In this work, the influence of material type and sample fill density was evaluated. One PLA material was tested. Test specimens having different fill structure and density were printed from this material. Full honeycomb and gyroid shapes were used for the fill structure. The specimens had four different fill percentages for each structure: 10%, 25%, 50% and 75%. These bodies were compared to samples that were printed with 100% fill. Tensile test was performed on printed test pieces. The Zwick / Roell Z100 was used for testing and the surface hardness of the test specimens was measured by the Shore D method on a DIGI-Test II hardness tester. Fracture surfaces were evaluated on an Olympus DSX 500 optodigital microscope. The results showed that the shape of the fill did not signifi-cantly affect the values obtained by the tensile test. The hardness measurement results showed a different hardness on the bottom surface that was in contact with the printing pad and the top printing surface. Fractographic analysis revealed different types of fracture surfaces related to the printed fill structure. © 2021 Manufacturing Technology. All rights reserved

Andrés, Lukáš

Dražan, Tomáš

Joska, Zdeněk

Maňas, Karel

Pokorný, Zdeněk

Sedlák, Josef

In this work, the influence of material type and sample fill density was evaluated. One PLA material was tested. Test specimens having different fill structure and density were printed from this material. Full honeycomb and gyroid shapes were used for the fill structure. The specimens had four different fill percentages for each structure: 10%, 25%, 50% and 75%. These bodies were compared to samples that were printed with 100% fill. Tensile test was performed on printed test pieces. The Zwick / Roell Z100 was used for testing and the surface hardness of the test specimens was measured by the Shore D method on a DIGI-Test II hardness tester. Fracture surfaces were evaluated on an Olympus DSX 500 optodigital microscope. The results showed that the shape of the fill did not signifi-cantly affect the values obtained by the tensile test. The hardness measurement results showed a different hardness on the bottom surface that was in contact with the printing pad and the top printing surface. Fractographic analysis revealed different types of fracture surfaces related to the printed fill structure.Department of Mechanical En-gineering, University of Defence in Brno [SV20-216]; Project for the Development of the Organization, DZRO Military autonomous and robotic systems

Institutional repository of Tomas Bata University Library

April 2021, Vol. 21, No. 2 MANUFACTURING TECHNOLOGY ISSN 1213–2489 indexed on: http://www.scopus.com 199 DOI: 10.21062/mft.2021.024 © 2021 Manufacturing Technology. All rights reserved.  http://www.journalmt.comInfluence of the Shape of the Filling on the Mechanical Properties of Samples Made by 3D Printing Zdeněk Joska1, Lukáš Andrés1, Tomáš Dražan1, Karel Maňas2, Zdeněk Pokorný1, Josef Sedlák3  1Department of Mechanical Engineering, Faculty of Military Technology, University of Defence, 662 10 Brno, Czech Republic. E-mail: zdenek.joska@unob.cz 2Department of Aircraft Technology, Faculty of Military Technology, University of Defence in Brno, 612 10, CZ Czech Republic. E-mail: karel.manas@unob.cz 3Department of Industrial Engineering and Information Systems, Faculty of Management and Economics, Tomas Bata University in Zlín, Mostní 5139, 760 01 Zlín, Czech Republic. E-mail: sedlak@utb.cz In this work, the influence of material type and sample fill density was evaluated. One PLA material was tested. Test specimens having different fill structure and density were printed from this material. Full honeycomb and gyroid shapes were used for the fill structure. The specimens had four different fill per-centages for each structure: 10%, 25%, 50% and 75%. These bodies were compared to samples that were printed with 100% fill. Tensile test was performed on printed test pieces. The Zwick / Roell Z100 was used for testing and the surface hardness of the test specimens was measured by the Shore D method on a DIGI-Test II hardness tester. Fracture surfaces were evaluated on an Olympus DSX 500 optodigital microscope.  The results showed that the shape of the fill did not signifi-cantly affect the values obtained by the tensile test. The hardness measurement results showed a different hardness on the bottom surface that was in contact with the printing pad and the top printing surface. Fractographic analysis revealed different types of fracture surfaces related to the printed fill structure. Keywords: 3D printing, tensile test, hardness, infill  Introduction A simple definition for 3D printing is that it is the process by which a three-dimensional object is created from a di-gital file. With the help of additive manu-facturing (AM) a process is achieved how to give a di-gital file a material shape by means of additive proces-ses [1]. However, a virtual design in the form of a CAD file must be performed before prin-ting can be-gin. This can be achieved either through the conven-tional design process in programs such as AUTOCAD or CATIA, or through more modern technology such as 3D scanning or recognition [2]. Not all 3D printers use the same type of technology, and it may be appro-priate to use more than one type for a given project. Since 2010, the American Society for Testing and Ma-terials (ASTM) "ASTM F42 - Additive Manufactu-ring" has developed a set of standards that categorize additive manufacturing processes into 7 basic types[3]. The FDM / FFF method is one of the most used and widespread technologies used in 3D printing. The principle of this technology is to melt thermoplastic or metal. The most used materials (thermoplastics) inc-lude, for example, ABS or PLA. The length of the print itself depends on the size and complexity of the prints, it can reach up to tens of hours. The FDM / FFF method can achieve very good mechanical pro-perties for the products, thanks to which these produ-cts can be used, for example, as mechanical compo-nents. An indisputable advantage is also the simplicity and the generation of minimal waste, which consists only of the already mentioned supporting material [4]. Disadvantages can be considered, for example, the li-mited accuracy, influenced by the material itself and the nozzle from which the material is extruded. It is also necessary to take into account the shrin-kage of the final product, which occurs when the material so-lidifies. However, this phenomenon can be compens-ated by corrections in the system preparing the print data [5,6]. It is the second most used and most uni-versal material for FDM / FFF technology and 3D printing in general. PLA is a thermoplastic polyester that is obtained from renewable sources such as po-tato or corn starch. Unlike ABS, this material is less prone to deformation and has good strength, even at lower temperatures. Disadvantages can be considered, for example, less resistance to higher temperatures (softening begins at 60 °C), which is related to ma-chine grinding, which is not recommended for this material, because the material is quickly heated in this process to the point where it begins to soften ( this problem can be prevented by cooling). PLA is also less flexible than ABS [7,9,10]. April 2021, Vol. 21, No. 2 MANUFACTURING TECHNOLOGY ISSN 1213–2489  200  indexed on: http://www.scopus.com   Experimental procedure  Tensile test is one of the basic tests used to deter-mine the mechanical characteristics to determine the quality of the material. The samples was printed accor-ding to the standard ČSN EN ISO 527-2[8]. The hard-ness of material was tested Shore D method on DIGI-Test II hardnes tester device. The samples used for testing have thickness of 4 mm.  Sample preparation For the experimental part, 45 samples were printed according to the ISO 527-2 standard. 20 with Full ho-neycomb fill pattern, 20 with Gyroid fill pattern with fill percentages of 10%, 25%, 50%, 75% and 5 samples with 100% fill for com-parison see Fig 1. and 2.  Fig. 1 Sample ISO 527-2 (Type A)  Five test specimens for each type and percentage of infill. Where the sample shell was 0.8 mm and only the infill was changed. PLA samples were printed with a 0.4 mm diameter nozzle at 215°C on a 35°C heated substrate pad with a layer height of 0.2 mm. The first two and last two layers were printed with a Rectilinear pattern at an angle of 45°.  Fig. 2 Samples Full honeycomb  Second serie of samples see Fig 3. and Fig 4. For experiment 45 samples were printed. 20 with Full ho-neycomb fill pat-tern, 20 with Gyroid fill pattern and 5 with 100% fill for comparison. 5 test specimens for each species and percentage of infill. Where, instead of the shell, only one perimeter was printed around a 0.4 mm wide test specimen. PLA samples were printed with a 0.4 mm diameter nozzle at 215 ° C on a 35 ° C heated substrate with a layer height of 0.2 mm.  Fig. 3 Own design of the modified sample (Type B)  Fig. 4 Full honeycomb (left), Gyroid (right)  Results Weight and time of printing of test samples  The weight and time of printing and the associated price of printing are probably the main reasons why to choose a different fill of prints and not leave the prin-tout full. Only the modified sample (Type B) will be compared because it does not distort the shell result. The results show that Gyroid offers a greater saving of printing time compared to Full honeycomb by about 20% see in Tab. 1. Because printing was perfor-med in batches, the table does not show the exact print time but the total print time of the batch divided by the number of pieces. Over time, the print head passes between prints are also taken into account, but this does not affect the percentage of time saved. At higher infill densities, Full honeycomb is better in weight, but at lower infill densities Gyroid. Only de-pending on the printing time and weight of the prin-tout, the Gyroid comes out better. April 2021, Vol. 21, No. 2 MANUFACTURING TECHNOLOGY ISSN 1213–2489 indexed on: http://www.scopus.com 201  Tab. 1 Print weight and time (Type B) Type of infill Printing time [min] Weight [g] Time saved [%] Weight saved [%] Full infill 79 13.55 0 0 Full honeycomb 75% 64 9.27 18.99 31.59 Gyroid 75% 40 10.17 49.37 24.94 Full honeycomb 50% 46 6.94 41.77 48.78 Gyroid 50% 24 7.25 69.62 46.49 Full honeycomb 25% 30 4.39 62.03 67.60 Gyroid 25% 13 4.18 83.54 69.15 Full honeycomb 10% 19 2.52 75.95 81.40 Gyroid 10% 7 2.29 91.14 83.10  Tensile test of standard sample (Type A)  Fig. 5 Sample with gyroid infill (Type A) April 2021, Vol. 21, No. 2 MANUFACTURING TECHNOLOGY ISSN 1213–2489  202  indexed on: http://www.scopus.com   Fig. 6 Sample with Full honeycomb infill (Type A) Tab. 2 Maximal force (Type A) Type infill Max. force F [N] Full infill 849 Full honeycomb 75% (Type A) 737 Gyroid 75% (Type A) 822 Full honeycomb 50% (Type A) 701 Gyroid 50% (Type A) 775 Full honeycomb 25% (Type A) 694 Gyroid 25% (Type A) 669 Full honeycomb 10% (Type A) 670 Gyroid 10% (Type A) 669     April 2021, Vol. 21, No. 2 MANUFACTURING TECHNOLOGY ISSN 1213–2489 indexed on: http://www.scopus.com 203  Tensile test of modified sample (Type B)  Fig. 7 Sample with gyroid infill (Type B)  Fig. 8 Sample with Full honeycomb infill (Type B) April 2021, Vol. 21, No. 2 MANUFACTURING TECHNOLOGY ISSN 1213–2489  204  indexed on: http://www.scopus.com  Tab. 3 Maximal force (Type B) Type of  infill Max. force F [N] Full infill 1809 Full honeycomb 75% (Type B) 942 Gyroid 75% (Type B) 966 Full honeycomb 50% (Type B) 600 Gyroid 50% (Type B) 578 Full honeycomb 25% (Type B) 309 Gyroid 25% (Type B) 334 Full honeycomb 10% (Type B) 177 Gyroid 10% (Type B) 205  Figures 5-8 show the results of tensile tests of in-dividual shapes of test bars with different shape and infill content. The results show that for type A samples the differences during the tensile test are less different than for type B samples. The achieved maximum for-ces given in Tables 2 and 3 show that the shape of the maximum force is again not affected by the infill shape. The results showed that the content of the in-file and the shape of the printing of the edge surfaces have a great influence on the course and results, which significantly influence the test values. For low infile contents of 10% and 25%, the differences are not as significant as for higher infile contents.  Hardness To compare the surface hardness of the printed si-des of samples was used method Shore D plastics. For experiment was used DIGI-Test II. The measure-ments were performed on five samples with full filling and were performed on both surfaces ten times. We only insert the average value from the measurement into the table. Tab. 4 Surface hardness Sample number Side in contact with the pad Upper side 1 77.6 67.7 2 77.1 68.8 3 77.0 66.0 4 77.0 69.8 5 76.6 66.9 Average value 77.0±0.32 68±1.35  The Table 4. shows that the surface hardness of the surface in contact with the pad is 13.6% higher than on the side that was not in contact with the prin-ting pad.  Fracture analysis  Fig. 9 Full honeycomb 25 %( left), Gyroid 75 %(right)  The effect of the shell on the fracture surface can be easily observed on this type of sample Fig 9… The fracture does not tend to change due to the type of filling or the percentage of filling. As an example, Full honeycomb 25% and Gyro-id 75% and the fractures are almost identical.  Fig. 10 Full honeycomb 75% surface (left), Gyroid 75% sur-face (right) For this type of sample, we can better observe the effect of the filling structure on the fracture of the sample. With Gyroid see Fig 10., the fracture is transverse due to the application of layers. With Full honeycomb, the fracture is slanted due to the positi-ons of the holes in the filling. April 2021, Vol. 21, No. 2 MANUFACTURING TECHNOLOGY ISSN 1213–2489 indexed on: http://www.scopus.com 205  Conclusion The measurement results showed that the printing of the Gyroid infill type is on average 23.73% faster than the Full honeycomb infill. Furthermore, the average weight of a print with the Full honeycomb pattern is 1.42% lower than that of the Gyroid. For the tensile test, measurements were performed on two types of samples with and without shell. For the smaller shell samples (Type A), the results were quite similar for all the different infill percentages. It can be observed that the shell has big influence on results of tensile test. For modified larger samples without shell with only one perimeter around the circumference (Type B), the results were more pronounced for the individual percentages of the infill. For the tensile test, only data of maximal tensile strenght was compared. For the Type A sample, the Gyroid type performed better in average strength by 6.81%, tensile strength by 12.59% than with the Full honeycomb type. For the Type B sample, the Gyroid type performed better with an average strength of 1.16%, tensile strength of 1.86% . The surface strength on the surface that was in contact with the printing pad is 13.6% higher than on the surface that was not in contact with the printing pad. Comparison of the fracture surfaces of the samples showed the influence of the type of infill on the fracture of the part. For Type B, where the result was not distorted by the shell, the Gyroid filling type turned out a little bet-ter than the Full honeycomb type, but with regard to the printing time, the Gyroid works better overall than the Full honeycomb. Acknowledgement The work presented in this paper has been supported by the specific research project 2020 „SV20-216“at the Department of Mechanical En-gineering, University of Defence in Brno and the Project for the Development of the Organization „DZRO Military autonomous and robotic sys-tems“. References  CHUA, C. K., LEONG, K. F., LIM, C. S. (2010) Rapid Prototyping: Principles and Applicati-ons. 3rd ed. New Jer-sey: World Scientific, 512 pp. ISBN 978-981-277-897-0.   DRÁPELA, M. (2006) Modul Rapid Prototyping. Centrum vzdělávání a poradenství Vysokého učení technického v Brně, 44 s.  The History of 3D Printing: 3D Printing Tech-nologies from the 80s to Today. Scuplteo [on-line]. 14. pros-ince 2016 [cit. 2019-04-11]. Do-stupné z: https://www.sculpteo.com/blog/2016/12/14/the-history-of-3d-printing-3d-printing-technologies-from-the-80s-to-today/.  MOLIKOVA, E. (2006) Materials and Produ-cts Testing. [Online]. 20th January 2006 [seen 8th December 2013]. 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Influence of the shape of the filling on the mechanical properties of samples made by 3D printing

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Influence of the shape of the filling on the mechanical properties of samples made by 3D printing

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