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Poor fatigue life is a huge issue of additively manufactured parts, despite the unique qualities characterizing this manufacturing process (such as low waste of material and geometry freedom). Fatigue life is strongly affected by both surface defects and internal defects, metal AM is characterized by extremely poor surface quality, internal porosities and lack of fusions. For this reason, many researchers investigated methods to improve manufacts quality. The most promising methods are surface finishing treatments and thermal treatments which provide an enhancement of fatigue behavior. A focal point of the research should be evaluating the respective contribution of surface treatments and thermal treatments. In order to evaluate the effectiveness of surface treatment, it is necessary to highlight the surface quality contribution in terms of fatigue life thus a specific testing method is necessary. Rotating beam fatigue test fits this requirement because each point of the specimen’s surface is subjected to the maximum stress. The aim of this work is to present the experimental setup for rotating beam fatigue testing that has been used to evaluate the fatigue behavior of AM SLM IN718 specimens.

Fluidized bed surface finishing of objects made by additive manufacturing technology has been investigated. Surface roughness is a crucial parameter for parts made with additive manufacturing technology, since it affects the dimensional accuracy and mechanical, tribological and corrosion resistance. Fluidized Bed Machining can be a suitable method for finishing parts with high geometrical complexity due to the high particles mobility. In this study, an experimental campaign has been carried out in a lab-scale fluidized bed apparatus with Aluminium alloy samples made by selective laser melting technology. Surface finishing has been evaluated in terms of wear and roughness under bubbling fluidization conditions while varying the sample orientation. Furthermore, the main mechanisms of particle removal are under investigation. In particular, inertial and frictional mechanisms are considered for the surface finishing process of metal parts in fluidized bed. Results show that the sample orientation affects the wear rate and the resulting roughness. Furthermore, energy dissipation models could be able to describe the finishing process of metal parts in fluidized beds.

The main goal of the proposed paper is the numerical and experimental investigation of multiple winglets influence on the reduction of induced drag. This results in the improvement of climbing performances of a motorglider or hang-glider. In a precedent work [1] a set of multiple winglets, very similar to the bird tip feathers called remiges, were designed and optimized for the hang-glider belonging to Angelo D’Arrigo, a world champion hang-glider pilot and record holder. The research aims was to optimize the CL1,5/CD parameter since this is directly proportional to the sink rate. In this work the effects of the multiple winglets, set on an elliptical wing and tested in a wind tunnel, are compared to the effects of three different single ‘classical’ winglets that were designed using a panel method code and were also tested in the same wind tunnel in order to compare their span efficiency to the one of the multiple winglets.

Friction Stir Welding (FSW) is one of the most used solid-state welding processes in the aeronautical, aerospace, ground transportation and naval fields. Stationary Shoulder Friction Stir Welding (SSFSW) is a recently introduced variant of the process allowing lower heat input into the joints, with beneficial effects in terms of joint mechanical properties, microstructure and top surface finish. In the paper, lap joints produced by SSFSW and made out of AA6082-T6 aluminum alloy sheets have been analyzed with the aim to investigate the effect of the stationary shoulder on the lap joints surface, metallurgical, and mechanical properties. The lap joints produced by SSFSW have been compared to the ones produced by “conventional” FSW in order to highlight the differences between the two processes. The top surface of the joints obtained with the two processes has been quantitatively evaluated. Finally, a dedicated numerical model has been utilized to highlight the causes of the observed differences through the distributions of the main field variables, namely temperature, strain and strain rate. It was found that SSFSW results in narrower weld nugget and smaller areas involved by micro hardness reduction caused by smaller peak temperature and high temperature zone. Additionally, better surface quality was found for the joint welded by SSFSW with lower heights and flash, allowing to avoid subsequent finishing operations needed for most industrial applications.

The in-situ contour strategy during Laser-Powder Bed Fusion (L-PBF) process remains one of the most promising solutions to improve the poor surface quality of the parts. On the other hand, it is well established that contour step affects the formation of sub-surface defects. The aim of this work is to assess the entity of sub-surface defects during the Laser-Powder Bed Fusion of Inconel 718 samples for which different contour processing conditions are considered. Cubic samples with 10 mm side were produced through L-PBF using a Concept Laser Cusing M2 L-PBF machine. The samples were printed with fixed bulk laser parameters, adopting a layer thickness of 30 μm and a chessboard laser scanning strategy. The in-situ contour conditions were changed in terms of laser scanning speed and hatch zone border. Afterwards, the samples were analyzed in terms of surface roughness (Sa) and sub-surface density through confocal microscopy. The results revealed that the surface roughness was the most affected output as a function of the varied process parameters, including the sample position on the building platform, with values ranging from 13 to 32 μm. On the other hand, the sub-surface density was always higher than 99%.

Ti-6Al-4V alloy is characterised by having excellent mechanical properties and corrosion resistance combined with low specific weight and biocompatibility. This material is ideal for many high-performance engineering applications. It is increasingly used in additive manufacturing (AM) thanks to the possibility of producing very complex lightweight structures, often not achievable with conventional manufacturing techniques, as well as to easily customise products according to specific customer requirements. In powder bed fusion (PBF) processes, only a small percentage of the powder is actually melted and solidified to achieve the final part while most is left after the build. Since the surface morphology and chemistry, the shape and size distribution of the un-melted particles are inevitably modified during the process, and this may affect the resulting properties of the final products, many companies tend to use virgin powders for AM builds to keep compliance with manufacturing requirements and minimise risk. From both an economic and environmental point of view, it results crucial to develop recycling methods to reuse the metal powder as many times as possible while maintaining compliance with manufacturing standards. In this work, the effect of Ti-6Al-4V powder reuse on the evolution of powder characteristics and mechanical properties of final products additively manufactured is investigated through a systematic approach based on design of experiments.

Nimonic 75 sheets were cold-spun under different processing conditions and then heat-treated. The microstructure evolutions occurring during the process were studied and discussed in details. The results obtained showed the feasibility of the process when adopting low values of the tool feed rate. Metal spinning produces a deformed microstructure, different in the several areas of interest of the final component. The chosen heat treatment promoted the annealing of the material across the whole part.

Self-healing coatings that are able to self-repair after being damaged represent an effective solution to provide a reliable and long-lasting protection of the underlying substrate. In this work, we developed self-healing waterborne polyurethane (PU) coatings through the introduction of Diels-Alder bonds in the polymer backbone. Although heat is typically used as trigger, here we exploited photothermal converters to allow also NIR light-induced self-healing. To this aim, we synthesized (3-aminopropyl)-triethoxysilane-modified graphene oxide nanosheets that were subsequently coated by nanometric polydopamine particles, which serve for imparting to the coating the NIR-responsive self-healing feature. Fourier transform infrared and X-ray photoelectron spectroscopy confirmed the successful synthesis of PDA-coated reduced graphene oxide nanoparticles, which were thus exploited to prepare nanocomposite PU coatings on bronze substrates on which they exhibited good adhesion. Once scratched, fast and effective self-healing was ensured upon irradiation with NIR light for only 30 s. In addition, electrochemical impedance spectroscopy analyses proved that the nanocomposite coatings exhibited improved barrier properties which resulted in an enhanced protection of the underlying metal from corrosion.

Organic coatings are extensively investigated as possible solution to prevent or at least retard the occurring of corrosion processes on metal surfaces. Their actual breakthrough is still hampered by the risk of barrier properties loss because of local failure of the coating integrity. To address this issue, self-healing coatings, which are intrinsically able to recover from damages upon exposure to external stimuli, are currently gaining increasing attention. Herein, waterborne polyurethanes (PU) are synthesized, and a Diels-Alder adduct is added into the polymeric backbone to endow the material with self-healing functionality. The effect of different diisocyanate in PU synthesis is explored, namely isophorone diisocyanate, 4,4 '-dicyclohexylmethane diisocyanate (HMDI), and hexamethylene diisocyanate. The obtained results highlight the key role of the interactions among soft and hard segments in ultimately defining the coating performances. Actually, the combination of Fourier transform infrared spectroscopy, atomic force microscopy and X-ray diffration analysis reveals that the HMDI-based PU have showed the best balance in terms of H-bonding strength among hard segments and crystallinity degree in the soft ones. This allows to reach a good compromise in terms of mechanical resistance, anticorrosion properties, and self-healing ability.

One of the most critical issues of a component realized by Additive Manufacturing is the surface quality. In particular, in case of high levels of roughness, the functionality of the component and its mechanical properties are significantly affected. Chemical finishing offers the advantage of acting on the whole surface, without the need of tools. In this preliminary work several specimen of AlSi10Mg have been treated firstly by Chemical Machining to remove the gross irregularities, followed by Chemical Brightening to further smooth the surface. The results are promising; the surface parameters analyzed indicate that the treatment improves the surface quality. © 2018 Society of Manufacturing Engineers (SME)

Poor surface quality represents one of the most critical drawbacks of metal parts produced by powder bed-based Additive Manufacturing (AM) technologies, such as Selective Laser Melting (SLM) and Electron Beam Melting (EBM). Among the several post-process surface finishing treatments, Fluidised Bed Machining (FBM) could represent an intriguing and cost effective option for the treatment of complex AM metal parts. This work illustrates the results of the preliminary tests carried out by means of the FBM technology in which an external contribution of rotational speed of the samples was introduced. Rotation of the samples was considered in order to increase the relative speed and energy dissipation between the parts and the fluidised abrasive particles, with the aim to increase the process efficiency in terms of surface roughness reduction. For the experiments, AlSi10Mg alloy square flat samples were built in vertical direction by means of SLM technology and dipped into an abrasive fluidized bed of silica sand. The preliminary tests were carried out by adopting a minimum fluidization regime of the abrasives and establishing, through the rotation of the samples, two values of mean superficial tangential speed of 1 m/s and 2 m/s. The effect of the latter was investigated in combination with different impact angles, considering a process time of 30 min. The surfaces were characterized quantitatively by means of confocal microscopy and weight loss measurements, while SEM images were acquired in order to observe the real morphology evolution after the treatment. The experimental results suggested a slight surface modification and roughness reduction for the investigated FBM process conditions, due to a low energy transfer from the abrasives to the surfaces. On the other hand, the results shown also that a greater surface smoothing effect was achieved when increasing the tangential speed and adopting low impact angles.

Electron Beam Melting is an Additive Manufacturing technology that allows the production of items using metal powder as raw material. The main advantage of Additive Manufacturing (AM) is realizing complex shape components; however one of the main defects is the poor quality of the surface. To this aim, different post processing treatments have been proposed such as machining, surface laser melting, sand blasting, etc. The main drawback of these technologies is the necessity to use tools that makes complex shape item difficult to handle. This inconvenient does not occur in chemical machining, since a chemical solution can operate in an undifferentiated way on the whole surface of a component. In this work some components in Ti6Al4V obtained through AM have been treated in acidic solutions containing HF and HNO3 with different HF/HNO3 molar ratio. All the solutions employed have proven to be effective in smoothing the metal surface, but the best results have been obtained with solutions with high content of HNO3. It should be noted that the process causes changes in the surface composition with respect to the received samples with an impoverishment of Al. This effect is partially mitigated by the passivating action of HNO3.

Poor surface quality represents an important issue that needs improvement for metal Additively Manufactured parts. Both short or long wavelength lasers have been applied for surface polishing in order to improve the surface finish. In this work, the possible use of a CO2 laser for the surface polishing of AlSi10Mg parts made by Laser-based Powder Bed Fusion (L-PBF) was explored. The high surface roughness in the as-built condition can lead to increased laser energy absorption. In order to assess the effects of the main laser-related process parameters, the experiments were carried out on L-PBF samples built vertically with respect to the build platform. Their effect on the surface were evaluated by means of the surface arithmetical mean height (Sa), surface skewness (Ssk) and primary profile root mean square slope (Pdq), obtained via confocal microscopy. Microstructure evolution was also investigated by means of SEM and EDS analysis. The results showed a large reduction in surface roughness, ranging from the 67% to the 85% of the starting value. Microstructure of the re-molten layer revealed an increased grain size and an increased Si content that led to an overall hardness increase from 85 to 121 HV.

Background: Hardness is considered an important parameter for evaluating the clinical performance of dental implant bone drills. It is connected to the chemical composition, microstructure conformation and manufacture of the surgical drills. Methods: Microstructure of five dental implant drills using scanning electronic microscopy (SEM) integrated with energy dispersive X-ray spectrometry. Vickers microhardness was measured using a CV 2000 microhardness tester with an indentation force of 500 g. Results: Composition of the implant drills was typical of martensitic stainless steel (MSS). The drills contained 13%&ndash, 17% of Cr, Mo, Si and Mn were present as minor ligands. The examined bone drills showed different external surface conformation and hardness in relation to the different industrial production processes. A rougher external surface and a higher hardness value are characteristics of the surgical bone drills produced by hot forming, the implant drills produced by machining showed mailing lines on their external surface and a lower hardness. Conclusions: Different compositions and treatments were used by the manufacturers to improve the hardness of the external layer of the dental implant drills making them prone to a diverse heat generation during the implant site preparation.

Additive Manufacturing (AM) can be considered today as a real production technology, which allows to realize parts with a complexity degree that, in some cases, is not achievable otherwise. However, one of the most relevant weak spots is the high surface roughness, especially for metal parts, making necessary the adoption of post-process finishing treatments. This paper deals with the preliminary investigations on the Fluidised Bed Machining (FBM) technology, in which a sample is dipped into a fluidized bed, i.e. a two-phase system where an abrasive, kept in motion through a gas, behaves like a fluid performing a huge number of impacts on the considered surface. This peculiarity could guarantee a high degree of homogeneity of the treated surface morphology. The influence of the impact angle has been investigated by conducting experiments with AlSi10Mg plates made by Selective Laser Melting Technology (SLM), and the fluidized bed operated in bubbling fluidization regime. The treatment has been carried out by dipping the samples for a total time of 3 hours and monitoring the results with a step of 30 min for the first 2 hours. The treated surfaces have been characterized by means of Confocal Microscopy and Scanning Electron Microscopy (SEM). Weight loss measurements have been carried out as well for a preliminary evaluation of wear. Results suggest a poor decrease in surface roughness (Sa), as also demonstrated by the poor weight loss, both due to a low impact energy of the abrasives. However, variations of other surface texture parameters (Sz, Ssk, Sku, Rdq), as well as SEM images, suggest that the main surface-abrasive flow interaction phenomena are micro-ploughing and micro-peening.Additive Manufacturing (AM) can be considered today as a real production technology, which allows to realize parts with a complexity degree that, in some cases, is not achievable otherwise. However, one of the most relevant weak spots is the high surface roughness, especially for metal parts, making necessary the adoption of post-process finishing treatments. This paper deals with the preliminary investigations on the Fluidised Bed Machining (FBM) technology, in which a sample is dipped into a fluidized bed, i.e. a two-phase system where an abrasive, kept in motion through a gas, behaves like a fluid performing a huge number of impacts on the considered surface. This peculiarity could guarantee a high degree of homogeneity of the treated surface morphology. The influence of the impact angle has been investigated by conducting experiments with AlSi10Mg plates made by Selective Laser Melting Technology (SLM), and the fluidized bed operated in bubbling fluidization regime. The treatment has been carried out ...

The effects of different heat treatments on Inconel 718 parts produced through selective laser melting were investigated. Different heat treatments, carried out by varying both temperature and time, were performed on 10x10x10 mm3 cubes. Aiming to study the effects of the treatments, microhardness measurements, optical and SEM observations were carried out on both the treated and the untreated samples. The results obtained proved the effectiveness of the treatment, if the conditions are properly set, in producing the typical microstructure of the cast Inconel 718 that is the starting point for the conventional heat treatments. A predominant influence of the temperature was also highlighted.The effects of different heat treatments on Inconel 718 parts produced through selective laser melting were investigated. Different heat treatments, carried out by varying both temperature and time, were performed on 10x10x10 mm3 cubes. Aiming to study the effects of the treatments, microhardness measurements, optical and SEM observations were carried out on both the treated and the untreated samples. The results obtained proved the effectiveness of the treatment, if the conditions are properly set, in producing the typical microstructure of the cast Inconel 718 that is the starting point for the conventional heat treatments. A predominant influence of the temperature was also highlighted.

Conventional and cooling assisted friction stir welded Al–Mg joints were investigated by visual inspection, optical macro plus microscopy, scanning electron micrographs, energy dispersive X-ray spectroscopy, X-ray diffractions, tensile testing and micro hardness indentation. The nugget zone is characterized by onion rings composed of different phases such as Mg in an Al matrix, Al in an Mg matrix as well as intermetallic compounds, Al 3 Mg 2 and Al 12 Mg 17 . A diffusion layer was detected on the Al side of the joint between the nugget and thermo-mechanically affected zones identifying a solid solution of Mg in Al. No diffusion layer was observed on the Mg side. The tensile strength of the dissimilar joints is enhanced by cooling assisted welding process due to the reduction in the amount of intermetallic compounds inside the weld bead. Congruently, higher hardness peaks are reported in the nugget zone of conventional FSW joint with respect to the CFSW joint. © 2019 Elsevier B.V.

Metal spinning is one of the oldest sheet metal forming processes, which involves a simple tooling and a spinning lathe, whatever manual or computer numerical controlled. However, for its high flexibility and the possibility to produce thin wall sectioned near net shape parts in a very cheap way, sometimes with high complexity geometries, could be revived as an interesting alternative in many applications fields such as automotive and aerospace, whereas other sheet forming processes like deep drawing does not match costs requirements for little dimension production batches. In this work, the production of a flame tube head sector prototype using an AISI 304L stainless steel is proposed, in order to evaluate the process feasibility for the required part geometry. The prototype production was carried out using a two-stage semiautomatic spinning process, starting from a 1mm thick sheet. No preheating of the sheet was adopted to enhance its ductility. The process effects in terms of wall thickness reduction, and hence in cold working, were investigated. Using optical microscopy and Scanning Electron Microscopy (SEM) techniques, the microstructural behavior of the metal subjected to the forming process was investigated, while for an evaluation of the hardness variation Vickers micro-indentation tests were performed. The main result of the process, as observed from all the investigation techniques adopted, is the formation of strain induced martensite, due to the severe plastic deformation and cold reduction of the material, ranging in this case from 30% to 50%. In some areas of the part section, some rips indicating an excessive tensile stress were also detected.