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Sviluppo e Industrializzazione di una macchina LPF e validazione attraverso l'ottimizzazione dei parametri di processo di Ottone CuZn42 e Acciaio Armonico C67
No full textLe tecnologie di costruzione additiva, dalla loro nascita alle prime applicazioni industriali, hanno fatto un grande salto in termini di sviluppo di hardware e materiali.
La continua ricerca di nuovi mercati e la crescente domanda hanno reso più accessibili i costi di tali tecnologie. Dall'uso dei polimeri per fare prototipi alle polveri metalliche per fare parti meccaniche reali i concetti sono sempre gli stessi, costruendo la parte strato per strato. In termini di denaro dagli anni Ottanta ad oggi il processo di stampa 3D mantiene un trend positivo con molti più aumenti per il futuro.
In termini di flussi monetari ed energetici durante la produzione di parti complesse, le tecnologie di costruzione additiva possono avere incrementi positivi. Con le tecnologie di costruzione additiva viene anche preso in considerazione l’aspetto legato alla misurazione del consumo energetico di produzione per le valutazioni dell'inventario del ciclo di vita. [2]
In molte catene di produzione tradizionali, dove stime affidabili del consumo energetico potrebbero non essere disponibili, l'adozione della tecnologia per costruzione additiva consente ai produttori di fornire ai propri clienti dati affidabili sull'energia incorporata nei prodotti o nei componenti durante la fase di produzione. [2]
È stato dimostrato che la selezione della configurazione dei costi minimi in Additive Manufacturing potrebbe portare all'effetto secondario della riduzione al minimo del consumo energetico di processo. [2]
La mia tesi di dottorato discuterà una specifica tecnologia di produzione additiva, basata sul processo di fusione del letto in polvere utilizzando un LASER come fonte di fusione.
Verranno analizzate le principali componenti costruttive presenti nella macchina prototipo, cercandone le principali criticità (sistema di filtraggio e recupero delle polveri, abbattimento polvere nera, flusso del gas in camera, misura delle perdite di carico nei tratti caratteristici dell’impianto, sistema di raccolta delle polveri, sistema di distribuzione e di deposizione delle polveri sul piatto di stampa) e, nel caso queste causino un arresto anomalo oppure un’irregolarità nella qualità nel componente stampato, se ne svilupperà una modifica oppure una sostituzione radicale del componente in esame.
Verificata la stabilità meccanica dell’intera macchina verranno analizzate le proprietà meccaniche dei campioni ottenuti con acciaio inossidabile X2CrNiMo17-12-2 - AISI316L, polvere di ottone CuZn42 e acciaio C67 - Acciaio Temperato. Le principali proprietà meccaniche richieste per un componente costruito per costruzione additiva sono in termini di resistenza meccanica porosità, densità, durezza Brinell, carico a rottura e tensione di snervamento.
In particolare, verranno effettuati dei rilevamenti della densità del provino mediante misurazione della densità volumetrica relativa con metodo di Archimede. Successivamente verrà stabilita la bontà della rugosità superficiale attraverso acquisizione di mappe per mezzo di un microscopio ottico e attraverso un software per l’analisi d’immagine ne verrà poi misurata la rugosità superficiale media. Lo stesso campione verrà poi utilizzato per misurare la durezza media del materiale per mezzo di un durometro.
Per testare il carico a rottura e il limite di snervamento verranno prodotti dei campioni con geometria ad osso di cane a sezione circolare a cui verrà montato un estensimetro analogico. Il software di elaborazione dei dati elabora la curva sforzo – deformazione.The additive manufacturing technologies, from their birth to the first industrial applications, made a big jump in terms of hardware and material development.
The continuing research for new markets along with a growing demand have made sure that the costs of such technologies have become more accessible. From the using of polymers to do prototypes to metal powders to do real mechanical parts the concepts are always the same, building the part layer by layer.
In terms of money from the eighties to present days the 3D printing process maintain a positive trend with much more increases for the future.
In terms of monetary and energy flows during the production of complex parts, the additive manufacturing technologies can have positive increments. Thus the adoption of Additive Manufacturing also simplifies measurement of the manufacturing energy consumption for life cycle inventory assessments.
In many traditional supply chains, where reliable estimates of cumulative energy consumption may be unavailable, the adoption of AM allows producers to provide their customers with reliable data on the energy embedded into products or component during the manufacturing stage.
It has been shown that selecting the minimum cost configuration in Additive Manufacturing is likely to lead to the secondary effect of minimizing process energy consumption.
My PhD thesis will discuss a specific additive manufacturing technology, based on the powder bed fusion process using a LASER as a melting source.
The main construction components present in the prototype machine will be analyzed, looking for the main critical issues (filtering and powder recovery system, black powder abatement system, in-chamber gas flow, measurement of load losses in the characteristic sections of the plant, powder collection system, distribution and powder deposition system on the printing plate) and, if these cause a crash or an irregularity in the quality in the printed component, a radical modification or replacement of this component will develop.
Once the mechanical stability of the entire machine has been verified, the mechanical properties of the samples obtained with stainless steel X2CrNiMo17-12-2 - AISI316L, CuZn42 brass powder and C67 steel - Tempered steel will be analyzed. The main mechanical properties required for a component built for additive manufacturing are in terms of mechanical strength porosity, density, hardness, ultimate tensile strength, and yield tension.
Measurements of the density of the specimen will be carried out by measuring the relative volumetric density by Archimedes method. Subsequently, the quality of surface roughness will be measured through the acquisition of maps by means of an optical microscope and through an image analysis software the average surface roughness will then be measured. The same sample will then be used to measure the average hardness of the material by means of a durometer.
To test the ultimate tensile strength and the yield strength, samples with circular section will be produced to which an analog extensometer will be mounted. Data processing software processes the strain -strain curve
Physical and chemical surface modification by laser polishing of CuZn42 parts produced by laser powder bed fusion
Get PDFThe widespread use of Cu-Zn alloys containing lead (Pb) in plumbing applications poses significant health risks due to potential Pb leaching into drinking water. In response to international legislation aimed at reducing or eliminating Pb in metal alloys, there is an increasing demand for environmentally friendly brass. In this experimental work, authors show that during the Laser Beam Powder Bed Fusion (PBF-LB) process of the CuZn42 (CW510L) alloy, small particles only a few microns large mixed with large particles that are hundreds of microns in size, are spattered from the material. Large particles show average Zn/Cu ratio around 0.22, while for small particles it increases up to 3, against a nominal value of 0.72 for the CW510L alloy. The fallout of such particles on the produced part enriches surface of Zn, thus altering the surface chemical composition with an increase in Zn concentration beyond the acceptance limit of 43 at.%. To restore the standard chemical composition of the surface, a treatment based on the ablation of the surface material by a laser beam was proposed. Results clearly show that, after the laser treatment, the chemical composition of the surface is completely restored, and the standard properties recovere
Reactive formation of C3N4 as a by-product of AISI 1070 parts produced by laser powder bed fusion in N2 atmosphere
Get PDFIn metal additive manufacturing (AM), inert gases are traditionally used to achieve a controlled atmosphere and mitigate the effects of residual reactive gases. However, the interaction between gases and laser processes, particularly in reactive laser powder bed fusion (RL-PBF) technology, offers the possibility of opening up new avenues for material synthesis. In this experimental work, the authors observed the presence of C3N4 in the residual powder during the manufacture of AISI 1070 steel parts by L-PBF, indicating a reactive process occurred during parts production. This investigation revealed the formation in the working chamber of a waste product containing C3N4 carbon nitride, due to the reaction between the carbon released from the steel and the nitrogen in the chamber. Remarkably, despite carbon depletion, the final product of AISI 1070 steel complies with the specifications of use. Hence, the L-PBF machine was modified to allow black powder sampling from various locations in the chamber. Authors attempted to enhance the production of the C3N4 material by increasing the SED up to 7143 J/mm2 to sublimate a pure graphite rod and concurrently manufacture parts in AISI 1070, in a nitrogen atmosphere. The results obtained at higher SED values showed that in both cases (graphite rod or AISI 1070 steel) a C3N4 compound in the black powder is formed in the investigated atmosphere by reaction of nitrogen atoms with the carbon atoms vaporized by the laser beam. Thus, the study highlights the novel achievement of synthesizing carbon nitride as a high-value by-product while producing functional AISI 1070 steel parts via L-PBF through reaction with nitrogen atmosphere
Use of an energy harvesting smart floor for indoor localization of people
Get PDFThe development of “intelligent” floors is a growing interest, but often the ensuing solutions involve high production costs as well as complicated installation and management. Aim of this paper is to propose a novel smart floor that makes use of an energy harvesting system in order to allow people localization and to track their movements in an indoor environment. The contribution starts from reviewing the state of the art of smart floor solutions, which are categorized according to the different applications they are addressed to. The system developed in this research is based on capacitive sensors that are mounted on a polymeric support and embedded between a bulk wooden base and floating parquet flooring. The paper outlines the detailed architecture of the proposed apparatus and reports the results of the preliminary test phase. The proposed solution is part of HDOMO, an Ambient Assisted Living (AAL) project aiming at the development of smart solutions for active aging
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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