STUDY OF CAVITY SURFACE EFFECT TO THE PLASTIC …umpir.ump.edu.my/3458/1/cd6259_97.pdf · ·...

STUDY OF CAVITY SURFACE EFFECT TO THE PLASTIC FLOW

MUMTAZ BINTI NORMAN

Thesis submitted in fulfillment of the requirements

for the award of the degree of

Bachelor of Manufacturing Engineering

Faculty of Manufacturing Engineering

UNIVERSITI MALAYSIA PAHANG

JUNE 2012

v

ABSTRACT

The cavity surface of the mould will give an effect to the plastic flow during

injection. The project is to experiment the effects of the various surface roughness to the

plastic flow during injection. The parameters included the cavity roughness, feeding

design and metering parameters. The surface roughness can be determined by surface

comparator and machine by Electrical Discharge Machining (EDM) die sinking. Cavity

pressure can be determined by cavity pressure sensor. Mould is designed by using 3D

software and analyse by Moldflow software. Result obtained by Moldflow software

need to be compared to the experimental to validate it.

vi

ABSTRAK

Permukaan acuan akan memberi kesan kepada aliran plastik semasa suntikan.

Projek ini adalah untuk mengkaji kesan pelbagai kekasaran permukaan kepada aliran

plastik semasa suntikan. Parameter yang dikaji termasuk kekasaran rongga, parameter

reka bentuk dan pemeteran. Kekasaran permukaan boleh ditentukan oleh perbandingan

permukaan dan dimesin dengan menggunakan mesin pelepasan elektrik ‘die-sinking’.

Tekanan rongga boleh ditentukan oleh alat pengesan tekanan. Acuan direka dengan

menggunakan perisian 3D dan dianalisis oleh perisian Moldflow. Keputusan yang

diperolehi oleh perisian Moldflow perlu dibanding dengan eksperimen sebenar untuk

pengesahan.

vii

TABLE OF CONTENT

Page

SUPERVISOR’S DECLARATION ii

STUDENT’S DECLARATION iii

ACKNOWLEDGEMENTS iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES xi

LIST OF FIGURES xii

LIST OF SYMBOLS xv

LIST OF ABBREVIATIONS xvi

CHAPTER 1 INTRODUCTION 1

1.1 Introduction 1

1.2 Project background 1

1.3 Problem statement 2

1.4 Objective

1.4.1 Objective of the project

1.4.2 Impact

2

2

2

1.5 Scope of the project 2

CHAPTER 2 LITERATURE REVIEW 4

2.1 Introduction 4

2.2 Material flow

2.2.1 Fundamental of mould flow

4

4

viii

2.2.2 Surface roughness

2.2.3 Effect of cavity surface roughness

2.2.4 Film or flash gate

4

5

6

2.3 EDM die-sinking

2.3.1 History

2.3.2 Fundamental

2.3.3 Applications

2.4 Injection moulding machine

2.4.1 Fundamental

2.4.2 Defects

2.4.3 Mould project in plastic injection mould

industries

2.5 Polypropylene (PP)

2.5.1 Properties of Propylene

7

7

7

8

9

9

11

11

12

13

CHAPTER 3 METHODOLOGY 14

3.1 Introduction 14

3.2 Flow chart of methodology 14

3.3 Literature Review 15

3.4 Mould design 15

3.5 Software

3.5.1 Moldflow software

3.5.2 DEWESoft software

3.5.3 Minitab software

21

21

27

29

3.6 Machining

3.6.1 Vertical milling machine

3.6.2 EDM die sinking

30

30

31

ix

3.6.3 Grinding machine

3.6.4 EDM super drill

33

35

3.7 Mould and sensor assembly 36

3.8 Injection moulding trial

3.8.1 Defects

38

42

3.9 Result and discussion 43

3.10 Conclusion and recommendation 43

CHAPTER 4 RESULT AND ANALYSIS 44

4.1 Introduction 44

4.2 Specific characteristics of semi-crystalline

thermoplastics

44

4.3 Cavity pressure curve 45

4.4 Data analysis

4.4.1 Moldflow analysis: gate thickness versus

pressure

4.4.2 Moldflow analysis: gate thickness versus filling

time

4.4.3 Moldflow analysis: gate thickness versus

pressure at V/P switchover

4.4.4 Injection moulding machine analysis

4.4.5 Cavity pressure sensor analysis

46

46

50

53

55

57

CHAPTER 5 CONCLUSION AND RECOMMENDATION

5.1 Introduction 66

5.2 Conclusion 66

5.3 Recommendation

66

x

APPENDICES

APPENDIXES A

APPENDIXES B

APPENDIXES C

xi

LIST OF TABLES

Table No. Title Page

3.1 Control factor and values for EDM die sinking machining 32

3.2 Fixed parameters in EDM die sinking machining 32

3.3 Fixed parameters in EDM Super Drill machine 35

4.1 Pressure for gate thickness 0.6 mm, 0.4 mm and 0.2 mm 48

4.2 Fill time for gate thickness 0.2 mm, 0.4 mm and 0.6 mm 51

4.3 Pressure for surface roughness 20 μ 54



4.6 Mean pressure for combined surface roughness 59

4.7 Cavity pressure for surface roughness 2 μ 61

4.8 Mean pressure for combined surface roughness 63

xii

LIST OF FIGURES

Figure No. Title Page

2.1 Surface characteristic and terminology 5

2.2 Film gate with main parts 7

2.3 Working principle of EDM 8

2.4 Injection moulding machine with reciprocating screw 10

2.5 Main stages of a mould project in a typical mould-making

industry.

12

3.1 Flow chart of methodology 15

3.2 Dimension of the cavity insert and the product 16

3.3 Side view of the cavity insert with gate thickness 0.2mm 17



3.6 The location of the sensor (top view) 19

3.7 The location of the sensor (side view) 19

3.8 The location of the sensor (front view) 20

3.9 The location of the sensor (isometric view) 20

3.10 Mould assembly (isometric view) 21

3.11 Product by using Moldflow 22

3.12 Import file window 23

3.13 Mesh window 24

3.14 Analysis Sequence window for gate location 24

3.15 Change Property Type window for gate 25

3.16 Change Property Type window for runner 26

3.17 Analysis Sequence window for Cool + Fill + Pack + Warp 27

3.18 Hardware setup 27

xiii

3.19 Channel Setup 28

3.20 File storing 28

3.21 Data Analysis 29

3.22 Vertical Milling Machine 30

3.23 Electrode machined by milling machine 31

3.24 Surface Comparator 32

3.25 Electrical Discharge Machine (EDM) machine 33

3.26 Reciprocating Surface Grinding Machine 34

3.27 Floor Mounted Utility Grinding Machine 34

3.28 Electrical Discharge Machining (EDM) Super Drill Machine 36

3.29 Cavity pressure sensor installation with spacer sleeve 37

3.30 Cavity pressure sensor 37

3.31 Complete mould assembly 38

3.32 Injection Moulding Machine 39

3.33 Mould opening 39

3.34 During ejection 40

3.35 Cavity side 40

3.36 Core side 41

3.37 Product 41

3.38 Short shot 42

3.39 Flashing 42

3.40 Bubbles 43

3.41 Warping 43

4.1 Graph cavity pressure versus time 45

4.2 Phase in cavity pressure curve 46

4.3 Pressure for 0.2 mm gate thickness 46

xiv



4.6 Graph injection pressure versus gate thickness 49

4.7 Fill time for 0.2 mm gate thickness 50



4.10 Graph fill time versus gate thickness 52

4.11 Pressure at V/P switchover for 0.2 mm gate thickness

53


53


54

4.14 Graph pressure at V/P switchover versus gate thickness 55

4.15 Graph pressure versus gate thickness for 20 μ surface roughness 58



4.18 Graph pressure versus gate thickness for combined surface

roughness

64

4.19 Graph pressure versus surface roughness 65

xv

LIST OF SYMBOLS

oC Celcius

μ Micron

xvi

LIST OF ABBREVIATIONS

3D Three-dimensional

ASTM American Society for Testing and Materials

CAD Computer Aided Design

CPVC Chlorinated Polyvinyl Chloride

EDM Electrical Discharge Machining

ESC Environmental Stress Cracking

PA Polyamide

PE Polyethylene

POM Polyoxymethylene

PP Polypropylene

PVC Polyvinyl chloride

PVDF Polyvinylidene fluoride

STL STereoLithography

UV Ultraviolet

CHAPTER 1

INTRODUCTION

1.1 INTRODUCTION

This chapter is discussed about the project background, the problem statement,

the objectives of the project and the project scope.

1.2 PROJECT BACKGROUND

Surface roughness plays an important role in filling the molten plastic into the

cavity (Ahsan, 2009). Surface roughness are expressed as deviation of the results of

various machining operations. Machined surface quality is characterized by precision

manufacturing with dimensions specified by the designer. Every machining operation

leaves evidence on the characteristics of machined surfaces. This evidence is in the

form of micro-fine irregularities left by the cutting tool. Each type of cutting tool leaves

its own pattern of individuals can be identified. This pattern is known as surface finish

or surface roughness.

For this project, the main objective is to determine the effects of the various

surface roughness to the plastic flow during injection. Different surface roughness gives

different effects to the plastic flow. There are several parameters that should be

considered and controlled which are injection pressure, surface roughness and different

thickness of the film gate while constant parameter is the size of the runner. Choosing

the best surface roughness is really important to produce very fine product. . Electrical

Discharge Machining (EDM) Die Sinking will be used to differentiate the surface

roughness based on the surface gauge comparator. There will be three different surface

roughness in this project. Each one of the surface roughness will have three different

gate thickness design.

2

1.3 PROBLEM STATEMENT

The terms surface finish and surface roughness are used very widely in industry

and are generally used to quantify the smoothness of a surface finish. Surface finish

could be specified in many different parameters. Due to the need for different

parameters in a wide variety of machining operations, a large number of newly

developed surface roughness parameters were developed (Mike, 1998). To determine

the best surface roughness, there are many parameters should be considered such as

injection pressure and the gate size. To overcome this problem, this research will help

the manufactures to predict the correct combination of parameters without wasting their

production time because the main purpose of this research is to determine the effects of

cavity surface roughness to the plastic flow.

1.4 OBJECTIVE

1.4.1 The objectives of this project are:

To determine effects of cavity surface roughness to the plastic flow.

To determine the suitable injection parameters.

To determine the effect of different thickness of gate to the plastic flow.

1.4.2 Impact

This research can be used in the manufacturing field for melt plastic flow

examination in the case of more complicated cavities and can help when having

some problems in processing because of part design. This research can help the

machinist to increase the productivity and can reduce troubleshooting time.

1.5 SCOPE OF THE PROJECT

This project will be carried out by the specific software and machine in the process

of designing the cavity. The research is limited to know the effect of cavity surface

roughness to the plastic flow by changing the parameters such as roughness, injection

parameters and types of gate. The software used are CAD modelling and , Moldflow

3

while for the machines are milling machine and surface grinding machine.There are

several limitations in this project which are:

i. Determine the best gate thickness for the film gate. Thickness of the gate

plays an important role for the molten plastic to flow into the cavity. If the

thickness is not suitable, the molten plastic might not fill the cavity totally.

In order to know what thickness is the best, many experiments have to be

conducted. Other parameters should also be considered such as injection

pressure.

ii. Determine the injection pressure inside the cavity. Pressure inside the cavity

can be measured by mold cavity pressure sensor only. To use the sensor

some wiring need to be done and the sensor have to be embedded to the

mold.

iii. The simulation software can not show exactly the defects that will occur.

The software just can show the defects that might occur on the product. Real

experiments have to be conducted in order to know the real defects.

CHAPTER 2

LITERATURE REVIEW

2.1 INTRODUCTION

This chapter will provide the article review for this final year project. The article

review is about material flow, Die Sinking Electrical Discharge Machining (EDM),

Injection Moulding Machine and Polypropylene (PP).

2.2 MATERIAL FLOW

2.2.1 Fundamental of Mold Flow

The material flow in mould runners can be controlled by the design and

manufacturing technology of the mould as well as by the processing conditions in order

to obtain the moulded parts with expected morphology, properties, shape, dimensions

and surface (Bociaga, 2011). There are many parameters need to be considered in the

plastic material flow but in this project, there are two parameters that need to be

considered which are surface roughness and the thickness of the film gate because the

other parameters are constant.

2.2.2 Surface roughness

The challenge of modern machining industries is mainly focused on the

achievement of high quality, in terms of work piece dimensional accuracy, surface

finish, high production rate, less wear on the cutting tools, economy of machining in

terms of cost saving and increase the performance of the product with reduced

environmental impact. Surface roughness plays an important role in many areas and is a

factor of great importance in the evaluation of machining accuracy (Subramanyam,

2010). When the thickness of a cavity is decreased until the roughness is comparable to

5

the dimension of the cavity, the effects of surface roughness become increasingly

important (Ong, 2009).

Mould surface roughness effects on the cavity filling of polymer melt were

investigated experimentally. With the same process parameters, the mould cavity that

has a higher surface roughness will result in a smaller moulded part with higher surface

roughness. This is due to the higher resistance to the flow of polymer melt during cavity

filling. For the limited range of injection rate investigated, it is not significant on the

surface roughness effects. When the melt temperature is kept constant, an increase in

mould temperature will decrease the effects of surface roughness. When the mould

temperature is kept constant, the change of melt temperature within the range allowed

by the process is not significant for the surface roughness effect. (H. L. Zhang, 2008).

Figure 2.1: Surface characteristic and terminology

Source: Subramanyam 2010

2.2.3 Effects of cavity surface roughness

Cavity surface roughness can play a significant role in the cavity filling process.

Researches show that the cavity surface roughness can influence the cavity filling

process. The major reasons are:

1. Enhanced heat transfer rate. With an increase of surface roughness, the contact

area between molten plastic and mould wall increases. Therefore, heat transfer

between them is enhanced as heart transfer rate that is proportional to the contact

surface area.

6

2. Reduced slippage. Rougher cavity surface led to a more stable flow of molten

plastic and a more cosmetically appealing surface on the moulding. It is better to

create a mould with a rougher surface to prevent slippage during filling

(Christian D. Smialek, 2001).

3. Effects on turbulence in the molten plastic flow. There is a relationship between

tool surface finish and the level of turbulence in the melt flow by varying the

process parameters such as melt and mold temperature and injection speed (C A

Griffiths, 2007).

The applications of surface roughness are in the automotive industries

that often involve sliding components. Another application is in shipbuilding,

specifically ship hull surfaces and propeller. The surface roughness of these

components should be on the order of several micrometers for hydraulically

smooth surfaces in high speed ships.

2.2.3 Film or flash gate

A film or flash gate consists of a straight runner and a gate land across either the

entire length or a portion of the cavity. It is used for long flat thin walled parts and

provides even filling. Shrinkage will be more uniform which is important especially for

fiber reinforced thermoplastics and where warpage must be kept to a minimum.

The even cavity filling depends on the design of runner system which are the

number of injection points and their locations, the shape and dimensions of runners and

gates, the accuracy of runner system manufacturing and the shape and dimensions of

injection moulded parts including the wall thickness and its distribution in the part

(Kuldeep 2010).

The dimension of the film gate size is small, typically 0.25mm to 0.6mm thick.

The gate length must also be kept small, approximately 0.6 to 1.0 mm long depend on

the size and weight of the product.

7

Figure 2.2: Film gate with main parts

Source: Kuldeep 2010

2.3 DIE SINKING ELECTRICAL DISCHARGE MACHINING (EDM)

2.3.1 History

The history of EDM Machining Techniques goes as far back as the 1770s when

it was discovered by an English Scientist. However, Electrical Discharge Machining

was not fully taken advantage of until 1943 when Russian scientists learned how the

erosive effects of the technique could be controlled and used for machining purposes.

When it was originally observed by Joseph Priestly in 1770, EDM Machining

was very imprecise and riddled with failures. Commercially developed in the mid

1970s, wire EDM began to be a viable technique that helped shape the metal working

industry we see today. In the mid 1980s.The EDM techniques were transferred to a

machine tool. This migration made EDM more widely available and appealing over

traditional machining processes (Shailesh, 2010).

2.3.2 Fundamental

Electrical discharge machining (EDM) is one of the earliest non-traditional

machining processes. EDM process is based on thermoelectric energy between the

workpiece and an electrode (Kuldeep 2010). Electro-Discharge Machining (EDM) is a

metal removal process by means of electrical energy released by spark discharges

occurred between an electrode and the workpiece with electrical conductivity to

8

produce a desired -shaped form in a work-piece. The electrode is moved downward

toward the work material until the spark gap that is the nearest distance between both

electrodes small enough so that the impressed voltage is great enough to ionize the

dielectric. Short duration discharges measured in microseconds are generated in a liquid

dielectric gap, which separates tool and work piece. The material in the form of debris is

removed with the erosive effect of the electrical discharges from tool and work piece.

EDM does not make direct contact between the electrode and the work piece where it

can eliminate mechanical stresses chatter and vibration problems during machining

(Anand, 2010). EDM Die-sink uses a copper or graphite to produce an electrode that is

a reversed shape of the final product.

Figure 2.3: Working principle of EDM

Source: Kuldeep 2010

2.3.3 Applications

Die sinking electrical discharge machining (EDM) is one of the most widely

used techniques for the fabrication of die and mold cavities which are finally used for

mass production of metals and polymer products by replication such as die casting and

injection molding. In any replication process, it is expected that the quality mold will

faithfully duplicate its shape and surface texture (Ahsan, 2009). EDM process find

application in various fields such as the automotive, medical, aerospace, electrical and

electronic industries.

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2.4 INJECTION MOULDING MACHINE

2.4.1 Fundamental

In recent years, plastic injection moulds are widely used for producing products

in various areas, such as aerospace, automotive, medical, electronics, and toys. The

quality of these products depends on the moulding parameters chosen. However, as the

wall thickness of plastic parts decreases, the injection moulding operation becomes

more difficult. During the production process, numerous factors cause defects in the

products, such as warpage, shrinkage, sink marks, and residual stress, which are

detrimental to the quality and accuracy of the products. Therefore, it is crucial that the

influencing factors are kept under control during the moulding procedure (Cebeli Ozek,

2012).

The injection moulding process requires the use of an injection moulding

machine, raw plastic material and a mould. These machines consist of two basic parts,

an injection unit and a clamping unit. The plastic is melted in the injection moulding

machine and then injected into the mould, where it cools and solidifies into the final

part. In this process, hot molten polymer is forced into a cold empty cavity of a desired

shape and is then allowed to solidify under a high holding pressure. The entire injection

moulding cycle can be divided into three stages: filling, post-filling and mould opening.

The injection moulding industry, the setting of machine process parameters has

crucial effects on the quality of products. Injection moulding manufacturers have to

obtain the optimal conditions for process parameters before they can produce faster,

cheaper and better quality product. Unsuitable machine process parameter settings can

cause production and quality problems, long cycle times and high production costs.

Final optimal process parameter setting is one of the most important steps in injection

moulding for improving the quality of moulded products Injection moulding processes

are affected by numerous parameters and it is not possible to identify the effects of all

these parameters. Therefore it is necessary to select the parameters that have major

effects on the output.

Some of the potential parameters for an injection moulding process might be the

material drying temperature, injection pressure, barrel temperature, injection time, pack

10

pressure, holding pressure, cooling time, mould temperature, injection speed and others.

In moulding industry, the machine set-up technician will choose the inputs of machine

process parameters and the outputs will depend on the product drawing and customer

requirements (S. Rajalingam, 2012).

Figure 2.4: Injection molding machine with reciprocating screw

Source: S. Rajalingam 2012

In injection moulding process, cavity pressure is the key factor to the product’s

quality and efficiency. If the cavity pressure can be momentarily measured and

monitored, it will provide evidence for the setup of V=P changeover and the end of

packing process, and so will help to cut the cost, shorten the moulding period, save the

mould and reduce the energy consumption. In the meantime, the study of cavity

pressure and melt flow characteristics during injection moulding can provide useful data

for evaluating the polymer’s process ability in injection moulding and designing the

process technology. Some progress has been made in the simulation and control of the

cavity pressure (Wu Hong-wu, 2007).

Manual ejection of the mould also added some variability into the process.

Several parts were plastically deformed while being removed, and gates and runners

were occasionally broken as well. If flatness were an important criterion being

considered, manual ejection would have caused a major effect on the response. In

addition, manual ejection caused some variability in the cooling time of the part. This

11

is because the mould cannot be removed and opened manually in a consistent amount of

time (A. Ghose, M. Montero, D. Odell).

2.4.2 Defects

In the injection molding process, hot melt of plastic is forced into a cold empty

cavity of desired shape called mold. Then, the hot melt is allowed to solidify. Solidified

net shape product is ejected out of the mold upon opening. Although the process is

simple, prediction of final part quality is a complex phenomenon due to the numerous

processing variables. Common defects in injection molding process can be classified in

to two ways. They are:

1. Dimensional related

2. Attribute related

Dimensional related defects can be controlled by correcting the mold

dimensions. But, attribute related defects are generally dependent on the processing

parameters. Some of the common attribute related defects are splay marks, sink marks,

voids, weld/meld lines, poor surface finish, air traps and burn marks. (D. Mathivanan,

2010).

2.4.3 Mould project in plastic injection mould industries

In the local mould-making industries, a large quantity of data is always involved

in every mould project. Mould data consist of data from the plastic product, the mould

design, mould manufacturing and mould testing. Additional data for every mould

project would also include the information of the costs involved in that particular mould

project.

The workflow of a mould project can be categorized into three main areas which

are mould design, mould manufacturing and mould testing. Within each of these main

areas, they can be broken down into stages and subsequently, be broken down further

into phases, within each stage. Figure 2.5 shows a general flowchart to depict the main

stages of a mould project in a typical mould-making industry. It can be seen that if the

start of the mould project were successful, it would then proceed on to have an initial

design stage followed by a detailed design stage. After the mould design, the tool start

can begin and the components are manufactured and assembled. The assembled mould

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