(Đồ án hcmute) research and design 8 cavities injection plastic mold of the laundry detergent closures for practical application

HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND EDUCATION FACULTY FOR HIGH-QUALITY TRAINING GRADUATION PROJECT RESEARCH AND DESIGN 8 CAVITIES INJECTION PLASTIC MOLD OF THE LAUNDRY DETERG

MINISTRY OF EDUCATION AND TRAINING

HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND EDUCATION

FACULTY FOR HIGH QUALITY TRAINING

GRADUATION PROJECT MAJOR MECHANICAL ENGINEERING

ADVISOR:

STUDENT:

DR VO XUAN TIEN TRAN TAN KIET BUI THI KHOI AN NGUYEN THANH TAM

S K L 0 0 9 9 2 2

RESEARCH AND DESIGN 8 CAVITIES INJECTION PLASTIC MOLD OF THE LAUNDRY DETERGENT CLOSURES FOR PRACTICAL APPLICATION

Ho Chi Minh city, February 2023

HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND EDUCATION

FACULTY FOR HIGH-QUALITY TRAINING

GRADUATION PROJECT

RESEARCH AND DESIGN 8 CAVITIES INJECTION PLASTIC MOLD OF THE LAUNDRY DETERGENT CLOSURES FOR PRACTICAL APPLICATION

BUI THI KHOI AN STUDENT ID: 18144001 NGUYEN THANH TAM STUDENT ID: 18144048

Major: MECHANICAL ENGINEERING Advisor: VO XUAN TIEN, Ph.D

TRAN TAN KIET

Ho Chi Minh City, February 2023

i

HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND EDUCATION

FACULTY FOR HIGH-QUALITY TRAINING

GRADUATION PROJECT

RESEARCH AND DESIGN 8 CAVITIES INJECTION PLASTIC MOLD OF THE LAUNDRY DETERGENT

CLOSURES FOR PRACTICAL APPLICATION

NGUYEN THANH TAM STUDENT ID: 18144048

Major: MECHANICAL ENGINEERING Advisor: VO XUAN TIEN, Ph.D

TRAN TAN KIET

Ho Chi Minh City, February 2023

ii

THE SOCIALIST REPUBLIC OF VIETNAM Independence – Freedom– Happiness

-

Ho Chi Minh City, February 10, 2023

GRADUATION PROJECT ASSIGNMENT

Student name: Bui Thi Khoi An Student ID: 18144001

Student name: Nguyen Thanh Tam Student ID: 18144048

Major: Mechanical Engineering Class: 18144CLA

Advisor: Ph.D Vo Xuan Tien Phone number: 0917556700

Date of assignment: 9/2022 Date of submission: 2/2023

1 Project title:

RESEARCH AND DESIGN 8 CAVITIES INJECTION PLASTIC MOLD OF THE LAUNDRY DETERGENT CLOSURES FOR PRACTICAL APPLICATION

2 Initial materials provided by the advisor:

- Sample product of a detergent bottle closure made of plastic PP126NK

- Using PP126NK or PP plastic material with equivalent function

- Three-plate mold with 8 cavities, 1 million shots warranty

- Using the plastic injection machine labelled CLF 120 or equivalent

3 Content of the project:

- Inverse designing the laundry detergent closure

- Researching on plastic, mold materials, heat treatments, mold parts, plastic injection machine, etc

- Designing 2D mold layout, list of parts

- Calculating runners, cooling system, injecting force, ejecting space, etc

- Designing 3D mold parts, assembling

CHAIR OF THE PROGRAM

(Sign with full name)

ADVISOR

(Sign with full name)

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THE SOCIALIST REPUBLIC OF VIETNAM Independence – Freedom– Happiness

-

Ho Chi Minh City, February 8, 2023

ADVISOR’S EVALUATION SHEET

Major: Mechanical Engineering

Project title:

RESEARCH AND DESIGN 8 CAVITIES INJECTION PLASTIC MOLD OF THE LAUNDRY

DETERGENT CLOSURES FOR PRACTICAL APPLICATION Advisor: Ph.D Vo Xuan Tien

EVALUATION

1 Content and workload of the project

2 Strengths:

3 Weaknesses:

4 Approval for oral defense? (Approved or denied)

iv

THE SOCIALIST REPUBLIC OF VIETNAM Independence – Freedom– Happiness

-

Ho Chi Minh City, February 10, 2023

PRE-DEFENSE EVALUATION SHEET

Major: Mechanical Engineering

Project title:

RESEARCH AND DESIGN 8 CAVITIES INJECTION PLASTIC MOLD OF THE LAUNDRY

DETERGENT CLOSURES FOR PRACTICAL APPLICATION Name of Reviewer: Ph.D Tran Minh The Uyen

EVALUATION

1 Content and workload of the project

2 Strengths:

3 Weaknesses:

4 Approval for oral defense? (Approved or denied)

v

THE SOCIALIST REPUBLIC OF VIETNAM

Independence – Freedom– Happiness

-

Ho Chi Minh City, February 18, 2023

EVALUATION SHEET OF DEFENSE COMMITTEE MEMBER

Major: Mechanical Engineering

Project title:

RESEARCH AND DESIGN 8 CAVITIES INJECTION PLASTIC MOLD OF THE LAUNDRY

DETERGENT CLOSURES FOR PRACTICAL APPLICATION Name of Defense Committee Member: Assoc Prof Pham Son Minh, PhD Tran Van Tron , PhD Tran Minh The Uyen, M.Eng Nguyen Thanh Tan, M.Eng Dang Minh Phung,

EVALUATION

1 Content and workload of the project

2 Strengths:

3 Weaknesses:

4 Approval for oral defense? (Approved or denied)

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Acknowledgments

We would like to express our deepest gratitude to Ph.D Tien Vo Xuan, who gave us a chance to experience the internship program at Duy Tan Precision Mold Co., Ltd From there, we have been raising and expanding our knowledge in plastic injection mold Besides, we could not have undertaken this journey without Mr Kiet Tran Tan, who has always been thoughtful and patient

We also would like to extend our sincere thanks to Ho Chi Minh City University of Technology and Education, the Faculty of High-Quality Training lecturers, and the Faculty

of Mechanical Engineering for the thorough instructions in the previous four years We have been gaining major knowledge from nothing and becoming the ones who are well-behaved, confident, and independent

Lastly, we would like to show our gratitude to our parents, classmates, and acquaintances who have encouraged and supported us in this project and our academic journey

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Abstract

The specific goal of this study was to design an injection mold for the product that would comply with the requirements and specifications outlined by the business Employing an artificially balanced runner to provide better-filling results in cavities These results are based on the findings of pressure at P/V switchover and fill time in Moldflow analysis Two adjustments were taken from a typical balanced H-type runner system and put through the process of analysis A pneumatic system layout inside the core inserts with a double-stage ejector improves the ejection system by lessening the vacuum force that would otherwise distort the product during ejection

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Table of Contents

GRADUATION PROJECT ASSIGNMENT ii

ADVISOR’S EVALUATION SHEET iii

PRE-DEFENSE EVALUATION SHEET iv

EVALUATION SHEET OF v

DEFENSE COMMITTEE MEMBER v

Acknowledgments vi

Abstract vii

Table of Contents viii

List of Figures xi

List of Tables xv

Keyword xv

Chapter 1 INTRODUCTION 1

1.1 Overview 1

1.2 Objective 2

1.3 Study restrictions 2

1.4 Research methods 2

1.5 Research subject and scope of the report 2

1.6 Outline 2

Chapter 2 TECHNICAL KNOWLEDGE 3

2.1 Plastic Material 3

2.1.1 Nature of plastics 3

2.1.2 Melt Flow Index MFI/MI 7

2.1.3 Treatments of materials 7

2.2 Required surface gloss 8

2.2.1 Factors influence the selection of plastic material 10

2.3 Injection Machine 10

2.3.1 Overview of plastic injection machine 10

2.3.2 Machine categories 11

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2.3.3 Major variables 14

2.4 Injection Mold 14

2.4.1 The injection molding 14

2.4.2 The main type of plastic injection mold 17

2.4.3 Ejection system 20

2.4.4 Injection system 24

2.4.5 Tolerance of mold parts 39

Chapter 3 PRACTICE ON CONCEPTUAL DESIGN 40

3.1 Design sequence 40

3.2 Sample receipt and design specifications 42

3.3 Product design 42

3.3.1 Material 42

3.3.2 Shrinkage 43

3.3.3 Surface roughness and gloss 44

3.3.4 Design process 44

3.3.5 Analysis 45

3.3.6 Export CAD 47

3.4 Mold design 48

3.4.1 Plastic injection machine 48

3.4.2 Layout design 50

3.4.3 Calculation 67

3.5 Analyzing 74

3.5.1 Analyzing process 74

3.5.2 Analyzing result 76

3.6 3D design 81

3.6.1 Design sequence 81

3.6.2 Design of cavity inserts 82

3.6.3 The mold plates 84

3.6.4 Ejecting system 88

3.6.5 Non-standard components 90

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3.6.6 Standard components 90

3.6.7 Assembling Instructions 91

3.6.8 Ventilation system design 98

3.6.9 Exporting CAD 99

Chapter 4 USE, STORAGE AND MAINTENANCE 101

4.1 Use 101

4.2 Storage 101

4.3 Maintenance 101

4.3.1 Maintenance of the cooling line 101

4.3.2 Maintenance of the mold surfaces 101

4.3.3 Maintenance of the gate system 101

Chapter 5 RESULTS, CONCLUSION, AND RECOMMENDATIONS 102

5.1 Result 102

5.2 Conclusion 102

5.3 Recommendations 102

References 103

Appendix 1: Bill of materials 106

Appendix 2: Drawings 106

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List of Figures

Figure 2.1 Molecular structure of monomers [3] 3

Figure 2.2 Polymer structure of thermoplastics and thermosets [3] 4

Figure 2.3 Amorphous molecular chains [5] 5

Figure 2.4 Crystalline molecular chains [5] 5

Figure 2.5 Material cooling characteristics 5

Figure 2.6 Melt flow index MFI apparatus [4] 7

Figure 2.7 The main components of the injection molding machine [15] 11

Figure 2.8 a) Toggle clamping; b) Hydraulic clamping 11

Figure 2.9 Hydraulic clamping [16] 12

Figure 2.10 Hydro-mechanical clamp [16] 12

Figure 2.11 Tederic Horizontal Injection 12

Figure 2.12 J-K Vertical Injection Molding Machine [17] 12

Figure 2.13 Injection molding machine with reciprocating screw [18] 13

Figure 2.14 Plunger injection cylinder [19] 13

Figure 2.15 Two stage plunger type cylinder [19] 13

Figure 2.16 Pre-plasticizer two-stage screw injection cylinder [19] 13

Figure 2.17 Summary of a molding cycle [3] 15

Figure 2.18 Functional analysis of an injection mold [5] 16

Figure 2.19 Typical European designation of components of an injection mold [5] 17

Figure 2.20 Basic two-plate construction [3] 18

Figure 2.21 Three-plate cold runner mold [3] 18

Figure 2.22 Hot runner mold [20] 19

Figure 2.23 Hot runner mold [20] 19

Figure 2.24 Pin and blades ejectors [3] 20

Figure 2.25 Sleeve ejection [3] 21

Figure 2.26 Stripper plate with integral hardened insert [3] 21

Figure 2.27 Stripper plate with moving hardened insert [3] 21

Figure 2.28 Air ejection on both cavity and core plates [21] 22

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Figure 2.29 Stripper plate plus mechanical valve ejection [3] 22

Figure 2.30 Slides [3] 22

Figure 2.31 Lifters [3] 22

Figure 2.32 Two-segment collapsible core [3] 23

Figure 2.33 Multi-segments collapsible core [3] 23

Figure 2.34 Rotating core unscrewing tool [3] 23

Figure 2.35 Standard double injection system [3] 24

Figure 2.36 Locating ring [5] 24

Figure 2.37 Sprue parameters [5], [22] 25

Figure 2.38 Cross-sections of injection mold runners [9] 26

Figure 2.39 Geometrically balanced runner layouts cause unbalanced filling and melt conditions [9] 26

Figure 2.40 Geometrical balanced design of a runner [3] 27

Figure 2.41 Graduated runner [4] 27

Figure 2.42 Typical gate types [9] 29

Figure 2.43 Dimensions for pin point gate [5], [21] 30

Figure 2.44 Ventilation system on the parting line [5] 30

Figure 2.45 Vent land depth for the variety of plastics [21] 31

Figure 2.46 Mold cooling design [5] 32

Figure 2.47 Some cooling designs [3] 34

Figure 2.48 Annular groove cooling [3] 34

Figure 2.49 Mold material advice [21] 36

Figure 3.1 Mold design sequence 40

Figure 3.2 Part design sequence [21] 41

Figure 3.3 Capping component on the final product 42

Figure 3.4 Characteristics of plastics [4] 43

Figure 3.5 Physical properties of POLIMAXX PP1126NK [26] 43

Figure 3.6 The injected product without air vents 45

Figure 3.7 Placement of air vents 46

Figure 3.8 Vent region pressure in case 2 46

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Figure 3.9 Re-placement of air vents 46

Figure 3.10 Vent region pressure in case 3 46

Figure 3.11 Parameters of injection machine CLF-120TX 49

Figure 3.12 Parameters of machine ejection rod (X – 21mm; Y – ø25mm; Z – M16) 49

Figure 3.13 Layout design sequence [19] 50

Figure 3.14 The mold layout drawing 51

Figure 3.15 A sketch of cavity and core inserts 52

Figure 3.16 Placement of insert clusters – top view 53

Figure 3.17 Placement of insert clusters – side view 53

Figure 3.18 Preliminary layout of runner system 53

Figure 3.19 Cavity insert with cooling and runner system 54

Figure 3.20 Cooling system placement on core inserts 54

Figure 3.21 Cooling system on fixed side 55

Figure 3.22 Cooling system on movable side 55

Figure 3.23(a & b) Two-stage single stroke ejector FW1800 [27] 56

Figure 3.24 Two-stage ejecting system in the mold 57

Figure 3.25 The assembly for executing ejection group 57

Figure 3.26 Additional air ejection 58

Figure 3.27 Vent land placements 58

Figure 3.28 Mold operation – step 1 64

Figure 3.29 Mold operation – step 2 65

Figure 3.30 Mold operation – step 3 65

Figure 3.31 Mold operation – step 4 66

Figure 3.32 Mold operation – step 5 66

Figure 3.33 Mold operation – step 6 67

Figure 3.34 Cylindrical thin-wall design 67

Figure 3.35 Design of the gate 68

Figure 3.36 Parameters of a completed runner system 68

Figure 3.37 A complete runner system 69

Figure 3.38 Mold opening strokes [9] 70

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Figure 3.39 Mold cavity pressure: Wall thickness graph [24] 71

Figure 3.40 Analyzing sequence 75

Figure 3.41 Properties of CP12-N0009 from CrossPoint Polymer Technologies 75

Figure 3.42 Meshed cooling circuits 76

Figure 3.43 Circuit Reynolds number 77

Figure 3.44 Circuit coolant temperature 77

Figure 3.45 Process setting for analysis 78

Figure 3.46 Case 1 processing parameter analysis result 79

Figure 3.47 Case 2 processing parameter analysis result 80

Figure 3.48 The typical H-type runner system filling process 80

Figure 3.49 The adjusted H-type runner system 81

Figure 3.50 Three-dimensional design sequence 81

Figure 3.51 The assembly of core inserts 82

Figure 3.52 The assembling of ejecting system 88

Figure 3.53 Mold standard components 91

Figure 3.54 Stationary mold assembling 95

Figure 3.55 Movable mold assembling 97

Figure 3.56 Mold closing 98

Figure 3.57 Parameters of an air vent [23] 98

Figure 3.58 Drawing of cavity insert 99

Figure 3.59 Drawing of mold plate 100

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List of Tables

Table 1 Values for the Gloss Percentage of Several Plastics [14] 9

Table 2 Minimum water flow corresponding to cold channel diameter [21] 33

Table 3 The hardness of P20 through temperature [25] 37

Table 4 Some SPI standard value 38

Table 5 Properties of injection machine CLF-120TX 48

Table 6 Selection of standard parts for plastic injection mold 59

Table 7 Cavity and core inserts 82

Table 8 Mold plates 84

Table 9 Mold components of ejecting system 89

Table 10 Non-standard components 90

Keyword

1

Chapter 1 INTRODUCTION 1.1 Overview

The global plastic injection molding market has remarked considerable growth due to the increasing demand in the packaging industry, the high usage of electronics and consumer goods, and the replacement of conventional plastics with thermoplastic elastomers in the automobile industry [1] Based on a report from Strait Research, the size

of the global plastic injection molding market was valued at USD 11385 million [1], which means around 1,34,240 kilo tons of plastics [2] in 2021 Recently, polypropylene has been mostly used in injection molding [1] The global polypropylene market is projected to generate USD 70652 million in 2030 and grow at a CAGR of 4% by 2030 [1] Packaging

is the largest market holder, supported by continued economic expansion and an acceleration in the food and beverage output [1] It was valued at USD 43917 million in

2021 [1] The plastic injection molding market share is segmented into 5 regions, and the Asia-Pacific is the largest revenue holder with 45562 million USD in 2021 China is the largest contributor to the market compared to other countries, valued at USD 19381 million

in 2021 India and Japan grew their market gradually, with a revenue of USD 10903 million and USD 8469 million in 2021 [1]

The European Union-Vietnam Free Trade Agreement (EVFTA), signed in August 2020, significantly improves the export rate of plastic products and the import rate of European feedstock in Vietnam This is both an opportunity and a challenge, as Vietnamese plastics must meet the stringent requirements of the EU Market regarding domestic feedstock, ISO TC6 certification, sustainable development, and environmental conservation As environmental concerns increase, the composition and life cycle of plastic packaging, which plays a crucial role in plastic production in Vietnam, must be evaluated As a result

of their reduced material content, thin-walled products are favored, although durability and recyclability take precedence

The packaging industry, or toiletries packaging, has been in operation for decades Inside the factories, improvements, and changes are occurring continuously Although these mold products have been manufactured extensively, a common point of relevant research in universities seems to be that there are very few applications of insert molds and multiple cavities molds for large-scale and massive production Thus, the learning and research process regarding molds is not yet close to the market After completing an internship, we selected the research topic of molds with multiple cavities in the production

of detergent bottle caps We want to portray a stage in the development of the Vietnamese plastics industry and assist non-professional mold researchers in taking a closer look at practical learning and evaluation

2

1.2 Objective

Inverse design of a detergent bottle cap from a selective model

Drafting up a design for an injection mold that can be used to manufacture the product

in compliance with the requirements outlined by the company

- Collecting the materials and information for the study

- Planning and providing suitable approaches to the tasks

- Conducting researches

- Evaluating the results

1.5 Research subject and scope of the report

Research subject: Three-plate injection plastic mold

Scope of the report: The design process of the plastic injection mold for the specified product

1.6 Outline

Chapter 1: Introduction

Chapter 2: Technical knowledge

Chapter 3: Practice conceptual design

Chapter 4: Use, storage, and maintenance

Chapter 5: Results, conclusion, and recommendation

Alloys, also known as polymer blends, consist of two or more polymers that are generated independently and then merged to produce new materials having properties not present in the component polymers.

Figure 2.1 Molecular structure of monomers [3]

Altering the relative amounts of the monomers involved or arranging them in different patterns throughout the molecular chain length can also affect individual copolymers' characteristics

2.1.1.1 Thermosets and thermoplastics

The plastics family consists of three primary branches: thermosets, thermoplastics, and elastomers

Thermoset is a plastic material that experiences a chemical change and "cures" when heated; it cannot be reformed and reheating degrades it

Figure 2.2 Polymer structure of thermoplastics and thermosets [3]

Both materials have linear chain structures Therefore, they perform similarly at the first heated process However, the structure of the thermoset polymer has chemically reactive sites interspersed along the molecular chains, which promote the joining or cross-linking

of nearby molecules when sufficient heat is applied, transforming the linear structure into

2.1.1.2 Amorphous and Crystalline Thermoplastics

The two basic categories of thermoplastic materials are amorphous and crystalline; however, certain materials can be found in either category, and some are composites of both

Amorphous substances are ones in which the molecular chain structure is random and becomes movable over a wide range of temperatures They become softer and softer as heat is absorbed until they degrade from absorbing excessive heat

5

Figure 2.3 Amorphous molecular chains [5]

Crystalline materials have a well-ordered molecular chain structure that only becomes mobile at the melting point

Figure 2.4 Crystalline molecular chains [5]

Both random and ordered structures exist in semi-crystalline materials Depending on the material, their polymer chains, 20–80%, have formed tight and strictly oriented crystals Amorphous chains surround the crystals

Figure 2.5 Material cooling characteristics

Most amorphous thermoplastics are transparent in their natural, unpigmented state, and most semicrystalline thermoplastics are translucent or opaque white in their solid natural form

6

Some examples:

- Amorphous materials: ABS, Acrylic, Cellulose propionate, Polyamide-imide, Polyarylate, Polycarbonate, Polyetherimide, Polyethersulfone, Polyphenylene oxide, Polystyrene, Polyurethane

- Crystalline Materials: Acetal, Cellulose butyrate, Liquid crystal polymer (LCP), Nylon, Polyester (PBT), Polyetheretherketone (PEEK), Polyethylene, Polyethylene terephthalate (PET), Polyphenylene sulfide, Polypropylene, PVC

- Elastomers: Acrylates, Butyls, Chlorosulfonated polyethylene, Fluorocarbons, Fluorosilicones, Polysulfides, Polyurethanes, Neoprenes, Nitriles, Silicones, Styrene

a) Amorphous

thermoplastics (ABS) [6]

b) A crystalline thermoplastic (PBT) [7]

c) Elastomer product (Silicon) [8]

Figure 2.6 Some plastic product 2.1.1.3 Shrinkage

Isotropic shrinkage, in which the rate of shrinkage is the same in all directions, is typical

of amorphous materials Anisotropic shrinkage, in which the rate of contraction is greater along than across the flow direction, is characteristic of crystalline materials Shrinkage is smaller along the flow direction and greater across it when reinforced materials are used Specifically, this is because of how the reinforcement fibers are oriented

Amorphous materials' softening and hardening processes occur over a wider temperature range Here is the shrinking percent range of different materials:

- Amorphous thermoplastics: 0.5 – 1%

2.1.2 Melt Flow Index MFI/MI

The melt flow index, in conjunction with capillary and nozzle rheometers, characterizes how a polymer flow Even though MFI is the most inaccurate method for defining non-Newtonian fluid, it is still the most commonly used method by most resin suppliers due to the low equipment cost and test cost The primary shortfall is that the melt flow index only indicates a material’s flow characteristics at a single, low shear rate and a single melt temperature [9] This low shear rate is far below that experienced by a melt during injection molding [9]

ASTM D1238 defines the MFI test The MFI test consists of extruding molten polymer through a standard die orifice at a specified temperature and under a specified load, the load and temperature varying for different types of materials The quantity of material extruded in 10 minutes, measured in grams, is quoted as the melt flow index for the material An easy-flowing grade of polythene may have an MFI of 30 or greater, whereas the stiff-flowing grades used for blow molding may have an MFI of less than 1 [3]

Figure 2.6 Melt flow index MFI apparatus [4]

2.1.3 Treatments of materials

Most molding materials need pre-drying in a box-type drying oven before going into the hopper drier

8

Pre-drying requires proper temperature and time because, even if dried for a long time,

moisture cannot be removed if the temperature is too low Use pre-dried material

immediately—pre-dry leftover material before using it days later

Some main types of driers being used at present:

Hot air drier: Hopper and box driers are typical for this kind Although this is a frequent

and simple drying procedure, it does not remove moisture

Dehumidified hot air drier: After eliminating air moisture, hot air is pushed over pellets

to evaporate their moisture

Reduced pressure heat transfer type drier: Heat transfer in a low-pressure environment

to evaporate pellet moisture Preventing plastic oxidation and additive effects, as well

as reducing heat loss

2.2 Required surface gloss

A uniform and consistent gloss is a quality criterion for numerous products Surface

gloss is a subjective impression created by the light flux reflected by a part It may be

quantitatively assessed with a gloss meter that, for a specified angle, measures the fraction

of light flux reflected in the specular direction when a parallel light beam illuminates the

specimen Spectrophotometers operating in the reflection mode and diffractive optical

sensors have also been used to study the gloss differences of injection molded plastic

products [10] Gloss varies with the refractive index of the polymer, the angle of incidence,

and the topography of the surface The topography and, consequently, the gloss of injection

molded parts depend on the mold finish and the replication accuracy [11] Several factors

influence the surface gloss of plastic parts One of the most important factors in obtaining

a high-quality glossy surface is the type of plastic being processed As regards the process

parameters, the temperature, pressure, and melt flow rate are considered those that strongly

affect the surface structure of injection- molded polymers [12] The materials processed at

a high filling rate exhibited a fairly constant gloss as the holding time increased regardless

of the position of the analyzed region

In contrast, a more significant decrease was noted in the case of the moldings processed

at the low filling rate The cooling time had a negligible effect on the gloss in comparison

to the effect of the filling rate [13] However, for Oliveira, Brito, and Costa, the mold

temperature commonly being considered the more important parameter to be controlled

[11]

Gloss is expressed in % It is determined by a device that measures the proportion of

incident light (typically 45 degrees) reflected from the film's surface Environmental

factors such as weathering and surface abrasion can also affect gloss

9

A gloss meter (or gloss meter) measures a surface's specular reflection (gloss) It has an incandescent light source and a photosensitive receptor sensitive to visible light However, the instrument is not sensitive to haze and orange peel, two other common effects that diminish image quality ASTM D523 and ASTM D2457 are the common standard methods for measuring the gloss of plastic materials Following ASTM D523, measurements by this test method correspond to visual observations of surface glossiness made at approximately the same angles ASTM D245 is a standard for measuring the gloss of plastic films and solid plastics, and it includes separate gloss angles: 60°, 20°, 45°, and 85° are recommended for films, while 75° is recommended for plastic siding and soffit

Table 1 Values for the Gloss Percentage of Several Plastics [14]

Polymer Name Min Value (%) Max Value (%)

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2.2.1 Factors influence the selection of plastic material

The plastic material must have a proper melt flow index for injection molding Lower melt index numbers have better physical qualities than higher levels for a given material When the MFI is low, the material has a high viscosity, making it difficult to dilute, slowing down the filling speed but leaving the state relatively unchanged, making the product flexible However, high MFI materials are flexible enough to fill the thin flow, albeit with

a more brittle result

Many variations exist at different operation temperatures, including the melting point

higher value results in better impact resistance and shorter cycle time

Ejection temperature is another factor that must be considered to balance costs while ensuring that the product is ejected without causing warp or excessive internal stress Along with the technical specifications for a product, stiffness, fatigue, wear resistance, chemical exposure, and thermal conductivity should also be considered

2.3 Injection Machine

2.3.1 Overview of plastic injection machine

Although there are advantages to horizontal and vertical molding, Horizontal molding

is the most common method of injection molding

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Figure 2.7 The main components of the injection molding machine [15]

Plastic injection molding machines are broadly classified into five categories:

- Clamping device: die plate, tie bar, ejector plate, clamping cylinder, ejector

- Injection device: nozzle, band heater, heating cylinder, screw, and screw lead

- Hydraulic power system: hydraulic pump, hydraulic motor, clamping cylinder, and injection cylinder

- Electrical control system: motion circuit, control circuit

- Other equipment includes a frame and an oil tank

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Figure 2.9 Hydraulic clamping [16]

Figure 2.10 Hydro-mechanical clamp [16]

- Motion direction: horizontal, vertical

Figure 2.11 Tederic Horizontal Injection

Molding Machine [17]

Figure 2.12 J-K Vertical Injection Molding Machine

[17]

13

- Pressing and plasticizing: screw, plunger, pre-plasticizing, two shot, thermosetting resin

Figure 2.13 Injection molding machine with reciprocating screw [18]

Figure 2.14 Plunger injection cylinder [19]

Figure 2.15 Two stage plunger type cylinder [19]

Figure 2.16 Pre-plasticizer two-stage screw injection cylinder [19]

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2.3.3 Major variables

When designing a mold, the following machine factors must be considered

- Mold clamping force (ton): the force required to hold the mold together during the injection

positions where the mold can be installed, the maximum mold size that can be installed, and the location of the clamping bolt holes

- Distance between tie bars: the actual size of the mold should be 20 to 50 millimeters smaller than the distance of the support bar, with vertical mounting being preferred

- Clamping stroke (mm): the maximum travel length to open the mold, which determines the maximum depth of the product, is typically at least two times the minimum product height

- Clamp bolt hole size, ejector rod mounting hole: being shown in the plates’ drawings

- Minimum mold height (mm): maximum limit of mold closing stroke

- Machine ejector rod position: the design of the ejecting system and the distribution

of forces within the mold are directly affected by the location of the ejector holes

- Maximum ejecting stroke (mm): the maximum distance that the product can be removed from the mold

2.4 Injection Mold

2.4.1 The injection molding

2.4.1.1 The injection molding cycle

A cycle starts with the mold closing phase, in which the mold is closed by actuating the press, or the clamping unit The mold should be closed as fast as possible to limit the undue strain on the mold or the machine until the mold protection facility is tripped [3] The mold protection phase happens at the final stage of mold closing right before the two mold halves meet to avoid damage caused by trapped moldings or shot-off areas on each half of the mold Next, the injection phase occurs rapidly, while not generating excessive shear stress

in the melt by short fill times An ideal fill time should prevent large reductions in melt temperature (less than 20°C) and avoid the generation of high injection pressure (more than 100MPa) [3]

The connection between the mold and plasticizing unit is maintained until the melt in the gate has solidified, called the holding and packing phase

During the packing phase, a small amount of additional material is forced into the mold The pressure prevents material from flowing back into the injection cylinder from the mold Then holding phase holds material at an equilibrium pressure until gate freeze occurs

is pushed out of the cavity by ejectors Avoid abrupt opening during the mold open phase

to prevent damage to the machine and the mold Ejection can be accomplished either automatically or automatically Afterward, the cycle is repeated

semi-Figure 2.17 Summary of a molding cycle [3]

2.4.1.2 Plastic injection mold components

In a plastic injection mold, the component is shaped by a core and cavity, whose hollow caused by assembling is where the molten plastic is contained, then cool down The basic tasks of a mold are accommodation and distribution of the melt, shaping, and cooling of the material, solidification of the melt, and ejection of the molding A mold comprises other components to obtain a functional mold whose products can meet the technical requirements These mold components are grouped based on their function in the mold A typical thermoplastics injection mold includes a platen, guiding and positioning system, sprue and runner system, ejection system, cavity (venting) system, heat exchange system, and accommodation of forces and motion transmission

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Figure 2.18 Functional analysis of an injection mold [5]

The positioning and guiding system aims to exact position two halves of the mold, which

is a stationary and movable cluster The runner system takes responsibility to position the nozzle and connect the nozzle to the mold to create the well-laminar flow of molten plastic from the barrel to the cavities The ejecting system helps to automatically eject the products out of the mold Ejecting system is normally placed on the movable side, where the machine rod can easily apply ejecting force on the system Based on the chosen ejecting method, the components being used in the mold are also different Some products have a special shape They may contain undercut, ribs, inner or outer thread, or prongs, which might need special care when ejected Therefore, an undercut release system is in place to release these significant details before the products are ejected completely

The air that remains in the cavity in the injecting process will case burn spots, and bubbles on the surfaces of the products Therefore, the venting system is located at the ends

of the flow paths Venting land is normally created by machining and unintended gaps in the mold assemble process The last one is the cooling system, which is important in controlling the mold temperature and cooling down the components, expanding the mold life cycle and productivity

Mold standards are pieces or modules whose dimensions are specified and characterized In accordance with the basic construction of a mold, they can be classified

as standards for the mold structure, the cavity, the gate system, the guides and centering, heat control, demolding, and for accommodating the mold in an injection molding machine

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Figure 2.19 Typical European designation of components of an injection mold [5]

1 – Compression spring; 2 – Ejector bolt; 3 – Movable clamping plate; 4 – Ejector and ejector retainer plates; 5 – Ejector pin; 6 – Central sprue ejector; 7 – Support plates; 8 – Straight bushing; 9 – Cavity retainer plate; 10 – Leader pin; 11 – Shoulder bushing; 12 – Parting line; 13 – Cavity retainer plate; 14 – Stationary clamping plate; 15 – Plug for cooling line connection; 16 – Locating ring; 17 – Sprue bushing; 18 – Cavity insert; 19 –

Cooling line; 20 – Support pillar

2.4.2 The main type of plastic injection mold

Molds' design is based on demolding functions, specific components, or particular applications Depending upon the design, the mold characteristics could be the transmission of motion, ejection system, number of parting lines, number of floating plates, alignment, the transmission of forces, and mounting to machine platen On the other hand, characteristics dependent upon molding are cavity, cavity layout, sprue and runner system, heat-exchange system, slides and lifters, and ejection system

2.4.2.1 Two-plate mold

Two-plate mold has one parting line, dividing the mold into two parts: cavity and core This is the simplest type of plastic mold

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Figure 2.20 Basic two-plate construction [3]

The properties of a two-plate mold are as follows:

- The structure is simple

- The design is simple to change

- Low price

- High performance and reliability

- Difficulty in separating the runner system and the product

2.4.2.2 Three-plate mold

Three-plate mold with two parting lines for product take-out and channel out, with plates: the runner stripper plate, the cavity plate, and the core plate

Three plate mold features:

- Parts and the runner system can be separated

- Cycle time is longer than with a two-plate mold

Figure 2.21 Three-plate cold runner mold [3]

2.4.2.3 Hot runner

The hot runner mold replaces the conventional sprue bushing with a hot sprue bushing

or a heated nozzle, allowing the material to be directed to the mold cavities without heat

or pressure loss, minimizing plastic and time waste

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Figure 2.22 Hot runner mold [20]

The hot runner manifold, heated with heating elements such as electric cartridges, keeps the material plasticized Individually controlled heater bands can be mounted

around the nozzle

Figure 2.23 Hot runner mold [20]

The manifold and the drops are the two components of a hot runner system The manifold has channels that transport the plastic in a single plane parallel to the parting line

to a point above the cavity; the drop, perpendicular to the manifold, transports the plastic from the manifold to the part There are two kinds of hot runner systems:

- Internally drops and manifolds: higher molding pressure, space for hung-up material, and offering better gate tip control

- Externally drops and manifolds: have the lowest pressure drop, are better for the color change, and are suitable for thermally sensitive materials because there is no residual material

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2.4.3 Ejection system

The ejection system is responsible for removing the cooled product from the mold When designing the ejection system, keep the following factors in mind:

- The materials and shapes of injecting products

- Product shape variant

- Traces from ejector pins

- Simple machining and maintenance

- The overall balance must be favorable

- Put extra thrust in places with complex shapes, such as undercuts, bosses, and ribs

2.4.3.1 Ejector pins and blades

The ejector pin has a simple structure and straight movement in the shape of a pin

Figure 2.24 Pin and blades ejectors [3]

Ejector pins can be used as gas vents by positioning them in the air-trapped position They are typically used in areas with a boss and a rib

Stepped ejector pins are ideal for very small holes or areas requiring increased firmness The ejector blade is ideal for thick ribbed spots It has a high impact force and is prone

to cracking, deformation, and leaving marks

2.4.3.2 Ejector sleeves

Sleeve ejectors are used to ejecting on round features such as circular pads, bosses, or recessed holes

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Figure 2.25 Sleeve ejection [3]

2.4.3.3 Stripper plate ejection

Typical applications include tubular parts and circular, square, or rectangular boxes

Figure 2.26 Stripper plate with integral hardened insert [3]

Figure 2.27 Stripper plate with moving hardened insert [3]

2.4.3.4 Air ejection

This method is used for products with a deep cavity because the inside and core of the mold have a large vacuum, making it difficult to exit the mold To obtain the product, an additional stripper plate or two air lines through two air valves on the core and cavity plate can be used

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Figure 2.28 Air ejection on both cavity

and core plates [21]

Figure 2.29 Stripper plate plus mechanical valve ejection [3]

2.4.3.5 Ejection system for undercuts

1) Slides/Lifters

Figure 2.30 Slides [3] Figure 2.31 Lifters [3]

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2) Collapsible core

Figure 2.32 Two-segment

collapsible core [3]

Figure 2.33 multi-segments collapsible core [3]

3) Automatic unscrew thread

Figure 2.34 Rotating core unscrewing tool [3]