LO STUDIO DELLA REALIZZAZIONE DI UN COMPONENTE AUTOMOBILISTICO IN LEGA DI TITANIO TI-6AL-4V MEDIANTE FORMATURA INCREMENTALE NELLA MODALITÀ A SINGOLO PUNTO (SINGLE POINT INCREMENTAL FORMING).

The present work focuses the attention on the Single Point Incremental Forming (SPIF) process of a scaled car door shell made by the Titanium alloy (Ti6Al4V). The effect of a temperature increase contemporary due to electric static heating and tool rotation speed was investigated. Preliminary tensile tests allowed to define the temperature level to be assured on the sheet in order to determine a consistent flow stress reduction. SPIF tests were carried out adopting rotation speed in the range 800–1600 RPM, while simultaneously changing the pitch value in the range 0.5–1.0 mm. Temperature during the forming process was continuously measured in the central area of the blank using a pyrometer. In addition a digital image correlation system was used for measuring the strain distribution over the formed part. The combination of the two approaches (heating by both electric bands and high tool rotation speed) revealed to be a feasible solution for manufacturing hard to work materials like Ti alloys, since the investigated case study was successfully formed by SPIF. In addition, a positive effect of the tool rotation speed in stabilizing the necking (thus allowing to reach higher level of stretching) was recognised.

The aim of this study is to investigate the possibility of manufacturing an aluminum automotive component (a small sized car door panel) using a highly reconfigurable and cheap forming process. Specifically, the sheet hydroforming process and rapid tooling technique were combined, with the objective of making the resulting process more flexible and less expensive.Sheet hydroforming experiments were carried out using a layered die created assembling 2D laser cut layers and testing three Al alloys (AA2024, AA5754, AA7475); process parameters (Closing Force and Pressure) were evaluated by means of finite element simulations, mainly focused on the curve defining the Closing Force as a function of the forming Pressure and on friction conditions, which have a significant effect on the distribution of sheet thickness in formed parts.Both numerical simulations and experimental tests highlighted that sound parts could be obtained if a hard enough sheet material together with the appropriate Closing Force and forming Pressure are used. The proposed approach, combining the hydroforming process with a rapid tooling technique, proved to be effective in rapidly manufacturing prototypes and thus in shortening the product design process.

The present work focuses the attention on the Single Point Incremental Forming (SPIF) of the Titanium (Ti) alloy Ti-6Al-4V. Tensile tests were carried out using the optical strain measurement system Aramis3D, in order to determine the mechanical behaviour of the alloy and to investigate the anisotropy of such alloy. Finite Element (FE) simulations of the SPIF process (using ABAQUS/explicit) were performed using a simple but non-axialsymmetric shape (truncated pyramid) with the aim of investigating the effect of both the tool/pitch ratio (D/p) and the draw angle (α), taking into account the anisotropic behaviour. The analysis of plastic strains and thinning maps, together with the evaluation of shape errors originated by the forming process, highlighted that the parameter D/p plays a key role in the SPIF. Results from the preliminary FE analysis were used for investigating the production by SPIF of an automotive component (car door shell). A specific subroutine was created by the authors for automatically generating the tool path to be used in both the FE simulations and the manufacturing of parts by SPIF on a CNC milling machine.

AFFRONTIAMO LA CARATTERIZZAZIONE DI UN LEGA DI ALLUMINIO FINALIZZATA ALLA CREAZIONE DI UN MODELLO NUMERICO DI UN PROCESSO DI FORMATURA SUPERPLASTICA. L’INDIVIDUAZIONE DEI PARAMETRI DEFORMATIVI OTTIMALI E DELL’EQUAZIONE COSTITUTIVA DEL MATERIALE HANNO PERMESSO DI ANALIZZARE LE CRITICITÀ DI PROCESSO NELLA REALIZZAZIONE DI UN COMPONENTE DI FORMA COMPLESSA NON REALIZZABILE CON TECNICHE CONVENZIONALI.

In this work the Warm Hydroforming (WHF) process for the production of a 6xxx series Al alloy component has been investigated using a numerical/experimental approach: both experimental and numerical hydroforming tests were carried out using the alloy AC170PX, a pre aged (T4 condition) Al alloy often adopted for automotive applications. In order to evaluate both the mechanical and strain behaviour of the material, tensile tests were carried out at different temperature and strain rate levels using the Gleeble system 3180, keeping also into account the ageing effect; in addition, formability (Nakazima) tests in warm conditions were performed by means of a specific equipment and the Forming Limit Curves at different temperature levels were evaluated according to the ISO standard 12004-2. Hydroforming experiments were carried out using a prototypal press machine specifically designed for WHF and SuperPlastic Forming tests. Such tests, scheduled by a DoE approach, were aimed at investigating the suitability of using the investigated Al alloy in the WHF process: attention was thus focused on those parameters mainly affecting the aging phenomenon (temperature, heating time and cycle time). In order to overcome the actual physical limitation of the hydroforming facilities, a Finite Element (FE) model of the WHF process was also created implementing experimental data (flow stress curves and FLCs) and tuned using data from preliminary WHF tests. In particular, after setting the Coefficient Of Friction (COF) according to temperature and verifying the robustness of numerical simulations, the FE model was used for investigating: (i) the influence of the Blank Holder Force (neglected in the experimental campaign); (ii) the adoption of quite smaller values of the parameter cycle time (being the aim to determine higher strain rates in the material). Through the definition of proper response variables (Flatness, Bursting Pressure and Thickness Ratio) both experimental and numerical results were analyzed by means of polynomial Response Surfaces in order to evaluate the optimal process conditions.

In this work, the mechanical and technological behaviour of AZ31 magnesium alloy laser welded joints is investigated. The forming behaviour of the joints is analysed by both tensile and biaxial stretch tests. Each test is monitored using a digital image correlation system in order to acquire the complete strain field during the whole test. Both in tensile and biaxial stretching tests, the strain maps reveal that the weld bead makes the strain path experienced by the welded specimen more critical than the one experienced by the base material, and this can be related to morphological defects of the weld bead.

The present work is aimed to determine the mechanical behaviour in hot condition (range 600-1200°C) of a super duplex stainless steel (SAF 2507) for applications in the Oil&Gas field (highly corrosive environments). A wide experimental activity (both tensile and creep tests) was carried out using the Gleeble system, using experimental settings able to make the test robust and replicable. In order to evaluate the constant parameters able to model the material behaviour according to the Norton equation, experimental conditions (in terms of temperature and applied stress) were designed: the Response Surface Methodology (RSM) and a subsequent double multi objective optimization were implemented within an integration platform. Finally, using Visual Basic routines model constants were evaluated and/or refined, thus being able to optimally fit real strain –time curves, also in the primary creep stage.

The effect of laser cutting parameters on the mechanical behavior of laser butt welded joints whose edges were obtained by laser cutting was investigated. The paper aims to demonstrate that new high power solid-state fiber lasers not only represent a valid and reliable alternative to the most established CO2 and Nd:YAG laser sources, but also allow to obtain cuts having edges well suited for subsequent direct laser welding. First Ti6Al4V 1 mm thick sheets having edges machined by milling were laser welded. Once the optimal welding condition was determined, the mechanical characterization of sheets cut by fiber laser and then laser welded was performed. Comparative strain analysis performed by a digital image correlation technique highlighted the effect of the gap between the sheets resulting from the different cut edge quality. Experimental results showed that the correct selection of laser cutting parameters allows to obtain butt joints characterised by mechanical properties comparable with the ones obtained by milling. Cutting edge quality in the optimal range of gap values allows to obtain the best mechanical performances of the joint.

The present work is focused on the Deep Drawing process in warm conditions and in particular on the evaluation of optimal working conditions and/or enhancement of the process limits using metamodels. Experimental tests were carried out with the aim of investigating the effect of the most important process parameters affecting the DD process: the blank holder pressure, the temperature of the Blank holder and the punch speed. The output variable “Progress” (defined as the ratio between the effective and the maximum punch stroke) was fitted using a separate parallel approach based on two different Response Surface construction algorithms. Further experimental tests were thus designed using an optimization approach based on the above mentioned RS, being the aim to enhance the process limits in terms of maximum achievable drawing ratio. The experimental results coming from the second campaign could be also used as a validation set for the results obtained from the initial optimization, thus allowing to identify which of the two initial RS was the most reliable in evaluating the process window.

INVESTIGHIAMO SULL’EFFICACIA DELL’UTILIZZO DI UN RISCALDAMENTO/ RAFFREDDAMENTO LOCALIZZATO E QUALE SIA LA MODALITÀ MIGLIORE DI REALIZZARLO PER UNA APPLICAZIONE PRATICA.

RACCONTIAMO L’APPLICAZIONE DI UN SISTEMA DI MISURA SENZA CONTATTO ALLO STUDIO DELL’ANOMALO COMPORTAMENTO DEFORMATIVO DI ALCUNI MATERIALI DI LARGO USO INDUSTRIALE (COME L’ACCIAIO E LE LEGHE DI ALLUMINIO) DOVUTO ALL’EFFETTO “PORTEVIN-LE CHATELIER” (PLC)

Surface hardening with discrete laser spot treatment is an interesting solution since the adoption of a single pulse allows the treatment of different surface geometries avoiding the effect of back tempering. The aim of this work is to find a suitable process window in which operate to get best results in terms of hardness, diameter and depth of the treated region. A single pulse out of a fiber laser source impinging on a bearing hypereutectoid steel was used using different power values, pulse energy and defocussing distances, in order to get the optimal process parameters. The dimensions of the hardened zone and its hardness were then acquired and related to the laser process parameters, to the prior microstructure of the steel (spheroidized and tempered after oil quenching) and to the roughness on the specimen before the laser treatment. Experimental results highlighted that both the surface condition (in terms of roughness) and the initial steel microstructure have a great influence on the achieved hardness values and on the dimension of the laser hardened layer. The pulse energy and power strongly affected the dimension of the hardened layer, too.

A numerical/experimental procedure is proposed for calculating the residual stress state during the cooling phase of the casting process of a superduplex stainless steel (ASTM A890 Gr. 5A). The experimental activity consisted of casting, tensile and creep tests. Casting tests were used to set (by acquiring temperature data at different points) and validate (by measuring displacements after releasing residual stresses by cutting) the Finite Element model. Tensile and creep tests were used to determine the material properties from room temperature to 1200 °C. A fully coupled thermo-mechanical analysis was conducted by neglecting the presence of the sand mould; instead, attention was focused on the material by modelling the creep behaviour using the Bailey-Norton formulation. Measurements of the of the displacements due to the stress release after EDM wire cuts revealed to be in good agreement with the numerical model and confirmed the key role played by viscosity during the cooling phase. Neglecting the viscous strain led to an overestimation (more than twofold) of the stress level in the cast part after the cooling phase in the sand mould. The good matching between experimental and numerical data indicated that a numerical model that incorporates the creep behaviour is able to accurately capture the investigated phenomenon, despite the simplification in the modelling of the casting process (sand mould replaced with virtual convection) which does not substantially affect its accuracy. The robustness of the methodology, which is characterized by small computational cost and good quality of results, was further proved simulating and comparing numerical and experimental results concerning a second casting geometry.

Surface hardening with discrete laser spot treatment is an interesting solution since the adoption of a single pulse allows the treatment of different surface geometries avoiding the effect of back tempering. The aim of this work is to find a suitable process window in which operate to get best results in terms of hardness, diameter and depth of the treated region. A single pulse out of a fiber laser source impinging on a bearing hypereutectoid steel was used using different power values, pulse energy and defocussing distances, in order to get the optimal process parameters. The dimensions of the hardened zone and its hardness were then acquired and related to the laser process parameters, to the prior microstructure of the steel (spheroidized and tempered after oil quenching) and to the roughness on the specimen before the laser treatment. Experimental results highlighted that both the surface condition (in terms of roughness) and the initial steel microstructure have a great influence on the achieved hardness values and on the dimension of the laser hardened layer. The pulse energy and power strongly affected the dimension of the hardened layer, too.

Presentiamo una metodologia sperimentale utilizzabile per valutare, in accordo con gli standard internazionali (la norma ISO 8688-1), i principali fenomeni di usura tipici delle lavorazioni ad asportazione di truciolo. In particolare, sono state eseguite dagli autori prove di fresatura frontale a secco su un centro di lavoro verticale, utilizzando un utensile da taglio a inserti in carburo di tungsteno/cobalto; le prove sono state eff ettuate utilizzando sia utensili non rivestiti che utensili rivestiti (con due diff erenti valori dello spessore) tramite un coating monolayer costituito da nitruro di titanio depositato per via fi sica da fase vapore. La suddetta metodologia è risultata dunque idonea a valutare le prestazioni tecnologiche dei rivestimenti per utensili da taglio, permettendo di diagrammare e quantifi care l’evoluzione temporale dell’usura al variare della tipologia e/o caratteristiche dell’utensile impiegato.

In questo articolo analizziamo le proprietà tecnologiche di rivestimenti a base di nitruro di zirconio, di tipo sia monolayer che multilayer nanostrutturati, depositati con un forno da laboratorio su inserti in carburo di tungsteno/cobalto. I rivestimenti oggetto di questo studio sperimentale, già sottoposti a prove di laboratorio i cui risultati sono stati presentati pochi mesi fa su questa stessa rivista [1], stavolta sono stati sottoposti a prove di fresatura frontale a secco in accordo con la metodologia basata su standard internazionali (ISO 8688-1) e presentata dagli autori nell’articolo pubblicato sullo scorso numero di “Utensili e attrezzature” a febbraio 2011. L’obiettivo ultimo è quantifi care la vita utile degli utensili da taglio rivestiti attraverso la misura dell’evoluzione temporale della curva d’usura e individuare possibili correlazioni tra i risultati delle prove di laboratorio e le prove sul campo al fi ne di spiegare le prestazioni tecnologiche degli utensili rivestiti e l’eff etto dell’adozione di diff erenti strutture di rivestimento (monolayer o multilayer) e/o diff erenti parametri del processo deposizione.