Study on the effect of injection molding parameters on the weld line strength for thermoplastic composite materials

Trang 1 MINISTRY OF EDUCATION AND TRAINING HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND EDUCATION FACULTY FOR HIGH QUALITY TRAINING CAPSTONE PROJECT ELECTRONICS AND TELECOMMUNICATIONS

MINISTRY OF EDUCATION AND TRAINING

HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND EDUCATION

FACULTY FOR HIGH QUALITY TRAINING

CAPSTONE PROJECT ELECTRONICS AND TELECOMMUNICATIONS

ENGINEERING TECHNOLOGY

STUDY ON THE EFFECT

OF INJECTION MOLDING PARAMETERS

ON THE WELD LINE STRENGTH FOR THERMOPLASTIC COMPOSITE MATERIALS

LECTURER: ASSOC PROF DO THANH TRUNG STUDENT : NGUYEN TAN LOI

NGUYEN THAI BINH

S K L 0 1 1 1 5 1

Ho Chi Minh City, July 2023

MINISTRY OF EDUCATION AND TRAINING

HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND

EDUCATION

FACULTY FOR HIGH QUALITY TRAINING

GRADUATION PROJECT

ID STUDENT:18143002 School year: 2018-2022

Major: Machine Manufacturing Technology

STUDY ON THE EFFECT OF INJECTION

MOLDING PARAMETERS ON THE WELD LINE STRENGTH FOR THERMOPLASTIC COMPOSITE

Graduation Project

Project

HCMC UNIVERSITY OF

TECHNOLOGY AND EDUCATION

FACULTY FOR HIGH QUALITY TRAINING

SOCIALIST REPUBLIC OF

VIETNAM

Independence – Liberty – Happiness

GRADUATION PROJECT TASKS Advisor: Assoc Prof Do Thanh Trung

Students perform: Nguyen Thai Binh ID: 18143002 Phone: 0983719600 Nguyen Tan Loi ID: 18143024 Phone: 0377611637

1 Topic name:

STUDY ON THE EFFECT OF INJECTION MOLDING PARAMETERS ON THE WELD LINE STRENGTH FOR THERMOPLASTIC COMPOSITE MATERIALS

2 Initial figures and documents:

- Injection molding process parameters

- Injection mold

3 Main contents of the project:

- Overview of plastic injection molding technology and its injection parameters

- Conducting the tensile tests and hardness on various injection molding specimens with different parameters

- Analyzing the SEM images

- Discussing the results

4 Expected products

- Creating plastic injection molding samples using ABS and TPU materials

- Analyzing the effects of mold temperature, plastic temperature, and injection pressure

on the tensile strength

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Project

5 Project delivery date:

6 Date of submission of the project:

7 Presentation language: The report: English  Vietnamese

Protection presentation:

English  Vietnamese

(Sign, specify fullname) (Sign, specify full name) (Sign, specify full name)

Graduation Project

Project HCMC UNIVERSITY OF

TECHNOLOGY AND EDUCATION

FACULTY FOR HIGH QUALITY TRAINING

SOCIALIST REPUBLIC OF

VIETNAM

Independence – Liberty – Happiness

GRADUATION PROJECT COMMENT SHEET (For Advisor)

Full name of students Nguyen Thai Binh Student ID 18143002 Council: 12

Nguyen Tan Loi Student ID 18143024 Council: 12

Topic name: STUDY ON THE EFFECT OF INJECTION MOLDING PARAMETERS ON THE

WELD LINE STRENGTH FOR THERMOPLASTIC COMPOSITE MATERIALS

Major: Machine Manufacturing Technology

Full name of instructor: Assoc Prof Do Thanh Trung

COMMENTS

1 Comment on the spirit and working attitude of students (do not type)

2 Comment on the results of the implementation of the SEA (no typing) 2.1 Structure and presentation of lines:

2.2 Project content: (The rationale, practicality, and applicability of the project, and research directions may continue to develop)

2.3 Results achieved:

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2.4 Limitations of the study:

3 Assessment:

1 Correct format with both the form and content

Objectives, tasks, overview of the topic 10

2

The ability to design and manufacture a system,

component, or process that meets requirements

Ability to use technical tools, specialized

3 Assessment of the applicability of the topic 10

4 Specific products of graduation project 10

Graduation Project

Project HO CHI MINH CITY UNIVERSITY OF

TECHNOLOGY AND EDUCATION

FACULTY FOR HIGH QUALITY TRANING

SOCIALIST REPUBLIC OF

VIETNAM

Independence – Liberty – Happiness

GRADUATION PROJECT COMMENT SHEET (For critical lecturers)

Full name of

student

Nguyen Thai Binh ID STUDENT 18143002 Council 12 Nguyen Tan Loi ID STUDENT 18143024 Council 12

Topic name: STUDY ON THE EFFECT OF INJECTION MOLDING PARAMETERS ON THE

WELD LINE STRENGTH FOR THERMOPLASTIC COMPOSITE MATERIALS

Major: Machine Manufacturing Technology

Full name of instructor: Assoc Prof Do Thanh Trung

COMMENTS

1 Comment on the spirit, working attitude of students (do not type)

2 Comment on the results of the implementation of the SEA (no typing)

2.1 Structure and presentation of lines:

2.2 Project content:

(The rationale, practicality and applicability of the project, research

directions may continue to develop)

2.3 Results achieved:

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Project

2.4 Limitations of the study:

3 Assessment:

1 Correct format with both the form and content

Objectives, tasks, overview of the topic 10

The ability to design and manufacture a system,

component, or process that meets requirements

Ability to use technical tools, specialized

3 Assessment of the applicability of the topic 10

4 Specific products of graduation project 10

Graduation Project

Topic name: Study on the effect of injection molding parameters on the weld line strength for thermoplastic composite materials

Full name of advisor: Assoc Prof Do Thanh Trung

Full name of the student: Nguyen Tan Loi

Student address: C9A/16/1, Group 10, Hamlet 3, Vinh Loc B Ward, Binh Chanh

District, Ho Chi Minh City

Contact phone number: 0377611637

Full name of the student: Nguyen Thai Binh

Student address: 12/2, Street 5, Linh Chieu Ward, Thu Duc District, Ho Chi Minh

City

Contact phone number: 0983719600

Graduation project submission date: 26/07/2023

Disclaimer: “I hereby declare that this graduation project is the work of my own research and implementation I do not copy from any published article without citing the source If there is any violation, I take full responsibility."

HCM City, 26 July 2023

Nguyen Tan Loi

Graduation Project

Thank you, Ho Chi Minh City University of Technology and Education! Five years, perhaps insignificant compared to a lifetime, but these years represent our youth, during which we studied here, and these memories will forever remain unforgettable for each of us

Being a member of the Ho Chi Minh City University of Technology and Education is both an honor and a source of pride Today, we carry with us the enthusiasm to teach and pass on the professional knowledge and valuable life experiences imparted by our teachers over the past five years We are truly grateful and appreciative of their guidance

Therefore, first and foremost, we would like to extend our heartfelt thanks to all those who work in the university, especially the lectures in the Faculty of Mechanical Engineering We sincerely express our gratitude to Ho Chi Minh City University of Technology and Education, and particularly the Faculty of Mechanical Engineering and Faculty for High Quality Training, for providing us with the most favorable conditions to study and pursue our graduation topic

In particular, our group would like to express deep gratitude and respect to Assoc Prof Do Thanh Trung, Assoc Prof Pham Son Minh, Dr Tran Minh The Uyen, and Dr Nguyen Van Thuc for their invaluable guidance and assistance throughout our research and implementation period, enabling us to complete our topic

to the best of our abilities

Finally, we would like to wish you all good health, happiness, and continued success in your teaching endeavors

Thank you!

HCMC, July 2023 Students implement:

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Injection molding is a shaping technology in molds, supported by an external heating system to melt the material, which is then pumped into the mold through a screw to form the corresponding product when the mold cools down However, injection molding still faces several challenges in material processing research, process improvement, and existing equipment to reduce defects in the molded products Common defects include weld lines, air traps, warping, among others Among these defects, weld lines occur due to the contact and intersection between two plastic flows, leading to undesirable aesthetics and reduced tensile strength of the products

To enhance the tensile strength of weld lines in plastic products, a localized heating method at the weld line position is proposed to improve the adhesion between the two plastic flows and increase the tensile strength of the welded product

The experimental research involves mixing two types of TPU with ABS in five different blending ratios and conducting injection molding to create tensile test specimens following ASTM standards Two main heating zones are applied during the experiment:

- Common temperature ranges currently recommended for each material (ranging from 30°C to 70°C)

- High-temperature zones created by heating the mold surface with hot air (reaching

a maximum temperature of 200°C)

Using SEM imaging technology, the author examines the surface microstructure of the damaged regions on the tensile test samples and observes a uniform microstructure and smoothness at the damaged surface area The results show that temperature significantly influences the tensile strength and fracture behavior of the plastic products Increasing the temperature in the weld line area improves the tensile strength of the product Additionally, increasing the thickness and temperature of the welding area also contributes to enhancing the tensile strength of the product

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Ép phun là công nghệ tạo hình trong khuôn với sự hỗ trợ của hệ thống gia nhiệt làm nóng chảy vật liệu từ bên ngoài và được bơm vào khuôn thông qua vít me để tạo thành sản phẩm tương ứng khi khuôn nguội Hiện nay, nhiều loại vật liệu có thể được sử dụng trong công nghệ ép phun Đặc biệt, vật liệu composite dẻo nhiệt ngày càng được sử dụng rộng rãi để chế tạo nhiều loại sản phẩm ép phun với hình dạng và kích thước rất đa dạng Hiện nay, ép phun vẫn đang đối mặt với nhiều thách thức trong nghiên cứu xử lý vật liệu, cải tiến quy trình sản xuất và thiết bị hiện có để hạn chế các khuyết tật trong ép phun Các khuyết tật thường gặp có thể kể đến như đường hàn, rổ khí, cong vênh… Trong nhóm khuyết tật này, khuyết tật mối hàn được hình thành do quá trình tiếp xúc và giao nhau giữa hai đường nhựa cũng chính vì đặc điểm này, các đường hàn xuất hiện trên hầu hết các sản phẩm nhựa, tính thẩm mỹ của sản phẩm không những bị ảnh hưởng xấu mà độ bền của sản phẩm cũng giảm đi đáng kể Vì vậy, để tăng độ bền kéo của đường hàn trên sản phẩm nhựa, phương pháp gia nhiệt cục bộ tại vị trí đường hàn được đề xuất nhằm tăng khả năng bám dính của hai đường nhựa, cũng như tăng độ bền kéo của đường hàn sản phẩm nhựa Nghiên cứu thực nghiệm bằng cách trộn 2 loại TPU với ABS theo 5 tỷ lệ trộn khác nhau, ép phun thanh thử kéo theo tiêu chuẩn ASTM, gia nhiệt thành 2 nhóm chính như sau:

- Các dải nhiệt độ phổ biến được khuyến nghị hiện nay cho từng loại vật liệu (dải nhiệt độ từ 300C to 700C)

- Vùng nhiệt độ cao được tạo ra bằng cách đốt nóng bề mặt khuôn bằng khí nóng (nhiệt độ cao nhất lên đến 2000C)

Bằng công nghệ chụp ảnh SEM, tác giả đã kiểm tra vi cấu trúc bề mặt hư hỏng của các mẫu thử kéo và nhận thấy sự đồng đều về cấu trúc tế vi và độ mịn tại bề mặt vùng hư hỏng Qua đó có thể thấy nhiệt độ ảnh hưởng rất lớn đến độ bền kéo của sản phẩm nhựa Tăng nhiệt độ tại khu vực mối hàn sẽ làm tăng độ bền kéo của sản phẩm Đồng thời, tăng độ dày

và nhiệt độ của khu vực đường hàn cũng làm tăng độ bền kéo của sản phẩm

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GRADUATION PROJECT TASKS i

GRADUATION PROJECT COMMENT SHEET (For Advisor) iii

GRADUATION PROJECT COMMENT SHEET (For critical lecturers) v

COMMITMENT vii

ACKNOWLEDGMENTS viii

ABSTRACT ix

TÓM TẮT x

LIST OF SYMBOLS xiv

LIST OF TABLES xv

LIST OF FIGURES xvi

CHAPTER 1: OVERVIEW 1

1.1 The urgency of the topic 1

1.2 The scientific and practical significance of the topic 1

1.2.1 Scientific significance 1

1.2.2 Practical significance 1

1.3 Research objectives 2

1.4 Scope of research on the topic 2

1.5 Scope of study 2

1.5.1 Method 2

1.5.2 Specific research methods 3

CHAPTER 2: THEORETICAL BASIS 4

2.1 Composite materials 4

2.1.1 Notion 4

2.1.2 Composite material structure 4

2.1.3 Characteristics of Composite 9

2.1.4 Advantages and disadvantages of composite materials 10

2.2 Injection molding process 11

2.2.1 Concept: 11

2.2.2 Features of injection molding technology 11

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2.2.3 The general structure of the injection molding machine 12

2.2.4 Injection mold classification 17

2.2.5 Preliminary second leg injection molding cycle 18

2.2.6 Defection 18

2.2.7 Pressing parameters 22

2.3 The theoretical basis of weld lines: 28

2.3.1 Notion 29

2.3.2 Causes and remedies 30

2.3.3 The effect of mold temperature on the product 33

2.4 Tensile strength 34

2.4.1 Tensile strength concept 34

2.4.2 Meaning of tensile strength 35

3.1 Hot air mold heating process 37

3.1.1 The injection mold 38

3.1.1 Insert plate design 42

3.2 Test sample products 43

3.3 ABS to TPU blending ratio: 44

3.4 Mold heating 45

CHAPTER 4: RESULTS AND DISCUSSION 46

4.1 The temperature distribution 46

4.2 Injection molding specimens 54

4.3 Results of hardness test 56

4.4 Results of tensile test 59

4.5 Results of SEM 68

CHAPTER 5: CONCLUSIONS 73

5.1 Conclusions: 73

5.2 Limitations of the study: 74

5.3 Future dissertation development: 74

REFERENCES 76

APPENDIX 78

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LIST OF ABBREVIATIONS

ASTM American Society for Testing and Materials

SEM Scanning Electron Microscope

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minute

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LIST OF TABLES

Table 1.1: Percentages of ABS and TPU 2

Table 2.1: Some possible defects when pressing, causes, and remedies 19

Table 2.2: The weld line causes and remedies 30

Table 3.1: Percentages of ABS and TPU 44

Table 3.2: Weights of ABS and TPU 44

Table 4.1: Parameters of Makita hot air blower 46

Table 4.2: Specifications of Infrared Camera Fluke TiS20 47

Table 4.3: Average temperature value at the center of the plate during heating with different times 47

Table 4.4: Injection molding parameters of testing specimens 55

Table 4.5: The average tensile strength for different TPU percentages and heating times 61

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LIST OF FIGURES

Figure 2.1: Composite structure 4

Figure 2.2: Classification diagram by shape 5

Figure 2.3: Cross-weaving patterns of fabric 7

Figure 2.4: Fiber core orientation distribution 7

Figure 2.5: Structure of injection molding machine 13

Figure 2.6: Clamping system 13

Figure 2.7: Structure of the mold 14

Figure 2.8: Injection system 16

Figure 2.9: Injection molding support system 16

Figure 2.10: Control system 17

Figure 2.11: Research directions of injection molding for composite materials [6] 29

Figure 2.12: Melt line formation in injection molding 30

Figure 2.13: Tensile test model 35

Figure 2.14: Basic Scheme of Shore Durometer 36

Figure 3.1: Some methods of heating injection molds 37

Figure 3.2: Movable mold section 38

Figure 3.3: Fixed mold section 38

Figure 3.4: 2-panel mold structure 38

Figure 3.5: Complete mold set 39

Figure 3 6: Upper clamping plate 39

Figure 3.7: Lower clamping plate 40

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Figure 3.8: Fixed mold plate 40

Figure 3 9: Mobile mold plate 40

Figure 3.10: Pillow support 41

Figure 3.11: Holding plates, push plates, and gyroscopes 41

Figure 3.12: Push plate 41

Figure 3.13: Fixed and movable mold plates after the redesign 42

Figure 3.14: ASTM D638 prototypes 43

Figure 4.1: Makita hot air blower 46

Figure 4.2: Infrared camera Fluke 47

Figure 4.3: Temperature distribution at the surface of the mold when heated with a time of 3 seconds 49

Figure 4.4: Temperature distribution at the surface of the mold when heated with a time of 6 seconds 50

Figure 4.5: Temperature distribution at the surface of the mold when heated with a time of 9 seconds 52

Figure 4.6: Temperature distribution at the surface of the mold when heated with a time of 12 seconds 53

Figure 4.7: The result of average temperature at insert plate when heating 53

Figure 4.8: Haitian injection machine 55

Figure 4.9: Injection molding parameters 55

Figure 4.10: Digital Durometer 57

Figure 4.11: The average value of hardness 58

Figure 4.12: Digital electronic tensile testing machine 60

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Figure 4.14: The tensile strength as a function of heating time for different 61

Figure 4.15: Stress–strain diagrams of ABS/TPU samples at different TPU percentages and heating times 62

Figure 4.16: Average value of tensile strength as a function of heating time 64

Figure 4.17: Average tensile strength as a function of TPU percentages 66

Figure 4.18: The main effects plot for means 67

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1.1 The urgency of the topic

Thermoplastic composite products produced using injection molding technology are increasingly being utilized in various industries due to their versatility in complex textures and shapes However, along with this advancement, defects in injection-molded products using composite materials are also becoming more prevalent, commonly known as weld lines, air traps, and warpage

Among these defects, weld line defects are created when two plastic flows come into contact and intersect As a result, weld lines can be found on almost all plastic products, negatively impacting their aesthetics and significantly reducing their durability

To address this issue, one common approach is to apply a layer of paint on the product's surface Despite this solution, the research topic chosen is "Study on the effect of injection molding parameters on the weld line strength for thermoplastic composite materials"

1.2 The scientific and practical significance of the topic

1.2.1 Scientific significance

The injection method with a high mold temperature zone is shown to be one of the solutions to improve the flowability of composite materials in the mold At the same time, the method of controlling the surface temperature of the mold with hot air can be applied

to the case of injection molding products with thin walls and thin tendons to increase the ability to fill the material

The increase in mold temperature can be carried out at the entire lumen of the mold

or several locations before the flow of material into thin-walled sites and thin veins

1.2.2 Practical significance

With the results of the project, the method of heating the surface of the mold will have

a new, more effective method in terms of the ability to:

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- Simple temperature setting control

- Suitable for products with a reduced monomeric structure

- Ideal price for cheap

- Large heating area

- Effect of injection pressure on the tensile strength of plastic products

- The impact of plastic temperature and mold temperature in the weld line area on the tensile strength of plastic products

1.4 Scope of research on the topic

Using quantitative methods in the calculation process, the heating analysis combined with experiments to verify the change of welding line strength

Table 1.1: Percentages of ABS and TPU

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- Collecting, analyzing, and compiling documents related to heating techniques for plastic injection molds: ensuring diversity, multidimensionality, and taking advantage of the results of the latest research by the research content of the topic Empirical analysis methods:

- Based on the results and failures in the experiment, the appropriate equipment is selected, optimizing the process of collecting experimental results

- Apply the experimental procedure to different designs of the local heating system

1.5.2 Specific research methods

Empirical studies with two main groups are as follows:

- Common temperature zones are currently recommended for each type of material (temperatures vary from 300 C to 600C)

- The high-temperature zone is created through the method of heating the mold surface with hot air (the highest temperature to 2000C)

Structurally, composite materials consist of one or more intermittent phases evenly distributed over a continuous background phase If the material has multiple stages of disruption, we call it a composite mixture The discontinuous phase is usually superior to the ongoing phase as shown in Figure 2.1

The continuous phase is called the background (matrix) The intermittent stage is called reinforcement, filler, or reinforce

Figure 2.1: Composite structure

2.1.2 Composite material structure

It serves as a concentrated stress carrier because the aggregate usually has higher mechanical properties than plastic The core is evaluated based on the

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environmental resistance; dispersion into fine plastic; heat transfer, good cooling; favorable for the processing process; lightweight, low cost

Figure 2.2: Classification diagram by shape

a) Forms distributed in space; b) 1-way reinforcement

c) 2-way consolidation; d) 3-direction Depending on the requirements for each product type, one can choose the appropriate variety of composite materials (Figure 2.2) There are three primary forms of core:

Granules are intermittent materials; other fibers are not the preferred size The most common type of composite material is concrete, which is often referred to as concrete for short, so we often see the material called composite fiber reinforced composite material

 Fabric form

A fabric core combines surface walls (sheets) of fiber-reinforced materials made using textile technology The most commonly used traditional weaving techniques are plain silk, fishy, cross-vein, highly modular fabric, and local weaving Weaving

is a way of knitting yarn, also known as a cross-yarn style (Figure 2.3) The composite's core components must meet the mining and technology requirements Mining requirements are requirements such as durability, hardness, and corrosion resistance in acidic and alkaline environments And the technological requirement

is the requirement of technical ability in the process of producing this core component

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a b c d e

Figure 2.3: Cross-weaving patterns of fabric

a Smooth silk; b Coarse silk; c Twill; d High modulus type; e Isotropic type

 Fiber aggregate

When designing and manufacturing composite fiber products, the biggest concern is the specific strength and elasticity of the fiber The properties of fiber reinforcement composite depend on 10 factors: the nature of the substrate and base material, the power of the base bond – the core on the boundary, the distribution and orientation of the fiber (Figure 2.4), the size, and shape of the thread

Figure 2.4: Fiber core orientation distribution

a) The fiber core is distributed in one dimension in parallel; b) Fiber cores are distributed in two dimensions in parallel c) Fiber cores are randomly distributed; d) Perpendicular three-dimensional knitting thread

 Chemical structure of ABS plastic:

ABS stands for Acrylonitrile Butadiene Styrene It is an impact-resistant engineering thermoplastic It has an amorphous polymer ABS is made up of three

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o Acrylonitrile: It is a synthetic monomer It is produced from propylene

and ammonia This component contributes to the chemical resistance & heat stability of ABS

o Butadiene: It is produced as a by-product of ethylene production from

steam crackers This component delivers toughness & impact strength to ABS polymer

o Styrene: It is manufactured by dehydrogenation of ethyl benzene It

provides rigidity & processability to ABS plastic

 Mehanical Properties of ABS:

Toughness at Low Temperature 20 – 160 J/m

There is no solid wintering stage, and the ability to construct and shape products

is easy to perform Manufacturing technology: stamping, extrusion, bending, welding… low bar The disadvantage is that it does not tolerate high temperatures, and processing the viscosity of the solution is difficult Plastic materials: nylon,

poly-phenylin, rolivxan, polysonphon, and thermoplastic polyester

2.1.3 Characteristics of Composite

Background materials

- As a binder and creates a dispersed environment

- The virtual reinforced phase guard is not damaged by the environmental attack

- Toughness (resistance to the development of cracks)

- Khips only then contribute other necessary properties such as insulation, toughness, and color

Reinforced materials (core)

- Acts as a concentrated stress point

- Resistance to environmental chemicals and temperature

- Good dispersion into the substrate material

- Convenient for processing

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- Good heat transfer and heat dissipation

- Close to the environment

- Lower cost but bring outstanding properties

2.1.4 Advantages and disadvantages of composite materials

- Good electrical and thermal insulation

- Heat-resistant, cold-resistant, fireproof

- Waterproof, non-toxic

- Longer leverage time fund (extended leverage time) Weather resistant,

anti-UV, and anti-aging, so it is very durable

- Fabrication is simple and easy, fast, diverse, and easy to shape, change and repair quickly

-Shortcoming

Besides the advantages of composite materials, we still need to know the weaknesses of this type of material for the software to be suitable:

- It is recycled and reused when damaged or wasted

- The raw material is relatively high; the processing method takes time

- The complex in the mechanical, physical, and chemical analysis of specimens

- The amount of raw materials is highly dependent on the qualifications of the workers

is ejected from the mold using an ejection system [2]

2.2.2 Features of injection molding technology

Injection molding technology is a molten plastic technology that is accurately dosed into a sealed mold with high pressure and fast speed, and after a short time, the product is shaped and the product is taken out Then continue the next cycle for the second product The time from mold closing, plastic spraying, the time to determine 34 product shapes, removing the product from the mold, close the mold

is called the cycle of one product pressing In addition to the above, injection molding technology has the following characteristics:

- The processed product is quite accurate in three dimensions because it is shaped in a sealed mold

- The plasticization and forming process are carried out in two separate stages

in different parts of the machine: plasticization in cylinders and mold shaping

- The forming process is formed only after sealing the two halves of the mold together

- Depending on the type of injection material, the heat regime varies For thermoplastics, the mold temperature is lower than the liquid plastic temperature For thermosetting plastics, the mold temperature is higher than the liquid plastic temperature

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- The forming area of the mold is filled with raw materials; then the mold is subjected to the force of the indirectly molded piston through the liquid plastic

- Depending on the shape or size of the product, the pressing cycle varies from

a few seconds to tens of minutes

- Processing by injection molding technology saves raw materials, and the

completion process takes less time

 Advantages

- Diversified products, high quality

- High yield

- Flexible materials and colors

- Low labor costs

- Flexible design

- Recyclable plastic

- High automation capabilities

 Disadvantages

- High investment costs

- Difficult cost calculation

- Complex process, applicable only to mass production

2.2.3 The general structure of the injection molding machine

Includes 5 parts: Clamping system, mold system, injection system, injection

molding support system, and control system

Figure 2.6: Clamping system 2.2.3.2 Mold System

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 General structure of the mold [3, 4]:

Figure 2.7: Structure of the mold

1 Hexagonal screws: link the mold plates and create aesthetics

2 Positioning ring: centered between the silver stalk and nozzle

3 Silver spray stalk: conducts the plastic from the injection molding machine into the plastic conduction channels

4 Female mold: product shaping

5 Silver positioning: ensures the position of correlation between male and female molds

6 Front clamp plate: hold the fixed part of the mold to the plastic injection machine

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Project 7 & 11 Female mold shells and male mold: are often made of cheaper materials

than female molds, so it helps reduce the cost of molds but still ensures the economic efficiency of molds

8 Core pin: return the push system to its original position when the mold closes

9 Male mold: shape the product

10 Positioning pin: helps the male and female molds link correctly

12 Support plate: increase mold strength during injection molding

13 Support pillow: create space for the push plate to work

14 Holding plate: hold the push pins

15 Push plate: push the push pins so that the product leaves the mold

16 The following clamping plate: secure the movable part of the mold on the plastic injection machine

17 Extra support pillow: increase mold durability during injection molding 2.2.3.3 Injection system

Perform the task of introducing plastic into the mold through the process of plastic supply, compression, degassing, melting plastic, spraying liquid plastic

into the mold, and shaping the product

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Figure 2.8: Injection system

This system has the following parts: hopper, barrel, heater band, screw,

return assembly, and nozzle

2.2.3.4 Injection molding support system

It is a system that helps operate injection molding machines This system consists of 4 subsystems: frame, hydraulic system, electrical system, and cooling system

Figure 2.9: Injection molding support system

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Project 2.2.3.5 Control system

The control system helps the machine operator monitor and adjust machining parameters such as temperature, pressure, injection speed, velocity and position

of the screw, and the position of the parts in the hydraulic system The control system communicates with the operator through the control panel and computer screen

Figure 2.10: Control system

2.2.4 Injection mold classification

Classification by a number of layers:

- 1-tier mold

- Multi-tiered mold

Classification by channel:

- The mold uses a cold channel (Cold Runner)

- The mold uses a hot channel (Hot Runner)

Classification by channel layout

- Two-plate mold

- Three-plate mold

Graduation Project

Project Classification by the number of plastic colors that create the product:

- Mold gives the product a color

- Molds for multicolored products

2.2.5 Preliminary second leg injection molding cycle

An injection molding cycle is usually very short, from 2 seconds to 2 minutes, consisting of 4 cycles [2]:

- Clamp: Before pressing the material into the mold, the two halves of the

mold must close Half of the mold is mounted on the press, and the other half

is attached to the mobile part of the press The clamp pushes the two halves

of the mold together and exerts enough pressure to ensure the mold stays sealed

- Pressing: The plastic (usually granular) is heated to a flowing state and is

quickly sprayed into the mold and filled with the mold

- Cooling: The molten plastic, after being sprayed into the mold, begins to

cool as soon as it comes into contact with the surface of the mold When the plastic cools, it solidifies in the shape of the mold

- Remove the mold: After some time, the mobile part of the press attached to

half the mold will open the mold When the mold is opened, a mechanism is used to get the cooled part of the product out And then, that mobile half of the mold is pushed back in preparation for the next pressing cycle

2.2.6 Defection

Like all other industrial processes, injection molding can create unfinished products In the field of injection molding, troubleshooting is usually done by inspecting defective parts for specific defects and addressing those defects Before mass production, we often force the product to predict possible defects and determine the appropriate specifications (Table 2.1)

External forces take products

The mold temperature

is too low, and irregular

Due to the product texture causes stress

Reduce the force exerted on the product

Increased mold surface temperature

Consider the design to improve flow

Burns

The product has the black burn marks

High injection pressure

High plastic temperature

High injection pressure

High plastic temperature

Lack of

plastic

Plastic does not fill full of molds

Lack of plastic

Injection or pressure speed

productivity is too low

Increase the volume of spraying

Increase speed or pressure spray rate

Fill in too quickly, and air not

escape in time

Exhaust system not good

Reduce the spray speed so that the air has enough time

Check and fix mold errors Increased mold clamping force

Decrease in injection pressure, injection speed

Lineless

Small line

on the back

of the core, where the two flows meet

The fusion of two plastic flows

Use low viscosity plastic Increase in plastic

temperature, mold surface temperature

Warping

The product

is deformed

or twisted - Take the

Take the product too early, the plastic temperature is high

Increase the cooling time of the product

Check the product design