HUNGARIAN JOURNAL OF INDUSTRY AND CHEMISTRY Vol. 49 pp. 59–64 (2021) hjic.mk.uni-pannon.hu DOI: 10.33927/hjic-2021-23 RESEARCH ON AND PRACTICE OF ADDITIVE MANUFACTURING TECHNOLOGIES PÉTER FICZERE*1 1Department of Railway Vehicles and Vehicle System Analysis, Budapest University of Technology and Economics, Műegyetem rkp. 3, Budapest, 1111, HUNGARY Today, additive manufacturing technologies are becoming increasingly popular. In order to take advantage of the oppor- tunities offered by these new technologies, a different way of thinking at the design stage needs to be adopted. This new design thinking must be introduced into engineering education. In order to achieve this at the right level, practical experience is needed in parallel with a theoretical background on the technologies. This paper provides a brief overview of my research and results in the field of additive manufacturing. Keywords: additive manufacturing, 3D printing, generative design, fused deposition modeling, ma- terial properties 1. Introduction The spread of additive manufacturing technologies con- tinues unabated. More and more applications are be- coming commonplace. However, in certain areas, they must be applied cautiously. In many areas, questions are raised about which materials and technology to use from health, mechanical and strength points of view. Similarly, whether it is economically worthwhile to use this manu- facturing process if other methods can be implemented to produce the part is a matter of debate. Since the process is becoming more and more preva- lent in industry, its inclusion in higher technical educa- tion is necessary. However, practical experience is also needed to ensure an adequate level of education. Another benefit of introducing additive manufacturing technolo- gies into education is that it is a novel, interesting and exciting field that attracts the interest of students, which in turn boosts research in this area. My research on additive manufacturing technologies began at the Department of Railway Vehicles and Ve- hicle System Analysis - formerly known as the Depart- ment of Vehicle Elements and Vehicle System Analy- sis (DRVVSA) at the Budapest University of Technol- ogy and Economics (BUTE) in 2007 through my PhD research. At that time, my research was supported by VARINEX Zrt. who produced test specimens for the in- vestigations. In 2015, the department also acquired two Fused De- position Modeling (FDM) 3D printers, increasing the number of opportunities and expanding the spectrum of *Correspondence: ficzere.peter@kjk.bme.hu my research. By this time, my investigations mainly fo- cused on handmade pieces. A significant proportion of the required measure- ments was carried out at the Department of Polymer En- gineering and in the research laboratories at the Biome- chanical Cooperative Research Centre both at the BUTE. The results of my research are presented in this paper. 2. Method A significant amount of experimentation is necessary to properly understand production technologies. During these experiments, questions often arise as to whether this or that can be achieved with this or that technol- ogy. Therefore, the fields of application were extended and the printers made available to students, which led to even more interesting and often questionable outcomes. As the printers purchased (Prusa i3 and Zortrax M200) are open-source, the production parameters could be set as desired and the effects of each setting tested. Another important and continuously explored as well as developed area is the investigation into the applicabil- ity of the technology. 3. Results 3.1 Accuracy tests Specimens of different shapes and geometries were pro- duced to determine the accuracy of the machine and the surface quality of the printed parts. Unfortunately, the studies did not provide precise and clear figures [1] since their accuracy is affected by https://doi.org/10.33927/hjic-2021-23 mailto:ficzere.peter@kjk.bme.hu 60 FICZERE • the geometry of the part to be printed (flat or curved surfaces, curvature rate, position of the planes (hor- izontal, vertical or inclined)); • tolerances of conversion from the original CAD ge- ometry to the STL file (input for the printer) • the layer thickness • the printing speed • the printing temperature • heating the table • the orientation • different levels of accuracy in the x-y (layer) plane and perpendicular (z-direction) to it Of course, these variables refer to printing using the same machine and different values may be obtained should another machine of an alternative type be applied. It is important to note that some errors due to the manufacturing principle can be eliminated by preliminary modifications of the CAD model (toolpath correction), but some more advanced CAM software (code genera- tors) are already capable of doing this. The size correction needed to connect parts in operat- ing assemblies was also investigated. 3.2 Fields of application Due to a lack of space, only some of the completed projects are presented here, but many other smaller ob- jects were printed, e.g., parts for robotic cars for the Bosch Future Mobility Challenge, miniature copies of traffic signs for sign-recognition simulations (for the De- partment of Automotive Technologies at the BUTE), var- ious sprockets, battery holders, unique pieces of “jew- ellery”, ornaments, parts, representation and marketing materials, utility items, educational aids, etc. Supply of spare parts In many cases, given that it is not possible to obtain spare parts for a component that has failed in an older device, a copy of the component in question must be manufactured, otherwise the device becomes inoperable and therefore worthless. Although this technology is particularly im- portant for veteran vehicles, in this case special attention must be paid to the stresses and strains on the components produced by the new method, moreover, should the part produced be non-compliant, it could even damage other irreplaceable parts [2]. Several individual parts that seemed to be irreplace- able have also been redesigned and manufactured (Fig. 1). Nowadays, it is also important to note that more and more people are considering this solution to the lack of spare parts, purely for economic reasons. In the case of a major automotive unit or structure, the supply of spare Figure 1: Replacement of individual parts [2] parts has to be ensured even decades after its produc- tion has stopped. It is of course impossible to determine in advance exactly how many parts will need to be re- placed. For this reason, manufacturers often accumulate unreasonably large stocks of specific parts, which are ex- tremely costly to store or the machines and tools that pro- duce them are costly to maintain. Prototype development Several prototypes have been developed at our depart- ment. One of the most interesting of which was the devel- opment of a medicine capsule. As is well known, the ac- tion of so-called retard capsules (composed of soft gela- tine that is dissolved by acidic conditions found in the human stomach) is delayed. This delay and the extent of its effect also depend on the individual, making it diffi- cult for the optimal dose of the active ingredient to be Hungarian Journal of Industry and Chemistry RESEARCH ON AND PRACTICE OF ADDITIVE MANUFACTURING TECHNOLOGIES 61 Figure 2: Prototype development (capsule) [3] Figure 3: The manufacture of assistive devices [3] determined correctly. The basic idea was to produce cap- sules of the same size as the original capsules, with vari- ous numbers of holes of different dimensions and shapes. The effect of such modifications on the rate and extent of release was then investigated. For the purposes of the studies, the individually designed capsules were printed and filled with a given quantity of caffeine pellets (Figs. 2 and 3) [3, 4]. It can easily be seen that designing a modified mould for a part produced in large quantities by injection mould- ing before stopping production and changing the mould for a few parts needed for testing is not a cost-effective solution, which can lead to a serious loss of revenue [5]. In the same case, in order to fill the miniscule and lightweight caffeine pellets (it was particularly difficult to fill the capsules with the amount measured out into small sachets to the nearest microgram), a small funnel was designed and printed within a few minutes. Making tools and moulds In many cases, high demands for the material the parts are composed of may be infeasible by applying some ad- ditive manufacturing technologies. In a case study when individual castings have to be produced, a casting mould for the remanufacture of a cylinder from the engine of a veteran vehicle can be seen in the middle photo of Fig. 4. On the left-hand side of the figure, a 3D CAD model is shown, which was used to print the mould from acry- lonitrile butadiene styrene (ABS) using an FDM printer to produce (and later functionally assemble) the casting (right-hand side of Fig. 4) [6]. Figure 4: CAD model, 3D-printed casting mould and casted cylinder [6] Figure 5: CAD model of a human metacarpal remodeled from CT scans and the printed pieces [8] The manufacture of medical implants and devices One of the areas where additive manufacturing is ex- pected to make the greatest amount of progress is the rapid and customizable production of medical implants and devices. Since the geometry of a given implant has to perfectly match the intact body parts of the person, very stringent requirements must be met with regard to the for- mal design (shape) of the model [7, 8]. However, these pieces also need to match the stiff- ness of a person’s individual bone in terms of mechanical strength. The department has carried out several research projects along these lines. In the case of the human metacarpal shown in Fig. 5 and 6, the geometry had to be modelled from CT scans. The stiffness of the real bone was measured, then the ge- ometry of the 3D CAD assigned to the model with the 3D-printed material properties and the internal geometry changed by shape optimization until the stiffness of the printed piece perfectly matched the stiffness of the origi- nal bone. Optical photostress investigations Since it is also possible to print from transparent (translucent) materials, the coating required for optical photostress investigations (which is difficult and time- consuming for complex geometries) can be easily printed given the right thickness and quality, thereby saving much time and reducing the amount of effort required (Fig. 7) [9, 10]. An additional advantage of this method is that it al- lows us to detect and determine the residual stresses that develop during production (Fig. 8) [11]. 49 pp. 59–64 (2021) 62 FICZERE Figure 6: Validation of the material model used by the nu- merical simulation of a human metacarpal with measure- ments on a real printed part [7] Figure 7: Fringe pattern on a 3D printed test specimen as a result of bending [9] 3.3 Economic analysis When printing individual parts, how manufacturing costs are affected by the production of the workpiece quickly becomes apparent. • chosen procedure • production time, the 3D printing speed • placement on the workspace • position, orientation • the quantitative requirement for support materials • type of support materials • percentage of filling • type of filling • layer thickness • choice of materials • number of units to be produced Several economic calculations have been made to identify areas where the technology offers real advantages over other manufacturing processes [12]. How the aforementioned parameters affect production costs either directly or indirectly has also been investi- gated [5, 13]. Figure 8: Residual stresses in specimens subjected to ten- sile testing [11] Figure 9: Test specimens produced in different directions and positions [14] 3.4 Material investigations Additive manufacturing technologies are characterized by the fact that they compose arbitrarily complex parts, even with hollow geometries inside, layer by layer [14]. This implies that the bonding of layers to each other is assumed to be different from the bond strength within the layers [15], which has been proven in several cases. In several manufacturing processes of different mate- rials, how the material properties (of lying and standing specimens) in different directions relate to each other has been investigated (Fig. 9). The tensile curves in the high- lighted directions were measured: • FullCure 720 produced by the PolyJet process [1] • FDM process and polylactic acid (PLA) [16] • FDM process and Acrylonitrile Butadiene Styrene (ABS) [17] • Selective Laser Sintering (SLS) process and polyamide 12 (PA12) [18] • FDM process and Soft PLA (flexible plastic) [19] • FDM process and High Temperature (HT) PLA (thermosetting plastic) [20] Apart from the SLS process, the results show that the be- havior of additively manufactured parts can be described by the model of an orthotropic material under all cir- cumstances. Therefore, the determination of the corre- sponding material properties is a more complex task [21], where it is insufficient to only use Young’s modulus E and Poisson’s ratio ν to describe the behavior of a material. In addition, the shear modulus of elasticity G must be mea- sured [22]. Hungarian Journal of Industry and Chemistry RESEARCH ON AND PRACTICE OF ADDITIVE MANUFACTURING TECHNOLOGIES 63 Figure 10: Validation of a material model by the optical photostress method [25] Figure 11: Identifying the causes of errors [25] Of course, after determining the material models and material properties using a tensile testing machine, the results need to be validated. For this purpose, a method has been developed [23]. The effects of certain manufacturing parameters on strength have also been determined [24] and the reasons for these explored (Figs. 10 and 11) [25]. Dynamic materials testing As certain components are also subject to dynamic loads, it is necessary to examine the parts manufactured by these processes for dynamic stresses. This test method has also been developed and performed on parts composed of PLA manufactured by FDM (Fig. 12) [26]. Modification options affecting material properties Several options have been investigated that influence the mechanical strength parameters, including active cool- ing [27], the effect of heat treatment (publication in progress) and ironing (publication in progress). 3.5 Examination of the impact of infill The possibilities of producing parts subjected to quasi- uniform stresses in a way that reduces the cumbersome and lengthy post-processing operations were also investi- gated. Such a method is the modification of the internal filling according to the stresses [28]. Figure 12: Difficult and easy to manufacture uniform strength supports [28] Figure 13: Drone to be manufactured by 3D printing using generative design 3.6 Generative design in terms of additive manufacturing technologies Artificial intelligence-based design methods that can be used to design geometries according to different crite- ria, which by and large can only be produced by additive manufacturing, are currently being investigated (Fig. 13). Acknowledgments The author would like to express their gratitude to György Falk (VARINEX Zrt.) who greatly helped with the research in terms of both printing and giving profes- sional advice. The author is grateful to Dr. László Lovas who, as the head of the department, recognized the research potential of 3D printing and purchased the printers for the depart- ment as well as the necessary materials. Last but not least, the author would like to thank Dr. Gábor Szebényi who provided the material investi- gations. 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