps in traditional die casting, also known as
high-pressure die casting, these are also the basis for any of the die casting
variations: die preparation, filling, ejection, and shakeout. The dies are prepared
by spraying the mould cavity with lubricant. The lubricant both helps control
the temperature of the die and it also assists in the removal of the casting. The
dies are then closed and molten metal is injected into the dies under high
pressure; between 10 and 175 Mega Pascal (1,500 and 25,400 psi). Once the
mould cavity is filled, the pressure is maintained until the casting solidifies. The
dies are then opened and the shot (shots are different from castings because
there can be multiple cavities in a die, yielding multiple castings per shot) is
ejected by the ejector pins. Finally, the shakeout involves separating the scrap,
which includes the gate, runners, sprues and flash, from the shot. This is often
done using a special trim die in a power press or hydraulic press. Other methods
of shaking out include sawing and grinding. A less labour -intensive method is
to tumble shots if gates are thin and easily broken; separation of gates from
finished parts must follow. This scrap is recycled by re-melting it. The yield is
approximately 67%.
The high-pressure injection leads to a quick fill of the die, which is
required so the entire cavity fills before any part of the casting solidifies. In this
way, discontinuities are avoided, even if the shape requires difficult-to-fill thin
sections. This creates the problem of air entrapment, because when the mould is
filled quickly there is little time for the air to escape. This problem is minimized
by including vents along the parting lines, however, even in a highly refined
process there will still be some porosity in the centre of the casting. The die
casted pipe is then chrome plated and it is threaded at both ends for attachments
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1.2.4 Description of Metal Pylons
 Titanium Pylon
Diameter 30 mm 30 mm
Weight 160 g 275 g
Material Titanium Titanium
Maximum weight 100 kg / 220 lbs. 136 kg / 300 lbs.
 Aluminium Pylon
Weight 155 g 240 g
Material Aluminium Aluminium
 Steel Pylon
Weight 195 g 315 g
Material Stainless steel Stainless steel
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1.3 RESEARCH OBJECTIVE AND SCOPE
1.3.1 Objective
The Pylon used in prosthetic lower limb is of fixed height if we need to
change the height of the pylon we need to replace the existing pylon with a new
one. The main objective is to design and develop an adjustable plastic pylon.
The pylon made up of metals which is higher in weight and cost and difficulties
in bulk production. The pylons made up of metals also cause inconvenience to
the amputees due to its higher weight. These factors can be nullified if the pylon
is made up of plastics.
The plastic material should be selected by carefully considering its
functional requirement. Plastic material selection involves analysing properties
such as mechanical, thermal, electrical, physical, optical and chemical
properties. Plastic product design factors are to be considered while carry out its
design and development. The product design is to be evaluated for its functional
and Processability requirements. Optimised designs are to be made and they
should be validated using ANSYS Moldflow softwares for confirming the
design as well as optimizing the process parameters respectively.
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1.3.2 Scope
The main scope of this work is to make the light weight adjustable plastic
pylon which reduces the cost of the part. This work involves understanding the
conversion of metal to plastic procedures, selecting suitable plastic material,
design & development of plastic Pylon, analysis and optimization of the
adjustable pylon and development of prototype model for design confirmation.
1.4 RESEARCH METHODOLOGY
The methodology for this research project is as follows:
 Literature survey related to metal to plastics conversion, material
selection and manufacturing process etc.
 Selecting the suitable plastics material for the adjustable plastic pylon.
 Design & development of adjustable plastic pylon.
 Analysis and optimization of adjustable plastic pylon.
 Processability Analysis of adjustable plastic pylon.
 Development of prototype for design confirmation.
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1.5 DESIGN CONSIDERATIONS:
There are multiple factors to consider when designing a prosthesis.
Manufacturers must make choices about their priorities regarding these factors.
o Performance.
o Elements of socket and foot mechanics that are invaluable for the
athlete, and these are the focus of today’s high-tech prosthetics
companies.
o Fit – athletic/active amputees, or those with bony residua, may require
a carefully detailed socket fit; less-active patients may be comfortable
with a 'total contact' fit and gel liner
o Energy storage and return – storage of energy acquired through
ground contact and utilization of that stored energy for propulsion
o Energy absorption – minimizing the effect of high impact on the
musculoskeletal system
o Ground compliance – stability independent of terrain type and angle
o Rotation – ease of changing direction
o Weight – maximizing comfort, balance and speed
o Suspension – how the socket will join and fit to the limb
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CHAPTER 2
LITERATURE REVIEW
The pylon which is the connecting rod between the socket and the foot. It
forms the skeleton of the lower prosthetic limb. The pylon used in low cost
prosthesis is made up of metal usually steel. The pylon is a hollow cylindrical
pipe like structure which supports the person’s weight. Pylon is attached to the
socket and the foot by the means of two threaded steel couplings to which the
pylon is joined by threads.
Pylon has to withstand the load of the person wearing. It should be with high
factor of safety to ensure the safer usage of the prosthetic limb.The major
disadvantage of the pylon is the high cost and difficulty in bulk production. It is
not adjustable, it has to be cut as per the user’s requirement, which also
increases the cost. Hence the low cost prosthetic has to be incorporated with a
plastic pylon of light weight with the capability to withstand the loads.
2.1 PLASTICS
Plastics are the high molecular weight compound formed by the
combination of small molecules of low molecular weight. Plastics have long
chain macro molecules, which are built up by the linking together of a large
number of small molecules, called monomer. The process by which the
monomer combines to form plastics or polymers is known as polymerization.
Plastics can have different chemical structures, physical properties, mechanical
behaviour, thermal characteristics, etc.
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In general plastic offers impressive advantages over metals, such as,
 No Corrosion
 Light weight with Good strength to weight ratio
 Very cost effective
 Faster production
 More Design freedom
 Good electrical insulation
 Available in wide range of colors
2.1.1 Classification of plastics
Although there are numerous minor classification schemes for plastics, it
is broadly classified into two types. They are;
a. Thermoplastics
b. Thermosets.
a. Thermoplastics
Thermoplastics are resins that repeatedly soften when heated and harden
when cooled. They are generally formed by the addition polymerization. Their
softening temperature varies with type and grade and no chemical changes takes
place during heating and cooling. When heated individual chains slip, causing a
plastic flow. Upon cooling, the chains of atoms and molecules are once again
held firmly. Because of this behaviour, these resins can be injection moulded,
blow moulded, extruded or formed via other moulding techniques. This
behaviour also allows reground or reusability of the production scraps. But the
percentage of scrap addition may leads to loss of mechanical properties. So the
amount of recycled resin mixing with the virgin material should be limited. Few
examples of thermoplastic materials are; Polypropylene (PP), Polyethylene
(PE), Polystyrene (PS), Polycarbonate (PC), Polymethylmethacrylate (PMMA),
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Polyamide (PA), Acrylonitrile Butadiene Styrene (ABS), Polyvinyl Chloride
(PVC), Polyethylene Terephthalate (PET), Polysulfone (PSU), Polyurethane
(PU), etc.
Thermoplastics are further classified by the arrangement of molecules.
They are amorphous and crystalline. In Crystalline material’s internal structure
the molecules are arranged in an orderly three-dimensional configuration. More
accurately referred to as a semi crystalline plastic because only portions of the
molecules are in crystalline form. Crystalline plastics are generally difficult to
process, requiring more precise control during fabrication, having higher melt
temperatures and melt viscosities. It tends to shrink and warp more than
amorphous types. They have relatively sharp melting point. They are usually
opaque, solvent resistant, excellent chemical resistant, fatigue / wear resistant,
have higher density, greater heat content, greater compressibility and greater
effect of orientation. Acetal, Polyethylene Terephthalate (PET), Polybutylene
Terephthalate (PBT), Polyamide (PA), Polyethylene (PE), Polypropylene (PP),
etc. are good examples of crystalline plastics.
A plastic that has no crystalline component, no known order, or pattern of
molecule distribution, and no sharp melting point, called amorphous plastics.
Amorphous plastics are usually transparent, have low shrinkage, low heat
content and low density. They have lower effect of orientation and sometimes
lower compressibility. They have poor fatigue / wear resistance and broad
softening point. Amorphous plastics have higher viscosities, solvent sensitive
and poor chemical resistance. Acrylonitrile-Butadiene-Styrene (ABS), Poly
methyl methacrylate (PMMA), Polycarbonate (PC), Polystyrene (PS), Polyvinyl
Chloride (PVC), etc. are good examples of amorphous materials.
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b. Thermosets
Thermosets are resins that undergo reaction during processing to become
permanently insoluble and infusible due to the formation of three dimensional
cross linked network structures when heat is applied. They are generally formed
by condensation polymerization and the molecular weight of these polymers is
higher than the molecular weight of thermoplastics. This network of polymer
chains tends to degrade, rather than soften, when exposed to excessive heat. So
it cannot be reshaped or reused. Few examples for thermosets are; Phenol
Formaldehyde (PF), Melamine Formaldehyde (MF), Urea Formaldehyde (UF),
Epoxies, Polyesters, Silicones, Alkyds, etc.
2.1.2 Poly Butylene Terephalate (PBT)
Polybutylene terephthalate is a thermoplastic semi crystalline polymer and a
type of polyester. PBT is resistant to solvents, shrinks very little during forming,
is mechanically strong, heat-resistant up to 150 °C (or 200 °C with glass-fibre
reinforcement)
Fig 2.1 Poly Butylene Terephthalate
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 High softening temperatures (glass-fibre-filled grades are better than
Polycarbonates and modified PPOs).
 High rigidity, with some filled grades having a flexural modulus as high
as 11000 MPa, a figure only exceeded by PPS amongst the engineering
thermoplastics.
 Good electrical insulation properties with exceptional tracking resistance
for an engineering thermoplastic and, in particular, for an aromatic
polymer. In tracking resistance most grades are generally superior to most
grades of polycarbonates, modified PPOs, PPS and the Polyetherimides.
 Low friction and good abrasion resistance.
 Good impact strength at low temperatures and excellent creep rupture
strength.
 Low water absorption and good chemical resistance, including resistance
to stress cracking.
 Good dimensional stability, partially as a consequence of the low water
absorption but also because of a low coefficient of thermal expansion.
 Capability of compounding to give UL94 V-0 flammability ratings.
 Good mould ability, with easy flow and rapid setting.
2.1.3 Polyacetal (PolyOxyMethylene)
Fig 2.2 Polyacetal
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Polyoxymethylene is also called polyacetal and polyformaldehyde.
Polyoxymethylene homopolymer is a crystalline polymer (75-85% crystalline).
Polyoxymethylene (POM), also known as acetal, polyacetal and
polyformaldehyde, is an engineering thermoplastic used in precision parts
requiring high stiffness, low friction and excellent dimensional stability. As
with many other synthetic polymers, it is produced by different chemical firms
with slightly different formulas and sold variously by such names as Delrin,
Celcon, Duracon and Hostaform. Typical applications for injection-molded
POM include high performance engineering components such as small gear
wheels, ball bearings, ski bindings, fasteners, knife handles, and lock systems.
The material is widely used in the automotive and consumer electronics
industry.
Characteristics of Polyoxymethylene
 High stiffness
 Low friction
 Excellent dimensional stability
 High strength, hardness and rigidity
 Tough material
 Very low coefficient of friction
 High abrasion resistance
 Low water absorption
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2.2 PLASTICS PRODUCT DESIGN
Product design is the process of creating a new product. It is the efficient
and effective generation and development of ideas through a process that leads
to new products. There are some essential factors to be considered while
designing any product. They are;
 Need
 Physical reliability
 Economic worthiness
 Financial feasibility
 Optimality
 Design Criterion
 Morphology
 Design process
 Reduction of uncertainty
Plastics product designer requires sound knowledge on plastics material
and its properties, various moulding methods and processes, post moulding
procedures, mould design and information on key design areas. The following
factors are to be considered while designing a plastics product;
 Wall thickness
 Draft or Taper
 Plastic Fasteners
 Threads
 Undercuts
 Fillets
 Parting line
 Ribs
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 Bosses
 Gussets
 Tolerance
 Shrinkage
 Surface finish
 Moulded holes and
 Metal inserts
Wall thickness determines the moulding possibility of the part. Wall
Thickness should be as uniform as possible to eliminate internal stresses,
Warpage, Sink mark, and Cracking. If different wall thickness in a part cannot
be eliminated they should be blended gradually. Wall thickness should not vary
more than a ratio of three to one. If thicker the wall, longer the part will have to
stay in the mould.
A taper is a slight draft angle in a mould wall designed to facilitate the
removal of the moulded part from the mould. Plastic parts must have taper on
all surfaces perpendicular to the parting line of the die. Draft should be provided
both inside and outside of the part uniformly. A minimum of ½ degree taper per
side is generally adequate. Thermoplastic materials require tapers ranging from
1/2° to 3°.
Plastics are joined by welding, riveting and mechanical means of
fastening. The lid and body of the pylon are designed to suit the clip fit
requirement by the customer. Hence, the mechanical means of plastics fastening
is preferred. Hinges, Clasps and Snap fits are used to hold two plastic parts
together. Strength of Snap fits comes from mechanical interlocking, as well as
from friction.
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Threads are used in plastics for the purpose of providing a secure
anchorage or locking device for a mating part. Threads in plastic parts are
obtained by 4 ways; They may be tapped, They may be moulded into the
plastic, Threaded metal inserts may be moulded in the part and Threaded inserts
may be pressed or cemented into place in the part after moulding. Threads used
in plastics are classified into six main types. They are; American standard
thread, Square thread, Acme thread, Buttress thread, Bottle thread and Sharp V
thread. The bottle thread is used for pylons and bottles. Also the bottle thread
can withstand 10% shear during ejection on PP materials, hence complicated
unscrewing mould methods can be avoided.
Undercut can be classified in to four types. They are; Internal undercut,
External undercut, Circular undercut and Undercut on the side wall.
Curves and fillets in a moulded part prevent stress concentrations, add
strength, streamlining the flow path, and helps to eliminate warpage. Corner
radii should be a minimum of ¼ of the part thickness for most thermoplastic
materials. Fillets should be placed at the junction of bosses and ribs with the
main body of the part. Plastic corner flow should present no problem if the
corner is rounded. Radii of fillets which junction bosses and ribs with main
body should be at least 0.25 mm and preferably 0.75 mm. Fillet reduce the cost
of the mould, and the corners of the moulded part are easier to keep clean of
dust.
Parting line should be located at the top of the part to facilitate finishing
operations. Avoid designing a part having a thin sharp wall at the parting line; it
will break very easily during finishing operations. It is classified into flat and
non-flat parting lines. Parting line is to be selected in such a way that it should
avoid unwanted undercut, which will leads to expensive moulds.
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Causes of the part shrinkage are internal stresses. Main factors which
causes increase in shrinkage are; increase in mould temperature, increase in
injection time and decrease of injection pressure.
2.3 FACTOR OF SAFETY
Factor of safety also known as safety factor or Margin of safety is a term
describing the structural capacity of a system beyond the expected loads or
actual loads. Many systems are purposefully built much stronger than needed
for normal usage to allow for emergency situations, unexpected loads, misuse,
or degradation. Factor of safety is often specified in design code or standard
such as American Society of Mechanical Engineers (ASME), American
Institute of Steel Construction (AISC), etc. The codes often specify the
minimum factor of safety.
Factors which affect the factor of safety are;
 Material strength basis: (Brittle or Ductile)
 Manner of loading: (Static or Repeated or Impact)
Environmental factors such as temperature, weather, radiation, chemical,
etc. and other factors such as its cost and weight of part are also play a role in
factor of safety. Material property for ductile material is based on its yield
strength and for brittle material it is based on ultimate strength. The factor of
safety for prosthetic limbs is generally between 6 to 8.
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2.4 COMPUTER AIDED DESIGN
2.4.1 Unigraphics
NX is an interactive Computer-Aided Design, Computer-Aided
Manufacturing, and Computer-Aided Engineering (CAD/CAM/CAE) system.
The CAD functions automate the normal engineering, design, and drafting
capabilities found in today's manufacturing companies. The CAM functions
provide NC programming for modern machine tools using the NX design model
to describe the finished part. The CAE functions provide a number of product,
assembly, and part performance simulation abilities, across a broad range of
engineering disciplines.
NX is a fully three-dimensional, double precision system that allows you
to accurately describe almost any geometric shape. By combining these shapes,
you can design, analyze, and create drawings of your products. The essential
goal of Synchronous Modelling remains that of presenting an approach for
design change with emphasis on modifying the current state of a model without
regard for how it was constructed, its origins, its associativity, or its feature
history.
To meet the demands of design change, Direct Modelling is now
Synchronous Modelling and is significantly enhanced with reliable and easy to
use core technology and new comprehensive capabilities
2.4.2 Application Overview
 Gateway
 Modelling
 Assemblies
 Drafting
 Analysis
 Quality Control
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Gateway
Gateway allows you to open existing part files, create new part files, save
part files, plot drawings and screen layouts, import and export various types of
files, and other general functions. It also provides consolidated view display
operations, screen layout and layer functions, WCS manipulation, object
information and analysis, and access to online help.
Gateway is the prerequisite for all other interactive applications,
and is the first application you enter when you open NX. You can return to
Gateway at any time from the other applications in NX by selecting it from the
Application pull-down menu.
Modelling
Solids Modelling
This general modelling application supports the creation of 2D and 3D
wireframe models, swept and revolved bodies, Boolean operations, and basic
associative editing. A solid modelling is the prerequisite for both Features
Modelling and Free Form Modelling.
Features Modelling
This feature-based Modelling application supports the creation and
associative edit of standard design features such as holes, slots, and pockets. It
allows you to hollow out solid models and create thin walled objects. A feature
can be located relative to any other feature or object and can be instanced to
establish associative sets of features. Solid Modelling is a prerequisite for this
application.
User-defined features
This application provides an interactive means to capture and store
families of parts for easy retrieval and editing using the concept of a user-
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defined feature (UDF). It allows you to take an existing associative solid model,
created using the standard NX Modelling tools, and establish relationships
between parameters, define feature variables, set default values, and decide the
general form the feature will take when started. Existing UDFs reside in a
library that can be accessed by anyone using the Features Modelling
application.
Assemblies
This application supports "top-down" and "bottom-up" assembly
modelling. It provides for rapid traversals of the assembly hierarchy and allows
direct access to the design model of any component or sub-assembly. It supports
the "design in context" approach in which changes can be made to the design
model of any component while working in the context of the assembly.
Assemblies Concepts
Components
Assembly part files point to geometry and features in the
subordinate parts rather than creating duplicate copies of those objects at each
level in the assembly. This technique not only minimizes the size of assembly
parts files, but also provides high levels of associativity. For example,
modifying the geometry of one component causes all assemblies that use that
component in the session to automatically reflect that change. Within an
assembly, a particular part may be used in many places. Each usage is referred
to as a component and the file containing the actual geometry for the component
is called the component part
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Top-down or Bottom-up Modelling
You are not limited to any one particular approach to building the
assembly. You can create individual models in isolation, then later add them to
assemblies (bottom-up), or you can create them directly at the assembly level
(top-down). For example, you can initially work in a top-down fashion, then
switch back and forth between bottom-up and top-down Modelling.
Mating Conditions
Mating conditions let you position components in an assembly. This
mating is accomplished by specifying constraint relationships between two
components in the assembly. For example, you can specify that a cylindrical
face on one component is to be coaxial with a conical face on another
component. The relationship between the two components is associative. If you
move the fixed component's location, the component that is mated to it also
moves when you update. For example, if you mate a bolt to a hole, if the hole is
moved, the bolt moves with it.
Machining of Assemblies
Assembly parts may be machined using the Manufacturing applications.
An assembly can be created containing all of the setup, such as fixtures,
necessary to machine a particular part. This approach has several advantages
over traditional methods:
• It avoids having to merge the fixture geometry into the part to be
machined.
• It lets the NC programmer generate fully associative tool paths for
models for which the programmer may not have write access
privilege.
• It enables multiple NC programmers to develop NC data in separate
files simultaneously.
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Assemblies Functionality
Some of the major features of Assemblies include:
• Component geometry is pointed to from the assembly, rather than
duplicated throughout the assembly.
• You can create assemblies using either a top-down or bottom-up
approach.
• Multiple parts can be opened and edited simultaneously.
• Component geometry can be created and edited in the context of the
assembly.
• Associativity is maintained throughout the assembly regardless of how
and where the edits are made.
• The graphical representation of an assembly can be simplified without
editing the underlying geometry.
• Assemblies are automatically updated to reflect the latest version of
referenced parts.
• Mating conditions let you position components in the assembly by
specifying constraint relationships between them.
• The Assembly Navigator provides a graphical display of the assembly
structure and lets you select and manipulate components for use in
other functions.
• You can use assemblies in other applications, particularly Drafting
and Manufacturing.
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Drafting
The Drafting application allows you to create engineering drawings from
3D models created in a Modelling application, or 2D design layouts created
using the built-in curve/sketch tools. Drafting supports automatic creation of
drawing layouts, including orthographic view projection, sectioning, auxiliary
and detail views, and isometric drafting. View-dependent and automatic hidden
line editing are also supported the file can be saved as default format directly
(such as *dwg)
2.5 COMPUTER AIDED ENGINEERING
Computer Aided Engineering (CAE) is defined as the use of computer
system to find the analytical solution for various engineering problems using
different numerical methods. There are three numerical methods available to
obtain analytical solution for engineering problems.
1. Functional approximation
2. Functional difference method
3. Finite Element Method (FEM) / Finite Element Analysis (FEA).
2.5.1 Finite Element Method
Finite Element Method is one of the very popular mechanical engineering
applications offered by existing CAD/CAM systems. It is the most popular
numerical analysis technique for obtaining approximate solutions to a wide
variety of engineering problems. It has grown out of the matrix analysis method
used in aircraft design. This method is based on dividing a complex shape into
small elements, solving the equilibrium equations at hand for each element, and
then assembling the element’s results to obtain the solution to the original
problem. The shape divisions, the choice of the element and the analysis types
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are among the important decisions for the success of the method. The
interpretation of the results of FEA requires a good understanding of the
principles of engineering such as linear / nonlinear mechanics, static and
dynamic, heat transfer, fluid mechanics, etc.
This method is general enough to handle any complex shape or geometry,
any material property, any boundary conditions and any loading conditions.
FEM fits the analysis requirements of today’s complex engineering systems and
designs. It can solve a wide variety of engineering problems.
Mesh contains nodes and elements. Elements are made from a number of
nodes. Different types of elements available are; one dimensional elements (eg.
Beam elements), two dimensional elements (eg. Triangular and Quadrilateral
elements) and three dimensional elements (eg. Tetrahedron and hexahedron
elements). The elements are also classified according to its shape. They are,
linear, quadratic and cubic elements. Mesh generation also classified into
automatic and manual. The good mesh produces the correct FEA results. The
requirements of good mesh are as follows;
 Nodal locations should be precise and should not go beyond the
boundary.
 Various element types and shapes should be available to provide the user
with more flexibility to meet the compatibility and requirements.
 Mesh gradation or mesh smoothing should be possible for users to control
the mesh size.
 To convert from one element type to another should be possible for the
user.
 Element aspect ratio should be close to one for better results.
 Mesh geometry and topology or mesh orientation should be uniform.
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 It should be compatible with different mesh generation types. Eg. Mid
plane meshing, fusion meshing and solid meshing.
 The time taken to generate mesh and the time taken to perform FEA
should be less.
The procedure in using an FEA program consists of three essential stages.
They are pre-processing, analysing and post-processing. Pre-processing
involves the mesh preparation, mesh correction, applying material, boundary
conditions and loading conditions. Next stage involves executing the analysis.
Last stage post-processing involves result interpretation.
The factors to be considered in FEA while making decisions are: type of
analysis, the number of nodes, the degrees of freedom at each node, the element
shape and type, the material type, the external loads, the boundary conditions
and interpretation of the results. FEA also have certain disadvantages such as,
lack of standardization between system codes of many software packages now
in use, deficiencies in the individual elements, selection of unsuitable element
types, poor assessment of output data, masking of important features by the
output post-processor, inadequate understanding of the assumptions and
limitations of the FEA technique and poor representation of the component by
the FEA model.
2.5.2 ANSYS Software
To analysis the static structural of the existing metal pylon and developed
adjustable pylon, the following softwares are used. The following table 3.2
represents the softwares which has been used.
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Table 2.1 Software used
Finite element analysis is a mathematical representation of a physical
system comprising a part/assembly (model), material properties and applicable
boundary conditions (collectively referred to as pre-processing, the solution of
that mathematical representation (solving), and the study of result of that
solution (post processing). Simple shapes and simple problems can be and often
are done by hand most real world parts and assemblies are far too complex to do
accurately, let alone quickly without use of a computer and appropriate analysis
software.
2.5.3 Fundamental FEA Concepts
The bulk of FEA is used for analysis problems addressed by ANSYS
simulation; linear/static stress, deflection, factors of safety, thermal and modal.
The typical user of simulation is occasional user of finite element analysis
spending most of his/her time designing in CAD and should have good
engineering common sense. This user may or may not be a degreed engineer but
most have good understanding of how the product being designed will be used
so that it may be properly simulated. While just about anybody can use this
class of tools, software cannot replace good critical thinking. Is the product
behaving as expected and ranges plotted from results are evaluated to design.
Activity Software tools
Meshing ANSYS Mechanical APDL 13.0
Loading and boundary condition
setup
ANSYS Mechanical APDL 13.0
Post processing ANSYS Mechanical APDL 13.0
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2.5.4 Steps in analysis of product using ANSYS
 Preprocessing
To do this, FEA software typically uses a CAD representation of the
physical model and breaks it down into small pieces called finite element. This
process is called meshing. The higher the quality of the mesh collection of
elements, the better the mathematical equation based on stiffness between
nodes; the type of elements used often depends upon the problem to be solved.
The behaviour of each element by itself is very well understood. By combining
the behaviours of each element using simultaneous equations, one can predict
the behaviour of shapes that would otherwise not be understood using basic
“closed form” calculations found in typical engineering handbook.
 Meshing
ANSYS simulation provides two forms of automated meshing. Fully
automatic and manually directed automatic. Both forms employ a fault tolerant
philosophy meaning that if a problem occurs, at least twelve attempts trouble
shooting are made before the mesh fails and tags the area of difficulty with a
label. Manually directed means that the user may specify meshing overrides on
specific areas of apart edges, faces, or the baseline mesh density on the entire
parts that differ from other parts within the assembly, either for accuracy or
efficiency purposes. These changes remain associative.
 ANSYS solving
ANSYS employs three of the ANSYS solvers and automatically chooses
the most appropriate or efficient solver for the job at hand. In addition to
linear/static, ANSYS performs coupled analysis types (thermal stress, stress
modal, thermal stress modal) as well as some limited nonlinear analysis types
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(thermal with temperature dependent material properties and convection,
geometric/contact supporting lift off). All solver settings and iteration
propagation from one solve step to the next are performed automatically.
 Post Processing
The output of a solver is generally a very substantially quantity of raw
data. The quantity of raw data would normally be difficult and tedious to
interpret without the data sorting and graphical representation referred to as post
processing. Post processing is used to create graphical displays that show the
distribution of stresses, strain, deformation, temperature and other aspects of the
model. Interpretation of these post processed results is the key to identify areas
of materials waste (areas of the model bearing load) or valuable information
another information another model performance characteristics that otherwise
would not be known as until a physical model were built and tested (prototype).
The post processing phase of FEA is where the most critical thinking must take
place, where the user looks at the results and compares results with what might
be expected. It cannot be stressed enough that it is up to user to determine if the
result make sense to be able to explain the results based upon engineering. If
results are other than expected on must search until an explanation can be found
before the result can be fully trusted.
2.6 INTRODUCTION TO MOLDFLOW
Moldflow, formerly known as C-Mold, is one of the leading software
used in process wide plastics solutions. It is used by designers and
manufacturers to produce optimal plastic parts. Many reputed companies use
Moldflow technology to produce billions of Injection moulded parts each year.
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2.6.1 Steps involved in Moldflow
1. Importing a model into Moldflow software.
2. Creating a mesh to represent the model geometry.
3. Repairing the mesh if it contains errors.
4. Checking the mesh for aspect ratio, element overlapping, intersecting,
thickness, etc.
5. Modelling the mould such as cavity layout, feed system and cooling.
6. Selecting the analysis type.
7. Selecting the gate location.
8. Selecting the material.
9. Specifying the moulding operation, moulding machine details, processing
parameters, etc.
10.Analysing the study.
11.Viewing and interpreting the results of the analysis.
12.Adjusting the moulding parameters based on the analysis results.
2.6.2 Types of mesh used in Moldflow
There are three types of mesh used in Moldflow, they are Mid plane,
Dual domain or fusion and Solid mesh. Mid plane mesh is preferred for parts
with uniform wall thickness. It uses triangular elements. Dual domain mesh is
preferred for thin parts with variable wall thickness. It also uses triangular
elements. Solid mesh is preferred for thick parts with variable wall thickness. It
uses tetrahedral elements. Feed systems and cooling circuits are created by
using one dimensional element for all mesh types.
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2.6.3 Types of analyses used in Moldflow
Various analyses can be executed in Moldflow software are;
 Fill analysis
 Pack analysis
 Cool analysis
 Warp analysis
 Shrinkage analysis
 Gate location analysis
 Runner balance analysis.
 Stress analysis
 Moulding window analysis
2.7 CONVERSION OF METAL TO PLASTICS:
Materials selection, part design, tool design, and fabrication processes are
all important in product design. They should be repeatedly evaluated as the
component evolves from concept to production. All areas influence each other
and should be worked on concurrently. Tooling and processing choices
determine the makeup of the design team (Figure 3.1).
A metals-replacement effort begins by evaluating the factors that shaped
the original manufacturing method, how the assembly is manufactured, the
assembly’s function, and the operating environment. These general
considerations lead to preliminary system concepts. Decisions on specific
components evolve from these concepts, especially preliminary decisions on
materials, part design, tooling, and processing. Part design is then refined and
prototypes are made from one or more plastic. Prototype testing leads to design
refinements, final materials selection, and the specification of production
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details. Although plastics can be tailored to meet a broad range of applications
and environments, they do not work in all situations.
Figure 2.3 Conversion road map
One must assess the requirements of the entire application early in the
design process to select an appropriate material. Plastic design requires care
since there are many plastics and fabrication is critical in product performance.
To cope with these and other factors, approach design from the broadest
possible context. First evaluate needs of the system rather than that of individual
parts or components. This approach helps assess opportunities for parts
consolidation. Then define all aspects of the system under development,
including its functional (mechanical, environmental, thermal, and electrical);
SELECT DESIGN TEAM
DEFINE DESIGN CRITERIA
DEVELOP SYSTEM AND
COMPONENT CONSCEPTS
DEVELOP INITIAL
COMPONENTS DESIGNS
MAKE TOOLING AND
PROCESSING CHOICES
CONDUCT SIMULATION AND
PROTOTYPING
SET FINAL DESIGN
REFINEMENT OF:
DESIGN
MATERIALS
TOOLING
PROCESSING
PRODUCTION
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aesthetic (appearance, colour, surface finish); and manufacturing (processing,
assembly and finishing) requirements.
The benefits of plastics include:
• Greater design freedom, e.g., part complexity
• Opportunity for parts consolidation
• Fewer assembly operations
• Reduced secondary finishing, e.g., machining
• Weight reduction
• Reduction in total system costs
• Broad range of properties tailored to specific applications
• Ability to withstand temperatures to more than 500°F
• Ability to withstand most chemicals and corrosive
• Made in many colours
• Obviating the need to paint parts
• Electrically non-conductive
• Insulation from electrical shock
• Good thermal insulators
• “Warm to the touch”
• Poor sound transmitters
• Tend to muffle noise
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2.8 GUIDELINES FOR METALS REPLACEMENT:
• Pay special attention to factors that can stress the system and its
components, not only during end use, but also during fabrication and assembly.
• Differentiate needs from wants, i.e., essential properties from
desirable ones. Give greater weight to the former to make the design process
and materials selection more efficient and effective.
• Define key requirements for the application, e.g., maximum and
minimum temperatures and tolerances, maximum loads or deflections, critical
dimensions, colour, and flammability.
• Beware of one-to-one replacement. Direct substitution of plastics
for metals rarely works. Plastics have very different performance, e.g.
mechanical (strength, stiffness, toughness, creep deformation, creep failure, and
fatigue), electric and thermal properties. These affect design features such as
wall thickness, ribs and other projections, radii at intersecting surfaces, holes,
and depressions.
• Build features around functional needs. This can lead to parts
combination, which often eliminates fabrication and assembly operations,
reduces weight, improves structural integrity, and lowers cost. The team should
think about the needs of the system, rather than those of individual components.
• Optimize cost-performance values by using the minimum amount
of plastics to satisfy structural, functional, moldability and economic demands.
• Factor manufacturing, maintenance, assembly, and disassembly
into the design to reduce costs of labour, tooling, finishing, and other areas. Use
total finished-part cost in the assembly to guide design.
• Make design, materials selection and fabrication decisions
concurrently, and refines these decisions continually throughout the process.
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2.9 CHOOSING THE RIGHT PLASTIC
The team fine tunes material selection as design proceeds to final form. In
choosing a plastic, maximize system performance at the lowest possible cost.
Plastic screening parameters must consider all factors, including chemical
resistance that may cause cracking, crazing, discolouring, softening, and
melting - whether during handling, assembly, finishing, or use. Materials
selection is particularly difficult because plastics offer literally tens of thousands
of options.
Plastic properties, such as heat resistance, stiffness and strength, cover a
broad range of performance when several different plastics are considered
Thermoplastics have a performance-based hierarchy - commodity, intermediate,
engineering and high performance grades. In moving through this hierarchy,
from commodity to high-performance categories, plastics generally have a
greater ability to carry loads, withstand impact and high temperature, and resist
attack by chemicals or solvents. Many polymers are formulated with
reinforcements and additives to control impact and mechanical strength,
shrinkage, warpage, lubricity, and other properties.
Plastics basic properties depend on polymer chemistry, chain length and
structure, and the bonds between chains. Basic properties are modified by
alloying different plastics and by blending in additives, fillers, and
reinforcements. Properties that can vary in different formulations include:
• Mechanical (impact resistance, strength, rigidity, creep, and
dimensional stability).
• Electrical (conductivity, dielectric strength, dielectric constant loss
factor, and surface tracking).
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• Environmental (resistance to chemicals, water, and ultraviolet
light).Thermal (thermal expansion, long-term thermal index, heat deflection
temperature, mechanical response at temperature, and plastic stability).
• Miscellaneous (plate ability, flame retardancy, transparency, and
lubricity).
In choosing a plastic for a specific application, consider processing and
end-use factors, such as:
Temperature
Higher temperatures generally make plastics more sensitive to
mechanical stresses and more vulnerable to chemical attack, while lower ones
generally make them less ductile. Carefully map the operating temperature
range using environmental variables and mechanical loads so that the part is not
thermally over- or under-engineered. Consider temperatures during assembly,
finishing, shipping, and in the final application.
Environment
Consider compatibility with solvents, acids, bases, fuels, and other
substances that may affect the part. Apply data from plastic suppliers,
considering exposure time, concentration, and temperature. Since chemical
mixtures often affect a plastic differently than an individual component, expose
plastics to mixtures they may meet in assembly or end use. Also consider
reactions to other factors, such as humidity, ultraviolet light, and radiation.
Agency approvals
These include Underwriters' Laboratories, the Canadian Standards
Association, the U.S. Food and Drug Administration, and the National
Sanitation Foundation, among many others. Anticipate agency requirements and
work with plastic suppliers to evaluate how to obtain the approvals.
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Assembly
Match assembly methods to the material. For example, some materials
are compatible with solvent bonding and others with ultrasonic welding, while
snap-fit designs require plastics that have good strength, flexibility and
dimensional stability.
Finish
Will the plastic attain the desired appearance in the mold? If gloss is
important, can it be controlled at consistent levels? If need be, can the plastic be
economically finished - painted or printed?
Availability
Ensure that the plastic will be available in the needed quantity.
2.10 PROTOTYPING
A prototype is an early sample or model built to test a concept or process
or to act as a thing to be replicated or learned from. It is a term used in a variety
of contexts, including semantics, design, electronics, and software
programming. A prototype is designed to test and trial a new design to enhance
precision by system analysts and users. Prototyping serves to provide
specifications for a real, working system rather than a theoretical one.
2.11 RAPID PROTOTYPING
Rapid Prototyping is the automated fabrication technologies of seamless
and rapidly creating accurate representative physical models of mechanical parts
directly from 3-Dimensional Computer Aided Design (CAD) data without the
use of tooling and with minimal human intervention.
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Rapid Prototyping (RP) uses state of the art laser technology, positioning
systems, materials and computer technologies in the various processes. There
are many RP processes that are widely used, each one using different methods
and materials to produce the final part.
2.11.1 Benefits or advantages of Rapid Prototyping:
 Reduces design phase cycle time and costs.
 Reduces the potential for expensive design errors.
 Reduces tooling costs on short-run parts.
 Impresses the customer with quick response.
 Reduces time to production and market.
2.11.2 Basic Process steps in Rapid Prototyping:
1. Create CAD model of the design.
2. Convert the CAD model to STL format.
3. Slice the STL file into thin cross-sectional layers.
4. Layer by layer construction.
5. Clean and finish the model.
2.11.3 Rapid Prototyping Materials:
1. Metals - Steel alloys, Aluminium, Titanium, super alloys.
2. Non-Metals - Plastics, ceramics, composites, blended materials in
a single part.
2.11.4 Rapid Prototyping Applications:
1. A design verification and optimization tool to qualify the form / fit /
function of individual parts and assemblies.
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2. Concept visualization tools to verify design details and gain internal
design acceptance and justification.
3. A communication tools for internal design reviews, for design reviews
with the customer and for dry fit installation checks.
4. As a three dimensional fixture for bending or routing tubing or cables.
5. As an inspection fixture for parts with complex or compound surfaces
and fixtures.
6. As a model to test airflow, ducting, diverters and channels.
7. To create light duty plastic parts for light duty use, such as ducting.
8. As a mold for gaskets, keypads, etc.
9. Most Rapid Prototyping parts may be machined, drilled and tapped,
sanded, painted, baked, plated, bonded and coated with EMI protection.
2.11.5 Feature development in Rapid Prototyping:
1. The first important development is accuracy and surface finish
(~0.08mm).
2. Another important development is increased size capacity.
3. Increase in the speed.
2.12 RAPID PROTOTYPING TECHNIQUES
There are six techniques are used in Rapid Prototyping Technology. They are;
1. Stereo lithography.
2. Laminated object manufacturing
3. Selective Laser Sintering
4. Fused Deposition Modeling
5. Solid ground curing
6. 3-D inkjet printing
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2.12.1 Stereolithography
Stereolithography (SLA), the first Rapid Prototyping process, was
developed by 3D Systems of Valencia, California, USA, founded in 1986.
Stereolithography is the most widely used rapid prototyping technology.
5.4 Highlights of Stereolithography
 The first Rapid Prototyping technique and still the most widely used.
 Inexpensive compared to other techniques.
 Uses a light-sensitive liquid polymer.
 Requires post-curing since laser is not of high enough power to
completely cure.
 Long-term curing can lead to warping.
 Parts are quite brittle and have a tacky surface.
 No milling step so accuracy in z can suffer.
 Support structures are typically required.
 Process is simple: There are no milling or masking steps required.
 Uncured material can be toxic. Ventilation is a must.
The implementation shown in Fig. 2.4 is used by 3D Systems and some
foreign manufacturers. A moveable table, or elevator (A), initially is placed at a
position just below the surface of a vat (B) filled with liquid photopolymer resin
(C). This material has the property that when light of the correct color strikes it,
it turns from a liquid to a solid. The most common photopolymer materials used
require an ultraviolet light, but resins that work with visible light are also
utilized. The system is sealed to prevent the escape of fumes from the resin.
A laser beam is moved over the surface of the liquid photopolymer to
trace the geometry of the cross-section of the object. This causes the liquid to
harden in areas where the laser strikes. The laser beam is moved in the X-Y
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directions by a scanner system (D). These are fast and highly controllable
motors which drive mirrors and are guided by information from the CAD data.
The exact pattern that the laser traces is a combination of the information
contained in the CAD system that describes the geometry of the object, and
information from the rapid prototyping application software that optimizes the
faithfulness of the fabricated object. Of course, application software for every
method of rapid prototyping modifies the CAD data in one way or another to
provide for operation of the machinery and to compensate for shortcomings.
After the layer is completely traced and for the most part hardened by the laser
beam, the table is lowered into the vat a distance equal to the thickness of a
layer. The resin is generally quite viscous, however. To speed this process of
recoating, early stereolithography systems drew a knife edge (E) over the
surface to smooth it. More recently pump-driven recoating systems have been
utilized. The tracing and recoating steps are repeated until the object is
completely fabricated and sits on the table within the vat.
Some geometries of objects have overhangs or undercuts. These must be
supported during the fabrication process. The support structures are either
manually or automatically designed.
Upon completion of the fabrication process, the object is elevated from
the vat and allowed to drain. Excess resin is swabbed manually from the
surfaces. The object is often given a final cure by bathing it in intense light in a
box resembling an oven called a Post-Curing Apparatus (PCA). Some resins
and types of stereolithography equipment don't require this operation, however.
After final cure, supports are cut off the object and surfaces are sanded or
otherwise finished.
Stereolithography generally is considered to provide the greatest accuracy
and best surface finish of any rapid prototyping technology. Work continues to
provide materials that have wider and more directly useable mechanical
properties.
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Fig 2.4 Stereolithography
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CHAPTER 3
MATERIAL SELECTION FOR PYLON
3.1 PYLON REQUIREMENT
Care to be taken while selecting the material for Pylon. The purpose and
functional requirements of the pylon are already known. The main property
requirements of the pylon used as a skeleton in prosthesis is summarised here;
 Adjustability
 Less weight
 Low cost
 Good shock absorption characteristics
 Good corrosion resistance
 Good chemical resistance
 Ease of use
 Service temperature support between -10o
C to 160o
C.
 Good Compressive Strength.
 Good fatigue resistance.
3.2 PLASTICS FOR PYLON
The conversion of metal pylon into a plastic pylon will give the following
advantages
 Light weight
 Low cost
 Easy handling
 Easy fabrication
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 Lesser Time for production
 High Productivity.
In addition to the above said advantages over metal pylon, plastics have
the following other advantages to suit the pylon requirement;
 Good strength to weight ratio
 Good corrosion and chemical resistance
 Less cycle time for production
The other pylon requirements such as low cost, easy processing and use,
shock absorption characteristics, & low water absorption will vary according to
the plastics material.
3.3 PLASTICS MATERIAL SELECTION FOR PYLON
Thermoplastics can be recycled and reusable, and can be used to mould
thin walled mouldings. The Pylon part can be moulded by Injection moulding
process due to its geometry. Also, the Injection Moulding process is ideally suited
to manufacture mass produced plastic parts of complex shapes requiring precise
dimensions with wide range of material to use. Hence, thermoplastic materials
are preferred.
There are two types of thermoplastics material; amorphous and crystalline.
The crystalline plastics have easier flow characteristics, crystalline resins have an
advantage in filling thin walled sections. Additionally, these resins generally have
superior chemical resistance, greater stability at elevated temperatures, better
fatigue and wear resistance over amorphous plastics. Hence, crystalline plastics
are preferred.
According to the Pylon requirements, the crystalline plastics are compared
for its properties. The following crystalline materials are identified for the
container requirements. They are
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 Polybutylene terephthalate ( PBT) 30 % Glass Filled
 Polyacetal (POM) 20% Glass Filled
 Polyamide (Nylon 6,6) 30% Glass filled
As Nylons are hygroscopic in nature their selection as a material for pylon is
undesirable in spite of their better mechanical properties. Hence by comparing
the other properties either Polyacetal or Polybutylene Terephthalate is preferred
as a material for the adjustable plastic pylon for low cost prosthesis.
3.3.1 Comparison of various important properties:
Property Nylon 6,6
30% Glass
Filled
POM 20 %
Glass Filled
PBT 30% Glass
Filled
Density g/cm
3
1.15-1.4 1.54-1.56 1.48 - 1.54
Water absorption after 24 Hrs (%) 5.5-6.2 0.25 0.06 - 0.08
Tensile Strength at (MPa) 140 59-62 97 - 135
Tensile Modulus (MPa) 7521 6210-6900 8970 - 10005
Tensile Elongation at Break (%) 3-7 6-12 2 – 4
Flexural Strength (MPa) 200 74-110 152 - 200
Flexural Modulus (MPa) 5520 4140-5037 5865 - 8280
Poisson’s ratio 0.39 0.35 0.39
Compressive Strength (MPa) 166-276 124 124 – 162
Service Temperature (o
c) -50 – 140 -40 - 110 -50 – 130
Hardness, Rockwell 96 90 90
Izod Impact Notched (J/cm of notch) 1.4-1.6 0.3-0.5 0.5 - 1.1
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Coefficient of Linear Thermal
Expansion(10-6/ºC)
15-54 33-81 15 – 25
Heat Deflection Temperature ( ºC) 127-260 174 216 – 260
Melting Temperature (ºC) 260-265 175-181 220 – 267
Processing Temperature(o
c) 266-304 177-249 227-277
Mold Shrinkage 0.00-0.006 0.009-0.012 0.002-0.008
Table .3.1 Comparison of various properties of materials
3.3.2 Characteristics of Polyacetal (POM)
 High softening temperatures (glass-fibre-filled grades are better than
Polycarbonates and modified PPOs).
 High rigidity, with some filled grades having a flexural modulus as high as
11000 MPa, a figure only exceeded by PPS amongst the engineering
thermoplastics.
 Good electrical insulation properties with exceptional tracking resistance
for an engineering thermoplastic and, in particular, for an aromatic
polymer. In tracking resistance most grades are generally superior to most
grades of polycarbonates, modified PPOs, PPS and the Polyetherimides.
 Low friction and good abrasion resistance.
 Good impact strength at low temperatures and excellent creep rupture
strength.
 Low water absorption and good chemical resistance, including resistance
to stress cracking.
 Good dimensional stability, partially as a consequence of the low water
absorption but also because of a low coefficient of thermal expansion.
 Capability of compounding to give UL94 V-0 flammability ratings.
 Good mould ability, with easy flow and rapid setting
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3.3.3 Characteristics of Polybutylene terephthalate.
 Reinforced grades offer exceptionally high mechanical strength and
rigidity
 High resistance to repeated impacts
 Toughness at low temperature (down to -40 Degrees Centigrade)
 Outstanding long-term fatigue endurance
 Excellent resistance to moisture, gasoline, solvents and many other
chemicals of neutral pH
 Excellent dimensional stability
 Natural lubricity
 Wide useful temperature range (in air -50 to +90 degree centigrade with
intermittent use up to 160 degree centigrade)
 Good electrical insulation characteristics.
 High abrasion resistance
 Low water absorption
3.3.4 Selection of Delrin® 570 NC000
There are many manufacturers and suppliers available for polyacetal
material. Each manufacturer / supplier sells the products in their own trade names.
Search was made for collecting information on various POM manufacturers and
their trade names. And we found out that Delrin® 570 NC000 produced by
DUPONT is available in the require grade and available in Moldflow analysis
too. POM is preferred mostly due to its self-lubricating property.
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Table 3.2 POM Data sheet
3.3.4 Selection of VALOX® 830
There are many manufacturers and suppliers available for polyacetal
material. Each manufacturer / supplier sells the products in their own trade names.
Search was made for collecting information on various POM manufacturers and
their trade names. And we found out that VALOX® 830U produced by SABIC
is available in the require grade and available in Moldflow analysis too. PBT also
preferable for its similar strength at comparatively lower cost, but it lacks in self
lubrication.
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CHAPTER 4
DESIGN OF ADJUSTABLE PLASTICS PYLON
4.1 EXISTING DESIGN OF METAL PYLON.
From the literature review the product details such as its functional
requirements, applications, etc. has been clear. The details of the original part
drawing for metal pylon is to be reviewed before designing it in plastics.
4.1.1 Existing drawing of Pylon:
Upper fixture
Upper fiture is a top for the pylon part. The upper fixture is threaded on
pylon. The Upper fixture connects the pylon rod with the upper socket and bolted
with the socket. The upper fixture is designed as per the detailing shown in figure
4.1
Pylon Part :
The pylon is the rigid mettalic frame of prosthetic leg. The Pylon is
attached to the socket and the foot by a set of couplings fitted with threads.
Fig. 4.1 Upper fixture detailed view
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Fig.4.2 Pylon detailed view
Lower Fixture:
Lower fixture is the lower part of the pylon which connects the pylon with
the foot, by the means of thread and bolted to the foot.
Fig. 4.3 Lower fixture detailed view
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Table 4.1(a) Calculation of weight
Part Volume in cm3
Density Weight in Grams
Top fixture 18.80 7.85 147.5
Pylon part 45.25 7.85 355.2
Bottom 16.12 7.85 126.4
Total 80.17 7.85 629.1
4.1.2 CAD model of the existing pylon assembly
Fig 4.4 Upper Fixture
Fig 4.5 Pylon Part
Fig 4.6 Lower Fixture
Fig 4.7 Assembly view of Metal Pylon Fig 4.8 Exploded view of Metal Pylon
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4.2 ANALYSIS OF METAL PYLON
The pylon thus designed is analysed using ANSYS software.
4.2.1 Dimensions and Units
The dimensions and units are used in the structural analysis is illustrated
as below table 4.2
Table 4.2 Dimension and Units
4.2.2 Software Used
To analysis the static structural of the existing PYLON, the following
softwares are used. The following table 4.3 represents the softwares which has
been used.
Dimension Unit
Length Mm
Force N
Pressure MPa
Meshing ANSYS Mechanical APDL 13.0
Loading and boundary condition setup ANSYS Mechanical APDL 13.0
Post processing ANSYS Mechanical APDL 13.0
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4.2.3 Material chosen for simulation
Existing material for pylon is steel. This material has chosen for the existing
Pylon.
4.2.4 Finite Element model
The following Fig 4.9 shows the existing adjustable pylon finite element
model, and triangular elements has been meshed for the simulation of structural
analysis by ANSYS.
Fig 4.9 Finite Element Model
Table 4.4 Mesh statistics
Nodes 61260
Elements 33418
ELEMENT Type Triangular mesh
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4.2.5 Boundary and Loading Condition
Boundary condition used for structural analysis of metal pylon are
described below and are shown in Fig 4.7
Fig 4.10 Boundary Conditions
• In the bottom of the Pylon all DOF are locked as it is attached to the
lower fixture in the foot.
• In the top side of pylon, 150 Kg static load is applied to negative Z
direction for compressive load.
4.2.6 Structural Analysis Results
For simple linear - isotropic stress analysis, only the material young’s
modulus and poisson’s ratio need to be provided. These data's are taken from test
results of standard. Von Mises Stress plot has been taken from the results of
Ansys software.
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Von Mises Stress plot (MPa)
In this plot, the maximum deflection and maximum stress has been
predicted. Von Mises stress plot results of the adjustable pylon is illustrated as
following figure 4.8.
Fig 4.11 Von Mises Stress Plot
Fig 4.12 Deformation
Maximum Von Mises stress is highly localized due to compression,
it will not cause failure.
Maximum Deflection = 0.00216134 mm
Maximum stress = 9.814 MPa
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4.3 PROPOSED PYLON
The Proposed pylon is a three part assembly, it consists of a threaded top
part, Bottom part with guide projections, and Adjusting ring with threads. The
parts are modelled and assembled using various constraints. The Threads used is
of pitch 2mm, clearance between the threads is provided to ensure smooth
rotation. The model is designed so that the rotary motion is transformed into
vertical motion as in the case of screw jack.
4.3.1 CAD model and Design
Figure 4.10 shows the CAD model of the Adjustable pylon, and figure
4.11 shows the detailing for the same.
Figure 4.13 CAD MODEL
TOP PART
ADJUSTING RING
BOTTOM PART
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4.3.2 Detailed Image of Top Part.
Fig 4.15 Detailed view of Adjusting Ring
Fig. 4.14 Top part detailed view
4.3.3 Detailed Image of Adjusting Ring
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4. 3.4 Detailed image of Bottom Part
4.4 Structural Analysis using ANSYS
The Designed Assembly is analysed using ANSYS by importing it as a
STEP file.
4.4.1 Software Used
To analysis the static structural of the adjustable pylon assembly, the
following softwares are used. The following table 4.5 represents the softwares
which has been used. Table 4.5 Software used
Meshing Ansys Mechanical APDL 13.0
Loading and boundary condition setup Ansys Mechanical APDL 13.0
Post processing Ansys Mechanical APDL 13.0
Fig. 4.16 Bottom part detailed view
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The Material Chosen for the Pylon is described in the below table 4.6
Trade Name Delrin® Valox®
Manufacturer DuPont SABIC
Material
Structure
Crystalline Crystalline
Material Code 570 NC000 830 U
Fibers 20% Glass filled 30 % Glass filled
Modulus 5000 8000
Poisson’s Ratio 0.35 0.36
Table 4.6 Material Table for analysis.
4.4.3 Calculation of Weight.
Assembly Volume in cm3
Density in g/cc Weight in Grams
108.3 1.56 168
4.4.4 Finite Element model
The following Fig 4.14 shows the adjustable plastic pylon finite element
model, and triangular elements has been meshed for the simulation of structural
analysis by Ansys.
Fig 4.17 Finite Element Model
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Table 4.7 Mesh statistics
4.4.5 Boundary and Loading Condition
Boundary condition used for structural analysis of metal pylon are
described below and are shown in Fig 4.7
Fig 4.18 Boundary Conditions
• In the bottom of the adjustable plastic Pylon all DOF are locked as
it is attached to the foot.
• In the top side of pylon, 150 Kg static load is applied as 1470N to
negative Z direction for compressive load.
4.4.6 Structural Analysis Results for DELRIN 570 NC
Nodes 318657
Elements 182657
ELEMENT Type Triangular mesh
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results of standard. Von Mises Stress plot has been taken from the results of
Ansys software.
following figure 4.19 The maximum stress was found to be 22.892 MPa, the
deflection was found to be 0.092 mm
Fig 4.20 Deformation
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Maximum Von Mises stress is highly localized due to compression, it will not
cause failure.
4.4.7 Structural Analysis Results for VALOX®
results of standard.
following figure 4.21 and the maximum stress was found to be 22.801 MPa and
the deformation was found to be 0.051 mm
Fig 4.22 Deformation in PBT
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Maximum Von Mises stress is highly localized due to compression, it will not
cause failure.
2.3.1 Calculation of factor of safety
Formula for calculation
Factor of Safety = Ultimate Stress / Usable Stress
Steel:
• FOR 150 Kg load
– Max. usage stress = 18.265 MPa (By Analysis)
– Materials ultimate compression strength=250Mpa (By
Data sheet)
– Factor of safety=13.6 (By Calculation)
Plastic:
• FOR 150 Kg load
– Max. usage stress = 20.823 MPa (By analysis)
– Materials ultimate compression strength=124Mpa (By
Data sheet)
– Factor of safety=6 (By Calculation)
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4.5 Processability study in the Adjustable pylon:
Designers can avoid the blindness in the course of designing the plastic
parts and moulds and can also modify the design scheme purposefully by making
use of Moldflow software which is the most popular CAE simulation analysis
software. Engineers can simulate the mould test in the computer before
manufacturing the mould and predict the influence of molding technology
parameters on the appearance and performance of the plastic parts. They can find
out the best molding technology parameters finally. In this way, the plastic
injection mould is designed properly and repeated mould test and repair can be
avoided by means of Moldflow software. The cost of manufacturing mould can
be reduced greatly, the quality of the mould and the plastic parts can be improved
and the cycle of manufacturing mould can be shorten greatly.
4.5.1 Software Used
To analysis fibre orientation and the static structural of the proposed
adjustable pylon, the following softwares are used. The softwares are listed below
table 4.2
Meshing Autodesk Moldflow Plastics Insight 2013
Flow simulation Autodesk Moldflow Plastics Insight 2013
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The fibre filled thermoplastic material chosen for fill and packing
simulation of proposed adjustable pylon model. The plastic material are listed
below
 Delrin POM (Polyacetal) 20% glass filled.
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4.6 FLOW SIMULATION
For Moldflow simulation the mesh should be very fine compared to the
structural FEA mesh. The cad model of the adjustable pylon is imported in
Moldflow Insight 2013. By reducing the Global edge length, fine mesh has
created. Moldflow follow three types of mesh, as follows
1. Fusion mesh
2. 3D Mesh
3. Mid plane mesh
Among the above mentioned types of mesh, 3Dmesh is best optimum for
this analysis. The pivot with 2D surface mesh is converted into 3D mesh by
specifying number of layers in the thickness
 The appropriate material is chosen from the material data available in
the Moldflow Plastic Insight database.
 Molding temperature and injection location are specified.
 There are many analysis sequence available, choose appropriate
sequence as per the requirement. Molding Window & FILL+PACK
analysis are chosen for the interface.
4.6.1 Molding Window Analysis
Quick analysis to evaluate the optimum conditions that are required to
produce the part. It helps to determine variation you can have in mold
temperature, melt temperature, injection time and make a good quality part.
By performing molding window analysis it saves time by running very less
iterations and also gives indication how much the processes can vary and still
produce good and quality part.
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 Analysis for Polyacetal 20 % GF
Fig 4.23 Quality Plot of Adjusting Ring 4.24 Zone Plot of Adjusting Ring
Fig 4.25 Quality Plot of Bottom Part 4.26 Zone Plot of Bottom Part.
Fig 4.27 Quality Plot of Bottom Part 4.28 Zone Plot of Bottom Part.
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4.6.2 Fill Time
A Fill analysis calculates a flow front that grows through the part
incrementally from the injection location. The analysis continues until the
velocity/pressure switch-over point has been reached. This part was analysed
its fill time and time taken for the initial fill for each part to reach the
velocity/pressure switch over point. All three parts were completely filled
without short shot. The result of analysis of fill time is shown below.
 Analysis for POM – Polyacetal 20% glass filled.
Figure 4.29 Fill time – Adjusting Ring
Fill Time for Adjusting Ring is 1.553 secs.
Figure 4.30 Fill time – Bottom Part
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Fill Time for Bottom part is 7.518 secs.
Figure 4.31 Fill time – Top Part.
Fill Time for top part is 4.140 secs.
4.6.3 Pressure at V/P Switch over Point
The pressure at V/P Switch over point is shown below.
Figure 4.32 Press at switch over – Top Part
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Figure 4.33 Press at switch over – Bottom part.
Figure 4.34 Press at switch over – Adjusting Ring
The Pressure at V/P Switch over Point of Top part is 3.063 MPa, Bottom
part is 3.343 MPa and Adjusting Ring is 2.834 MPa.
4.6.4 Analysis of weld lines
The Weld lines result displays the angle of convergence as two flow
fronts meet. The presence of weld lines may indicate a structural weakness
and/or a surface blemish. The term “weld line” is often used to mean both weld
and meld lines. The only difference between them is the angle at which they are
formed; weld lines form at lower angles than meld lines. Weld lines can cause
structural problems and make the part visually unacceptable, but they are
unavoidable when the flow front splits and comes together around a hole, or if
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the part has multiple gates. Consider the processing conditions and position of
the weld lines to determine whether the weld lines will be high quality. Weld
and meld lines should be avoided, particularly weld lines in areas that require
strength or a smooth appearance, and the weld line regions of all the parts are
shown below.
Figure 4.34 Weld Lines – Bottom Part
Figure 4.36 Weld Lines - Adjusting Ring
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Figure 4.37 Weld Lines - Adjusting Ring
4.6.5 Orientation of fiber:
The fiber orientation level of the parts of adjustable pylon assembly is shown in
the figure below
Figure 4.38 Fibre orientation – Adjusting ring
Figure 4.39 Fibre Orientation – Bottom Part.
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Figure 4.40 Fibre Orientation – Top Part.
4.6.6 Shear Stress at Wall
The Shear stress at wall for all the components of adjustable plastic pylon
is shown in the below figure, and found to be in accordance with material value.
Figure 4.41 Shear Stress at wall – Top Part.
The maximum Shear stress at wall for top part is 0.2321 MPa, Bottom
Part is 0.2909 MPa and the adjusting ring is 0.7133 MPa .
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Figure 4.42 Shear Stress at wall – Bottom Part.
Figure 4.43 Shear Stress at wall – Adjusting ring.
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4.6.7 Air Traps:
The air trap regions of the components of the adjustable pylon assembly
is shown in below figure
Fig 4.44 Air Traps
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CHAPTER 5
PROTOTYPING OF ADJUSTABLE PYLON
The miniature rapid prototype of Adjustable plastic pylon assembly is
produced by using OBJECT 350 V, 3D printer with layer resolution of 16 microns
by giving the input file in the .stl (Stereo lithography file) of the individual parts
and then assembled. The miniature of the model is done by reducing its height by
half and then scaling it to 1:0.8 to reduce the prototype cost. The ultimate aim of
the prototype is to demonstrate the adjusting mechanism.
5.1 OBJET EDEN 350 V – 3D PRINTER
Fig 5.2 Objet – Eden 350 V
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Table 5.1 Details of prototype.
Machine Manufacturer: OBJECT, USA
Machine Model Eden, 350 V
Maximum Build Size 340 x 340x 200 mm
Materials Transparent, Opaque, Rubber like and flexible
Accuracy 0.1 – 0.3 mm
Selected Material Vero Blue
Support Material Vero Blue
Volume of Material used Material – 144 Grams
Support material – 142 Grams
Build Time for prototype 3 hours and 29 Minutes
The prototyped sample is taken out of the 3D printer and it is cleaned and
checked by assembling.
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5.2 Prototype of adjustable pylon
Fig 5.2 Individual Parts
Fig 5.3 Prototype in opened and closed position
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CONCLUSION
Thus the dimensions, properties, and the load acting on the steel pylon
is studied and the suitable plastic material is chosen as Polyacetal (POM)
with 20% Glass Filled considering all the features required. The feasibility
study of the adjusting mechanism is made, and a suitable mechanism using
threads is chosen for designing the pylon. The adjustable pylon is analysed
using ANSYS in the standard rest and lifted position. The design is then
optimised by considering all the required conditions, and a design is
finalised. The parts are then analysed for Processability using Moldflow
software. The adjustable pylon is prototyped to confirm the design.
The new adjustable plastic pylon eliminates the replacement, reduces
the weight of the conventional pylon. This also reduces the cost if mass
produced.
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REFERENCES:
1. Hugh G. watts,M.D ,Clinic prof. orthopedic surgery university of California
Los Angles.
2. Forester, C. S. Flying Colours. Little, Brown, 1938. Sabolich, John. You 're
Not Alone. Sabolich Prosthetic and Research Center, 1991. Shurr, Donald G. and
Thomas M. Cook. Pros the tics and Orthotics. Appleton and Lange, 1990
3. Design And Manufacturing Of A New Prosthetic Low Cost Pylon For Amputee
Prof.Dr .Muhsin J.Jweeg, Al-Nahrain University, Dr.Kadhim K. Resan, Al-
Mustansiriya University, Muhanad N. Mohammed
4. VETERANS ADMINISTRATION PROSTHETICS CENTER
RESEARCH REPORT, Anthony Staros, M .S .M.E., Director, Edward Peizer,
Ph . D., Deputy Director, Edited by Max Nacht, Technical Writer/Edito VAPC
5. Plastics Product Design by Donald D Peck.
6. Plastics Materials 7th
Edition by J A Brydson
7. www.prostheticclinic.com
8. Ms. OTTO BOCK India Ltd., Chennai.
9. Michael sepe, The Art and Science of Metal to Plastic Replacement, UL, 2007.
10. Abler www.ablersite.org
11. Clare goldsberry, Tim Peterson, Problems in Metal to Plastic Conversion of
Rain Master Case, Industrial molds group
12. Design And Manufacturing Of A New Prosthetic Low Cost Pylon For
Amputee, Journal of Engineering and Development, Vol. 14, No. 4, December
(2010) ISSN 1813-7822
85
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