A COMPARATIVE STUDY OF RAPID PROTOTYPING SYSTEMS. University of Missouri. In Partial Fulfillment. Of the Requirements for the Degree

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1 A COMPARATIVE STUDY OF RAPID PROTOTYPING SYSTEMS A Thesis presented to the Faculty of the Graduate School University of Missouri In Partial Fulfillment Of the Requirements for the Degree Master of Science by CHEN-YU LIU Dr. Luis G. Occeña, Thesis Supervisor May 2013

2 The undersigned, appointed by the Dean of the Graduate School, have examined the thesis entitled A COMPARATIVE STUDY OF RAPID PROTOTYPING SYSTEMS Presented by Chen-Yu Liu A candidate for the degree of Master of Science And hereby certify that in their opinion it is worthy of acceptance. Professor Luis G. Occeña Professor Cheng Alec Chang Professor Sherif El-Gizawy Professor Michael Klote

3 ACKNOWLEDGEMENTS I would first like to thanks my advisor Professor Dr. Luis G. Occeña for giving me the opportunity to improve my knowledge, for all his guidance and tireless instruction throughout my graduate studies at the University of Missouri, Columbia. I would also like to express my appreciation to Mr. Michael Klote for his support, encouragement, dedication, all his helps, and providing insight into the Rapid Prototyping process. Finally, grateful acknowledgement is made to my parents for their support and everything they gave to me. ii

4 Table of Contents ACKNOWLEDGEMENTS... ii LIST OF FIGURES... vi LIST OF TABLES... viii ABSTRACT... x Chapter 1: INTRODUCTION Rapid Prototyping Selective Laser Sintering (SLS) PolyJet Fused Deposition Modeling (FDM) D Printing (3DP) Objectives Chapter 2: LITERATURE REVIEW Dimensional Accuracy Mechanical Properties Chapter 3: METHODOLOGY Experiment scheme Materials and sample preparation iii

5 3.3 Shape of test specimen Dimension measurement Tensile testing Water absorption Shore Hardness Microscopy Chapter 4 RESULTS AND ANALYSIS Dimensional accuracy SLS Dimensional accuracy PolyJet Dimensional accuracy FDM Dimensional accuracy DP Dimensional accuracy Summary Dimensional accuracy Tensile Properties SLS Tensile Properties PolyJet Tensile Properties FDM Tensile Properties DP Tensile Properties Summary Tensile Properties iv

6 4.3 Water absorption Shore Hardness Microscopy and Analysis Chapter 5: CONCLUSION AND FUTURE WORK Conclusion Future work REFERENCES v

7 LIST OF FIGURES Figure Page 1. Schematic view of SLS process Schematic view of PolyJet process Schematic view of FDM process Schematic view of 3DP process Specimens in three build orientations in each RP system Shape of test specimen for tensile testing (mm) Four measurement points on the specimen (mm) The test specimen is clamped by the jaws of the test machine Specimens for water absorption sealed in a plastic bag OHAUSE ScoutPro SP200 balance ASTM Type D Ergo Durometer Measurement points for Shore hardness Stereo Microscope MEIJI Techno EMZ-5TR Dimensional Accuracy of four measurement points in SLS AVG Dimensional Accuracy of three build orientations in SLS Dimensional Accuracy of four measurement points in PolyJet vi

8 17. AVG Dimensional Accuracy of three build orientations in PolyJet Dimensional Accuracy of four measurement points in FDM AVG Dimensional Accuracy of three build orientations in FDM Dimensional Accuracy of four measurement points Dimensional Accuracy of four measurement points AVG Dimensional Accuracy of three build orientations AVG Dimensional Accuracy of three build orientations Dimensional Accuracy SLS Tensile Strength PolyJet Tensile Strength FDM Tensile Strength DP Tensile Strength Tensile Strength Elongation Elongation at Break FDM specimen at 10 times magnification vii

9 LIST OF TABLES Table Page 1. Current RP systems in the market Rapid Prototyping systems at the University of Missouri, Columbia Materials used in RP systems at the University of Missouri, Columbia Three build orientations Dimensions of tensile test specimen (ASTM D Type IV) Measured results in SLS Measured results in PolyJet Measured results in FDM Measured results in 3DP Dimensional Accuracy Summary SLS Tensile Properties PolyJet Tensile Properties FDM Tensile Properties DP Tensile Properties Tensile Properties The relative rate of Water Absorption in the four RP systems Shore Hardness viii

10 18. Stereo microscope pictures of the fracture surfaces of tensile testing specimens Experiment results summary (Boldface indicate the best performance) ix

11 ABSTRACT A general comparative study of the literature sources across different Rapid Prototyping systems and performance in different build orientations has shown that the publications are few in number. This research aims to provide general information including dimensional accuracy and tensile properties for different build orientations, and relative water absorption and Shore hardness properties between different Rapid Prototyping systems. Test specimens were fabricated in four popular commercial Rapid Prototyping systems: Selective Laser Sintering (SLS), PolyJet, Fused Deposition Modeling (FDM), and 3D Printing (3DP) at the University of Missouri, Columbia. The results can be used as a preliminary guide to help users determine optimal strategies for rapid prototyping system selection. x

12 Chapter 1: INTRODUCTION 1.1 Rapid Prototyping Rapid Prototyping (RP) is a process which fabricates a part layer-by-layer. This technology has also been referred to as layered manufacturing, additive manufacturing, and rapid manufacturing. Rapid prototyping automatically generates physical objects directly from 3D CAD data by depositing material layer by layer, unlike conventional methods, where material is removed to obtain the final object. Fundamentally, the development of Rapid Prototyping technology can be split into four primary aspects: Input, Method, Material, and Applications [1]. Input refers to the electronic information required to describe the physical object with numerical data. In the last decade, a number of techniques for Rapid Prototyping have been developed. There are several methods employed in different Rapid Prototyping systems provided by each vendor. The materials used in different rapid prototyping systems are also varied. The initial state of these materials can be either a solid, liquid, or powder state. Applications can be grouped into design, education, engineering and analysis, and manufacturing and tooling [1]. A wide range of industries can benefit from rapid prototyping technology. 1

13 Rapid Prototyping is the term that has been coined for processes that can produce an accurate model from a computer-aid design (CAD) database without any additional tooling or machining [2]. Because Rapid Prototyping can build solid model so quickly, it has revolutionized the way industries approach their product development cycles. With Rapid Prototyping, an engineer can design and build prototype models within a small amount of time. The ability to quickly verify a design prevents the investment of time and money in a poorly conceived project or component. The benefits provided by Rapid Prototyping include reduced lead time and cost to produce components, improved ability to visualize design geometry directly, earlier detection and reduction of design errors, and optimized part design to meet customer requirements. Also, Rapid Prototyping is advantageous in the elimination of waste and costly late design changes [3]. In order to create a part using Rapid Prototyping techniques, several steps have to be performed. All RP systems generally have similar process steps: 1. Create a CAD model to describe the physical object. 2. Convert the CAD model to a STereoLithography (STL) file format. 3. File preprocessing: correct file errors, slice the model into cross-sectional layers, and distribute model orientation. 4. Build the prototype. 2

14 5. Postprocessing: clean and remove excess material from the model. These steps are a generalization of Rapid Prototyping process, and each system can include its own individual steps. There are currently many Rapid Prototyping systems in the market. According to Kruth [4], the material accretion technologies may be divided by the state of the prototype material before part formation. All Rapid Prototyping systems can be categorized into (1) liquid-based (2) solid-based and (3) powder-based [1]. Table 1 shows a summarized category of RP systems. In the following sections, Rapid Prototyping systems at the University of Missouri, Columbia: Selective Laser Sintering (SLS), PolyJet, Fused Deposition Modeling (FDM), and 3D Printing (3DP) will be discussed in detail. Table 1. Current RP systems in the market [1] Liquid-Based Solid-Based Powder-Based Stereolithography (SLA) Objet s PolyJet Cubital s Solid Ground Curing (SGC) Ballistic Particle Manufacture (BPM) Laminated Object Manufacturing (LOM) Fused Deposition Modeling (FDM) Selective Laser Sintering (SLS) 3D Printing (3DP) Laser Engineered Net Shaping (LENS) 3

15 1.2 Selective Laser Sintering (SLS) The Selective Laser Sintering (SLS) process produces solid components using a carbon dioxide (CO 2 ) laser to heat powdered materials layer by layer so that the surface tensions of the grains are overcome and they fuse together. Before the powder is sintered, the entire chamber is heated to just below the melting point of the material in order to minimize thermal distortion and facilitate fusion to the previous layer [5]. The laser selectively fuses powdered materials by tracing the cross-sectional slices from a 3D digital description of the part. The interaction of the CO 2 laser beam with the powder raises the temperature to the melting point, resulting in particle bonding, fusing the particles to themselves and the previous layer to form a solid [1]. The laser beam with adjustable intensity fuses the powder only in areas defined by the part s geometry. The powder not melted or fused during processing serves as support structure. Therefore, there is no need to have support material in the SLS process. After each cross-section is completely drawn, the powder bed is lowered by one layer thickness, and an additional layer of powder is deposited via a roller mechanism on top of the previous layer. The process: (1) new layer deposited, (2) laser beam trace, and (3) entire powder bed lowered is repeated until the part is complete. Figure 1 shows SLS process in brief with a diagram. 4

16 Figure 1. Schematic view of SLS process [6] After the SLS build process, the build chamber is moved to a post-processing station. The loose powder simply falls away, and the SLS parts require some post-processing such as sanding with high pressure air and glass bead mixture, and cleaning with pressurized air. There is a wide range of initial material available for the SLS system. At present, nylon, nylon composites, polycarbonates, metals, sand, wax, and ceramics are in use [1, 7]. However, the materials employed by the system are sensitive to the different heating and laser parameters and each material requires specified settings. 5

17 The products form the SLS system tend to have poorer surface finish due to the relatively large particle sizes of the powders used. 1.3 PolyJet The manufacturer, Objet Geometries, was the first company to successfully jet photopolymer material using its patented PolyJet technology to produce a complex model from a 3D geometry file in early 2000 [8]. A composed printing head injects a 20 μm thick layer of photopolymer material on the build tray only in the areas that correspond to the cross-sectional profile from a 3D digital description of the part. Simultaneously, the photopolymer layer is cured by UV light after it is jetted, and each layer is adjusted to 16 μm by a roller that is moved across the build tray immediately after deposition [9]. The repeated addition and solidification of photopolymer material layers produces a solid three-dimensional model until it is complete. To avoid the collapse of structures during production, a gel-like support material, which is specially designed to support complicated geometries, is injected together with the model material. When the model is completed, the support material is easily removed by hand and water jetting to leave only the hardened photopolymer material. Figure 2 shows Objet s PloyJet technology in brief with a diagram. 6

18 Figure 2. Schematic view of PolyJet process [8] Objet s PolyJet provides a wide variety of materials for different geometries, mechanical properties, and colors; use of the same support material for all model types makes switching material easy and fast. Furthermore, PolyJet Matrix Technology enables simultaneous jetting of different types of model materials. It can jet two distinct photopolymer model materials in preset combinations. 7

19 1.4 Fused Deposition Modeling (FDM) Scott Crump, the president and CEO of Stratasys Inc, developed the Fused Deposition Modeling (FDM) process in 1988 and the patent was awarded in the U.S. in 1992 [1, 3]. The FDM process fabricates parts by extruding semi-molten material thought a extrusion head that traverses in X axis and Y axis to create each two dimensional layer of the part [10]. The movable extrusion head composed of two extrusion nozzles: one for build material and the other for support material [1, 7, 11]. This process can be seen in Figure 3. The extrusion head deposits a filament of molten material either build material or support material onto a foam base. The build material is heated to 0.5 C above its melting point so that it solidifies about 0.1s after extrusion and cold welds to the previous layers [7]. In general, an outline of the perimeter of the part is extruded from the head first and then the interior is raster filled by the extruder head [10]. Once a layer is built, the platform lowers, and the extrusion head deposits another layer. The machine continues to build the part layer by layer until it is complete. When the part is finished, it is removed from the machine and the support material need to move away to reveal the finished product. There are two types of support material: Soluble support system and Break-Away Support System (BASS) [12]. It can be removed with specialized equipment utilizing water-based sodium 8

20 hydroxide solution, or break it away by hand. Figure 3. Schematic view of FDM process [13] In the FDM process, there is also a large range of colors and materials available, such as investment casting wax and thermoplastic [7]. The material generally used is a thermoplastic including ABS plastic, medical grade ABS (MABS), elastomers, polycarbonate, polyphenyl-sulfone (PPSF), and Ultem 9085 [1, 14]. The main advantages of using FDM technology are fabrication of functional parts, minimal material wastage, ease of support material removal, and ease of material change [1]. A disadvantage of using FDM technology is that the surface finish of the parts 9

21 is worse than other rapid prototyping systems due to the resolution of the process which is dictated by the filament thickness [7, 15]. The other disadvantage is that the building process is slow, as the whole cross-sectional area needs to be filled with building material. Unpredictable shrinkage is also a disadvantage of using FDM technology. As the FDM process extrudes the build material from its extrusion head and cools them rapidly on deposition, stresses induced by such rapid cooling invariably are introduced into the model. As such, shrinkages and distortions caused to the model built are a common occurrence and are usually difficult to predict [1] D Printing (3DP) Z Corporation commercialized its first 3D Printer, the Z 402 System, based on three-dimensional technology (3DP) in 1997 [1]. The core technology was invented and patented at the Massachusetts Institute of Technology. It was subsequently licensed and further developed by Z Corporation. Z Corporation was acquired by 3D Systems on January 3, 2012 [16]. The 3D Printing (3DP) process is similar to the Selective Laser Sintering (SLS) process, but instead of using a CO 2 laser to sinter the powdered material, an ink-jet printing head deposits a liquid adhesive that binds the material. The 3D Printing machine has two pistons: one for feeding the powder and 10

22 the other for lowering/raising the building chamber shown in Figure 4. Figure 4. Schematic view of 3DP process [17] The 3D Printing process begins with the powder supply being raised by a piston and a leveling roller distributing a thin layer of powder to the top of the build chamber [17]. The multi-channel ink-jet printing head then deposits binder solution onto the loose powder, forming the first cross-section [1]. These regions of powder are glued together wherever the binder is printed. The remaining powder remains loose and supports the part during the process. When the cross-section is completed, the build piston is lowered, the powder feed piston is raised, and a new layer of powder is 11

23 added on the previous layer by the leveling roller. The process is repeated and the part grows layer by layer on the build piston until the part is finished. Finally the build piston is raised and the loose powder is brushed and the part removed [1]. 3D Printed parts are typically infiltrated with a hardener to improve strength and surface finish. The main advantages of using 3D Printing technology are color capability, shorter build times, and inexpensive raw materials when compared to other rapid prototyping systems [1, 6]. No support structures needed is also an advantage of 3D Printing. The powder bed provides self-support to allow complex geometry to be created. The disadvantages of using 3D Printing technology are the printed part is relatively fragile compared to other rapid prototyping systems, the infiltration post-processing is needed, and the surface finish is relatively poor [6]. 1.6 Objectives Rapid Prototyping is a fast growing technology that can substantially help engineers shorten the time and decrease the cost of developing a new product from the initial idea to production. There are also many restrictions with many rapid prototyping procedures, primarily in the number of available materials and their properties, which may differ significantly from the properties of end product material. 12

24 The research objective of this thesis is to develop combined experiments and analyses approach to compare the specimens fabricated in different build orientations and different rapid prototyping systems. In this research, test specimens were made in four popular commercial rapid prototyping systems: SLS (EOS Formiga P100), PolyJet (Objet Eden 350V), FDM (Dimension Elite 3D Printer), and 3DP (Z Corporation Spectrum Z510). This research includes (1) Dimensional Accuracy: to provide comparative information of dimensional accuracy when specimens are fabricated in three build orientations (Horizontal, Side, and Vertical) in each of four rapid prototyping systems. A comparative study of dimensional accuracy across different rapid prototyping systems is also provided in this research (2) Tensile Property: provide a comparative study of tensile property based on specimens produced in three build orientations (Horizontal, Side, and Vertical) and four different rapid prototyping systems (3) Water Absorption: provide information about the relative water absorption across different rapid prototyping systems will be included in this research (4) Shore hardness: the Shore hardness of test specimens fabricated in different rapid prototyping systems will be presented in this research. The lack of knowledge in the performance of different build orientations across different rapid prototyping systems is motivation for this investigation. The main objective of this research is to provide users with a preliminary guide to help determine optimal strategies for rapid 13

25 prototyping system selection. A literature review is presented in Chapter two to review and discuss previous work performed by researchers on four rapid prototyping systems. In Chapter three, the experiment methodology is presented. In Chapter four, the experiment results of dimensional accuracy, tensile property, water absorption, and Shore hardness are presented and discussed. In Chapter five, the conclusions and future work are discussed. 14

26 Chapter 2: LITERATURE REVIEW Rapid prototyping is a term that the manufacturing industry has struggled with for many years. In the early day, layer-based rapid prototyping (RP) technologies were mainly concerned with producing physical parts as quickly as possible from a design concept, for the purpose of design verification [18]. The initial term, established by 3D Systems (Valencia, CA), was StereoLithography, or three-dimensional printing. The growing field has been widely referred to in technical and industrial publications as Rapid Prototyping. Nowadays, with the fast development of rapid prototyping technologies: more available materials, with various mechanical properties to meet a variety of applications, and higher accuracy of parts produced, rapid prototyping technologies have been used for fabrication of functional parts and tooling [19, 20]. As rapid prototyping parts are made by additive processes, they may have properties that are quite different from parts that are made by conventional manufacturing processes. It is difficult to directly compare the many properties of rapid prototyping parts, as these depend not only on the material being used, but also on the direction in which the property is being measured. In this study, the properties: (1) dimensional accuracy, (2) 15

27 tensile property, (3) water absorption, and (4) Shore hardness were investigated. The following sections will present previous work and literature resource related to these topics. 2.1 Dimensional Accuracy Dimensional accuracy of a rapid prototyping product is influenced by a specific rapid prototyping technique used, the material chosen, and the operating parameter values. Due to different processes and materials used in rapid prototyping technologies, parts differ in their tendency to shrink or deform. In the paper by Durham et al. [21], the shrinkage of the Stereolithography (SLA) epoxy was significantly less than the Selective laser sintering (SLS) plastic material, and the small shrinkage of Stereolithography (SLA) resins was simple to predict and easy to control. In 1997, D.T. Pham and R.S. Gault [7] presented and summarized different rapid prototyping technologies. The paper presented an overview of rapid prototyping technologies and commented on their strengths and weaknesses. In this study, data such as layer thickness, system accuracy and speed of operations were given. The following rapid prototyping technologies were included in this paper. 16

28 Material addition technologies Processes involving liquid Processes involving discrete particles Stereolithography (SLA) Liquid thermal polymerization (LTP) Beam interference solidification (BIS) Solid ground curing (SGC) Holograhpic interference solidification (HIS) Electrosetting (ES) Ballistic particle manufacture (BPM) Fused deposition modelling (FDM) Three dimensional welding (3DW) Shape deposition manufacturing (SDM) Fusing of particles by laser Selective laser sintering (SLS) Gas phase deposition (GPD) Joining of particles with a binder Three dimensional printing (3DP) Spatial forming (SF) Technologies which use solid Laminated object manufacture (LOM) Solid foil polymerisation (SFP) Material removal technology Desktop milling (DM) The accuracy data in this paper was obtained from technical publications and from company literature. There was no comparative information available for different build orientations. In 2003, Steve Upcraft and Richard Fletcher [6] represented an overview study for various rapid prototyping technologies including Stereolithography (SLA), Selective laser sintering (SLS), Laminated object manufacturing (LOM), Fused 17

29 deposition modeling (FDM), Multi-jet modeling (MJM) and Three dimensional printing (3DP). Build method, advantages, disadvantages and main suppliers of these rapid prototyping systems were listed. The test specimens were made by SLA, SLS, LOM and FDM to investigate surface roughness and dimensional accuracy. Mechanical properties including tensile strength, elastic modulus and Shore hardness were available in the paper. The data presented were supplied by the material suppliers or equipment manufacturers. There was also no comparative information of different build orientations. The surface finish is one major issue with using rapid prototyping technologies. In 2006, Armillotta [22] presented an investigation into the surface finish of FDM parts. The main research topic is the stair-stepping effect caused by layered fabrication. By using the method in the research, it could build FDM parts with the shape of millimeter scale features, a layer thickness of 0.127mm. In 2010, Weiss E et al. [23] developed the multi-directional layers disposition method to decrease the model errors. Two model errors were discussed and analyzed: (1) external errors and (2) internal errors. External errors of models include: conversion error, staircase and error of slicing into layers. Internal errors of models are related to the method of filling the interior of disposed layer. This paper proposed the solution, the multi-directional layer disposition method, to decrease these two errors. By using this 18

30 method, it enables users to prepare individual strategy of material layer disposition for each desired case. 2.2 Mechanical Properties In this section, the literature source related to mechanical properties is presented. The choice of deposition strategy plays an important role in the Fused Deposition Modeling (FDM). Different deposition strategies may cause different performance in mechanical properties. In 1999, Kulkarni and Dutta [24] investigated the effects of different deposition paths on the FDM process. They compared the experimental results (material properties) of parts manufactured by the different strategies. An analytical model developed using laminate analysis was taken. The result of using their laminate model can be used to help a designer tailor the deposition strategy. In 2002, Ahn S. et al. [25] developed six build rules that can improved the tensile strengths, compressive strengths and quality of FDM parts. The rapid prototyping machine they used was Stratasys Fused Deposition Modeling Tensile strengths and compressive strengths of FDM fabricated specimens were also compared with specimens created by injection molding ABS P400 material. The same material was used for specimens produced by both FDM and injection molding. For the FDM parts, the typical tensile strength ranged between 65 and 72 percent of the 19

31 strength of injection molding ABS P400, while the compressive strength ranged from 80 to 90 percent of the injection molding. The following build rules were obtained from the paper by Ahn S. et al. [25]: (1) Build parts such that tensile loads will be carried axially along the fibers. (2) Be aware that stress concentrations occur at radiused corners. This is because the FDM beads (or roads; this is the thickness of the bead that the FDM nozzle deposits.) exhibit discontinuities at such transitions. (3) Use a negative air gap to increase both strength and stiffness. (4) Consider the issues of bead width. (5) Consider the effect of build orientation on part accuracy. (6) Be aware that tensile loaded area tends to fail easier than compression loaded area. By applying these build rules, the strength and quality of FDM parts can be improved. In 2009, Ana P. et al. [26] presented an experimental analysis of material properties for rapid prototyping technologies. The test specimens were manufactured in the 3D Printing (ZPrinter 310 Plus) and the PolyJet (Objet Eden 330) systems. The materials used for the test specimens made on the Objet Eden 330 are VeroBlack, VeroBlue and FullCure 720, while the ZPrinter 310 Plus used zp 102 powder, zb 56 binding agent and Loctite 406 and Loctite Hysol 9483 A&B reinforcers glue. The experiment results included the analysis of the dimensions, roughness of surfaces and mechanical properties (flexural properties and tensile properties). The results of measuring dimensions showed the PolyJet (Objet Eden 330) is more accurate than the 20

32 3D Printing (ZPrinter 310 Plus). The surface of test specimens made by the ZPrinter 310 Plus were rougher than VeroBlack and VeroBlue material which were used on the PolyJet system, while the FullCure material showed the lowest value of surface roughness. The best mechanical properties (flexural properties and tensile properties) showed in the test specimens made of FullCure on the PolyJet technology. The worst mechanical properties are from the test specimens made of powder which used on the 3D Printing system. 21

33 Chapter 3: METHODOLOGY Different build orientations in specified rapid prototyping systems may have significant effects on physical and mechanical properties. This paper presents a comparative study in three build orientations across four rapid prototyping systems: Selective Laser Sintering (SLS), PolyJet, Fused Deposition Modeling (FDM), and 3D Printing (3DP) at the University of Missouri, Columbia. The investigations of dimensional accuracy and tensile properties testing for three build orientations are provided in this paper. Furthermore, the experiments of water absorption and Shore hardness across these four rapid prototyping systems are also available in this study. 3.1 Experiment scheme The test specimens were made by Selective Laser Sintering (SLS), PolyJet, Fused Deposition Modeling (FDM), and 3D Printing (3DP) at the University of Missouri, Columbia. Table 2 shows the manufacturers and models of these four rapid prototyping systems. Their technical characteristics can be found in the literature [27-31]. In determining the dimensions of the test specimens, a digital caliper was used, with the measurement range 0-150/0.01 mm. The ADMET expert

34 universal testing system was used to test the tensile properties. Tests were performed at a temperature of 72 F with air-conditioning. The horizontal build orientation was been chosen to make specimens for investigating their water absorption rate and Shore hardness. Table 2. Rapid Prototyping systems at the University of Missouri, Columbia System Manufacturer Model SLS EOS Formiga P100 PolyJet Objet Eden 350V FDM Dimension Elite 3D Printer 3DP Z Corporation Spectrum Z Materials and sample preparation Materials used in this study were commercially available polyamide, photopolymer resin, ABS plastic, and gypsum. Table 3 shows the materials and the machine settings that were used in the specified rapid prototyping systems. The materials that were used in this research were the most popular in the current commercial marketplace. The machine settings were also listed in Table 3.The test specimens were fabricated by these four RP systems in three build orientations as shown in Table 4, and the dimensions conformed to ASTM D638 Type IV. Figure 5 illustrates the three build orientations in each RP system. For 3D 23

35 Printing technology, the Z-Corporation Model Spectrum Z510 3D printer constructed the test specimens. Materials for the specimens consisted of ZP 131 (gypsum) powder and Z-Bond 90 binder. Once the part was completed and the support powder was removed, the part was dipped in binder and dried for 24 hours. Table 3. Materials used in RP systems at the University of Missouri, Columbia System Material Machine Setting SLS Default PA 2200 Balance 1.0 Standard calibration for PA2200 (polyamide 12) Z-Axis = mm PolyJet Default FullCure 835 VeroWhitePlus Print mode = High Quality (UV curable acrylic plastic) Z-Axis = mm Default FDM ABSplus-P430 Model interior fill = Sparse - High density (ABS plastic) Support Fill = Sparse Z-Axis = inch ( mm) 3DP ZP 131 (gypsum) Default Powder = ZP 131 Z-Axis = inch ( mm) 24

36 Table 4. Three build orientations Build Orientation Horizontal Side Vertical 25

37 Figure 5. Specimens in three build orientations in each RP system 3.3 Shape of test specimen The tensile properties of rigid and semi-rigid plastics were determined according to the ASTM D standard, and the Type IV specimen was used when directly comparing between different rigid materials. Table 5 presents the dimensions of the tensile test specimen. Figure 6 shows the location of these dimensions and the shape of the test specimen for tensile testing. A minimum of five test specimens are recommended by the standard. The testing speed for the specimen ASTM D638 Type 26

38 IV is 5 ±25% mm/min, and the higher speeds 50 ±10% mm/min and 500 ±10% mm/min were used, which attains rupture within 1/2 to 5-min testing time. Table 5. Dimensions of tensile test specimen (ASTM D Type IV) ASTM D Type IV Dimensions (mm) W Width of narrow section 6 L Length of narrow section 33 WO Width overall, min 19 LO Length overall, min 115 G Gage length 25 D Distance between grips 65 R Radius of fillet 14 RO Outer radius 25 T Thickness 4 Figure 6. Shape of test specimen for tensile testing (mm) 27

39 3.4 Dimension measurement Five ASTM D638 Type IV specimens were made in each of three build orientations (Horizontal, Side, and Vertical) in the SLS, PolyJet, and FDM systems. Considering the relatively fragile material used in the 3DP system, eight ASTM D638 Type IV specimens were made in each of three build orientations (Horizontal, Side, and Vertical). There are four measurement points: width of narrow section (W), width overall (WO), length overall (LO), and thickness (T) on each specimen as shown in Figure 7. Dimension of the specimen was measured by a Pittsburgh digital caliper with the measurement range 0-150/0.01 mm. The measurements were done on each measurement point, and the values were then recorded. For the measurement point of width overall, both side on each specimen were measured, and the values were then recorded. For the measurement point of thickness, two ends and middle on each specimen were measured, and then the values were recorded. The average values and standard deviation of each measurement point for specified build orientations and rapid prototyping systems were then calculated. 28

40 Figure 7. Four measurement points on the specimen (mm) 3.5 Tensile testing Five to eight ASTM Type IV specimens were made in each of three build orientations (Horizontal, Side, and Vertical) in each rapid prototyping systems (five specimens in each of three build orientations for SLS, PolyJet and FDM systems; eight specimens in each of three build orientations for 3DP). Tensile tests were performed on a universal testing machine (ADMET expert 2611) equipped with a 10 kn load cell. All the tests were conducted at the same temperature of 72 F. For determining the tensile properties the test specimen is clamped by the jaws of the test machine as shown in Figure 8 and extended with force, at testing speed 5 mm/min as defined by ASTM D standard. The reported data are the average values from five/eight replications. 29

41 Figure 8. The test specimen is clamped by the jaws of the test machine 3.6 Water absorption The Horizontal build orientation was chosen to make specimens for investigating the relative rate of water absorption by plastics when immersed. The reason to choose Horizontal build orientation was the shortest machine duration compared with Side and Vertical. For the water absorption investigation, the independent variable was the specified rapid prototyping system and its relative 30

42 material used, and the dependent variable was the weight change when water absorbed. The independent variable, build orientations, was not included in this investigation. Two specimens were made in each of four rapid prototyping systems. Prior to infiltration, all specimens were sealed in a zip lock plastic bag for one week (168 hours) at the same environment condition as shown in Figure 9. This step kept all specimens under the same environment condition and decreased experimental errors. When the desired time was reached, all specimens were immediately measured for the initial weight. The specimens were placed in a container of distilled water maintained at a temperature of 72 ±1 F and entirely immersed for 24 hours. When the desired time was reached, the specimens were then taken out, wiped gently with a dry tissue paper and weighed immediately. The specimens were weighed using a precision balance, OHAUS ScoutPro Series SP200 with 200g x 0.1 g tolerance as shown in Figure 10. Percentage of moisture absorption was calculated based on the weight change as shown in Equation 1. Equation 1: Water absorption (percent) Weight after conditioning for 24 hours (g) initial weight (g) = [ ] 100 initial weight (g) 31

43 Figure 9. Specimens for water absorption sealed in a plastic bag Figure 10. OHAUSE ScoutPro SP200 balance 32

44 3.7 Shore Hardness The Horizontal build orientation was chosen to create specimens in the four rapid prototyping systems for investigating the Shore hardness. Two specimens were made in each of the four rapid prototyping systems. Hardness of elastomers and most other polymer materials (Thermoplastics, Thermosets) is measured by the Shore D scale. The durometer, Pacific Transducer Corp. Model 409 ASTM Type D, as shown in Figure 11, was used to measure the Shore hardness. The durometer is a hand-hold device consisting of a needle-like spring-loaded indenter, which is pressed into the test specimen surface, and the penetration of the needle is measured directly from a scale on the device in terms of degrees of hardness. There were six measurement points (three on each side) on each specimen as shown in Figure 12. The measurement was done three times in each measurement point and the average value was then recorded. 33

45 Figure 11. ASTM Type D Ergo Durometer Figure 12. Measurement points for Shore hardness 34

46 3.8 Microscopy A stereo microscope, MEIJI Techno EMZ-5TR equipped with MA502 eyepieces as shown in Figure 13, was used to capture magnified photographs from the specimens after tensile properties testing to investigate their internal structure. The magnification capability is 7 times to 45 times. A digital camera, Moticam 10, was used to connect the stereo microscope and capture large scale images for documentation purposes. The software, Motic Images Plus 2.0, was used to capture JPEG images as a multi-media demonstration platform. All specimens made for tensile testing in three build orientations in SLS, PolyJet, FDM, and 3DP systems were examined using the stereo microscope to observe their fractured surface. The results are presented in Section 4.5 Microscopy. Figure 13. Stereo Microscope MEIJI Techno EMZ-5TR 35

47 Chapter 4 RESULTS AND ANALYSIS 4.1 Dimensional accuracy Before doing tensile property test, all specimens were measured to investigate their dimensional accuracy. Dimensional accuracy for each measurement point and each fabricated orientation from specified rapid prototyping systems was also presented in the following sections. Equation 2 shows how to calculate Dimension Change Rate. Equation 3 shows Dimensional Accuracy which is the absolute value of dimension change rate from Equation 2. Measured results and the standard deviations were presented in the following sections. Equation 2: Measured value (mm) Dimension Change Rate (percent) = [ 1] 100 Desired value (mm) Equation 3: Measured value (mm) Dimensional Accuracy (percent) = [ 1] 100 Desired value (mm) 36

48 4.1.1 SLS Dimensional accuracy In this section, the measured results of the specimens for three build orientations in the Selective Laser Sintering (SLS) system would be presented. Table 6 lists the measured average values, standard deviations, dimension change rate, and dimensional accuracy. The average dimensional accuracy of four measured points was also included in the last row of Table 6. Figure 14 shows the average dimensional accuracy for each measured points on three fabricated orientations. Dimensional analysis indicated that build orientation had a significant effect on accuracy. The measured value of the length overall in Vertical build orientation provided the most accuracy (0.0470%). Through analysis of Table 6 and Figure 14, it appears that measured points of Vertical build orientation are less variable than Horizontal and Side build orientations. 37

49 W 6 WO 19 LO 115 T 4 ASTM Type IV (mm) Table 6. Measured results in SLS SLS Horizontal Side Vertical AVG SD Dimension Change Rate (%) Dimensional Accuracy (%) AVG SD Dimension Change Rate (%) Dimensional Accuracy (%) AVG SD Dimension Change Rate (%) Dimensional Accuracy (%) AVG SD Dimension Change Rate (%) Dimensional Accuracy (%) SD Dimensional Accuracy AVG Dimensional Accuracy (%)

50 0.4667% % % % % % % % % % % % 6.00% SLS 4.00% 2.00% 0.00% W WO LO T Horizontal Side Vertical Figure 14. Dimensional Accuracy of four measurement points in SLS The average dimensional accuracy of four measured points indicates that Vertical build orientation provided the best accuracy (0.5093%) as shown in Figure 15. Vertical build orientation is more accurate in the SLS system. 3.00% 2.00% % SLS AVG Dimensional Accuracy % 1.00% 0.00% % Horizontal Side Vertical Figure 15. AVG Dimensional Accuracy of three build orientations in SLS 39

51 Statistical Analysis One-Way ANOVA was chosen to analyze the experiment results for the SLS technology. It can be seen in the ANOVA table below from Minitab that the p-value of factor (Orientation) is less than Therefore, we can say the build orientation significantly affects the dimensional accuracy in the SLS system. In the Normal Plot of Residual, we can find that most of the points displayed near the straight line and few points are a little far from the line. We can say that these experiment results can mostly satisfy the model adequacy and the points follow the normal distribution. The boxplot shows the Vertical build orientation is more accurate than the Horizontal and Side orientations. 40

52 SLS Accuracy Percent Normal Probability Plot (response is SLS Accuracy) Residual Boxplot of SLS Accuracy H S Orientation V PolyJet Dimensional accuracy Table 7 and Figure 16 show the results of four measured points in the PolyJet system. The measured points of T (thickness) in Horizontal orientation provided the most accurate results (0.1000%). Comparing the measured results of Horizontal and 41

53 Side build orientation in Figure 16, the values of Horizontal shows a more stable trend than Side. W 6 WO 19 LO 115 T 4 Table 7. Measured results in PolyJet ASTM Type IV (mm) PolyJet Horizontal Side Vertical AVG SD Dimension Change Rate (%) Dimensional Accuracy (%) AVG SD Dimension Change Rate (%) Dimensional Accuracy (%) AVG SD Dimension Change Rate (%) Dimensional Accuracy (%) AVG SD Dimension Change Rate (%) Dimensional Accuracy (%) SD Dimensional Accuracy AVG Dimensional Accuracy (%)

54 0.1667% % % % % % % % % % % % 6.00% PolyJet 4.00% 2.00% 0.00% W WO LO T Horizontal Side Vertical Figure 16. Dimensional Accuracy of four measurement points in PolyJet Figure 17 shows the average dimensional accuracy of three orientations in the PolyJet system. It can be seen that the difference in build orientations results in the different accuracy of specimens. In Figure 17, the Horizontal build orientation provided more accuracy (0.3227%) than the Side and Vertical orientations for the PolyJet system. 2.00% PolyJet AVG Dimensional Accuracy % % 1.00% 0.00% % Horizontal Side Vertical Figure 17. AVG Dimensional Accuracy of three build orientations in PolyJet 43

55 Statistical Analysis One-Way ANOVA was chosen to analyze the experiment results in PolyJet. In the ANOVA table below from Minitab, the p-value of factor (Orientation) is less than We can say the build orientation significantly affects the dimensional accuracy in PolyJet. In the Normal Probability Plot, most points displayed near the straight line, we can say that these experiment results can mostly satisfy the model adequacy and the points follow the normal distribution. In the ANOVA table and the boxplot, it can be seen that the Horizontal build orientation is more accurate than the Side and Vertical orientations. 44

56 Polyjet Accuracy Percent Normal Probability Plot (response is Polyjet Accuracy) Residual Boxplot of Polyjet Accuracy H S Orientation V FDM Dimensional accuracy In this section, the dimensional accuracy of three build orientations in the Fused Deposition Modeling (FDM) system are discussed. Table 8 tabulates the measured results of four points for three build orientations. The most accurate value (0.1617%) 45

57 appears in the measured point of LO (length of overall) in the Horizontal orientation. Figure 18 shows the dimensional accuracy of four measured points for each build orientation. From at through analysis of Table 8 and Figure 18, it can be seen that measured points of Horizontal build orientation are less variable than others. W 6 WO 19 LO 115 T 4 ASTM Type IV (mm) Table 8. Measured results in FDM FDM Horizontal Side Vertical AVG SD Dimension Change Rate (%) Dimensional Accuracy (%) AVG SD Dimension Change Rate (%) Dimensional Accuracy (%) AVG SD Dimension Change Rate (%) Dimensional Accuracy (%) AVG SD Dimension Change Rate (%) Dimensional Accuracy (%) SD Dimensional Accuracy AVG Dimensional Accuracy (%)

58 0.4316% % % % % % % % % % % % 6.00% FDM 4.00% 2.00% 0.00% W WO LO T Horizontal Side Vertical Figure 18. Dimensional Accuracy of four measurement points in FDM Figure 19 shows the average value of dimensional accuracy in four measured points. It can be seen that the most accurate build orientation appears in the Horizontal orientation. Considering the variation of all measured points, Horizontal also provides less variability as shown in Figure 18. Therefore, we can say that Horizontal build orientation is more accurate than Side and Vertical in the FDM system. 3.00% 2.00% 1.00% % FDM AVG Dimensional Accuracy % % 0.00% Horizontal Side Vertical Figure 19. AVG Dimensional Accuracy of three build orientations in FDM 47

59 Statistical Analysis One-Way ANOVA was chosen to analyze the experiment results in FDM. In the ANOVA table below from Minitab, the p-value of factor (Orientation) is less than 0.05, therefore we can say the build orientation significantly affects the dimensional accuracy in FDM. Most points are displayed near the straight line in Normal Probability Plot. Therefore, we can say that these experiment results can mostly satisfy the model adequacy. In the ANOVA table and the boxplot, it can be seen that Horizontal build orientation is more accurate than Side and Vertical. 48

60 FDM Accuracy Percent Normal Probability Plot (response is FDM Accuracy) Residual Boxplot of FDM Accuracy H S Orientation V 49

61 DP Dimensional accuracy A Z-Corporation Model Spectrum Z510 3D printer constructed the test specimens. Materials for the specimens consist of ZP 131 (gypsum) powder and Z-Bond 90 binder. In 3DP system, the post-processing hardening is required. Once the part is completed and the support powder is removed, the part needs to be dipped in a binder (Z-Bond 90) and so that its strength can be improved. The measured values of Before Harden and After Harden for dimensional accuracy were tabulated in Table 9. Comparing the measured results between hardening post-processing, it can be found that the dimensional tolerance becomes more accurate after hardening. The most accurate value (0.1696%) can be found in the Side build orientation of LO (length of overall) in 3DP After Harden. Figure 20 and Figure 21 show dimensional accuracy of four measured points in each build orientation in 3DP Before Harden and 3DP After Harden. 50