Papers by Author: Luigi Tricarico

Abstract: 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.

Abstract: In this work authors present a study of the influence of the pressure profile on forming time and on post-forming characteristics of superplastically formed parts. Material parameters of an aluminium superplastic alloy (ALNOVI-U) were estimated on the basis of experimental tests and of a numerical approach. A numerical model of the forming process was then created and used for evaluating the pressure profile able to keep the maximum strain rate value close to a target value. Pressure profiles were calculated using a strain rate control algorithm, firstly following a conventional approach and monitoring the whole sheet, and then considering only the elements most deformed at the end of the forming process. Experimental results from different numerical pressure profiles are then compared, in terms post-forming characteristics, to test the effectiveness of the approach.

Abstract: The high strength to weight ratio and good corrosion resistance of titanium alloys, have led to an increasing use of these materials, particularly in the aerospace industry. The laser cutting technique may be a promising tool in machining titanium alloy parts like those with subsequent welding requirement: in this case, surface quality of the kerf edges is of great importance. The low thermal conductivity and the high chemical activity of titanium alloys lead, in fact, to alterations of the surface properties of the machined zone. This paper presents the results of titanium alloy laser cutting using a 2 kW fiber laser. The cutting process was performed in continuous wave mode and using Argon as shear gas. Laser cuts were realized on titanium alloy Ti6Al4V sheets 1mm thick. Image analysis and microscopy, were carried out to examine the cutting edge quality features including thickness of the recast layer and heat-affected zone.

Abstract: CO2 laser - Metal Inert Gas (MIG) hybrid welding process was investigated in the butt welding of Ti-6Al-4V titanium alloy sheets of 3.0mm in thickness. Using a Design of Experiment (DoE) approach, bead on plate tests were planned with the aim to analyze the effect of laser and laser-MIG welding parameters on the bead shape, hardness profiles in the weld cross section and welding efficiency. Butt welds performed in correspondence of the bead on plate working conditions which assure the complete penetration of the samples, the absence of undercuts and the maximum welding efficiency, confirm the results of the bead on plate tests and highlights the gap bridging ability of the hybrid welding process.

Abstract: Numerical 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.

Abstract: The present paper is focused on the Finite Element modeling of the Marciniak stretch-forming test in warm condition. Such a test was proposed by the authors for evaluating the warm formability of the Mg alloy AZ31 according to the most important parameters: the temperature and the strain rate. Tensile tests confirmed the large influence of the strain rate on the deformation of the AZ31, especially when the test temperature is over 200°C. Three dimensional FE simulations were thus carried out in order to analyze the strain and strain rate evolutions during the formability test at the temperature of 200°C. In particular, simulations were aimed at investigating the effect of the specimen’s geometry on the strain rate evolution in the central region, where failure occurs during the Marciniak stretch-forming test. An equation for calculating the punch speed profile able to keep a constant equivalent strain rate in the central region of the specimen has been furnished according to the geometry of the specimen. Its efficiency was validated by means of additional simulations implementing the punch speed profile calculated using the proposed approach.

Abstract: Laser butt-welding of AA5083 has been investigated using a high quality CO2 laser in continuous wave regime. The effect of laser power, welding speed and specimen thickness on mechanical properties of the welded joints were evaluated by employing a general full factorial experimental plan design. The experimental results indicate important suggestion to choose proper combinations of process parameters and achieve high strength butt welded joints.

Abstract: Using the optimum blank in sheet metal forming process not only can decrease the material wasting but also avoid possible defects such as local severe thinning, wrinkling and fracture. Since it is practical technology for industrial production, many blank optimization methods have been proposed and their validity was verified by some forming tests of typical or complicated components. However, all the forming tests were carried out at room temperature or under isothermal condition. In present work, a blank optimization method was employed to evaluate its efficiency in deep drawing of rectangular magnesium alloy cups under non-isothermal condition. It is proved by experiment that the employed blank optimization method can predict successfully the optimum initial blank shape for the component with specified shape and dimension.

Abstract: In this work a method, based on bulge tests performed on a blow forming equipment, for evaluating the superplastic material characteristics is proposed. The pressure imposed on the sheet and the height of the dome of the specimen during the test are used as characterizing parameters. Different pressure levels are applied subsequently in the same test and the strain rate sensitivity index is calculated starting with analytical considerations and then with an inverse approach based on a simple finite element numerical model of the test. The change of the slope in the specimen dome height curve, due to the change of the pressure, is correlated to the strain rate in the sheet. The method has been verified applying other load profiles on the sheet and good agreement has been found between experiments and numerical results obtained by the inverse analysis.

Abstract: In the present work the definition of a test procedure for evaluating the formability of Mg alloy thin sheets was investigated taking into account both temperature and strain rate. A numericalexperimental approach was adopted by the authors: numerical simulations were run with the aim of: (i) defining the punch geometry of the formability test equipment in order to have a uniform, fast and constant temperature distribution on the specimen; (ii) setting the test operating conditions in order to force the specimen failure in a region where temperature and strain can be easily acquired. Some formability tests were performed and strain fields were measured using an optical measurement system.