Antonio Piccininni

Characterization of a superplastic titanium alloy with an experimental and numerical approach based on free-inflation tests

It’s well known that the microstructure dramatically affects the strain behaviour of superplastic materials. Virtually, each batch should be characterized ex novo: optimal ranges of temperature and strain rate as well as material constants have to be defined. An accurate and simple characterization methodology based on a strain condition close enough to the real forming process is of great industrial interest. In this work, a characterization methodology based on an experimental and numerical approach is proposed. Experimental free inflation tests with a pressure jump were carried out on a titanium alloy. Results were used as reference data for an inverse analysis based on the height evolution of the dome. Material constants were calculated by means of a genetic algorithm. The approach was verified with further experimental results and a good correlation was found.

Experimental validation of the Carbone–Mangialardi–Mantriota model of continuously variable transmissions:

We present detailed experiments to validate the Carbone–Mangialardi–Mantriota model of continuously variable transmissions. Experimental tests were carried out in different working conditions for increasing values of the torque load. Steady-state conditions as well as shift manoeuvres were considered. A detailed comparison with the theoretical predictions of the Carbone–Mangialardi–Mantriota model shows good agreement with the experimental results. This is even more remarkable when it is considered that the Carbone–Mangialardi–Mantriota model is fully self-consistent and completely predictive. It does not need any parameter to be specifically tuned or measured. The results from the present research allows the Carbone–Mangialardi–Mantriota model to be definitely proposed as a very accurate and completely predictive model of the continuously variable transmission variator, and as a very promising tool to develop advanced real-time control of continuously variable transmissions for engineering applications.

Improving the Hydromechanical Deep-Drawing Process Using Aluminum Tailored Heat Treated Blanks

The present work demonstrates the effectiveness of combining the hydromechanical deep-drawing process with the Tailored Heat Treated Blank (THTB) technique. In the hydromechanical deep-drawing process, the fluid pressure is used for postponing the fracture occurrence in the blank, while the THTB technique allows to create a material property gradient through a suitable artificial aging treatment carried out prior to the forming process. Since the number of process variables is large, in the present work the authors propose an optimization loop for the determination of the parameters controlling the extension of the blank regions to be subjected to the aging treatment and the temperature levels to be set during the heat treatment. The proposed methodology couples a simple finite element model (Abaqus) with a multi-objective optimization platform (modeFRONTIER). A preliminary experimental campaign was carried out for determining the effect of the aging treatment on the mechanical (through tensile tests) and deformative (through formability tests) behavior of the AC170PX aluminum alloy. Optimization results prove the effectiveness of the adopted methodology and put in evidence that the adoption of properly aged blanks in the hydromechanical deep drawing allows to increase the limit drawing ratio and to simplify the process since it is conducted at room temperature.

Application of the Warm Hydroforming Process to the Manufacturing of Pre-Aged 6xxx Series Components Using a Numerical/Experimental Approach

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.

Numerical/experimental investigations about the warm hydroforming of an aluminum alloy component

The present work investigates the Hydro Forming process in warm conditions using a numerical/experimental approach; an Al alloy (AA6061 T6) component is used as case study. Experimental tests were carried out for characterizing the material and setting the numerical model. A preliminary experimental step based on both tensile and formability tests allowed to characterize both the mechanical and deformative characteristics of the material according to temperature, orientation and strain rate. Finite Element simulations using ABAQUS/explicit were carried out changing (according to a simulations plan created using the Design of Experiment approach) the process parameters which mostly affect the HF process in warm conditions: the forming pressure, both the initial and final Blank Holder pressure and the Temperature (oil pressure and Blank Holder pressure were related to the material yielding strength). The contour plots of an ad hoc response parameter (LN), able to take into account both the risk of rupture and the level of deformation, allowed to evaluate the regions where process parameters guarantee the optimal working conditions.The present work investigates the Hydro Forming process in warm conditions using a numerical/experimental approach; an Al alloy (AA6061 T6) component is used as case study. Experimental tests were carried out for characterizing the material and setting the numerical model. A preliminary experimental step based on both tensile and formability tests allowed to characterize both the mechanical and deformative characteristics of the material according to temperature, orientation and strain rate. Finite Element simulations using ABAQUS/explicit were carried out changing (according to a simulations plan created using the Design of Experiment approach) the process parameters which mostly affect the HF process in warm conditions: the forming pressure, both the initial and final Blank Holder pressure and the Temperature (oil pressure and Blank Holder pressure were related to the material yielding strength). The contour plots of an ad hoc response parameter (LN), able to take into account both the risk of rupture a...

Multi objective genetic algorithm to optimize the local heat treatment of a hardenable aluminum alloy

The continuous research for lightweight components for transport applications to reduce the harmful emissions drives the attention to the light alloys as in the case of Aluminium (Al) alloys, capable to combine low density with high values of the strength-to-weight ratio. Such advantages are partially counterbalanced by the poor formability at room temperature. A viable solution is to adopt a localized heat treatment by laser of the blank before the forming process to obtain a tailored distribution of material properties so that the blank can be formed at room temperature by means of conventional press machines. Such an approach has been extensively investigated for age hardenable alloys, but in the present work the attention is focused on the 5000 series; in particular, the optimization of the deep drawing process of the alloy AA5754 H32 is proposed through a numerical/experimental approach. A preliminary investigation was necessary to correctly tune the laser parameters (focus length, spot dimension) to...

Investigation about the Oil Pressure Rate in the Warm Hydroforming of an Al-Mg Alloy Component

In this work, the hydroforming process in warm conditions was used for manufacturing an Al-Mg alloy (AA5754) benchmark component displaying different strain levels due to its geometry. The attention was focused on the effect of the rate to increase the forming pressure (PR), strictly related to the strain rate the material is subjected to. In fact, preliminary tensile and Nakajima tests (both at room temperature and in warm conditions) revealed that the mechanical and formability properties of the investigated alloy are strongly affected by the strain rate. Warm Hydroforming tests were conducted in order to investigate both the working temperature and the parameter PR. The Blank Holder Force profile was varied according to an experimentally determined profile able to avoid oil leakages. Experimental results were collected in terms of output variables related to the die cavity filling and to the strain level reached on the component: in such a way a multi-objective optimization could be carried out using the commercial integration platform modeFRONTIER. The best compromise between the high level of the component deformation and the cycle time could be obtained by conducting the warm hydroforming process at the temperature of 250°C and setting the parameter PR equal to 0.1 MPa/sec.

Combining the pressure effect with local heat treatment for improving the sheet metal forming process

The present work deals with the advantages in the Hydromechanical Deep Drawing (HDD) when AA5754 Tailored Heat Treated Blanks (THTBs) are adopted. It is well known that the creation of a suitable distribution of material properties increases the process performance. When non heat-treatable alloys are considered, the THTB approach can be successfully applied to increase the Limit Drawing Ratio (LDR) by changing the peripheral zone into the annealed state starting from a cold-worked blank. If this approach is combined with the advantages of a counterpressure, even more remarkable improvements can be achieved. Due to the large number of involved parameters, the optimized design of both the local treatment and the pressure profile were investigated coupling an axial symmetric Finite Element model with the integration platform modeFRONTIER. Results confirmed the possibility of increasing the LDR from 2.0 (Deep Drawing using a blank in the annealed state) up to about 3.0 if combining the adoption of a THTB with the optimal pressure profile.

Multi-objective optimization of the hydroforming process considering different plastic yield criteria

The present work aims at determining the optimal working conditions for the manufacturing of the AA6061-T6 Al alloy by the hydroforming process. As case study a stepped geometry was used. A numerical model was created using the commercial explicit Finite Element code LS-DYNA. The plastic behaviour of the investigated alloy was modelled implementing experimental data (flow stress curves, Lankford coefficients and Forming Limit Curves) and using two different yield criteria: an anisotropic one (Barlat ‘89) and the conventional isotropic one (Von Mises). Finite Element models were tuned using experimental data from warm hydroforming tests: comparing both the sheet thinning and the die cavity filling, quite different friction conditions had to be supposed for obtaining a good fitting with both the yield criteria.Finite Element models were finally used for evaluating the working range of the hydroforming process: results from a CCD simulation plan were imported within an integration platform (modeFRONTIER) to evaluate the optimal hydroforming conditions based on a multi-objective genetic algorithm optimization. Quite different results in terms of optimization and working range were obtained when adopting different yield criteria.