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Creating metal parts by Fused Deposition Modeling and Sintering
Journal Pre-proofs Creating metal parts by Fused Deposition Modeling and Sintering Bin Liu, Yuxiang Wang, Ziwei Lin, Tao Zhang PII: DOI: Reference:
S0167-577X(19)31884-1 https://doi.org/10.1016/j.matlet.2019.127252 MLBLUE 127252
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
18 June 2019 21 November 2019 23 December 2019
Please cite this article as: B. Liu, Y. Wang, Z. Lin, T. Zhang, Creating metal parts by Fused Deposition Modeling and Sintering, Materials Letters (2019), doi: https://doi.org/10.1016/j.matlet.2019.127252
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2019 Published by Elsevier B.V.
Creating metal parts by Fused Deposition Modeling and Sintering
Creating metal parts by Fused Deposition Modeling and Sintering Bin Liua, Yuxiang Wanga, Ziwei Lina, Tao Zhangb （a National Engineering Research Center of Novel Equipment for Polymer Processing, Key Laboratory of Polymer Processing Engineering of Ministry of Education, Guangdong Provincial Key Laboratory of Technique and Equipment for Macromolecular Advanced Manufacturing, South China University of Technology, Guangzhou 510641, China b
Print-Rite Unicorn Image Products Company Limited of Zhuhai, Zhuhai 519000, China）
ABSTRACT: Conventional 3D metal printings are generally high energy consuming and expensive. As an alternative, Fused Deposition Modeling and Sintering (FDMS) was proposed for fast making metal parts at low energy consumption and low cost. Metal/polymer composite filament is printed by the printer based on Fused Deposition Modeling (FDM), and then debinding and sintering are conducted on the printed parts to form compact metal parts. Microstructural characteristics of the 316L/POM filament, printed parts and the final FDMS 316L parts are observed. Besides, the hardness, tensile properties, relative density, and part shrinkage were measured to understand the characteristics of the sintered
FDMS 316L parts. Because the internal porosity and defects decrease the mechanical properties, the FDMS metal parts are suitable for applications without stringent requirements of strength, such as the functional products. KEYWORDS: Fused Deposition Modeling; Sintering; Microstructure; Mechanical properties
1. Introduction Additive manufacturing (AM) or 3D printing technology can fabricate parts with complex shapes which cannot be achieved using traditional machining. Due to its flexibility, AM has been widely used in
Page 1 of 11
Creating metal parts by Fused Deposition Modeling and Sintering
jewelry, construction, biomedical, aerospace, military industries, etc. Metal parts can be fabricated by AM techniques such as Selective Laser Melting (SLM), Direct Metal Laser Sintering (DMLS), Electron Beam Melting (EBM), Laser Engineered Net Shaping (LENS), etc. [1]. However, it is necessary for the above-mentioned techniques to adopt high-energy beams including laser or electron beam as heating sources to fuse the metal powders during the whole manufacturing processing to obtain the final complete metal parts, which is very energy-consuming. In addition, these techniques usually require large investments for metal powders, machinery, and maintenance, limiting their applications mainly to the high value-added industries which are cost-insensitive. Therefore, it is of practical significance to explore other economical metal 3D printing techniques with less energy consumption. Fused Deposition Modeling (FDM) is a cheaper 3D printing technique mainly developed for the additively manufacturing of polymer materials. During the manufacturing process, filamentous polymer is first melted in the printing nozzle at a temperature slightly higher than the melting point of the printing polymer, then deposited onto the printer hotbed layer by layer under the control of computer, and finally fused with the bottom adjacent layers. A number of investigations have been conducted to diversify the materials suitable for FDM. It has been reported that the inclusion of metal particles, such as copper (Cu) or ferrum (Fe), in polymer matrices can improve the flowability of the polymer melt [2,3]. After modeling, the mechanical properties of the FDM polymer matrix parts with high inclusion of metal powders are much lower than that of FDM pure polymer parts [4]. To date, parts composed of metal with high melting points cannot be directly fabricated by FDM, while those can be produced by FDM, debinding and sintering using the newly invented BASF Ultrafuse 316LX metal filament highly filled with 316L powders [5].
Page 2 of 11
Creating metal parts by Fused Deposition Modeling and Sintering
Fused Deposition Modeling and Sintering (FDMS) is a novel AM method based on FDM in which filaments are Metal/polymer composites with a high loading of metal powders, and the printer is further optimized on the basis of the conventional FDM printer. Fig. 1 shows a schematic illustration of the FDMS process. For the sake of simplicity, we define the printed part as ‘Green Part’, the debinded part as ‘Brown Part’, and the sintered metal part as ‘FDMS Part’, respectively. Firstly, Green Parts are printed from metal/polymer composite filament by FDM, during which polymer is melted as the binder but the metal particles remain solid. Later, Brown Parts was obtained by subjecting the Green Parts to a debinding process to remove most of the polymer binder. The rest polymer binder in the Brown Parts can avoid the spreading of the metal particles and thus preserve the shape of the parts. Finally, the Brown Part is sintered to fuse the metal particles together to form dense FDMS Parts. Compared to other AM processes that can fabricate metal parts only at temperatures higher than the melting points of the printing metals which are usually above 1000 ℃, the FDMS can achieve the Green Parts at temperatures slightly higher than the melting points of polymers which are usually below 300 ℃. Additionally, although it is necessary to sinter the Brown Parts at relatively high temperature, the sintering process, as well as the debinding process, can be processed in batches. Thus, FDMS is a more energy-saving process to fabricate metal parts compared to other AM technique.
Fig. 1 Schematic illustration of FDMS.
2. Experiment
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Creating metal parts by Fused Deposition Modeling and Sintering
2.1 Materials The metal/polymer composites filament, consisting of a polymer matrix and dispersed 88wt% 316L stainless steel particles with size in 30-50 μm. The polymer matrix is composed of polyformaldehyde (POM) and other additives such as polypropylene (PP), dioctyl phthalate (DOP), dibutyl phthalate (DBP), and zinc oxide (ZnO) to increase the fluidity, plasticity, and thermo-stability of the composite. The melt flow rate of the composite filament at 230 ℃ with a load of 2.16 kg is 23.56 g per 10 min. 2.2 Experiment method First, using a CoLiDo metal 3D printer from Print-Rite Unicorn Image Products Company Limited of Zhuhai, Green Parts were fabricated using the optimized process parameters with a layer thickness of 0.2 mm, a printing temperature of 230 ℃, and a filling pattern of perimeter shells and rectilinear internal filling. Then, catalyst debinding to achieve the Brown Parts was conducted to remove the POM binder in the Green Parts at 120 ℃ for 8 h under nitrogen whose rate is 1 L/h. Finally, the Brown Parts were subjected to a sintering process by first removing the remaining binder apart from POM at 600 ℃ for 2 h and then sintering at a temperature of 1360 ℃ for 2 h under the protection of argon gas.
3. Results and discussion 3.1 Microstructure Fig. 2a shows the scanning electronic microscopic images of the cross-section of the filament used in FDMS. The binder in the filament forms a continuous phase and the 316L particles with different sizes are uniformly dispersed in the binder matrix, as indicated by the arrows and other microspheres in Fig. 2a. Since the binder plays a principle role in the printing process, the requirement on the morphology of the dispersed metal particles, regarding the sphericity, fluidity and size distribution, is not as rigorous as that
Page 4 of 11
Creating metal parts by Fused Deposition Modeling and Sintering
for SLM or other metal 3D printing methods. Thus, the metal particles used in this filament for FDMS are much easier to be obtained. Due to the same reason, any metal with a melting point above 300 ℃ can be applied in FDMS. Fig. 2b shows the cross-section of a manufactured Green Part. Since the flat filiform composite extruded from the nozzle cannot seamlessly fuse with the deposited bottom layer, slit-shaped printing gaps were found, which can be attributed to the fast solidification of the extruded melt. The filling pattern of rectilinear is 45° inclined to the horizontal, so the printing gaps in the internal zone A and zone B in Fig. 2b is longer and wider than that in C perimeter shell zone. Furthermore, the slicing software can set a few bottom layers as solid layers leading to the printing gaps in zone D of Fig. 2b much smaller and leaner.
Fig. 2 SEM images of the cross-sections of a) Filament and b) Green Part. Fig. 3 shows the microstructure of the FDMS 316L Part after the debinding and sintering processes. Pores at micron level formed and uniformly distributed throughout the cross-section, and most of them are preferentially spherical. The tiny printing gaps in the shell (zone C in Fig. 2b) and bottom layers (zone D in Fig. 2b) of the Green Part has been repaired during the sintering process. Although printing gaps can still be observed in the areas with relatively big gaps, as shown in zone A and zone B in Fig. 3b, they shrunk after the sintering process and are much smaller than those in the Green Part (Fig. 2b). More specifically, the bigger printing gaps in zone A turned to closed narrow cracks, the smaller ones in zone B turned to irregular pores with sizes at several tens microns. The inherent flaws, especially the printing
Page 5 of 11
Creating metal parts by Fused Deposition Modeling and Sintering
gaps, becomes potential cracking sources, which will result in the lower strength of the FDMS Parts. A further parametric study to optimize the printing and sintering process should be carried out in the future to reduce the pores and internal defects. After sintering, a full austenite phase with twin crystals was achieved in the FDMS 316 Part as shown in Fig. 3b. The twin crystals in the final products will increase its hardness and toughness [6].
Fig. 3 Optical microscopy of microstructure in FDMS 316L Part 3.2 Hardness and tensile strength The mechanical properties were obtained based on the averaged value of five sintered FDMS 316L specimens. The micro Vickers hardness of the FDMS 316L Parts is 145.2±6.7 HV, which is slightly lower than that of AISI type 316L parts (155HV [7]), but significantly lower than that of SLM 316L parts (232HV [8]). Although the formed twin crystal (Fig. 3b) during the sintering process can improve the hardness, the relatively high porosity dramatically decreases the hardness since the FDMS Parts with the pores or the printing gaps can be easily pressed into by the indenter of the hardness tester. The tensile properties were measured for the FDMS Parts and was compared with those of metal parts manufactured using other techniques in Table 1. It can be seen that the FDMS 316L Parts possesses lower mechanical properties in terms of the yield strength, ultimate tensile strength, and elongation at break, especially for the ultimate tensile strength. Considering the relatively lower mechanical properties of the final products from FDMS, this forming process is unsuitable to manufacture structural parts, but
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Creating metal parts by Fused Deposition Modeling and Sintering
suitable to fabricate functional products with relatively low requirements on mechanical performance. Table 1 Tensile properties of the fabricated specimens. Tensile properties
FDMS 316L
AISI type 316L [7]
SLM 316L [9]
Yield strength (MPa)
194±19
205
539
Ultimate tensile strength (MPa)
441±27
515
600
Elongation at break (%)
29.5±3.8
60
28
3.3 Relative density and part shrinkage According to the Archimedean drainage method, the measured density of the FDMS 316L Part is 7.36 g/cm3, indicating that the relative density (actual density/ theoretical density) is 92.23% and the porosity is 7.77%. This porosity is relatively high for a metal part, which means FDMS has the potential to reduce the weight of metal parts without a significant reduction of their mechanical properties. Although no evident dimensional change was observed during the debinding process, significant shrinkage about 17% in each direction occurs during the sintering process. The uniform shrinkage reveals that the Green Parts is isotropic and the composition is homogeneous in the Green Parts. Since the shape of the parts keeps unchanged during the whole process, the dimensional shrinkage can be compensated in the very first CAD model.
4. Conclusion Using metal/polymer composite filament as the printing ink, an advanced AM method, namely FDMS, was proposed in this paper to manufacture metal parts by FDM printing, catalyst debinding and sintering. The FDMS can fabricate parts of metals whose melting points are higher than the printing temperature. It is a metal AM method with low cost in the feedstock, device, energy consumption, and
Page 7 of 11
Creating metal parts by Fused Deposition Modeling and Sintering
maintenance, compared to the other metal AM methods. After the sintering process, the parts shrunk equally in each dimension and turned to the final porous FDMS 316L Parts with a full austenite phase containing twin crystals. Attributed to the porous structure, the hardness, tensile strength, relative density are not as high as those of the AISI type 316L parts and SLM 316L parts. Further experiments can focus on the printing accuracy and the sintering process to achieve a denser parts with enhanced mechanical properties.
Acknowledgment We thank the Science and Technology Planning Project of Guangdong Province (No.2017B090913003) for the financial support.
References [1] D.D. Gu, Int. Mater. Rev. 57 (2012) 133-164. [2] N.M.A. Isa, N. Sa’ude, M. Ibrahim, S.M. Hamid, K. Kamarudin, AMM. 773–774 (2015) 8–12. [3] H. Garg, R. Singh, Rapid Prototyping J. 22 (2016) 338–343. [4] S. Fafenrot, N. Grimmelsmann, M. Wortmann, A. Ehrmann, Materials. 10 (2017). [5] H. Gong, D. Snelling, K. Kardel, JOM. 71 (2019) 880–885. [6] M.S. Pham, B. Dovgyy, P.A. Hooper, Mater. Sci. Eng., A. 704 (2017) 102–111. [7] http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=mq316q, 2019 (accessed 11 June 2019) [8] X. Mei, X. Wang, Y. Peng, H. Gu, G. Zhong, S. Yang, Mat Sci Eng A. 758 (2019) 185–191. [9] Z. Brytan, Arch Metall Mater. 62 (2017) 2125–2131.
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Creating metal parts by Fused Deposition Modeling and Sintering
Highlights
FDMS is a much cheaper 3D printing method for metals
Printing gaps in ‘Green parts’ are hard to eliminate
Mechanical properties is poorer than other processing methods
FDMS metal parts is porosity and shrink during sintering
Author Contribution Statement Bin Liu: Conceptualization, Methodology, Writing - Review & Editing; Yuxiang Wang: Formal analysis; Investigation; Writing - Original Draft; Ziwei Lin: Validation; Data Curation; Tao Zhang: Resources; Project administration
AUTHOR DECLARATION
We wish to draw the attention of the Editor to the following facts which may be considered as potential conflicts of interest and to significant financial contributions to this work. We confirm that the manuscript has been read and approved by all named authors and that there are no other persons who satisfied the criteria for authorship but are not listed. We further confirm that the order of authors listed in the manuscript has been approved by all of us. We confirm that we have given due consideration to the protection of intellectual property associated with this work and that there are no impediments to publication, including the timing of publication, with respect to intellectual property. In so doing we
Page 9 of 11
Creating metal parts by Fused Deposition Modeling and Sintering
confirm that we have followed the regulations of our institutions concerning intellectual property. We understand that the Corresponding Author is the sole contact for the Editorial process (including Editorial Manager and direct communications with the office). He is responsible for communicating with the other authors about progress, submissions of revisions and final approval of proofs. We confirm that we have provided a current, correct email address which is accessible by the Corresponding Author and which has been configured to accept email from [email protected]. Signed by all authors as follows: Bin Liu, Yuxiang Wang, Ziwei Lin, Tao Zhang, June 18, 2019
Declaration of interests ☐ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
☒The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
Table.1 Tensile properties of the fabricated specimens.
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Creating metal parts by Fused Deposition Modeling and Sintering
Tensile properties
AMSS 316L
AISI type 316L[6]
SLM 316L[8]
Yield strength (MPa)
194±19
205
539
Ultimate tensile strength (MPa)
441±27
515
600
Elongation at break (%)
29.5±3.8
60
28
Page 11 of 11
S0167-577X(19)31884-1 https://doi.org/10.1016/j.matlet.2019.127252 MLBLUE 127252
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
18 June 2019 21 November 2019 23 December 2019
Please cite this article as: B. Liu, Y. Wang, Z. Lin, T. Zhang, Creating metal parts by Fused Deposition Modeling and Sintering, Materials Letters (2019), doi: https://doi.org/10.1016/j.matlet.2019.127252
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2019 Published by Elsevier B.V.
Creating metal parts by Fused Deposition Modeling and Sintering
Creating metal parts by Fused Deposition Modeling and Sintering Bin Liua, Yuxiang Wanga, Ziwei Lina, Tao Zhangb （a National Engineering Research Center of Novel Equipment for Polymer Processing, Key Laboratory of Polymer Processing Engineering of Ministry of Education, Guangdong Provincial Key Laboratory of Technique and Equipment for Macromolecular Advanced Manufacturing, South China University of Technology, Guangzhou 510641, China b
Print-Rite Unicorn Image Products Company Limited of Zhuhai, Zhuhai 519000, China）
ABSTRACT: Conventional 3D metal printings are generally high energy consuming and expensive. As an alternative, Fused Deposition Modeling and Sintering (FDMS) was proposed for fast making metal parts at low energy consumption and low cost. Metal/polymer composite filament is printed by the printer based on Fused Deposition Modeling (FDM), and then debinding and sintering are conducted on the printed parts to form compact metal parts. Microstructural characteristics of the 316L/POM filament, printed parts and the final FDMS 316L parts are observed. Besides, the hardness, tensile properties, relative density, and part shrinkage were measured to understand the characteristics of the sintered
FDMS 316L parts. Because the internal porosity and defects decrease the mechanical properties, the FDMS metal parts are suitable for applications without stringent requirements of strength, such as the functional products. KEYWORDS: Fused Deposition Modeling; Sintering; Microstructure; Mechanical properties
1. Introduction Additive manufacturing (AM) or 3D printing technology can fabricate parts with complex shapes which cannot be achieved using traditional machining. Due to its flexibility, AM has been widely used in
Page 1 of 11
Creating metal parts by Fused Deposition Modeling and Sintering
jewelry, construction, biomedical, aerospace, military industries, etc. Metal parts can be fabricated by AM techniques such as Selective Laser Melting (SLM), Direct Metal Laser Sintering (DMLS), Electron Beam Melting (EBM), Laser Engineered Net Shaping (LENS), etc. [1]. However, it is necessary for the above-mentioned techniques to adopt high-energy beams including laser or electron beam as heating sources to fuse the metal powders during the whole manufacturing processing to obtain the final complete metal parts, which is very energy-consuming. In addition, these techniques usually require large investments for metal powders, machinery, and maintenance, limiting their applications mainly to the high value-added industries which are cost-insensitive. Therefore, it is of practical significance to explore other economical metal 3D printing techniques with less energy consumption. Fused Deposition Modeling (FDM) is a cheaper 3D printing technique mainly developed for the additively manufacturing of polymer materials. During the manufacturing process, filamentous polymer is first melted in the printing nozzle at a temperature slightly higher than the melting point of the printing polymer, then deposited onto the printer hotbed layer by layer under the control of computer, and finally fused with the bottom adjacent layers. A number of investigations have been conducted to diversify the materials suitable for FDM. It has been reported that the inclusion of metal particles, such as copper (Cu) or ferrum (Fe), in polymer matrices can improve the flowability of the polymer melt [2,3]. After modeling, the mechanical properties of the FDM polymer matrix parts with high inclusion of metal powders are much lower than that of FDM pure polymer parts [4]. To date, parts composed of metal with high melting points cannot be directly fabricated by FDM, while those can be produced by FDM, debinding and sintering using the newly invented BASF Ultrafuse 316LX metal filament highly filled with 316L powders [5].
Page 2 of 11
Creating metal parts by Fused Deposition Modeling and Sintering
Fused Deposition Modeling and Sintering (FDMS) is a novel AM method based on FDM in which filaments are Metal/polymer composites with a high loading of metal powders, and the printer is further optimized on the basis of the conventional FDM printer. Fig. 1 shows a schematic illustration of the FDMS process. For the sake of simplicity, we define the printed part as ‘Green Part’, the debinded part as ‘Brown Part’, and the sintered metal part as ‘FDMS Part’, respectively. Firstly, Green Parts are printed from metal/polymer composite filament by FDM, during which polymer is melted as the binder but the metal particles remain solid. Later, Brown Parts was obtained by subjecting the Green Parts to a debinding process to remove most of the polymer binder. The rest polymer binder in the Brown Parts can avoid the spreading of the metal particles and thus preserve the shape of the parts. Finally, the Brown Part is sintered to fuse the metal particles together to form dense FDMS Parts. Compared to other AM processes that can fabricate metal parts only at temperatures higher than the melting points of the printing metals which are usually above 1000 ℃, the FDMS can achieve the Green Parts at temperatures slightly higher than the melting points of polymers which are usually below 300 ℃. Additionally, although it is necessary to sinter the Brown Parts at relatively high temperature, the sintering process, as well as the debinding process, can be processed in batches. Thus, FDMS is a more energy-saving process to fabricate metal parts compared to other AM technique.
Fig. 1 Schematic illustration of FDMS.
2. Experiment
Page 3 of 11
Creating metal parts by Fused Deposition Modeling and Sintering
2.1 Materials The metal/polymer composites filament, consisting of a polymer matrix and dispersed 88wt% 316L stainless steel particles with size in 30-50 μm. The polymer matrix is composed of polyformaldehyde (POM) and other additives such as polypropylene (PP), dioctyl phthalate (DOP), dibutyl phthalate (DBP), and zinc oxide (ZnO) to increase the fluidity, plasticity, and thermo-stability of the composite. The melt flow rate of the composite filament at 230 ℃ with a load of 2.16 kg is 23.56 g per 10 min. 2.2 Experiment method First, using a CoLiDo metal 3D printer from Print-Rite Unicorn Image Products Company Limited of Zhuhai, Green Parts were fabricated using the optimized process parameters with a layer thickness of 0.2 mm, a printing temperature of 230 ℃, and a filling pattern of perimeter shells and rectilinear internal filling. Then, catalyst debinding to achieve the Brown Parts was conducted to remove the POM binder in the Green Parts at 120 ℃ for 8 h under nitrogen whose rate is 1 L/h. Finally, the Brown Parts were subjected to a sintering process by first removing the remaining binder apart from POM at 600 ℃ for 2 h and then sintering at a temperature of 1360 ℃ for 2 h under the protection of argon gas.
3. Results and discussion 3.1 Microstructure Fig. 2a shows the scanning electronic microscopic images of the cross-section of the filament used in FDMS. The binder in the filament forms a continuous phase and the 316L particles with different sizes are uniformly dispersed in the binder matrix, as indicated by the arrows and other microspheres in Fig. 2a. Since the binder plays a principle role in the printing process, the requirement on the morphology of the dispersed metal particles, regarding the sphericity, fluidity and size distribution, is not as rigorous as that
Page 4 of 11
Creating metal parts by Fused Deposition Modeling and Sintering
for SLM or other metal 3D printing methods. Thus, the metal particles used in this filament for FDMS are much easier to be obtained. Due to the same reason, any metal with a melting point above 300 ℃ can be applied in FDMS. Fig. 2b shows the cross-section of a manufactured Green Part. Since the flat filiform composite extruded from the nozzle cannot seamlessly fuse with the deposited bottom layer, slit-shaped printing gaps were found, which can be attributed to the fast solidification of the extruded melt. The filling pattern of rectilinear is 45° inclined to the horizontal, so the printing gaps in the internal zone A and zone B in Fig. 2b is longer and wider than that in C perimeter shell zone. Furthermore, the slicing software can set a few bottom layers as solid layers leading to the printing gaps in zone D of Fig. 2b much smaller and leaner.
Fig. 2 SEM images of the cross-sections of a) Filament and b) Green Part. Fig. 3 shows the microstructure of the FDMS 316L Part after the debinding and sintering processes. Pores at micron level formed and uniformly distributed throughout the cross-section, and most of them are preferentially spherical. The tiny printing gaps in the shell (zone C in Fig. 2b) and bottom layers (zone D in Fig. 2b) of the Green Part has been repaired during the sintering process. Although printing gaps can still be observed in the areas with relatively big gaps, as shown in zone A and zone B in Fig. 3b, they shrunk after the sintering process and are much smaller than those in the Green Part (Fig. 2b). More specifically, the bigger printing gaps in zone A turned to closed narrow cracks, the smaller ones in zone B turned to irregular pores with sizes at several tens microns. The inherent flaws, especially the printing
Page 5 of 11
Creating metal parts by Fused Deposition Modeling and Sintering
gaps, becomes potential cracking sources, which will result in the lower strength of the FDMS Parts. A further parametric study to optimize the printing and sintering process should be carried out in the future to reduce the pores and internal defects. After sintering, a full austenite phase with twin crystals was achieved in the FDMS 316 Part as shown in Fig. 3b. The twin crystals in the final products will increase its hardness and toughness [6].
Fig. 3 Optical microscopy of microstructure in FDMS 316L Part 3.2 Hardness and tensile strength The mechanical properties were obtained based on the averaged value of five sintered FDMS 316L specimens. The micro Vickers hardness of the FDMS 316L Parts is 145.2±6.7 HV, which is slightly lower than that of AISI type 316L parts (155HV [7]), but significantly lower than that of SLM 316L parts (232HV [8]). Although the formed twin crystal (Fig. 3b) during the sintering process can improve the hardness, the relatively high porosity dramatically decreases the hardness since the FDMS Parts with the pores or the printing gaps can be easily pressed into by the indenter of the hardness tester. The tensile properties were measured for the FDMS Parts and was compared with those of metal parts manufactured using other techniques in Table 1. It can be seen that the FDMS 316L Parts possesses lower mechanical properties in terms of the yield strength, ultimate tensile strength, and elongation at break, especially for the ultimate tensile strength. Considering the relatively lower mechanical properties of the final products from FDMS, this forming process is unsuitable to manufacture structural parts, but
Page 6 of 11
Creating metal parts by Fused Deposition Modeling and Sintering
suitable to fabricate functional products with relatively low requirements on mechanical performance. Table 1 Tensile properties of the fabricated specimens. Tensile properties
FDMS 316L
AISI type 316L [7]
SLM 316L [9]
Yield strength (MPa)
194±19
205
539
Ultimate tensile strength (MPa)
441±27
515
600
Elongation at break (%)
29.5±3.8
60
28
3.3 Relative density and part shrinkage According to the Archimedean drainage method, the measured density of the FDMS 316L Part is 7.36 g/cm3, indicating that the relative density (actual density/ theoretical density) is 92.23% and the porosity is 7.77%. This porosity is relatively high for a metal part, which means FDMS has the potential to reduce the weight of metal parts without a significant reduction of their mechanical properties. Although no evident dimensional change was observed during the debinding process, significant shrinkage about 17% in each direction occurs during the sintering process. The uniform shrinkage reveals that the Green Parts is isotropic and the composition is homogeneous in the Green Parts. Since the shape of the parts keeps unchanged during the whole process, the dimensional shrinkage can be compensated in the very first CAD model.
4. Conclusion Using metal/polymer composite filament as the printing ink, an advanced AM method, namely FDMS, was proposed in this paper to manufacture metal parts by FDM printing, catalyst debinding and sintering. The FDMS can fabricate parts of metals whose melting points are higher than the printing temperature. It is a metal AM method with low cost in the feedstock, device, energy consumption, and
Page 7 of 11
Creating metal parts by Fused Deposition Modeling and Sintering
maintenance, compared to the other metal AM methods. After the sintering process, the parts shrunk equally in each dimension and turned to the final porous FDMS 316L Parts with a full austenite phase containing twin crystals. Attributed to the porous structure, the hardness, tensile strength, relative density are not as high as those of the AISI type 316L parts and SLM 316L parts. Further experiments can focus on the printing accuracy and the sintering process to achieve a denser parts with enhanced mechanical properties.
Acknowledgment We thank the Science and Technology Planning Project of Guangdong Province (No.2017B090913003) for the financial support.
References [1] D.D. Gu, Int. Mater. Rev. 57 (2012) 133-164. [2] N.M.A. Isa, N. Sa’ude, M. Ibrahim, S.M. Hamid, K. Kamarudin, AMM. 773–774 (2015) 8–12. [3] H. Garg, R. Singh, Rapid Prototyping J. 22 (2016) 338–343. [4] S. Fafenrot, N. Grimmelsmann, M. Wortmann, A. Ehrmann, Materials. 10 (2017). [5] H. Gong, D. Snelling, K. Kardel, JOM. 71 (2019) 880–885. [6] M.S. Pham, B. Dovgyy, P.A. Hooper, Mater. Sci. Eng., A. 704 (2017) 102–111. [7] http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=mq316q, 2019 (accessed 11 June 2019) [8] X. Mei, X. Wang, Y. Peng, H. Gu, G. Zhong, S. Yang, Mat Sci Eng A. 758 (2019) 185–191. [9] Z. Brytan, Arch Metall Mater. 62 (2017) 2125–2131.
Page 8 of 11
Creating metal parts by Fused Deposition Modeling and Sintering
Highlights
FDMS is a much cheaper 3D printing method for metals
Printing gaps in ‘Green parts’ are hard to eliminate
Mechanical properties is poorer than other processing methods
FDMS metal parts is porosity and shrink during sintering
Author Contribution Statement Bin Liu: Conceptualization, Methodology, Writing - Review & Editing; Yuxiang Wang: Formal analysis; Investigation; Writing - Original Draft; Ziwei Lin: Validation; Data Curation; Tao Zhang: Resources; Project administration
AUTHOR DECLARATION
We wish to draw the attention of the Editor to the following facts which may be considered as potential conflicts of interest and to significant financial contributions to this work. We confirm that the manuscript has been read and approved by all named authors and that there are no other persons who satisfied the criteria for authorship but are not listed. We further confirm that the order of authors listed in the manuscript has been approved by all of us. We confirm that we have given due consideration to the protection of intellectual property associated with this work and that there are no impediments to publication, including the timing of publication, with respect to intellectual property. In so doing we
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Creating metal parts by Fused Deposition Modeling and Sintering
confirm that we have followed the regulations of our institutions concerning intellectual property. We understand that the Corresponding Author is the sole contact for the Editorial process (including Editorial Manager and direct communications with the office). He is responsible for communicating with the other authors about progress, submissions of revisions and final approval of proofs. We confirm that we have provided a current, correct email address which is accessible by the Corresponding Author and which has been configured to accept email from [email protected]. Signed by all authors as follows: Bin Liu, Yuxiang Wang, Ziwei Lin, Tao Zhang, June 18, 2019
Declaration of interests ☐ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
☒The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:
Table.1 Tensile properties of the fabricated specimens.
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Creating metal parts by Fused Deposition Modeling and Sintering
Tensile properties
AMSS 316L
AISI type 316L[6]
SLM 316L[8]
Yield strength (MPa)
194±19
205
539
Ultimate tensile strength (MPa)
441±27
515
600
Elongation at break (%)
29.5±3.8
60
28
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