ANALISI DELL’EVOLUZIONE MICROSTRUTTURALE DURANTE IL PROCESSO DI ESTRUSIONE DELLA LEGA AA6060 MEDIATE SIMULAZIONI FEM

La previsione della microstruttura finale dopo l’estrusione delle leghe di alluminio è un argomento che hasuscitato un grande interesse negli ultimi anni, visto che le proprietà meccaniche e la qualità degli estrusisono fortemente dipendenti dall’evoluzione e del tipo di microstruttura. Questo lavoro pone come obiettivolo studio dell’evoluzione microstrutturale della lega di alluminio AA6060 durante l’estrusione, mediatesimulazioni FEM utilizzando il Codice Deform 3D. Allo scopo di determinare i coefficienti dei modellidi ricristallizzazione da inserire nel codice FEM, sono state prodotte delle prove sperimentali mediantel’estrusione inversa di coppe a diverse temperature e velocità di deformazione. Dall’analisi metallograficadei campioni estrusi è stato possibile determinare i coefficienti del modello dinamico di ricristallizzazione indotazione al codice FEM Deform 3D. Le coppe sono state successivamente trattate termicamente in forno perfar avvenire la ricristallizzazione statica, e sono stati determinati i coefficienti del modello di ricristallizzazionestatica. Una volta convalidati i modelli, si è passato alla simulazione del processo reale di estrusione di unabilletta cilindrica. L’evoluzione della microstruttura presenta delle zone con dei grani allungati ed altre con deigrani ricristallizzati con fenomeni di accrescimento. I risultati delle simulazioni sono stati confrontati con lemicrostrutture delle billette estruse, mostrando una buona corrispondenza

Mechanical and in vitro biological properties of uniform and graded Cobalt-chrome lattice structures in orthopedic implants

Human bones are biological examples of functionally graded lattice capable to withstand large in vivo loading and allowing optimal stress distribution. Disruption of bone integrity may require biocompatible implants capable to restore the original bone structure and properties. This study aimed at comparing mechanical properties and biological behavior in vitro of uniform (POR-FIX) and graded (POR-VAR) Cobalt-chrome alloy lattice structures manufactured via Selective Laser Melting. In compression, the POR-VAR equivalent maximum stress was about 2.5 times lower than that of the POR-FIX. According to the DIC analysis, the graded lattice structures showed a stratified deformation associated to unit cells variation. At each timepoint, osteoblast cells were observed to colonize the surface and the first layer of both scaffolds. Cell activity was always significantly higher in the POR-VAR (p < 0.0005). In terms of gene expression, the OPG/RANKL ratio increased significantly over time (p < 0.0005) whereas IL1β and COX2 significantly decreased (7 day vs 1 day; p < 0.0005) in both scaffolds. Both uniform- and graded-porosity scaffolds provided a suitable environment for osteoblasts colonization and proliferation, but graded structures seem to represent a better solution to improve stress distribution between implant and bone of orthopedic implants

Modellazione di processo, previsione di microstruttura e proprietà meccaniche di ghise sferoidali colate in sabbia

Questo lavoro presenta i risultati di un’attività di caratterizzazione numerico-sperimentale di un processo dicolata in sabbia di una ghisa sferoidale ferritico-perlitica. L’indagine si è avvalsa di un’attrezzatura di colataopportunamente progettata e realizzata per fornire moduli termici differenziati, tali da sottoporre il materiale adiverse condizioni di raffreddamento e solidificazione. Il sistema di colata è stato studiato mediante simulazionenumerica, che ha permesso di replicare con adeguata accuratezza le condizioni di processo poi monitorate.Le caratteristiche microstrutturali sono state stimate attraverso modelli numerici implementati nel codice dicalcolo PROCAST™ v.2011 per la previsione delle diverse microstrutture ottenute al variare delle condizionilocali di raffreddamento. La validazione delle simulazioni è stata effettuata comparando i dati ottenuti, conquelli ricavati da un accurato studio microstrutturale svolto su oltre 2000 micrografie ottiche, avvalendosi diun software di analisi d’immagine. Sono stati in particolare valutati: porosità percentuale, numero di noduli digrafite per unità di superficie, area media dei noduli, morfologia media dei noduli, frazioni grafitica, ferritica eperlitica. Sono state quindi sviluppate relazioni empiriche in grado di permettere la valutazione delle proprietà atrazione del materiale noti i soli parametri microstrutturali ottenibili dalla simulazione numerica

Effect Of Die Design On Strength And Deformability Of Hollow Extruded Profiles

In this paper, the behaviour of two different die design concepts in the production of the same industrial profile is described by both experimental tests and numerical FEM analysis. The investigated parameter is the shape of the leg for the extrusion of an AA6060 round tube 80mm in diameter and 1mm in thickness. Press loads and profile temperatures were monitored during the production. The processes are simulated by means of Deform 3D fully coupled simulations. and the results compared with the experimental ones. The profile are characterized by means of tensile tests in order to evaluate strength and deformability of the joints, and the results are related to the welding parameters as they were obtained by FEM. Finally, the die stress is investigated in order to explain tool life behaviour of the dies as it was observed during their whole life. \ua92007 American Institute of Physic

Seam welds modeling and mechanical properties prediction in the extrusion of AA6082 alloy

This work summarizes the outcome of recent research by the authors on modeling the formation of seam welds in aluminum extrusion and on evaluating the related mechanical properties on the final products. A profile with a seam weld in the middle section was produced with different die designs in order to investigate the relation between die design and local welding parameters, such as contact pressure, temperature, time of contact, strain and strain rate paths. The local welding conditions were evaluated by complete thermo-mechanical 3D FEM simulation of the processes. Specimens were extracted from the profiles and tensile tested, the resulting mechanical properties being discussed with respect to the local welding conditions. The possibility to adopt criteria for assessing the welding quality is discussed, together with the effect of high speed damage cracking

Latest Advances In Extrusion Technology and Simulation In Europe and 2nd Extrusion Benchmark

The demand for properties and quality in extruded profiles stretches the ability of extruders and die makers to the limit: ever more complex sections, hard alloys, emerging technologies and microstructure control are just some of manufacturers\u2019 every-day concerns. Key factors for innovation and competitiveness are skilled engineering analysis and reliable software; however, no reference community exists for the extrusion analyst and there is no common base for evaluating commercial code capabilities. This two-in-one event provides a unique opportunity: * to learn about the state of the art of emerging technologies, innovation and simulation capabilities in the extrusion of light alloys; * to get guidelines for best process analysis and product optimization; * to understand the potential of your current simulation tool; * to have the widest possible range of information on extrusion simulation today. WORKSHOP: "Latest Advances In Extrusion Technology and Simulation In Europe" The conference is focused on the latest advances in the extrusion of light alloys and related simulation issues. The workshop is open to researchers from industries and universities worldwide. Invited papers by leading industries will give the state of the art about ongoing research in extrusion technology. Invited papers will be presented on perspectives and ongoing research in extrusion technology and simulation. Contributions with experimental validation of the results will be preferentially selected for the oral session. Workshop Topics: * Process Simulation: Models, Validation, Optimization, Material Flow, Friction; * Product Quality: Defects, Distortions, Microstructure, Seam Welds, Maximum Press Speed; * Materials: Hard/New Alloys, Magnesium Alloys, Composites; * New Processes: Thixoextrusion, Hot Profile Bending, Reinforced Profiles Extrusion; * Dies: High Production Rates; Oriented Design, Die Life, Coatings, Correction Strategies. 2nd EXTRUSION BENCHMARK The benchmark is aimed at exploiting FEM codes capabilities and users' knowledge in the simulation of an industrial extrusion process which as it was realized and monitored by the conference organizers. The comparison of the "blind" simulations by the participants with the experimental results should allow users to check if their settings are generally adequate to the problem and software house to verify the sensitivity of their solving methods. If the previous benchmark held in Zurich was focused on the accuracy of simulating the contact between die and material in the bearings, in this case the attention was driven toward the simulation of pockets and their effectiveness in affecting the material flow. A multi-hole die with four L-shaped profiles was built and the effect of different pocket shapes on process behavior was evaluated. Finally, two different profile thickness have been chosen in order to evaluate the effect of profile thickness on pocket effectiveness. Participants are asked to simulate the extrusion of an industrial case (an especially designed multi-hole die for emphasizing process-related issues), on the base of die geometry, material properties, temperature of billet and die system, ram speed. The results will be compared to the experiments, as performed by the organizers, on the base of extruded length, profile temperature, profile distortions, press load