Key Engineering Materials Vol. 956

Abstract: Fused Material Deposition Modelling (FDM) is one of the most extensive 3D printing processes. However, its integration and application to structural parts remain limited to some extent, due to the polymeric materials that can be processed, generally PLA and ABS. FDM printing involves a large number of manufacturing parameters, which can also influence the mechanical properties of the final part. Although the static mechanical properties of FDM components are well documented, the dynamic mechanical properties are not yet fully analyzed. Similarly, in the field of composite materials, reinforced thermoplastics are increasingly used in structural load-bearing applications due to its high specific strength and ease of processing. Therefore, it is necessary to focus on the reinforcement influence on the mechanical behavior of printed parts. The fatigue response of these materials is strongly influenced by the anisotropy of the properties, due to the orientation and composition of the reinforcement. It should be noted that, despite the fact that short-fiber or particle-reinforced polymers generally fail in a macroscopically brittle manner, the underlying failure mechanisms are, nevertheless, not due to crack growth. Difficulty in correctly identifying underlying failure mechanisms, during material characterization, can lead to erroneous conclusions in service life predictions. Consequently, present work focuses on the reinforcement influence analysis on the fatigue behavior with PLA-based parts manufactured by FDM, showing how the fatigue behavior life worsen with short fiber and particle reinforcement.

Abstract: Digital manufacturing is one of the pillars of Industry 4.0, additive manufacturing is certainly evolving very quickly, with more and more technologies being developed and materials being applied to this production area. However, with this growth and the capacity associated with this type of processes, it is extremely important to understand these processes, so that they can respond quantitatively and qualitatively to market needs. The present work intended to contribute to the improvement of the metal binder jetting process by simulating the manufacturing process of a proposed part, using the Simufact™ software and Desktop Metal software. After validating the parts with manufacturing with Binder jetting additive process. Subsequently, the metrological inspection and analysis of the respective results were carried out. Simulations were carried out for different values of powder size and density of the green part to assess their impact on the quality of the final part. The parts were produced in 17 – 4PH steel using a Shop System Desktop Metal machine. Were produced 5 parts with the following parameters, part (A) model with compensation obtained by Desktop software, part (B) model compensated by the Simufact additive software with 20% scale, part (C) model with scale 1: 1.2, part (D) model obtained by the Simufact additive software and part (E) model without scale. The measurements for the dimensional analysis were made with a digital caliper, while for the geometric analysis, measurements were made on a CMM machine.The simulations revealed smaller errors for larger granule sizes and also for larger green part densities. The inspection of the produced part, on the other side, exposed greater dimensional inaccuracy in X and less in Z direction. It also showed that, for the same element of the part, there is still a relationship between the ratio of the measured dimensions and the ratio of the deviations obtained. The results also showed that parts simulated by two software’s (A and D) are the ones with the best final quality, they presented smaller dimensional and geometric deviations in relation to the proposed model. The highest tolerance grades of these parts were in ISO standard IT15 and IT14 for part D and part A respectively.

Abstract: Additive manufacturing is considered an important alternative way for the fabrication of high quality polymer parts for various applications. Especially, Acrylonitrile styrene acrylate (ASA) is a promising thermoplastic polymer, exhibiting favorable mechanical properties and is also resistant to environmental conditions and various chemical substances. Given that it is possible to process this material through Fused Filament Fabrication (FFF) technology, it is required that optimal conditions are determined based on various criteria. Especially, as manufactured parts are expected to withstand various types of loads, the fabrication process should ensure adequate mechanical behavior under different conditions. For that reason, it is important both to determine the appropriate printing settings and investigate the mechanical behavior of additively manufactured ASA parts. In the present study, compression tests are conducted and statistical analysis is performed on the obtained results, in order to determine the mechanical properties of ASA parts with different infill densities for two different infill patterns. The results indicated that the reduced mechanical properties, in respect to the infill density are inversely correlated with the infill density and that honeycomb infill pattern is superior to gyroid in every case for the same infill density.

Abstract: 3D printing is emerging in the healthcare field. Being able to reproduce organ models with low-cost and sustainable technology is generating a big impact on professionals working in the medical industry. This work aims to illustrate the potential of the material extrusion technique by replicating 3D models used for helping surgeons in pre-operative planning. The properties of a standard thermoplastic PLA for 3D printing are compared with other thermoplastics with elastomeric properties whose application is arising nowadays in this field, namely PEBA, TPO, and TPU. This research covers three real cases of study: a pulmonary fistula, a bone tumor, and a replication of the spinal column. The cases helped anticipate potential problems during surgery and achieve good quality in educating and training new professionals. Finally, an optimal printing configuration is presented. The settings of the printing parameters selected are the ones that maximize the inter and intra-layer bonding, which is important to achieve good shape results and consistency of the models. Although the printed parts are not meant to support a big mechanical effort, it is important to relate the selection of the printing parameters to the adhesion of filaments in order to reduce the quantity of material deposited during the manufacturing process, and consequently, reduce the printing time. Also, to achieve a realistic model that can be of effective help for the medical faculty when preparing their interventions and during their diagnostic process.

Abstract: This paper investigates the machinability of Selective Laser Melted 17-4 Precipitation Hardening Stainless Steel (17-4 PH SS). For this purpose, turning tests were carried out on wrought and SLM specimens and the results were compared. Wear tool, surface roughness, surface integrity and chip morphology were analyzed for both materials. For the tested cutting conditions, the machinability of the SLM material was inferior to that of the commercial material. Dissimilarities in machinability between both materials are a consequence of variations in their microstructures resulting from the manufacturing process.

Abstract: The design flexibility of Additive manufacturing (AM) processes combined with optimal structure selection has greatly expanded the research for lattice like structures. The development of elastic materials such as Thermoplastic polyurethane (TPU) was enhanced by the existence of compatible additive technologies, which resulted in the interest in the inclusion of this material in all types of product and industrial applications. Several studies established the critical role in the influence on the performance of elastic structures powered by changes in geometrical and manufacturing parameters. These findings enhanced the possibility of designing lattice like structures with different performances in order to be implemented in several applications with specific elastic needs. Therefore, the objective of this work focused on the characterization of closed-wall lattice structures through the analysis of the performance as a function of the design parameters and material used. In this way, several lattice structures were manufactured and tested. The results showed a correlation between the geometric variables and specimen’s stiffness. A substantial variation of the stiffness as a function of the thickness of the unit cell and the height of the layer was found. Same stiffness values can be achieved using different materials and geometric parameters. Similar stiffness values using recycled materials obtained favorable results.

Abstract: Laser metal deposition (LMD) industrial use demands research about the influence of the parameters in the built parts density, accuracy and mechanical properties. Especially for the thin-wall parts, knowledge about the correlations between processing parameters and the final result is indispensable. This study explores the relationship between process parameters and the quality of AISI316L stainless steel thin-walled parts produced by LMD. A six-axis robot equipped with a deposition head allowed relative spatial movement between the powder nozzle and laser beam and substrate with high accuracy. Controlled energy input provided by continuous wave Ytterbium fibre laser allows using less material flow rate and the production of thin layers in test samples. Three processing parameters were selected to investigate the effects on part characteristics using a Box-Behnken experimental design. Through this method, each parameter was evaluated between 600 W to 800 W laser power, 6 mm/s to 14 mm/s feedrate and 0.2 mm to 0.4 mm layer thickness. All remaining parameters were fixed using argon to provide an inert atmosphere, 8.8 g/min powder feeding rate and 1.5 mm spot diameter. The method was used to test the manufacture of thin-wall cylindrical specimens with 10 mm in height and 75 mm in diameter. Fabricated AISI316L samples were evaluated regarding the dimensional and geometrical characteristics. It was observed that higher energy input density during the laser additive manufacturing implies lower geometric precision. Feedrate and layer thickness has the highest impact on both the wall thickness and vertical accuracy. Given the inability to produce parts with an acceptable final surface, the process finds great applicability when complemented with additional finishing technologies.

Abstract: The use of additive manufacturing by fused deposition is a versatile, cost-effective and simple prototyping and manufacturing technique that is generating and accelerating a revolution in equipment and filaments. However, materials are limited to a small number of polymers. It is a scientific challenge to bring new characteristics and properties to the parts obtained. In this work, a new filament has been designed with the combination of PLA (poly lactic acid) as matrix and PTFE (polytetrafluoroethylene) as filler. This filament has improved the water repellency of the parts obtained. Cleaning, demoulding, anti-adherence, anti-frost, anti-humidity and anti-bacterial applications can be deployed with this new filament. Extruded filaments have been obtained with PLA beads and PTFE micropowder. Flat test tubes have been produced with this filament. The experiments included PTFE fillers (1% to 40% by weight). The surfaces have been characterised by sliding angle (SA) and static contact angle (CA) tests, surface roughness (Sa and Sz), flatness error and % water adsorption. The results indicate, as expected, that the higher the fluoropolymer content, the higher the hydrophobicity, reaching values of 125° for CA and 9° for SA, and the % adsorption decreases. In terms of roughness, the surfaces are less rough when the PTFE load increases. On the other hand, the flatness is a property strongly affected by the % PTFE load and at values higher than 15% it produces intense warping and deformation of the specimens. Finally, the PTFE loading thresholds in the PLA matrix have been obtained below which the wettability and dimensional reproduction properties are balanced and optimal.

Abstract: The 3D printing technology is being applied more and more every day, this is a consequence of its applicability and low waste generation, becoming one of the best options to obtain good quality pieces. Sometimes, post machining processes are necessary to fulfil tight tolerances or achieve complex geometries by means of the connection between different pieces printed using this technology. The field of knowledge and studies focused on 3D printing is in constant evolution. There are plenty of materials that can be used to apply 3D printing technology. Among them, PEEK is one of the best options when good mechanical properties are required. Being applied in aeronautic or automobile industry, is also used in biomedical applications, such as prosthesis or mechanical components among others. Within the machining processes, milling, turning, and drilling are the most widespread. Orthogonal cutting is a machining process in which the cutting edge of the tool is perpendicular to the cutting speed, and it is commonly used when a simple and pure study of the mechanism behind a material removal process is required. In this study, tests that analyze the orthogonal cutting on 3D printed PEEK samples using different orientations (0o and ±45o) have been conducted. The influence of cutting speed (30, 60 and 90 m/min) and depth of cut (50, 100 and 150 μm) is studied through the analysis of cutting forces and surface finish quality. As a general approximation, it can be seen that the fiber orientation affects significantly to the forces monitored but unexpectedly, lightly to the surface finish.

Abstract: Metal Additive Manufacturing (AM) has been established as one of the most promising solutions when producing new components due to its advantages in creating complex geometries and adding new functionality to the parts. An example of the last, is the usage of conformal cooling in the tooling industry to improve the thermal behaviour of components in-service. The application of this solution is even more meaningful when using metallic materials with high thermal conductivities (e.g. Aluminium alloys). These are mainly selected when the final weight is a key factor in the final component performance, compared with other conductive materials like copper alloys. This study presents the improvement of the thermal behaviour of a drilling tool case manufactured in Aluminium. The selected application case lacks the possibility of evacuating the heat produced by an engine. A redesign of the component is presented, considering the advantages of Powder Bed Fusion – Laser/Metal (PBF-L/M). Both passive and active heat dissipation are analysed by including the reticular structure and internal cavities with forced air. The study is performed first at coupon level and later in the redesigned case manufactured by PBF-L/M. Infrared Thermography (IRT) inspections are conducted to investigate the thermal dissipation when heating the components, and also to monitor the cooling down process. A comparative thermal analysis between the initial case manufactured by the conventional process and the redesigned AM case is also presented.