1,720,958 research outputs found
Wearing Evaluation in nickel super-alloys turning for the development of a predictive model for CAM Optimization
No full textNickel super-alloys are characterized by: high temperatures resistance, high hardness and low thermal conductivity. For this reason they are widely used in critical operating conditions. However, due to their excellent mechanical properties, nickel super-alloys are hard to machine. Tool wear is a major problem in nickel super-alloys machining; the high temperature at the tool rake face is a principal wear factor. Flank wear is the most common type of tool wear; it offers predictable and stable tool life evaluation. In this work, the authors present a flank wear evaluation in Inconel 718 turning, in order to develop a predictive model for CAM optimization. An appropriate database has been developed thanks to an experimental activity (V-B as a function of: the cutting time T, cutting speed S and feed rate F). The objective of the optimization procedure is to maximize the Material Removal Rate (MRR) under the constraint represented by the flank wear limit. The developed procedure operates directly on the part program code, using the original one as starting point for the application of the knowledge about the wear behaviour. After the optimization phase the given output is represented by a new part program code obtained in accordance with: the maximum MRR within the respect of the wear limi
Nickel Superalloy Components Surface Integrity Control through Numerical Optimization
Full text linkDifferent parameters are used to evaluate the machined surface quality; roughness, residual stress and white layer are the most common factors that affect the surface integrity. Residual stress, in addition, are one of the main factors that influence the component fatigue life. Superficial residual stresses depend on different factors, such as cutting parameters and tool geometry. This article describes the development of an automated optimization procedure that allows the matching of a residual stress Target Profile by varying process parameters and tool geometry for a typical aeronautic superalloy, such as Waspaloy, for which a reliable numerical model has been developed for comparison to experimental data. The objective of this procedure is to maximize the Material Removal Rate under physical constraints represented by appropriate limits assigned to: Cutting Force, Thrust Force, Tool Rake Temperature and residual stress Target Profile. The developed optimization procedure has shown its effectiveness to match a given residual stress profile in accordance to process responses numerically evaluated
Optimization of cutting conditions using an evolutive online procedure
Full text linkThis paper proposes an online evolutive procedure to optimize the Material Removal Rate in a turning process considering a stochastic constraint. The usual industrial approach in finishing operations is to change the tool insert at the end of each machining feature to avoid defective parts. Consequently, all parts are produced at highly conservative conditions (low levels of feed and speed), and therefore, at low productivity. In this work, a framework to estimate the stochastic constraint of tool wear during the production of a batch is proposed. A simulation campaign was carried out to evaluate the performances of the proposed procedure. The results showed that it was possible to improve the Material Removal Rate during the production of the batch and keeping the probability of defective parts under a desired level
Numerical-experimental correlation of distortions induced by machining process on thin-walled nickel super alloy forged components
No full textAero Engines main components made by nickel super alloys are mainly obtained by
machining of large forged parts. The work piece machining process generates distortions and in
some cases they may be relevant. In this contest, in many cases the removed volume in the
machining operations represents a large percentage of the forged component in order to obtain the
thin-walled wanted geometry. Due to this reason, the residual bulk stresses induced by the process
history can lead to significant 3D geometric distortions in the machined component with
unacceptable dimensions and shapes of the obtained product for comparison with the wanted
geometry. Moreover, it is a matter of fact how, the final component distortions depend by the
cutting strategy adopted in the machining process. The experimental study of such cutting strategies
on real components are particularly time consuming and costly and for this reason the chance to
study the problem using reliable numerical models it is particularly welcome. In the present work
authors report the numerical model development to simulate the forging and machining processes
needed for the production of an aircraft engine component and the comparison of the obtained
results with the ones physically measured from a production batch
Super-Nickel Orthogonal Turning Operations Optimization
No full textAbstractThe machining processes simulation are commonly used by manufacturing industries in order to produce high quality and very complex products in a short time. These machining processes simulation include large number of input parameters which may affect the cost and quality of the products. Selection of optimum machining parameters in such machining processes is very important to satisfy all the conflicting objectives of the process. There are two options to choose the optimal cutting parameters for a given economic objective. The first one is concerned with the need of a machine expert that manually selects the machining parameters on the basis of its own experience and by means of a proper machining handbook. That way generates many uncertainties and drawbacks in terms of efficiency of solutions and time/cost requirements. As an alternative to the above mentioned approach, many research efforts have been made to state a comprehensive mathematical model of a turning process that, in practice, entails a set of cutting constraints to be handled. Machining optimization problems become tricky whenever a given objective function must be optimized with respect to a large number of constraints. This paperwork is focused about the generation of an automated optimization procedure, for turning processes of nickel superalloys, under certain process conditions. For the automated optimization procedure the response surface methodology (RSM) has been used to detect the influence of the process variables on its performances
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
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