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Design, Analysis & Optimization of Injection Mold for Production of Plastic
Safety Helmet
Thesis · October 2019
DOI: 10.13140/RG.2.2.17082.41922
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KATHMANDU UNIVERSITY
SCHOOL OF ENGINEERING
DEPARTMENT OF MECHANICAL ENGINEERING
PROJECT REPORT ON
DESIGN, ANALYSIS AND OPTIMIZATION OF INJECTION MOLD FOR
PRODUCTION OF PLASTIC SAFETY HELMET
In Partial Fulfillment of the Requirements for the
Bachelor’s Degree in Mechanical Engineering
Dilip Bhattrai Upadhyay (42090)
Nirajan Ghimire (42133)
Parbat Thapa (42115)
October 2019
© 2019
Dilip Bhattrai Upadhyay
Nirajan Ghimire
Parbat Thapa
AUTHORIZATION
I hereby declare that we are the author of the thesis.
I authorize the Kathmandu University to lend this thesis to other institutions or
individuals for the purpose of scholarly research. I further authorize the Kathmandu
University to reproduce the thesis by photocopying or by other means, in total or in part,
at the request of other institutions or individuals for the purpose of scholarly research.
___________________________________________
Dilip Bhattarai Upadhyay
___________________________________________
Nirajan Ghimire
___________________________________________
Parbat Thapa
October 2019
PROJECT EVALUATION
“Design, Analysis and Optimization of Injection Mold for Production of Plastic
Safety Helmet”
by
Dilip Bhattrai Upadhyay (42090), Nirajan Ghimire (42133), Parbat Thapa (42115)
This is to certify that I have examined the above Dissertation and have found that it is
complete and satisfactory in all respects, and that any and all revisions required by the
thesis examination committee have been made.
_____________________________
_____________________________
Prof. Dr. Bhola Thapa
Asst. Prof. Pratisthit Lal Shrestha
[Project Supervisor]
[Project Supervisor]
_________________________________________
Assoc. Prof. Dr. Daniel Tuladhar
Head of Department
Department of Mechanical Engineering
___________________________________________
Name:
Designation:
[External Supervisor]
October 2019
ACKNOWLEDGMENTS
We would like to express our deepest gratitude to the Department of Mechanical
Engineering, Kathmandu University for providing us with an opportunity to work on
“Design, Analysis and optimization of injection mold for the production of safety
helmet. We would like to give especial thanks to our supervisors, Professor Dr. Bhola
Thapa and Assistant Professor Pratisthit Lal Shrestha for their constant supervision
and support. Without their guidance, the project could never be completed.
We are extremely thankful to Design Lab for providing us space and working
environment throughout the project. Also special thanks goes to Polymer engineer Mr.
Biraj Dhungana for his guidance on material aspect and to visiting faculty member
from KU School of Arts, Mr. Tejas man Shakye.
Also we would like to express our sincerest of appreciations to Mr. Pallab Shrestha,
Mr. Abishek Karki, Sandhya Mishra and Rejsha Khoteja for for their technical and
moral support.
Finally, we wish to thank our parents for their love and encouragement, without whom
we would never have enjoyed so many opportunities.
i
TABLE OF CONTENTS
ACKNOWLEDGMENTS ............................................................................................... i
TABLE OF CONTENTS ............................................................................................... ii
LIST OF FIGURES ....................................................................................................... vi
LIST OF TABLES ......................................................................................................... x
ABSTRACT .................................................................................................................. xi
LIST OF ABBREVIATIONS ...................................................................................... xii
LIST OF SYMBOLS ...................................................................................................xiii
CHAPTER 1 INTRODUCTION .................................................................................... 1
1.1 Background........................................................................................................... 1
1.2 Problem Statement ................................................................................................ 2
1.3 Objectives ............................................................................................................. 2
1.4 Scope..................................................................................................................... 2
1.5 Limitation ............................................................................................................. 2
CHAPTER 2 LITERATURE REVIEW ......................................................................... 3
2.1 Injection Molding Machine .................................................................................. 3
2.1.1 Introduction ................................................................................................... 3
2.1.2 Components of molding machine .................................................................. 3
2.1.3 Injection Molding Process ............................................................................. 4
2.1.4 Defects in Injection Molding ......................................................................... 5
2.2 Injection Mold ...................................................................................................... 6
2.2.1 Mold Structure ............................................................................................... 7
2.2.2 Types of Mold ............................................................................................... 8
2.2.3 Mold Functions ............................................................................................ 11
2.2.4 Mold Standards ............................................................................................ 11
2.2.5 Fundamentals of Mold Development .......................................................... 14
2.3 Fundamentals of Mold Design ........................................................................... 15
ii
2.3.1 Uniform Wall Thickness ............................................................................. 15
2.3.2 Draft ............................................................................................................. 16
2.3.3 Parting Plane Design ................................................................................... 17
2.3.4 Core and Cavity Insert Creation .................................................................. 18
2.3.5 Mold Base Sizing ........................................................................................ 18
2.3.6 Cavity Layout .............................................................................................. 18
2.3.7 Mold Cavities Filing .................................................................................... 19
2.3.8 Viscous Flow ............................................................................................... 19
2.3.9 Feed System Layout .................................................................................... 19
2.3 Mold Components Design Analysis ................................................................... 20
2.3.1 Cavity Filling Analysis ................................................................................ 20
2.3.2 Feed System Design .................................................................................... 21
2.3.3 Feed System Analysis.................................................................................. 21
2.3.4 Gating Design .............................................................................................. 22
2.3.5 Cooling System Design ............................................................................... 23
2.3.6 Shrinkage and warpage................................................................................ 25
2.3.7 Ejection system design ................................................................................ 25
2.4 Design of Experiment ......................................................................................... 27
2.4.1 Terminologies in Design of Experiment (DoE) .......................................... 28
2.4.2 Full Factorial Design: .................................................................................. 29
2.4.3 Fractional factorial design ........................................................................... 29
2.5 Taguchi Method .................................................................................................. 29
2.5.1 Taguchi loss function .................................................................................. 30
2.6 Tools Used .......................................................................................................... 31
2.6.1 Microsoft Visual Basic ................................................................................ 31
2.6.2 MoldEx3D ....................................................................................................... 31
2.6.3 IMOLD V13 ................................................................................................ 31
2.7 Plastic Raw material ........................................................................................... 36
2.7.1 Material Selection Process: ......................................................................... 36
2.7.3 Properties of HDPE ..................................................................................... 38
iii
2.8 Mold Material ..................................................................................................... 39
2.9 Mold development process ................................................................................. 41
2.9.1 CNC ............................................................................................................. 41
2.9.2 Lathes .......................................................................................................... 42
2.9.3 Plasma cutters .................................................................................................. 42
2.9.5 CNC Machine Programming ....................................................................... 43
2.9.6 UG CAM ..................................................................................................... 43
2.10 Mold Installation and Trial test ........................................................................ 43
2.11 Molding Defects ............................................................................................... 45
2.12 Basic Mold Maintenance [19] .......................................................................... 50
More Advanced Mold Maintenance ......................................................................... 51
CHAPTER 3 METHODOLOGY ................................................................................. 53
3.1 Designing improved safety helmet ..................................................................... 54
3.2 Developing CAD model of sample model for experiment ................................. 54
3.3 Analyzing sample product for mold development ............................................. 54
3.4 DOE optimization using Taguchi method .......................................................... 57
3.5 Interpretation of Results ..................................................................................... 57
3.6 Developing user interface to automate mold design process.............................. 57
3.7 Mold Design’s Calculation Parameters .............................................................. 58
3.8 Steps of CAD Design of Mold............................................................................ 61
3.9 Product Development ......................................................................................... 62
CHAPTER 4 RESULTS AND DISCUSSION ............................................................ 63
4.1 Product Design ................................................................................................... 63
4.2 Calculations ........................................................................................................ 63
4.3 Wizard Development for Calculation ................................................................. 66
4.4 Mold Design ....................................................................................................... 67
4.5 Analysis in MoldEx3D ....................................................................................... 75
4.4.1 Solver parameter setup ................................................................................ 75
4.4.3 Analysis ....................................................................................................... 77
iv
4.4.4 Process Condition Optimization .................................................................. 81
4.4.5 Design of Experiment .................................................................................. 86
4.4.5 DOE Optimized Results .............................................................................. 90
4.6 Model and Prototype development ..................................................................... 93
4.8 Cost Calculation and Analysis ............................................................................ 95
4.8.1 Cost for Mold development in Nepal .......................................................... 95
4.8.2 Cost of Mold if imported from India ........................................................... 95
4.8.3 Cost of Plastic Product ................................................................................ 95
4.8.4 Cost of helmet from fiber glass ................................................................... 96
CHAPTER 5 CONCLUSION ...................................................................................... 97
5.1 Calculation wizards’ development ..................................................................... 97
5.2 Conclusion on Mold Design ............................................................................... 97
5.3 Analysis and Optimization part .......................................................................... 97
5.4 Prototype development and market feedback ..................................................... 97
RECOMMENDATION ................................................................................................ 98
REFERENCES ............................................................................................................. 99
APPENDIX A ............................................................................................................ 102
Code of GUI wizard ............................................................................................... 102
CAD Drawing of components ................................................................................ 104
v
LIST OF FIGURES
Figure 1 Injection Molding Machine [4] ........................................................................ 3
Figure 2 Components of Injection Molding Machine [4] .............................................. 4
Figure 3 Stages in injection molding [4] ........................................................................ 5
Figure 4 Fish pond diagram [4] ...................................................................................... 6
Figure 5 Injection Mold .................................................................................................. 7
Figure 6 Structural View of two plate mold [4] ............................................................. 8
Figure 7 View of molding ejecting from injection mold [4] .......................................... 8
Figure 8 Two plate mold [4] ........................................................................................... 9
Figure 9 Section of the open three plate mold [4] ........................................................ 10
Figure 10 Mold Functions [4]....................................................................................... 12
Figure 11 Mold Base [4]............................................................................................... 12
Figure 12 Mold development process [5] ..................................................................... 15
Figure 13 System architecture for mold design [5] ...................................................... 16
Figure 14 Mold Opening Direction [5] ........................................................................ 18
Figure 15 Feed System Layout [4] ............................................................................... 20
Figure 16 Edge Gate [4] ............................................................................................... 22
Figure 17 Pin Point Gate designed with the inverted sprue [4] .................................... 23
Figure 18 Cooling channel in Conformal cooling [4] .................................................. 25
Figure 19 Side view of opening mold [4] ..................................................................... 26
Figure 20 Diagram showing where Design of Experiments can be used for various
functions [7].................................................................................................................. 28
Figure 21 Overview of IMOLD [15] ............................................................................ 32
Figure 22 4-cavity layout [15] ...................................................................................... 33
Figure 23 Mold base [15] ............................................................................................. 34
Figure 24 Cavity and core for a phone cover [15]........................................................ 34
Figure 25 Slider ............................................................................................................ 35
Figure 26 Cooling channels on a mold base ................................................................. 35
Figure 27 Ejector .......................................................................................................... 36
Figure 28 Modulus vs frequency graph ........................................................................ 38
vi
Figure 29 Mechanical, Thermal and heat capacity of HDPE [17] ............................... 38
Figure 30 Flow Lines [20] ............................................................................................ 45
Figure 31 Burn Marks [20] ........................................................................................... 46
Figure 32 Warping [20] ................................................................................................ 47
Figure 33 Vacuum Voids [20] ...................................................................................... 48
Figure 34 Sink Marks [20] ........................................................................................... 49
Figure 35 Weld Lines ................................................................................................... 50
Figure 36 Inspection of Injection Mold ........................................................................ 52
Figure 37 Research approach ....................................................................................... 53
Figure 38 Sample product ............................................................................................ 54
Figure 39 Analysis flow ............................................................................................... 55
Figure 40 Meshing of sprue and runner ....................................................................... 56
Figure 41 Gate filling analysis ..................................................................................... 56
Figure 42 Optimized melt flow time ............................................................................ 56
Figure 43 Optimized Melt temperature ........................................................................ 56
Figure 44 Tabulated data of Taguchi parameters ......................................................... 57
Figure 45 CAD Design of Safety Helmet ..................................................................... 63
Figure 46 Helmet dimension in mm ............................................................................. 63
Figure 47 GUI Interface made using Visual studio ...................................................... 66
Figure 48 Calculation of parameters from developed wizard ..................................... 67
Figure 49 Parting plane of helmet ................................................................................ 67
Figure 50 Core and Cavity extraction .......................................................................... 68
Figure 51 Drawing of Core........................................................................................... 68
Figure 52 Drawing of Cavity ........................................................................................ 68
Figure 53 Assembly of designed mold ......................................................................... 69
Figure 54 Assembly view of mold base ....................................................................... 69
Figure 55 CAD Design of (a) moving half (b) fixed half ............................................ 70
Figure 56 CAD Design of mold base ........................................................................... 70
Figure 57 Drawing of mold base .................................................................................. 71
Figure 58 Drawing of Sprue bushing ........................................................................... 71
vii
Figure 59 Drawing of locating ring .............................................................................. 72
Figure 60 (a) Design of Leader pin (b) Leader pin bushing ........................................ 72
Figure 61 Cooling circuit 1, 2 and 3 ............................................................................. 72
Figure 62 Solver Setup of full scale mold .................................................................... 76
Figure 63 Thickness analysis of helmet ....................................................................... 77
Figure 64 Analysis of gate contribution ....................................................................... 77
Figure 65 Analysis of melt front time .......................................................................... 78
Figure 66 Analysis of filling pressure .......................................................................... 79
Figure 67 Analysis of filling shear stress ..................................................................... 79
Figure 68 Analysis of volume shrinkage ...................................................................... 80
Figure 69 Analysis of total warpage displacement....................................................... 81
Figure 70 Analysis of warpage displacement in z axis ................................................ 81
Figure 71 Graph of volumetric shrinkage versus iteration ........................................... 82
Figure 72 Results of volumetric shrinkage ................................................................... 83
Figure 73 Results of total warpage displacement ......................................................... 83
Figure 74 Results of filling melt front temperature ...................................................... 84
Figure 75 Results of filling melt front time .................................................................. 84
Figure 76 Results of filling pressure ............................................................................ 85
Figure 77 Results of shear stress .................................................................................. 85
Figure 78 Factor response plot ..................................................................................... 88
Figure 79 Relation of melt temperature with S/N ratio ................................................ 89
Figure 80 Sensitive analysis of melt temperature ......................................................... 89
Figure 81 Response surface graph of packing time vs warpage .................................. 90
Figure 82 Optimized result of volumetric shrinkage .................................................... 90
Figure 83 Optimized result of shear stress ................................................................... 90
Figure 84 Optimized result of filling melt front temperature ....................................... 91
Figure 85 Optimized result of melt front time.............................................................. 91
Figure 86 Optimized result of volume shrinkage ......................................................... 91
Figure 87 Optimized result of warpage ........................................................................ 92
Figure 88 3D Printed model of core and cavity ........................................................... 93
viii
Figure 89 3D printed model of full scale safety helmet ............................................... 93
Figure 90 Top view of fiber glass safety helmet .......................................................... 93
Figure 91 Side view of fiber glass safety helmet ......................................................... 94
ix
LIST OF TABLES
Table 1 Solver Parameter Setup ................................................................................... 75
Table 2 Operating parameters for injection mold of safety helmet .............................. 76
Table 3 Setup condition for process condition optimization ........................................ 82
Table 4 Design of experiment variable and range ........................................................ 86
Table 5 Design of experiment quality criteria .............................................................. 86
Table 6 Taguchi L9 (3^4) Orthogonal array ................................................................ 86
Table 7 DOE Results .................................................................................................... 87
Table 8 Factor effects on warpage................................................................................ 87
Table 9 ANOVA Method for analyzing quality factor ................................................ 88
Table 10Market feedback ............................................................................................. 94
x
ABSTRACT
Injection Molding is rapid method for production of Plastic Parts. Its complexity and
the enormous amount of process parameter manipulation during real time production
create very intense effort to maintain the process under control. This project is primarily
concerned towards designing, analyzing and finding optimal set of process parameters
on the molding machine and auxiliary equipment and other subsystem provided.
The main goal in injection molding process is to improve the quality of injection molded
parts, together with reducing the cycle time and production cost. The design of this
product is done in Solidworks, which is simulated using MoldEx3D. Design of
experiment (DoE) is employed and Taguchi orthogonal array is used to find out the most
significant process variables affecting the injection molding. High Density Polyethylene
(HDPE) have been used as helmet material. After several simulations on the MoldEx3D
and using design of experiment, optimum parameter value for the injection molding of
designed safety helmet was obtained.
xi
LIST OF ABBREVIATIONS
ABS
Acrylonitrile Butadiene Styrene
ANOVA
Analysis of Variance
CAD
Computer Aided Design
CATIA
Computer Aided Three-Dimensional Interactive Application
DOE
Design Of Experiment
FDA
Factorial Design Analysis
GA
Genetic Algorithm
HDPE
High-Density Polyethylene
LDPE
Low Density Polyethylene
KE
Kinetic Energy
KU
Kathmandu University
MPa
Mega Pascal
OA
Orthogonal Arrays
PC
Polycarbonate
PU
Polyurethane
PVC
Poly Vinyl Chloride
SOA
School of Arts
SOE
School of Engineering
TDS
Top Dead Centre
xii
LIST OF SYMBOLS
B
Breadth of the object
[m]
C
Absolute component of velocity
[m/s]
D
Diameter of the shaft
[m]
E
Kinetic energy
[Joules]
Pa
Actual power output
[kW]
Q
Flow rate
[m3/s]
ρ
Density of liquid
[m3/kg]
xiii
CHAPTER 1 INTRODUCTION
1.1 Background
Manufacturing industry in Nepal is a challenging field as it is surrounded by two
giant nations India and China which are major competitors in field of manufactured
goods in the global market regarding price, design, quality and volume [1]. Despite
this, many manufacturing firms are in operation producing different parts ranging
from small plastic parts to different construction parts. Most of the plastic safety
helmets that we see around us are made using injection molding technique. This
project is focused in designing a better safety helmet than existing one and crating
its mold for mass production, analyzing it by running simulation and optimizing the
mold using DoE method [2].
Injection molding is a common method for mass production and is often preferred
over other processes, given its capability to economically make complex parts to
tight tolerances. Injection molding has been growing in steady rate since its
beginning. This technique has been pivotal in mass production of simple items to
complicated parts in medical and aerospace industry. Plastic injection molding is a
versatile process and plays a major role in today’s plastic manufacturing industries
[3].
Design of Experiment (DoE) is a tool for planning, conducting, analyzing and
interpreting experiments so that we can reach to the desired conclusion efficiently,
effectively and economically. So, in this research work Design of Experiment (DoE)
technique will be used using Taguchi orthogonal array using simulation as well as
Experimental verification. MoldEx3D analyses are carried out by utilizing the
combination of process parameters based on variable influences then responses. This
process uses Taguchi method to determine which variables have most influences in
specific criteria, and then run extensive factorial experiments on most significant
input variables to determine how they impact part quality. Solidworks is used to
design the safety helmet, MoldEx3D for the Simulation of Injection molding process
and for Design of Experiment.
1
1.2 Problem Statement
Type 1:

Injection melded products are manufactured without design standard, design
modelling, analysis and only with intuitive design

No fixed calculation set (data book) are used for ease to design mold’s
process and parameters

Commissioning process of injection mold is trial and error and defects are
uncertain
Type 2:

Problem in comfort, air-vent, quality in plastic safety helmets
1.3 Objectives

To analyze and optimize the injection mold parameters and process
conditions of plastic safety helmet

To develop a parameters calculation user interface wizard for injection
molding using visual basic

To design and draft full scale injection mold of plastic safety helmet

To 3D print safety helmets, cast with fiber glass and 3D print it’s core and
cavities
1.4 Scope

Calculation wizard developed from visual studio will only work for two plate
mold

Simulations and analysis is done one only one full scale injection mold
1.5 Limitation
The main limitations of the project are:

Analysis of mold in MoldEx3D will be limited to it’s main parameters and
components

Casted product through fiber glass is limited to verification of the designed
part and not for it’s regular use

3D printed mold will be limited as a model and not for its actual use
2
CHAPTER 2 LITERATURE REVIEW
Literature review was broadly carried out to achieve three major objectives: Product
development, Mold design, analysis and optimization, and user interface
development to facilitate ease and accuracy in mold designing process.
2.1 Injection Molding Machine
2.1.1 Introduction
In the current manufacturing industry, injection molding is one of the most common
processes for plastic parts production. There are generally three steps in the injection
molding process:
 Plasticizing the material which then flows into the mold under pressure
 Solidifying molten plastic into the desired objects by the confines of the mold
components
 Opening the mold to eject the solidified plastic part
2.1.2 Components of molding machine
Figure 1 Injection Molding Machine [4]
3
Hopper: Raw material is supplied in the form of small pellets. Main purpose of the
hopper is to hold these pellets. These pellets are fed into the screw barrel through
hopper throat by the aid of gravity.
The Barrel: Barrel Supports screw or plunger. Together with screw, it provides the
bearing surface where shear is imparted to the plastic materials. In these particular
research machine four stages of heating is provided to the barrel.
The screw: Screw is helical and hard steel shaft that rotates within the barrel to
mechanically process and advance the molten plastic being prepared. The Screw
consists of three zones – The feeding zone, the Transition zone and the metering
zone. While the outside diameter of the screw remains constant, the depth of the
flights on the reciprocating screw decreases from the feed zone to the beginning of
the metering zone.
The Nozzle: The nozzle connects the barrel to the sprue bushing of the mold and
forms a seal between the barrel and the mold.
Figure 2 Components of Injection Molding Machine [4]
2.1.3 Injection Molding Process
Injection molding process begins with feeding the pallets into the hopper. These
pallets are subsequently passed into the barrel where they are heated, melted and
made to flow. Thus obtained molten material is injected at high pressure into the
mold, where it is held under pressure until it is removed in solid state duplicating the
cavity of the mold. [4]
Different stages in injection molding process
4
1. Plasticization: The PVC pallets in the hopper are heated to the optimum
temperature and made to flow in the plasticator.
2. Injection: Controlled volume of molten PVC is then supplied, with the aid
of screw barrel into the closed mold under pressure. Programmable Logic
controller (PLC) is provided to control the pressure, temperature and cooling
process during the course of injection process. Solidification of molten
material starts inside the mold. Injected molten PVC is kept under pressure
for the specified time in order to prevent the volumetric shrinkage and back
flow of the injected material during the course of solidification.
3. Packing/Cooling: Cooling channels are provided in the molding machine,
which are controlled through PLC. Injected PVC part is cooled until the part
is sufficiently rigid before being ejected.
4. Demold/ Ejection: Thus, obtained injection molded part is ejected and the
mold is closed again so that we can start next molding cycle
Figure 3 Stages in injection molding [4]
2.1.4 Defects in Injection Molding
The main causes of defect in injection molding can be because of mold design,
process parameters, machine, operator or material. Details of the process parameters
which directly affect the injection molding process are shown in fish bone diagram.
5
Figure 4 Fish pond diagram [4]
2.2 Injection Mold
A basic mould consists of two plates that form an impression into which molten
material is injected. The surfaces on the two plates (core and cavity) that meet to
form a seal when the mould closes are the parting surfaces. The pair of opposite
directions along which the two plates of the mould separate are the parting lines.
Recesses or projections on the moulded piece that prevent its removal from the
mould along the parting directions are called undercuts. Depending on the types of
undercut, different mechanical devices such as sliders and lifters are used to help
clear the undercut. In general, core, cavity, slider(s), and lifter(s) form the
fundamental sub-assembly of a complete injection mould. In addition, an injection
mould includes the following components:
 runners and gates
 mould base
 cooling pipes
 ejection pins
 standard parts, such as screws and location rings
The arrangement of these components is based on the number of cavities and their
layout in the injection mould. Figure 1 shows a complete injection mould in a 3-D
exploded view [5].
6
Figure 5 Injection Mold
2.2.1 Mold Structure
Mold is constructed of a number of plates bolted together with socket head cap
screws. These plates commonly include the top clamp plate, the cavity insert retainer
plate or “A” plate, the core insert retainer plate or “B” plate, a support plate, and a
rear clamp plate or ejector housing. To hold the mold in the injection molding
machine, toe clamps are inserted in slots adjacent to the top and rear clamp plates
and subsequently bolted to the stationary and moving platens of the molding
machine. A locating ring, usually found at the center of the mold, closely mates with
an opening in the molding machine’s stationary platen to align the inlet of the mold
to the molding machine’s nozzle. The use of the locating ring is necessary for at least
two reasons. First, the inlet of the melt to the mold at the mold’s sprue bushing must
mate with the outlet of the melt from the nozzle of the molding machine. Second,
the ejector knockout bar(s) actuated from behind the moving platen of the molding
machine must mate with the ejector system of the mold. [4]
7
Figure 6 Structural View of two plate mold [4]
Figure 7 View of molding ejecting from injection mold [4]
2.2.2 Types of Mold
There are basically two types of mold:

Two plates mold
The simplest and most reliable mold design is the two-plate tool. This is because
it normally has the fewest number of moving parts and is straight forward
to manufacture and run in production. Because of its simpler construction it is
usually cheaper to manufacture than more complex designs.
8
Given the simplicity of its design and manufacture, mold design engineers should
make sure that all possibilities of using a two-plate design have been exhausted
before other more complex designs are considered. This means that the component
should be examined carefully to see whether any undercut features could be
designed out of the part. Screw threads are a prime example of this point. Threads
normally require split tools, collapsible cores or more complex automatic
unscrewing devices, but sometimes they can be jumped out of the cavity. A typical
two plate mold is shown in figure below. [4]
Figure 8 Two plate mold [4]

Three plates mold, multi cavity family mold
Unlike two plate mold, three plate mold provides a third plate that floats between
the mold cavities and the top clamp plate. The three-plate mold is so named since it
provides a third plate that floats between the mold cavities and the top clamp plate.
Figure 8 shows a section of a three- plate mold that is fully open with the moldings
still on the core inserts. As shown in Fig. 8 the addition of the third plate provides a
second parting plane between the “A” plate assembly and the top clamp plate for the
provision of a feed system that traverses parallel to the parting plane. During
molding, the plastic melt flows out the nozzle of the molding machine, down the
sprue bushing, across the primary runners, down the sprues, through the gates, and
into the mold cavities. The feed system then freezes in place with the moldings.
When the mold is opened, the molded cold runner will stay on the stripper plate due
to the inclusion of sprue pullers that protrude into the primary runner. [4]
9
Figure 9 Section of the open three plate mold [4]

Hot Runner, Multi-gated, Single Cavity Mold
The term “hot runner” is used since the feed system is typically heated and so
remains in a molten statue throughout the entire molding cycle. As a result, the hot
runner does not consume any material or cycle time associated with conveying the
melt from the molding machine to the mold cavities. The hot runner system includes
a hot sprue bushing, a hot manifold, and two hot runner nozzles as well as heaters,
cabling, and other components related for heating. Hot runner system can facilitate
the molding of thinner parts with faster cycle times than either two-plate or three
plate molds, while also avoiding the scrap associated with cold runners. [4]
Table 1 Comparison between types of mold [4]
Performance measure
Two plate
Three plate
Hot runner
Gating flexibility
Poor
Excellent
Excellent
Material consumption
Good
Poor
Excellent
Cycle times
Good
Poor
Excellent
Initial investment
Excellent
Good
Poor
Start-up times
Excellent
Good
Poor
Maintenance cost
Excellent
Good
Poor
10
2.2.3 Mold Functions
The injection mold is a complex system that must simultaneously meet many
demands imposed by the injection molding process. The primary function of the
mold is to contain the polymer melt within the mold cavity so that the mold cavity
can be completely filled to form a plastic component whose shape replicates the
mold cavity. A second primary function of the mold is to efficiently transfer heat
from the hot polymer melt to the coolant flowing through the mold, such that
injection molded products may be produced as uniformly and rapidly as possible. A
third primary function of the mold is to eject the part from the mold in an efficient
and consistent manner without imparting excessive stress to the moldings.
These three primary functions—contain the melt, transfer the heat, and eject the
molded part(s)—also place secondary requirements on the injection mold. Figure 10
provides a partial hierarchy of the functions of an injection mold. For example, the
function of containing the melt within the mold requires that the mold: [4]

Resist displacement under the enormous forces that will tend to cause the
mold to open or deflect. Excessive displacement can directly affect the
dimensions of the moldings or allow the formation of flash around the
parting line of the moldings. This function is typically achieved through the
use of rigid plates, support pillars, and interlocking components.

Guide the polymer melt from the nozzle of the molding machine to one or
more cavities in the mold where the product is formed. This function is
typically fulfilled through the use of a feed system and flow leaders within
the cavity itself to ensure laminar and balanced flow.
2.2.4 Mold Standards
The designs depicted in this chapter were designed from computer aided design
(CAD) files of mold bases from DME Company. A “mold base” is essentially a
blank mold or template design that includes all the plates, pins, bushings, and other
components that may be purchased as a fully assembled system and modified for a
specific molding application. Figure 1.10 is provided as the prototypical mold base.
This particular design [2] was made in 1944 by Ivar Quarnstrom, the founder of
Detroit Mold Engineering (DME Company). It is remarkable how similar the design
of figure 6 is to that of figure 11 and other designs commonly observed today.
11
Figure 10 Mold Functions [4]
Figure 11 Mold Base [4]
There are many benefits for mold designs that rely on the use of the standard mold
bases. These include:

First and foremost, the design of the mold base including its many detailed
fits and tolerances would require extensive analysis and care in
manufacturing. In other words, most mold designers and mold makers would
12
have difficulty designing as good a mold base at as low a cost as a standard
product that could be purchased off the shelf with minimal risk and lead
times.

Second, the use of standards provides for potential interoperability of mold
bases and mold base components across molding applications as well as
different molding facilities. For example, a mold designer may wish to
provide six identical molds so that two copies of each mold are operable in
Europe, the Americas, and Asia. The use of a mold base not only supports
the mold design with respect to a CAD library, but also the provision of the
replacement components using the mold base supply chain should mold
components become damaged or worn.

Third, the use of a standard mold base supports for more rapid
communication of the mold design with other industry practitioners. For
example, consider the use of a mold base with a sprue bushing compared to
a custom design that threads the molding machine nozzle directly into a mold
cavity. The use of the sprue bushing may increase the component count, but
supports ready replacement and standard interfacing to a variety of molding
machines. Conversely, the directly threaded nozzle eliminates the sprue
altogether and so provides better molding productivity, but requires more
skill in designing and operation. There is certainly the opportunity for mold
designers, mold makers, and molders to outperform mold bases using custom
mold designs from scratch. These masters have developed significant
experience and insight into their molding applications that motivates and
supports their custom designs.
For all these reasons, mold designers and makers in developed countries, where labor
is relatively expensive compared to the mold materials and components, will
typically use standard mold bases. There are many suppliers of mold bases who
compete with different strategies including material technology, quality, lead time,
cost, size, breadth of product line, unit systems, regional distribution, and others.
Product designers, mold designers, mold makers, and molders should verify what
system of suppliers is to be used in a given application.
13
2.2.5 Fundamentals of Mold Development
First, the mold designer will lay out the mold design by specifying the type of mold,
the number and position of the mold cavities, and the size and thickness of the mold.
After- wards, each of the required sub-systems of the mold is designed, which
sometimes requires the redesign of previously designed subsystems. For example,
the placement of ejector(s) may require a redesign of the cooling system while the
design of the feed system may affect the layout of the cavities and other mold
components. Multiple design iterations are typically conducted until a reasonable
compromise is achieved between size, cost, complexity, and function.
To reduce the development time, the mold base, insert materials, hot runner system,
and other components may be ordered and customized as the mold design is being
fully detailed. Such concurrent engineering should not be applied to unclear aspects
of the design. However, many mold makers do order the mold base and plates upon
confirmation of the order. As a result of concurrent engineering practices, mold
development times are now typically measured in weeks rather than months.
Customers have traditionally placed a premium on quick mold delivery, and mold
makers have traditionally charged more for faster service. With competition,
however, customers are increasingly requiring guarantees on mold delivery and
quality, with penalties applied to missed delivery times or poor quality levels.
After the mold is designed, machined, polished, and assembled, molding trials are
performed to verify the basic functionality of the mold. If no significant deficiencies
are present, the moldings are sampled and their quality assessed relative to
specifications. Usually, the mold and molding process are sound but must be
tweaked to improve the product quality and reduce the product cost. However,
sometimes molds include “fatal flaws” that are not easily correctable and may
necessitate the scrapping of the mold and a complete redesign. [6]
14
Figure 12 Mold development process [5]
2.3 Fundamentals of Mold Design
A detailed review of the plastic part design should be conducted prior to the design
and manufacture of the injection mold. The design review should consider the
fundamentals of plastic part design, as well as other concerns related specifically to
mold design.
2.3.1 Uniform Wall Thickness
Parts of varying wall thickness should be avoided due to reasons related to both cost
and quality. The fundamental issue is that thick and thin wall sections will cool at
different rates: thicker sections will take longer to cool than thinner sections. When
ejected, parts with varying wall thickness will exhibit higher temperatures near the
thick sections and lower temperatures near the thin sections. These temperature
differences and the associated differential shrinkage can result in significant
15
geometric distortion of the part given the high coefficient of thermal expansion for
plastics. Extreme differences in wall thicknesses should generally be avoided if at
all possible since internal voids may be formed internal to the part due to excessive
shrinkage in the thick sections even with extended packing and cooling times.
Figure 13 System architecture for mold design [5]
2.3.2 Draft
Draft refers to the angle of incline placed between the vertical surfaces of the plastic
moldings and the mold opening direction. Draft is normally applied to facilitate
ejection of the moldings from the mold. Product designers frequently avoid the
application of significant draft, since it alters the aesthetic form of the design and
16
reduces the molding’s internal volume. Even so, draft is commonly applied to plastic
moldings to avoid ejection issues and extremely complex mold designs.
Draft angles on ribs must be carefully specified. In the previous rib design shown in
figure 13 for instance, a 2° draft angle was applied to facilitate the ejection of the
molded part from the mold. In terms of product functionality, a lesser draft angle
may be desired since this allows for taller and thicker ribs with greater stiffness.
Unfortunately, lower draft angles (such as ½ or 1°) may cause the part to excessively
stick in the mold.
2.3.3 Parting Plane Design
The parting plane is the contact surface between the stationary and moving sides of
the mold. The primary purpose of the parting plane is to tightly seal the cavity of the
mold and prevent melt leakage. This seal is maintained through the application of
literally tons of force (hence the term “clamp tonnage”) that are applied normal to
the parting plane. While the term “parting plane” implies a flat or planar surface, the
parting plane may contain out-of-plane features. Prior to determining the parting line
and designing the parting plane, the mold designer must first determine the mold
opening direction.
There are two factors that govern the mold opening direction:

First, the mold cavity should be positioned such that it does not exert undue
stress on the injection mold. The mold cavity is typically placed with its
largest area parallel to the parting plane. This arrangement allows the mold
plates, already being held in compression under the clamp tonnage, to resist
the force exerted by the plastic on the surfaces of the mold cavity.

Second, the mold cavity should be positioned such that the molded part can
be ejected from the mold. A typical molded part is shaped like a five-sided
open box with the side walls, ribs, bosses, and other features normal to its
largest area. If so, then the part ejection requirement again supports the mold
opening direction to be normal to the part’s largest projected area.
17
Figure 14 Mold Opening Direction [5]
2.3.4 Core and Cavity Insert Creation
With the definition of the parting plane and all necessary shut-offs, the core insert
and the cavity insert have been completely separated. To create the cavity and core
inserts, the length, width, and height of the inserts must be defined. Cavity and core
insert sizing guidelines are described that have been developed so that the length and
width of the cavity and core inserts are large enough to:

enclose the cavity where the part is formed,

withstand the forces resulting from the melt pressure exerted upon the area
of the cavity,

contain the cooling lines for removing heat from the hot polymer melt, and

contain other components such as retaining screws, ejector pins, and others

cavities placed around a circle
2.3.5 Mold Base Sizing
The size of the mold base is determined primarily by the area required to
accommodate all the cavity inserts per the designed cavity layout. A primary issue,
however, is the potential for conflict between the placements of the cavities and other
mold components (such as leader pins, guide bushings, and others). Furthermore,
there is the potential for conflict between cavity support systems (such as cooling
lines, ejector pins, support pillars, etc.) and other mold components (such as leader
pins, guide bushings, and others). Due to these conflicts, mold bases are often sized
larger than what would first be considered.
2.3.6 Cavity Layout
The goal of cavity layout design is to produce a mold design that is compact, is easy
to manufacture, and provides molding productivity. If a single cavity mold is being
designed, then the cavity is typically located in the center of the mold, though gating
18
requirements may necessitate placing the mold cavity off center. For multicity
molds, there are essentially three fundamental cavity layouts:

cavities placed along one line

cavities placed in a grid
2.3.7 Mold Cavities Filing
The part and mold design must be developed such that the mold cavity can be
completely filled by the polymer melt at workable melt pressures. For this reason,
filling analysis of the mold cavity should be performed to verify the part wall
thickness for a given material and assist in the gate selection and processing
conditions. Modern molding machines can typically deliver injection pressures of
approximately 200 MPa (30,000 psi). However, a lower melt pressure should be
assumed for filling the cavity to allow for:

a lower required clamp tonnage,

reasonable pressure drop in the feed system, and

a factor of safety for errors in assumptions
2.3.8 Viscous Flow
To analyze the polymer flow, it is necessary to understand the relationship between
the shear stress, shear rate, and viscosity [1]. The shear stress, 𝜏, is a measure of how
much force per unit area is being exerted by the fluid as it flows.
The shear rate, 𝛾, is a measure of the rate at which the melt velocity changes. The
shear stress is related to the shear rate through the viscosity, h, which is a measure
of the fluid’s resistance to flow
𝜏 = 𝜂.𝛾
2.3.9 Feed System Layout
A series layout of cavities can most compactly deliver the polymer melt to many inline cavities through a single primary runner with many subsequent runners leading
to individual cavities. Such a scenario is shown in figure 14. Unfortunately, since
the secondary runners branch off at different locations down the length of the
primary runner, the pressure drop along the length of the primary runner will cause
lower flow rates to be delivered to cavities further from the sprue. This no uniform
19
flow can be abated somewhat by reducing the diameters of the secondary runners
closer to the sprue as shown by the secondary off the right primary runner in figure
14.
Figure 15 Feed System Layout [4]
2.3 Mold Components Design Analysis
2.3.1 Cavity Filling Analysis
Mold filling analysis is useful to ensure that the mold cavity can be filled with the
plastic melt given the melt pressure that can be delivered by the molding machine.
Typically, the melt pressure required to fill the cavity is less than 100 MPa (about
15,000 psi) even though most modern machines can supply twice this amount. This
safety margin between the required and available melt pressures provides an
allowance for the pressure drop in the feed system, and also ensures that the mold
can be filled given possible variances in the material proper- ties or molding process.
Cavity filling analysis is also performed to ensure that the filling pressures are not
too low, since very low melt pressures are indicative of a poor molded part design
or improper processing conditions. Excessively thick wall sections will result in low
pressures, excessive material costs, and extended cycle times. In such cases, the
nominal wall thickness should be decreased and ribs or other features used to provide
the necessary strength and stiffness. In some cases, very low melt pressures can
indicate improper filling time, mold temperature, or melt temperature. These
processing conditions should be adjusted to reduce the processing time and cost at
the expense of higher melt pressures.
Following are some main Objectives of cavity filling analysis:
20

Ensure complete filling of mold cavities

Avoid uneven filling and over-packing

Control the melt flow
2.3.2 Feed System Design
The purpose of the feed system is to convey the polymer melt from the molding
machine to the mold cavities. The best feed system design is a function of the
production volume, availability of molding pressure, and level of allowable
investment.
Objectives of Feed system design:

Conveying the polymer Melt from Machine to Cavities

Impose Minimal Pressure Drop

Consume Minimal Material

Control Flow Rates
2.3.3 Feed System Analysis
Mold designers should verify that the mold can be filled given the cavity geometry
and the material properties. However, the filling analyses require the processing
conditions, including the melt temperature and either the linear velocity or
volumetric flow rate of the melt. It is recommended that mold designers assume a
melt temperature in the middle of the melt temperature range recommended by the
material supplier, since this provides the molder with some freedom to adjust
temperatures up or down to correct molding problems or reduce cycle time
Feed System should:

Impose a minimal pressure drop, typically no greater than 50 % of the
pressure required to fill the mold cavities or 50 MPa;

Consume a minimum amount of material, typically no greater than 30 % of
the volume of the mold cavities for cold runner molds or 100 % of the volume
of the mold cavities for hot runner molds; and

Not extend the mold cooling time.
Based on the analysis, Feed System is design follow following steps:

Determine type of Feed system

Determine Feed System Layout
21

Estimate pressure drop

Calculate Runner volume

Optimize Runner diameter

Balance flow Rates

Estimate the Runner cooling time
2.3.4 Gating Design
Gates provide the important function of connecting the runner to the mold cavity,
and initiating the flow of the melt into the cavity. There are many different types of
gates, with the most common types of gates being the edge and pin-point gates.

Edge gate
The edge gate is a very common type of gate used to connect a cold runner to the
edge of a mold cavity. The design and redesign of an edge gate for the cup has been
previously discussed with reference to Fig. 8. Another edge gate design is shown in
Fig. 10. In this design, the edge gate connects to the inner periphery of the bezel’s
supporting frame. Since this gate location is internal to the screen assembly, any
vestige remaining after the gate removal will not be observed by the end- user of the
molding. Therefore, the edge gate can and should utilize the full thickness of the
adjacent wall section, and need not be gated underneath the lower surface of the
frame. [4]
Figure 16 Edge Gate [4]
22

Pin-Point Gate
The pin-point gate is a common type of gate used to connect a sprue or runner to the
mold cavity via a small cylindrical opening as shown in Fig. 7.4. The pin-point gate
is frequently used due to its small size which provides for ease of de-gating and
minimal gate vestige. Pin-point gates are often used with three-plate molds having
sprues with a reverse taper. Due to the pin-point gate’s small size, the de-gating is
readily accomplished upon the opening of the mold as discussed in Section 6.3.2.
Pin-point gates are also often used in two-plate molds to connect the runner to the
side walls of the mold cavity. Compared to other types of gates, how- ever, the flow
of the melt through such a small orifice will incur high pressure drops and shear
rates. [4]
Figure 17 Pin Point Gate designed with the inverted sprue [4]
2.3.5 Cooling System Design
The cooling system is extremely important to the economics and operation of the
designed mold. Improperly designed cooling systems often result in at least two
undesirable out- comes. First, cooling and cycle times are much longer than what
could have been achieved. Second, significant temperature gradients arise across the
mold, causing differential shrinkage and warpage of the moldings.
Major Objectives in designing cooling system:

Maximize heat transfer rate

Maintain uniform wall temperature

Minimize mold cost, Volume and Complexity
23

Maximize Mold usage and Reliability Cooling System design process
Designing a cooling system involves calculation of various parameters to ensure
proper cooling of melt within a preset time. Designing effective cooling system
includes following processes.

Calculate the required cooling time

Evaluate required heat transfer rate

Assess Coolant flow rate

Assess Cooling line diameter

Select Cooling line depth

Select Cooling line Pitch

Cooling line Routing
Conformal Cooling
A conformal cooling line design is provided in Fig. 12 in which the coolant is routed
to the center of the insert and then branches to a series of arteries like an internal
water fountain, thereby eliminating the temperature gradients. Making use of
cooling lines (inside the mold core and cavity) curving and closely outlining the
geometry of the molding cavity, conformal cooling promotes a faster and more
uniform temperature control and, as so, significantly increases the performance of
the injection cycle, on both production rate and quality of the plastic part. The
conformal cooling channels are closer to the part being molded and an equal distance
can be set between the part surface and the closest channel, resulting in a uniform
cooling of the molded part. A homogeneous temperature in the part promotes its
quality insofar as defects (e.g., warpage), sink marks, differential shrinkage, and
weld lines, are minimized. Cooling channels that better contour the molding cavity
also contribute to a 40%–60% lower cooling time. Playing a role in the part quality
and in the reduction of the injection cycle time, conformal cooling is likely to
increase the injection molding productivity and to reduce the production costs of
molded parts as well as the energy and material consumption.
24
Figure 18 Cooling channel in Conformal cooling [4]
2.3.6 Shrinkage and warpage
Injection molding can make discrete parts that can have complex and variable crosssections as well as a wide variety of surface textures and characteristics using almost
all thermoplastics. The product quality of injection molded plastic parts is the result
of a complex combination of many factors including materials used, processing
parameters, part and mold designs which can affect the shrinkage behavior of the
injection part. Shrinkage is defined as the reduction in the size of part as compared
to the size of the mold. Uniform shrinkage does not cause part deformation and
change in shape, but it simply becomes smaller. The shrinkage varies in the space
and it is usually quoted at room temperature just after the part has been ejected from
the mold.
Polymers materials normally shrink in thickness direction in order of the different
profiles of temperature, while in-plane shrinkage is restricted by the already
solidified layers. The limitation of these two theories can be changed by combine
the thermodynamic analysis with a thermo-mechanical one. The cooling rate is high
near the mold wall where the orientation caused by the stresses induced by the flow
is not able to relax. The interior will cool down more slowly due to the insulation
effect of the already solidified polymer. The resulting high thermal gradient and the
constrained shrinkage introduce residual stresses in the moldings. [4]
2.3.7 Ejection system design
The ejection system is responsible for removing the moulded part(s) from the mould
after the mould opens. The ejector assembly (consisting of the ejector plate, ejector
25
re- trainer plate, return pins, ejector pins, stop pins, and other components) is housed
between the rear clamp plate, support plate, and rails.
Figure 19 Side view of opening mold [4]
At this time in the moulding cycle, the moulded part has shrunk onto the core side
of the mould and has been pulled from the mould cavity as the moving side of the
mould is retracted from the stationary side of the mould. In a few moments, the
moulding machine will push the ejector knock-out rod against the ejector plate to
actuate the ejector assembly and strip the moulded parts off the core. At this time,
however, a clearance exists between the ejector knock-out rod and the ejector plate.
Objectives of Ejector system design are:

Allow mold to open

Transmit ejection forces to moldings

Minimize distortion of moulding

Maximize ejection speed
Ejector system design process
The ejector system design is determined first by the required layout of the mold’s
parting surfaces, and subsequently by the detailed design of the various components
required to eject the molding(s). The following design process assumes that the
molded part has been properly designed with a minimum number of under- cuts, etc.
Otherwise, the mold designer should revisit the part design to simplify the mold’s
ejection system design.

Identify Mold parting surfaces
26

Estimate ejection forces

Determine ejector push area and perimeters

Specify type, number and size of ejector

Layout ejector
2.4 Design of Experiment
Design of experiment is a tool widely used by researchers and engineers to find the
effect of input parameters on output. It is the process of planning experiments for
appropriate data collection through the least number of experiments. Design of
Experiment was first proposed by R. A. Fisher in England in the 1920s [6]. DoE
uses statistical methodology to analyze data and predict product performance under
all possible conditions within the limits selected for the design of Experiment [7].
With design of Experiment methods, the quality of the process can be improved
systematically, in a cost-efficient way in short time period. DoE is one element of
the Six Sigma Strategy which is a zero-defect approach [8].
There are several systems of Design of Experiments in use today. The two main
types are classical and Taguchi arrays [9]. In Japan, where great improvements in
quality have been made over the last 50 years, the progression has been from
inspection to SPC to DoE [10]. Design of experiment can be full factorial or
fractional factorial. The type of factorial design is chosen on the basis of the
availability of resources, complexity of process, time constraints and area of
application i.e. if there are any chances of interaction between the process variables.
The advantages of Design of Experiment can be enlisted as follows:
1. Simultaneous optimization of Several Factors
2. Simultaneous Cost Reduction and quality Improvement
3. Elimination of the Effect of the Cause without Eliminating the Cause
4. Use of Fractional Factorial Design to reduce size and cost
5. Rapid data collection and Decision Making
6. Consideration of Noise in the Experiment also referred to as robust design
(Condra, 2001)
27
Figure 20 Diagram showing where Design of Experiments can be used for various functions
[7]
2.4.1 Terminologies in Design of Experiment (DoE)
Factors: Factors are
independent variables, sometimes referred to as the input
variables. These are the variables which are intentionally changed according to a
predetermined plan.
Levels: Levels are the values at which the factors are set in an experiment.
Effects: Effects are the dependent variables in an experiment, called as output
variables. They are the results of an experiment. They are also called response.
Interaction: Interaction is the influence of the variation of one factor on the results
obtained by varying another factor.
Controllable factors: Controllable factors are the factors which the experimenter
can, or wishes to, control in an experiment.
Uncontrollable Factors: Uncontrollable factors are the factors which are not
controlled. They are factors which the experimenter does not consider important, or
which are unknown
Noise: Noise is the effect of all the uncontrolled factors in an experiment
28
2.4.2 Full Factorial Design:
A Factorial Design Analysis (FDA) approach was used for statistical computation
and design. FDA includes more than one independent variable. The main advantage
of factorial design is that we can test the effect of more than one independent variable
and the interactive effect between the various independent variables. Factorial
designs are widely used in experiments involving several factors where it is
necessary to study the joint effect of the factors on a response. DoE can be full
factorial or fractional. Full factorial DoE considers all possible combinations for a
given set of factors and their levels. Full factorial DoE requires nk number of
experimental runs, where n is the number of factor levels and k is the number of
factors to be considered. Full factorial DoE considers both main effects and
interaction effects, hence requires large number of experimental runs expensive and
time consuming. [11]
2.4.3 Fractional factorial design
In fractional factorial design, small set of experimental runs are selected from full
factorial design and interaction effects are often disregarded. Fractional factorial
designs require less experimentation but do not define all the interactions that can
be present [12]. A key question is, for a given number of factors, how to select the
number of runs, the design, and the analysis method. Resolution is a number that
clarifies the assumptions that we need to make in order to estimate the different terms
in polynomial expansion for given fractional factorial design. Both resolution and its
refinement, called aberration, introduced by, have proven useful in choosing specific
experimental designs [9].
2.5 Taguchi Method
Taguchi’s philosophy is an efficient tool for the design of high-quality
manufacturing system. Dr. Genichi Taguchi, a Japanese quality management
consultant, has developed a method based on orthogonal array experiments, which
provides much-reduced variance for the experiment with optimum setting of process
control parameters. By studying the effect of individual factors on the results, the
best factor combination can be determined [13]. Taguchi built upon W. E. Deming’s
observation that 85% of the poor quality can be attributed to the manufacturing
29
process and only 15% to worker [13]. Thus, the integration of design of experiments
(DOE) with parametric optimization of process to obtain desired results is achieved
in the Taguchi method. Orthogonal array (OA) provides a set of well balanced
(minimum experimental runs) experiments and Taguchi’s signal-to-noise ratios
(S/N), which are logarithmic functions of desired output serve as objective functions
for optimization. This technique helps in data analysis and prediction of optimum
results. In order to evaluate optimal parameter settings, Taguchi method uses a
statistical measure of performance called signal-to-noise ratio. The S/N ratio takes
both the mean and the variability into account. The S/N ratio is the ratio of the mean
(signal) to the standard deviation (noise). The ratio depends on the quality
characteristics of the product/process to be. His thoughts produced an exclusive and
fundamental quality improvement technique that changes from traditional methods.
His techniques arise entirely out of following ideas. [14]
The key concepts are:

Quality should be designed into product not inspected into it.

Quality is best achieved by minimizing the deviation from the target. The
product should be designed in such a way that it is immune to external
uncontrollable factors.

The cost of quality should be measured as a function of deviation from the
standard and losses should be measured system - wise. [13]
2.5.1 Taguchi loss function
Taguchi’s Loss function is used to measure financial loss to society resulting from
poor quality. The quality losses occur when the product deviates beyond
the
specification limit, thereby becoming unacceptable [13]. Taguchi proposed, any
deviation from a characteristic’s target value results in a loss and a higher quality
measurement is one that will result in minimal variation from the target value. The
loss can be measured using a quadratic function and action is taken to systematically
reduce the variation from the target value [12]. Taguchi’s loss function is broadly
classified into the three major types.
These are as follows:
I. Smaller the better characteristics
II. Nominal the better characteristics
30
III. Larger the better characteristics
In the context of the nominal the better quality characteristics, the target will be at
the center and the two sides of the specification give the upper and lower
specification limits.
This can be formulated as follows:
L(y) = k (y − m)
Where, L(y) is the loss associated with particular quality characteristics. m is the
nominal value and y is the target value. k is the loss coefficient and it depends upon
the specification limits and the spread.
2.6 Tools Used
2.6.1 Microsoft Visual Basic
Visual Studio is an Integrated Development Environment (IDE) developed by
Microsoft to develop GUI (Graphical User Interface), console, Web applications,
web apps, mobile apps, cloud, and web services, etc. With the help of this IDE, you
can create managed code as well as native code. It uses the various platforms of
Microsoft software development software like Windows store, Microsoft
Silverlight, and Windows API, etc. It is not a language-specific IDE as you can use
this to write code in C#, C++, VB (Visual Basic), Python, JavaScript, and many
more languages. It provides support for 36 different programming languages. It is
available for Windows as well as for mac OS.
2.6.2 MoldEx3D
Moldex3D is the world leading CAE product for the plastic injection molding
industry. With the best-in-class analysis technology, Moldex3D can help you carry
out in-depth simulation of the widest range of injection molding processes and to
optimize product designs and manufacturability.
2.6.3 IMOLD V13
Developed by a research team from the Department of Mechanical and Production
Engineering, National University of Singapore, IMOLD® is a knowledge-based
software designed to capture the designer's intents and apply the expertise in the
specific discipline of plastic injection mould design. Built on top of Unigraphics, a
31
schematic diagram of the IMOLD® system structure is shown in Figure below
Starting with a 3-D part model as input, it provides a comprehensive set of functional
modules that help the user to complete a mould design process from core and cavity
creation to cooling and ejector system design. The output is a complete mould
assembly in 3-D which components can be used either collectively or individually
for downstream applications. Two notable features of IMOLD® are parametric
modelling and automation of routine design tasks. With parametric modelling, the
database is concise while a wide range of components with similar shapes can be
accommodated easily. Besides, tedious geometric manipulation tasks such as core
and cavity creation and assembly are made automatic. Moreover, since many
industrial design knowledge and practices are incorporated into the parametric
models of the functional parts in an injection mould, the design task is simplified as
a user can select from the available alternatives. [15]
Figure 21 Overview of IMOLD [15]
32

IMOLD® functional modules
Under IMOLD® version 3.1, there are a total of9 functional modules that cover the
design tasks for an injection mould. Each module is briefly described in a traditional
design sequence as follows:
a) Data preparation and filling module
Upon receiving a 3-D part model, the Data Preparation Module provides
options to define part shrinkage and ejection direction. Part model can be
imported into IMOLD® from models created using various 3-D CAD
software through IGES or STEP. The Filling Module provides various
runners, gates, and automatic cavity layout for multi-cavity molds of up to
128 cavities.
A 4-cavity layout created using IMOLD® is shown in Figure
Figure 22 4-cavity layout [15]
b) Mold base module
IMOLD® offers a unique 3-D Mould base Module, which automatically
creates parametric standard mould bases from mould-makers such as DME,
RASCO, and FUTABA. In addition, IMOLD® provides user-friendly tools
for easy customization of mould bases that are unique to a particular
company. It also provides other standard components associated with a
mould base, such as screws, pillars, and sprue bushings. A mould base
created using IMOLD® is shown in Figure 23. [15]
33
Figure 23 Mold base [15]
c) Parting module
After a containing block is created to enclose the part, the next step is to split the
containing block along the parting lines for the creation of core and cavity. The
Parting Module provides user-friendly tools for specifying the parting lines
interactively. An automatic parting line search algorithm is also available. The
parting lines range from simple planar to complex free-form. The module also
provides a tool for assisting in patching holes on the part before splitting. Based on
the parting lines, the module generates the parting surfaces and carries out the
splitting automatically. Figure 24 shows the core and cavity for a phone cover after
parting.
Figure 24 Cavity and core for a phone cover [15]
d) Slider module
The Slider Module assists in creating sliders for external undercuts.
Commonly used slider types and their components are stored in the database
as parametric models. Users can simply specify the undercut area and a slider
head is generated automatically. Upon selecting a slider type, the slider body
34
and its associated components are created automatically according to the
dimensions of the slider head and mold base. Moreover, customized slider
types can be easily added to the database for a particular company. A slider
created using IMOLD® is shown in Figure
Figure 25 Slider
e) Cooling Module
The cooling module provides extensive options for creating virtually every
conceivable type of cooling channel used in the mould design industry today.
Besides cooling channels, this module also provides extensive library of
standard components such as baffles, O-rings, connectors, and plugs. Figure
26 below shows some cooling channels created on a mould base.
Figure 26 Cooling channels on a mold base
f) Ejection module
The Ejection Module assists in creating ejector pins and adding them into the
partially completed mould assembly. It has a library of commonly used ejector
pin types based on commercial catalogues. Upon selecting a pin type, diameter,
and its location, this module calculates the pin's length and trims the head
35
according to the core's profile automatically. Furthermore, interference check
between the ejector pins and cooling channels, and other components is carried
out automatically. Figure 27 shows a set of ejector pins designed using
IMOLD®.
Figure 27 Ejector
2.7 Plastic Raw material
Plastics were considered as “Replacing Materials”. In today’s world, plastics are
unreplaceable materials on the same level as the classic materials:
-
Primarily due to special combination of properties (profiles & material
combinations)
-
Plastics offers solutions, that are not possible with classic materials
(Electronics, Medical care, Automotive industries etc.)
-
Low weight, allows high accelerations & decelerations.
-
Weather resistance (Corrosion) is better than resistance of metallic
materials.
-
Good Electrical Isolation properties (Housings of Electrical devices)
-
Low manufacturing costs, especially with injection moulding technology
2.7.1 Material Selection Process:


Identify application requirements
-
Mechanical (Load, Impact, Stiffness etc)
-
Thermal (Temperature range, maximum use, temperature etc.)
-
Environmental consideration
Identify the chemical environment
36

Define the chemical stress, temperature, contact time and type
Identify special needs
-
Regulatory (UI, FDA etc)
-
Outdoor or UV exposure
-
Light transmission (clear to opaque)
-
Fatigue and creep requirements

Define economics

Define processing considerations


-
Injection molding
-
Blow molding
-
Extrusion
-
Thermoforming
-
Foam molding
Define assembly requirements
-
Painting/ plating
-
Shielding
-
Adhesion
Chemical Resistance
Resistance of thermoplastics with various chemicals is dependent on:
•
Time (of contact with the chemical)
•
Temperature
•
Stress (molded- in stress and any external stress to which the
application is subjected)
•
Concentration of the chemical
37
2.7.3 Properties of HDPE
Figure 28 Modulus vs frequency graph
Figure 29 Mechanical, Thermal and heat capacity of HDPE [17]
38
2.8 Mold Material
Mold designers consider a variety of factors when selecting the mold metal
including, machining ease, weldability, abrasion resistance, hardness, corrosion
resistance, and durability. Metals can range from the soft, low-melt-temperature
alloys used in inexpensive, cast-metal, prototype molds to the porous metal used in
vent inserts. Metals are chosen based not only on the cost, manufacturing, and
performance requirements of the mold or component, but also on the experience and
comfort level of the mold design and construction shop. Aluminum, long a popular
choice for prototype molds, is gaining acceptance in moderate-run production
molds. [17]
Improved aluminum alloys, such as QC-7, exhibit greater strength and hardness than
standard aircraft-grade aluminum, and sufficient durability for some production
molds. Hard coating san raise the surface hardness of aluminum molds to more than
50 Rock well C (HRC) for improved wear resistance. Steel inserts and mechanical
components are usually used in high wear areas within the aluminum mold to extend
mold life. Aluminum offers easier machining and faster cycle times than
conventional mold steels at the expense of wear resistance and mold durability. Most
high production injection molds designed for engineering plastics are fabricated
from high-quality tool steel. Mold bases are usually made of P-20 Pre-hardened to
30 – 35 HRC and are often plated to resist corrosion. Specifications for high-quality
molds, especially for medical parts, often specify 420 stainless steel to eliminate
corrosion concerns. [17]
Cavity and cores steels vary based on the production requirements, machining
complexity, mold size, mechanical needs, and the abrasive or corrosive nature of the
molding resin. P-20 steel (30-36 HRC) provides a good mix of properties for most
molds running non-abrasive materials such as unfilled PC or ABS. Pre-hardened 420
stainless (30-35 HRC) can also be used when corrosion resistance is needed. For
longer mold life and increased durability, many medical molders select 420 stainless
hardened to 50-52 HRC for their molds running unfilled resin grades. This highly
publishable stainless steel resists corrosion and staining but provides less efficient
cooling than most other mold steels.
39
Most abrasive glass or mineral-filled resins require mold steels with hardness ratings
of at least 54 HRC. Air hardened steels, such as H-13, machine more easily than prehardened steels and can be hardened to 54 HRC for use with most abrasive glass or
mineral-filled resins. Air hardened S-7 sees similar applications as H-13, but can be
hardened to 54-56 HRC for higher-wear areas. Air hardened D-2 (54-56 HRC)
provides superior abrasion and is often used in high wear areas such as runner and
gate inserts for abrasive materials.
Small inserts and components that see steel-to-steel wear can be manufactured from
steels that can achieve hardness levels greater than 56 HRC such as O-1, O-6, A-2,
and A-10. Table 7-3 lists some of the common steels used in mold making. Steel
manufacturers also offer a variety of specialty grades with properties tailored to mold
making. The heat-treating process used to achieve the high hardness values of some
of the mold steels, can result in cracks in large cores, particularly if the crosssectional thickness is not consistent. Consider pre-hardened mold steels for these
applications.
As a general rule, the Rockwell hardness of mold components that slide against each
other, such as bypass cores, should differ by at least 2 HRC to reduce galling and
damage to both components. The less expensive or more easily replaced component
should have the lower hardness. Inserts made of Be-CU or high-conductivity alloys
can reduce heat buildup in difficult-to-cool areas of the mold. The metals with the
best thermal conductivity tend to be the softest. To protect the soft metals from
abrasion and deformation, they are often inserted into harder steel cores or
components. [17]
Table 2 Mold steel in tabular form [17]
Mold components
Common steels
Cavity blocks and inserts
P20, H13, 57, L6, A2, A6, P2, P6, 420ss
Clamping plates
P20, H13, S7
Core Blocks and inserts
P20, H13, S7
Ejector (knockouts) pins
Nitride H13
Ejector plates
P20, H13, S7
40
Guide Pins and Bushings
O1, A2, P6
Leader Pins
Nitride H13
Retainers
P20, H13, S7
Slides
Nitride p20, O1, O2, O6, A2, A6, P6
Sprue Bushings
O1, o2, L6, A2, A6, S7, P6
2.9 Mold development process
2.9.1
CNC
Numerical control (NC) is the automation of machine tools that are operated by
precisely programmed commands encoded on a storage medium, as opposed to
controlled manually via hand wheels or levers, or mechanically automated via cams
alone. Most NC today is computer numerical control (CNC), in which computers
play an integral part of the control.
In modern CNC systems, end-to-end part design is extremely machine-controlled
victimization computer-aided design (CAD) and computer-aided manufacturing
(CAM) programs. The programs produce a data file that's interpreted to extract the
commands required to work a selected machine via a post processor, and so loaded
into the CNC machines for production. Since any particular part would possibly need
the utilization of variety of various tools drills, saws, etc. trendy machines typically
mix multiple tools into one "cell". In alternative installations, variety of various
machines area unit used with an external controller and human or robotic operators
that move the part from machine to machine. In either case, the series of steps
required to supply any part is extremely automated and produces a part that closely
matches the original CAD design.
CNC like systems area unit currently used for any process that may be described as
a series of movements and operations. These include laser cutting, welding, friction
stir welding, ultrasonic welding, flame and plasma cutting, bending, spinning, hole
punching, pinning, gluing, fabric cutting, sewing, tape and fiber placement, routing,
choosing and placing (PnP), and sawing.
CNC mills use computer controls to cut different materials. They are able to translate
programs consisting of specific number and letters to move the spindle to various
locations and depths. Many use Gcode, which is a standardized programming
41
language that many CNC machines understand, while others use proprietary
languages created by their manufacturers. These proprietary languages while often
simpler than G-code are not transferable to other machines. [18]
2.9.2 Lathes
Lathes are machines that cut spinning pieces of metal. CNC lathes are able to make
fast, precision cuts using index able tools and drills with complicated programs for
parts that normally cannot be cut on manual lathes. These machines often include 12
tool holders and coolant pumps to cut down on tool wear. CNC lathes have similar
control specifications to CNC mills and can often read G-code as well as the
manufacturer's proprietary programming language. [18]
2.9.3 Plasma cutters
Plasma cutting involves cutting a material using a plasma torch. It is commonly used
to cut steel and other metals, but can be used on a variety of materials. In this process,
gas (such as compressed air) is blown at high speed out of a nozzle; at the same time
an electrical arc is formed through that gas from the nozzle to the surface being cut,
turning some of that gas to plasma. The plasma is sufficiently hot to melt the material
being cut and moves sufficiently fast to blow molten metal away from the cut. [18]
2.9.4 EDM
Electric discharge machining (EDM), sometimes colloquially also referred to as
spark machining, spark eroding, burning, die sinking, or wire erosion, is a
manufacturing process in which a desired shape is obtained using electrical
discharges (sparks). Material is removed from the work piece by a series of rapidly
recurring current discharges between two electrodes, separated by a dielectric fluid
and subject to an electric voltage. One of the electrodes is called the tool-electrode,
or simply the ‗tool‘ or ‗electrode‘, while the other is called the work pieceelectrode, or ‗work piece‘.
When the distance between the two electrodes is reduced, the intensity of the electric
field in the space between the electrodes becomes greater than the strength of the
dielectric (at least in some point(s)), which breaks, allowing current to flow between
42
the two electrodes. This phenomenon is the same as the breakdown of a capacitor.
As a result, material is removed from both the electrodes. [18]
2.9.5 CNC Machine Programming
The way an operator tells the machine what exactly to do is through specialized
programming. The program is written with a bunch of sentences like commands.
Every single command is composed of particular CNC words which have both a
letter and number element. The letter describes the ―kind‖ and the number
describes the value. These instructions are literally step-by-step guidelines on what
the machine should do at any given point in the machining process.
Someone called a CNC programmer must first visualize the entire process as it
would happen during implementation. Then they would need to insert those steps
into the program via the different available commands/words. [18]
2.9.6 UG CAM
Application-specific software significantly improves the productivity of the NC
programmer compared to the use of generic functions. Turbo-machinery milling
With NX, you can reduce programming effort by applying specialized 5-axis NC
programming operations for complex multibladed rotational parts, such as bliss and
impellers. Simultaneous 5-axis roughing enables you to efficiently remove material
between the blades by specifying parameters, such as cut level offsets, drive pattern
and tool axis. [18]
2.10 Mold Installation and Trial test
2.10.1 Mold Installations [19]
The installation process of the injection moulding machine is as follows:
1. Installation method of mould positioning ring for injection moulding
machine:

Press the button [to open the mould] first, and then press the button [to
retreat] so that the seat enters the cylinder and retreats to the end.

Put the mould on the lower template, press the button and stop the upper
template from a certain position (about 15mm) of the mould. Re-adjust the
43
position of the positioning ring of the mould and the center of the upper
template to the center of the hole. Then press the button until the upper
template is close to the mould.

Turn off the motor, and then fix the die with pressure plate or screw directly.
The die is installed.

Set the pressure, speed, position and time of opening and closing the die.
2. Installation method of non-mould positioning ring for injection moulding
machine:

Press the button [to open the mould] first, and then press the button [to
retreat] so that the seat enters the cylinder and retreats to the end.

Put the mould on the lower template, press the button and release the upper
template from a certain position (about 15mm) of the mould, and stop the
closing action.

Press the [seat entry] key, release the hand when the nozzle is about to touch
the gate of the mould, then see whether the nozzle is directly opposite to the
gate from front to back, adjust the position of the mould to make the two
completely coincide. First press [seat back] to keep the nozzle away from the
gate, then a thin sheet of paper or a bit of mud is coated on the gate, and then
press [seat entry] to make the nozzle contact with the mould. Gate, and
finally take out the paper to observe its marks or mud marks to determine, if
not correct, readjust.

Press the [seat back] button to make the seat back to the end. Then press the
button to make the upper template close to the die, turn off the motor, and
fix the die with pressure plate or screw.

Set the pressure, speed, position and time of opening and closing the die.
44
2.11 Molding Defects
There are lot of room for expensive errors when it comes to injection molding.
Quality issues in injection-molded products can range from minor surface defects to
more serious problems that can affect the safety, performance and function of the
product. They can be caused by problems related to the molding process, material
use, tooling design or a combination of all three. Different types of defects are as
follows: [20]
Molding defects often caused by process problems:
1. Flow Lines
Flow lines appear as a wavy pattern often of a slightly different color than
the surrounding area and generally on narrower sections of the molded
component. They may also appear as ring-shaped bands on a product’s
surface near the entry points of the mold, or “gates”, which the molten
material flows through. Flow marks won’t typically impact the integrity of
the component. But they can be unsightly and may be unacceptable if found
in certain consumer products, such as high-end sunglasses.
Figure 30 Flow Lines [20]
Causes

Due to variation in the cooling speed of the material as it flows in different
directions throughout the mold.

Due to differences in wall thickness, the material cools at different rates,
leaving behind flow lines.

For Example, molten plastic, cools very quickly during the injection process
and flow marks are evident when the injection speed is too slow. The plastic
45
becomes partially solid and gummy while still filling the mold, causing the
wave pattern to appear.
Remedies

Increase the injection speed, pressure and material temperature to ensure the
material fills the mold before cooling

Round the corners of the mold where wall thickness increases to help keep
flow rate consistent and prevent flow lines

Relocate mold gates to create more distance between them and the mold
coolant to help prevent the material from cooling too early during flow

Increase the nozzle diameter to raise flow speed and prevent early cooling
2. Burn Marks
Burn marks typically appear as black or rust-colored discoloration on an edge or
surface of a molded plastic part. Burn marks generally don not affect part integrity,
unless the plastic is burned to the extent of degradation.
Figure 31 Burn Marks [20]
Causes

The usual causes of burn marks in injection molded parts is trapped air, or
the resin itself, overheating in the mold cavity during injection.

Excessive injection speeds or heating of the material often lead to
overheating that causes burns
46
Remedies

Lower the melt and mold temperature to prevent overheating

Reduce the injection speed to limit the risk of trapping air inside the mold

Enlarge gas vents and gates to allow trapped air to escape the mold

Shorten the mold cycle time so that any trapped air and resin don’t have a
chance to overheat
3. Warping
Warping is deformation that can occur in injection molded products when
different parts of a component shrink unevenly. Just as wood can warp when it
dries unevenly, plastic and other materials can warp during the cooling process
when uneven shrinkage puts undue stress on different areas of the molded part.
This undue stress results in bending or twisting of the finished part as it cools.
This is evident in a part that’s meant to lie flat but leaves a gap when laid on a
flat surface.
Figure 32 Warping [20]
Causes

Rapid Cooling of the parts causes Warping

Excessive temperature or low thermal conductivity of the molten material
causes warping.
Remedies

Ensure the cooling process is gradual and long enough to prevent uneven
stresses on the material

Lower the temperature of the material or mold
47

Try switching to a material that shrinks less during cooling (e.g. particlefilled thermoplastics shrink much less than semi-crystalline materials or
unfilled grades)

Redesign the mold with uniform wall thickness and part symmetry to ensure
greater stability in the part during cooling
4. Vacuum voids / air pockets
Vacuum voids, or air pockets, are trapped air bubbles that appear in a
finished molded component. Quality control professionals typically consider
voids to be a “minor” defect void. But larger or more numerous voids can
weaken the molded part in some cases, as there’s air below the surface of the
part where there should be molded material.
Figure 33 Vacuum Voids [20]
Note: Voids are more difficult to avoid in molded parts which are thicker
than 6 mm
Causes

One of the chief causes of voids is inadequate molding pressure to force
trapped air out of the mold cavity.

The material closest to the mold wall cools too quickly, causing the material
to harden and pull the material toward the outside, creating an abscess. Due
to this its density changes significantly from the molten to hardened state and
causes Vacuum Voids.
Remedies

Raise the injection pressure to force out trapped air pockets
48

Choose a grade of material with lower viscosity to limit the risk of air
bubbles forming

Place gates close to the thickest parts of the mold to prevent premature
cooling where the material is most vulnerable to voids
5. Sink marks
Sink marks are small recesses or depressions in an otherwise flat and
consistent surface of a molded part. These can occur when the inner part of
a molded component shrinks, pulling material from the outside inward.
Figure 34 Sink Marks [20]
Causes

Due to the slow cooling of the molten materials results shrinkage which pulls
the outside material inward before it’s had a chance to adequately cool,
leading to a depression.
Remedies

Increase holding pressure and time to allow the material near the part’s
surface to cool

Increase cooling time to limit shrinkage

Design your mold with thinner component walls to allow for faster cooling
near the surface
6. Weld Lines
Weld lines can appear on the surface of a molded part where the molten material
has converged after splitting off into two or more directions in a mold. The hair-like
weld line is the result of weak material bonding, which lowers the strength of the
part.
49
Figure 35 Weld Lines
Causes

Two or more fronts of polymer or other molten material need to maintain a
certain temperature when colliding. Otherwise, they become partially
solidified and won’t sufficiently bond where they meet, resulting in weld
lines.
Remedies

Increase material temperature to prevent partial solidification

Raise injection speed and pressure to limit cooling before the material has
filled the mold

Redesign the mold to eliminate partitions

Switch to a material with a lower melting temperature or viscosity to allow
faster flow and prevent early cooling
2.12 Basic Mold Maintenance [19]
Conduct your most basic maintenance check before and after every cycle: This
will help to keep parts to spec and ensure that no debris or other foreign matter can
damage the mold. The below steps should comprise your standard, every-cycle
process.
Clean mold cavities with a gentle solvent: Material residue within the cavity can
affect the shape and structural integrity of your parts. A simple cleaning goes a
long way.
50
Use compressed air to blow out dust, debris and water: Especially in more
complex molds, those particles can be more difficult to reach. Don’t overlook them,
however: They can affect the part and cause greater damage during the production
cycle.
Be sure that the entire mold is completely dry before storage: We mentioned
water above, but it bears repeating, because water is the worst enemy of metal molds.
There’s one simple reason: Rust. A rusty mold is much more likely to fail or be
damaged, and will produce a much higher proportion of rejected pieces. Caught
early, mold can be cleaned and removed — though the best solution is simple
prevention.
Check runners, sprues and all other areas of the mold : The mold cavity isn’t the
only area that needs to be inspected as part of your maintenance. Debris and water
can cause big problems in other parts of the mold, as well. Be sure to inspect, clean
and blow out those areas, too.
Inspect mold hardware and connectors : This step is an overall look at the major
components of the mold, like bolts, plates and other pieces. Check them for wear,
fit, tightness and other standard maintenance issues.
Note the date and extent of your mold maintenance steps: This step ensures that
no matter who is conducting the maintenance, he or she knows the details (and any
potential issues) from the last process. It’s also a great way to keep you and your
employees accountable for regular maintenance.
More Advanced Mold Maintenance
These steps are just a few of those that should be conducted at longer intervals: say,
every 10,000 cycles or every 10 days. While the above is a good overview of a basic
yet effective preventative maintenance process, this area is more of a sample.
Inspect ejection pins and mechanisms. With an empty mold and the ejection
mechanism fully engaged, inspect pins and other components for wear, damage or
malfunction. This is also a good time to ensure that all ejection components are
51
sufficiently lubricated. The more complex your ejection mechanism, the more
involved this step should be.
Figure 36 Inspection of Injection Mold
Inspect all mold components. While a daily visual check should be conducted for
major components, as mentioned above, it’s also important to carry out a more
detailed check at regular intervals (like every 50,000 or 100,000 cycles), as well.
This involves checking springs, valves, O-rings, gaskets and other intricate mold
components, and replacing them as necessary.
52
CHAPTER 3 METHODOLOGY
Figure 37 Research approach
Theoretical and conceptual work flow
The design and analysis of the safety helmet was started with conceptual design of
improved safety helmet. In collaboration with design team working on project of
development of improved safety helmet, the project members jointly conducted
survey to address problems in existing safety helmet. Along with the development
process, the project members carried out analysis and mold development process for
the existing helmet. To facilitate ease in mold design, the project members developed
user interface using Visual Basic to calculate parameters for injection mold design.
After completion of the improved safety helmet design, the project members
developed full scale injection mold and carried out its analysis and optimization
using Taguchi DOE method. Also the project members’ printed the CAD design of
helmet in full scale and developed its model from fiber glass.
In order to design, optimize and analyze, all the works have been divided into
following steps.

Designing improved safety helmet.

Developing CAD model of sample/existing model for experiment

Analyzing sample product for developing mold
53

Developing mold for sample/existing mold

Developing user interface to automate mold design process

Analyzing final product for developing mold

Developing mold for improved safety helmet

Development of user interface for mold calculation using visual basic

Development of prototype using fiber glass
3.1 Designing improved safety helmet
•
Comparison of different existing safety helmets
•
Discussion with Neuron surgeon Dr. Salikhe to understand critical parts of
head
•
Discussion with Polymer engineer Mr. Biraj Dhungana to understand
property of polymer material for helmet
•
Survey conducted in different industrial area of Patan and construction site
to identify problems in existing helmets while assisting team inr product
design steps of new helmets
3.2 Developing CAD model of sample model for experiment
Instead of direct analysis on final product we first developed sample product and its
mold to understand simulation result.
Figure 38 Sample product
3.3 Analyzing sample product for mold development
Analyses of injection mold for sample product in Moldex3D
54
Figure 39 Analysis flow
55
Figure 40 Meshing of sprue and runner
Figure 41 Gate filling analysis
Optimized result for sample product
Maximum Filling Melt Front time
Maximum Filling Melt Front temperature
Initial Value: 3.048 s
Initial Value: 220.17 °C
Optimized Value: 2.57 s
Optimized Value: 216.50 °C
Figure 42 Optimized melt flow time
Figure 43 Optimized Melt temperature
56
3.4 DOE optimization using Taguchi method
Taguchi method is orthogonal array experiments. Provide much-reduced variance
for the experiment with optimum setting of process control parameters. Use the
signal-to-noise (S/N) ratio instead of the average to convert the trial result data into
a value for the characteristic in the optimum setting analysis. The S/N ratio reflects
both the average and the variation of the quality characteristic. Nominal is best (NB),
lower the better (LB) and higher the better (HB).
Control Factor
Initial levels (value)
Optimized
Value
L1
L2
L3
L4
Max. Injection Pressure (Mpa)
237.5 245.83
254.16 262.50 237.5
Filling time (sec)
2.37
2.54
Max.
Packaging
2.45
pressure 237.5 245.83
2.62
2.541
254.16 262.50 237.5
(Mpa)
Packing time(sec)
2.85
Mold temperature (˚C)
Melt temperature (˚C)
2.95
3.05
3.15
2.85
33.25 34.41
35.58
36.75
33.25
209
223.67 231.00 216.33
216.33
Figure 44 Tabulated data of Taguchi parameters
3.5 Interpretation of Results
Based on the Analysis and its optimized data, the data had been interpreted to
conclude the desired solution.
3.6 Developing user interface to automate mold design process
Microsoft Visual Studio 16.0 had been used to generate user interface model for
making mold calculator software and exe file had been generated. Since mold
calculation is a linear and time consuming process, so project members generate
individual command for calculation of each components of mold like cooling
channel, shot capacity, cooling time, runner diameter, gate diameter and so on.
57
3.7 Mold Design’s Calculation Parameters
1. Parts Details:
Name of Component:
Plastic Material Types:
Density of Material (𝞀) :
Specific Heat capacity of Material (S):
Melting Temperature range:
Viscosity of Material (when melted):
Shrinkage consideration: (
)%
Volume of parts (V):
Weight of component (W):
Number of cavities (N):
Projected area of the component (A) :
2. Weight of Molding:
Actual weight of component (W) =𝞀 x V
W= Actual weight of component (gram)
𝞀 = Density of plastic material (gm/cm3)
Total Weight = W X Number of Cavities =
Weight of Sprue and Runner =
Multiplication Factor (M.F) =
Total weight of single component with feed system= Total Weight X M.F =
3. Clamping Tonnage:
Clamping tonnage required = Total Projected area of mold X Cavity Pressure X No.
of Cavities =
Injection pressure required =
Cavity Pressure = 1/x of Injection Pressure =
Factor of Safety = x % of actual tonnage pressure =
Total Clamping tonnage required = Clamping tonnage required + Factor of Safety =
4. Plasticizing Capacity 𝞺𝒔 :
58
Plasticizing Capacity = Plasticizing rate of material X
𝑇𝑜𝑡𝑎𝑙 𝐻𝑒𝑎𝑡 𝑜𝑓 𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙 𝑋
𝑇𝑜𝑡𝑎𝑙 ℎ𝑒𝑡 𝑜𝑓 𝑚𝑎𝑡𝑒𝑟𝑖𝑎𝑙 𝑌
Machine Capacity > Plasticizing capacity of Material (Kg/hr)
5. Shot Capacity (SC):
Shot is mass of the plastic melts at plasticizing temperature and pressure
Shot capacity (Kg) = Swept Volume X Density of material X Const.
Swept Volume: Capability of machine expressed in cubic centimeters of swept
volume in Injection cylinder. Screw type is rated in terms of swept volume of
injection cylinder (From machine Specifications)
Constant: Correction factor for percent volume expansion of the plastic at the
molding temperature
6. Number of Cavities:
Calculation of Number of Cavities based on Shot capacity:
Ns = 0.85 X Shot Capacity / Weight of component =
Rate shot capacity = 85%
Depending of shot capacity, mold can be design to accommodate N no. of cavities
Calculation of Number of Cavities Based on Plasticizing Capacity:
Np =
0.80 𝑋 𝑃𝑠 𝑋 𝑇𝑠
𝑊𝑠
Ps = Plasticizing capacity of material
Ts = Cycle time in Second
Ws = Weight of component in grams
Depending on plasticizing capacity the mold can be designed to N no. of cavity
7. Wall thickness of Core/Cavity Inserts:
3
𝐶𝑃𝑑4
Insert wall thickness (d) = √
𝐸𝑦
C = Constant based on ratio of cavity based on length to depth =
P = Cavity Pressure =
d = Depth of cavity =
E = Modulus of elasticity =
y = Permissible deflection for the insert =
59
Minimum wall thickness of core/cavity (t) required for safe design =1.5mm
8. Design of Guide Pillar:
2
4𝑋𝑄
Guiding diameter of the guide pillar (dp) = √𝜌 𝑋 𝑁
𝑝 𝑋 𝑓𝑠
Q = Side thrust
Np = Number of Guide Pillars =
fs = Working shear stress for the guide pillar material, Kg/mm2
Side thrust (Q) = di X h X Pc
di = Height of core in mm
h = Maximum side of the core in mm
Pc = Pressure in the cavity in Kg/ cm3
9. Feeding System Design:
Runner Design:
4
Runner Diameter (D) =
√𝑊 𝑋 √𝐿
3.7
W = Weight of the Component
L = Length of the runner =
Gate Design:
According to the size and shape in this design, gate is selected and employed to feed
the component
Gate Width (w) =
ℎ 𝑋 √𝐴
30
h = Constant = (Based on Material Properties)
A = Total surface area of the cavity (mm2) =
Gate depth (hg) = Average width of gate/ Average thickness of components
10. Mold Cooling Calculations:
Heat to be transferred from mold per hour (Q): n X m X qb
Q = Heat transferred per hour (cal/hr)
60
m = Mass of plastic material injected into mold per shot (g)
n = number of shot per hour (shots/hr) [Taken from machine data]
qb = Heat content of plastic material (cal/g)
Heat is conducted by Conduction, Convection and Radiation. In practice 50% of the
heat input is carried away by the water-cooling system.
So, Amount of heat removed by cooling water (Qd) = 0.5 X Q =
𝑸 𝑿 𝟎.𝟓𝟓
Amount of water to be circulated per hour to dissipate heat (mw) = 𝑲 (𝑻
𝒐𝒖𝒕 − 𝑻𝒊𝒏 )
K = Thermal conductivity of water
K = 0.65 for direct cooling
K = 0.5 for indirect cooling
Tout = Outgoing water temperature(˚C)
Tin = Incoming water temperature(˚C)
Sw = Specific heat of water
mw = Amount of water required to remove 50% of heat
3.8 Steps of CAD Design of Mold
Injection mold design of helmet had been drawn on SolidWorks 2016. With IMOLD
V13 (Add Ins of SolidWorks), mold design of helmet had been done.
The steps followed in mold design of safety helmet are:
1. Core and Cavity Extraction:

Selection of opening plane and direction

Draft analysis of core and cavity had been done

2 Degree draft of core part

Parting line generation

Parting line analysis

Core and cavity extraction

Individual saving of core, cavity and part
2. Mold Base Creation:

Design of the core and cavity pattern
61

Design of suitable size of DME standard mold base containing top
plate, base plate, ejector plate, core plate and cavity plate for concern
core and cavity with selection of mold base material in IMOLD
3. Ejector Pin Design
4.

Creation of point for the location of ejector pin

Selection of ejector pin diameter, length and material standards

Generation of pin

Trimming the pin to required plane
Sprue, Runner and Gate design

Defining point for creating gate point

Defining type of gate and its dimension

Creation of gate

Similarly, defining point for runner and its dimension
5. Component Design

Design of locating ring, sprue bushing, screw by selecting from the
toolbox of IMOLD
6. Cooling Channel Design

Cooling channel layout planning

Creation of inlet and outlet point

Selection of calculated diameter and dimension for drilling the hole
in cooling channel
7. Drafting and Drawing

Drafting of the parts and extruded component in SolidWork
3.9 Product Development

The designed product, core and cavity had been printed with 3D
printer

Product had been developed with fiber glass with help of 3D printed
part
62
CHAPTER 4 RESULTS AND DISCUSSION
4.1 Product Design
CAD Design of the safety helmet had been designed by team members with project
titled “Design and Analysis of Safety Helmet”.
Figure 45 CAD Design of Safety Helmet
Figure 46 Helmet dimension in mm
4.2 Calculations
The first step for mold analysis and design is to calculate the parameters for its
design and analysis. Calculation of the components had been done below.
1. Parts Details:
Plastic Material Types: HDPE
63
Density of Material (𝞀): 0.97 g/cm3
Specific Heat capacity of Material (S): 1900 J K-1 Kg-1
Melting Temperature range: 160º C - 175ºC
Shrinkage consideration: (1-3 )%
Volume of parts (V): 366.22 cm3
Weight of component (W) = Volume X Density = 348.65 gram
Number of cavities (N): 1
Projected area of the component (A) :582.40 cm2
Feed system weight = 5 % of component weight = 17.43 gm
Short weight of component = Part weight + Feed system weight = 366.08 gm

Injection Pressure and Packaging Pressure
Injection Pressure =
𝑃𝑟𝑒𝑠𝑠𝑢𝑟𝑒 𝑎𝑟𝑒𝑎 𝑜𝑓 𝑝𝑖𝑠𝑡𝑜𝑛 𝑋 𝐻𝑦𝑑𝑟𝑎𝑢𝑙𝑖𝑐 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒
𝑆𝑐𝑟𝑒𝑤 𝑝𝑟𝑒𝑠𝑠𝑢𝑟𝑒 𝑖𝑛𝑛𝑒𝑟 𝑎𝑟𝑒𝑎
Injection pressure required for processing 100% polypropylene to produce an
engineering part is 1600 gm/ cm maximum.
½ of injection pressure, as cavity pressure for easy flow material with 100% filled
has good flow ability hence ½ of injection pressure may be assumed as the cavity
pressure.

Clamping Tonnage
Clamping tonnage required = Total projected area of the mould X Cavity Pressure
X no. of cavities = 582.40 X ½ X 1600 X 1 = 465920 Kg
Factor of safety of 1.3 (30% of actual tonnage) = 465920 X 1.3 = 605696 Kg
Minimum machine tonnage required = 605.69 Tonne

Plasticizing Capacity (𝞺𝒔 )
Plasticizing capacity of the machine is calculated as follows:
Rated Plasticizing capacity of the material is:
Plasticizing rate = with material PP X
𝑞𝑎
𝑞𝑏
Plasticizing capacity of the machine for PP is 187.2 Kg/hr

Shrinkage allowance
Design of guide pillar:
Guiding diameter of the guide pillar, 𝑑𝑝
64
4𝑋𝑄
𝑑𝑝 = √(𝜋 𝑋 𝑁
𝑝 𝑋 𝑓𝑠
)
Np = Number of guide pillars = 4
Cavity pressure = 800 kg/ cm2
fs = Working shear stress for the guide pillar material
Q = Side thrust = height of core X Maximum side length of core X pressure
= di X h X Pc = 20.62 X 33.00 X 800 = 544368.00 Kg
4 𝑋 544368
𝑑𝑝 = √𝜋 𝑋 4 𝑋 1600 = 34.50 mm =3.5 cm

Feeding system design
Gate system:
Vertical Sprue is selected as a type of gate because its only a single cavity mold.
4
√𝐿
4
1
𝐷 = √𝑊 𝑋 3.7 = √366.08 𝑋 √131 3.7 = 18.33 mm
Sprue bushing inlet end point diameter = 18.33 mm
Sprue bushing outlet diameter = D X Angle of tapered (2.60º ) = 11.00 mm

Mold Cooling Calculation
Calculations are done based on coolant required and heat transfer rate, as follows:
Heat to be transferred from mould per hour (Q):
Q = n X m X qb
Where,
Q = Heat to be transferred per hour (cal/hr)
m =Mass of the plastic material injected into the mould per shot (g) = 366.08 g
n = number of shots per hour (240 shots/hr)
qb = Heat content of plastic material = 130 cal/g
Q = 240 X 366.08 X 130 = 11421.696 Kcal/hr
But in practice heat is removed by three ways Conduction, Radiation, Convection.
It is found in practice, that approximately 50 % of the total heat input is carried away
by the water cooling systems in mold.
Therefore, amount of heat removed by cooling water is
Qd = 0.5 X Q = 0.5 X 11421.69 = 5710.54 KCal/hr
Amount of water to be circulated per hour to dissipate heat (mw):
65
Amount of water to be circulated to remove 50% of Heat is calculated as
𝑄 𝑋 𝑂.5 𝑋 𝑆
m = 𝐾 (𝑇
𝑜𝑢𝑡 −𝑇𝑖𝑛
11421696.2 𝑋 0.5
=
)
0.64 𝑋 5
= 1784 𝐾𝑔/ℎ𝑟
where,
m= water flow rate
K = 0.64 for Cooling channels bored in cavity plate or male core
K = 0.5 for Cooling channels bored in back plate
K = 0.1 for Cooling channels in copper pipe
Tout = Outgoing water temperature
Tin = Incoming water temperature
W =Specific heat of water=4.186 J/gm
m =Amount of water required to remove 50% of heat.
Assuming a reasonable temperature difference of Tout –Tin = 5º C
4.3 Wizard Development for Calculation
Mold calculation is a linear and time consuming process, so project members
generate individual command for calculation of each components of mold like
cooling channel, shot capacity, cooling time, runner diameter, gate diameter and so
on. Based on the above calculation parameters, the GUI interface of wizard had been
created.
Figure 47 GUI Interface made using Visual studio
66
Figure 48 Calculation of parameters from developed wizard
4.4 Mold Design
Injection mold design of helmet had been drawn on SolidWorks 2016. With IMOLD
V13 (Add Ins of SolidWorks), mold design of helmet had been done.
The steps followed in mold design of safety helmet are:

Selection of opening plane and direction

Core and Cavity Extraction:
Figure 49 Parting plane of helmet
67
Cavity
Core
Figure 50 Core and Cavity extraction
Figure 51 Drawing of Core
Figure 52 Drawing of Cavity
68

Mold Base Design: Design of suitable size of DME standard mold base
containing top plate, base plate, ejector plate, core plate and cavity plate for
concern core and cavity with selection of mold base material in IMOLD.
Figure 53 Assembly of designed mold
Figure 54 Assembly view of mold base
69
(a)
(b)
Figure 55 CAD Design of (a) moving half (b) fixed half
Mold base consist of two half known as moving half and fixed half. Moving half
consist of core part, core plate, ejector plate, ejector pin and base plate.
Figure 56 CAD Design of mold base
70
Figure 57 Drawing of mold base

Components design
Figure 58 Drawing of Sprue bushing
71
Figure 59 Drawing of locating ring
(a)
(b)
Figure 60 (a) Design of Leader pin (b) Leader pin bushing

Cooling channel design
Figure 61 Cooling circuit 1, 2 and 3
72

Bill of Material
S.N Components
Material
Specification
Quantity
Dimension
(mm)
1
Cavity plate
1.2738 (special DME
p20)
Core plate
1
496 x 49 x180
1
Standard
1.2738 (special DME
p20)
Standard
EN31
DME
496 x 380 x 26
1
back EN31
DME
496 x 380 x 20
1
496 x 26 x 28
2
496 x 546 x 36
1
496 x 546 x 36
1
1
Ejector plate
Ejector
496 x 496 x 220
plate
Standard
Spacer blocks
EN31
DME
Standard
Top plate
EN31
DME
Standard
Bottom plate
EN31
DME
Standard
Core insert
S (136)
DME
225 x 397.5 x 15
Cavity insert
S (136)
DME
250
x
330
x 1
194.253
Cooling
135 x 357.5 x 15
1
225 x 397.5 x 15
1
235 x 397.5 x 15
1
circuit 1
Cooling
circuit 2
Cooling
circuit 3
Vertical
20.44 x 20.45 x 1
runner
33.81
Sprue bush
1.7131
D1= 18.3, D2=11
1
Locator ring
St 37-2
D1=100.0,
1
d2=52.0
Leader
pin 1.7131
DME
bushing
l=195.0,
d2=33
73
d1=43, 1
Leader pin
SS, Grade 18
DME
d1= 28, l=393
1
Screw t1
IS
M 10 X 25
4
Screw t2
IS
M 12 X 75
4
Screw t3
IS
M 12 X 105
4
Screw t4
IS
M 16 X 240
4
Ejector pin t1
WS
HASCO
D8 x L395.2
1
Ejector pin t2
WS
HASCO
D8 x L305.2
1
Ejector pin t3
WS
HASCO
D8 x L309.2
1
Ejector pin t4
WS
HASCO
D8 x L305.2
1
Ejector pin t5
WS
HASCO
D8 x L423.1
1
Ejector pin t6
WS
HASCO
D8 x L340.2
1
Ejector pin t7
WS
HASCO
D8 x L339.7
1
Ejector pin t8
WS
HASCO
D8 x L310.7
1
Ejector pin t9
WS
HASCO
D8 x L336.5
1
Ejector pin t10 WS
HASCO
D8 x L394.6
1
Ejector pin t11 WS
HASCO
D8 x L340.2
1
Ejector pin t12 WS
HASCO
D8 x L378.9
1
Ejector pin t13 WS
HASCO
D8 x L384.8
1
Ejector pin t14 WS
HASCO
D8 x L342.4
1
74
4.5 Analysis in MoldEx3D
After the calculation of parameters, the mold of the product had been calculated
using MoldEx3D software. The procedure and results had been displayed below.
4.4.1 Solver parameter setup
Table 3 Solver Parameter Setup
S.N
Conditions for setup
1
Mesh Type
3 Layer BLM
2
Mesh
Triangular mesh
3
No of nodes
111545
4
No of elements
240459
5
Inlet let point
Centre point of sprue bushing
6
Sprue and gate type
Vertical sprue
7
Gate Diameter (D1)
11 mm
8
Gate Diameter (D2)
18 mm
9
Cooling channel (D)
15 mm
10
No. of inlet and outlet 2
of cooling channel
75
Figure 62 Solver Setup of full scale mold
4.4.2 Analysis Parameters Set up
For the mold analysis, Analysis parameters had been set up in MoldEx3D software.
Table 4 Operating parameters for injection mold of safety helmet
S.N
Operating condition parameters
1
Injection pressure (MPa)
160 MPa
2
Melt temperature (ºC)
220
3
Mold temperature (ºC)
35
4
Injection time (s)
1.6 s
5
Injection Volume (cm3)
380.3
Packing time (s)
3.2 s
5
Hold pressure (MPa)
39 MPa
6
Specific gravity
1.21
7
Back Pressure
10 MPa
76
4.4.3 Analysis

Thickness Analysis: The maximum thickness of material was found to be
5mm. Since there is uniform thickness of the material so there hadn’t been
problem of ununiformed shrinkage.
Figure 63 Thickness analysis of helmet

Confidence of fill: From the melt flow analysis under the setup condition,
100 %, confidence of fill had been obtained. It means the provided injection
and packing pressure was enough under the setup condition

Figure 64 Analysis of gate contribution
77

Melt Front Time: The maximum filling time obtained was 1.55s. As
material flow rate and filling time is directly linked, the filling at the bottom
of the part takes more time because of its surface area.
Figure 65 Analysis of melt front time

Filling Pressure: The maximum pressure at the tip of helmet was 10.46
Mpa. Since there had been pressure drop while material flows downward the
part, so, pressure at bottom part of helmet had been found 1.5 MPa. The
ununiformed pressure distribution will results into ununiformed shrinkage
and warpage.
78
Figure 66 Analysis of filling pressure

Shear Stress: Maximum shear stress during the analysis had been found in
the upper slots of helmets, It can be reduced either by design modification or
through parameters optimization.
Figure 67 Analysis of filling shear stress

Volumetric Shrinkage: Volumetric shrinkage shows the analysis chart of
total shrink in initial volume of the plastic parts. Since plastic material has
properties of high fluctuation on density variation with change in
temperature so special consideration should be made. The obtained analysis
79
showed maximum volumetric shrinkage of 3.5 %. Further optimization is
necessary of reduction of volumetric shrinkage.
Figure 68 Analysis of volume shrinkage

Warpage displacement: Warpage displacement is resulted with uninform
shrinkage ratio. Warpage displacement should be obtained within the
tolerance limit for the quality product of the helmet. The analyzed value of
total warpage displacement in x, y and z direction is around 3mm which
should be reduced.
80
Figure 69 Analysis of total warpage displacement
Figure 70 Analysis of warpage displacement in z axis
4.4.4 Process Condition Optimization
In the above analysis, there is problem of over shrinkage, warpage displacement,
uneven shear pressure distribution, maximum filling time e.t.c which should be
resolved. The project members initially had taken two major parameters for
81
improving the process condition for resolving the above problem of shrinkage,
warpage, shear pressure e.t.c
Table 5 Setup condition for process condition optimization
Based run
Optimized run
Melt Temperature (º C)
220
209
Mold Temperature (º C)
35
--
Filling Time (s)
1.6
1.52
Packing Time (s)
3.2
3.36
Cooling Time (s)
4
--
Figure 71 Graph of volumetric shrinkage versus iteration
Above graph shows volumetric shrinkage along with the time. Initially volumetric
shrinkage was obtained high but after some iteration the volumetric shrinkage had
been reduced from 17.28% to 11%.
82

Result of Volumetric shrinkage
Figure 72 Results of volumetric shrinkage

Result of total warpage displacement
Figure 73 Results of total warpage displacement
83

Results of filling melt front temperature
Figure 74 Results of filling melt front temperature

Results of filling melt front time
Figure 75 Results of filling melt front time
84

Results of filling pressure
Figure 76 Results of filling pressure

Results of shear stress
Figure 77 Results of shear stress
85
4.4.5 Design of Experiment
DOE uses Taguchi method to determine which variable have most influence on
specific quality criteria, and then run extensive factorial experiment on most
significant input variables to determine how they impact the part quality. The
process variables, their ranges for design of experiment and weightage to specific
quality criteria are assigned after extensive literature review, machine technical data,
plastic injection molding handbook, consultation with the technicians, supervisors
and production manager in the industry.
Table 6 Design of experiment variable and range
S.N Variables
Min value
Middle value
Max Value
1
Mold surface temperature (ºC)
35
-
-
2
Melt temperature (ºC)
209
220
231
3
Packing time (s)
3.04
3.2
3.36
4
Injection pressure (MPa)
171
180
189
Table 7 Design of experiment quality criteria
S.N
Quality Criteria
Goal
Weight
1
Injection Pressure
Minimum
6
2
Warpage displacement
Minimum
7
3
Temperature at flow front
Minimum
5
4
Volumetric shrinkage
Minimum
7
5
Cycle time
Minimum
8
In this DOE, the project members used three parameters and three results to know
the quality dependence and effects of each values.
Orthogonal array: Orthogonal array reduces the experiment size. The total run
condition for L=3, N=4 is 9.
Table 8 Taguchi L9 (3^4) Orthogonal array
Run
F1
F2
F3
F4
R1
1
1
1
1
86
R2
1
2
2
2
R3
1
3
3
3
R4
2
1
2
3
R5
2
2
3
1
R6
2
3
1
2
R7
3
1
3
2
R8
3
2
1
3
R9
3
3
2
1
Table 9 DOE Results
Expt. Melt
Packing
Injection
no
Time(s)
Pressure (s) displacement
Temperature
Warpage
(ºC)
1
209
3.04
171
6.97
2
209
3.2
180
6.94
3
209
3.36
189
6.92
4
220
3.04
180
7.22
5
220
3.2
189
7.19
6
220
3.36
171
7.17
7
231
3.04
189
7.49
8
231
3.2
171
7.46
9
231
3.36
180
6.92
The result of Taguchi DoE simulation experiment has been shown in the table above.
From the table with the operating condition of melt temperature of 209°C, packing
time of 3.36 s and injection pressure of 171 °C, the warpage obtained was minimum.
Table 10 Factor effects on warpage
Level
Melt Temperature
Packing Time
87
Injection Pressure
1
6.944
7.227
7.201
2
7.196
7.201
7.202
3
7.465
7.177
7.203
0.050476
0.00176
Effect 0.5207
Table 11 ANOVA Method for analyzing quality factor
Factor
Sum of square
DOF
Variance
Contribution
(%)
Melt Temperature
0.4069
2
0.2034
99.068
Packing Time
0.0038
2
0.0019
0.930
Injection Pressure
0.00058
2
0.000029
0.0014
Error
0
0
0
0
Total
0.41804
6
From above table it is concluded that Melt temperature has highest effects in
warpage improvement and for better quality factor.

Factor response plot
Figure 78 Factor response plot
The above figure shoes the direct relation of melt temperature with quality factor.
88
Figure 79 Relation of melt temperature with S/N ratio
The above graph signifies the relation of S/N ratio with melt temperature. From
graph, lower the temperature, higher the S/N ratio has been obtained. The effective
temperature for process condition is 209ºC.

Sensitive Analysis
Figure 80 Sensitive analysis of melt temperature
89
Figure 81 Response surface graph of packing time vs warpage
4.4.5 DOE Optimized Results
Figure 82 Optimized result of volumetric shrinkage
Figure 83 Optimized result of shear stress
90
Figure 84 Optimized result of filling melt front temperature
Figure 85 Optimized result of melt front time
Figure 86 Optimized result of volume shrinkage
91
Figure 87 Optimized result of warpage

Table of comparison of the analyzed result
S.N Parameters
Normal
result DOE
(Average value)
Optimized
result
(Average value)
1
Confidence of fill
100 %
100%
2
Melt front time
1.57 s
1.53 s
3
Packing time
3.04 s
3.36 s
3
Melt front temperature
230 ºC
209 ºC
4
Injection pressure
180 M Pa
171 MPa
4
Filling Pressure
4.17 MPa
3.48 MPa
5
Shear stress
0.4 MPa
0.127 MPa
6
Volumetric shrinkage
4.2 %
2.58%
7
Warpage displacement
5.92 mm
4.15M
92
4.6 Model and Prototype development
The extracted core, cavity and part had been printed with 3D printer in Design lab.
Full scale helmet had been printed by splitting it into two parts.
Figure 88 3D Printed model of core and cavity
Figure 89 3D printed model of full scale safety helmet
After 3D printing of mold, further the prototype has been developed with fiber glass.
Since 3D printing multiple product will be costly, so fiber glass has been used for
market testing of the helmet.
Figure 90 Top view of fiber glass safety helmet
93
Figure 91 Side view of fiber glass safety helmet
4.7 Market feedback of prototyped helmet
Table 12 Market feedback
S.N. Buyers
Location
Feedback
1.
Rajesh
Hardware
Dhumbarahi,
Kathmandu

2.
Joshi
Hardware
Dillibazar,
Kathmandu

3.
Narayani
Hardware
Pvt.Ltd
Narayanghat,
Chitwan

4.
Manakamana Narayanghat,
trade
Chitwan
suppliers

94
Remarks
interested only
if this helmet is
provided
in
competitive
price of the
market
Shape is quite interested
good and the
ventilation
for
this helmet is
more fascinating.
Its shape and its Very interested
ability to cover
whole
critical
part of head
attracted them to
buy it.
New looks can Very interested
penetrate
the
market.
The shape is slim
due to this it
looks attractive
than
existing
helmet.
4.8 Cost Calculation and Analysis
4.8.1 Cost for Mold development in Nepal
S.N
Item
Specifications
Price
1
Mold Base
DME Standard, R50-50
90,000/-
2
Core and Cavity
HSS, 250 X 250 X250
60,000/-
3
Mold
Guide bush, Screws, Locating 8,000/-
Components
ring, sprue bushing, Guide pin,
Ejector pin
4
Design
15,000/-
5
Milling, CNC and
20,000/-
surface finishing
6
Assembly
and
15,000/-
setup
Total
2,08,000/-
4.8.2 Cost of Mold if imported from India
S.N
Item
Specifications
Price
Mold base and Sales, initial service and initial 4,40,000
design package
setup along with logistic and tax
4.8.3 Cost of Plastic Product
S.N
Item
Specification
Price(Rs)
Raw material cost
1.
Raw material
HDPE, Shell weight (w)=360 54
gram, market rate=150/Kg
2
Head
Band Chinese standard band
price(imported
from
25
china)
Operation cost
3
Electricity cost per pc
4
Labor cost per pc
5
Logistic and maintenance
1
Cost per month/ quantity
3
3
95
6
Mold cost
7
Machine cost
If machine life time is 10 years
2
8
Total Production Cost
Rs. 96
4.8.4 Cost of helmet from fiber glass
S.N
Item
Specification
Price(Rs)
Fiber glass (600 gram)
110
Raw material cost
1.
Raw material
2
Head
Band Chinese standard band
price(imported
from
25/pc
china)
3
Labor cost
4
Pattern cost
50/pcs
If total pcs is 10,000
2/pcs
Total
NRs 185
Fiber glass helmets are expensive and only be useful for market review.
96
CHAPTER 5 CONCLUSION
5.1 Calculation wizards’ development
Calculation wizard using GUI has been successfully developed. User can calculate
the mold parameters with help of this wizard. Exe file will help in each of sharing
the generated file.
5.2 Conclusion on Mold Design
Full scale injection mold with single cavity and two plate mold has been developed.
BOQ has been prepared and its drafting has been compiled along with its
components.
5.3 Analysis and Optimization part
After the analysis, problem has been diagnosed. The parameter has been optimized
with taguchi methods. Project members found that melt temperature has been the
contributing factor on quality of mold.
5.4 Prototype development and market feedback
Prototype has been developed with fiber glass. Market feedback has been take and
further work will be done accordingly.
97
RECOMMENDATION
The project members has got holistic experience by working on the project. After
working on the project for long, the project members like to recommend following
things for future improvement:

Analysis of helmet should be done by varying design parameters like runner,
gate, no. of cavities e.t.c

Calculation wizard should be developed for its holistic use

Commercialization of helmet should be done after receiving quality feedback
from the buyers and customers
98
REFERENCES
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101
APPENDIX A
Code of GUI wizard
102
103
CAD Drawing of components
104
Locating Ring
Sprue Bushing
Top Plate
Cavity Plate
Cavity
Core
Core Plate
Support Plate
Ejectior Pin
Ejectior Plate
Bottom Plate
MOLD ASSEMBLY
MATERIAL:
DRAWN BY: TEAM HELMET
SHEET: 1 OF 14
CHECKED BY:
SCALE: 1: 5
DATE: 21/10/2019
ALL DIMESNSION ARE IN MM
36
380
36
56
126
20
180
496
220
546
26
46
MOLD BASE
MATERIAL: BRASS
DRAWN BY: TEAM HELMET
SHEET: 2 OF 14
CHECKED BY:
SCALE: 1: 5
DATE: 21/10/2019
ALL DIMESNSION ARE IN MM
17.49
330
206.23
97.66
34.54
250
250
MOLD BASE
MATERIAL: BRASS
DRAWN BY: TEAM HELMET
SHEET: 3 OF 14
CHECKED BY:
SCALE: 1: 5
DATE: 21/10/2019
ALL DIMESNSION ARE IN MM
17.49
330
34.54
250
142.39
191.44
124.96
CAVITY
MATERIAL: HSS
DRAWN BY: TEAM HELMET
SHEET: 4 OF 14
CHECKED BY:
SCALE: 1: 5
DATE: 21/10/2019
ALL DIMESNSION ARE IN MM
166.96
106
12.19
279.36
208.07
HELMET
MATERIAL: PP
DRAWN BY: TEAM HELMET
SHEET: 5 OF 14
CHECKED BY:
SCALE: 1: 2
DATE: 21/10/2019
ALL DIMESNSION ARE IN MM
50
A
0
.3
18
102
3
131
2.60°
6
4
A
26
27
50
ISOMETRIC VIEW
R15.
50
SPRUE BUSHING
MATERIAL: BRASS
DRAWN BY: TEAM HELMET
SHEET: 6 OF 14
CHECKED BY:
SCALE: 1: 2
DATE: 21/10/2019
ALL DIMESNSION ARE IN MM
B
15
8.40
0
B
100
0
90
A
52
A
SECTION B-B
M8
SECTION A-A
ISOMETRIC VIEW
LOCATING RING
MATERIAL: BRASS
DRAWN BY: TEAM HELMET
SHEET: 7 OF 14
CHECKED BY:
SCALE: 1: 2
DATE: 21/10/2019
ALL DIMESNSION ARE IN MM
34
4
B
195
46
B
0
7.50
SECTION B-B
5
LEADER PIN BUSHING
MATERIAL: BRASS
DRAWN BY: TEAM HELMET
SHEET: 8 OF 14
CHECKED BY:
SCALE: 1: 2
DATE: 21/10/2019
ALL DIMESNSION ARE IN MM
41
179.50
4
ISOMETRIC VIEW
B
0
0
B
35
SECTION B-B
LOCATING SLEEVE
MATERIAL: BRASS
DRAWN BY: TEAM HELMET
SHEET: 9 OF 14
CHECKED BY:
SCALE: 1: 2
DATE: 21/10/2019
ALL DIMESNSION ARE IN MM
6
4.50
46
195
33
B
B
SECTION B-B
7.50
6
ISOMETRIC VIEW
LEADER PIN BUSHING
MATERIAL: BRASS
DRAWN BY: TEAM HELMET
SHEET: 10 OF 14
CHECKED BY:
SCALE: 1: 2
DATE: 21/10/2019
ALL DIMESNSION ARE IN MM
6
4.50
46
195
33
B
B
SECTION B-B
7.50
6
ISOMETRIC VIEW
LEADER PIN BUSHING
MATERIAL: BRASS
DRAWN BY: TEAM HELMET
SHEET: 10 OF 14
CHECKED BY:
SCALE: 1: 2
DATE: 21/10/2019
ALL DIMESNSION ARE IN MM
197.50
28.01
42
46
ISOMETRIC VIEW
6
B
7
195.50
SECTION B-B
41
B
FSC LEADER PIN 0
MATERIAL:
DRAWN BY: TEAM HELMET
SHEET: 12 OF 14
CHECKED BY:
SCALE: 2 : 1
DATE: 21/10/2019
ALL DIMESNSION ARE IN MM
225
Cooling Circuit 1
397.50
357.50
397.50
15
135
Cooling Circuit 2
235
Cooling Circuit 3
4
8
339.12
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