Search

Aluminum has become increasingly important in the automotive sector due to its ability to reduce vehicle weight without compromising structural performance. However, joining different types of aluminum alloys can be challenging due to their different thermal and mechanical characteristics. Concurrently, friction stir processing (FSP) is a material processing technique that has garnered considerable attention for its versatility and industrial applicability, and it may represent a preliminary phase to correctly perform friction stir welding, which is a welding technology used to join different types of aluminum alloys. In this context, this study presents an extensive experimental campaign of FSP performed on 5754-H111 and 6082-T6 alloys, varying two rolling directions and four welding speeds. The processed materials were characterized, including cupping and tensile tests, microstructure analysis, and a correlation between welding parameters, microstructure, and mechanical resistance. In addition, a numerical method was proposed to simulate the Erichsen tests and predict the formability of the materials, before and after the FSP processes. The results showed that both alloys exhibited good formability after the FSP process, but with different behavior. AA6082 underwent internal decohesion and dynamic recrystallization, resulting in the absence of defects and an increase in ductility and cold formability. AA5754 experiences more difficulty with material flow during FSP and showed the presence of tunnel defects in all analyzed process conditions. However, the alloy 5754 did not undergo softening and had comparable mechanical behavior and cold formability to the base material. These results were validated by the numerical method proposed. [ABSTRACT FROM AUTHOR]

Additive manufacturing has revolutionised the field of manufacturing, allowing for the production of complex geometries with high precision and accuracy. One of the most promising applications of additive manufacturing is in the production of composites, which are materials made by combining two or more substances with different properties to achieve specific functional characteristics. In recent years, the use of Continuous Filament Fabrication (CFF) in additive manufacturing has become increasingly popular due to its ability to produce high-quality composite parts which have fibres with a complex orientation and high curvature. This paper aims to investigate the influence of fill pattern and stacking sequence on the open-hole tensile strength of composites manufactured using CFF and made of an innovative matrix composed of nylon and short carbon fibres, i.e., Onyx, and with continuous carbon fibre as reinforcement. By systematically varying the fill pattern and stacking sequence, we aim to identify the optimal combination that can achieve the highest open-hole tensile strength in these composites. The results of this study will provide valuable insights into the design and manufacture of high-strength composites using additive manufacturing. Open-hole strength and elastic properties are strongly influenced by the infill strategy and stacking sequences adopted, and show different failure modes. The results also point out a technological issue characterising the process and indicate some guidelines for designing and manufacturing 3D printing composites. [ABSTRACT FROM AUTHOR]

In recent years, the overall performances of inertial Micro-Electro Mechanical Sensors (MEMSs) exhibited substantial improvements to values very close or similar to so-called tactical-grade sensors. However, due to their high costs, numerous researchers are currently focusing on the performance enhancement of cheap consumer-grade MEMS inertial sensors for all those applications (as an example, small unmanned aerial vehicles, UAVs), where cost effectiveness is a relevant request; the use of redundancy proves to be a feasible method for this purpose. In this regard, the authors propose, hereinafter, a suitable strategy aimed at fusing raw measurements provided by multiple inertial sensors mounted on a 3D-printed structure. In particular, accelerations and angular rates measured by the sensors are averaged according to weights associated with the results of an Allan variance approach; the lower the noise figure of the sensors, the greater their weight on the final averaged values. On the other hand, possible effects on the measurements due to the use of a 3D structure in reinforced ONYX (a material capable of providing better mechanical specifications for avionic applications with respect to other solutions for additive manufacturing) were evaluated. The performance of a prototype implementing the considered strategy is compared with that of a tactical-grade inertial measurement unit in stationary conditions, exhibiting differences as low as 0.3 degrees in heading measurements. Moreover, the reinforced ONYX structure does not significantly affect the measured values in terms of both thermal and magnetic field while assuring better mechanical characteristics with respect to other 3D printing materials, thanks to a tensile strength of about 250 MPa and a specific stacking sequence of continuous fibers. Finally, a test conducted on an actual UAV highlights performance very close to that of a reference unit, with root-mean-square error in heading measurements as low as 0.3 degrees in observation intervals up to 140 s. [ABSTRACT FROM AUTHOR]

In this work, three cooling strategies were proposed to increase the cooling rate and avoid extensive exposure to higher temperatures during the manufacturing of components in Inconel 625 using wire arc additive manufacturing (WAAM): forced cooling with compressed dry air jet, interpass idle time and the combination of both strategies. These strategies were compared for two welding technologies within gas metal arc welding (GMAW) process: pulsed and cold metal transfer (CMT). The results show that deposition using the GMAW-CMT welding mode showed better quality and uniformity than the GMAW-pulsed mode. The tested interpass idle time did not cause a significant effect on the mechanical properties, while the forced cooling using an air jet slightly improved the properties and may be used to increase productivity, especially for larger components. [ABSTRACT FROM AUTHOR]

Among the several additive manufacturing techniques, fused filament fabrication (FFF) is a 3D printing technique that is fast, handy, and low cost, used to produce complex-shaped parts easily and quickly. FFF adds material layer by layer, saving energy, costs, raw material costs, and waste. Nevertheless, the mechanical properties of the thermoplastic materials involved are low compared to traditional engineering materials. This paper deals with the manufacturing of composite material laminates obtained by the Markforged continuous filament fabrication (CFF) technique, using an innovative matrix infilled by carbon nanofibre (Onyx), a high-strength thermoplastic material with an excellent surface finish and high resistance to chemical agents. Three macro-categories of samples were manufactured using Onyx and continuous carbon fibre to evaluate the effect of the fibre on mechanical features of the novel composites and their influence on surface finishes. SEM (Scanning Electron Microscopy) analysis and acquisition of roughness profile by a confocal lens were conducted. Tensile and compression tests, thermogravimetric analysis and calorimetric analysis using a DSC (differential scanning calorimeter) were carried out on all specimen types to evaluate the influence of the process parameters and layup configurations on the quality and mechanical behaviour of the 3D-printed samples. [ABSTRACT FROM AUTHOR]

This paper investigates the dissimilar friction stir lap welding of AA2198 and AA7075 sheets. The influence of processing parameters, namely welding speed and tool rotational speed on joint features, microstructure, and mechanical properties were studied by implementing a full factorial design of experiments. Axial and transversal forces were continuously measured during the welding process using a sensed fixture aiming at the correlation of processing parameters, forces, and quality of the achieved joints. Obtained outcomes showed hook formation for all the combination of parameters and the existence of a very narrow processing window in which it is possible to avoid the formation of internal defects, such as grooves and tunnels. The influence of the weld bead morphology on the lap shear strength was elucidated proving that the strength is ruled by the hook morphology. The microstructure of the joints was studied and discussed considering also the microhardness distribution. [ABSTRACT FROM AUTHOR]

This work deals with the investigation and characterization of Ti6Al4V parts produced with an intriguing manufacturing process belonging to the Wire Arc Additive Manufacturing (WAAM) family: the Cold Metal Transfer technology (CMT). Wall‐shaped parts were produced according to different process parameters, namely the wire feed speed and voltage–current combinations, leading to different energy inputs. The parts were characterized in terms of surface morphology, microhardness, microstructure, tensile properties, and fatigue crack growth. The results suggested that the investigated deposition parameters led to similar results. Moreover, the mechanical and fatigue crack growth behavior was in line with parts of the same alloy produced through other manufacturing routes, whereas the microstructure type was the result of the fast cooling of the molten material. Finally, considering the simple system adopted to avoid oxidation during the deposition stage, the results suggested that CMT is a promising manufacturing technique for titanium alloy semifinished parts. Highlights: Wall‐like parts made of Ti6Al4V alloy were produced through WAAM‐CMT technologySound parts with minimum oxidation were produced through a simple enveloping systemThe parts had properties similar to those of more traditional manufacturing routesThe microstructure, tensile, and fatigue crack growth behavior were quite isotropic [ABSTRACT FROM AUTHOR]

Additive manufacturing is an advanced technology able to produce parts with different grades of complexity, including its shape, microstructure, functionality and material. Regarding material complexity nowadays, it is possible to produce polymer parts with customized reinforced fibre filling such as carbon, Kevlar or glass. However, their mechanical behaviour is still under investigation and no data are available on the bearing strength for additively manufactured composites. The aim of this work is to provide a contribution on this topic to ensure safe joint design with the current and innovative technologies. In this article the authors present the experimental characterization of polymer filled with Kevlar to pin bearing test. Samples have been designed as a function of filling and geometry parameters. Results have been analysed with statistical methods. Finding highlight similar and different behaviour regarding samples produced with conventional process. The most interesting result is that the authors demonstrate how the pin diameter is significant for the results, particularly for the stiffness keeping constant the bearing strength. [ABSTRACT FROM AUTHOR]

Chromium carbides are widely used as functional coatings on steel structures in high-end applications, from energy to marine and aerospace sectors thanks to their corrosion and wear resistance at elevated temperatures. In the present work, a low-power compact plasma spray (CPS) equipment was used to deposit Cr 3 C 2 -based cermet coatings on carbon steel substrate. Design of experiment was applied to select and optimize the spraying parameters, namely current, stand-off distance, scanning speed, plasma gas rate and powder feeding rate. ANOVA analysis was conducted to estimate the effect of the spraying variables on morphology and mechanical properties of the coatings and evaluate the optimal spraying condition. Dense and compact coatings were fabricated by using the CPS. By optimizing the processing parameters, coating hardness equal to approximately 600 HV and average thickness ranging around 600 μm were obtained, while the adhesion strength was approximately equal to 14 MPa. Intermediate phases of Cr carbides were produced by the dissolution of the primary Cr 3 C 2 induced by melting and re-solidification of the particles. The presence of weaker carbide phase, inter-lamellae different features and porosity also caused the scattered hardness values observed in the coatings. • Low power compact plasma spray technique demonstrated to produce sound chromium carbide-based cermet coatings. • The properties of the Cr 3 C 2 -NiCr coating are mainly influenced by current, stand-off distance and plasma flow rate. • Coating adherence and hardness obtained under optimal configuration meet the requirements for applications in CSP plants. • The inflight dissolution of Cr 3 C 2 and the related porosity led to a decrease in the mechanical properties of the coatings. [ABSTRACT FROM AUTHOR]

This study investigates the potential of Fluidized Bed Finishing (FBF) of square flat AlSi10Mg specimens manufactured via Laser-Powder Bed Fusion (L-PBF) additive manufacturing technology. Two FBF operational modes were experimentally investigated: I) with stationary specimens; II) with specimens under controlled rotational motion. Four different abrasive materials have been tested, quartz sand, corundum, irregular steel and cut wire steel particles, characterized by different hardness, density and shape. The effect of the abrasive material, processing time and specimen tilt angle was investigated. Results showed moderate smoothing under stationary specimen configuration, while good finishing for rotation-assisted tests, maximum reduction of the surface roughness of 12% and 67%, respectively. Steel particles were the most effective bed material, with particle density overtaking hardness as key particle property. The optimal tilt angle was the one that maximized sliding and shear. Altogether, surface finishing is driven by surface shear forces dominated by inertial stresses in particulate phase. [Display omitted] • Fluidized Bed Finishing (FBF) of specimens made by additive manufacturing is investigated. • Rotation-assisted FBF is more efficient than stationary FBF. • Particle density is the key to the abrasive potential of powders in FBF conditions. • Plain shear flow of abrasives close to the specimen maximizes the surface finishing. • The finishing mechanism is associated with particle removal and plastic deformation. [ABSTRACT FROM AUTHOR]