1,720,963 research outputs found
Real-time laser spot modulation in Laser Powder-Directed Energy Deposition via wobbling: A path to superior 316L stainless steel components
Full text linkAAchieving high-quality Laser Powder-Directed Energy Deposition (LP-DED) components require the precise tuning of process parameters such as laser power, scanning speed, and laser spot size. Among these, laser spot size is a particularly critical factor. The use of a large spot size led to high building rate and process efficiency at the expense of surface finish and geometrical accuracy. This investigation aimed to understand how a variable laser spot affects the thermal history of LP-DED AISI 316L stainless steel components and consequently their microstructure and mechanical properties. The study first examined the effects of the laser spot and sample geometry on the microstructural features using optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and X-ray diffraction (XRD). Secondly, the characterization of mechanical properties was conducted via tensile tests and the effects of the variable laser spot on ductility and on the various strengthening mechanisms were analysed. The results revealed that using a larger laser spot leads to heat accumulation, which becomes especially crucial when depositing geometries characterized by a small cross section. These findings lay the groundwork for enhancing the LP-DED process efficiency in a more viable manner taking advantage of the different solidification conditions
On the use of areal roughness parameters to assess surface quality in laser cutting of stainless steel with CO2 and fiber sources
Full text link"Laser cutting provides various advantages such as high flexibility in terms of process parameters and cut material type, as well as the
possibility to obtain complex geometry in different dimensions with high precision. From industrial point of view, the two more competitive
laser cutting technologies are based on the use of CO2 and active fiber sources, which produce samples visually different, with non-uniform
surface and different depth of the striations. The quality assessment between the two laser systems within the industry is commonly based on
standard ISO 9013; that covers several aspects of quality, the most used are the surface roughness and edge perpendicularity; however 2D
profilometers adopted for measures are not able to analyze the complex 3D surface topography of the cutting edge. As a result, despite the fact
that the differences are visually appreciated, measured 2D roughness values of different CO2 and fiber laser cutting conditions are very similar.
Recently, a greater diffusion of 3D surface profilometry devices is present. These devices allow areal surface roughness parameters to be
defined, which are potentially suitable to better quantify the laser cut quality. This work points out the use of a focus-variation microscopy to
acquire 3D surfaces and evaluate analytically the surface quality of laser cut edges using areal surface roughness parameters. In particular, the
purpose is to define a simple and repeatable method to identify the type of cutting process analyzed through the reconstruction of surface
characteristics and quality of the cut-edge. As a case study, two stainless steel samples with the same geometry obtained with different laser
sources, CO2 and active, fiber is presented. For comparison purposes the cutting conditions were fixed to represent the state of the art of
respective laser cutting technologies, which actually show distinct cutting edge characteristics.
Directed energy deposition of 18NiM300 steel: effect of process and post processing conditions on microstructure and properties
Full text linkThis current study investigates the effect of Direct Energy Deposition (DED) process conditions on the properties and microstructure of M300 maraging steel samples. The investigation centers on two key factors: laser power and deposition environment. The microstructure of this tool steel is analyzed by computing the Primary Cellular Arm Spacing. The findings revealed a significant influence of both inert atmosphere and laser power on cooling conditions. These different cooling rates influence the phase content as demonstrated by X-Ray Diffraction and Electron Backscatter Diffraction measurements. It was demonstrated the presence of different content of residual austenite at cell boundaries. These distinct microstructural features caused variations in the hardness values of the printed samples. Furthermore, a direct aging heat treatment was implemented, that was chosen from Differential Scanning Calorimetry measurements results. This heat treatment proves effective in achieving consistent hardness increases and eliminated the differences among samples built in different process conditions. This outcome suggests the possibility of selecting the most economically viable DED parameters for optimal results
Performance and efficiency of an industrial direct diode source with an extremely low BPP in laser cutting of Fe-based and reflective alloys
No full textThe performance and efficiency of a 2kW industrial direct diode laser source with an extremely low BPP are investigated when carbon
and stainless steels as well as aluminium and brass sheetsare laser cut. The results confirm the industrial feasibility and robustness of the
direct diode laser source as tool for laser processes. In particular in the oxidation laser cutting of iron-based alloys the low BPP together
with relative larger transport fiber diameter allows quality and cutting speed equivalentto the active fiber and disk laser sources in a very
large range of thickness (up to 15 mm). When higher power densities are required, because inert laser fusion cutting of structural steel is
carried out or because high reflective alloys need to be cut, the low BPP and the shorter wavelength are favorable figures and produce
comparable performances with the mentioned laser sources
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Laser Cutting of Copper and Brass Alloys by High Brilliance Diode Source with an Extremely Low BPP
No full textCopper and copper-based alloys are difficult materials
to laser cut due to their high thermal conductivity, high
reflectivity and tendency to lose zinc on the zone
adjacent to the cut. The study explores the potential of
laser cutting process of copper and brass sheets with a
TeraDiode TeraBlade direct diode source whose high
brilliance is given by the very low BPP and by the
small fiber diameter (100 micron). Results show that it
is possible to obtain good quality cuts operating with
nitrogen and oxygen assist gas in the case of brass and
copper alloys respectively. Moreover larger process
stability, higher productivity and easier-to-cut
conditions are obtained cutting brass alloys than pure
copper
Study of single tracks with alsi10mg and composites powders
No full textDirect Metal Laser Sintering (DMLS) is a powder-bed additive manufacturing technology capable to produce fully dense metal parts layer-by-layer from a 3D CAD model. The consolidation and the properties of the metal components strongly depend on each laser melted track. The understanding of the interaction between the thermal and physical properties of the powder and the building parameters is a key factor to achieve a good consolidation and can represent a basis for the development of new and innovative AM materials. In this study, the effects of the building parameters, such as laser power and scan speed, on the shape and the microstructure of a single scan track were evaluated. Powders of AlSi10Mg were laser scanned in order to investigate the phenomena that arise in the melt pool such as the balling effect and the spreading of the molten phase. The experiments were carried out in argon atmosphere on an AlSi10Mg platform with fixed laser spot (100 μm) and building platform temperature (100 °C)
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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