Công nghệ in 3D SLS là một cơng nghệ có nhiều tiềm năng nên việc phát triển
và mở rộng các đề tài liên quan là rất cần thiết. Đề tài trong đồ án này sẽ là nền tảng và có thể mở rộng phát triển nghiên cứu sâu hơn. Hướng phát triển đề tài này như sau:
- Tăng cường nghiên cứu thêm các thơng số có thể ảnh hưởng đến chất lượng sản phẩm để thấy được một cách toàn diện hơn, rõ hơn về quá trình in 3D SLS. - Không chỉ dừng lại nghiên cứu độ bền kéo mà có thể mở rơng ra các chỉ số chất lượng sản phẩm như: độ nhám, độ bền va đập, độ bền mỏi, độ bền uốn, dung sai,…
- Đầu tư cải tiến máy in 3D SLS để quá trình nghiên cứu diễn ra dễ dàng, thuận lợi và độ chính xác cao hơn.
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TÀI LIỆU THAM KHẢO
Tiếng Việt
[1] Cục thông tin khoa học và công nghệ quốc gia (2017), “Tổng luận số 7: In 3D Hiện tại và tương lai”.
[2] Trần Văn Khiêm (2017), “Phương pháp Taguchi và ứng dụng trong tối ưu hóa chế độ cắt”, Tạp chí Cơ khí Việt Nam số 4 (trang 76 – 82)
[3] Lê Chánh Minh và các tác giả, “Đồ Án Tốt Nghiệp: Máy in 3D từ vật liệu bột nhựa”, Đại học Sư Phạm Kỹ thuật TPHCM, 2019.
Tiếng Anh
[4] W. Ruban, V. Vijaykumar, P. Dhanabal and T. Pridhar, “Effective process parameters in seclective laser sintering”, Int. J. Rapid Manufacturing, Vol. 4, Nos. 2/3/4, 2014 (pp.148 – 164)
[5] Sharanjit Singh, Anish Sachdeva and Vishal S.Sharmar, “Optimization of selective laser sintering process parameters to achieve the maximum density and hardness in polyamide parts”, Springer International Publishing Switzerland 2017. [6] Manfred Schmid, Antonim Amado and Konrad Wegener, “Polymer Powder for Selective Laser Sintering (SLS)”, AIP Publishing LLC 2015.
[7] Singh S, Sharma VS, Sachdeva A, Sinha SK (2013), “Optimization and analysis of mechanical properties for selective laser sintered polyamide parts”, Mater Manuf Process 28 (2), pp.163–172
[8] Sachdeva A, Singh S, Sharma VS (2013), “Investigating surface roughness of parts produced by SLS process”. Int Jadv Manuf Technol 64, pp.1505–1516
[9] Singh S, Sharma VS, Sachdeva A (2016), “Progress in selective laser sintering using metallic powders: a review”, Mater Sci Technol 32, pp.760–772
Link
[10] https://www.re-fream.eu/portfolio/3d-printing-stereolithography-sla/
[11] https://3dservices.edu.vn/khoa-hoc-thiet-ke-san-pham-va-van-hanh-may-in-3d [12] https://scantechvn.com/cong-nghe-in-3d-vat-lieu-ben-sls-sctvn617
75 PHỤ LỤC Phụ lục 1: Trang bìa chính Phụ lục 2: Trang bìa phụ Phụ lục 3: Mục lục Phụ lục 4: Danh mục các bảng biểu Phụ lục 5: Danh mục các từ viết tắt Phụ lục 6: Danh mục các biểu đồ và hình ảnh
Phụ lục 7: Thơng tin kết quả nghiên cứu của đề tài Phụ lục 8: Tài liệu tham khảo
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INFLUENCE OF 3D PRINTING SLS PROCESS PARAMETERS ON TENSILE STRENGTH OF PRODUCT
Nguyen Tan Khoa1, Nguyen Trung Kien1, Nguyen Tien Phong1 1HCMC University of Technology and Education
ABSTRACT: Selective laser sintering (SLS) is a powder-based rapid prototyping (RP) technology in which
parts is built by CO2 laser. This research work presents an optimal method to determine the influence of geometry for SLS in order to fabricate parts with enhanced component integrity and reduced overall costs using plastic powder. Moreover, the geometry printing during the installation process have a significant effect on the characteristics of the printing elements, they are closely related and need to be studied. In this project, we focus on studying the influence of printing parameters on the tensile strength of the product, thereby optimizing the geometry parameters to the product to achieve the highest tensile strength. The process consists of making test samples with 3 geometry printing to be tested: shell, layer height and infill density. The results of the project implementation are: geometry parameters have a certain influence on the tensile strength of the product, of which the laser height is the most affected.
Keywords: RP (Rapid prototyping) - SLS (Selective laser sintering) – AM (Additive
manufacturing)
1. INTRODUCTION
Additive manufacturing (AM) or three-dimensional (3D) printing techniques are emerging to initiate a new round of manufacturing revolution by providing greater freedom for design and fabrication of customized products with complex geometries [1-5]. The 3D model of an object is constructed through computer-aided design (CAD) and mathematically sliced into many thin layers, according to the automatic deposition and scanning process for its various cross sections [6-10]. Over the years, AM has branched out from enrich serving as a prototyping technique, into the production of functional parts and end-use products [11-14]. Prototype is an important and vital part of the product development process. Prototypes play several roles in the product development process like experimentation and learning, testing and proofing, communication and interaction, synthesis and integration, scheduling and markers. Prototyping processes have gone through three phases of development like manual prototyping, soft or virtual prototyping and rapid prototyping. The last two of which have emerged only in last two decades like the modelling process in computer graphics. The prototyping of the physical model is growing through its third phase, since the lifecycle of product is getting shorter due to the rapid industrial development and customer diverse needs, the reduction of the time, for new product development time should be the significant issue[21]. Rapid prototyping (RP) technology used form late 1980s has taken its place in CAD/CAM and has been expected to cope with dynamic manufacturing environment. RP is a material additive manufacturing (AM) process or layered manufacturing (LM) process where a 3D computer model is sliced and reassembled in a real space layer-by-layer based on the original form of material used and hardening method, the various systems such as stereo lithographic apparatus (SLA), selective laser sintering (SLS), laminated object manufacturing (LOM), fused deposit modelling (FDM), and soling ground curing (SGC) have been introduced to the market.
77 Among the different AM processes the SLS is a powder based RP process which directly forms solid components according to a 3D CAD model by selective sintering of successive layers of powdered raw materials. While the capability of SLS produces functional objects directly from metals is under development, indirect methods of producing functional objects from metals have been widely used. The materials used in SLS system can be broadly classified into three groups: DuraForm materials (such as GF plastics (glass filled polyamide), PA plastics (durable polyamide), EX plastic (impact resistant plastic) Flex plastic (thermo plastic elastomer with rubber) and AF plastic (polyamide), LaserForm materials such as A6 (steel) material, ST-200 material (special stainless steel composite) and ST-100 material (Powdered stainless steel) and finally, the CastForm PS material. A CAD model is first tessellated and sliced into layers of 0.05–0.3 (http://www.3dsystems.com/). SLS uses fine powder which is spread by a re-coater on the machine bed and scanned directly by a CO2 laser such that the surface tension of the grains overcome and they are sintered together. The interaction with the laser beam with the powder raises temperature of the powder to the point of melting, resulting in particle bonding, fusing the particles to themselves and the previous layer to form a solid. The building of the part is done layer-by- layer. Each layer of the building process contains the cross sections of one or many parts. The next layer is then built directly on the top of the sintered layer after an additional layer of powder is deposited. After allowing sufficient time for the sintered layer to cool down without causing significant internal stresses, the part bed moves down by one layer thickness to facilitate new powder layer, spread by a re-coater. The sintered material forms the part while the un-sintered powder remains in its place to support the structure and may be cleaned away and recycled once the build is complete. These layers are joined together or fused automatically to create the final shape. The primary advantage to additive fabrication is its ability to create almost any shape or geometric feature. The standard data interface between CAD software and the machines is the STL file format[19][20][22].
The challenge of modern industries is mainly focused on achieving high quality, in terms of workpiece dimensional accuracy, surface finish and high production rate, economy of production in terms of cost saving and increasing the performance of theEffective process parameters in selective laser sintering 151 product with reduced environmental impact[17]. Surface roughness plays an important role in many areas and is a factor of great importance in the evaluation of machining accuracy. In order to fabricate the parts to a close tolerance, it is essential that the process parameters are to be maintained at appropriate levels.Hence it is very essential to observe the parameters influencing surface finish during fabrication. The SLS produced parts tend to have poor surface finish due to the relatively large particle sizes of powder used. The system requires high power consumption due to the high wattage of the laser required to sinter the powder particles together[18].
Efficient analysis of the process and its influencing parameters is necessary to realise all its merits. The experiments were conducted to estimate the intensity of influence of geometry printing namely thickness of shell, layer height and infill density on tensile strength. The different types of optimisation techniques have been identified for this problem and the suitable one was considered to optimise the parameters[16]. There is need to understand the influences of parameters affecting surface roughness, dimensional accuracy and hardness while fabrication using SLS. However their optimum values for better surface finish, dimensional accuracy and hardness are to be explored. The proposed work deals with
78 formulation of experiments using factorial design of experiments, conducting experiments, collection of necessary data and Conclusion on the effect of printing parameters on the tensile strength of products.
2. METHODOLOGY
This section provides information regarding ASTM D638 standard for determining tensile strength of SLS 3D printed specimens. ASTM D638 is prepared by applying tensile force to a test piece and measuring the various properties of a test piece under stress. Although ASTM D638 measures many different tensile properties. In addition, 3D printing manufacturing process and design parameters along with the 3D printer, the testing machine.
The process of manufacturing products with three geometry parameters to check: shell thickness (Fig 1), layer height (Fig 2) and infill density (Fig 3). And PE plastic powder is material
PE (polyethylene): PE plastic powder, is a polyethylene, smooth, with different types of colors, in which green is the dominant color, porous, melted in high temperature conditions. It is widely used in the pastic industry, for manufacturing rods, zig hangs in plating, electrical insulating material and industrial adhesives, or coatings on metal surfaces. Properties of PE resins should be very resistant to acids and alkalis.
2.1. Test specimen design
The first step in the study is to design the test specimens for determining tensile strength per ASTM D638 (Fig 4) and a 3D model is created in Inventor per geometry and dimensions given in the standard.
2.2 Specimen manufacturing
All of the specimens are built base on the fundarmental parameters of Repetier-Host and changed the parameter that needed to test. Shell (ABCDE), layer height for specimens (FGHIJ) and infill density (KLMNO) like Table 1 Specimens in the test plan.
Table 1 Specimens in the test plan
Parameter Laser power Feed Shell Layer height Infill density
Specimen 1 A 2.3 465 0.5 0.7 50 B 0.8 C 1 D 1.3 E 1.5
79 Specimen 2 F 2.4 465 1.5 0.4 50 G 0.5 H 0.6 I 0.7 J 0.8 Specimen 3 K 2.5 470 1.3 0.6 30 L 40 M 45 N 50 O 60
With the selected process parameters, samples for the investigation are prepared in the four steps listed below.
1. A three-dimensional (3D) model of the test coupons is prepared; using commercial computer aided design (CAD) software (SolidWorks) and saved as a stereolithography (.stl) file.
2. The .stl file is then exported into a file on the 3D printing software (Repetier-Host) and set up the parameters to ready for printing is generated
3. The sample is produced after adjusting the machine setup (adjusting building sheet, installing material, etc.).
4. The built sample is removed from the machine, and the support material is removed if applicable
2.3 Specimen testing and reporting
Once the manufacturing of the specimens (Fig 5) was completed, tensile testing was performed to find tensile strength and failure strain. A mechanical testing machine with a constant displacement speed of 50 mm/min along with an extensometer is used for testing. The specimens were tested to obtain failure loads and strains and further statistical analysis was performed to study the mechanical performance of the specimens, provides crucial information regarding failure mode and gives insight into ultimate tensile strength values. In a subsequent section, experimental results are presented including stress-strain graphs. The paper wraps up with a conclusion and recommendations for future work.
3. RESULTS AND DISCUSSION
Specimens as described in the test plan (Table 1). With laser power is 2.3mmW, feed rate is 466 mm/m, layer height is 0.7 and infill density is 50%. We compare the specimens about laser power (Fig 6) with A (0.5 mm) is the base specimen can see B (0.8 mm) showed 8.7%
80 increase in tensile. Like specimen B, specimen C (1 mm) showed 3.4% increase in tensile with B is the base specimen. specimen D (1.3 mm) showed 5.9% increase in tensile with C is the base specimen. And specimen E (1.5 mm) showed 6.7% increase in tensile with D is the base specimen. Each parameters of different shell of products has different durability, because each products has different parameters, so it tends to the quality of the sample. Through test results, tensile strength increase steadily. when we increase parameters of shell, the tensile strength of the product also increases.
By the same way at the chart of layer height (Fig 7), with laser power is 2.4 mW, feed rate is 465 mm/m, shell of product is 1.5 mm and infill density is 50%. The base specimen is F (0.4 mm), we can see G (0.5 mm) showed 29.2% decrease in tensile. Specimen H (0.6 mm) showed 30.2% decrease in tensile with G is the base specimen. We have insignificanly vary by compared with specimen I (0.7 m/m) showed 3.9% decrease in tensile with H is the base specimen. And specimen J (0.8 mm) showed 31.2% decrease in tensile with I is the base specimen. From the investigation, it is observed that, The shell of products will effect to the tensile of the sample.
By the chart of infill density (Fig 8), With laser power is 2.5 mW, feed rate is 470 mm/m, shell of product is 1.3 mm and Shell is 0.6 mm. The base specimen is K (30%), we can see L (40%) showed 22.8% decrease in tensile. Specimen M (45%) showed 7.3% decrease in tensile with L is the base specimen. However we can see that specimen N (50%) showed 21.2% increase in tensile with M is the base specimen. And specimen O (60%) showed 17.3% increase in tensile with N is the base specimen. The thickness of each printing layer affects the tensile strength of the sample inversely proportional, increasing the layer height will reduce the thickness of the sample significantly. Therefore, the higher the thickness of the sample, the higher the thickness of each layer, but also increases the printing time. The influence of the thickness of each printing layer on the tensile strength of the product is very significant.
4. CONCLUTIONS
The current study investigated the effects of SLS Printing Parameter on the tensile properties. Three geometry parameters, namely: Shell, layer height and infill density are considered in the investigation. Among the parameters considered, the thickness of the shell affects the tensile strength of the sample proportionally, increasing the thickness of the shell will help create a more durable specimen. The difference in durability between specimens is not high. Layer height affects the tensile strength of the specimen inversely proportional, increasing the thickness of each printing layer will reduce the thickness of the sample significantly. Therefore, the higher the thickness of the specimen, the higher the thickness of each layer, but also increases the printing time. The influence of layer height on the tensile strength of the product is very significant.With the increasing of printing density, the tensile force decrease and then increases again. This may be due to inaccurate testing, erroneous prototyping or tensile testing. Under permitted conditions, this parameter should be manufactured and tested in for more accurate results. The result of this paper can be use like datas for set up parapeter of 3D printing and for the next investigations. Since the current study is limited to the investigation of process parameters at three parameters, it is recommended that future studies increase the number of parameter, so that a more accurate result can be obtained.
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