1,721,164 research outputs found
Object-Oriented analysis and design of a manufacturing feature representation
No full textThis paper describes the modelling of a manufacturing feature by taking geometry and tolerancing into account. This modelling is based on a conceptual definition of the manufacturing feature based on interactions between the primary features extracted from the Computer Aided Design (CAD) model: form features, precision features and technological features. The phase of specification was carried out with the use of the Object-Oriented System Analysis (OOSA) method. The data representation and processing are presented through the description of the eight models of the OOSA method. A classification of the manufacturing features is proposed according to the possible interactions between the primary features. A Topological and Technological Interaction (TTI) graph shows the level of complexity of the interconnection of the features. The extracting mechanism of primary features from the CAD system is described. The manufacturing features, automatically extracted from the CAD model defined in a CATIA environment, are manipulated by a Generative Computer Aided Process Planning (GCAPP) system to generate the machining operation sequences automatically. The manufacturing feature representation proposed is of extreme interest thanks to the geometry but especially to the tolerancing which is too often ignored
Effect of forming and calibration operations on the final shape of large diameter welded tubes
No full textLarge welded tubes are primarily used in oil pipelines and offshore platforms. They are actually produced by the steelmaker industry
ILVA-Laminati Piani, Taranto (Italy). The production process is characterised by three phases: (1) forming; (2) welding and (3) calibration.
In addition, the first phase is composed by three steps: the forming of the longitudinal border of the blank (C-forming); the air bending of
the C-formed blank (U-bending) and the forming inside a circular shaped die of the U-formed blank (O-forming). After the welding phase,
the final forming operation (calibration) is performed to correct the tube distortion due to the thermal input using a special purpose machine
(expanding machine).
In the present work, the calibration phase is investigated using the finite element (FE) method. Both 2D and 3D FE models have been
used. The 2D analysis has been aimed to obtain the tube profile after the forming phase (simulation of the C–U–O forming steps); in addition
the simulation of the calibration phase has also performed under the hypothesis of plane strain condition, but not accurate results have been
obtained. On the contrary, the 3D FE analysis has allowed to accurately investigate the calibration phase; two different numerical models have
been used: the first one considering a cylindrical tube (the tube profile obtained by the previous 2D simulation was simply extruded along a
straight line); the second one modelling the tube inflections due to residual stress after welding (the real tube section has been extruded along
a circular path, according to experimental data).
The aim of this search is to investigate stress and strain state in the tube; in particular the action of the expanding machine is simulated and
the effect on the tube section end profiles and on the tube lengthwise inflection have been evaluated. The possibility of both obtaining a good
circular shape of the tube section and correcting the lengthwise inflection is investigated. The FE model is defined according to data coming
from the workshop: the sheet material is X70 steel and initial blank dimensions are 14,000mm×3000mm×27.5 mm
Experimental investigation of laser beam welding of explosion-welded steel/aluminum structural transition joints
No full textThe steel/aluminum structural transition joints are widely used in shipbuilding industry due to the advantages of joining these two materials with important weight savings while exploiting their best properties. The use of laser welding to strongly connect components made of Fe and Al alloys as base materials with Fe/Al structural transition joints is very attractive. The authors report results achieved during the laser welding of these particular joints with the scope to evaluate effects of the laser-induced thermal loads on the integrity of the Fe/Al bond interface, from metallurgical and mechanical points of view. The increase of both inter-metallic film thickness and extension were detected as a result of the laser beam induced heat on the Fe/Al bond interface. These increases did not cause severe reductions of the mechanical resistance of the investigated structural transition joint
Characterizing a superplastic AA5083 alloy by the blow forming technique and numerical finite element analysis
No full textLocal Italy. I domini del "settore comunità" in Italia.
Full text linkIl volume “Local Italy” intende promuovere una riflessione sul quadro di
asset
, regole e competenze utili allo sviluppo del settore “comunità” in Italia.
Con questo obiettivo, il volume analizza due filoni principali: l’esperienza di
un contesto maturo come quello britannico e l'inquadramento degli ambiti
organizzativi, economici e politici che hanno affrontato questo tema nel
nostro Paese. Il dibattito sollecitato dal volume è volto alla promozione di un
ecosistema competente e di un processo di cambiamento organizzativo
capace di sostenere nuove infrastrutture sociali in grado di intercettare la
crescente offerta, anche nel nostro paese, di beni e servizi pubblici da
valorizzare per scopi di interesse collettivo. Una riflessione utile a suggerire
possibili orizzonti di coordinamento strategico, in particolar modo rispetto
alle trasformazioni imprenditoriali ed organizzative da formule di
business tradizionale (occupate da terzo settore, impresa sociale ma anche delle
imprese di capitali) verso approcci ed interessi poco definiti ma promettenti,
che non fanno riferimento ad attività codificate, ma a qualità funzionali
Le Community Enterprises in Gran Bretagna: imprese sociali come modello di rigenerazione
Full text linkNel dibattito italiano, sia accademico che giornalistico, le questioni che riguardano la riduzione della spesa pubblica, la dismissione del patrimonio pubblico, la rigenerazione urbana delle periferie, la partecipazione ed il coinvolgimento delle comunità nei processi di pianificazione, rappresentano temi di crescente rilevanza.
In risposta a queste problematiche, la Gran Bretagna - paese in cui da sempre la pianificazione del territorio ha una dimensione multidisciplinare - ha riconosciuto il ruolo di alcune imprese sociali definite community enterprises. Queste organizzazioni sono nate da processi spontanei e distinti, in uno stretto dualismo tra l’azione locale e gli indirizzi delle politiche nazionali, affermandosi come strumento di rigenerazione urbana sostenibile. L’efficacia d’azione delle community enterprises consiste nella promozione di processi di capacity bulding, che pongono al centro della rigenerazione le comunità con le proprie risorse, favorendone l’attitudine ad operare per il proprio welfare e proponendo formule redistributive di sviluppo urbano. La recente trasformazione culturale e politica nota come “from the Big State to Big Society” ha riconosciuto la capacità d’azione di queste imprese, ma ne ha allo stesso tempo messo in discussione il ruolo, individuando come maggior limite delle stesse la dipendenza dal sostegno pubblico quale elemento necessario a garantirne lo sviluppo e la loro azione sui territori.
In questo contributo1 si propone una lettura dell’evoluzione delle politiche urbane del Regno Unito e un inquadramento generale delle diverse tipologie di community enterprises, con particolare riferimento ai Community Development Trust. Nello specifico è stato approfondito il caso del Westway Development Trust di Londra, il suo potenziale di sviluppo e i risultati raggiunti in termini di attività e capacità economiche
Luoghi – spazi e strumenti per l'accesso al cibo
Full text linkNonostante la riconosciuta universalità del diritto al cibo, ancora ampie porzioni della popolazione mondiale si vedono negata la possibilità di accesso a cibo conforme ai loro bisogni a causa della permanenza di condizioni di povertà che, oggi, assume nuove forme, tra cui quella alimentare. La presente pubblicazione, condotta da Fondazione Giangiacomo Feltrinelli in collaborazione con CIRFOOD, interpreta e rilancia la necessità di avviare una riflessione profonda sull’andamento del settore agroalimentare, guardando alle evoluzioni recenti e prossime del comparto produttivo e di quello dei consumi, così come ai soggetti che ne sono protagonisti per identificare linee di indirizzo e previsioni di sviluppo che possano essere opportunamente orientate per garantire maggiore equità
The role of the numerical simulation in superplastic forming process analysis and optimization
No full textNumerical simulation took root in the last few decades in the superplastic forming field as one of the most dominant tools for process analysis and optimization. The big role of the simulation can be found in many areas concerning the study and the implementation of the forming process. The purpose of this paper is to outline some of the main applications of the numerical simulation in superplastic forming that can be found in the material characterization phase, in the simulation of forming tests and in the optimization of the process. A brief overview of results that can be found in literature is given with special regard to Finite Element numerical simulation of metal sheet Superplastic Forming
Characterization of a superplastic aluminium alloy ALNOVI-U through free inflation tests and inverse analysis
No full textNumerical methods are widespread in forming applications since a deeper understanding and a finer calibration of the process can be reached without most of the assumptions used in analytical approaches. In this calibration procedure the characterization of the material behaviour is an important preliminary step that cannot be avoided. Experimental tests can be numerically modelled and material constants can be found by inverse methods making numerical results as close as possible to experimental ones. In this work material parameters of a superplastic aluminium alloy have been found by experimental forming tests and an inverse analysis. Constant pressure free inflation tests were firstly performed to find the optimal range for temperature and strain rate values. Material constants were then calculated, on the basis of these tests, minimizing errors between experimental and numerical data through a gradient based optimization iterative procedure. Constant strain rate experimental tests were finally used to refine material parameters and to gain a better agreement between experiments and numerical simulations
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