Development of Standardized Efficiency Indicators for ... · Development of Standardized Efficiency...

Development of Standardized Efficiency Indicators

for Plastic Injection Moulds

Mariana Joaquina Borralho Gil

Thesis to obtain the Master of Science Degree in

Mechanical Engineering

Supervisors: Prof. Inês Esteves Ribeiro

Prof. Paulo Miguel Nogueira Peças

Examination Committee

Chairperson: Prof. Rui Manuel dos Santos Oliveira Baptista

Supervisor: Prof. Paulo Miguel Nogueira Peças

Members of the Committee: Eng. Eduardo João de Almeida e Silva

Prof. Inês da Fonseca Pestana Ascenso Pires

November 2015

ii

Acknowledgments

I wish to express my sincere thanks to Prof. Paulo Peças and Prof. Inês Ribeiro, for providing me all

the necessary guidance for this dissertation. For all the understanding and support, and most

importantly, their friendship.

I would like to thank especially to Maria Pissarra and Pedro Cavaco for their friendship, help and

support in this dissertation and thank to all my friends, “Artolazz” for their friendship throughout these

university years.

Also, I would like to thank to Rita Bravo and Ana Raposo for their companionship during these last

months and lunch hours.

Finally and the most important thank, is for my parents and brothers, who always believed in me even

when I did not, for the continuous encouragement, support, attention and patience.

iii

Resumo

O conceito de Eficiência Operacional, rácio entre input e output de um negócio, foi adaptado ao

processo de moldação por injeção de plásticos de modo a criar Indicadores de Eficiência. Propõem-

se nesta dissertação Indicadores de Eficiência de consumo de massa e de energia.

O input, é a quantidade mínima de recursos necessários ao processo, denominada de Valor Base, e o

output é a quantidade real de recursos consumida, denominada de Valor Real. Os valores utilizados

para o cálculo do Valor Base são obtidos através de relações empíricas e teóricas. Os valores

utilizados para o cálculo do Valor Real são obtidos através de um software de simulação do processo

de injeção. Para calcular a energia mínima requerida e a energia real, é utilizado um modelo de

energia. Quando se utiliza o modelo de energia é necessário reunir uma base de dados de máquinas

de injeção disponíveis no mercado de modo a obter uma equação linear que relacione a potência

instalada da máquina com a sua força de fecho.

O objetivo dos Indicadores de Eficiência é possibilitar a comparação de alternativas de design de

molde e a comparação de moldes de dimensões e designs diferentes. Nesta dissertação foram

realizadas análises de sensibilidade à variação de material e à variação do número de cavidades do

molde. Com os resultados obtidos foram criados e propostos rótulos de classificação para moldes.

Palavras-chave: Moldação por injeção; Eficiência Operacional; Indicadores de Eficiência;

Alternativas de design de molde; Etiqueta classificativa para moldes;

iv

Abstract

Operational Efficiency, a ratio between input and output of a business, was adapted in this study to

Injection Moulding process in order to create the Standardized Efficiency Indicators for Plastics

Injection Moulds. The proposed indicators regards to mass and energy consumption.

The input, the minimum amount of resources required, was named Baseline, and the output, the real

amount of resources consumed, was named Actual Value. The values used in the calculation of the

Baseline are based on theoretical and empirical knowledge. The values used in the calculation of

Actual Value are obtained from injection moulding simulation software. To calculate the Baseline’s and

Actual Value’s energy consumption is used an energy consumption model. To use the model is

created an injection moulding machine databases in order to obtain a standard installed

power/clamping force equation.

The Standardized Efficiency Indicators aim is to compare moulds with different design alternatives and

parts with different sizes. Sensitive analyses were performed to material variation and number of

cavities. With the results obtained were developed and proposed classification labels for moulds.

Keywords: Injection Moulding; Operation Efficiency; Standardized Efficiency Indicators; Design

mould alternatives; Mould Label;

v

Table of Contents

Resumo.................................................................................................................................................. iii

Abstract ................................................................................................................................................. iv

List of Figures ..................................................................................................................................... viii

List of Tables .......................................................................................................................................... x

Nomenclature ...................................................................................................................................... xiii

1. Introduction .................................................................................................................................... 1

2. Plastic Injection Design of the mould and the injection process ............................................. 3

2.1. The Process .......................................................................................................................... 3

2.1.1. The moulding cycle ................................................................................................... 4

2.2. Injection machine ................................................................................................................... 5

2.3. Parameters and variables of the process .............................................................................. 6

2.4. Material .................................................................................................................................. 8

2.5. Mould ..................................................................................................................................... 9

2.5.1. Feeding System ...................................................................................................... 11

2.5.2. Cold Runner System ............................................................................................... 11

2.5.3. Hot Runner System ................................................................................................ 13

2.5.4. Cooling System ....................................................................................................... 14

2.6. Simulation Software - Moldflow ........................................................................................... 14

3. Efficiency of the production systems in a Life Cycle Perspective ......................................... 16

3.1. Global trends in improving the efficiency of the production systems .................................. 16

3.2. Methodologies and Analysis of Energy and Environmental Efficiencies ............................. 17

3.3. Efficiency in Equipment ....................................................................................................... 18

3.4. Standards and labels ........................................................................................................... 19

3.5. Efficiency in Injection Moulding ........................................................................................... 20

4. Proposed Methodology ............................................................................................................... 22

4.1. Input and Output definitions................................................................................................. 22

4.1.1. Case Study ............................................................................................................. 23

4.2. Baseline ............................................................................................................................... 24

4.2.1. Mass Baseline ........................................................................................................ 24

4.2.2. Energy Baseline ...................................................................................................... 24

4.3. Actual Value ......................................................................................................................... 27

vi

5. Alternative Mould Design Solutions .......................................................................................... 29

5.1. Influence on performance .................................................................................................... 29

5.1.1. Feeding system ...................................................................................................... 29

5.1.2. Cooling system ....................................................................................................... 30

5.2. Case Study .......................................................................................................................... 30

5.3. Modelling Mould Design Alternatives .................................................................................. 30

5.3.1. Import CAD Model .................................................................................................. 31

5.3.2. Mesh ....................................................................................................................... 31

5.3.3. Material Selection ................................................................................................... 32

5.3.4. Gate Location ......................................................................................................... 33

5.3.5. First Fill Analysis ..................................................................................................... 34

5.3.6. Feeding System and Fill Analysis ........................................................................... 35

5.3.7. Cooling System ....................................................................................................... 38

5.3.8. Cooling Analysis ..................................................................................................... 40

5.3.9. Cool +Fill + Pack + Warp Analysis ......................................................................... 43

5.4. Actual Value Calculation ...................................................................................................... 46

5.4.1. Energy consumption ............................................................................................... 46

6. Standardized Efficiency Indicators ............................................................................................ 49

6.1. Mass Baseline ..................................................................................................................... 49

6.2. Energy Baseline .................................................................................................................. 49

6.2.1. Calculation of Thermodynamic Energy ................................................................... 49

6.2.2. Calculation of Energy Consumption of the injection machine ................................ 50

6.2.3. Determination of the coefficients ............................................................................ 51

6.3. Mass Indicator ..................................................................................................................... 52

6.4. Energy Indicator .................................................................................................................. 54

6.5. Assessment of Material Variation ........................................................................................ 58

6.5.1. Baseline comparison .............................................................................................. 58

6.5.2. Standardized Efficiency Indicators ......................................................................... 60

6.6. Cavities Assessment ........................................................................................................... 62

7. Proposed Methodology for Standardized Efficiency Indicators ............................................. 66

8. Conclusions ................................................................................................................................. 70

Future Work .......................................................................................................................................... 71

Bibliography ......................................................................................................................................... 72

Annexes ................................................................................................................................................ 77

Annex A. Feeding and Cooling Systems. .................................................................................. 77

vii

Annex B. Cooling Results: Definitions and ranges ................................................................... 78

Annex C. Material Variation and Cavities Assessment ............................................................. 79

viii

List of Figures

Figure 2-1 Injection Moulding Process - Machine and its units ............................................................... 4

Figure 2-2 Injection Moulding Cycle ........................................................................................................ 5

Figure 2-3 Mould Base [5] ..................................................................................................................... 10

Figure 2-4 Mould Channels [5] .............................................................................................................. 10

Figure 2-5 Gates ; Feed System Element [19] ....................................................................................... 11

Figure 2-6 Runners; Feed System Elements [19] .................................................................................. 11

Figure 2-7Cross Section Types [19] ...................................................................................................... 12

Figure 2-8 Sprue; Feed System Elements [24] ..................................................................................... 13

Figure 2-9 a) Externally Heated; b) Internally Heated; c) Insulated [24] ............................................... 13

Figure 2-10 Cooling System Elements [31] ........................................................................................... 14

Figure 2-11 a) Element Types; b) Types of Mesh [34] ........................................................................... 15

Figure 3-1 Approximate Energy Cost Distribution for Plastics Processing [53] .................................... 20

Figure 4-1 Parts ..................................................................................................................................... 23

Figure 4-2 Study Methodology .............................................................................................................. 24

Figure 4-3 Installed Power vs. Clamping Force - ENGEL MACHINES [62] [63] .................................. 25

Figure 5-1 Overview of tasks and analysis ............................................................................................ 31

Figure 5-2 Model oriented with -Z direction; Part1 ................................................................................ 31

Figure 5-3 Mesh Statistics; a) Part1; b) Part2; c) Part3 ........................................................................ 32

Figure 5-4 PP 3120 MU5 Properties ..................................................................................................... 33

Figure 5-5 Best Gate Locations; Part1 .................................................................................................. 33

Figure 5-6 a) Flow Resistance Indicator; b) Gate Location; Part1 ........................................................ 33

Figure 5-7 Fill Time Result; a) Contour; b) Shading; Part2 ................................................................... 34

Figure 5-8 Pressure at V/P Switchover; Part2 ....................................................................................... 34

Figure 5-9 a) Bulk Temperature; b) Flow Front Temperature; Part2 ..................................................... 35

Figure 5-10 Design of the Feeding Systems ......................................................................................... 35

Figure 5-11 Moulding Window; Part2 .................................................................................................... 36

Figure 5-12 Feeding Systems; a) Cold Runner; b) Hot Runner; Part2 ................................................. 37

Figure 5-13 a)Shear stress at wall; b) Shear Rate; Part2 ..................................................................... 38

Figure 5-14 Log file:Shear Stress at wall; Part2 .................................................................................... 38

ix

Figure 5-15 Wizard Cooling System; Part1 .......................................................................................... 39

Figure 5-16 a) Conventional Cooling System; b) Conformal Cooling System; Part2 ........................... 40

Figure 5-17 Cooling Results: a) Coolant Temperature; b) Reynolds Number; Part2 CC ...................... 40

Figure 5-18 a) Average part temperature; b) Maximum part temperature: Part2 CN ........................... 41

Figure 5-19 Temperature profile; Part2 CN ........................................................................................... 41

Figure 5-20 a) Mould Temperature; b) Part Temperature; Part2 CN ..................................................... 42

Figure 5-21 Time to reach Ejection; Part2 CN....................................................................................... 42

Figure 5-22 a) Frozen Layer Fraction; b) Volumetric shrinkage at Ejection; Part2 CN ......................... 43

Figure 5-23 a) Hold Pressure; b) Deflections: All effects; Part2 CN...................................................... 44

Figure 5-24 a) Shrinkage Effect; b) Cooling Effect; c) Orientation Effect; Part2 CN ............................. 45

Figure 6-1 Mass Consumption Indicators .............................................................................................. 52

Figure 6-2 Energy Consumption Indicator............................................................................................. 55

Figure 6-3 Baseline Energy Fractions ................................................................................................... 55

Figure 6-4 Actual Value Energy Fractions ............................................................................................. 55

Figure 6-5 Thermodynamic and Machine Energy of each material ...................................................... 59

Figure 6-6 Cycle time for each material ................................................................................................ 60

Figure 6-7 Mass Indicator of different materials .................................................................................... 60

Figure 6-8 Energy Indicator for each material ....................................................................................... 61

Figure 6-9 Energy per Part of different moulds; Actual Value ............................................................... 63

Figure 6-10 Time Indicator..................................................................................................................... 64

Figure 6-11 Energy Indicator ................................................................................................................. 65

Figure 6-12 Machine Energy Fluctuations ............................................................................................. 65

Figure 7-1 MoldFlow scheme guide ...................................................................................................... 67

Figure 7-2 Overview of the Energy Model applied to Baseline and Actual Value ................................. 67

Figure 7-3 Mould Label: Mould Design Alternative comparison ............................................................ 68

Figure 7-4 Mould Label: Part's Dimensions comparison ....................................................................... 68

Figure 7-5 Mould Label: Material comparison ....................................................................................... 68

Figure 7-6 Mould Label- Cavities comparison ....................................................................................... 69

Figure A-1 Feedings Systems ............................................................................................................... 77

Figure A-2 Cooling Systems .................................................................................................................. 77

x

List of Tables

Table 2-1Characteristics of Injection Machines - comparison [11] .......................................................... 6

Table 2-2 Thermoplastics - Properties resume ........................................................................................ 8

Table 4-1 Design Mould Alternatives ..................................................................................................... 23

Table 4-2 Machines Available on Market – ENGEL [62] [63] ................................................................. 28

Table 5-1 Parts Dimensions................................................................................................................... 30

Table 5-2 Engineering Solutions Combinations .................................................................................... 30

Table 5-3 Mesh Elements Length .......................................................................................................... 31

Table 5-4 Gate Dimensions ................................................................................................................... 36

Table 5-5 Feeding System Dimensions [mm] ........................................................................................ 37

Table 5-6 Fill Analysis Results ............................................................................................................... 38

Table 5-7 Cooling Channels Design Parameters[71] ............................................................................ 39

Table 5-8 Cooling Results...................................................................................................................... 43

Table 5-9 Cool+Fill+Pack+Warp Analysis Results................................................................................. 45

Table 5-10 Values obtained from Moldflow Simulation .......................................................................... 46

Table 5-11 Material Properties - PP 3120 MU5 ..................................................................................... 46

Table 5-12 Thermodynamic Energy....................................................................................................... 47

Table 5-13 Thermodynamic Power of each part .................................................................................... 47

Table 5-14 Machine Characteristics: Clamping Force and Installed Power ......................................... 47

Table 5-15 Energy Model Coefficients ................................................................................................... 48

Table 5-16 Machine Energy for each part ............................................................................................. 48

Table 5-17 Total Energy for each part ................................................................................................... 48

Table 6-1 Material Properties: PP 3120MU5 [73][74][75][76] ................................................................ 49

Table 6-2 Property Parts ........................................................................................................................ 49

Table 6-3 Thermodynamic Energy for each part ................................................................................... 49

Table 6-4Theoretical values of Injection Pressure, Projected Area and Clamping Force ..................... 50

Table 6-5 Determination of Maximum Flow Rate [63] ........................................................................... 50

xi

Table 6-6 Theoretical Injection Times .................................................................................................... 50

Table 6-7 Mould open/close times ......................................................................................................... 51

Table 6-8 Theoretical cycle time for each part ....................................................................................... 51

Table 6-9 Thermodynamic Power for each part .................................................................................... 51

Table 6-10 Energy Model Coefficients ................................................................................................... 51

Table 6-11 Machine Energy for each part .............................................................................................. 51

Table 6-12 Total Energy for each part ................................................................................................... 52

Table 6-13 Final Volume; Hot runners ................................................................................................... 53

Table 6-14 Mass Fluctuations ................................................................................................................ 53

Table 6-15 Total Mass Fractions- Cold Runner System ........................................................................ 54

Table 6-16 Final Volume; Cold Runners ................................................................................................ 54

Table 6-17 Energy Fluctuations ............................................................................................................. 56

Table 6-18 Pressure Fluctuations .......................................................................................................... 57

Table 6-19 Cycle time and Installed Power Fluctuations ....................................................................... 57

Table 6-20 Total Energy; Baseline ......................................................................................................... 59

Table 6-21 Total Energy, Machine Energy and Thermodynamic Energy Fluctuations .......................... 61

Table 6-22 Cycle Time Fluctuations ...................................................................................................... 61

Table 6-23 Clamping Force, Real Installed Power, Open/close time and Cycle time for each mould;

Actual Value ........................................................................................................................................... 63

Table 6-24 Machine Plates Dimensions and Mould Dimensions; Actual Value .................................... 63

Table 6-25 Time per Part ....................................................................................................................... 64

Table C-1 Material Properties ................................................................................................................ 79

Table C-2 Mass Values; Thermodynamic Energy; Baseline.................................................................. 79

Table C-3 Clamping Force; Baseline ..................................................................................................... 79

Table C-4 Installed Power and Filling time; Baseline ............................................................................ 79

Table C-5 Cooling Time; Open/close Time and Cycle Time; Baseline .................................................. 79

Table C-6 Thermodynamic Power, Model Coefficients, Machine Energy and Total Energy; Baseline . 80

Table C-7 Filling Simulation Results ...................................................................................................... 80

Table C-8 Cooling Simulation Results ................................................................................................... 80

Table C-9 Cool+Fill+Pack+Warp Analysis Results ................................................................................ 80

xii

Table C-10 Simulation Results .............................................................................................................. 80

Table C-11 Thermodynamic Energy and Thermodynamic Power; Actual Value ................................... 80

Table C-12 Installed Power, Model Coefficients, Machine Energy and Total Energy; Actual ................ 81

Table C-13 Baseline Values ................................................................................................................... 81

Table C-14 Thermodynamic Power, Thermodynamic Energy, Machine Energy, Total Energy; Baseline

............................................................................................................................................................... 81

Table C-15 Actual Values ....................................................................................................................... 81

Table C-16 Thermodynamic Power, Thermodynamic Energy, Machine Energy, Total Energy; Actual

Value ...................................................................................................................................................... 81

Table C-17 Installed Power, Cycle Time and Machine Power Coefficient Fluctuations ........................ 82

xiii

Nomenclature

CC Cold Runners and Conformal Cooling

CN Cold Runners and Normal Cooling

EUROMAP European Association for Plastics and Rubbers Machinery Manufacturers

HC Hot Runners and Conformal Cooling

HN Hot Runners and Normal Cooling

LCA Life Cycle Assessment

LCC Life Cycle Cost

LCSP Lowell Center for Sustainable Production

MTs Machine Tool System

NMR Next Manufacturing Revolution

PA6 Polyamide 6

PC Polycarbonate

PP Polypropylene

PS Polystyrene

WSCSD World Business Council for Sustainable Development

1

1. Introduction

Nowadays companies want to stay competitive while reducing the environmental impact of processes

and products, therefore they are realizing the financial and environmental benefits of practising

sustainable manufacturing. Coupled with the concept of sustainability, methodologies like Life Cycle

Assessment, Eco-efficiency, Eco-Design etc. have emerged and become the main evaluation and

decision tools for process and products development focused on resource efficiency. It is mandatory

that these processes become more and more resource efficient in order to be sustainable and to

guarantee the desired competitiveness level.

In this thesis the concept of operational efficiency is applied to formulate the Standardized Efficiency

Indicators for Plastic Injection Moulds. Injection moulding process is a manufacturing process with

great prominence in the processing of polymers materials. The mould is the main tool that shapes the

part to be produced. Therefore the design and the quality of the mould are very important to ensure

that the consumed resources are minimized and a cyclic reproduction of plastics without defects.

To improve the efficiency of injection moulding process efforts are made to reduce the cycle time and

improve the cooling, in order to produce products with quality and increase productivity.

Depending on the part to produce and on the company production volume required, the design mould

alternatives can be more or less advantageous. With the several engineering solutions available for

mould design, it is important to know what the best suited choice for a particular part is. The main

issue is how injection moulding companies can compare moulds and moulds’ efficiency, from different

potential suppliers. With the lack of a decision tool, it is pertinent to develop a metric that attempt to

classify moulds, making their comparison fair, comprehensive and accurate as possible.

The Standardized Efficiency Indicators methodology are proposed in order to compare the

performance of different mould designs in the injection moulding process, regarding three main

aspects: mass and energy consumption, related with resources efficiency; and execution time, related

with productivity. The efficiency is calculated using simple ratios between the minimum input required

to accomplish the process (Baseline values) and the real or expected actual time and resources

consumed (Actual value). The minimum process resources consumptions are estimated by empirical

and theoretical models and the actual values can be estimated by numerical simulation of injection

moulding (or real industrial data if available). The aims of this thesis are to propose and validate the

concept behind these indicators, to assess if they can be used in the future as a standard to

characterize the performance and efficiency of the injection moulds.

As an application case for the developed indicators, three plastics parts were designed with different

dimensions. For each part, four mould design alternatives were considered to analyse two types of

feeding system and two types of cooling systems. Additionally a sensitivity analysis to the material and

to the number of cavities variation was performed.

2

This thesis starts with a state of the art of the injection moulding process, presented in chapter 2, and

an overview about efficiency of the production systems, particularly the injection moulding process,

presented in chapter 3. In chapter 4 the methodology of Standardized Efficiency Indicators is proposed

and the energy model equations are described. The parameters to calculate the Actual value were

obtained from simulation, so in chapter 5 the procedures are described. In chapter 6 the Standardized

Efficiency Indicators are calculated and discussed. In chapter 7 an explanation on how the energy

model is used for Baseline and for the Actual Value, the tasks performed in simulation software and

the proposed mould labels are presented. Finally in chapter 8, the conclusions and future work are

presented.

3

2. Plastic Injection Design of the mould and the injection

process

The increasing needs of the world population have been intensifying the plastics consumption in

various sectors of the industry, automotive, aeronautical, electronic, etc. This demand has raised the

level of rising of industry standards, leading to the development of manufacturing processes, requiring

more speed with competitive final costs.

Due to its potential, injection moulding has become a very important manufacturing process with great

prominence in processing components of polymeric materials, which are increasingly used due to its

characteristics such as low weight, flexibility, low electrical conductivity / thermal, impact resistance,

low melting point and easy colouring [1].

The development of this process led to the development of plastics, improving their characteristics,

properties and capabilities of forming and moulding. This development also led to the emergence of

new materials (e.g biodegradable polymers). The injection moulding process can process

thermoplastic, thermosetting, rubber and also silicone [2]. This process allows the production of a wide

range of parts, varying in size, complexity and application, with dimensional accuracy [2].

2.1. The Process

The injection moulding process was patented in 1872 by the Hyatt brothers[2]. Over the 20th century it

had a great evolution regarding the moulding machines and the range of materials to be processed.

The injection moulding process consists in the heating of the material until it reaches a low viscosity to

be injected in the mould. Then the material is cooled and finally the produced part is ejected. This

process requires an injection machine, a mould and the raw plastic material.

Raw material pellets are introduced in the hoper and fall into the barrel where they are compressed

forming a “solid bed”[3]. The pellets start to melt due to the heat transferred from the barrel walls and

also due to the heat that is generated from the screw rotation [2].

During compression the air exits through the hopper. The hopper simply directs the pellets to the

screw feed zone. In modern machines the hopper was replaced by a silo that dries the material,

saving time and energy because it avoids the transport of the pellets[4]. Another advantage of the silo

is keeping the material hot until it reaches the screw feed zone, which makes the melting of the

material easier.

The material moves past the hydraulic screw and the advance of the material makes the screw move

backwards. When the volume of material needed to fill the mould cavity is in the front of the screw, the

screw moves forward, injecting the material into the mould. This amount of material that is injected is

4

referred to as the shot [5].The parts cool and solidify, then the mould opens and ejectors pins move

forward removing the injected parts. The injection mould closes and the process repeats itself (Figure

2-1).

Figure 2-1 Injection Moulding Process - Machine and its units

The injection moulding process has several variants like Bi-injection, Insert Moulding, thin wall

injection moulding, co-injection etc. Bi-injection is a variant of multiple-component moulding process.

In general is used with two plastics that may be compatible or incompatible according part to produce.

It is used to produce parts like toothbrushes and mobile casting. Insert Moulding is an injection

moulding process where the material is injected around an insert or inserts previously positioned in the

cavity of the mould. The resulting part is a strong bonded assembly. The inserts are encapsulated by

the injected material. The Thin wall injection moulding arises in the attempt of create smaller and

lighter parts. The range of thickness consider “thin” vary according the type of product and industry. Is

used to produce part for several types of industries such as medical, automotive, optical, electronics,

computing equipment, etc. [6]. In Co-injection moulding process are injected two different but

compatible polymers. One is the skin plastic and then the other is the core plastic. This type of

injection combines the two material properties in one part and maximizes the overall performance/cost

ratio[7].

2.1.1. The moulding cycle

The optimization of the injection moulding cycle is essential in order to ensure the economic

competitiveness since the initial investment in equipment is very high. To achieve successful and

efficient injection moulding, the processing conditions like injection pressure, temperature of the mould

and melt, injection velocity, have to be adjusted according the material properties, geometry of the

part and the final specifications of the product[2][8].

The process is composed of five sequential phases: Mould closing, fill, pack and hold, cooling and

open eject (Figure 2-2).

5

Figure 2-2 Injection Moulding Cycle

The mould closing is the beginning of the cycle. The two halves of the mould must be securely

closed. The clamping unit is responsible for the mould closing, therefore this phase is also known as

Clamping[5].The closing of the mould should be done as fast as possible. The speed must be suitable

to the dimensions of the plates of the machine and avoid damage in the surfaces of the mould. The

speed depends on the mould characteristics and on the closing distance [2].

The filling of the mould cavity is performed by the motion of the screw that forces the material into

the mould. The injection starts when the nozzle of the barrel is in contact with the mould. The injection

phase ends when 95% of the cavity is full[2]. The velocity of the filling it is adjusted according to the

part’s final quality.

After injection the cavity continues under pressure in order to reduce the contraction effect due to the

cooling – this is the pack & hold phase. This pressure should not be excessive otherwise it will

damage the part making ejection difficult. This phase ends when the gate freezes or when the part is

cooled enough that inhibits the material flow [2].

After the gate freezes the screw restarts its rotation to melt the pellets for the next cycle. The cooling

phase ends when the part reaches the extraction temperature, i.e., the temperature that allows the

ejection of the part without distortion. The cooling phase is controlled by the thickness of the part and

by the design of the cooling system[2].

The mould opens and the ejection pins move forward to eject the part. In this phase the feed system

is detached from the part.

2.2. Injection machine

The injection moulding machine is composed of the following units: power unit, injection unit, clamping

unit and control unit plus the mould. The power unit provides power to the actuators, the hydraulic

cylinders and the hydraulic motors. The latter unit is characteristic of hydraulic machines. Electric

machines are directly driven by electric motors. The injection unit is the unit responsible for the

transport, heating, melting, injection and pressurization of the material. The clamping unit is

responsible for the opening and close of the mould. It must have the necessary strength to open and

close the mould, and to maintain the mould closed during the injection. The clamping force depends

6

on the injection pressure and on the projected area. The clamping system also integrates the ejectors

pins.

There are three types of injection machines: Hydraulic machines, Semi-hydraulic machines and All

Electrics machines (Table 2.1).

Hydraulic machines were the only available machines until 1983, when Nissei Plastic Industrial Co.,

LTD introduced the first all-electric injection moulding machine[9]. Electrics machines are the most

precise ones but Hydraulic machines are the most predominant around the world.

The main advantage of All Electric machines towards other machines is reduction of operations costs

through energy savings, from 30% to 70%[10].

All-Electric moulding machines are usually referred as assuring good repeatability, accuracy,

consistency [11] and as being faster than hydraulic machines, however they are in general more

expensive machines [11]. They are cleaner machines since they don’t use hydraulic oil, require lower

maintenance and are quiet. All-Electric machines imply the use of servomotors on both clamp and

injection end [11]. This type of machines can have problems with reactive power, power that returns to

the grid, that affects voltages of the systems [12].

Semi-hydraulic also known as Hybrid Moulding Machines [10], combine the best advantages of

hydraulic, pressure-generating capability, and of All-Electric machines, the precision and energy

efficiency of the electric motor. In Hybrid machines the screw is driven by an electric motor, and the

clamp unit uses a hydraulic system. This kind of machine allows faster cycles (open and close) and

faster injection in thin walls parts as resemblance to the all electrics machines.

All-Electric Hybrid Hydraulic

Energy Best Better Good/Poor

Accuracy/repeatability Highest High Poor

Cleanliness Excellent Ok Poor

Noise Low Medium High

Maintenance Low Medium High

Use of existing moulds Low adaptability Easy Easy

Cost High Medium Low Table 2-1Characteristics of Injection Machines - comparison [11]

In hydraulic machines most of the required energy it is used by the hydraulic pump-motor 80%[11].

Even in periods of low hydraulic demand, for example in cooling, the pump consumes the same

energy and the motor only needs about 20%, so most of the energy is wasted. Variable Speed Drives

allow energy savings, because enables the process to be dependent on the demand for hydraulic fluid

power [11].

2.3. Parameters and variables of the process

The set of process parameters are those who are defined before the process begins and the operator

can’t change them. These parameters are defined in the selection of the equipment and in the project

phase of mould [2].

7

The most important process parameters are the geometry of the part, the feed system, its geometry

and location, the capacity of the injection moulding machine, the geometry of the nozzle and the

temperature distribution on the cavity surface [13].

The variables are the processing conditions that can be adjusted by the operator. The most important

variables are: temperature profile in the barrel, mould temperature, injection speed, injection pressure,

second pressure, second pressure time, screw rotation velocity, cooling time, open/close velocity,

clamping force and cycle time [2].

The temperature profile of the material along the barrel is due to the heat generated between the

polymeric material and the barrel walls and the screw. The profile temperature depends on the

material to melt, on the screw geometry and on the cavity geometry. The profile temperature must

meet a certain range of temperatures in order to guarantee the flow of the material without causing its

degradation. High injection temperatures increase cycle time and the energetic consumption, benefit

contraction, brightness and transparency[2]. Low temperatures difficult the filling of the cavity

enhancing the weakening welding lines.

The mould temperature influences and determines most of the properties of the injected part because

it influences the structural development of the polymer during the cooling phase. The mould

temperatures range depends on the nature of the material. The mould temperature varies a lot during

the injection cycle. This temperature is regulated during the injection cycle in order to reduce the

mould’s thermal amplitude. High temperatures increase brightness, contraction and transparency. Low

temperatures increase internal tensions.

The injection speed is the progression of the screw across time, so is the mass flow rate that is

injected. This processing condition is very important in the process in order to ensure a low flow

viscosity and reduce heat losses during the injection phase. However very high injection speed can

cause defects on the mould. The optimal injection speed corresponds to the minimum injection

pressure. In the end of the injection phase is recommended to reduce the injection speed in order to

reduce equipment wear. The speed rotation of the screw is important to obtain a homogenous melt

along the process. High speed rotation is used when a fast melt of the raw material is needed.

After the injection phase, pressure is applied to the cavity. This pressure as the purpose of

compensate the volumetric contraction that the material is subject to during the cooling phase. With

the freezing of the material in the gate, the pressure drops and the pack phase ends.

The cooling time is accounted after the end of the pressure phase until the extraction temperature for

the material is reached.

The Clamping force is required to keep the mould closed during injection process; (it is usually

expressed in ton or kN). This force will oppose to the pressure exercised by the injected material in the

mould cavity. The clamping force must be adjusted to be higher than the required to avoid mould

opening during injection.

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2.4. Material

In the injection moulding process the most used raw plastic materials are thermoplastic and

thermosetting polymer .The materials to be processed have specific characteristics that must be take

into account for a good process performance. The plastics have low thermal diffusivity, are bad heat

conductors, making the thermal changes that must occur to their melting/cooling difficult.

Melted thermoplastics are fluids of high viscosity. The viscosity is function of the deformation rate of

the material that with high deformation velocities can be lower. So is recommended to inject the

material with high velocity [2]. The density of polymeric materials has high thermal dependence. With

the increase of the temperature the linear expansion coefficient values increase, and in the cooling

phase with the decrease of temperature the material contracts [2].

Thermoplastics Density [g/cm3]

λ Tmelt ºC α [mm2/s]

Semi-Crystalline

PP 0.91755 0.75 118 0.0908

PBT 1.3533 0.55 201 0.0792

PA6 1.358 0.4 200 0.1040

PET 1.405 0.45 232 0.1116

Amorphous

ABS 1.0281 0 98 0.1272

PS 1.0518 0 100 0.0792

PC 1.1859 0 143 0.1335

Table 2-2 Thermoplastics - Properties resume

Thermoplastics are suitable for injection because they have a great ability to smooth and flow after

heating. They can be easily recycled without negatively affecting the material properties[14], have a

reduced environmental impact and their versatility allows being used in several applications.

Thermoplastics materials have interesting properties like low density, high resistance, transparency

and shine (some of them) and chemical and environmental resistance(some of them) [2]. A

disadvantage of thermoplastic polymers is that they melt if heated, what causes problems in some

applications[14].

The thermoplastics can be divided into two classes based on the molecular structure: amorphous or

semi-crystalline. Amorphous thermoplastics molecular chain is completely chaotically arranged. A

semi-crystalline thermoplastic has a crystalline molecular structure in some areas [15]. They can be

characterized also by the degree of crystallinity and glass transition temperature [15]. The differences

between amorphous and semi-crystalline thermoplastics have more significant effect on behaviour

during processing [16]. At solid state amorphous and semi-crystalline thermoplastics present different

molecular structures, however in melt state both molecular structures are amorphous [16]. In Table 2-2

are presented some properties of thermoplastics, where λ is the degree of crystallinity, Tmelt is the

glass transition temperature and α is the thermal diffusivity.

A thermoset resin is a polymer that require a two stage-polymerization and the polymerization is

permanent and irreversible [17]. The curing of this polymer can be induced by heat and/or radiation.

After solidification a thermoset resin cannot be reheated or melt to be reshaped and are resistant to

9

solvents[18]. Amino, epoxy, phenolic, polyimides, silicone and unsaturated polyesters are known as

thermosets [18]. Regarding their chemical structure, thermosets have cross-linked molecular chains

and the thermoplastics have linear molecular structure.

Thermoset materials are stronger than thermoplastics due to its structure, a three dimensional network

of bonds known as cross-liking, and are also more suitable to high-temperature applications [19] and

grant more dimensional stability than most of the thermoplastics [18]. They are more brittle than

thermoplastics and tend not to be recycled due to its permanent shape [19]. Thermosets are used in

applications such as electronics chips, fibre-reinforced composites, polymeric coatings and dental

fillings [18]. Thermoset are cheaper than thermoplastics but as mentioned before they cannot be

recycled. In a thermoset polymer is more difficult the surface finish [14].

In the injection moulding process thermoplastics are safer than thermosetting because thermosetting

must be injected in a certain time otherwise it will cause chemical crosslinking in the screw and in the

valves and potentially damage da injection machine. Thermoplastics have a fast and easy processing

that leads to competitive manufacturing processes.

The most important properties of the material in injection moulding process are the viscosity,

contraction, thermal sensibility and anisotropic character [2].

2.5. Mould

The mould is the tool where the part is produced. The design of the mould is dependent on the size

and shape of the part to produce. The mould may have several cavities and it may vary in amount of

the various constituent elements and their arrangement. The design of the mould depends also on the

size and capacity of the injection machine were it will be placed[20]. The thermal properties of the

mould material are very important to achieve a good and uniform cooling of the part. Seeing the mould

as a heat exchanger the mould material must have good thermal conductivity. Moulds are typically in

aluminium, hardened steel and pre-hardened steel [21][22]. The determining factor in the choice of the

material to build a mould is the cost of the material [21].

The mould splits in two halves. Each half is mounted to the mould base. The mould base is attached

to the plates inside of the injection machine. One half of the mould is fixed and the other slides to open

and close the mould. The two main components of the mould are the mould cavity and the mould core

[5]. When the mould is closed the space between the halves forms the part cavity, the space that will

be filled with the melted material.

The mould cavity includes the mould cavities and the feeding system. The mould core has the ejection

system that ejects the solidified part out of the mould (Figure 2-3).

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Figure 2-3 Mould Base [5]

The nozzle connects the injection machine to the mould and this connection is just made by contact.

The temperature of the nozzle is an important parameter, and it must be set close to the melting

temperature of the material to facilitate the injection process.

The runner system is responsible for the distribution of the molten plastic flow into the mould cavities.

The sprue is the channel where the material flows from the nozzle to the runners. The runners carry

the material from the sprue to the cavities. The gate is a small entrance that prevents the material to

return to the runner after the injection because it solidifies first because of its small dimension. The

material that solidifies inside the runner is attached to the part and it must be separated after the part

has been ejected from the mould. The mould also contains the cooling system, a group of channels

wherein a fluid flows in order to cool the part. The figure 2-4 shows the mould channels and elements.

Figure 2-4 Mould Channels [5]

A good injection mould should ensure a good flow of the material as well as an easy removal of the

produce part, so the mould walls must have a draft angle [5]. In the design of the mould should be

taken into account a good distribution of the feed and cooling channels. It is very important to have a

good cooling system, to provide a homogeneous cooling and consequently obtain a quality part [23].

The quality of the part is also influenced by the location of the gate, thickness variations, contraction,

warping and gases output, so all of these must be considered in the design of the mould.

11

Figure 2-6 Runners; Feed System Elements [19]

Figure 2-5 Gates ; Feed System Element [19]

2.5.1. Feeding System

The feeding system begins to be designed by defining the gate location for the part and the other

elements are placed depending on it. The feeding system must be designed with the objective of

guarantee a balanced flow to fill the each cavity part ate the same rate. To achieve this goal it must be

taken into account if the mould has a single cavity or multiple cavities, the design of the cavity, the

location of the sprue in the mould, and the shape of the sprue, runners and gates[24]. The feeding

system whenever possible must have short channels and the lowest shot weight. The feeding system

can be cold or hot runner system.

2.5.2. Cold Runner System

A cold system is constituted by the sprue, runners and gate. It’s named cold because the material

inside the system is cooled along with the part. Since the material solidifies, to make the extraction

easier, the channels of the system must have a draft angle. Besides the draft angle, when designing

cold runner system it is important that has a higher thickness than the part to produce. This ensures

that the melted material can be packed into the part and can cool without restriction [25]. The feeding

system is ejected with the part and removed after. The removal usually leaves a mark in the part.

Gate

The gate is a small orifice through which the material enters the mould cavity. For each part it must be

selected the type of gate, location and dimensions. Gate design depends on the part specifications,

the material, and is very important regarding part quality and productivity[26] ( Figure 2-5).

The gate can be a single or multiple. A single gate gives better results “unless the length of the melt

flow exceeds practical limits”[26]. A single gate ensures a more uniform distribution of material,

temperatures, packing and better orientation effects. Multiple gates create weld lines where the flows

from the several gates meet [26]. The cross-section shape defined for the gate must be the same for

the other channels of the system. Smaller dimension allows an easy detachment and reduces the

visible mark on the part. Gate sizing is adjusted according the appearance, residual stress and

dimensional stability required.

The gate location is the best location that guarantees a fast and uniform mould filling. The gate

location should be a location with low flow resistance and an area with low external stress since the

gate location is a location with high residual stress [26].

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Figure 2-7Cross Section Types [19]

Runner

The runners are the channels that direct the melt flow from the sprue to the mould cavity (Figure 2-6).

A proper runner design will allow a balanced filling, an easy ejection of the part, good control of the

filling/packing/cycle time[26] and will minimize material and energy consumption.

Large runners allow a good flow of material at relatively low pressure, but once they are thicker they

require more material, more time to cool and higher clamping force. Small runners maximize material

and energy consumption efficiency[26]. However small runners are constrained by the moulding

machine injection pressure capability available on market. A small diameter increases shear heating

and the material reaches a temperature higher than in the barrel. This higher temperature can cause

the degradation of the material if it exceeds the material limit but reduces residual stress level and the

warp [24].

There are several geometries for runners, but the more used and balanced are the circular runners

and trapezoidal[26](Figure2-8).

Circular runners minimize pressure drop and heat losses due to have a good volume-to-surface ratio,

i.e. the circular cross section provides the greatest proportion of melted material[24]. These type of

runners are machined in both halves of the mould (semi-circular sections), that must be perfectly

aligned when the mould is closed, what increasing the tooling costs (Figure 2-8).

Trapezoidal runners are machined in one half of the mould and are cheaper than circular runners. This

type of runner provides acceptable flow and a good ejection[24]. Trapezoidal runners are used in

three-plate moulds, wherein the circular runners can’t be properly ejected or wherein circular runners

interferes with the mould sliding action[26].

Sprue

As referred the sprue is the channel that connects the nozzle to the runners. The sprue

dimensions depend on the part thickness and it must not freeze before any cross section to guarantee

the transmission of holding pressure. The sprue must be easily ejected along the rest of the feed

system and therefore has the draft angle (Figure 2-9).

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Figure 2-8 Sprue; Feed System Elements [24]

2.5.3. Hot Runner System

The main difference between a hot runner system and the cold runner system is that the material

inside the hot runner system stays melted [20]. Due to the material staying melted the draft angle in

the channels aren’t necessary. In this alternative there is no wasted material .The material stays

melted because the channels are heated ( internally or externally) or insulated [27]. (Figure 2-10).

Figure 2-9 a) Externally Heated; b) Internally Heated; c) Insulated [24]

The internal heat is supplied by a probe and torpedo located in circular flow passages and the external

heat consists of a cartridge-heated manifold with interior flow passages [27]. The externally heated

systems are well suited to polymers that are sensitive to thermal variations. Internally heated systems

offer better flow control [28]. The insulation keeps the plastic in a molten state.

Hot runners system are well suited for high volume production of small parts so the price per part

decreases and makes the hot runner system more cost effective [29]. Hot runners allow faster cycle

times, better temperature control and an better distribution of heat [27]. The faster cycle times are

justified through the smaller cooling time because they’re only dependent on the part and not on the

runners as cold feed system. Concerning colour material change, it is more difficult to do once the

material stays melted inside the runners [28].This type of runners aren't suitable to heat sensitive

materials and thermoplastics resins[28] [29]. Designing hot runners should take into account the

thermal expansion of various mould components [27].

Hot runners are used for moulds that have a lot of cavities, for expensive materials and when high

quality part is required, because this type of feed system leaves minimal gates vestiges [25].

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2.5.4. Cooling System

The cooling system (Figure 2-11) has the function of reducing the temperature of the part, until the part

reaches a temperature where it can be ejected without being damaged. The cooling phase has the

greatest importance because it greatly affects the productivity and the quality of the final part [30], so it

must be a commitment between a fast and a uniform cooling. The uniform cooling ensures the part

quality by decrease residual stress and keeping dimensional accuracy and stability[26][23]. Heat

transfer is therefore very important in injection moulding.

Figure 2-10 Cooling System Elements [31]

In the design of the cooling channels there are some parameters that can be improved to have a

better and uniform cooling. These parameters are the channels diameter, the distance between

channels and the mould and also the thermal properties of the mould material. These parameters are

constrained by several rules and considerations. The coolant conditions are also very important. To

guarantee an effective heat extraction the coolant flow must be turbulent

The cooling channels configurations are in parallel or in series. The more recommend and used

configuration is serial cooling channels[26].

With research and development of cooling systems regarding channel size, location, coolant flow rate

and thermal properties of mould material it led to another type of cooling, the conformal cooling.

Conformal cooling is defined by Lin as channels that should conform the mould cavity surface [32].The

conformal cooling system causes a homogenized cooling of the part because it follows the contour of

the part. It is expected that a part with conformal cooling has better surface quality than with

conventional cooling.

2.6. Simulation Software - Moldflow

Despite the development and knowledge about the injection moulding process, companies still have

some difficulties in the systematization of the process, the optimization of the tools (mould), and

control of process variables. This is where the numerical simulation of the process becomes an

essential tool, helping to establish the process parameters and changing the variables to predict its

15

impact on the final part. The simulations allows the reduction and optimization of the cycle time that

will lead to cost savings, otherwise the process would be optimized through error attempt that would

rise the costs.

Moldflow Software is one of the software programs used to assess and optimize the moulding injection

process, allowing the companies to improve the response to market and competitiveness.

This software imports a model created in 3D modelling software, so the part itself to be studied is not

design in Moldflow, but only analysed regarding the injection moulding process. What is design in

Moldflow are the mould feeding and cooling systems. Moldflow uses Finite Elements to perform the

several analysis to the part, therefore a finite element mesh is created on the part. Moldflow allows to

perform the following analysis independently or in sequence: Fill, Cool, Pack and Warp [33].

A mesh is a group of small elements that are defined by nodes (coordinates in space) that are used to

make the calculations inside Moldflow [34]. The mesh can be composed of three different elements:

beam, triangle and tetrahedron. The beam elements are used in the feed system and cooling system.

The triangle elements, composed of three nodes are used to describe the part and mould inserts. The

tetrahedron four-nodded element used to describe the parts, cores, feed system, etc. [34]. (Figure 2-

11-a)).

Figure 2-11 a) Element Types; b) Types of Mesh [34]

There are three types of mesh that can be applied: Mid Plane, Dual Domain and 3D [33]. The Mid

Plane is a two-dimensional mesh constituted by triangular elements that represents the middle surface

of part. This type of mesh requires fewer elements than the other types but has the disadvantage of

requiring a model of the middle surface of the part. The Dual Domain (Fusion) allows the direct

importation of a 3D model and is constituted by two-dimensional elements that covers all the model

surface. This type of mesh generates good results if it has a good correspondence between elements

of each side of the model [33]. The 3D mesh is composed of tetrahedral four-node elements that

allows the simulation of the melted flow inside the cavity, but has the disadvantage of being more

demanding computationally [33]. In Figure 2-11-b) the three types of mesh are showed.

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3. Efficiency of the production systems in a Life Cycle

Perspective

3.1. Global trends in improving the efficiency of the

production systems

Social awareness of environmental issues has led to consider topics like energy and resources and

their efficiency in manufacturing. Nowadays energy management is not only about the “carbon

footprint issue” but also focused on the productivity and competitiveness of the companies. In this way

Energy efficiency has become one of the most relevant topics of 21st century[35]. The concern about

energy and its efficiency is mostly justified by the eminent rise of its price in the last years.

In production systems, it has been noticed through the years that significant energy consumption also

occurred during idle or pause time of the production equipment’s [36]. Despite this, there is a lack of

industrial applications in order to fix or reduce the waste of energy, due to the lack of information on

how to do it and which benefits come from that. The uncertainty of obtaining successful results and the

potentially negative effects has hold back the efforts on its improvement [36]. A big issue that causes

the lack of information is the imprecise tracking of energy, where the energy is being consumed.

As consequence, manufacturers are realizing about the financial and environmental benefits of

practising sustainable manufacturing, not only because of improvements in energy but also in another

resources.

Sustainable Manufacturing can be defined as the creation of products or services through economic

processes that minimize the environmental impacts while conserving energy and natural resources

[37]. Practice sustainable manufacturing not only improves the product safety but also the employees’

and the community’s. Worldwide there are already companies whose mission is to help implementing

and improving sustainable manufacturing.

The Next Manufacturing Revolution,"… is a non-profitable collaboration that aims to unlock significant

performance improvement in the manufacturing sector."[38], currently focused on the United Kingdom.

NMR stands that for a company to succeed it must do continuous improvement in innovation and in all

forms of productivity. To help the companies NMR has elaborated a report about resource efficiency

for UK manufacturing. In this report Next Manufacturing Revolution approaches areas such as

Energy Efficiency, Process Waste Reduction, Packaging Optimisation, Circular Resource Flows,

Transport Efficiency, Supply Chain Collaboration and Revenue Growth from Non-Labour Resource

Productivity[39].

Another company in the development of sustainable manufacturing is the Lowell Center for

Sustainable Production. The Lowell Center for Sustainable Production, LCSP, was founded at the

University of Massachusetts Lowell. The main goal of LCSP is to redefine environmentalism and

safety and conciliate this concepts with new systems of production and consumption, being this new

17

systems healthy for workers, economically viable and environmental and social correct. The LCSP

stands that "Sustainable production must not only protect workers from occupational hazards, but

must involve them in the task of creating conditions of work that are productive, healthy, and

rewarding." [40].

To improve the efficiency of the production systems and implement sustainable manufacturing,

companies need to apply methodologies and perform analyses that allow to identify and minimize the

resources consumption while reducing the environmental impacts. In the next sub-chapter are

presented some methodologies and analysis of energy and environmental efficiencies.

3.2. Methodologies and Analysis of Energy and

Environmental Efficiencies

There are some methodologies and analysis that help to evaluate and compare products or process

regarding their energy consumption and environmental impact. These assessments can be made

about the design and production of the products/process and/or about their use phase. With

sustainable manufacturing these methodologies become very important tool decisions.

Over the years it has become evident that industrialization and economic growth are directly related

with environmental degradation. Eco-efficiency appears as one of the main strategic tools that helps

the transition from unsustainable development to one of sustainable development.

The aim of Eco-efficiency is reduce consumption of resources and the environmental impact while

increasing the value of a certain product or company and also increase the economic efficiency. The

World Business Council for Sustainable Development, WBCSD, developed the concept of eco-

efficiency and describes how eco-efficiency is achieved: “Eco-efficiency is reached by the delivery of

competitively priced goods and services that satisfy human needs and bring quality life, while

progressively reducing ecological impacts and resource intensity …”[41]

Eco-efficiency is based on the concept of supply of goods and sustainable services while reducing

environmental impact and the consumption of natural resources. In order to guide businesses to

become more eco-efficient, several aspects were established. They are: reducing material intensity of

goods or services, reduce energy intensity, reduce dispersion of toxic substances, enhance

recyclability, maximum use of renewable resources, extend product durability and increase service

intensity[42].

To achieve targets and monitoring the product/service are used indicators. An eco-efficient indicator is

the ratio between a product value and its environmental influence[43]. The indicators are based in 8

principles that guarantee that the indicators are accurate, useful, environment relevant and

scientifically supportable for all types of business.

Eco-efficiency is used to compare products and decide what is the best solution regarding the cost

and the environmental impact of the product. To evaluate the environmental impact usually Life Cycle

Assessment (LCA) methodology is used, and for the evaluation/determination of the cost of a product

18

Life Cycle Costing (LCC) is used. Life Cycle Assessment, LCA, evaluates the environmental impact

of a certain product, process or service. LCA is essentially a decision tool. According to ISO

14040:2006, LCA is defined as the "compilation and evaluation of the inputs, outputs and the potential

environmental impacts of a product system throughout its life cycle”[44].

For this analysis is defined a scope and boundaries. This evaluation starts with the production of the

product and continues through to its eventual disposal, considering the amount of energy, resource

inputs as well as the polluting outputs to land, air and water. It is used to compare environmental

impacts of a product with a reference or with other products with the same function, and to identify the

manufacturing phases with higher contribution for the environmental impact [45]. The main advantage

of performing a cycle life perspective of a product or system is the possibility of avoiding problems in

shifting from one stage to another [42]. In a life cycle analysis it is important to define the functional

unit, referred in ISO 14040:2006 as “quantified performance of a product system for use as a

reference unit".

Eco-Design is a concept used in the industrial product design. Eco-Design considers that the effect

that a certain product has on the environment should be consider and reduced as possible in the

product life cycle, being in this way an additional decision factor. An Eco designed product must have

certain characteristics such as reliability, durability, degradability and be reusable. An eco-design

product is intend to have a clean production, i.e., reduce and/or avoid waste and toxic substance in

the production stage. Nowadays it is important to apply the eco-design methodology in the products

for several reasons. Regarding the global reasons like to be in agreement with the legislation, to have

products that are suitable to the markets and costumers demands, guarantee that the company has a

good image and stays competitive ahead. Regarding the company itself applying the Eco-Design

methodology increases the power of innovation of the company, the quality of the products, improves

the productivity and reduces costs.

Concluding, all the several methodologies and analysis presented focus on the resources efficiency

and on how is important to improve it, to achieve sustainable manufacturing and to have good and

competitive products.

3.3. Efficiency in Equipment

An equipment machine tool system (MTs), causes more environmental impact in the use phase

comparatively to other life cycle phases because of the amount of energy consumed. MTs require an

enormous amount of energy to transform raw materials in finished products[46].

In machine tools one of the biggest problems is to link the specific consumed energy in machining with

the parameters that could influence it. The specific consumed energy is difficult to establish because

of the lack of knowledge in efficiency model. In F.Draganescu et al.[47] is purposed a statistic

modelling of machine tool efficiency in order to determine the electric energy consumption for

machining. In machine tools a way to reduce power consumption is focusing on the servo and spindle

motors that are responsible for the highest energy demand in machine tools. In M.Mori et al. were

19

investigated the major causes of power consumption and performed several case studies like, power

consumption reduction during deep hole drilling, in order to reduce the power consumption[48].

Sustainable machine tools consume less energy and have low costs during their life cycle. To design

this type of equipment is relevant an evaluation of their energy efficiency and costs. Gotze et al. [49]

proposed an approach for the evaluation of machines tools. Their methodology consists in the

measurement of energy consumption, modelling of the energy flows and simulate analysis of energy

saving potentials and also an energy life-cycle cost concept. The measurements performed allow to

identify how much energy is being consumed by each components of MTs and, in this way, helps to

define which ones required more efforts to improve energy efficiency. With the simulation analysis of

design alternatives it’s easier to evaluate which design alternatives lead to a better energy efficiency.

With the increase of energy prices, the energy consumption of machine tools is a very important factor

regarding to ecological and economic targets. ISO 20140 “Environmental and energy efficiency

evaluation method for manufacturing system”, ISO 22400 “Key performance indicators for

manufacturing operations management” and ISO 14955 “Environmental evaluation of machine tools”

are being developed to improve MTs with the objective of reducing energy consumption and maintain

performance and cost-effectiveness[49].The European Eco-design directive 2009/1257EG requests

energy savings of goods inclusive the MTS.

Through the research, it was noted that the main concern and difficulty regarding equipment efficiency

is to relate the energy consumption with the parameters that influence it. Measuring the energy

consumption allows to identify which parameters or components influence energy consumption the

most. The studies performed to improve energy efficiency of the equipment are pertinent once energy

efficiency is directly related to environmental directives and economic targets.

3.4. Standards and labels

The purpose of standards and labels is to allow organizations to define the systems and processes

required to improve energy performance, regarding energy efficiency, use and consumption. The

implementation of this kind of tools in some way leads to the reduction of environmental impacts and

energy waste.

Standard IS/ISO 50001:2011 is used to the certification and registration of an organization’s energy

management system model. It is applicable to all types of organizations, independent of geographical,

cultural or social conditions. IS/ISO 50001:2011 specifies the requirements regarding energy use and

consumption, measurements, documentation and reporting, the design and selection of equipment,

system and process[50]. The strategy of ISO 50001 is to review the energy consumption in order to

identify significant energy use activities, set up energy baseline and also uses energy performance

indicators. It is very important to be in agreement with the regulatory requirements, and set up energy

objectives and implementation plans[51].

The present labelling system consists of several energy label scales, from A to G, A+++ to D, etc. This

Label was introduced in 1995, but energy efficiency has improved along the years and so most of the

20

products on market are currently in the top of efficiency class. The European commission has

proposed a revised Energy, with a scale from A to G, in order to make it easier for the consumers to

identify the most efficient products. With the restructuration of scale the products will be re-classified.

Regarding Energy Labelling of Products, there is a code that has the purpose of guiding and establish

technical details regarding the requirements on energy efficiency labelling for products like, air

conditioners, refrigerating appliances, washing machines etc. [52].

In sub-chapter 3.2 were described methodologies that help the companies to improve efficiency of the

process and products. The Standards allow the companies to define the systems and processes

required to improve efficiency. Labels classify the products allowing the consumers to identify the most

efficient products. In the next sub-chapter a review of the efficiency in Injection Moulding is presented,

as well as, the standards and labels that exist for injection mould machine and injection moulds.

3.5. Efficiency in Injection Moulding

The evolution of sustainable manufacturing has led to the development of processes efficiency

studies. Injection moulding is one of the most important manufacturing process in the processing of

polymeric materials and thus is relevant to analyse the material and energy consumption of injection

moulding systems and possible savings of these resources. To improve process efficiency it is crucial

to understand where the energy and other resources are being consumed.

Producers and managers should be able to identify and divide the energy consumption in plants in

order to reduce it. Although this is a relatively easy task to perform only a few are doing it. The efforts

to reduce energy consumption must be suitable to the amount of energy consumed [53]. In Figure 3-1

is showed the energy cost for plastics processing, although it may vary according to the process used.

Figure 3-1 Approximate Energy Cost Distribution for Plastics Processing [53]

Energy mapping is an excellent and easy method to detect where energy is being used in a plant. This

way it is easier to evaluate what areas should be improved [53]. Besides da Mapping is important to

monitor the energy consumption in order to identify cost-reduction opportunities.

Godec et al. [54], analyses the influence of processing parameters in the energy efficiency of the

injection moulding process, like material, part thickness and temperature regulation. In Godec et al.

[54] is considered that the energy efficiency of the process should be considered at the phase of the

mould design, considering the design of the part and the material of the part. The material is a

21

parameter that influences the quantity of energy required to obtain a good injection moulding process.

In the case of amorphous thermoplastics, they have lack of frictional energy that needs to be

compensated by conductive energy. A part that is produced with a semi-crystalline material usually has

a poor quality, so in order to compensate that, the barrel temperature or the screw temperature must

be increased. Regarding the part design, a factor that influences the amount of energy consumed is

the wall thickness, i.e., with increasing thickness there is an increase in the cooling time, then in the

total cycle time. Combining a suitable choice of material that enables producing thinner walls, the

overall cycle time will be reduced, then in a mass production case there will be significant energy

savings [54].

In the injection moulding process it is very important the regulation of temperature of the wall cavity of

the mould to guarantee the part quality. The quality of the part depends mostly on the part cooling,

therefore it is important to have a good efficiency of the mould. The efficiency of the mould is

influenced by the mould material and by the design of the cooling system.

The efficiency of the process depends also the injection machine. It is important the choice of the

machine for each mould, and with the large range of injection machines that the market provides it

isn't easy to select the best machine regarding energy consumption.

The project EUROMAP 60 was developed with the purpose of comparing the electrical energy

consumption between injection moulding machines with the same size. EUROMAP is the European

association for plastics and rubber machinery manufacturers [54]. This association provides

information about the market and the most reliable equipment manufacturers of plastics and rubber in

Europe, and also gives technical recommendations. Their technical recommendations are organized

into the following categories: General, Injection moulding, Extrusion, Blow moulding and Presses.

EUROMAP 60 is composed of two parts: Part 1: Determination of related Energy Efficiency Class;

Part 2: Determination of Product Related Energy Consumption. The Part 1 specifies the determination

of the classification of the machines based on their specific energy consumption and idle

characteristics. "For the description of the energy efficiency of injection moulding machines without

regarding tool or costumer influences for comparison reasons.”[55].The Part 2 defines the

determination of electrical energy consumption of a selected machines to produce a specified

product.“ This recommendation defines the determination of electrical energy consumption for a

specified machine for manufacturing a specific product with a specific process for comparison” [56].

For the injection moulding process efficiency, besides the machine selection, it is also important the

selection of mould. The design of the mould is very complex and important task that greatly influences

the efficiency of the process regarding mass and energy consumption and productivity. As described

in this sub-chapter EUROMAP 60 project provides a guide to compare injection moulding machines,

making the selection of the machine easier, but regarding the mould there isn’t a tool, standard or

label that guides and makes the choice of the most efficient mould for a specific part easier. A tool

decision adequate to the mould, would be profitable for the injection moulding process.

22

4. Proposed Methodology

In injection moulding one of the main goals is to reduce the total cycle time, in order to increase

productivity and reduce production costs. Every part design requires a different mould and even for the

same part the mould can be different in terms of the design of the feeding and cooling channels,

among other design features. The different possible designs of the channels across the mould

influence the performance of the process and by consequence the part quality.

The mould feeding system can be based on cold runners or hot runners[24] and concerning the

cooling system it can be a normal/conventional or a conformal system[31]. The differences between

cold and hot runners, and normal and conformal cooling system, were already discussed in section

2.5.

Aiming to evaluate the efficiency of the process regarding energy and material consumption in

different mould designs and in different moulds sizes, Standardized Efficiency Indicators are proposed

in this thesis.

The formulation of Standardized Efficiency Indicators it is based on the concept of operational

efficiency. Operational efficiency is a ratio between the input and out of a business [57]. Once the

matter of study in this thesis is a manufacturing process and not a business the inputs and outputs are

defined as follows.

The input is defined as a minimum amount of a certain variable (resource) required for the injection

moulding of a specific part. The output is defined as the real amount of that variable that is actually

used in the process. The variables select for analysis are: part material and the energy consumption of

the injection moulding process, as referred previously. The equation (1) is the ratio between input and

output, i.e., the Standardized Efficiency Indicator.

Baseline

Standardized Efficiency Indicator % Actual Value

(1)

4.1. Input and Output definitions

The input, as mentioned before, is the minimum amount of material or energy required for the injection

moulding process that from now on is called Baseline.

The Baseline concept intends to represent the amount of variables that would be required in an ideal

process. Therefore all values assumed in the calculation of the Baseline are based on theoretical and

empirical knowledge.

The output is the actual value of material or energy consumed in the process. This amount can be

obtained directly from the production system (part injection moulding industrial data) or as done in this

thesis, through injection moulding simulation software. To apply this concept was defined a Case

Study.

23

To calculate the energy consumed for the Baseline and for the Actual Value the energy consumption

model proposed by Ribeiro et al.[58] is used. Regarding material consumption the Mass Baseline is

calculated based on theoretical and empirical knowledge and the actual value is obtained from

Simulation Software.

4.1.1. Case Study

The Case study objective is to assess the influence of the design characteristics of the mould along

with the variation of the parts size. To analyse the influences of each type of feeding and cooling

system it was defined a geometry similar to a cup with three sizes, in polypropylene PPC 3120 MU5,

from TOTAL Refining & Chemicals. The geometries are denominated as Part1, Part2 and Part3

(Figure 4-1).

Figure 4-1 Parts

To obtain the variables and parameters of the process for Actual Value, Software Moldflow Insight was

used. For each part four design mould alternatives are analysed (Table 4-2), resulting in the total in 12

alternatives, so 12 Actual Values.

Cold runners Hot runners

Conventional cooling 1,2,3 1,2,3

Conformal cooling 1,2,3 1,2,3

Table 4-1 Design Mould Alternatives

In Figure 4-2 the approach to the development of Standardized Efficiency Indicator is summarized.

24

Figure 4-2 Study Methodology

Next will be presented the methodology to calculate the Baseline and the Actual Value.

4.2. Baseline

As mentioned before it will be evaluated the efficiency of the process regarding energy and material

consumption. Therefore is calculated a Mass Baseline and Energy Baseline.

4.2.1. Mass Baseline

The mass baseline is calculated through equation (2), where V is the volume of the part and the

material density.

m V (2)

The mass baseline is the minimum quantity of material required to produce a part without accounting

with the feeding system.

4.2.2. Energy Baseline

As mentioned before the energy is calculated using the energy consumption model proposed by

Ribeiro et al.[58]. The Total Energy is the sum of the Thermodynamic Energy with the Energy

Consumption of the injection machine.

The Thermodynamic Energy is the energy needed to melt the raw plastic material that is injected. The

energy consumption of the injection moulding machine includes the machine and part specifications.

25

Figure 4-3 Installed Power vs. Clamping Force - ENGEL MACHINES [62] [63]

The Total Energy is given by equation (3), the Thermodynamic Energy is given by equation (4) and the

Machine Energy is given by (5).

total thermo machineE E E (3)

,

( )p melt ambient F inj

thermo

melt fill

mc T T mH pVE

(4) ( ) c

machine inst

tE CfM CfP P

CfT (5)

The values used to calculate the thermoE derived from the material properties and from the part

characteristics. The machineE , equation (5), depends on coefficients , on the installed power and on the

cycle time of the process. In order to estimate a theoretical cycle time for each part, the cycle time is

defined as the sum of: -injection cooling mould open times [59][60].

4.2.2.1. Determination of cycle time

Injection time

The injection time, time in which the material is injected in the cavity mould, is estimated by equation

(6) as reported by [59] .

max

2 cavity

fill

Vt

Q (6)

maxQ is the maximum flow rate of the material from the nozzle. To find the value of the maximum flow

rate, it’s required the selection of a machine available on the market with the nearest installed power

regarding the theoretical value.

The theoretical installed power, instP , is determined by the linear regression equation that relates the

installed power of the machine and its clamping force, Figure 4-2.

26

The clamping force required for each part is given by equation (7) according [2], where the injP is the

injection pressure and projA is the projected area. The projected area was calculated using equation

(8).

proj injClamping Force A P (7)

2

proj tA r (8)

As mentioned by [61] the clamping force required for PP is 2 to 4 tonnes per square inch of projected

area. So 2 tonnes per square inch were assigned to the smallest part, 3 tonnes per square inch to the

medium part and 4 tonnes per square inch for the biggest part.

In equation (9) the x is the Clamping Force and y is the installed power.

0.1585 19.771xy (9)

Though equation (9), replacing the x with the value of the Clamping force, the value of the installed

power is determined. With the value of installed power is possible to select a machine available on

market that best suits the installed power and clamping force calculated. From catalogues or

databases of machines is it possible to find the maximum flow rate of the material from the nozzle for

the selected machine.

Cooling time

The cooling time, as explained before, is the most relevant time of the total cycle time. Since the

concept of baseline is the minimum amount of the variables, the cooling time to take into account is

the cooling time for hot runners that minimizes the cycle time.

The equation (10) allows to calculate the cooling time for hot runners. The set of temperatures needed

to calculate Y depends on the selected material. The s is the part thickness,ef is the thermal

diffusivity and k is the thickness coefficient of the part and is given by equation 11.

2

2

2

ln( . ), hot runners

ln(0.692 ), cold runners23.14

ef

cooling

ef

inj mould

ext mould

sk Y

tD

Y

T TY

T T

(10)

2

4 if 3

8 if 3

k s mm

k s mm

(11)

Mould open/close time

Mould open/close time is the time that the mould opens to eject the part and then closes to a new

injection cycle. Mould open/close time can be estimated through equation (12) according [59].

27

/ max

1 1.75 strokeopen close d

stroke

Lt t

L

(12)

dt is the dry cycle time of the machine and strokeL is the opening stroke of the machine . The dry cycle

time and strokeL are obtained from the catalogue for the selected machines.

4.2.2.2. Determination of the coefficients

CfM - Machine Type Coefficient

– Electric vs. Hydraulic

For the Case Study it was assumed that the machines are Hydraulic, so the 1CfM

estCfP - Machine Power Coefficient

1.5079 0.084thermest

inst

PCfP

P (13)

The theoretical installed power, instP , is calculated through equation (9).The calculation of

thermodynamic power , thermP ,is given by equation (14),

1000

thermotherm

c

EP

t

(14)

where ct is the cycle time for each part previously calculated and thermoE values are the ones

calculated according equation (4) also for each part.

CfT - Thickness Coefficient

The thickness coefficient is given by the following equation, where s is the thickness part.

0.0884 0.7629CfT s (15)

With all coefficients, installed power and cycle time values it is possible to calculate the machine

energy for each part, equation (5) and finally the total energy, equation (3).

4.3. Actual Value

Like the Baseline the Actual Value for Mass and Energy Consumption are calculated. The variables

and parameters of the process required to calculate the Actual will be obtained from injection moulding

simulation software Moldflow Insight.

28

Each part and design alternatives will be simulated on Moldflow Insight. Through Moldflow results and

log files it is possible to obtained the mass, cycle time, clamping force, the injected volume, the

injection pressure etc. These parameters and variables will be used to calculate the energy

consumption, using the same energy model used in the Baseline (Equation 3). The material properties

required to the energy model are taken from Moldflow Database’s. Beside the processing conditions

and parameters of the process, the characteristics of the part are also provided by Moldflow analysis.

As referred the cycle time is directly obtained from Moldflow and used in the energy model, in contrast

to the cycle time used in Baseline that is calculated through the sum of injection + cooling + mould-

open/close times (Equations 6, 10, 12).

In the calculation of the machine energy, the value of the installed power , instP , will be a real installed

power, from a machine available on market (Table 4-2) and not the theoretical value as used in the

Baseline.

Machine Clamping

Force [ton]

Total Power [KW]

Machine Clamping

Force [ton]

Total Power [KW]

Engel DUO 23050/2000

2000 334 Engel 300 HL-V 300 73


1700 283 Engel 300 HL-V 300 64


1500 274 Engel VC

1350/300 Tech 300 66.3


1500 239 Engel VC 1800/260

260 62.3


1300 204 Engel VC

1050/180 Tech 180 46.3


1000 199 Engel 150 HL-V 150 48

Engel DUO 5550/900

900 163 Engel VC 650/120

120 37.3

Engel DUO 7050/800

800 149 Engel VC 650/120

120 35.3

Engel VC 3550/600 Tech

600 143 Engel VC

650/110 Tech 110 31.8

Engel 600 HL-V 600 115 Engel VC

330/80 Tech 80 24.2

Engel VC 3550/350,400

400 104 Engel 75 HL-V 75 22

Engel VC 2550/400 Tech

400 89 Engel 45 HL-V 45 18

Table 4-2 Machines Available on Market – ENGEL [62] [63]

29

5. Alternative Mould Design Solutions

In this chapter first are described the influences of the several mould design alternatives regarding

feeding and cooling systems on the injection moulding process. Next for the defined Case Study,

composed of the three parts are presented the combinations of the Engineering Solutions and its

nomenclature. Finally the simulation performed in the injection moulding simulation software is

described and the results obtained are discussed.

5.1. Influence on performance

The mould is the main tool of injection moulding process. As mentioned in chapter 2, the mould has

feeding and cooling systems that are constituted by several elements and channels. In the next sub-

section are described briefly the influences of the variants of feeding and cooling systems in the

quality part and in the process itself.

The part geometry, the part material and the quality required, delineate and guide the design of the

mould. The size and the amount of parts to be produced also influence the mould, with more or less

cavities, so influence the final size of the mould.

5.1.1. Feeding system

The feeding system as referred in chapter 2 can be with cold runners or hot runners.

Cold runners system can accommodate a wide variety of polymers and allows quick colour changes.

With robotic assistance in removing the runners it is possible to achieve fast cycle times [28]. This

removal usually leaves a mark on the part. With cold runners there is a waste of plastic.

In a cold feeding system the cooling time is dependent on the cool of the runners because the runners’

thickness is bigger than the thickness of the part. So even if the part is already frozen, it only can be

ejected when 50 % to 80 % of the runners are frozen [64]. Cold runners are cheaper to produce and

maintain than hot runners but cycle times are higher because of the cooling time of the runner material

[28].

In hot runners system the material stays melted, keeping a balanced melt flow at a constant

temperature throughout all the system to fully fill and pack the cavities [65]. Hot runners allows to take

full advantage of the highly accurate cavities and therefore plastic parts can be produced with great

dimensional accuracy and quality [65].

Hot runners are adequate for medium and large part volumes [66]. Usually with hot runner systems

are used lower injection pressures, which will reduce the mould deflection.

With hot runners system there is no wasted material and isn’t necessary an additional operation to

remove the runners. However becomes more difficult to change colour because the material stays in

the channels. So it leads to a longer setup time when colour change is required. Hot runners have

higher manufacturing and maintenance costs[29].

30

5.1.2. Cooling system

The design of the cooling system is a very important step in mould design. The cooling phase

influences significantly the quality of the part and the productivity. A conformal cooling system can

improve the efficiency and quality of the production comparatively to the conventional cooling [67].

With little engineering analysis is expected to achieve a 10% cycle time reduction. With more

engineering analysis for designing a proper conformal cooling it is possible to achieve better moulds

and reduce the cycle time. A properly engineered conformal cooling system it is expected 20% to 40%

of cycle time reduction [68].

5.2. Case Study

The methodology explained on chapter 4 is applied to the case study, composed of three parts, with 2

mm of thickness each, each one with four design alternatives (Table 5-2). Their dimension varies

proportionally (Table 5-1). The Engineering Solutions regarding feeding and cooling systems were

matched and further ahead will be referred using the nomenclature presented in Table 5-2.

Part 1 Part 2 Part 3

h mm 50 150 500

][ Bd mm 27.44 82.32 274.39

Td mm 42.68 128.05 426.83

Table 5-1 Parts Dimensions

Cold runners Hot runners

Conventional (normal) Cooling CN HN

Conformal Cooling CC HC

Table 5-2 Engineering Solutions Combinations

5.3. Modelling Mould Design Alternatives

Through simulation will be defined the feeding and cooling systems that guarantee a good mould

performance for the parts, in order to estimate values like cycle time and mass, required for the

calculation of mass and energy consumption. The Software used to perform the simulation was

Moldflow Insight.

Modelling in Moldflow requires knowledge about the injection moulding process. It is important to know

the different phases of the process, the parameters and the processing conditions. The Figure 5-1 is

an overview of the analyses and tasks that must be performed.

31

Figure 5-1 Overview of tasks and analysis

Those analysis and tasks will be explained and justified in detail in the next topics. The approach is the

same for the three parts in study.

5.3.1. Import CAD Model

The parts were modelled in software SolidWorks and then imported to Moldflow in .IGS format[33].

The model imported must be correctly oriented with the –Z direction, that is the injection direction[69].

The Figure 5-2 shows as an example a model correctly oriented.

Figure 5-2 Model oriented with -Z direction; Part1

5.3.2. Mesh

Moldflow software uses Finite Elements to perform the analysis, so the first task at hand is to apply a

mesh to the part. The type of mesh selected was “Dual Domain”. This type of mesh was selected

because generates good results if it has a good mesh correspondence, allows direct importation of a

3D model and it is not too demanding computationally. For each part it was applied a different element

size mesh according to the dimensions of the part. In the next table is showed the length of the mesh

elements.

Part Elements Length [mm]

1 1

2 2

3 10 Table 5-3 Mesh Elements Length

32

Is very important to guarantee the quality of the mesh, because it will influence the quality of the

analyses results. Through Mesh Statistics Tool it can be assessed if it’s good or not (Figure 5-3). The

Aspect Ratio, the edge details, the orientation details, the intersection details and the match

percentage of the mesh were verified for the three parts under study. The Match Mesh Ratio Fusion

must be at least 85 % to prevent warnings in flow analysis and at least 90% for good warp results [33].

In the Case Study the only problem to be solved in the imported models was the Aspect Ratio.

Figure 5-3 Mesh Statistics; a) Part1; b) Part2; c) Part3

The Aspect Ratio, is the ratio of the width to the height of the elements (triangular elements). In the

simulation models the Aspect Ratio was improved until it reached a value under 6 (Figure 5-3). For

flow analysis the aspect ratio tolerated can be about 20, but for cool and warp analysis it must be

below 6 [33]. The improvements were made using the mesh tools, like “move node”, “merge nodes”,

“insert node”, etc.[33]. After improving the aspect ratio it was checked the thickness of the part. Some

mesh elements may change its thickness during the improvement of the Aspect Ratio, which will

influence greatly the cool analysis.

5.3.3. Material Selection

The default material in Moldflow is a GENERIC PP since it is the most injected material. Through the

left tasks column it was selected the polypropylene PP 3120 MU5, from TOTAL Refining & Chemicals,

for the case study models. The Figure 5-4 presents the recommend processing of this material.

33

Figure 5-4 PP 3120 MU5 Properties

5.3.4. Gate Location

The gate location analysis evaluates which are the best locations to place the gate in the part. Since

the geometry of the parts is symmetrical according Z direction, it was expected that the best location

to inject the material was in the bottom centre of the cup (Figure 5-5). In the Figure 5-6-a) is possible

to see the flow resistance and that the bottom centre of the cup has the lower flow resistance, so is the

best location to place the gate too. The selected location to place the gate was the bottom centre of

the cup according to these two results (Figure 5-6- b)).

Figure 5-5 Best Gate Locations; Part1

Figure 5-6 a) Flow Resistance Indicator; b) Gate Location; Part1

34

5.3.5. First Fill Analysis

After setting the gate in the model the first filling analysis was performed. The results of this analysis

were used as reference for the next fill analysis with feeding system.

The first result check was the “fill time” plot. Through this plot it is possible to observe if the filling is

balanced and if it is, it means that the fill time is appropriated. In a balanced fill time the contours lines

are equally spaced. The space between the lines indicates the flow speed of the material. Another

characteristic of a good fill time is if the flow reaches the extremities of the part at the same time. In

the results the blue zones represent the first places filled and the red ones the last places filled [69]. In

the Figure 5-7 is showed a fill time plot with outline and with shading.

Figure 5-7 Fill Time Result; a) Contour; b) Shading; Part2

In the three parts the fill times were good and with a balanced flow, so there weren´t problems to

solve. After that the pressure at V/P Switchover was checked. The Velocity/pressure switch-over point

is the point where occurs the transition from the filling phase to the packing phase. The minimum

pressure must occur in the front flow and the maximum pressure must occur in the injection location.

In Figure 5-8 is showed the pressure at V/P Switchover for part 1 as example.

Figure 5-8 Pressure at V/P Switchover; Part2

35

The other results analysed were the bulk and flow front temperatures. The Bulk temperature is the

weighted average temperature across thickness. For both results it was check the range of

temperatures. The Bulk Temperature range should be less than 20ºC and the Flow Front Temperature

range should be less than 5ºC [69] (Figure 5-9; a); b)). Further ahead with the feed system and with

Moulding Window analysis these two temperature results will be analysed again and improved if

necessary.

Figure 5-9 a) Bulk Temperature; b) Flow Front Temperature; Part2

In the filling phase it is also important to guarantee that the shear stress at wall is not above the

material limit. This property can be consulted in Moldflow databases and for Polypropylene 3120 MU5

the maximum shear stress allowed is 0.26 MPa (Figure 5-4).

Then it was checked other plots like weld lines, air traps and orientation at skin in order to evaluate the

filling behaviour, once they can cause structural and visual defects. In the studied models the only

problem identified was the air traps. In this simulation air traps are acceptable because they are few,

of small dimension and the surface does not have to be visually perfect.

5.3.6. Feeding System and Fill Analysis

Next the feeding systems, cold and hot runners system, were designed for each part. Initially they

were created using the default wizard runner system and then each system dimensions were

improved concerning the filling result values (Figure 5-10).

Feeding Systems

Design for

Part1, Part2, Part3

Default Wizzard

Runner system

Cold or

Hot

Improvements

regarding

injection time

bulk temperature

flow front temperature

shear rate

shear stress at wall for

Figure 5-10 Design of the Feeding Systems

36

The feeding system cross section type is a circular cross-section because obtains the best results as

discussed in chapter 2. The main rule in order to compare further ahead the performance of the cold

and hot system was to assign the same initial diameter to the channels. So the difference between the

systems is the draft angle in cold runners. The initial diameter of the channels was 5 mm, the default

value in Moldflow.

For the Part1, the fill analysis with 5 mm channels was performed and there were obtained good

values for the injection time, bulk and flow front temperatures, shear rate and shear stress at wall for

the selected material. In order to have a feeding system that wastes less material but also allows a

good filling, the diameter was reduced until a value that guarantees the quality of the filling (Table 5-5).

For Part2 the diameter of 5 mm for the sprue and runner was kept. This dimension caused problems

in the shear rate, bulk and shear rate at wall for the drops and top attacks so it was increased until a

value where the shear rate, bulk and shear stress at wall were under the limit for the material. For

Part3, since it has a bigger volume to fill, the 5mm dimension was not appropriate. The dimensions of

the runners were increased until 20 mm, value that gave acceptable filling results (Table 5-5).

The draft angle used was the default angle of Moldflow, 3º, except for Part2 drops’, wherein was used

the value of 2º in order to reduce the material waste of the cold feeding system.

The gate diameter was sized using the material shear rate as reference [69]. In order to keep the

shear rate below the material limit, 100000 1/s, the gate size was increased to 1.6 mm diameter (Table

5-4).

Regarding the gate length for Part2 and Part3 initially was used 1.5 mm of length that gave acceptable

results for the filling analysis. However for the cooling analysis, this value was changed to 3 and 5 mm

respectively, in order to improve the cooling results that will be presented further ahead (Table 5-4).

Recommended range Used Values

Diameter 25% to 75% of the thickness

[24]

s= 2mm D=1.5 mm

D= 1.6 mm

Length 0.5 to 1.5 mm [24]

Part1 Part2 Part3

1 mm 3 mm 5 mm Table 5-4 Gate Dimensions

The Table 5-5 lists the dimensions of each element of the feeding systems for each part in study.

These dimensions were established after re-running the filling analysis until it reach acceptable values

for the analysis results referred above. To help reaching these acceptable values it was used the

Moulding Window Analysis.

Figure 5-11 Moulding Window; Part2

37

This analysis recommends an injection time and mould and melt temperatures (Figure 5-11). These

temperature values must be compared with the recommended range of temperatures for the material

(Figure 5-4) and should be close to the middle of this range [69]. Sometimes the moulding window

results were used and in other cases, the average recommended processing values of the material.

The following figure show the feeding system of Part2 as example and in Table 5-5 are presented all

the feeding systems and their dimensions, wherein D is the diameter, draft ° is the draft angle, Din is

the initial diameter of the top attacks, Dend is the final diameter of top attacks, and L is the length of the

channels.

Figure 5-12 Feeding Systems; a) Cold Runner; b) Hot Runner; Part2

Coordinates Sprue Runner Drops Top attacks

X Y Z D draft

° L D D

draft °

Din Dend L

Part1 Cold

0 12.5 25 3 3

25 3 3 3

3 1.6 1 Hot 0 0

Part2 Cold

0 25 40 5 3

50 5 8.5 2

8.5 1.6 3 Hot 0 0

Part3 Cold

0 70 150 20 3

150 20 20 3

20 1.6 5 Hot 0 0

Table 5-5 Feeding System Dimensions [mm]

The others feeding systems are presented in Annex A.

In Table 5-6 are presented the values of injection time, bulk and flow front temperatures, shear rate

(Figure 5-13-b) and shear stress at wall for each part and type of feeding and cooling system. The

injection time increases with the dimensions of the parts, which was expected since there is more

material to inject. The value of the pressure in the switchover point is smaller for hot runners, as

expected, being that difference more evident in Part2 and Part3. The Bulk temperature variation

increases along the parts. For Part3 the range is exceeded because the part is very long making

harder to design a feeding system that fulfil all requirements. The Flow Front temperature, the shear

rate bulk and the shear stress at wall accomplish the established limits.

38

Part Mould Design

Alternatives

Injection time [s]

V/P [MPa]

Bulk T [ºC] Flow Front T

[ºC]

Shear Rate, bulk [1/s]

Shear stress at wall [MPa]

1 CN ; CC 0.2185 18.27 244.3-249.4 244.9-245.4 95689 0.1975

HN ; HC 0.216 18.23 242.6-248.4 243.1-243.3 92410 0.1941

2 CN ; CC 0.6157 24.77 252.4-260.1 255.4-256.0 95653 0.2357

HN ; HC 0.6145 22.76 260.8-269.9 265.0-265.5 91492 0.2193

3 CN ; CC 1.68 56.2 251.3-271.5 263.6-264.5 91765 0.2457

HN ; HC 1.677 52.57 255.1-277.3 268.4-270.5 81435 0.2243

Material Limit values Δ<20ºC Δ <5ºC 100000

l/s 0.26 MPa

Table 5-6 Fill Analysis Results

A result that requires special attention is the shear stress at wall. In Figure 5-13-a) is showed a shear

stress at wall value higher than the maximum allowed in the feeding system and bellow the limit in the

part. Analysing the log file result (Figure 5-14), is verified that the shear stress at wall for the part was

higher during the filling but also under than the material limit. Shear stress at wall is important on the

part but not on the feed system [70]. Once the shear stress at wall value in the part is less than the

material limit it is possible to proceed.

Figure 5-13 a)Shear stress at wall; b) Shear Rate; Part2

Figure 5-14 Log file:Shear Stress at wall; Part2

5.3.7. Cooling System

After the optimization of the filling phase the next step was to design the cooling systems. The

Moldflow wizard cooling system was not appropriate to the parts geometry (Figure 5-15-a)). Therefore

the cooling systems, conventional and conformal, were all created manually using tools of the

39

Geometry menu. In the modelling of the cooling systems, were created beams for the conventional

cooling (Figure 5-15-b)), and beams and curves for the conformal cooling. To these elements were

assigned properties, applied a mesh and finally the coolant inlets

Figure 5-15 Wizard Cooling System; Part1

The systems were improved by trial and error. The optimization process was to analyse the cooling

results and if need delete and create new beams or curves adjusting their location closer or further

way from the part. After that were assigned properties, apply a mesh and finally the coolant inlets. The

coolant used in this simulation was water at 25ºC.

The channels dimension and the distance between the channels and the mould cavity follow the

ranges proposed by A. F. De Souza et al. [71](Table 5-7).

Wall Thickness of moulded

product [mm]

Hole Diameter [mm] b

Centreline Distance

between holes [mm] a

Distance between

centre of lines and cavity

[mm] c

0-2 4 - 8 2 -3b 1.5-2b

2-4 8- 12 2 -3b 1.5-2b

4-6 12 -14 2 -3b 1.5-2b

Table 5-7 Cooling Channels Design Parameters[71]

For the first cooling analysis the cooling channels were placed inside of the parts geometry because

the inside area was the hottest area of the part. Then the cooling channels were also created in the

outside area of the part to improve cooling results, e.g. Temperature profile,part, result that will be

presented further ahead. In the conformal cooling the cooling channels were designed inside and

outside of the parts following its shape in order to achieve a more uniform cooling comparatively to the

conventional cooling system. In Figure 5-16 is showed a final conventional cooling system and a

conformal cooling system for Part2. The others cooling systems are presented in Annex A.

40

Figure 5-16 a) Conventional Cooling System; b) Conformal Cooling System; Part2

5.3.8. Cooling Analysis

It is important to have a uniform cooling to achieve effective heat transfer. Therefore the following

cooling analysis results were analysed: the Coolant Temperature, the Coolant Flow, the Average part

temperature, the Maximum Temperature, the Profile Part Temperature, the Part Temperature, the

Mould temperature and the Time to reach Ejection.

In these cooling results there were verified some conditions that guarantee a good and uniform

cooling. The definition and proper ranges of each result are included in the Annex B. In this sub-

section are presented and discussed the final cooling results for all the parts and mould design

alternatives (Table 5-8).

The Coolant Temperature was set initially at 25ºC for all design mould alternatives (Figure 5-17-a)).

For HC systems, the inlet temperatures were changed after, in order to improve the cooling of the

parts. Regarding the range of temperatures to accomplish, all the design mould alternatives are in

agreement with it, except for Part2 and Part3 with HC systems (Table 5-8).

Figure 5-17 Cooling Results: a) Coolant Temperature; b) Reynolds Number; Part2 CC

41

The Coolant Flow was ok for all of the systems, with Reynolds number at 10000 (Figure 5-17-b)).

The Average temperature, part result (Figure 5-18-a)) is between the mould temperature and the

ejection temperature for all parts. The Temperature, maximum, part result (Figure 5-18-b)) for Part2

and Part3 with cold runners, is way below the ejection temperature because of the longer cycle time

that this type of feeding system imposes.

Figure 5-18 a) Average part temperature; b) Maximum part temperature: Part2 CN

The Temperature Profile, part result is below the ejection temperature for all the parts, and varies

across the thickness less than 10ºC (Figure 5-19).

Figure 5-19 Temperature profile; Part2 CN

The mould temperature should be within 10ºC for amorphous materials and within 5ºC for semi-

crystalline materials, but this guideline is very difficult to achieve for most moulds[72] (Figure 5-20-a).

The part temperature varies mostly in a 10ºC range over each mould face. Close to the gate location

or in the top of the parts the temperature varies more than 10ºC. After improvements some of these

values weren’t within the range but once the majority of the part was, it was proceeded with the study

(Figure 5-20-b)) (Table 5-8). The Part3 as poor part and mould temperature results.

42

Figure 5-20 a) Mould Temperature; b) Part Temperature; Part2 CN

The Time to reach ejection temperature, part result decreases for all the parts between

conventional and conformal cooling. The behaviour of this result between the feeding systems is

dependent on the melt temperatures (Table 5-6, Flow Front temperature).

Figure 5-21 Time to reach Ejection; Part2 CN

43

Average T [ºC]

Circuit coolant T

[ºC]

T, Maximum

[ºC]

T Profile

[ºC]

T, Mould [ºC]

T, Part [ºC] t

eject [s]

Part1

CN 72.89-85.35 25.01-25.98 102.2 102.2 35.16-54.26 42.06-64.47 9.016

CC 75.55-83.38 25.00-26.30 105.9 105.9 30.74-43.71 37.84-55.01 8.574

HN 71.54-83.60 25.01-26.15 101.5 101.5 33.23-53.77 39.62-63.90 8.97

HC 76.92-84.25 20.1-21.00 25.01-26.27

108.7 108.7 28.09-39.90 36.79-51.57 8.365

Part2

CN 30.04-41.06 25.01-25.81 41.74 41.74 25-38.96 28.19-41.74 8.33

CC 34.39-39.14 25.01-27.47 41.77 41.77 25-39.03 28.24-41.77 8.312

HN 49.99-71.39 25.02-27.09 75.02 75.02 45.76-61.39 56.57-68.47 10.17

HC 53.81-67.87 25.01-29.5 30.00-36.72

72.99 72.99 31.15-58.15 39.99-65.72 10.05

Part3

CN 36.86-46.92 25.02-25.50 48.46 48.46 27.06-47.46 28.46-48.46 8.849

CC 30.96-40.34 25.01-27.69 45.93 45.93 25.35-44.46 26.32-44.84 8.304

HN 59.42-75.82 20.00-21.42 79.51 79.51 39.78-68.27 46.84-74.00 10.9

HC 56.00-74.97 20-21.49;

15.03-27.96 84.62 84.62 36.64-79.22 44.09-84.62 11.14

Table 5-8 Cooling Results

5.3.9. Cool +Fill + Pack + Warp Analysis

The final analysis gathers the filling, cooling, packing and warp analysis where the volumetric

shrinkage at ejection, the frozen layer fraction, the hold pressure and the deflection results were

checked (Table 5-9). The packing analysis is important since the packing pressure and time influences

the part weight [72].

When the gate freezes, no more material can enter the cavity so the packing phase ends. The gate

thickness controls the packing time. To set the packing time it was used the Frozen Layer fraction

result (Figure 5-22-a)). In this result is possible to see when the gate and part freezes.

Figure 5-22 a) Frozen Layer Fraction; b) Volumetric shrinkage at Ejection; Part2 CN

44

The volumetric shrinkage is dependent on the pressure on the plastic when it freezes (Figure 5-22-

b)) High pressure values reduce shrinkage. The variation of shrinkage across the part is due to the

pressure gradient across the part. The method of packing can be a constant pressure or a pressure

profile. Packing pressure profile method usually gives a more uniform volumetric shrinkage compared

to a constant pressure method. For all the parts were tested both methods. The constant pressure

method produced better results for Part1 and Part2, and the pressure profile method produced better

results for Part3. The packing pressure was initially set at 100%, and increased until a value that gave

the closest Baseline mass value.

Next was checked the hold pressure result (Figure 5-23-a)) to see if a big variation of the pressure

occurs. A big variation on hold pressure means that the pressure isn’t transferred to the extremities of

the cavity. This variation can be caused by a poorly designed mould, not enough packing pressure, a

short packing time or an inappropriate gate sizing or location. For the Part1 and Part2 the hold

pressure varies about 3MPa maximum, and for Part3 varies 10MPa maximum (Table 5-9). The

pressure gradients across the part prevents the area at the end of the filling to have a pressure equal

to the pressure near the gate, so it is expected that the shrinkage at the end of the filling to be higher

than around the gate (Figure 5-23-b)).

Figure 5-23 a) Hold Pressure; b) Deflections: All effects; Part2 CN

The deflection (Table 5-9) in the parts is mostly due to the shrinkage effect, the cooling effect is

reduced and the orientation effect is null (Figure 5-24).

45

Figure 5-24 a) Shrinkage Effect; b) Cooling Effect; c) Orientation Effect; Part2 CN

In the three parts with cold runners system the highest shrinkage is near the end of the filling as

expected, but with hot runners system the highest shrinkage happens near the gate location. The

Part3 is the only part where the cooling effect contributes significantly to the deflection besides the

shrinkage effect. This is because it was the part where cooling has worse results regarding the

recommended temperature ranges.

Part Design

Altr.

Hold Pressure

[MPa]

Volumetric shrinkage at ejection (máx)[%]

Deflection, all effects [mm]

1

CN 30.86-31.20 3.62 2.30E-01

CC 30.85-33.51 3.80 2.25E-01

HN 25.86-27.03 15.85 2.58E-01

HC 27.68-29.34 15.87 2.53E-01

2

CN 46.85-49.83 8.79 6.11E-01

CC 46.85-49.72 7.56 5.88E-01

HN 43.29-46.16 15.98 7.05E-01

HC 43.30-45.99 15.98 6.38E-01

3

CN 105.5-115.5 12.10 1.63E+00

CC 106.5-117.9 11.34 1.51E+00

HN 98.13-106.8 14.1 3.54E+00

HC 97.22-107.6 14.28 1.95E+00 Table 5-9 Cool+Fill+Pack+Warp Analysis Results

46

In Table 5-10 are presented the parameters obtained from Moldflow that are required to calculate the

Actual Value.

Part Altr. m [Kg] injp

2[ / ]N m

3 [m ]injV Cycle

time [s]

Clamping Force [ton]

1

CN 1.07E-02 20.9E+06 12.1743 15.625 4.7127

CC 1.07E-02 20.7E+06 12.1743 15.125 4.7133

HN 1.02E-02 20.5E+06 11.5625 14.625 3.8592

HC 1.02E-02 20.4E+06 11.5625 13.625 4.1298

2

CN 9.99E-02 50.6E+06 113.052 45.8 63.0602

CC 1.00E-01 39.0E+06 113.052 41.8 63.1436

HN 9.59E-02 35.7E+06 108.5009 22.8 57.6944

HC 9.62E-02 36.2E+06 108.5009 21.8 57.7565

3

CN 1.22E+00 01.2E+08 1379.01 333.775 1617.831

CC 1.22E+00 01.2E+08 1379.01 276.775 1636.499

HN 1.10E+00 01.1E+08 1222.333 29.775 1487.833

HC 1.10E+00 01.1E+08 1222.333 28.775 1471.439

Table 5-10 Values obtained from Moldflow Simulation

The mass values presented in Table 5-10 are the Actual Values of Mass consumption.

5.4. Actual Value Calculation

With the values obtained from Moldflow (Table 5-10) and the material properties of Table 5-11, where

is the material density, Cp is the polymer specific heat, Hf is the heat fusion for a 100% crystalline

polymer, is the thermal diffusivity, is the degree of crystallization,Tmelt is the melt temperature, will

be calculated the Actual value of energy consumption for each alternative design of the three parts.

[ / [K.Kg]]Cp J ºTmelt C /Hf J Kg 3 [ / ]kg m

1800 118 0.75 207000 917.55

Table 5-11 Material Properties - PP 3120 MU5

5.4.1. Energy consumption

5.4.1.1. Calculation of Thermodynamic Energy and Thermodynamic Power

For the calculation of Thermodynamic Energy, equation(4), the ambient temperature considered is

25°C and the ,melt fill , the melt filling coefficient is 0.8. The other required values to the calculation are

presented in Table 5-10 and Table 5-11 (Table 5-12 ). The Thermodynamic Power, equation(14), was

calculated with the cycle times from Table 5-10 and thermodynamic energy values from Table 5-12

(Table 5-13).

47

[ ]thermoE KWh

Part CN CC HN HC

1 1.29E-03 1.29E-03 1.22E-03 1.22E-03

2 1.32E-02 1.28E-02 1.21E-02 1.21E-02

3 1.91E-01 1.93E-01 1.68E-01 1.68E-01

Table 5-12 Thermodynamic Energy

[ ]thermoP KWh

Part CN CC HN HC

1 0.30 0.31 0.30 0.32

2 1.04 1.10 1.91 2.01

3 2.07 2.51 20.34 20.99 Table 5-13 Thermodynamic Power of each part

5.4.1.2. Calculation of Energy Consumption of the injection machine

To calculate the Machine Energy Consumption (Table 5-16), equation(5), are required the Cycle

Time (Table 5-10), the Real Installed Power (Table 5-14) and the Energy Model Coefficients (Table

5-15).

The installed power as explained in chapter 4, is calculated through linear regression equation(9) that

relates the installed power of the machine and its clamping force. The real installed power is the

closest machine power available on market (Table 5-14).

Part Design

Alt.

Clamping Force

[ ]ton instP KW instReal P KW

1

CN 4.71 20.15 22

CC 4.71 20.15 22

HN 4.68 20.14 22

HC 4.13 20.05 22

2

CN 63.06 29.46 31

CC 63.14 29.47 31

HN 57.69 28.60 31

HC 57.76 28.61 31

3

CN 1617.83 277.60 283

CC 1636.50 280.58 283

HN 1487.83 256.85 274

HC 1471.44 254.24 274 Table 5-14 Machine Characteristics: Clamping Force and Installed Power

The Machine Power Coefficient, equation(13), was calculated with the Real Installed Power values

from Table 5-14 and with the Thermodynamic Power values from Table 5-13. The following table

shows the Energy Model Coefficients. The Machine Type Coefficient and the Thickness Coefficient

were calculated in chapter 4.

48

Part

CfM

CfT estCfP

CN CC HN HC

1

1 0.94

1.04E-01 1.05E-01 1.05E-01 1.06E-01

2 1.34E-01 1.37E-01 1.77E-01 1.82E-01

3 9.50E-02 9.74E-02 1.96E-01 2.00E-01

Table 5-15 Energy Model Coefficients

Machine Energy [KWh]

Part1 Part2 Part3

CN 1.06E-02 5.36E-02 2.60E+00

CC 1.03E-02 5.00E-02 2.24E+00

HN 9.95E-03 3.41E-02 4.43E-01

HC 9.41E-03 3.35E-02 4.31E-01 Table 5-16 Machine Energy for each part

5.4.1.3. Total Energy

The Total Energy, equation (3), was calculated using the values of Thermodynamic Energy from Table

5-12 and the values of Machine Energy from Table 5-16.

Total Energy [KWh]

Part1 Part2 Part3

CN 1.19E-02 6.96E-02 2.84E+00

CC 1.16E-02 6.33E-02 2.45E+00

HN 1.12E-02 4.90E-02 6.41E-01

HC 1.06E-02 4.84E-02 6.33E-01 Table 5-17 Total Energy for each part

49

6. Standardized Efficiency Indicators

As presented in chapter 4, the Standardized Efficiency Indicators are calculated through a general

equation, the equation(1). In the chapter 5 the procedures to obtain the Actual Values for each mould

design alternative and the values themselves were described. Next using the methodology explained

in chapter 4 the values of the Baseline regarding Mass and Energy Consumption of each part will be

presented.The Table 6-1 presents the material properties considered in the calculation of Baseline,

where is the material density, Cp is the polymer specific heat, Hf is the heat fusion for a 100%

crystalline polymer, is the thermal diffusivity, is the degree of crystallization, p is the average

injection pressure, Tmelt is the melt temperature, Tinj is the injection temperature, Text is the

extraction temperature and Tmould is the mould temperature.

3 [ / ]kg m [ / [K.Kg]]Cp J /Hf J Kg

2 [ / ]mm s

917.55 1800 207000 0.096 0.75

p MPa ºTmelt C ºTinj C ºText C ºTmould C

2.76-103 118 240 110 60

Table 6-1 Material Properties: PP 3120MU5 [73][74][75][76]

6.1. Mass Baseline

The parts were designed in SolidWorks software. The volume of each part was obtained from “Mass

Properties” of each model part. The volumes are presented in Table 6-2. The mass of the parts was

calculated according the equation(2), wherein the density is the density showed in Table 6-1.

Part 3 [ ]V cm Mass g

1 11.45 10.51

2 107.42 98.57

3 1210.28 1110.50

Table 6-2 Property Parts

6.2. Energy Baseline

6.2.1. Calculation of Thermodynamic Energy

In the calculation of thermodynamic energy, the ambient temperature considered is 25°C and the

,melt fill is 0.8. The Table 6-3 shows the thermodynamic energy for each part, calculated using the

values from Table 6-1 and the equation(4).

Part [ ]thermoE KWh

1 1.19E-03

2 1.30E-02

3 1.68E-01

Table 6-3 Thermodynamic Energy for each part

50

6.2.2. Calculation of Energy Consumption of the injection machine

To calculate the Machine Energy Consumption (Table 6-11), equation(5), are required the Cycle

Time (Table 6-8), the Theoretical Installed Power (Table 6-5) and the Energy Model Coefficients

(Table 6-10).

6.2.2.1. Determination of cycle time

The injection time, is estimated by equation(6). In Table 6-4 the typical values of injection pressure,

the calculated values of projected area (equation(8)) and clamping force (equation(7)) for the three

parts are presented. With the clamping force [ton] and theoretical installed power (equation(9)) is

defined the injection machines for each part. In Table 6-5 are presented the installed power and the

maximum flow rate of each machine and Table 6-6 the theoretical injection times.

Part injp

2[ / ]ton in

injp

2[ / ]kg mm

injp

2[ / ]N m

2[ ]projA m

Clamping Force

[ ]N

Clamping Force

[ ]ton

1 2 3.10 3.04E+07 0.001 43508 4.44

2 3 4.65 4.56E+07 0.013 587451 59.88

3 4 6.20 6.08E+07 0.143 8702643 887.12

Table 6-4Theoretical values of Injection Pressure, Projected Area and Clamping Force

Part instP KW instReal P KW

Machine

maxQ

3 [ / ]cm s

1 20.47 20.3 ENGEL VC 60/60 81

2 29.26 30.7 ENGEL VC 500/110 250

3 160.38 163 ENGEL DUO 5550/900 760

Table 6-5 Determination of Maximum Flow Rate [63]

Part [ ]fillt s

1 0.28

2 0.86

3 3.18

Table 6-6 Theoretical Injection Times

The cooling time for hot runners (equation(10)), depends on the thickness and material part. Since all

the parts have the same thickness and the same material, the cooling time is the same for all.

6.43 scoolingt

The Mould open/close time, equation(12), was calculated with dry cycle time, Lstroke and Lstroke max,

obtained from the ENGEL catalogue for the machines presented in Table 6-5. The Lstroke and Lstroke max

are the same once the extraction of the parts can be automated through robotics or manually, which

implies different opening strokes. This way the maximum opening stroke allows both types extraction.

51

Part [ ] d st strokeL mm max

strokeL mm / [s]open closet

1 1.5 100 100 3.63

2 1.6 200 200 3.80

3 3.3 430 430 6.78

Table 6-7 Mould open/close times

The cycle time: /injection cooling mould open close , for each part is presented in the

following table.

Part [s]cyclet

1 10.34

2 11.09

3 16.39 Table 6-8 Theoretical cycle time for each part

6.2.3. Determination of the coefficients

The Machine Power Coefficient, equation(13), was calculated with the Theoretical Installed Power

values from Table 6-5 and with the Thermodynamic Power values from Table 6-9. The Thermodynamic

Power, equation(14), was calculated with the cycle times from Table 6-8 and thermodynamic energy

values from Table 6-3.

Part [ ]thermoP KW

1 0.41

2 4.23

3 36.84

Table 6-9 Thermodynamic Power for each part

The following table shows the Energy Model Coefficients. The Machine Type Coefficient and the

Thickness Coefficient were calculated in chapter 4.

Part CfM CfT estCfP

1

1 0.94

0.11

2 0.30

3 0.43

Table 6-10 Energy Model Coefficients

Part Machine Energy [KWh]

1 7.16E-03

2 2.89E-02

3 3.34E-01 Table 6-11 Machine Energy for each part

6.2.3.1. Total Energy

The Total Energy, equation(3), was calculated using the values of Thermodynamic Energy from Table

6-3 and the values of Machine Energy from Table 6-11 (Table 6-12).

52

Part Total Energy [KWh]

1 8.35E-03

2 4.20E-02

3 5.02E-01 Table 6-12 Total Energy for each part

With the Baseline values and the Actual Values it is possible to calculate the standardized efficiency

indicators. First the Mass Indicator and then the Energy Indicator it will be calculated and discussed.

6.3. Mass Indicator

The Mass indicator is calculated with equation (16) using the values from Table 5-10 and Table 6-2

(Figure 6-1). The indicator is calculated for the three parts, for the four design mould (Table 5-2).

% =

mass

Mass Baseline

Mass Actual Value (16)

Figure 6-1 Mass Consumption Indicators

This indicator can be analysed relatively to the variation mass consumption through the moulds design

alternatives and also about what occurs to mass consumption for different parts dimensions.

The efficiency of hot runners systems is over 100%, so the mass baseline is higher than the actual

values. This result is justified by the final part volume. When the parts are ejected they are at a

temperature that allows ejection but not necessarily at the ambient temperature, so the part continues

to cool and volumetric shrinkage occurs. This volumetric shrinkage represents the decrease in local

volume, so the parts simulated on Moldflow have smaller volumes (Table 6-13) and by consequence

smaller mass values. The model parts perhaps should have a bigger volume to compensate this

volumetric shrinkage.

53

Part Design

Alt. Baseline

Volume [m3]

Final Volume

[m3]

1 HN

1.15E-05 1.11E-05

HC 1.11E-05

2 HN

1.07E-04 1.05E-04

HC 1.05E-04

3 HN

1.21E-03 1.19E-03

HC 1.19E-03 Table 6-13 Final Volume; Hot runners

In Figure 6-1 is obvious that there is a difference in mass consumption for the three parts between

cold and hot runners systems.

Moulds with hot runners system have better material efficiency than moulds with cold runners system.

These results were expected since that in cold runners system, as descried in chapter 2, the runner

system is ejected with the part, so there is a consumption of the runner material. For the three parts

the behaviour is the same, being for Part3 more evident because the cold runner system is

considerable bigger.

To understand better the differences of mass consumption values and their sources, the following

table shows the values of mass obtained for mould design alternatives of each part and also the

fluctuations relatively to the mass baseline.

Part Baseline Mass (g)

Design Alt. Case Study

Mass (g) Absolute

Fluctuation Relative

Fluctuation

1 10.51

CN 10.71 0.20 1.91%

CC 10.71 0.21 1.95%

HN 10.17 -0.34 -3.23%

HC 10.18 -0.32 -3.09%

2 98.57

CN 99.95 1.38 1.40%

CC 100.18 1.61 1.64%

HN 95.89 -2.67 -2.71%

HC 96.19 -2.37 -2.41%

3 1110.50

CN 1216.46 105.97 9.54%

CC 1221.61 111.11 10.01%

HN 1095.26 -15.23 -1.37%

HC 1096.05 -14.44 -1.30%

Table 6-14 Mass Fluctuations

As referred before, the cold runners have lower values in the mass efficiency indicator due to the mass

that is consumed in the runner system, so it is important to know the fraction of mass that corresponds

to the part and how much mass is wasted in the cold runners (Table 6-15). The runners mass gains

weight for Part3. This result is a consequence of the increase of the runner diameter to guarantee the

properties material limits.

54

Part Design

Altr. Part mass

[g]

Runner System Mass [g]

Part Mass Runner System Mass

Fraction Fraction Relative

Fluctuation

1 CN 10.16 0.55 94.88% -3.31% 5.12%

CC 10.16 0.55 94.88% -3.26% 5.12%

2 CN 96.08 3.87 96.13% -2.53% 3.87%

CC 96.13 4.05 95.96% -2.47% 4.04%

3 CN 1097.78 118.69 90.24% -1.15% 9.76%

CC 1103.36 118.25 90.32% -0.64% 9.68% Table 6-15 Total Mass Fractions- Cold Runner System

With the separation of the total mass in part mass and runner mass, it is possible to state that the part

mass is also smaller than the mass baseline through the negatives relative fluctuations. This occurs

for the same reasons explained for hot runners (Table 6-16).

Part Design

Alt. Baseline

Volume [m3]

Final Volume

[m3]

1 CN

1.15E-05 1.11E-05

CC 1.11E-05

2 CN

1.07E-04 1.05E-04

CC 1.05E-04

3 CN

1.21E-03 1.20E-03

CC 1.20E-03 Table 6-16 Final Volume; Cold Runners

Comparing the cooling systems, with hot runner system the relative fluctuation (Table 6-14) is always

smaller for conformal cooling. For cold runner system (Table 6-15) analysing only the mass part

fraction, the relative fluctuation behaves similarly. Therefore the conformal cooling system for the three

parts is slightly better than the normal cooling, due to a better cooling and less warp.

Comparing the three parts, is possible to affirm that the material efficiency isn’t drastically affected by

the dimension of the part. The range of efficiency values is similar for the three parts. To notice that

using cold runners system in Part3, the efficiency decreases a little bit, so it wastes more material then

the others. Concluding the Mass Efficiency Indicator distinguish the efficiency of cold runners to hot

runners as expected. For a part with big dimensions, like Part3, efforts should be made to improve the

feeding system in order to minimize the waste of material. The improvement of the design of conformal

cooling should be a matter of study since the difference in regard to the conventional cooling is not

very significant.

6.4. Energy Indicator

The Energy Indicator is calculated with equation (17) using the values from Table 5-17 and Table 6-12.

(Figure 6-2). The indicator is calculated for the three parts, for the four design mould (Table 5-2).

% =

energy

Energy Baseline

Energy Actual Value (17)

55

Figure 6-2 Energy Consumption Indicator

This indicator can be analysed relatively to the evolution of energy efficiency through the moulds

design alternatives and also about what occurs to energy with the increase of parts dimensions. In

Figure 6-2 is obvious that there is an evolution on energy efficiency along the mould design

alternatives. Therefore is important to identify the variable or variables that influence energy the most.

First was assessed the contribution and evolution of the Thermodynamic and Machine Energy in the

Total Energy along the three parts, either for Baseline (Figure 6-3) and Actual Value (Figure 6-4).

Figure 6-3 Baseline Energy Fractions

Figure 6-4 Actual Value Energy Fractions

56

Regarding the Energy Baseline values, with the increase of the part dimensions the Thermodynamic

Energy increases and the Machine Energy decreases. The Thermodynamic Energy (equation(4))

increases because there is more material to melt. For Part1 and Part2 the Energy Actual Value

behaviour is the same as for the Baseline, but for Part3, with cold runners design the machine energy

is once again the highest percentage of the total energy. To understand better the behaviour of energy

along the parts and design moulds alternatives let’s go backwards in the Energy Model, in order to

identify the variables that influence energy.

First was analysed the fluctuations of the Total Energy (Table 5-17), Thermodynamic Energy (Table

5-12) and Machine Energy (Table 5-16) Actual Values in regard to the Baseline (Table 6-12);( Table

6-3);(Table 6-11) for all parts and alternatives (Table 6-17).

Part Design

Alt.

Total Energy [KWh]

Thermodynamic Energy [KWh]


Absolute Fluctuation

Relative Fluctuation





1

CN 3.54E-03 42.41% 9.96E-05 8.38% 3.44E-03 48.05%

CC 3.27E-03 39.14% 9.95E-05 8.38% 3.17E-03 44.24%

HN 2.82E-03 33.80% 3.33E-05 2.80% 2.79E-03 38.94%

HC 2.28E-03 27.29% 3.46E-05 2.91% 2.24E-03 31.34%

2

CN 2.76E-02 65.87% 1.67E-04 1.28% 2.75E-02 94.90%

CC 2.14E-02 50.93% -2.61E-04 -2.01% 2.16E-02 74.73%

HN 7.08E-03 16.89% -9.25E-04 -7.11% 8.01E-03 27.68%

HC 6.45E-03 15.38% -8.73E-04 -6.71% 7.32E-03 25.30%

3

CN 2.34E+00 466.60% 2.39E-02 14.23% 2.32E+00 693.42%

CC 1.95E+00 387.50% 2.52E-02 15.02% 1.92E+00 574.26%

HN 1.39E-01 27.63% 5.40E-04 0.32% 1.38E-01 41.33%

HC 1.31E-01 26.05% 9.33E-05 0.06% 1.31E-01 39.08%

Table 6-17 Energy Fluctuations

It is clear that the energy consumption has a higher fluctuation for moulds with cold runners than with

hot runners and that conventional cooling has a higher fluctuation than conformal cooling. The

Thermodynamic Energy is mostly dependent on the mass and pressure values. The negative

Thermodynamic Energy fluctuations in Part2 are justified by the value of pressure used in the baseline

that turns to be higher than the value of pressure obtained from simulation (Table 6-18).

Part Pressure Baseline

[MPa] Design Alt.

Pressure Actual Values [MPa]

Absolute Fluctuation Relative Fluctuation

1 2.76E+06

CN 20.85E+06 18.09E+06 655.47%

CC 20.71E+06 17.95E+06 650.32%

HN 20.49E+06 17.73E+06 642.39%

HC 20.40E+06 17.64E+06 639.13%

2 5.29E+07

CN 50.55E+06 -02.33E+06 -4.40%

CC 38.98E+06 -13.90E+06 -26.28%

HN 35.74E+06 -17.14E+06 -32.41%

HC 36.23E+06 -16.65E+06 -31.48%

3 1.03E+08 CN 115.43E+06 12.43E+06 12.07%

CC 117.00E+06 14.00E+06 13.59%

57

Part Pressure Baseline

[MPa] Design Alt.

Pressure Actual Values [MPa]


3 1.03E+08 HN 107.28E+06 04.28E+06 4.15%

HC 106.02E+06 03.02E+06 2.93%

Table 6-18 Pressure Fluctuations

The total energy for Part3 with cold runners stands out again relatively to the Baseline value. This

fluctuation is due to the increase of the machine energy (Figure 6-4).The machine energy, equation(5),

depends on the Model coefficients, on the Cycle time and on the Installed power.

The Model Coefficients, as presented before on Table 5-15 the Machine Type Coefficient and the

Thickness Coefficient don’t vary, so they aren’t an increasing factor of the Machine Energy. The

Machine Power Coefficient, equation(13) increases along the mould alternatives for the three parts.

So the Machine Power Coefficient is an increasing factor in Machine energy, but not the one

responsible for the high fluctuation in cold runner alternatives of Part3.

As expected the cold runners feeding system alternatives have the highest Cycle times (Table 5-10).

To notice that for Part3 the cycle times with cold runners are way higher comparatively to the baseline

value and to the hot feeding system cycle time fluctuation (Table 6-19). This result of high cycle time

fluctuation is justified by the higher cooling time of the cold feeding system in regard to the cooling

time for hot runners consider in the baseline.

Finally, analysing the Installed Power, it’s possible to see that it increases along with parts’

dimensions. For a bigger part a bigger installed power and clamping force is required (Equation(9)).

For Part1 and Part2 the installed power required is the same for all the design mould alternatives, but

for Part3 with cold runners, is required a bigger clamping force, that leads to a bigger installed power

(Table 6-19).So the root causes of the variation of the Machine Energy are the installed power and the

cycle time, particularly for Part3 with cold runners because of the standing out values of these

variables.

Part Design

Alt.

Cycle time [s] Installed Power [KW]





1

CN 5.29 51.18% 1.53 7.45%

CC 4.79 46.34% 1.53 7.45%

HN 4.29 41.51% 1.53 7.45%

HC 3.29 31.83% 1.53 7.45%

2

CN 34.71 313.10% 1.74 5.94%

CC 30.71 277.02% 1.74 5.94%

HN 11.71 105.65% 1.74 5.94%

HC 10.71 96.63% 1.74 5.94%

3

CN 317.39 1936.76% 122.62 76.46%

CC 260.39 1588.94% 122.62 76.46%

HN 13.39 81.69% 113.62 70.84%

HC 12.39 75.59% 113.62 70.84%

Table 6-19 Cycle time and Installed Power Fluctuations

58

Looking at the evolution of Machine Energy across mould design alternatives (Figure 6-4) is pertinent

to say that, once analysed the Installed Power, the Model Coefficients and the Cycle time, that the

Cycle time is the variable that controls the Machine Energy Value.

Concluding, the Energy Indicator is a good indicator because it is in accordance with theoretical and

empirical knowledge. The Energy Indicator has a decreasing behaviour with the increase of the part’s

dimensions, when used cold runner feeding system. By comparing the mould design alternatives it is

possible to affirm that cold runners have lower energy efficiency in regard to the hot runners feeding

system, and that conformal cooling has a slightly higher efficiency comparing with the conventional

cooling system.

6.5. Assessment of Material Variation

The aim of this assessment is to analyse how the Standardized Efficiency Indicators behave for

different materials. This assessment was performed only in Part1, because the results would be

similar for the other parts. Four thermoplastics were defined, two of them semi-crystalline, PP and

Polyamide 6 (PA6) and the others amorphous, Polystyrene (PS) and Polycarbonate (PC).

This assessment is dived in two sub-assessments. The first assessment is a comparison between the

Baseline of each material and the second is the assessment of the mass and energy consumption

efficiencies of each material, so is, once again, applied the Standardized Efficiency Indicators

methodology.

For the first assessment in regard to the mass consumption is obvious that the material that has the

highest density will have highest mass consumption, but for energy consumption it isn’t possible to

take immediate conclusions. The second assessment was performed for Part1 with hot feeding

system and with conventional cooling system.

Once the approach to obtain the Baseline and the Actual Value was explained step by step before, all

the intermediate and final values of the Baseline and Actual Values of each part are presented in

Annex C. In this sub-section are presented and discussed the properties and values required for the

comparison of materials.

6.5.1. Baseline comparison

The chosen materials were two semi-crystalline thermoplastics, PP and PA6, and two amorphous

thermoplastics, PS and PC. First are presented and compared the energy results for the Part1 with the

different material. The mass comparison results is pretty obvious, since it depend on the density of the

materials, so this result is incorporated in the presentation of the Standardized Efficiency Indicators

(Figure 6-7).

Semi-crystalline thermoplastics consume more energy than amorphous thermoplastics (Table 6-20). In

order to understand where the differences between the two types of thermoplastics and in each type

come from and what variables influence the energy, is pertinent to go backwards on the Energy Model.

59

Materials Total Energy [KWh]

PP 8.35E-03

PA6 8.42E-03

PS 6.85E-03

PC 7.30E-03 Table 6-20 Total Energy; Baseline

Analysing the Thermodynamic Energy (Figure 6-5) of each material is possible to state that semi-

crystalline thermoplastics require more Thermodynamic Energy than amorphous thermoplastics. The

equation(4) used to calculate the Thermodynamic Energy, considers the degree of crystallinity. For

amorphous thermoplastics the degree of crystallinity is null, justifying in this way the lower values of

Thermodynamic Energy (Table C-2).

Figure 6-5 Thermodynamic and Machine Energy of each material

Thermoplastic PA6 requires more Thermodynamic Energy than PP because it has higher values of

mass (Table C-2) and melt temperature (Table C-1). Thermoplastic PC requires more Thermodynamic

Energy than PS because it has higher values of mass (Table C-2), specific heat and melt temperature

(Table C-1). Regarding Machine Energy (Figure 6-5), equation(5), the Machine Type Coefficient and

the Thickness Coefficient (Table C-6) don’t vary and the Installed Power is very similar for the four

materials (Table C-4). So the Machine Power Coefficient and the Cycle time are the variables that

influence Machine Energy. The Machine Power Coefficient depends on the Thermodynamic Power,

Equation(14) that depends on the Thermodynamic Energy, already discussed, and on the Cycle time.

60

Figure 6-6 Cycle time for each material

By plotting the Cycle time for each material (Figure 6-6) it is possible to state that the Cooling time

differs for all materials once it is dependent on their properties. A higher ratio between Thermodynamic

Energy and Cycle time will increase the Thermodynamic Power and, as consequence, the Machine

Power Coefficient, that is the case of PA6. However PA6 isn’t the material that requires more Machine

Energy because of its short cycle time. The highest multiplication between cycle time and Machine

Power Coefficient values, results in the biggest Machine Energy value, which is the case for PP.

6.5.2. Standardized Efficiency Indicators

The Mass indicator is calculated with equation (16) using the values of Baseline (Table C-2) and

Actual Value (Table C-10).

Figure 6-7 Mass Indicator of different materials

Like in subchapter 6.1 the efficiencies are above 100%, once again these results are justified by the

smaller final volume and volumetric shrinkage. The amorphous thermoplastics have lower efficiency,

the mass actual value is closer to the Baseline value, due to the smaller volumetric shrinkage

61

comparatively to the semi-crystalline thermoplastics. Annex C. The Energy Indicator is calculated

with equation (16) using the values of Baseline (Table 6-20) and Actual Value (Table C-12). In Figure

6-8 is presented the Energy Indictor of each material. As concluded in sub-section 6.5.1 the semi-

crystalline thermoplastics consume more energy than amorphous thermoplastics, however it isn’t

possible to affirm that semi-crystalline are more efficient than amorphous thermoplastics or vice-versa.

Figure 6-8 Energy Indicator for each material

Analysing the fluctuations of total energy, machine energy an thermodynamic energy, is stated that the

PC has the lower total energy fluctuation despite having the highest thermodynamic energy

fluctuation, and that the PA6 that has the highest total energy fluctuation is the one that has higher

machine energy fluctuation. So machine energy is the variable that controls efficiency.

Material

Total Energy [KWh]

Thermodynamic Energy [KWh]








PP 2.83E-03 33.85% 3.49E-05 2.94% 2.79E-03 38.98%

PA6 4.38E-03 52.06% 1.90E-05 0.98% 4.29E-03 66.17%

PS 2.18E-03 31.89% 7.99E-05 20.05% 3.60E-03 55.89%

PC 5.14E-04 7.03% 2.82E-04 27.53% 1.28E-03 20.31% Table 6-21 Total Energy, Machine Energy and Thermodynamic Energy Fluctuations

In the sub-section 6.5.1 was stated that the energy is highly dependent on the cycle time, more

specifically the machine energy. By analysing the cycle times and their fluctuations it is possible to

conclude that the material with higher cycle time fluctuation is the one with lower energy efficiency.

Material Baseline

Cycle Time [s]

Actual Cycle Time [s]



PP 10.34 14.63 4.29 41.51%

PA6 6.55 14.00 7.45 113.85%

PS 11.43 17.00 5.57 48.75%

PC 8.69 10.00 1.31 15.10% Table 6-22 Cycle Time Fluctuations

62

The Actual cycle times obtained from simulation highly depend on the design of the mould created,

that turn to be better suited to PC, the material that presents the lower time fluctuations.

Through this indicator it is possible to conclude that the selection of the material affects the mass and

energy efficiencies. When is intended to compare moulds with different design alternatives the

material should be the same, once the material conditions the level of mass and energy consumed.

6.6. Cavities Assessment

In this sub-section moulds with different number of cavities regarding their energy consumption are

compared. As analysed before, the cycle time is the variable that controls the machine energy, so is

proposed a sub indicator related to time. Regarding the Thermodynamic Energy it is expected a linear

behaviour increasing with the number of cavities since the Thermodynamic Energy depends on the

mass and injected volume.

The Cavities assessment was performed for Part1 with hot feeding system and with conventional

cooling system, the same part used in the assessment of material variation. For this part moulds with

1, 4, 16, 36 and 64 cavities were assessed and compared.

The values of Part1 used in this assessment were the Baseline value calculated in sub-section 6-1

and 6-2, the values obtained in chapter 5, simulation values (Table 5-10) and the Actual Value. (Table

5-11 to Table 5-17). To obtain the total energy required for each mould size the same energy model

was used (equation(3)). The intermediate calculations to obtain the Baseline and Actual Value of each

mould that aren’t present in this sub-section are presented in the Annex C. Next are described and

presented the calculations performed for Actual Value. For Baseline the logic was the same.

The calculation of the mass value for the several cavities, was the multiplication of the mass of part by

the number of cavities. It wasn’t considered the mass of the feeding system since the considered

alternative is with hot runners. The same logic was applied to the calculation of the injected

volume[77]. The injection pressure value used is the same value for all the cavities.

The cycle time for each mould was calculated based on the cycle time obtained for the mould with one

cavity. The difference between the cycle times is that a mould with more cavities is bigger so it has a

longer open/close time. To the cycle time of the mould with one cavity was deducted the open/close

time and then added the open/close time calculated for each mould size (Table 6-23). To know the

open/close time, first the injection moulding machine must be defined and to define the injection

moulding machine the clamping force must be known. The clamping force obtained from simulation for

the mould with one cavity was multiplied by the number of cavities of each mould and then trough

equation(9) it was calculated the respective installed power. The machines were selected from

ENGEL’s catalogue that contained all the parameters required to calculate the open/close time

(Equation(12)).

63

Cavities Clamping

Force [ton]

Installed Power [KW]

Real Installed

Power [KW]

L [mm]

L max [mm]

Dry cycle time [s]

Open/close time [s]

Cycle time[s]

1 3.86 20.01 22 450 450 1.50 3.63 14.63

4 15.44 21.86 22 450 450 1.50 3.63 14.63

16 61.75 29.25 31 500 500 1.60 3.80 14.80

36 138.93 41.57 45.3 600 600 1.73 4.03 15.03

64 246.99 58.81 64 900 900 2.20 4.85 15.85 Table 6-23 Clamping Force, Real Installed Power, Open/close time and Cycle time for each mould; Actual Value

For the selected machines is important to verify if the plates’ dimensions are well suited to the

dimensions of the mould. The distance considered between the centre line of each cavity was 120 mm

and the distance between the centre line of the cavity and the extremity of the mould is 100 mm. The

mould dimensions depend on how the cavities are arranged. In the following table are presented the

machine's plates’ dimensions and the dimensions of each mould. All the selected machines were well

suited to each mould.

Cavities Machine Plates

Dimensions [mm] Mould Dimensions

[mm]

1 670x600 100x100

4 670x600 320x320

16 740x680 560x560

36 860x830 800x800

64 1100x1000 1040x1040

Table 6-24 Machine Plates Dimensions and Mould Dimensions; Actual Value

After the determination of the cycle times and selection of the injection moulding machines, the Energy

Consumption was calculated for all the moulds. The Total Energy of each mould was divided by the

respective number of cavities resulting on the energy consume per part. Analysing the Figure 6-9 it is

clear that a mould with one cavity has a higher consume per part compared with the other moulds. For

moulds with 16, 36 and 64 cavities the energy per part has a slight variation.

Figure 6-9 Energy per Part of different moulds; Actual Value

64

The cycle time is longer for a mould with more cavities. By calculating a unitary time, the time per part,

it decreases with the increase of the number of cavities (Table 6-25). To compare the time per part of

each mould with the time of a mould with a single cavity it is created an indicator (Figure 6-10). This

indicator measures the times that a mould with more than one cavity is faster relatively to a mould with

a single cavity. This time per part can’t be measured since all the parts are injected, cooled and

ejected at the same time, is just a reference value. The time indicator is calculated by the following

equation:

(%)

Time per partTime Indicator

Cycle time (18)

Cavities 1 4 16 36 64

Time per Part [s] 14.63 3.66 0.93 0.47 0.25

Table 6-25 Time per Part

Figure 6-10 Time Indicator

Next was analysed the Energy Indicator calculated with equation(17), using the values from Table

C-14 and Table C-16(Figure 6-11).

65

Figure 6-11 Energy Indicator

With the increase of the number of cavities the efficiency also increases. The Thermodynamic Energy

has the same fluctuation between the Baseline and Actual value for all number of cavities. This result

was expected since the values of Baseline and Actual Value for the several number of cavities, are the

result of the multiplication by the number of cavities. The Machine Energy is responsible for the

different efficiencies.

Cavities Machine Energy [KWh]


1 2.38E-03 31.57%

4 1.84E-03 13.18%

16 3.75E-03 9.66%

36 6.30E-03 7.80%

64 8.77E-03 6.22%

Figure 6-12 Machine Energy Fluctuations

In order to understand these fluctuations the Installed Power, the Cycle Time and the Machine Power

coefficient were analysed (Table C-17). This variables don’t have a linear behaviour, so the machine

energy is dependent on their multiplication. The non-linear behaviour of the Installed Power, Cycle

time and Machine Power coefficient is due to the selection of the machine. The Clamping Force is

different between the Baseline and the Actual Value which influences the machine that is selected and

therefore the Installed Power (Equation(9)). The installed power of the machine affects the Machine

Power Coefficient and the Cycle Time (open/close time).

Concluding, this indicator is very sensitive to the selection of the machine, specifically regarding the

clamping force value. In the Baseline the empirical and scientific range used for the clamping force

doesn’t consider the part dimensions. Therefore there isn’t a criteria that relates the clamping force

with the part’s dimensions, being the Baseline Clamping Force higher than the Actual Value Clamping

Force.

66

7. Proposed Methodology for Standardized Efficiency

Indicators

In this chapter the proposed methodology for the Standardized Efficiency Indicators is described. The

global perspective is to propose and validate the concept behind these indicators, to assess if they

can be used in the future as a standard to characterize the performance and efficiency of the injection

moulds.

This methodology allows the comparison of the performance of different mould designs in the injection

moulding process, regarding three main aspects: mass and energy consumption, related with

resources efficiency; and execution time, related with productivity.

This methodology is composed of three phases:

Baseline Calculation

Actual Value Calculation

Standardized Efficiency Indicators calculation

To calculate the Baseline it is required the compilation of the material properties relative to the

injection moulding process, the part or parts data and an injection moulding machine database (Table

4-2). With the injection moulding machine database the user must do a linear regression equation that

relates the installed power of the machine and its clamping force. This equation is used in in the

Baseline’s and Actual Value’s calculations. In a future use of this methodology as an efficiency

standard, this linear regression should also be a standard with periodic updates.

For the selected part, the parameters and processing conditions required to calculate the Actual Value

can be obtained through part injection moulding industrial data or through injection moulding

simulation software.

If the user is going to perform the calculation of the Actual Value with values obtained through injection

moulding simulation software, the following scheme is an overview of the tasks to perform, in Moldflow

Insight software (Figure 7-1).

In the Baseline and Actual Value calculations is applied the same energy model proposed by Ribeiro

et al. [58]. In the future use of this methodology, this energy model can be already improved or other

energy models can be available .The following scheme is an overview of the energy model, applied to

the Baseline and to the Actual Value. In the scheme is also presented the required inputs, and shown

which ones differs from Baseline to the Actual Value (Figure 7-2).

Through the calculated Indicators and performed analysis were elaborated mould labels that

characterize the performance and efficiency of the injection moulds. This labels are a suggestion how

the results of the methodology may be presented and used as a future standard (Figure 7-3; Figure

7-4; Figure 7-5; Figure 7-6).

67

Import CAD Model Mesh Select the Material Gate Location

Feeding System &

Moulding WindowFilling AnalysisDesign Cooling SystemCooling Analysis

Cool+Fill+Pack+Warp

Analysis

.IGS format

Type: Dual

Domain

Mesh

Statistics

Tool: Aspect

Ratio, etc.

Wizard Cooling

System; or

Manual Cooling

system:

Geometry menu

Assign properties

Apply mesh

Ccoolant inlets

Injection time

Injection Pressure

Bulk Temperature

Flow Front

Temperature

Shear rate

Shear stress at wall

for

Flow

Resistance

Indicator

Best Gate

Location

Default

Wizzard

Runner

system: Cold

or Hot

runners

Recommended

Processing

Coolant Temperature

Coolant Flow

Average Temperature

Maximum Temperature

Temperature Profile

Mould and Part Temperature

Time to reach ejection

Temperature

Process order

Actions

Improvements

regarding

Frozen Layer

fraction

volumetric

shrinkage

hold pressure

deflection

Figure 7-1 MoldFlow scheme guide

Part:

Volume

Mass

Thickness

Material:

Cp

Tmelt

Tamb

Injection Pressure

λ

Hf

ε melt

α ef

T ext

T mould

BASELINE ACTUAL VALUE

Obtained from Simulation:

Part:

Mass

Injected Volume

Process:

Injection Pressure

Clamping Force

Cycle TIme

Mass

Indicator

Energy

Indicator

Remaining Material and Part

data: similar to Baseline.

Time

Indicator

LABELS

Thermodynamic

Energy

Equation 4

Machine Energy

Equation 5

Filling time (Equantion 6)

Cooling Time (Equation 11)

Open/close Time (Equation

12)

CfM (Equations 13 &14)

CfP

CfT (Equation 15)

Total Energy:

Baseline

Equation 3

Model

Coefficients Cycle Time

Installed Power

Equation 9

Thermodynamic

Energy

Equation 4

Machine Energy

Equation 5

CfM (Equations 13 &14)

CfP

CfT (Equation 15)

Total Energy: Actual

Value

Equation 3

Model

Coefficients Cycle Time

Installed Power

Equation 9

Figure 7-2 Overview of the Energy Model applied to Baseline and Actual Value

68

S.E.I 2015

STANDARD EQ:

ENERGY

MATERIAL: PPMOULD DESIGN: HNCAVITIES:1PROJ. AREA:1.45E-03 m2

TIME INDICATOR: 1

75%

MASS 100%

S.E.I 2015

STANDARD EQ:

ENERGY

MATERIAL: PPMOULD DESIGN: CNCAVITIES:1PROJ. AREA:1.45E-03 m2

TIME INDICATOR: 1

70%

MASS 98%

Figure 7-3 Mould Label: Mould Design Alternative comparison

S.E.I 2015

STANDARD EQ:

ENERGY


TIME INDICATOR: 1

75%

MASS 100%

S.E.I 2015

STANDARD EQ:

ENERGY


TIME INDICATOR: 1

78%

MASS 100%

Figure 7-4 Mould Label: Part's Dimensions comparison

S.E.I 2015

STANDARD EQ:


TIME INDICATOR: 1

S.E.I 2015

STANDARD EQ:

MATERIAL: PCMOULD DESIGN: HNCAVITIES:1PROJ. AREA:1.45E-03 m2

TIME INDICATOR: 1

MASS

ENERGY 75%

100% MASS

ENERGY 82%

100%

Figure 7-5 Mould Label: Material comparison

69

S.E.I 2015

STANDARD EQ:

ENERGY


S.E.I 2015

STANDARD EQ:

TIME INDICATOR: 15.81

ENERGY


TIME INDICATOR: 1

75% 93%

MASS 100% MASS 100%

Figure 7-6 Mould Label- Cavities comparison

70

8. Conclusions

This work was performed in order to develop Standardized Efficiency Indicators for Plastic Injection

Moulds. The proposed Standardized Efficiency Indicators are calculated using simple ratios between

the minimum input required to accomplish the process (Baseline values) and the real or expected

actual time and resources consumed (Actual value). These indicators allow the comparison between

different types of mould design, different mould sizes, different number of cavities and the efficiency of

the mould for different polymers.

The Standardized Efficiency Indicators are in regard to mass and energy consumption, related with

resources efficiency; and execution time, related with productivity. For the energy consumption

estimation a published energy model was used. To use this energy model was necessary to elaborate

an injection moulding machine database with available machines on market, to establish a linear

equation that relates the machine Installed Power with the machine Clamping Force. In a future use of

the Standardized Efficiency Indicators, this machine database should be de updated according the

machines available on market.

For the defined Case Study, first was analysed the Mass Efficiency Indicator. Through this indicator it

was noted that cold runners have lower mass efficiency than hot runners, as expected, due to the

material that is wasted in the feeding system. Between the cooling systems, the differences were very

small, being the conformal system more efficient. Regarding the dimensions of the part, it was

observed that the dimensions do not drastically influence the Mass Efficiency.

Some Mass Efficiencies were above 100% due to the final part volume being smaller than the value

calculated on Baseline. This result is caused due to the fact that volumetric shrinkage was not

considered in the initial part design, as is usual in every mould design process. If the shrinkage effects

are considered, this indicator will be only a measure of the wasted material in each shot.

For the Energy Efficiency Indicator analyses, the total energy was divided in the Thermodynamic

Energy and Machine Energy. By going backwards on the energy model was identified that the

Machine Energy is the predominant energy, and the variable that influences it is the Cycle Time.

In the Materials assessment, the comparison of the Baselines allowed to understand that each

material has its own level of mass and energy consumption, depending on the materials properties.

Once again in the Energy Efficiency Indicator analysis, the Cycle time is a variable that greatly

influences the efficiency. When is intended to compare moulds with different design alternatives the

material should be the same, once the material conditions the level of mass and energy consumed.

Regarding the Cavities assessment, was calculated the energy per part of the several moulds

concluding that with the increase of the number of cavities, the energy per part decreases. The

proposed Time Indicator allows to measure the times that a mould with more than one cavity is faster

relatively to a mould with a single cavity. In this assessment it was analysed that the variable that

influences Energy Efficiency the most is the selection of the machine in the Baseline and in the Actual

71

Value, depending on the Clamping Force defined for Baseline and obtained from the simulation, for

the Actual Value.

In the several assessments performed some fluctuations values were negative, which indicates that

the Baseline is higher than the Actual Value. This occurred for some values of injection pressure and

clamping force. To improve these results it is recommended a review and a more extensive research

of information regarding the material properties and processing conditions for the Baseline, to better

adjust the available ranges of values to the part sizes.

Finally the proposed labels gather and relate the several studied Standardized Efficiency Indicators,

representing how the indicators can by implemented in moulds. A data collection during the testing

mould phase, allows that the final Standardized Efficiency Indicators Label is characteristic of the

same mould.

Future Work

In this sub-section some suggestions to future work are proposed.

The proposed methodology was performed using an Actual value obtained through simulation data. Is

suggested a collection of injection moulding industrial data in order to improve the precision of the

proposed methodology.

For the review and improvement of the Baseline data is suggested the development of models that

relate the Clamping Force and the Injection Pressure with the part geometry. Is also suggested the

improvement of the energy model.

72

Bibliography

[1] T. & F. Group, “Polymers: A Properties Database,” 2014. [Online]. Available: http://www.polymersdatabase.com/entry.do?id=1344&exno=1344&method=view&si=POLY. [Accessed: 11-Oct-2015].

[2] A. Cunha, “Moldação por Injecção e Materiais PLásticos - Volume 2,” in Manual do Projectista para moldes de injeção de plástico, Departamento de Enga de Polímeros da Universidade do Minho, 2001.

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Annexes

Annex A. Feeding and Cooling Systems.

Figure A-1 Feedings Systems

Figure A-2 Cooling Systems

78

Annex B. Cooling Results: Definitions and ranges

The first result verified was the coolant flow. The coolant flow must be turbulent. Turbulent regime is

defined by a high Reynolds number. Reynolds number depends on the diameter of the channels, on

the flow rate and on the viscosity of the coolant. The recommend value for Reynolds number is

10,000[72]. The flow rate should not be beyond what is required because it will be a waste of energy.

Regarding the coolant temperature it must be uniform. The recommend surface temperature of the

mould is typically 10ºC to 30ºC above the coolant temperature. The recommend surface temperature

for the mould is 35ºC, and the coolant temperature was set in to 25º as referred before. The decrease

of this temperature value allows a better heat transfer and reduces cycle time but it must be kept

within a certain range. The coolant inlet/outlet temperature variation, should vary no more than 2ºC

to 3ºC [72].

The Average temperature, part result is the average temperature across the part thickness. This

result should be between the mould temperature and the ejection temperature. The Temperature,

maximum, part result is the maximum temperature in the part and it must be below the ejection

temperature, 110ºC, at the end of the cooling to guarantee that the part is successfully ejected.

The Temperature Profile, part result shows the temperature distribution of the part (top to bottom)

through thickness. By selecting the hottest region of the part, it is possible to assess if the variation of

the temperature is close to the recommend ejection temperature for the material. If it is, it means that

the cooling time is good.

The temperature, part result and the temperature, mould result are used to find hot or cold spots

that may affect the cycle time and part warpage. The part temperature should vary within 10ºC over

each mould face and should vary 10ºC to 20ºC above the coolant inlet temperature. The mould

temperature should be within 10ºC for amorphous materials and within 5ºC for semi-crystalline

materials, but this guideline is very difficult to achieve for most moulds[72]. This result is typically

between 10ºC to 30ºC above the coolant inlet temperature.

The Time to reach ejection temperature, part result is the time that the part requires to reach

ejection temperature. When this time begins is considered that the part is already filled. Areas of the

part that take more time to cool may indicate that they are hot spots or have more thickness.

Hold pressure result shows the maximum pressure in each area during the packing phase.

79

Annex C. Material Variation and Cavities Assessment

PP PA6 PS PC

3 [ / ]kg m

917.55 1358 1051.8 1185.9

/ .Cp J K Kg 1800 1700 1200 1800

/Hf J Kg 207000 145000 0 0

0.75 0.4 0 0

2 ( / )mm s 0.096 0.1040 0.0792 0.1335

injP MPa 2.76E+06 3.45E+06 5.52E+06 5.52E+06

ºTmelt C 118 200 100 143

ºText C 110 195 90 143

ºTinj C 240 255 235 305

ºTmould C 60 85 30 85

Table C-1 Material Properties

Material Part Volume [cm3] m [g] Thermodynamic Energy [KWh]

PP

11.45

10.51 1.19E-03

PA6 15.55 1.93E-03

PS 12.05 3.98E-04

PC 13.58 1.02E-03

Table C-2 Mass Values; Thermodynamic Energy; Baseline

Material Pressure [N/m^2]

Projected area [m2]


PP 30E+06

1.43E-03

4.44

PA6 45E+06 6.65

PS 30E+06 4.44

PC 75E+06 10.94 Table C-3 Clamping Force; Baseline

Material Installed Power [KW]

Real Installed

Power [KW] Machine Q max t fill

PP 20.26 22 ENGEL

VC 60/60

81 0.28 PA6 20.45 22

PS 20.37 22

PC 21.15 22 Table C-4 Installed Power and Filling time; Baseline

Material coolingt [ ] d st strokeL mm max

strokeL mm / [s]open closet [s]cyclet

PP 6.43

1.5 100 100 3.625

10.34

PA6 2.64 6.55

PS 7.52 11.43

PC 4.78 8.69

Table C-5 Cooling Time; Open/close Time and Cycle Time; Baseline

80

Material Thermodynamic

Power [KW] CfM CfT CfP


Total Energy [KWh]

PP 0.41

1 0.94

0.12 7.07E-03 8.25E-03

PA6 1.06 0.16 6.43E-03 8.36E-03

PS 0.13 0.09 6.34E-03 6.74E-03

PC 0.42 0.11 6.20E-03 7.23E-03

Table C-6 Thermodynamic Power, Model Coefficients, Machine Energy and Total Energy; Baseline

Material Injection time [s]

V/P [MPa]

Bulk T [ºC] Flow Front T

[ºC]

Shear rate,

bulk [1/s]

Shear stress at wall [MPa]

PP 0.22 18.23 242.6-248.4 243.1-243.3 92410 0.19

PA6 0.84 22.13 286.8-295.5 289.9-290.5 24780 0.31

PS 0.52 22.54 242.3-251.9 245.6-246.0 38459 0.22

PC 1.18 63.31 302.4-333.2 311.5-316.7 21075 0.50 Table C-7 Filling Simulation Results

Material Average T

[ºC]

Circuit coolant T

[ºC]

T, Maximum [ºC]

T Profile

[ºC] T,Mould [ºC] T,Part [ºC]

Ejection time [s]

PP 75.55-83.38 25.00-26.30 105.90 105.90 30.74-43.71 37.84-55.01 8.57

PA6 83.57-90.08 25.01-25.70 109.20 109.20 36.07-49.08 48.00-63.17 4.75

PS 54.93-60.58 25.01-25.81 66.04 66.04 36.78-47.42 44.01-54.63 7.81

PC 86.98-93.89 25.01-25.86 110.30 110.30 42.09-56.53 53.24-73.97 4.66

Table C-8 Cooling Simulation Results

Material Hold Pressure

[MPa] Volumetric contraction at ejection (máx)[%]

Deflection, all effects [mm]

PP 25.86-27.03 1.43-5.04 8.64-15.85 0.09-0.26

PA6 44.28-45.51 2.67-7.98 0.195-0.48

PS 40.94-45.04 -0.46-2.32 0.03-0.08

PC 73.54-79.32 0.29-4.62 0.05-0.13 Table C-9 Cool+Fill+Pack+Warp Analysis Results

Material m [Kg] Injection Pressure

[N/m2]

Injected Volume [m^3]

Cycle Time [s]


PP 1.01E-02 38.0E+06 1.16E-05 14.625 5.44

PA6 1.48E-02 28.8E+06 1.16E-05 14 6.58

PS 1.19E-02 26.2E+06 1.16E-05 17 6.14

PC 1.34E-02 79.3E+06 1.16E-05 10 11.03 Table C-10 Simulation Results

Material Thermodynamic Energy

[KWh] Thermodynamic Power

[KW]

PP 1.28E-03 0.32

PA6 1.95E-03 0.50

PS 4.78E-04 0.10

PC 1.30E-03 0.47

Table C-11 Thermodynamic Energy and Thermodynamic Power; Actual Value

81

Material Installed

Power [KW]

Real Installed

Power [KW] CfM CfT CfP


Total Energy [KWh]

PP 20.2630 22

1 0.9397

0.11 1.00E-02 1.13E-02

PA6 20.4457 22 0.12 1.08E-02 1.27E-02

PS 20.3746 22 0.09 1.01E-02 1.05E-02

PC 21.1548 22 0.12 7.55E-03 8.86E-03 Table C-12 Installed Power, Model Coefficients, Machine Energy and Total Energy; Actual

Cavities Assessment

Mass [kg]

Cp [J/[K.Kg]]

Tmelt [K]

Tambient [K]

Injection Pressure [N/m2]

Injected Volume

[m3] λ

Hf [J/Kg]

e melt

1 10.51

1800 391.15 298.15 2.8E+06

1.15E-05

0.75 207000 0.8

4 42.03 4.58E-05

16 168.12 1.83E-04

36 378.28 4.12E-04

64 672.49 7.33E-04 Table C-13 Baseline Values

Cavities Thermodynami

c Power [W] Thermodynamic

Energy [KW] CfM CfP

s [mm]

CfT Machine Energy [KWh]

Total Energy [KWh]

1 0.41 1.19E-03

1

0.11

2 0.94

7.55E-03 8.74E-03

4 1.63 4.75E-03 0.19 1.39E-02 1.87E-02

16 6.51 1.90E-02 0.39 3.88E-02 5.78E-02

36 14.34 4.28E-02 0.56 8.07E-02 1.23E-01

64 23.68 7.60E-02 0.62 1.41E-01 2.17E-01

Table C-14 Thermodynamic Power, Thermodynamic Energy, Machine Energy, Total Energy; Baseline

Cavities Mass

[g] Cp

[J/[K.Kg]] Tmelt

[K] Tambient

[K]

Injection Pressure

[N/m2]

Injected Volume

[m3] λ

Hf [J/Kg]

e melt

1 10.10

1800 391.15 298.15 20.5E+06

1.16E-05

0.75 207000 0.8

4 40.39 4.63E-05

16 161.58 1.85E-04

36 363.55 4.16E-04

64 646.31 3.70E-04

Table C-15 Actual Values

Cavities Thermodynamic Power [KW]

Thermodynamic Energy [KW]

CfM CfP s

[mm] CfT

[mm]


Total Energy [KWh]

1 0.30 1.21E-03

1

0.10

2 0.94

9.94E-03 1.11E-02

4 1.19 4.85E-03 0.17 1.58E-02 2.06E-02

16 4.72 1.94E-02 0.31 4.26E-02 6.20E-02

36 10.47 4.37E-02 0.43 8.70E-02 1.31E-01

64 17.04 7.50E-02 0.49 1.46E-01 2.21E-01

Table C-16 Thermodynamic Power, Thermodynamic Energy, Machine Energy, Total Energy; Actual Value

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Cavities

Installed Power [KW] Cycle Time [s] Machine Power Coefficient







1 0 0.00% 4.29 41.51% -0.01 -7.02%

4 -2.2 -9.09% 4.11 39.15% -0.02 -10.53%

16 -0.8 -2.52% 4.29 40.81% -0.08 -20.12%

36 0 0.00% 4.29 39.95% -0.13 -22.97%

64 -2.3 -3.47% 4.29 37.11% -0.12 -19.74%

Table C-17 Installed Power, Cycle Time and Machine Power Coefficient Fluctuations

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