1,720,970 research outputs found
Formatura laser di manufatti in acciaio inossidabile a geometria complessa
No full textHigh power diode laser is potentially attractive in several manufacturing domains. Transfer efficiency by far higher than competitors, long lasting source, easy setting-up and automation, lack of maintenance as well as moderate investment and running costs make diode laser extremely promising in forming process. Available technologies are numerous, but laser forming has the advantages of limited springback, lack of molds and sophisticated auxiliary equipment. Nevertheless, the achievement of complex shape with high dimensional accuracy and precision by forming with diode laser is still poorly investigated. The nearly unpredictable influence of the material properties and initial geometries on the final shapes and the need for composite forming strategy has up today discouraged the accomplishment of systematic investigations. In order to bridge the gap, 3d forming strategies of flat stainless steel substrates with variable shapes by high power diode laser is herein investigated making use of Design of Experiment (DoE). The strongly innovative aspect of the work is related to the use of a high power diode laser as “thermic tool” to generate the bend in the metal sheet, using the thermal stresses generated in the material by laser irradiation.
The research has first provided a study of the laser bending on different linear scanning geometries, then go on to address the problem of the study of 3D forming, both on curved scanning geometries that for right bending angles; finally it was studied the achievement of sharp bending angles with small fillet radius.
As part of the studies and experiments, the order that was followed, is therefore:
- Linear laser bending study for different scanning geometries;
- 3D Laser forming for curved scanning geometries;
- 3D Laser forming mechanically assisted by bending at a right angle;
- 3D Laser forming mechanically assisted by bending at a sharp angle.
For each experimental study, 3D shape objects were also obtained, whose bending angles were measured by means of a Coordinate Measurement Machine (CMM) and some of these have been sandblasted and coated for exposure and aesthetic effect. The resulting bending angles were collected and analyzed by Analysis of Mean (ANOM), Analysis of Variance (ANOVA) and Interactions Plots (IP) and 3D maps of the bending angles according to the most significant operational parameters were also plotted.
The obtained results demonstrate the feasibility and flexibility of the technology to generate different shapes. In conclusion, laser forming was found to be a promising forming technology, being it suitable to generate arbitrary 3D forms through the implementation of tailored laser scanning paths and appropriate settings of the operational parameters
Se con la formatura laser si segue la tecnica origami
No full textIn this work, the achievement of complex shapes by a diode laser forming process operated according to origami's technique is investigated. In particular, the manufacturing of a geometric item called "origami spoon" was looked into, trying to form the bottom spoon alone. The experimental approach allowed the selection of a technological window, in which high bending angles are achievable without impairing the surface. In addition, required paths and appropriate operational routes to conform the most the manufactured items to the prescribed design were identified
Laser-assisted bending of titanium grade-2 sheets: experimental analysis and numerical simulation
No full textExternal force laser-assisted bending of Titanium Grade-2 flat sheets to achieve sharp bending angles (>140°) with small fillet radii is herein investigated. In particular, the influence of the operational parameters, laser power, scan speed, number of passes, on bending angles and fillet radii of the metal substrates is analysed. The experimental results show that shaping of the substrates can be performed with great reliability, being springback largely minimised in broad operational ranges. Exploratory Data Analysis (EDA) allows the design of first approximation technological models and, in turn, the development of 3d processing maps. Based on the experimental findings, numerical modelling of the bending process by the Finite Element Method (FEM) through ABAQUS/Explicit software is also developed. The numerical model is found to match with great accuracy the experimental results, being it also extremely flexible and responsive to the change of the operational parameters
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-Assisted Bending of Sharp Angles With Small Fillet Radius on Stainless Steel Sheets: Analysis of Experimental Set-Up and Processing Parameters
Full text linkAchievement of sharp bending angles with small fillet radius on stainless steel sheets by mechanical bending requires sophisticated bending device and troublesome operational procedures, which can involve expensive molds, huge presses and large loads. In addition, springback is always difficult to control, thus often leading to final parts with limited precision and accuracy. In contrast, laser-assisted bending of metals is an emerging technology, as it often allows toperform difficult and multifaceted manufacturing tasks with relatively small efforts. In the present work, laser-assisted bending of stainless steel sheets to achieve sharp angles is thus investigated. First, bending trials were performed by combining laser irradiation with an auxiliary bending device triggered by a pneumatic actuator and based on kinematic of deformable quadrilaterals. Second, laser operational parameters, that is, scanning speed, power and number of passes, were varied to identify the most suitable processing settings. Bending angles and fillet radii were measured by coordinate measurement machine. Experimental data were elaborated by combined ANalysis Of Mean (ANOM) and ANalysis Of VAriance (ANOVA). Based on experimental findings, the best strategy to achieve an aircraft prototype from a stainless steel sheet was designed and implemented
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
Progress in Tridimensional (3d) Laser Forming of Stainless Steel Sheets
Full text linkAchievement of complex shapes with high dimensional accuracy and precision by forming process is a demanding challenge for scientists and practitioners. Available technologies are numerous, with laser forming being progressively emerging because of limited springback, lack of molds and sophisticated auxiliary equipments. However, laser forming finds limited applications, especially when forming of tridimensional (3d) complex shapes is required. In this case, cost savings are often counterbalanced by the need for troublesome forming strategies. Therefore, traditional alternatives based on mechanical devices are usually preferred to laser systems. In the present work, 3d laser forming of stainless steel sheets by high power diode laser is investigated. In particular, the set of scanning patterns to form domes from flat blanks by simple and easy-to-manage radial paths alone was found. Numerous 3d items were also processed by diode laser to manufacture a number of complex shapes with high flexibility and limited efforts to modify the auxiliary forming equipment. Based on the experimental results and analytical data, the high power diode laser was found able to form arbitrary 3d shapes through the implementation of tailored laser scanning patterns and appropriate settings of the operational parameters
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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