study on the effect of geometric shape on the torsional strength of injection molded plastic products

Overview of plastic injection molding technology Injection molding technology is the process of injecting molten plastic to fill the cavity of the mold.. Plastic injection machine struct

MINISTRY OF EDUCATION AND TRAINING

HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND EDUCATION FACULTY FOR HIGH QUALITY TRAINING

GRADUATION PROJECT

MECHANICAL ENGINEERING TECHNOLOGY

STUDY ON THE EFFECT OF GEOMETRIC SHAPE ON THE TORSIONAL STRENGTH OF

INJECTION-MOLDED PLASTIC PRODUCTS

LECTURER: DO THANH TRUNGSTUDENT: LE QUANG LINH

VU MANH HOANG PHI HOANG MINH

S K L 0 1 2 6 3 8

HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND EDUCATION

FACULTY OF INTERNATIONAL EDUCATION

GRADUATION THESIS

Advisor : Assoc Prof Dr Do Thanh Trung Students : Le Quang Linh ID: 19143026 Vu Manh Hoang ID: 19144071 Phi Hoang Minh ID: 19144156

Ho Chi Minh City, 2024

STUDY ON THE EFFECT OF GEOMETRIC SHAPE ON THE TORSIONAL STRENGTH OF INJECTION-MOLDED

PLASTIC PRODUCTS

HCMC UNIVERSITY OF TECHNOLOGY AND EDUCATION

Faculty of International Education

THE SOCIALIST REPUBLIC OF VIETNAM

Independence – Freedom – Happiness

GRADUATION THESIS PROJECT TASKS

Semester 1/ year 2023-2024

Instructor: Assoc Prof Dr Do Thanh Trung

Students: Le Quang Linh ID: 19143026 Education system CLA

Phi Hoang Minh ID: 19144156 Education system CLA Vu Manh Hoang ID: 19144071 Education system CLA

1 Project reference number: CTM-18

- Thesis: study on the effect of geometric shape on the torsional strength of molded

injection-2 Initial data and documents

- Test model: Torque-flexible structure

- Plastic material: Common plastic material (PP, PA6, ABS…) - Sample fabrication method: Injection molding

- Variable parameters: Approximately 4 main parameters of the model 3 Main content of the project

- Overview of plastic injection molding technology

- Fabrication of test samples corresponding to different geometric parameters

- Evaluation of the influence of geometric shape on torsional strength

4 Planned products - Experiment samples - Final project report 5 Project date:

HCMC UNIVERSITY OF TECHNOLOGY AND EDUCATION

Faculty of International Education

THE SOCIALIST REPUBLIC OF VIETNAM

Independence – Freedom – Happiness

ASSESSMENT FORM OF ADVISOR

Students: Le Quang Linh ID: 19143026 Education system CLA

Phi Hoang Minh ID: 19144156 Education system CLA Vu Manh Hoang ID: 19144071 Education system CLA Major: Mechanical Engineering Technology

Thesis: Study on the effect of geometric shape on the torsional strength of injection-molded

Advisor: Assoc Prof Dr Do Thanh Trung COMMENT

1 Regarding the thesis content and implementation volume:

3 Cons:

6 Score:……… (Words: )

Advisor

(Signature & full name)

HCMC UNIVERSITY OF TECHNOLOGY AND EDUCATION

Faculty of International Education

THE SOCIALIST REPUBLIC OF VIETNAM

Independence – Freedom – Happiness

ASSESSMENT FORM OF THESIS ADVISOR

Students: Le Quang Linh ID: 19143026 Education system CLA

Phi Hoang Minh ID: 19144156 Education system CLA Vu Manh Hoang ID: 19144071 Education system CLA Major: Mechanical Engineering Technology

Thesis: Study on the effect of geometric shape on the torsional strength of injection-molded

Thesis advisor: COMMENT

1 Regarding the thesis content and implementation volume:

3 Cons:

6 Score:……….(Words: )

(Signature & full name)

Le Quang Linh 19143026 0329983805 19143026@student.hcmute.edu.vn Vu Manh Hoang 19144071 0376532564 19144071@student.hcmute.edu.vn Phi Hoang Minh 19144156 0368521604 19144156@student.hcmute.edu.vn - Class: 19144CLA

- Project submission date (Graduation thesis): 03/2024

- Commitment: “We hereby declare that this graduation thesis is the work of the authors ourselves We have not copied from any previously published articles without proper citation If there is any violation, we will take full responsibility”

• Assoc Prof Dr Pham Son Minh – teacher and project leader supported the design and durability testing of the product

• Dr Tran Minh The Uyen – teacher guides and supports machines during the process of assembling molds, plastic injection products and testing product durability

• Teachers have participated in teaching and guiding us and the students in the university class majoring in Mechanical Engineering Technology 19144CLA to complete our graduation thesis

• Teachers teaching at the Department of Mechanical Engineering, Student Affairs Office, Ho Chi Minh University of Technology and Education helped us throughout our study and study process at school

• We would like to thank the Board of Directors of Ho Chi Minh City University of Technology and Education has created conditions for groups of students to study, study and practice at the school

However, during the process of making the project, due to not having much practical experience, the group still made some mistakes while implementing the project, presenting and evaluating the problem We hope to receive comments and evaluations from subject teachers on the group's thesis to further improve it

The group sincerely thank you! Le Quang Linh Vu Manh Hoang

Phi Hoang Minh

LIST OF TABLES

Table 1: Mold structure 8

Table 2: Commonly used coolants 12

Table 3: Product mass and volume 34

Table 4: Plastic shrinkage of different types of plastic 35

Table 5: Contact table between product surface and ejector plate thickness [5] 58

Table 6: Input parameters 71

Table 7: Taguchi parameters for some types of situations 71

Table 8: Compare the torque and rotation angle of 4 parts 95

LIST OF FIGURES

Fig 1: Plastic injection machine HAITIAN MA1200III 4

Fig 2: Plastic injection machine structure 4

Fig 3: Cavity plate and core plate in the closed state 6

Fig 4: Mold structure 7

Fig 5: Two-plate mold structure 12

Fig 6: Three-plate mold 13

Fig 7: Hot runner mold structure 14

Fig 8: Torque – rotation angle of a compliant 18

Fig 9: Typical neuron network architecture 19

Fig 10: Structure of torsional strength tester 21

Fig 11: Product design constant-torque 23

Fig 12: Select New and module part to design the product 23

Fig 13: Profile and size when using extrude command 24

Fig 14: Shape and dimensions part 1 24

Fig 15: Shape and dimensions part 2 24

Fig 16: Shape and dimensions part 3 25

Fig 17: Shape and dimensions part 4 25

Fig 18: The products 26

Fig 19: Model mesh & boundary conditions part 1 27

Fig 20: Model mesh & boundary conditions part 2 27

Fig 21: Model mesh & boundary conditions part 3 28

Fig 22: Model mesh & boundary conditions part 4 28

Fig 23: 3D model of the CTM part 1 29

Fig 24: Torque-rotation angle, θ (degree) part 1 29

Fig 25: 3D model of the CTM part 2 30

Fig 26: Torque-rotation angle, θ (degree) part 2 30

Fig 27: 3D model of the CTM part 3 31

Fig 28: Torque-rotation angle, θ (degree) part 3 31

Fig 30: Torque-rotation angle, θ (degree) part 4 32

Fig 31: Check mass and volume part 1 34

Fig 32: Shrinkage coefficient 36

Fig 33: Selecting folder 39

Fig 34: Creating family mold 39

Fig 35: Workpiece coordinate 40

Fig 36: Creating workpiece part 1 40

Fig 37: Creating workpiece part 2 41

Fig 38: Creating workpiece part 3 41

Fig 39: Creating workpiece part 4 41

Fig 40: Mold cavities arrangement 42

Fig 41: Selecting mold draft direction 42

Fig 42: Defining regions 43

Fig 43: Selecting edge patch 43

Fig 44: Designing parting surface 44

Fig 45: Defining cavity and core 44

Fig 46: Core plate and cavity plate part 1 45

Fig 47: Merging cavity plate 45

Fig 48: Merging core plate 46

Fig 49: Selecting the sprue size 46

Fig 50: Circular runner 47

Fig 51: Selecting a fan gate 47

Fig 52: Choosing style and diameter of runner 48

Fig 53: Injection gate specifications and layout 48

Fig 54: 3D design of cavity and runner 48

Fig 55: Filling simulation 49

Fig 56: Air trap simulation 50

Fig 57: Filling pressure simulation 51

Fig 58: Filling temperature simulation 51

Fig 59: Warpage_Total displacement simulation 52

Fig 60: Types of molds 53

Fig 61: Mold specification FUTABA_SC 54

Fig 62: Cooling system parameter 54

Fig 63: Design cooling channel 55

Fig 64: Cooling temperature simulation 55

Fig 65: The arrangement of air vent grooves on ejector pin 56

Fig 66: The arrangement of air vent grooves on ejector pin 56

Fig 67: The clearance of the ejector system 57

Fig 68: Product surface area 58

Fig 69: Sprue bushing according to Misumi standard 60

Fig 70: Locating ring according to Misumi standard 60

Fig 71: Return pin according to Misumi standard 61

Fig 72: Guide pin according to Misumi standard 62

Fig 73: Guide bushing according Misumi standard 62

Fig 74: Ejector pin according to Misumi standard 63

Fig 75: Type of runner lock pins 63

Fig 76: The size of the runner lock pin 64

Fig 77: Runner lock pin according to Misumi standard 64

Fig 78: Install the guide bushing into the top plate 65

Fig 79: Assembling sprue bushing into the top plate 65

Fig 80: Assembling locating ring and 2 bolts into the top plate 66

Fig 81: Assembling the cavity plate into the top plate 66

Fig 82: Assembling guide pins into the cavity plate 67

Fig 83: Assembling runner lock pin, ejector pin, spring into the retainer plate 67

Fig 84: Assembling retainer plate into core plate 67

Fig 85: Assembling the ejector plate into retainer plate 68

Fig 86: Assembling 2 spacer block, bottom plate, and 4 bolts into the core plate 68

Fig 87: Assembling core plate and cavity plate 69

Fig 88: Assembling eyebolts, water pipe 69

Fig 90: Reality mold 70

Fig 91: Mold mounted on Haitian injection molding machine 71

Fig 92: Change injection pressure 73

Fig 93: Change holding pressure 73

Fig 94: Change holding time 74

Fig 95: Change plastic melting temperature 74

Fig 96: Change mold temperature 74

Fig 97: Result after injecting 25 cases 75

Fig 98: Structure of fixture to testing torque part 1 76

Fig 99: Structure of fixture to testing torque part 2 76

Fig 100: Structure of fixture to testing torque part 3 77

Fig 101: Structure of fixture to testing torque part 4 77

Fig 102: 3D design of the fixture for the products 78

Fig 103: Secure the product using the fixture 79

Fig 104: Assembling the product into fixture 79

Fig 105: Completely assembling the product into fixture 80

Fig 106: Complete assembly 80

Fig 107: Experimental torque graph part 1 82

Fig 108: Experimental torque graph part 2 83

Fig 109: Experimental torque graph part 3 83

Fig 110: Experimental torque graph part 3 84

Fig 111: Training result part 1 85

Fig 112: Prediction result graph ANN part 1 85

Fig 113: Training result part 2 86

Fig 114: Prediction result graph ANN part 2 86

Fig 115: Training result part 3 87

Fig 116: Prediction result graph ANN part 3 87

Fig 117: Training result part 4 88

Fig 118: Prediction result graph ANN part 4 88

Fig 119: Torque graph CAE, experiment, ANN part 1 89

Fig 120: Torque graph CAE, experiment, ANN part 2 90

Fig 121: Torque graph CAE, experiment, ANN part 3 91

Fig 122: Torque graph CAE, experiment, ANN part 4 92

Fig 123: Torque simulation CAE graph 4 parts 93

Fig 124: Torque Experiment graph 4 parts 93

Fig 125: Torque simulation ANN graph 4 parts 94

LIST OF ABBREVIATIONS

CTM Constant-Torque Mechanism CMs Compliant Mechanisms CAE Computer Aided Engineering ANN Artificial Neuron Network PP Polypropylene

PinjInjection pressure PholdHolding pressure TmeltMelting temperature TmoldMold temperature tholdHolding time

Contents

GRADUATION THESIS PROJECT TASKS i

ASSESSMENT FORM OF ADVISOR ii

ASSESSMENT FORM OF THESIS ADVISOR iii

COMMITMENT iv

ACKNOWLEDGEMENT v

LIST OF TABLES vi

LIST OF FIGURES vii

LIST OF ABBREVIATIONS xii

CHAPTER 2: LITERATURE REVIEWS 4

2.1.Overview of plastic injection molding technology 4

2.2.Overview of mold 5

2.3.Overview of plastic 15

2.4.Operational principle of the CTM 18

2.5.Artificial neuron networks in MATLAB 18

2.6.Torsional strength tester 20

CHAPTER 3: PRODUCTS AND MOLD DESIGN 23

3.1.Products design 23

3.2.Mold design 33

CHAPTER 4: RESULTS OF SIMULATION AND EXPERIMENT 70

CHAPTER 1: INTRODUCTION

1.1 Rationale

CTM (Constant-Torque Mechanism) is an important aspect in the field of mechanics and engineering, widely applied in many different fields including technology, healthcare and daily consumer products CTM is defined as the ability to provide stable output torque without being affected by variations in the input rotation angle

Currently, there are many articles and studies on CTM mechanism such as Chia-Wen Hou, Chao-Chieh Lan researched “Functional joint mechanism with constant-torque outputs” [1], Phan Thanh Vu, Pham Huy Tuan researched “Design and Analysis of a Compliant Constant-Torque Mechanism for Rehabilitation Devices” [2], Piyu Wang, Sijie Yang and Qingsong Xu researched “Design and Optimization of a New Compliant Rotary Positioning stage with Constant Output Torque” [3], Hari Nair Prakashah, Hong Zhou researched “Synthesis of Constant Torque Compliant Mechanisms” [4], many of these papers and studies primarily concentrate on optimizing design and developing CTM mechanisms with a broad constant torque region, without delving into the creation of prototypes with varied geometric designs to assess the degree of influence of geometric designs on torque

Today, to meet practical demands, models designed according to the CTM must exhibit large and consistent torque with adequate flatness Plastic materials are frequently utilized for designing structures due to their simplicity, lightweight nature, and cost-effectiveness Thanks to their excellent mechanical properties, wear resistance, dimensional stability, and lack of lubrication requirement, as well as elasticity To address this issue, our team has undertaken a study involving different models varying in style and size, all designed according to the CTM mechanism Prototypes constructed will undergo evaluation through experimentation to compare the impacts of model variations and size on torsional strength

Continuing from there, the group narrowed down our choice of thesis: “Study on the effect of geometric shape on the torsional strength of injection molded.”

1.2 Scientific and practical significance of the thesis

- Scientific significance: applying knowledge about plastic injection molds, delving into

study to design molds effectively

- Practical significance: the project contributes to the creation of structures that help

people in restoring joint function, and devices that support human mobility 1.3 Scopes

- The thesis limits the scope of knowledge to the design and fabrication of prototypes with different geometric parameters by plastic injection molding method, samples with

constant torque mechanism

- The product has PP plastic material After injection molding, the product will be tested for torsional strength by torque testing machine

1.4 Object of study

- Studying the CTM structure and manufacturing plastic injection molds contributes to creating products that can be applied in dynamic and static balancing of machinery and equipment to restore child joint function people and moving equipment

- Applying the materials and knowledge learned to the thesis helps students gain experience and feel more confident when graduating

1.5 Methods of study

To carry out this thesis, we used several methods:

- Refer to articles, magazines, books about CTM From there, the idea of designing the shape of the CTM structural product was formed After that we use ANSYS

software to check mechanical simulation with torque output

- Refer to the documentation about the template Knowledge over time has been accumulated Reference materials are collected through books, textbooks and the

Internet

- Use NX 12.0 software to design the product, then proceed to the next steps such as

mold separation, analysis

- Use Moldex3D software to analyze the injection molding process - Processing external injection molds

- Conduct pressing and torque testing at the mechanical department workshop 1.6 Structure of thesis

Chapter 1: Introduction Chapter 2: Literature reviews

Chapter 3: Products and mold design

Chapter 4: Results of simulation and experiment

Chapter 5: Conclusions and future develop

CHAPTER 2: LITERATURE REVIEWS

2.1 Overview of plastic injection molding technology

Injection molding technology is the process of injecting molten plastic to fill the cavity of the mold Once the plastic is cooled and solidified in the mold, the mold is opened and the product is ejector out of the mold thanks to the ejector system, during this process there is no chemical reaction (Fig.1)

Fig 1: Plastic injection machine HAITIAN MA1200III

2.1.1 Plastic injection machine structure

The injection molding machine is composed of the following parts (Fig.2):

Clamping

Injection system

Control systemMold

Fig 2: Plastic injection machine structure [5]

- Hydraulic system: frame, hydraulic system, electrical, cooling system

- Injection system: hopper, barrel, heater band, screw, non-return assembly, nozzle - Clamping system: machine ejector, clamp cylindero, moverable platen, stationary

platen, tie bars

- Mold system: two fixed plate and one movable plate, 4 tie bars, locking mold cylinder, hydraulic cylinder, adjustment of mold, front and back safety doors

- Control system: computer screen, control panel

2.1.2 Principle of operation

Raw materials are fed into the injection molding machine periodically After being plasticized, the raw material is injected into the mold (which has been clamped tightly) The shape of the mold will create the shape of the product After being shaped and cooled in the mold, the mold opening process is performed to get the product

The characteristic of injection molding technology is that the production process takes place in a cycle

Cycle time depends on the weight of the product, the temperature of the mold cooling water and the efficiency of the mold cooling system

The quality and productivity of the product depends on the quality of the injection molding machine and the quality of the mold

2.2 Overview of mold

2.2.1 Mold concept

A mold is a tool (equipment) used to shape a product using the shaping method The mold is designed and manufactured to be used for a certain number of cycles, which can be one time or many times time The structure and size of the mold designed and manufactured depends on the shape, size, quality and quantity of the product to be created In addition, there are many other issues that need to be considered such as the technological parameters of the product (tilt angle, mold temperature, pressure, machining, etc.), and the properties of the processed materials (shrinkage, elasticity, hardness,), economic indicators of the mold set A plastic product production mold is a cluster of many parts assembled, divided into two main mold parts:

- Cavity part (main mold part, fixed mold part): mounted on the fixed plate of the plastic injection machine

- Core part (male mold part, movable mold part): mounted on the movable plate of the plastic injection machine

In addition, the space between the cavity and core (product forming part) is filled with molten plastic Then, the plastic is cooled, solidified and then removed from the mold using a product removal system or by hand The resulting product has the shape of the mold cavity In a set of molds, the concave part will determine the external shape of the product called the mold cavity, while the protruding part will determine the internal shape of the mold The product is called a core (also known as positive mold, male mold, punch, core) A set of molds can have one or more mold cavities and cores The contact area between the mold cavity and the core is called the mold parting surface (Fig.3) [5]

Cavity plate

Parting lineCore plate

Fig 3: Cavity plate and core plate in the closed state [5]

According to some color to make product: - Single-color mold

- Multi-color mold

2.2.3 Mold structure

In addition to the core and cavity, there are many other parts in the mold These parts assemble together to form the basic systems of the mold set, including (Fig.4) [5]:

- Guidance and positioning system: includes all guide pins, guide rings, locating rings, locators, return pins, responsible for keeping the correct working position of the two mold parts when joining together to create precise mold cavities

- Plastic delivery system into the mold cavity: includes injection stem, plastic channel and nozzle, which is responsible for supplying plastic from the injection molding head into the mold cavity

- Side core system: includes side core, core cheek, guide bar, oblique pin cam, hydraulic cylinder, responsible for removing parts that cannot be removed (undercut) immediately in the opening direction of the mold

- Vent system: includes vents, responsible for removing air remaining in the mold cavity, allowing the plastic to easily fill the mold cavity and preventing the product from bubbling or burning

- Cooling system: includes water lines, grooves, heat pipes, connectors, responsible for stabilizing mold temperature and cooling the product quickly

Fig 4: Mold structure [5]

Table 1: Mold structure

1 Locating ring 6 Guide bushing 11 Ejector retainer plate

2.2.3.1 Cold runner 2.2.3.1.1 Runner

The runner is the connection between the sprue bushing and the sprue Perform the task of putting plastic into the mold of cavity [5]

Therefore, when designing, it is necessary to comply with some technical principles to ensure the quality of most products Here are some guidelines to follow:

- Minimize changes in runner cross-section

- The plastic in the runner must drain the mold easily

- The entire runner length should be as short as possible, so that it can be quickly filled without pressure and heat loss during the filling process

- The size of the runner depends on the different type of material One side of the runner must be small enough to reduce scrap, shorten the cooling time, reduce clamping force On the other hand, it must be large enough to transfer a significant amount of material, fill the mold bed quickly, resist and suffer little pressure loss

For this product, the channel should be designed so that the flow of plastic is smooth and always stable so that it is easy to fill the plastic into the mold

There are many options for choosing channel cross section such as: circular section, square section, trapezoidal section, to meet the flow requirements as well as ease of processing, we choose a runner with a circular cross-section

- The optimal sprue position will create a smooth flow of plastic

- Place the sprue in a non-critical position of the product because the place where the sprue is located tends to exist residual stress during machining

- The sprue should be positioned so that all air can be expelled from the vent without creating air trap in the product

- Place the sprue so that no weld line is left, especially when using multiple sprues - For circular sides, the cylinder needs to place the sprue at the plate to maintain

concentricity

- The sprue is usually held to the smallest size and expanded as needed However, consideration should be given to limit the time to perform additional cutting and avoid creating marks on the product

2.2.3.2 Vent system 2.2.3.2.1 Concept

The inside of the mold always contains air that needs to be ejector out when the plastic fills the mold This air must be drained quickly throughout the filling process As such, the vent system is to provide multiple pathways for air trapped in the mold to be released quickly and easily The vent system needs to be designed so that air easily escapes but does not allow molten plastic to pass through

When there is no vent system or the vent system is not well designed, it will cause some serious defects on the product such as welding seams, burn marks, unfilled parts,

The most used vent system is the air outlet grooves on the face of the mold and the grinding surface around the product tire In addition, the gas in the mold can also escape through the coolant line, small gaps of the sliding system, the graft

2.2.3.2.2 Indicate the vent types

In fact, there are many exhaust options that can be used, depending on the structure of the mold bed, the location of the injection port, machinability, injection pressure,

Some of the options that are widely used today include: - Vent through the vent groove on the mold face

- Vent through the propulsion system on the mold - Vent through the vacuum system

- Vent through the cooling system, insert, slide,

2.2.3.3 Ejector system

2.2.3.3.1 How to get products out of the mold?

The worker will take the product, inspect the product, and cut the runner lock pin (if any) after each injection molding cycle Often applied to large products, difficult to arrange

the propulsion system in the mold, or need to carefully check the quality of the injection product

Using a robotic hand system, applying high automation but high initial cost Use a product ejector system, this is the most common way

2.2.3.3.2 The concept of ejector system

After the product in the mold is cooled, the mold is opened, at this time the product is still stuck on the mold bed due to the vacuum suction and the product tends to shrink after being cooled, so it needs a ejector system to ejector the product out

- Simplified (not too complicated for molds, the structure is small, lightweight, and efficient)

- The hardness of the ejector pin is about 40 ÷ 45 HRC, precision machined and installed according to the shaft system, good wear resistance because the injection molding process has a very small cycle, the bearing does not self-lubricate, so it wears very quickly, the service life will be reduced

- The speed of action on the product is fast, affecting many places at the same time for products with a large width (mitochondria), local effects on short products (floating plates), impacts on non-flat products (bushings), or products with depth (compressed air)

- There is suitable ejector plate and ejector force to ejector the product

- The product can be removed easily and does not affect the product shape, aesthetics of the product

- The ejector system should be on a movable mold (2-plate mold)

2.2.3.3.3 General principles

After finishing the plastic filling process and the cooling process, the press will open the mold and the ejector rod will ejector the two ejector plates and through the eject parts (ejector pin, ejector blade, ejector hose, removal plate, ) eject the product out

During the ejector process, the ejector plate compresses the spring of the mold When the eject shaft of the press returns to its original position, the force acting on the ejector plate is no longer available, at this time the spring compression will help the ejector plate return to its original position, this process involves the guidance of the return pin

2.2.3.3.4 Commonly used ejector system

- Ejector system using pins

- Ejector system using eject blades - Ejector system using eject tubes - Ejector system using removal plate - Pneumatic ejector system

2.2.3.3.5 Some points to keep inmind when designing a ejector system

Always installed in the movable half of the mold, except for some special cases, the ejector system is installed in the fixed half of the mold

Position ejector pins or ejector plate at the corner, edge, or tendon of the product The eject stroke is equal to the greatest depth of the product in the direction of mold opening plus 5÷10 mm

The peaks of the ejector pin should be horizontal to the face of the mold to ensure that no marks are left on the surface of the product

Place ejector pins in positions that do not require aesthetics

Eject is of paramount importance to mold design, causing the product to fall off without affecting the product as well as the mold

2.2.3.4 Cooling system

2.2.3.4.1 The importance and purpose of the cooling system

- The importance of the cooling system

Cooling time accounts for about 60% of the mold cycle time, so it is important to reduce the cooling time but still ensure product quality, the melting temperature of the plastic put into the mold is usually about 150°C ÷ 300°C, when plastic materials are introduced into the mold at this high temperature, a large amount of heat from plastic raw materials is transferred to the mold and through the mold cooling system If the cooling system for some reason has not effectively introduced heat to the mold, the temperature in the mold is constantly increasing, increasing the production cycle

- The purpose of the cooling system

Keep the mold at a stable temperature so that the plastic material can cook evenly Cool down quickly, avoid the case that the heat does not catch up, causing product deformation causing waste products

Reduce cycle time, increase production productivity 2.2.3.4.2 Some coolants

Table 2: Commonly used coolants [5]

Common coolants

Refrigeration-resistant or heated water 0 ÷ 90

To identify the type of two-plate mold, look at the state when opening the mold to take the product out and you will see that the mold dividing surface is opened and divides the mold into 2 separate parts: the channel part and the product part located together side

The two-plate plastic mold is used in manufacturing simple household products, has short design time and short processing time but still has high accuracy to bring to market soon

Fig 5: Two-plate mold structure [5]

- Easy to remove the lock pin • Disadvantage:

- The automation process is not high because there is no system for self-cutting lock pin ends, so it is necessary to hire workers to cut lock pin ends Therefore, it is not optimal for mass production of products in large quantities such as three-plate molds

- Two-plate plastic injection molds cannot be used in processing products that require high complexity

2.2.4.2 Three-plate mold

Three-plate plastic injection mold is a mold structured with 3 main plates: fixed plate, movable plate and lock pin holding plate When opening the mold, there is a gap to get the product out and a gap to get the lock pin (Fig.6)

For three-plate molds, the product and residue are always automatically separated when the product and residue are removed from the mold

Fig 6: Three-plate mold [5]

• Advantage:

- The automation process of the three-plate mold is higher than that of the two-plate mold because the residure can be automatically separated

- The product and the residure tail will automatically separate after opening the mold - Complex products that require many nozzles always require this type of three-plate

mold

• Disadvantage:

- Investment costs for molds are high because the mold structure is complex

- Although it is more automated than a 2-plate mold, a robot is still required to remove the residure

- The structure of the runner is complex, so the material used to make the mold is expensive, and there is a lot of excess plastic after the product is injection

- Because the mold structure is complex, assembly and maintenance of the mold will also be more complicated

- The distance between the nozzle and the mold grooves is long, reducing the injection pressure, leading to the creation of many material hoppers

- High cost

2.2.4.3 Hot runner mold

The mold uses a hot channel that always keeps the plastic flowing in the nozzle roller The channel and nozzle only solidify when it flows into the cavity of the mold When the mold opens, only the product (sometimes with a cooling channel) is removed When the mold closes, the plastic in the channel remains hot and continues to fill the mold cavity directly The channel in the mold can include a cold channel and a hot channel (Fig.7)

Sprue bushing

Sprue

GateFig 7: Hot runner mold structure [5]

For this type of mold, the nozzle must be placed in the center of the mold cavities, which means that the channels must be placed away from the parting surface, but this does not cause any design problems This type of mold is also suitable for molds with many small cavities or molds with complex channel systems and a lot of material

• Advantage: - Save materials

- There are no spray nozzle marks on the product - Reduce time cycle

- Controls the filling of the plastic flow • Disadavantage:

- High cost than two-plate mold - Difficult to change material color

- The temperature control system is easily damaged - Not suitable for materials with poor heat resistance

2.3 Overview of plastic

2.3.1 Mechanical characteristics of plastic resins

Mechanical properties related to the displacement or breakdown of plastics due to some mechanical changes are the same as applied to some loads [6]

Mechanical properties depend on temperature, Force (load), and load time applied It can be affected by ultraviolet rays when used externally

2.3.2 Thermal characteristics of plastic resins

Thermal properties include heat resistance or flammability

Thermoplastics have a greater coefficient of thermal expansion and flammability and less thermal conductivity or heat than other materials such as metals

2.3.3 Chemical properties of plastic resins

Resistance to chemical corrosion, resistance to chipping rifts, resistance to changing environments as chemical properties

When a plastic encounters chemicals, there are several types to change After a plastic encounters the chemical under no cracking for about a week, changes in appearance, weight and size of the plastic are checked Varieties, changes are called chemical properties

2.3.4 Electromagnetic properties of plastic resins

Electromagnetic properties are called magnetic properties, Electromagnetic properties include electrical insulation, electrical conductivity and electrical insulation properties

Due to their good electrical insulation, plastics are heavily used in the plastics industry However, plastic also has its shortcomings; they are easily electrified

2.3.5 Physical properties

Specific gravity, refractive index and moisture absorption are called physical properties The density of plastic is small, and each type of plastic varies depending on the bonding of the polymer, or the heat and mechanical treatment of the plastic

2.3.6 Some common plastic in injection molding

2.3.6.1 Polyamide (Nylon) (PA)

• Characteristic

- Extremely impact resistant and has chemical strength, low temperature resistance as well as good electrical insulation

- At high melting point, good heat resistance

- Due to its self-lubricating properties, it is often used as the gear of machine parts • Application

- Often used moving parts in machines (gears, ball bearings, cams) or bolts

- Often used for very large details or extremely thin details

- Because it has very good fatigue strength, it is often used as cyclic load-bearing hinge couplings

- Food packaging, household electrical appliances, auto parts, artificial lawns, suitcase covers, medical equipment, plastic bags,

products such as phi containers

- Beverage containers, bottles and jars, wrappers, plastic bags, food wrap,

2.3.6.4 Acrylonitrile butadienstylene (ABS)

• Characteristic

- Elastic and difficult to break

- As "Amorphous plastics", it is capable of withstanding bad climatic temperatures - Easy to achieve dimensional accuracy, material stability

- It is a material that is easy to perform further machining (electroplating mechanical machining, flow welding, etc.)

- High flow temperature, viscosity fusing is also high

- The molding shrinkage rate is quite small (0.5 - 0.8%), and is not affected by the position of the gates

- Does not soften below 150

- Extremely good impact resistance • Application

- Used as parts with durability requirements or resistant to dynamic loads and large loads

- Make CDs, DVDs, lenses, headsets, helmets,

2.4 Operational principle of the CTM

Most ideal compliant mechanisms (CMs) will obey the Hooke’s law when they are operated in the elastic regime However, some special CMs such as the CTM will exhibit an irregular torque curve that differs from the purely elastic mechanism as shown in Fig 8 It includes two regions: the pre-stress stage and the working range During the initial loading process, any elevation of the input rotation angle would lead to the increment of the reaction output torque If a CTM is properly designed, after this stage, the torque will remain stable in a certain range despite of the increasing of the rotation angle It is the working range of the CTM [2]

Fig 8: Torque – rotation angle of a compliant [2] 2.5 Artificial neuron networks in MATLAB

2.5.1 ANN concept

ANN-Artificial neuron network is an information processing model that mimics the way biological neuron systems process information It is made up of many elements (called

neurons) connected to each other through links (called link weights) that work to solve a particular problem

ANN, particularly deep artificial neural networks, have become known for their proficiency at complex identification applications such as face recognition, text translation, and voice recognition These approaches are a key technology driving innovation in advanced driver assistance systems and tasks, including lane classification and traffic sign recognition There are three common learning methods: supervised learning, unsupervised learning, and reinforcement learning Supervised learning is the most used method, typically the backpropagation technique

There are three common types of neural networks used for engineering applications: - Feedforward neural network: Consists of an input layer, one or a few hidden layers,

and an output layer (a typical shallow neural network)

- Convolutional neural network (CNN): Deep neural network architecture widely applied to image processing and characterized by convolutional layers that shift windows across the input with nodes that share weights, abstracting the (typically image) input to feature maps You can use pretrained CNN networks, such as SqueezeNet or GoogleNet

- Recurrent neural network (RNN): Neural network architecture with feedback loops that model sequential dependencies in the input, as in time-series, sensor, and text data; the most popular type of RNN is a long short-term memory network (LSTM)

Artificial neuron network is configured for a specific application (pattern recognition, data classification, ) through a process learned from a set of training patterns In essence, it is the process of calibrating the bond weights between neurons so that the error function value is minimal

2.5.3 Learning process of ANN

2.5.3.1 Assess the elements of the learning process

Weighting initialization: Since the nature of the error back-propagation algorithm is a method of reducing gradient deviation, initializing the initial values of random small value weights will cause the network to converge to different minimum values

Learning step α: Choosing the initial arithmetic constant is very important For each problem, we have a different arithmetic option When a back-propagation training process converges, it cannot be said that it has converged to the optimal solution We need to experiment with some initial conditions to ensure that we get the optimal solution

2.5.3.2 Using ANN in MATLAB

The MATLAB Toolbox are collections of m-files that allow extending the capabilities of MATLAB to several modern control techniques, data optimization processing and ANN, ANN Toolbox provides 12 high-performance training functions To use this toolbox, we must define a structure including creating input data and target data matrices, calling the ANN Toolbox in an m-file to set and select network parameters

2.6 Torsional strength tester

2.6.1 Torsional strength tester structure

Torsional strength tester is composed of motor, speed reducer, encoder, 3-jaw chuck, torque sensor, PLC control circuit, computer (Fig.10)

Torque sensor3-jaw chuck

Fig 10: Structure of torsional strength tester

2.6.2 The principle of operation

Initially turn on the power switch supplied to the motor to help the motor rotate and create torque This torque is transmitted to the axis attached to the steering wheel through a gear belt transmission with a gear ratio of 1:2 This shaft is made of steel with a high load capacity to withstand torque from the force of rotating the steering wheel [8]

The steering wheel shaft is connected in series to the input shaft of the gearbox through a rigid coupling This coupling helps to drive from the steering wheel shaft to the gearbox continuously and accurately The gear reducer is used to reduce the rotational speed and increase the torque on the output shaft

The output shaft of the gearbox connects to the chuck by means of a rigid coupling The rigid coupling ensures the torsional drive correctly

On the shaft attached to the chuck, a pair of 1:1 gear wheel is mounted to transmit rotation from the shaft attached to the chuck The tooth belt transmission helps synchronize movement to provide a torsion angle to the encoder The encoder is used to collect the torsion angle of the test specimen, allowing the twist data to be observed and recorded through a small screen

Movable chuck is connected to the twisted test specimen through an intermediate part to link the chuck and sample together Unlike movable chuck, the other chuck in this model is fixed and cannot rotate

Torque sensor is used to measure the torque of the test specimen It is attached to the chuck fixed through an intermediate detail designed in accordance with the input and output of the sensor Torque sensor captures torque from the test sample allowing observation and recording of torque data

As the motor rotates, the transmission of torque through parts in the model helps to create torque in the prototype, while measuring the torque angle through the encoder and torque through the torque sensor This process allows torsional strength testing and data collection for analysis and evaluation of the mechanical properties of the test specimen

CHAPTER 3: PRODUCTS AND MOLD DESIGN

3.1 Products design

3.1.1 Designing

Fig 11: Product design constant-torque

Based on the Fig 11 groups changed the geometry of the arm while retaining the outer diameter dimensions: ∅100 mm, height: 3mm, width of the arm: 1mm

Design products using Inventor 2022 software Click New to start creating the working program

Use module Part the process of design the product

Use mm units

Fig 12: Select New and module part to design the product Step 1: Use command Extrude diameter 100mm, high 2.5mm (Fig.13)

Fig 13: Profile and size when using extrude command Step 2: Use command Extrude design some small details (Fig.14, 15, 16,17)

Fig 14: Shape and dimensions part 1

Fig 15: Shape and dimensions part 2