1,720,995 research outputs found
Ring rolling with flat dies: An analytical method to optimize geometry, time or energy
No full textRing rolling process is a plastic deformation process used in the production of seamless rings having diameters in a range of meters. During production, rings simultaneously undergo to a width and height reduction and a diameter expansion, however located in different ring cross sections as a function of idle, axial and driving rolls action. Despite roll motion law could be set independently, their combination influences ring accuracy, production time and energy required. Accordingly, based on the results of simulation plan, the authors present an analytical model able to optimize rolls motion laws as a function of required geometrical accuracy and minimizing production time and energy. The analysis of these latter, allowed the definition of their regression models as a function of Idle roll feed rate and ring rotational speed. These models were then expressed as a function of selected geometrical precision parameter and a weighting factor, for balancing time and energy of the process. Afterwards, geometry and energy models were arranged to define an objective function that, once minimized, allowed to assess the optimized values of the process parameters able to achieve the selected ring precision while decreasing process time and energy. The proposed methodology was applied on different combinations of geometrical and weighting factors, and the resulting optimized conditions were tested by finite element simulations. The good comparison between modeled and simulated ring accuracy and energy, demonstrates the model efficacy in the selection of proper motion laws of ring rolling equipment
An analytical micro-milling force model based on the specific cutting pressure-feed dependence, in presence of ploughing and tool run-out effects
No full textThe growing request of extremely accurate small parts in the last decades led to the disruptive employment of micro-milling processes. Despite conventional milling knowledge is widespread in the industrial field, its application at micro-level remains a big effort because of phenomena usually neglectable at macro-scale, such as the so-called size-effect and tool run-out. Therefore, to correctly evaluate micro-milling forces, a model able to consider these effects is mandatory. In this paper a mechanistic model for predicting cutting forces in micro-milling of Ti-6Al-4V specimens, considering ploughing and tool run-out effects, is presented. The proposed model concerns the introduction of a dedicated coefficient for considering ploughing and shearing effects on tangential and radial components of the cutting forces. Differently from the previous scholars, the coefficients related to ploughing regime have been considered as a function of the specific cutting pressure. In turn, this latter has been characterized by a regression power law dependent on the feed rate since, in this regime, it has a significant influence. The good agreement between analytical and experimental results enforces the proposed model capabilities
Finite element simulation of tool wear in machining of nickel-chromiumbased superalloy
Full text linkThe phenomenon of tool wear strongly affects the efficiency of machining and the quality of machined products. The experimental approach to investigate tool wear requires several time consuming tests. Finite Element Methods (FEM) can be utilized to predict tool wear and tool life as function of process parameters and tool geometry. The commercial software for Finite Element Analysis (FEA) are limited by the impossibility to update the geometry of the worn tool. This research utilizes a self-released subroutine in order to modify the tool geometry in DEFORM 3D simulations by considering the volume reduction of the tool. The model was validated with experimental data obtained by drilling tests on Inconel 718 using conventional metal working fluids (MWF). The correct profile of the simulated worn tool was individuated by comparing the prediction of the simulation with the real tool geometry. The FEM simulation allowed to predict how torque changes during the tool life. In a predictive maintenance perspective, the model can be implemented to optimize the tools replacement
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
Analytical modeling of micro-milling operations on biocompatible Ti6Al4V titanium alloy
Full text linkAmong the biocompatible materials, Ti6Al4V titanium alloy is widely spread due to its properties, such as corrosion and fatigue resistance combined with low density. Ti6Al4V can be processed by Additive Manufacturing technologies, such as Power Bed Fusion (PBF). The biomedical applications require good surface finishing to ensure biocompatibility with tissues and organs. Machining is an adequate process to ensure low final roughness of components. The necessity to realize miniaturized features implicates the usage of micro mills with diameter lower than one millimeter. It implicates several issues, such as size effects, higher than expected cutting forces, rapid tool wear which can be addressed by experimental tests and process modeling. This work reports the results of micro-milling performed on additively manufactured samples in Ti6Al4V. PBF process was utilized to manufacture the samples by employing laser source (PBF-LB). The machining center was equipped with a loadcell to acquire cutting force signal. An analytical cutting force model was calibrated on the experimental data with the purpose of predicting loads on the tool by considering ploughing- and shearing- regimes. Specific machining tests were performed to calculate the Minimum Uncut Chip Thickness (MUCT) and to calibrate the unknow parameters of the model, while further tests allowed to verify the reliability of the model about the cutting force prediction. The elaboration of the cutting force data was performed by an iterative methodology based on the Particle Swarm Optimization (PSO) algorithm
A feasibility study of promoting osseointegration surface roughness by micro-milling of Ti-6Al-4V biomedical alloy
No full textThe reliability of a prosthetic implant needs durability, biocompatibility, and osseointegration capability. Accomplishing these characteristics, Ti-6Al-4V alloy is the main used material for implant fabrication. Moreover, it can be processed by additive manufacturing technique, permitting to meet the needs of patience-tailored, often complex shaped, prosthesis topologies. Once an implant is realized, it is finished by machining operations and its osseointegration capability is heavily influenced by the resulting surface roughness. Consequently, the assessment of this latter is mandatory to evaluate the prosthesis durability. This paper presents the analysis of surface roughness of Ti-6Al-4V micro-milled specimens produced by plastic deformation, selective laser melting, and electron beam melting processes. A central composite design was employed for planning the cutting tests. The comparison between surface roughness results and its values for enhancing osseointegration, firstly permitted to individuate the range of micro-milling suitable applications, which have been individuated as ball joints, bone plates, and screws. Next, the statistical analysis of the experimental measurements allowed the identification of the most influential micro-milling parameters together with the determination of the mathematical models of surface roughness by response surface methodology. The good comparison among calculated and experimental results revealed the reliability of the model, allowing the prediction of achievable surface roughness once micro-machining parameters are selected, or their optimization as a function of a desired surface roughness value
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