the application of 3d printing material on investment casting

MINISTRY OF EDUCATION AND TRAINING HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND EDUCATION FACULTY FOR HIGH QUALITY TRAINING Ho Chi Minh City, March 2024GRADUATION PROJECT MACHINE MANUF

MINISTRY OF EDUCATION AND TRAINING

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

Ho Chi Minh City, March 2024GRADUATION PROJECT

MACHINE MANUFACTURING TECHNOLOGY

THE APPLICATION OF 3D PRINTING MATERIAL ON INVESTMENT CASTING

LECTURER: NGUYEN THANH TANSTUDENT: DAO HAI SON

S K L 0 1 2 6 3 5

HO CHI MINH CITY UNIVERSITY OF TECHNOLOGY AND EDUCATION FACULTY OF INTERNATIONAL EDUCATION

Ho Chi Minh City, March 2024

THE APPLICATION OF 3D PRINTING MATERIAL ON INVESTMENT CASTING

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THE SOCIALIST REPUBLIC OF VIETNAM

Independence – Freedom– Happiness

-

Ho Chi Minh City, March 2024

GRADUATION PROJECT ASSIGNMENT

Student name: Dao Hai Son Student ID: 19143070

Major: Machine Manufacturing Technology

Class: 19143CLA1

Supervisor: M.E Nguyen Thanh Tan Phone number: 0938004496

Date of assignment: 01/09/2023 Date of submission: 11/03/2024

1 Project title: The application of 3D printing material on investment casting

2 Initial materials provided by supervisor: - Rigid 10K

- Formlabs Form 3 printer

3 Content of the project:

- Overview 3D printing technology - Overview investment casting

- Design and manufacturing wax injection molds - Experiment

- Analyze and Evaluation

4 Final product: - The report

- Experimental results - Wax injection molds

CHAIR OF THE PROGRAM

(Sign with full name)

SUPERVISOR

(Sign with full name)

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DISCLAIMER

- Topic title:

The application of 3D printing material on investment casting

- Instructor: M.E Nguyen Thanh Tan - Members:

Dao Hai Son ID: 19143070 Phone: 0358280149

- Email:

19143070@student.hcmute.edu.vn

We declare that this graduation thesis is the result of our research and work We have

not copied any published articles without proper citation If any violation is found, we take full responsibility for it

Ho Chi Minh City, 2024

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ACKNOWLEDGEMENTS

First, I would like to express to my university and faculty, Ho Chi Minh City University of Technology and Education, the Faculty of International Education, and the Faculty of Mechanical Engineering Their dedication to creating an exceptional learning environment and providing valuable tools and resources has greatly enriched our academic and practical experiences

Secondly, I would like to express deep gratitude to M.E Nguyen Thanh Tan, who gave me a chance to conduct this thesis The enthusiastic and dedicated instructor, whose specific instructions and suggestions helped me complete this project

Thirdly, I would also like to express our gratitude to Juki and 3D Smart Solutions Company for kindly giving me the facilities required for my research The business has provided me with an outline and particulars of the steps involved in creating a product with the funding casting technology, enabling us to improve our project's research even more

Fourth, I acknowledge M.E Nguyen Thanh Tan and Ph.D Tran Van Tron for financially supporting my study

Finally, the support of my family and friends gives me more motivation to overcome many difficulties in carrying out my work

Due to a lack of time and relevant experience, the project will have limits and implementation mistakes I would greatly appreciate any guidance or recommendations you may provide to make the project more comprehensive We wish you well and success in your professional endeavors We are grateful that you joined us on this trip

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ABSTRACT

The investment casting process is a foundry method for producing high-precision metal castings Previously, molds used for investment casting have been fabricated by conventional machining methods However, this technique may lead to extra time and cost when the number of parts is low The low-cost and time technique for fabricating molds is three-dimensional printing In this study, 3D printing molds and aluminum molds are fabricated for investment casting Then, these molds are compared and evaluated in terms of surface roughness and cooling time The results showed that the average surface roughness of the mold obtained in the 3D printed mold is higher than that in the aluminum mold, 1.7 µm compared to 0.25 µm After the wax injection and casting process, the average surface roughness of the wax patterns and castings obtained through the two types of molds are 1 µm and 2.9 µm, respectively Numerical simulation temperature is applied to predict the cooling time of the two types of molds The numerical simulation results showed that the cooling time of the 3D printed mold and the aluminum mold after 100 s are 34.41℃ and 26.04 ℃, respectively These findings can help manufacturers use 3D printing in investment casting with a great alternative, flexible design, low cost, and short lead time for low- to medium-volume production

TÓM TẮT

Đúc mẫu chảy là một phương pháp đúc để sản xuất vật đúc kim loại có độ chính xác cao Trước đây, khuôn dùng để đúc mẫu chảy được chế tạo bằng phương pháp gia công cơ Tuy nhiên, kỹ thuật này có thể dẫn đến tốn thêm thời gian và chi phí khi số lượng sản phẩm đúc ít Kỹ thuật chế tạo khuôn khác có chi phí thấp và tốn ít thời gian là in 3D Trong nghiên cứu này, khuôn in 3D và khuôn nhôm được sản xuất cho đúc mẫu chảy Sau đó, các khuôn này được so sánh và đánh giá về độ nhám bề mặt, thời gian làm nguội Kết quả cho thấy, độ nhám bề mặt trung bình của khuôn thu được trong khuôn in 3D cao hơn so với khuôn nhôm, 1.7 µm so với 0.25 µm Sau quá trình phun sáp và đúc, độ nhám bề mặt trung bình của các mẫu sáp và chi tiết đúc thu được qua hai loại khuôn lần lượt là 1 µm và 2,9 µm Nhiệt độ mô phỏng số được áp dụng để dự đoán thời gian làm nguội của hai loại khuôn Kết quả mô phỏng số cho thấy thời gian nguội của khuôn in 3D và khuôn nhôm sau 100 s lần lượt là 34.41℃ và 26.04 ℃ Những phát hiện này có thể giúp các nhà sản xuất sử dụng in 3D trong đúc mẫu chảy với một giải pháp thay thế tuyệt vời, thiết kế linh hoạt, chi phí và thời gian thấp cho ngành sản xuất đơn lẻ và trung bình

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TABLE OF CONTENTS

GRADUATION PROJECT ASSIGNMENT I DISCLAIMER II ACKNOWLEDGEMENTS III ABSTRACT IV TABLE OF CONTENTS V LIST OF TABLES VII LIST OF FIGURES VIII LIST OF KEYWORDS X

2.2.4 Application of 3D printing technology 16

CHAPTER 3: MATERIALS AND METHODS 20

3.3.2 Preparation of aluminum molds 26

3.3.3 Preparation of 3D printing molds 27

3.3.4 Wax pattern injection molding process 30

3.3.5 Shell mold preparation 31

CHAPTER 4: RESULTS AND DISCUSSION 32

4.1 EVALUATE THE SURFACE ROUGHNESS OF THE CAVITY IN 3D PRINTING MOLDS,ALUMINUM MOLDS, AND CASTED PART IN INVESTMENT CASTING 32

4.2COMPARE COOLING TIME BETWEEN 3D PRINTING MOLDS AND ALUMINUM MOLDS 39

4.3EFFECT OF PROCESS PARAMETERS ON SHRINKAGE POROSITY 43

CHAPTER 5 CONCLUSION 50

5.1LESSONS LEARNED 50

5.2FUTURE WORKS 50

REFERENCES 51

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LIST OF TABLES

Table 2 1: Comparison of accuracy and efficiency of different casting processes [21] 7

Table 2 2: Summarize of common 3DP technologies [9] 15

Table 3 1:Thermal conductivity of wax 20

Table 3 2: Thermal conductivity of rigid 10k [35] 20

Table 3 3: Chemical composition of Al 6061 [36] 21

Table 3 4: Thermal conductivity of Al6061 [37] 21

Table 3 5: Chemical composition of SKD 61 [38] 21

Table 3 6: Technical parameters for cooling time simulation of two molds 23

Table 3 7: Technical parameters for cooling time simulation of two molds 24

Table 3 8: Levels of process parameters 25

Table 3 9: Design of Experiments 25

Table 3 10: Post-processing parameters for 3D printing molds 29

Table 3 11: Technical parameters of the wax injection process 30

Table 4 1 The surface roughness between 3D printing molds and aluminum molds 34

Table 4 2: The surface roughness of wax patterns 36

Table 4 3: The surface roughness of casting parts 38

Table 4 4: Average value for surface roughness in each process 39

Table 4 5: The cooling time of aluminum mold and 3D printing molds 40

Table 4 6: Numerical simulation data 44

Table 4 7: S/N ratio for microporosity and Niyama 45

Table 4 8: Average effect response table of S/N ratio for microporosity 46

Table 4 9: Average effect response table of S/N ratio for MRR Niyama 47

Table 4 10: ANOVA for microporosity 48

Table 4 11 ANOVA for Niyama 49

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LIST OF FIGURES

Figure 2 1: Schematic illustration of conventional investment casting process [7] 6

Figure 2 2: Process flow chart of 3D printing [31] 10

Figure 2 3: The diagram of the SLA 3D printing 11

Figure 2 4: The diagram of the FDM 3D printing [29] 12

Figure 2 5: The diagram of SLS 3D printing [29] 13

Figure 2 6: The diagram of LOM 3D printing [33] 14

Figure 2 7: The diagram of the inkjet 3D printing method [29] 15

Figure 3 1: The Mitutoyo SJ-210 surface roughness tester 22

Figure 3 2: Steps to get the results of the simulation 23

Figure 3 3: Assembly method 26

Figure 3 4: Design of the model 26

Figure 3 5: Aluminum molds after preparing 27

Figure 3 6: Form3 machine 28

Figure 3 7: Process preparing 3D printing molds [19] 29

Figure 3 8: Process printing mold 29

Figure 3 9: 3D printing molds after preparing and assembly process 30

Figure 3 10: The wax pattern after preparing 30

Figure 4 1: The positions of molds will be measured The names (a1), and (2) in the figure belong to aluminum molds and 3D printing molds, respectively 33

Figure 4 2: The surface roughness between 3D printing molds and aluminum molds 35

Figure 4 3: The positions of wax patterns will be measured The names (a1), and (2) in the figure belong to aluminum mold and 3D printing molds, respectively 35

Figure 4 4: The surface roughness of wax patterns 37

Figure 4 5: The positions of casted parts will be measured The names (a1), and (2) in the figure belong to aluminum mold and 3D printing molds, respectively 37

Figure 4 6: The surface roughness of casting parts 38

Figure 4 7: The average surface roughness in each process of both molds 39

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Figure 4 8: Compare the cooling time of both molds 43

Figure 4 9: The lowest and highest value of microporosity 44

Figure 4 10: The lowest and highest values of Niyama 44

Figure 4 11: Microporosity distribution 45

Figure 4 12: Niyama distribution 46

Figure 4 13: Effect of process parameters on microporosity 47

Figure 4 14: Effect of process parameters on Niyama 48

FDM Fused Deposition Modeling

FFF Fused filament fabrication

SLS Selective Laser Sintering

DLP Digital Light Processing

AM Additive Manufacturing

UV Ultraviolet

CNC Computer Numerical Control

ANOVA Analysis of Variance

To produce wax patterns for the investment casting process, conventional mold manufactured via the machining process is being used Furthermore, mold is fabrication using traditional methods such as machining limitations including restrictions on minimum wall thickness, the need to eliminate sharp corners, and undercuts which require increased angles of inclination and result in increased fabrication costs [10] On the other hand, using conventional tooling for wax model production may lead to extra time and cost, resulting in a reduction of overall throughput and reducing the benefit of using such an approach, particularly for batch production [11] With the disadvantage above, the developing of new designs with low volume production or prototypes is not effective in cost and time [5]

These disadvantages of investment casting could be overcome by using AM technology [8], [9], [12] This process also known as 3D printing or rapid prototyping is a process of joining materials to make objects from 3D model data, usually layer upon layer, as opposed to subtractive manufacturing methodologies This toolless manufacturing approach can give the industry new design flexibility, reduce energy use, and shorten time to market [13] This method can save a lot of time and cost because it avoids using dies, patterns, and tools, which are time and money-consuming for preparation [14] So, rapid investment casting refers to the use of AM technologies in investment casting, the application of 3D printing models can replace wax models with fast time and low cost, especially in small quantities and with complex shapes [15] According to Jiayi Wang et al The lead time and production costs can

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be reduced by 89% and 60%, respectively by using AM in investment casting [12] However, for a medium number of casting parts and products is difficult to use 3D printing models, traditional methods and large production preparation time are still limited [5], [10], [16]

Chander Prakash et al say that the use of AM in investment casting reduces not only cost and time but also energy consumption and CO2 emission [15] The application of 3D printing technology to producing mold is also applied in this case such as the plastic injection molding industry There is some research to evaluate using 3D printing to make injection mold [17], [18], [19], [20] Rossella Surace et al design optimal cooling channels for 3D printing molds in plastic injection molding to reduce the cycle time The result showed that the rectangular channel is the most effective [17] John Ryan C Dizon et al make injection molds with different 3D printing ways and materials in polymers to compare their dimensional accuracy As a result, SLA and polyjet showed the best finish while that of FFF printed mold using PEEK material appeared delamination after printing [18] Faryar Etesami et al used a device that they manufactured to help resin producers identify the most important properties that influence mold performance The findings demonstrate that these materials react differently to load, temperature, and time John Ryan C Dizon et al [19] experiment of the polylactic acid is injected into 3D printing molds created via SLA and FDM, and the quality of the injected parts is evaluated by dimensional precision and mechanical damage mechanisms Furthermore, it is feasible to avoid the use of wax injection molds when producing prototypes or units of casting, but doing so requires adding new materials to the manufacturing system with particular characteristics such as silicone rubber mold Using AM to design molds has several advantages, including faster and cheaper production less material is to more versatile designs, and the ability to create complex shapes and intricate surface details [20]

1.2 Objective

The work of this study consists of:

Design and manufacture wax injection mold by using 3D printing and CNC methods

Compare and evaluate the surface roughness of 3D printing molds to aluminum mold: This objective will be achieved by measuring the surface roughness of both types of molds using the surface roughness tester machine

Compare and evaluate the cooling time of 3D printing molds to aluminum mold: This objective will be achieved by measuring the time it takes for molten metal to cool in both types of molds

This study also researches the effect of pouring temperature, and preheat temperature on the shrinkage porosity of SKD 61tool steel and finds the optimized process parameters for the

1.3 Research limitations

- Scope of the report: university materials laboratory, company support

- Research subjects: papers, research, and documents on 3D printing and investment casting

- Study period: 4 months

1.4 Research methods

- Collect and analyze data

- Numerical simulation

- Experimental measurements

This technique is applied for many centuries for producing many things such as jewelry, idols, and casting parts The jewelry is found in many places in the world such as Central/South America, Europe, Greece, etc Eddy et al (1974) described multiple applications and benefits of the investment casting technique for the modern era It is used for generating everything from power cables to hip replacement implants, turbocharger wheels to golf club heads, general engineering to aerospace engineering, and defense outlets By value, steel investment casting contributes to a third of the overall output Aluminum and its alloys have a wide range of applications among the non-ferrous alloys Metallurgical requirements do not apply to investment castings This method has a great advantage because of its excellent surface finish It is possible to cast letters, splines, bosses, holes, and even certain threads This technique can create very thin pieces and intricate details This approach does not need complex or expensive tools For example turbine blades in aircraft engines, and so on The conventional machining method could not meet the high requirements of the war so investment casting has been chosen as an alternative method It recommended the way to produce many complex shape components, undercut parts, etc Investment casting can create many kinds of products so it is the reason why it is developing [21]

2.1.2 Process

According to S Pattnaik et al, the process of investment casting includes seven main steps:

Step 1: Pattern making

The first step in the investment casting process is to create a wax pattern of the desired part This can be done using a variety of methods, such as injection molding, 3D printing, or hand carving The pattern must be accurate and have a smooth surface finish, as this will be reflected in the finished casting If injection molding is used, a master die of the part is first created The master die is then used to create a cavity mold, which is used to produce the wax patterns If 3D printing is used, the wax pattern is printed directly from a CAD file If hand carving is used, the wax pattern is carved from a solid block of wax

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The pattern wax requires several characteristics: First, a material to form a shape with the best dimensional precision, it should have the lowest possible thermal expansion Secondly, minimize the formation of surface cavitation and distortion of thick portions, its melting point should not be significantly greater than the surrounding temperature Third, it must be able to withstand breaking Fourth, produce a final cast item with a smooth surface, it must have a smooth and wettable surface When melted, it ought to have a low viscosity to fill the die's thinnest regions After forming, it ought to be effortlessly extracted from the die Fifth, ensure that there is no ash left inside the ceramic shell, it should contain very little ash Finally, it ought to be safe for the environment [21]

Step 2: Shell building

Melted metal is poured into a thin-walled ceramic shell that has been constructed to create an investment casting According to the nature of the casting alloy, a high level of trust in the shell itself is essential since the cost of a failed shell during casting can be unacceptably large, leading to both material loss and plant delay To effectively cast the necessary component in investment casting, the ceramic shell needs to meet specific specifications The conditions required are: First the green strength of the ceramic shell should be adequate to resist the removal of wax without breaking Secondly, enough fired strength to support the weight of the metal in the cast Third, High resistance to heat shock (to avoid cracking while pouring metal) Fourth, high chemical resistance (to stop the metal from growing mold) Finally, sufficient thermal conductivity (to maintain enough heat transfer through the mold wall and so allow the metal to cool) While these specifications remain true for the most part, in certain unique situations, such as casting super alloys, etc., the ceramic shell needs to satisfy additional requirements [21]

Step 3: Dewaxing

Following the coating comes the last phase of creating the ceramic shell needed for casting the necessary component Wax needs to be removed from the ceramic structure's interior after the shell has been created Usually, the wax is removed, cleaned to get rid of any contaminants from the process, and then used again to create fresh designs

Heating the ceramic shell and letting the molten wax flow out of the mold is typically how the wax is removed from the inside of the ceramic shell The mold needs to be heated up quickly The moderately expanding ceramic shell will be cracked by the rapidly expanding wax if the mold is heated slowly

Conventionally, dewaxing has been done by autoclave dewaxing, flash fire dewaxing, etc Dewaxing is often done in industrial autoclaves, where ceramic molds with wax patterns

Step 6: Shell breakout

After the metal solidifies, the refractory is knocked, shaken out, or chipped out A pneumatic vibration machine or physical labor can be used to chip out a layer of ceramic refractory To obtain the last component, the casting tree's riser and gate are divided It is important to complete this process carefully to lower post-machining costs Refractory should have high collapsibility and be quickly knocked out after solidification, but imperfections and a lack of refractory qualities make it difficult to remove the shell Nevertheless, it is discovered that adding alkali salts to earth metal makes shell removal easier

Step 7: Post-processing

The casting may be further processed, such as machining, heat treating, or finishing This will depend on the specific requirements of the application

Figure 2 1: Schematic illustration of conventional investment casting process [7]

The performance comparisons of different casting processes are illustrated in Table 2 1 It is worthwhile to notice that as far as the dimensional accuracy is concerned, the lost wax

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investment casting process remains the most accurate process in which the typical percentage linear dimensional tolerance is 0.05 (5 parts/1000) This ultimately resolves the issue of dimensional accuracy, a property for which lost wax investment are unsurpassed

Table 2 1: Comparison of accuracy and efficiency of different casting processes [21]

Casting process Sand casting

Lost wax process

Lost foam

process Freeze cast process

Linear dimensional tolerance (mm/254

mm)

Percentage linear dimensional

2.1.3 Limitations

Despite the wide range of applications in many industries, the standard investment casting process practiced in modern foundries has its drawbacks High tooling costs and lengthy lead times are associated with the fabrication of metal molds required for producing the sacrificial wax patterns used in investment casting High tooling costs involved in conventional investment casting result in cost justification problems when small numbers of castings are required [7]

High tooling costs and lengthy lead times are associated with the fabrication of metal molds required for producing the sacrificial wax patterns used in investment casting The high tooling costs involved in conventional investment casting result in cost justification problems when small numbers of castings are required

To produce wax patterns for the investment casting process, conventional mold manufactured via the machining process is being used Furthermore, mold is fabrication using traditional methods such as machining limitations including restrictions on minimum wall

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thickness, the need to eliminate sharp corners, and undercuts which require increased angles of inclination and result in increased fabrication costs [10] On the other hand, using conventional tooling for wax model production may lead to extra time and cost, resulting in a reduction of overall throughput and reducing the benefit of using such an approach, particularly for batch production [11] With the disadvantage above, the developing of new designs with low volume production or prototypes is not effective in cost and time [5]

Another limitation is that the microporosity in high-performance castings can reduce mechanical properties and consequently degrade both component life and durability Therefore, casting engineers must be able to both predict and reduce casting microporosity Porosity formed in castings leads to a decrease in the mechanical properties One of the most effective ways to minimize porosity defects is to design a feeding system using porosity prediction modeling In such a way, the casting analysis can determine the location and magnitude of porosity such that the feeding system can be redesigned This process is repeated until porosity is minimized and not likely to appear in the critical areas of the castings [22] Microporosity still occurs in superalloy castings even though they are vacuum refined and vacuum melted The porosity can be detrimental to the mechanical properties of high-temperature superalloys because it reduces the fatigue and stress rupture properties Many advances in melt processing and casting design procedures have been made to reduce this defect; nevertheless, it is still an important concern in the production of superalloy castings Many modern foundries have resorted to experimental and numerical research to minimize, and if possible, eliminate this defect, predicting the formation or avoidance of porosity in castings as a timely research topic [23] Susan et al investigated how casting porosity affected the mechanical performance of investment casting Studies are conducted on 17-4PH stainless steel and the impact of heat treatment on the alloy's susceptibility to casting flaws The yield strength and ultimate tensile strength are decreased by porosity, which is created during the solidification and shrinkage of the alloy This reduction is usually proportionate to the decrease in the load-bearing cross-section They look into how casting porosity affects ductility For the high-strength H925 condition, they discovered that 10% porosity decreased the ductility of 17-4PH stainless steel by over 80% The alloy's ductility is further decreased by tensile testing at -10C (263 K), both with and without pores [24] Both the shrinkage during solidification and entrapped gas in the product cause the porosity The shrinkage porosity is divided into micro or macro shrinkage This defect is quite sensitive to casting geometry, running process parameters, and gating-system design Volumetric shrinkage upon solidification causes the porosity The volumetric shrinkage creates the shrinkage porosity if casting parameters are not properly controlled which tends to be distributed in the last areas to solidify [25] The mechanical properties and strength will be weakened if exist defects, such as shrinkage defects and gas porosity As the CAE analysis can offer conclusions for

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production[4], consequently, it is essential to experience CAE analysis for arranging a reasonable gating system [26] Yadav et al investigated the effects of process parameters on porosity formation and surface roughness They find that the surface roughness reduces with the rise in the mold temperature and grain fineness number while that of porosity rises when the firing time, pouring temperature, grain fineness number, and preheating temperature [27] Li et al showed that the microporosity and mechanical properties of the cast patterns are affected by the shell preheat temperature, pouring temperature, and melt hydrogen content They came to find that the hydrogen content and its ability to preheat temperature are the key process variables influencing the quantity of microporosity in the investment casting By raising the shell preheat temperature and hydrogen content, the porosity is raised High mechanical properties are typically produced by the low pouring temperature [28]

2.2 3D printing 2.2.1 Introduction

3D printing is an AM technique for fabricating a wide range of structures and complex geometries from 3D model data The process consists of printing successive layers of materials that are formed on top of each other This technology is developed by Charles Hull in 1986 in a process known as SLA, which is followed by subsequent developments such as powder bed fusion, FDM, inkjet printing, and 3D printing, which involves various methods, materials, and equipment, has evolved over the years and can transform manufacturing and logistics processes AM has been widely applied in different industries, including construction, prototyping, and biomechanical The uptake of 3D printing in the construction industry, in particular, is very slow and limited despite the advantages e.g less is te, freedom of design, and automation [29]

In recent years, 3D printing has become such a popular research issue that nearly everyone talks about it and its applications have spread to practically every industry It has been used in every aspect of manufacturing, raising the possibility that manufacturing techniques could eventually be replaced Rapid prototyping technology, which first appeared in the 1980s, is where 3D printing gets its start Prototype technology is, by definition, just a means of assisting in the production of new items for demonstration and testing their dimensions and geometry This approach can save a great deal of money and time since it eliminates the need to prepare patterns and dies using more traditional techniques Prototypes are only produced via 3D printing; final products are made for applications such as form analysis, for demonstration or to be utilized in the creation of a mold to make an actual casting Because it does not require the lengthy preparation of dies or tools, it appears rapid [30]

Methods of AM have been developed to meet the demand for printing complex structures at fine resolutions Rapid prototyping, the ability to print large structures, reducing printing defects, and enhancing mechanical properties are some of the key factors that have

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driven the development of AM technologies The most common method of 3D printing that mainly uses polymer filaments is known as fused FDM In addition, AM of powders by SLS, SLM, or liquid binding in 3D printing, as well as inkjet printing, contour crafting, SLA, direct energy deposition, and LOM are the main methods of AM These methods are briefly explained, their applications and suitable materials for each method are introduced, and their benefits and drawbacks are discussed [29]

2.2.2 Process flow of AM technology

According to Botao Hao, et al 3D printing process includes four main steps which are designing 3D model, preprocessing, prototyping, and post-processing [31] The process flow is illustrated in Figure 2 2

Figure 2 2: Process flow chart of 3D printing [31]

3D model: The AM technology is directly driven by a three-dimensional CAD data model Consequently, creating an accurate 3D CAD data model needs to be the first step in the AM process Currently, STL is the data file format that is fully accepted by many software programs To approximate the original solid model and the original 3D data model, a huge number of tiny triangle planes should be used

Preprocessing: to acquire the two-dimensional shape information of the cutting layer, choose the proper molding direction, and cut the 3D model using a sequence of planes spaced the same along the direction of the molding height The better the molding accuracy and the greater the molding efficiency, the smaller the spacing height and the longer the molding time

Prototyping: A two-dimensional scanning movement can be carried out using a forming head that is operated by a computer By the contour data of the cross-section of each layer, the materials of each layer are stacked and joined to create the final three-dimensional solid A nozzle or a laser head can serve as the forming head

SLA is one of the earliest methods of AM, which is developed in 1986 It uses UV light (or electron beam) to initiate a chain reaction on a layer of resin or monomer solution The monomers (mainly acrylic or epoxy-based) are UV-active and instantly convert to polymer chains after activation (radicalization) After polymerization, a pattern inside the resin layer is solidified to hold the subsequent layers The unreacted resin is removed after the completion of printing A post-process treatment such as heating or photo-curing may be used for some printed parts to achieve the desired mechanical performance A dispersion of ceramic particles in monomers can be used to print ceramic-polymer composites or polymer-derived ceramifiable monomers e.g silicon oxycarbide SLA prints high-quality parts at a fine resolution as low as 10 μm On the other hand, it is relatively slow, and expensive and the range of printing materials is very limited Also, the kinetics of the reaction and the curing process are complex The energy of the light source and exposure are the main factors controlling the thickness of each layer SLA can be effectively used for the AM of complex nanocomposites [29]

Figure 2 3: The diagram of the SLA 3D printing

2.2.3 FDM 3D printing

FDM technology also known as FFF is currently the most widespread way to rapid production of items utilizing AM This method is a well-known technology patented in 1989

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by Scott Crump, a co-founder of the Stratasys company 3D printing by FDM consists of depositing a filament of thermoplastic material A portion of filament from a reel passes through a hot head, with a temperature higher than the melting point of the filament, and then is extruded in the XY plane creating a layer of solid material on the build plate Creating a model can be done by depositing a layer contour, and then filling the inside with plasticized material by zigzag movement of the head After printing one layer, the head moves along the Z-axis initiating the build-up of the next layer Using this technique, we can create complex shapes with a minimum of preparatory processes The production process begins with creating a model in the CAD program, then the model is incorporated into the program enabling control of process parameters such as head movement, feed rate, layer thickness, infill, head and table temperatures, slicing, support application, etc Such a program generates a G-code, which uploaded in a 3D printer enables making a real model The model removed from the printer needs finish machining, for instance, to remove the supports and imperfections [32]

Figure 2 4: The diagram of the FDM 3D printing [29]

2.2.4 SLS 3D printing

SLS utilizes a laser to fuse powder-based materials Developed initially by Carl Deckard and John Beaman at the University of Texas-Austin in 1987, SLS is comprised of a roller that deposits a layer of powder, e.g., protein, metal, ceramic, plastic, at a prespecified thickness, in a parts bed, which is heated to just under the material’s melting point The layer has a pattern, as determined by the STL file, selectively traced in the part bed by a laser, e.g., CO2 or Nd: YAG, which heats the powder to the melting point, thereby fusing the material Once the layer is complete, the building platform lowers before the roller deposits another uniform layer of powder and the process repeats until the device is completed Excess powder is removed from the completed part using compressed air and collected for future use The resolution of an SLS printer, typically 10− 15 μm, is dependent on the focus power of the laser and the particle size of the powders Alternatively, when the material in question is a metal alloy the process is often referred to as selective laser melting [33]

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Figure 2 7: The diagram of the inkjet 3D printing method [29]

Table 2 2: Summarize of common 3D printing technologies [9]

Types Principle Material Advantage Disadvantage

SLA UV laser Solidify

Photosensitive resin

High dimensional accuracy and fine detail; high-quality surface finish; wide range of materials

can be printed including wax and non-wax; relatively

fast; low cost of desktop machines;

transparent parts

High cost of consumables; resin drainage of thin-walled

parts is a challenge; working with QuickCast technology

requires experience; post-processing is

required

FDM Materials

extrusion Plastic wire

Both wax and wax patterns can be printed; strong non-

non-wax parts can be handled easily; high

printing speed; can print thin walls;

large variety of

Poor surface finish; high melting temperature of Acrylonitrile butadiene

styrene (ABS); to achieve high surface

finish and high dimensional accuracy,

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machine configurations with

comparatively low cost; low cost of

consumables

many process parameters, layer thickness being the most prominent, need

to be adjusted, which leads to long printing

time

SLS

Laser melting sintering

Powder

Surface roughness close to SLA; high speed of printing; using polystyrene-based Windform material allows casting of highly reactive alloys; easy post-processing and removal of support

structures when using True Form

PM material

High thermal expansion when using Duraform

material; low dimensional accuracy

with polystyrene material; incapability of

using only a portion of printing bed; high cost

of powder

LOM

Laser cut hot melt adhesive bonding

Foil Low cost; high speed

Low dimensional accuracy; inferior surface quality; more

suitable for sand casting

2.2.4 Application of 3D printing technology

Various fields are applying 3D printing:

Aerospace industry: Unique design freedom is possible with 3D technology for both components and production The use of 3D printing technology in the aerospace sector holds promise for producing parts with enhanced and complicated shapes that are lightweight and

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consume less energy and resources In addition, the adoption of 3D printing technology might result in fuel savings since less material is needed to make aircraft parts Additionally, many aircraft components, like engines, have spare parts made possible by 3D printing technology Engine parts need to be replaced regularly because they are prone to deterioration As a result, 3D printing technology offers a practical way to get these replacement parts Nickel-based alloys are highly favored in the aerospace sector because of their tensile qualities, resistance to oxidation and corrosion, and ability to withstand damage [34]

Automotive industry: The phenomenon of 3D printing has brought new lights, enabling the quick creation of lighter and more intricate structures For example, in 2014, Local Motor produced the first electric car using 3D printing technology In addition to automobiles, Local Motors produced a 3D-printed bus known as OLLI, expanding the broad use of 3D printing technology OLLI is a 3D-printed, electric, recyclable, and incredibly intelligent bus Additionally, Ford is a pioneer in the application of 3D printing technology, using it to create prototypes and engine parts BMW also produces hand tools for automobile testing and assembly using 3D printing technology In the meantime, AUDI and SLM Solution Group AG started working together to build prototypes and replacement components in 2017 As a result, the automobile industry's use of 3D printing technology allows businesses to test out many options and prioritize early in the improvement process, leading to the creation of optimal and efficient car design Simultaneously, the technique of 3D printing can minimize material is te and consumption Additionally, 3D printing technology can save money and time, making it possible to test new designs quickly [34]

Food industry: The need for food that is specially made for people with specific dietary needs—athletes, kids, pregnant women, patients, and so on—is rising at the moment These people need different amounts of nutrients, so food manufacturers are trying to reduce the amount of unnecessary ingredients and increase the amount of healthy ones Nevertheless, the creation of personalized meals needs to be done with great care and creativity, which is where 3D food printing comes into play Food layer manufacturing, sometimes referred to as 3D-food printing, is the process of creating food by physically depositing layers upon layers of computer-aided design data Certain materials can be combined and processed into a variety of intricate structures and shapes utilizing 3D printing technology One can make new food items with intricate and fascinating shapes and designs by combining ingredients like sugar, chocolate, pureed food, and flat foods like pasta, pizza, and crackers Food production can now produce food with excellent energy efficiency, cheap cost, and good quality control thanks to 3D printing technology Because 3D printing opens up new possibilities for food customization and can adapt to individual needs and preferences, it can be beneficial to human health Diets that enforce themselves might be viable if meal preparation and ingredients

Fabric and Fashion Industry: As 3D printing technology makes its way into the retail sector, items like apparel, jewelry, shoes, and consumer products will start to appear on the market Fashion and 3D printing may not seem like a good match, but this is beginning to change and become ubiquitous worldwide Large corporations such as Adidas, New Balance, and Nike, for example, are working to develop 3D-printed shoes that can be produced in large quantities These days, 3D-printed sneakers, custom shoes, and athlete's shoes are made The ability to create products with bespoke fits and styling on demand is one of the benefits of employing 3D printing technology in product creation In the interim, supply chain costs can be decreased by the use of 3D printing technology [34]

Electric and Electronic Industry: Since conductors may be embedded into 3D printing devices, a variety of 3D printing methods have already been widely employed for structural electronic devices, such as electrodes, active electronic materials, and devices with mass customization and adaptable design Utilizing the FDM Modelling method of 3D printing, the production process for the 3D electrode offers an economical and expedient method for mass-generating electrode materials In contrast to standard electrodes made of copper, aluminum, or carbon, the 3D electrode's surface area and design are easily customizable to fit a specific need Additionally, the highly precise and fully automated 3D printing procedure for the electrode allowed for the completion of the fabrication of eight electrodes in just thirty minutes [34]

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Casting industry: Designers have far more creative freedom with the layer-by-layer production approach, which also offers excellent efficiency and reduced costs While new designs like supports and ribs must be taken into consideration, some conventional casting designs like draft and parting lines are no longer required The most significant development is that the design of castings, patterns, cores, and molds will be completely transformed by layer-by-layer AM techniques The solid wall construction will be replaced by a net or lattice-like shell supported by a truss system [30]

Layer-by-layer appearance

Because of the nature of AM, layer-by-layer appearance presents another challenge The appearance might not be as important if the 3D printing component is concealed in the final product—such as scaffolds for tissue engineering A flat surface is preferred over a layer-by-layer look in many applications, such as toys, buildings, and aerospace One physical or chemical post-processing method that can reduce this error is sintering, although it will be more expensive and need more time to complete

Overall, investment casting waxes are intricate blends of several substances, such as water, solid organic fillers, natural or synthetic resin, and wax or synthetic The complicated thermomechanical and thermal behavior of investment casting waxes, however, makes it challenging to characterize the material properties because of the additions used in them

In this study, a wax mixture of 118174 Freeman Flakes Wax—Super Pink from (Freeman Manufacturing & Supply Company, Avon, OH, USA) is used The thermal conductivity is presented in Table 3 1

Table 3 1:Thermal conductivity of wax [35]

The SLA 3D printing injection mold made of Rigid 10K resin (Formlabs Ltd., Somerville, MA, USA) is used The Rigid 10K resin is selected for analysis because it is characterized by the highest thermal conductivity of all the photopolymer resins offered by Formlabs The thermal conductivity of Rigid 10k is presented in

Table 3 2

In this study, 6061 aluminum material is used to manufacture aluminum mold 6061 is popular in wax molding so it has excellent thermal conductivity, excellent corrosion, low price, etc [13] [35] It can create a large number of casting patterns Table 3 3 presents the chemical composition of 6061 aluminum

Table 3 3: Chemical composition of Al 6061 [36]

SKD 61 is presented in Table 3 5

3.2.1 Surface roughness measurement

To determine the surface roughness of aluminum mold and 3D printing M, the Mitutoyo 210 (Mitutoyo, Ka is aki, Kanagawa, Japan) surface roughness measurer is used for indicating the surface roughness of each particle with different positions As a probe moves on the flat of these molds, the surface roughness readings of these molds are recorded on the work line Three indexes can be obtained by the results of Mitutoyo SJ- 210 surface roughness measurement including Ra, Rz, and Ry Roughness parameters Ra is chosen to measure Units are measured by micrometer (µm)

SJ-Figure 3 1 illustrates the Mitutoyo SJ-210 surface roughness machine To compare the surface roughness, the measuring tool uses two kinds of mold with six different positions to inspect the surface roughness

Figure 3 1: The Mitutoyo SJ-210 surface roughness tester

3.2.2 Niyama criterion

The Niyama criterion is presently the most widely used criterion function in metal casting It is used to predict feeding-related shrinkage porosity caused by shallow temperature gradients All casting simulation software packages calculate the Niyama criterion as a standard output; foundries worldwide use this criterion to predict the presence of shrinkage