Key Engineering Materials Vol. 956

Abstract: Bioresorbable alternatives are emerging on the market as alternatives to the cardiovascular stents that are implanted nowadays. Permanent drug-eluting stents are no longer the only viable option during an angioplasty surgical procedure. The new generation of medical stents aims to degrade the device within the artery walls after its function has been completed. In this context, biological materials that degrade inside the body without creating toxic residues such as silk fibroin (SF) are very promising materials for such applications. Moreover, SF has been reported to have non-thrombogenic properties and to reduce the immune response compared to other synthetic polymers, making it ideal for this application. SF has been printed through additive manufacturing techniques such as direct ink write. This study proposes to fabricate a composite stent by combining polylactic acid (PLA) and SF. In this way, it is expected to obtain a stent with potential for a two-phase drug release. A fast burst with the degradation of the SF and a slower drug release period with the degradation of the PLA. For this purpose, stents were fabricated with a PLA and chloroform ink (24.5 % w/v). The last layer of the stent was fabricated with a SF water-based ink at 56.69-60.09 % w/w. Finally, the stents were immersed at different times in ethanol and exposed to 30' of ultraviolet light for sterilization purposes. The degradation results indicate that 24h is sufficient to degrade almost completely the last layer of SF. These results are significant as the SF layer could potentially be used as a carrier for drug delivery, providing biocompatibility and drug release at the earliest post-intervention stage.

Abstract: The aim of our study was to determine changes in the microstructure and mechanical properties of AISI 316L steel processed by additive SLM technology which will be induced by additional processing using HIP technology and solution annealing. The specimens for this experiment were made in the form of bars with a diameter of 5 mm for tensile testing. The specimens were additively manufactured in the vertical direction with respect to the position of the build plate using standard process parameters. The HIP processing of the specimens was performed at a temperature of 1150 °C and pressure of 150 MPa. Some of the specimens were heat treated using solution annealing at 1150 °C after the SLM and HIP processes. The analyses performed consisted of metallographic analysis of the microstructure using light and scanning electron microscopy methods, which were further complemented by basic mechanical property tests, namely tensile testing and HV1 hardness measurements. The tensile test showed that the solution annealing of the printed specimens reduced the ultimate strength from 545±6.2 MPa to 508±0.0 MPa and increased the ductility from 44±5.4 % to 56±0.4 %. The HIP process reduced the ultimate strength to 522±2.7 MPa and the further annealed specimens to 514±1.8 MPa. The ductility of the specimens after HIP treatment was higher than that of the additively manufactured specimens, corresponding to 52±0.3 %. After solution annealing, it reached values like those of the specimens annealed after 3D printing. The metallographic analysis carried out showed a positive effect of the HIP process on the porosity achieved after 3d printing, whose volume was reduced as a result.

Abstract: Fused Deposition Modelling (FDM) is a common technique used when rapid prototyping is needed to perform a preliminary evaluation of the suitability of a part. For this purpose, several materials, as PLA, ABS, PET-G and others, are easily available in the market along with a wide range of commercial 3D printers at affordable prices. Prototypes manufactured under this technique are usually made of a single material and, for most of the applications, it is enough to fulfill the required specifications. However, the increasing demand for the manufacturing of parts made of more than one material suggests that prototyping via FDM using two dissimilar materials should be assessed to assure that such technique is still acceptable to perform a preliminary evaluation of a part. For this purpose, a methodology using a commercial FDM 3D printer is proposed to characterize the flexural and shear bonding behavior of two dissimilar materials. This methodology implements four steps: The selection of the applicable UNE standards as main reference, the design and manufacture of the test specimens based on these standards, the execution of the structural tests to characterize the behavior of those specimens and the analysis of the test data along with the conclusions. This methodology has been validated using ABS and PLA as base materials. The coherence and accuracy of the results obtained from this specific case substantiate that it is a valid methodology to evaluate the structural behavior of the bonding of two dissimilar materials, beyond PLA and ABS, using commercial and affordable off-the-shelf 3D printers.

Abstract: Fused Filament Fabrication (FFF) is a growing additive manufacturing technology for various applications in the engineering field. The mechanical properties of 3D printed materials in FFF technology depends on various parameters and the literature suggests that infill pattern and infill density are the parameters that most affect the mechanical properties of 3D printed parts.These factors have direct influence on the time of production and amount of material used. In this work it was analyzed the influence of infill parameter on stiffness of the final parts, considering the printing time and amount material used. For this purpose, the Taguchi method was used and then the statistical method of ANOVA to calculate the influence of each parameter.Test specimens were printed according to ASTM Standard D790 dimensions, in Polyethylene terephthalate glycol (PETG). The specimens were printed in the same position on the printing bed to reduce as much as possible the influence of external factors on the results. A visual and dimensional inspection of the specimens was carried out for further analysis. The best combination between production and stiffness, with 350 MPa/mm, was obtained with 15% infill density, concentric pattern, 45º orientation, with 4 perimeters path, layer thickness of 0.1 mm and speed of 45 mm/s. The results obtained allow us a broader view of how to save 3D printing time and the amount of material consumed during the production of a part.

Abstract: Additive Manufacturing (AM) [1] is playing every day a bigger role in the automotive industry because of its cost competitiveness, short delivery lead times and potential for design flexibility and optimization. Plastics and polymers are the most common materials used to produce AM parts in this sector, however metal AM is increasing its importance as there are specific applications that require mechanical characteristics that can only be achieved with metals such as stainless steel, titanium, hard steel, copper, aluminum, and others. There is an increasing number of metal AM technologies and Original Equipment Manufacturers (OEMs) competing in the industry with a very widespread list of advantages and disadvantages of each of them. We are at a point where automotive manufacturers need to make a complex decision on which metal AM equipment to purchase. This paper describes the main metal AM technologies and highlight the advantages and disadvantages of each of them. Additionally, three of the most competitive Metal AM technologies are compared: Powder Bed Fusion (PBF), Metal Filament Deposition Modeling (MFDM) and Bound Metal Deposition (BMD) on a specific experimental sample. For this study, a very common and representative automotive part has been chosen that is well suited to be printed in metal and can be manufactured in the three chosen technologies. A nozzle from the automotive body plant used to distribute accuratey a sealant bead onto a body panel before the final assembly operation was selected. These sample parts have been trialed for function and evaluated in general terms from a quality point of view. The conclusions included in this paper will help the automotive industry players understand which technology to use for this specific part and other parts with similar characteristics. Additional work will focus on specific quality characteristics such as material composition, mechanical properties, dimensional accuracy, and specific defects found to compare these technologies in detail. Furthermore, a selection of other automotive parts and technologies will be necessary to enlarge the knowledge on the application of metal AM on this field.

Abstract: Manufacturing effectiveness is highly demanded in the aerospace industry; therefore, hybrid manufacturing technologies have gained considerable attention in order to overcome the limitations of a single manufacturing technology. Actually, the hybridisation of different manufacturing processes consists in taking advantage of the strengths of each process and compensating the weaknesses. In this work, the Laser Directed Energy Deposition (L-DED) process is hybridised with forging. The L-DED is an Additive Manufacturing technology which enables to add material on existing parts in order to add geometrical details or repair damaged areas. Thereby, the flexibility of the L-DED can be combined with the high-productivity and lower cost of the forging. A nickel-based superalloy employed in aeronautical applications is selected, the Inconel 718, which is suitable for high-temperature applications, such as the turbine casing of jet engines. Depending on the manufacturing process and final heat treatment, the Inconel 718 presents different properties. Hence, simulation tools are considered as a key element for the material properties characterization, where digital testing is becoming a fundamental pillar. Thermal and mechanical simulations with FEM enable the evaluation of the complete thermal history of the part and the resulting mechanical behaviour in-service conditions. In this work, the feasibility of hybridising forging and L-DED is studied. For this purpose, the resulting properties of the parts manufactured by each individual process are quantified and the interaction between both processes is analysed. Moreover, a test part is manufactured to show the hybridisation capabilities. Afterwards, to determine the behaviour of such demonstrator, a digital testing is performed by means of finite element modelling. Both thermal and structural analysis are carried out and the results obtained for the hybrid component are compared with those of an entirely forged part, focusing on a critical assessment of the performance of each manufacturing approach.

Abstract: The Laser Directed Energy Deposition (L-DED) is an Additive Manufacturing process based on the direct injection of the filler material into the desired areas of a substrate. Damaged components can be repaired or coated in order to enhance their properties and increase their lifespan. However, this process is highly material dependent and to assure the quality of the deposited material, the process parameters need to be optimised. In the present work, a novel material for the L-DED is developed, the 15CDV6 aeronautical steel. The material was atomized ad hoc and the obtained powder was characterized (particle shape, size distribution, and chemical composition) in order to ensure its quality. Once the powder was analysed, the suitability of the 15CDV6 steel for the L-DED process was studied through a methodology consisting of three sequential steps: single clad tests, layer deposition and wall construction. The main process parameters (laser power, feed rate and powder feed rate) were controlled during these tests. Nevertheless, the initial tests showed high levels of porosity, which required considering additional process parameters to reduce them, such as the carrier and shielding gas flows, preheating, or the laser beam diameter. Consequently, the porosity formation mechanisms were identified and the most relevant process parameters established, which for the 15CDV6 steel were the gas flows. The effect of the shielding gas flow in the powder distribution below the nozzle was studied experimentally by digital image analysis to better interpret the obtained results and determine the optimum process parameters for achieving defect free parts. The quality of the deposited material was studied through metallographic analysis and an Acicular Ferrite structure was observed, ensuring good mechanical properties. To summarise, this research work proves the viability of employing 15CDV6 steel in the L-DED process and has determined the main process parameters to obtain porosity-free parts.

Abstract: Nowadays, tools such as Additive Manufacturing (AM) contribute directly to an increase in the value of Industrial Design through the development of new products focused on customization. Specifically, the acoustic guitar is a good example of this, because it is a complex product to study due to the great variety of possible designs depending on the materials and the way they are obtained, which has repercussions on the final sound of the instrument. Due to the above, this paper develops a methodology for the study of the acoustic response depending on the design of an acoustic guitar using AM with Polylactic Acid (PLA) material. The methodology is divided into two types of tests: an acoustic test to capture the frequencies emitted by transmitting a sweep of frequencies across the audible spectrum to the soundboard, and another to visualize the vibrational patterns at five specific harmonic frequencies of the guitar by analyzing the movement of the soundboard and the influence of the bracing. This second test includes the PLA designed top with a reinforcement structure in its soundboard and a case in order to compare this design with a wooden guitar of the same size whose top has no reinforcement at all. From the tests carried out, it can be seen that the acoustics recorded by a top made of PLA can provide a good acoustic response compared to a wooden guitar, giving the possibility to create customized guitars according to the musician's tastes.

Abstract: Metal powder bed fusion additive manufacturing technologies are increasingly being adopted in industrial applications, but their widespread implementation on an industrial scale is hindered by the high manufacturing cost. This study investigates two strategies to improve the build rate of Ti-6Al-4V alloy processed by powder bed fusion using a laser beam (PBF-LB/Ti6Al4V), which is a critical factor that affects the cost of an additive manufacturing part. The first strategy involves increasing the layer thickness from 30 µm to 60 µm, while the second strategy entails increasing the particle size of the raw material from 25-45 µm to 45-106 µm while maintaining a layer thickness of 60 µm.The experiment involved modifying the process parameters based on the energy density (J/mm2), combining laser powers between 180-470 W, scanning speeds between 600-2611 mm/s, and distance between passes from 0.12 to 0.21 mm. With the highest density level process parameter combinations, a comparative study of manufacturing times for a given geometry showed a productivity improvement of up to 50%. The static mechanical properties of the specimens were evaluated by performing tensile tests. The roughness of the melt was determined for each strategy. The study concludes that modification of process parameters can reduce the build rate of PBF-LB/Ti6Al4V while maintaining its tensile strength and surface roughness.