1,720,954 research outputs found
A cost-driven process planning framework for selective laser melting
No full textSelective Laser Melting (SLM) is an additive manufacturing (AM) method, capable of producing end-use metal parts by selectively melting layers of powder with a moving laser. The process can create complex lightweight geometries in a single build, and offers an opportunity to improve product value through greater design freedom, part consolidation, reduced tooling and reduced supply chain complexity for a range of different industries. However, SLM also poses a number of materialand process-related challenges, which prevent wider adoption of this process for enduse part production. Due to high residual stresses characteristic of this process, build failure and poor part quality are still common issues. The cost of this process is also relatively high, while the need for post-processing leads to additional, and sometimes unexpected, costs. Effective process planning can mitigate these problems, however, this is not an easy task due to the large number of interdependent process parameters and their combined effects on the process cost, time and quality. Part build orientation is one such important parameter, which affects the surface roughness, build cost and time, as well as the need for support structure. Due to the anisotropic material properties produced by SLM and the effects of part geometry on the residual stress profile, there is also a complex relationship between build orientation, part quality and the risk of build failure. Moreover, the build orientations of multiple parts determine how many SLM machines are required to build all those parts. The placement of parts inside AM machines is known as a bin packing problem, and its link to build orientation has been acknowledged throughout the literature. Existing approaches have optimised build orientation and bin packing as two separate problems, limiting the optimality of the overall solution. Thus, this thesis provides a cost-driven framework for optimising build orientation and bin packing of multiple parts in SLM, and provides two heuristics for solving these two problems simultaneously. The cost model used to drive the framework is developed based on a thorough literature review, and incorporates build cost and post-processing cost. Additionally, by considering SLM in the context of lean manufacturing two distinct production scenarios are identified, and referred to as Identical Batch Production (IBP) and Mixed Batch Production (MBP). Thus, each heuristic vi is aimed at a specific production scenario. For IBP, a Tabu search procedure is developed by solving the build orientation problem along with a cutting-stock problem, as bins are assumed to be identical. To improve the efficiency of this search heuristic an area-based approximation strategy is proposed, which can reduce the solution time by as much as 50%, as indicated by the computational results. The effect of build orientation on residual stresses is also considered, by extending the above Tabu search to address the multi-objective problem of cost and residual stresses in the context of IBP. Due to the high computational cost of this problem, two alternative approximation strategies are proposed, and coupled with the multiobjective Tabu search. The two strategies are demonstrated on a single test part of medium complexity; the results demonstrate the validity of this approach, as better, albeit less obvious trade-off solutions were found by the proposed Tabu search than by an experienced SLM operator. Finally, an Iterative Tabu Search Procedure (ITSP) is developed for the MBP scenario. Because the solution space of this problem is much larger and more complex than the IBP, the ITSP consists of six distinct stages, where each stage is aimed at exploring a different area of the solution space. The procedure is benchmarked against commercial software, indicating an average cost improvement of 14.6% for 27 test instances
Cost-driven build orientation and bin packing of parts in Selective Laser Melting (SLM)
No full textSelective Laser Melting (SLM) is an additive manufacturing process capable of producing mixed batches of parts simultaneously within a single build. The build orientation of a part in SLM is a key process parameter, affecting the build cost, time and quality, as well as batch size. Choosing an optimal arrangement of multiple heterogeneous parts inside the SLM machine also presents a challenging irregular bin packing problem. Since the two problems are interdependent, this paper addresses the combined problem of finding an optimal build orientation and two-dimensional irregular bin packing solution of a mixed batch of parts across identical SLM machines. We address this problem specifically in the context of low-volume high-variety (LVHV) production in the aerospace sector, using total build cost as the objective function. To solve this problem, we present an Iterative Tabu Search Procedure (ITSP), which consists of six distinct stages. We test each stage in the ITSP on 27 manually generated instances, based on 68 unique geometries ranging in convexity and size, including six real-life components from the aerospace industry. Two of the six stages, which are driven by support structure volume, returned the highest improvement in cost. Overall, the results showed an average cost improvement of 16.2% over the initial solution. The initial solution of the procedure was benchmarked against a commercial software, showing comparable results
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
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
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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