Selective Laser Melting (SLM) is an Additive Manufacturing process (AM) that built parts from powder using a layer-by-layer deposition technique. The control of the parameters that influence the ...melting and the amount of energy density involved in the process is paramount in order to get valuable parts. The objective of this paper is to perform an experimental investigation and a successive statistical optimization of the parameters of the selective laser melting process of the 18Ni300 maraging steel. The experimental investigation involved the study of the microstructure, the mechanical and surface properties of the laser maraging powder. The outcomes of experimental study demonstrated that the hardness, the mechanical strength and the surface roughness correlated positively to the part density. Parts with relative density higher than 99% had a very low porosity that presented closed and regular shaped pores. The statistical optimization determined that the best part properties were produced with the laser power bigger than 90W and the velocity smaller than 220mm/s.
•The analysis of microstructure has been corrected.•The build pattern was explained.•A paragraph on the hardness was added.
Statistical based experimental analysis techniques are particularly useful in the engineering world for improving the understanding of the manufacturing processes and the development of new ones. In ...this paper the innovative arc-laser welding process (hybrid welding) is investigated by means of a regression model and a full factorial experiment. Both the regression model and the factorial experiment output were checked by the analysis of variance. In particular the main effects and interactions between process parameters on weld penetration for 3mm 5005 Al-Mg alloy bead-on-plate samples were calculated and plotted. The results showed the significance of some parameters and indicated the way to maximize the weld penetration.
This paper treats of the analysis of the effect of arc and laser powers on the quality of the arc assisted fiber laser welding of an Al–Mg alloy in the butt configuration. Grain size, weld geometry ...defects, porosity, and magnesium loss were measured. Magnesium content of the fused zone decreased as the laser power increased while the porosity increased with laser power. Microhardness profiles and tensile properties were explained on the basis of the joint microstructure and defects and related to the power distribution. The porosity level and Mg content in the fused zone affected both tensile strength and ductility. The power distribution that stabilized the welding process and minimize the weld porosity was defined.
•Study of the hybrid fiber laser welding soundness of Al‐MgAl–Mg weld.•Effect of the arc and laser power distribution on the weld quality.•Emphasis on metallurgy and mechanical properties of the weld.•Reduction of Al–Mg laser welding porosity.•Determination of the power distribution that stabilized the welding process.
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In this paper, the feasibility of using a fiber laser to perform a dissimilar metal joining was explored. AZ31B magnesium and 316 stainless steel were autogenously joined in butt ...configuration. The weldability between different materials is often compromised by a large difference in thermal properties and poor metallurgical compatibility. Thus, the beam was focused onto the top surface of the magnesium plate, at a certain distance from the interfaces (offset), and without using any interlayer or groove preparation. Such a method was called laser offset welding (LOW). Results proved a very good capability. The ultimate tensile strength exceeded the value of 100MPa, since a resistant and thin layer of hard intermetallic compounds is formed within the fusion zone. The rupture was observed within the magnesium side, far from the centerline. The metallurgy of fusion zone indicated the effectiveness of phases coalescence, without mixing at liquid states. LOW was demonstrated to be a promising technique to join dissimilar metal welds, being capable to produce an effective bonding with good tensile strength.
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•Low temperature heat treatments lead to microstructural evolution in 5754-Ti6Al4V laser welds.•The microstructural evolutions change with heat treatment temperature and laser heat ...input.•Due to the heat treatment, the Al3Ti compound grew at the Al-Ti weld interface.•The growth of the intermetallic layer and particles decreases the joint tensile performances.•The hardness of 5754/Ti6Al4V alloy slightly decreases/increases with heat treatment.
This paper presents the effects of the post welding heat treatments (PWHT) performed at 350 °C and 450 °C on the microstructure evolution and mechanical properties of AA5754 and Ti6Al4V dissimilar laser welds. The microstructure and tensile properties of the welds before and after low temperature treatment were analyzed.
The off-set welding technique was applied to limit the formation of brittle intermetallic compounds during the welding process. The laser beam was directed onto the titanium side at a small distance from the aluminum edge. The keyhole formed and the full penetration was reached in the titanium side of the weld. Thereafter, the aluminum side melted as the heat that formed the keyhole transferred from the titanium fused zone. Two different energy lines (32 J/mm and 76 J/mm) were used. In this manner, a fused and a heat affected zones was revealed on both sides of the weld. Several intermetallic compounds formed in the intermetallic layer between the two metals. The thickness and the composition of the intermetallic layer depended on the welding parameters and the post welding heat treatment.
The hardness and tensile properties of the welds before and after the post welding heat treatment were measured and analyzed.
This paper presents a whole body control framework for the control of a dual arm underwater vehicle manipulator system developed in the context of the MARIS Italian research project, which deals with ...the control and coordination of underwater vehicles for manipulation and transportation problems. The proposed framework is the extension of the one used in the successful TRIDENT FP7 project that has been improved to be able to deal with multidimensional inequality control objectives. After the presentation of the mathematical background, the paper presents some simulation results showing the good performances of the proposed algorithm.
•The depositions showed the presence of voids and cracks.•The microstructure showed cellular and columnar dendrite grain shapes.•EDS analysis revealed elements diffusion due to high temperature ...gradient during the deposition process.•A heterogeneous elements distribution was detected along the deposition interface.•XDR analysis identified the λ + FeTi brittle phases.
In this study, the Laser Direct Metal Deposition technique was employed to deposit AISI 316 stainless steel powder on Ti6Al4V substrate. Microstructure characterization and composition distribution were studied by scanning electron and optical microscopy. The elements along the metal deposition were detected by the energy dispersive spectroscopy (EDS). X-ray diffraction (XRD) revealed a mixture of intermetallic compounds, which are responsible for the bond brittleness. The metal deposition had a complete wetting of the grain boundary matrix by the second phase.
Preputial urolithiasis in a rabbit Circella, E.; Casalino, G.; Lombardi, R. ...
Journal of small animal practice,
September 2021, Letnik:
62, Številka:
9
Journal Article
•Colmonoy 30 layers samples were built and characterized.•Roughness, adhesion, microstructure, microhardness and density were studied.•The hatch spacing and step height optimal values were ...determined.•Good adhesion to the substrate and low defects microstructure were obtained.•High density and low roughness samples were obtained.
This paper presents a study on process parameters and building strategy for the deposition of Colmonoy 227-F powder by CO2 laser with a focal spot diameter of 0.3mm. Colmonoy 227-F is a nickel alloy especially designed for mold manufacturing. The substrate material is a 10mm thick plate of AISI 304 steel. A commercial CO2 laser welding machine was equipped with a low-cost powder feeding system. In this work, following another one in which laser power, scanning speed and powder flow rate had been studied, the effects of two important process parameters, i.e. hatch spacing and step height, on the properties of the built parts were analysed. The explored ranges of hatch spacing and step height were respectively 150–300μm and 100–200μm, whose dimensions were comparable with that of the laser spot. The roughness, adhesion, microstructure, microhardness and density of the manufactured specimens were studied for multi-layer samples, which were made of 30 layers. The statistical significance of the studied process parameters was assessed by the analysis of the variance. The process parameters used allowed to obtain both first layer-to-substrate and layer-to-layer good adhesions. The microstructure was fine and almost defect-free. The microhardness of the deposited material was about 100HV higher than that of the starting powder. The density as high as 98% of that of the same bulk alloy was more than satisfactory.
Finally, simultaneous optimization of density and roughness was performed using the contour plots.
PurposeTo report the clinical course and the optical coherence tomography angiography (OCTA) findings of patients presenting with paracentral acute middle maculopathy (PAMM) and central retinal vein ...occlusion (CRVO).MethodsRetrospective case series. Clincal records and multimodal imaging findings of patients presenting with PAMM and CRVO were reviewed.ResultsThree eyes of three patients (2 males; mean age: 66 years) were included in the study. Mean follow-up was 9 months and images using OCTA (AngioVue OCT angiography system, Optovue, Inc., Fremont, CA, USA) were available at the last follow-up visit. During follow-up, best corrected visual acuity (BCVA) of case 1 was unchanged at 85 ETDRS letters and OCTA revealed a mild attenuation of the perifoveal deep capillary plexus (DCP); in case 2, BCVA changed from 83 to 77 ETDRS letters and OCTA revealed patchy areas of attenuation and pruning of the DCP; in case 3, BCVA decreased from 26 to 8 ETDRS letters and OCTA revealed extensive areas of DCP dropout.ConclusionThe natural course of visual acuity in patients with PAMM secondary to CRVO may vary. In these patients, the extent of DCP dropout on OCTA may reflect the extent of visual acuity impairment.
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