Luigi Carrino

Experimental Study of the Forces Acting on the Tool in the Friction-Stir Welding of AA 2024 T3 Sheets

In this paper, AA 2024 T3-rolled sheets were joined in butt joint configuration through the friction stir welding process. Different joints were carried out varying the principal process parameters (i.e., tool welding speed and tool rotational speed). The aim of this work was the study and the experimental characterization of the influence of the process parameters on the forces acting on the tool during the FSW process. Furthermore, it was studied the correlation between the forces and the grain size, in particular with the extension of the heat-affected zone. Forces acting along the axis parallel to the tool are actually greater than those acting along welding direction. All the recorded forces are strictly dependant on the process parameters adopted. No correlation has been found between the grain dimension within the weld bead and the recorded forces, while the greater the forces, the narrower the extension of the heat-affected zone.

Beta Forging of a Ti6Al4V Component for Aeronautic Applications: Microstructure Evolution

Ti–6Al–4V is an alloy increasingly used for structural applications in aeronautics due to its characteristics of high mechanical properties, lightness, and corrosion resistance. This alloy is conventionally forged below the beta transus temperature in order to control the microstructure evolution, to obtain a component with the desired properties. In this paper, some experiences of an innovative beta forging process of the Ti–6Al–4V alloy are reported. A preliminary campaign of forging tests in the beta field on cylindrical coupons was carried out in order to study the microstructural evolution in different forging conditions, in terms of both temperature and strain rate. Moreover, in order to study the microstructural evolution due to the beta forging in a complex shaped component, a case study is presented. The forged component showed a microstructure coherent with the forging process experienced; moreover, the hardness values measured were similar to the ones of the Ti–6Al–4V alloy in mill-annealed conditions.

Negative and positive incremental forming: Comparison by geometrical, experimental, and FEM considerations

ABSTRACT This study compares negative incremental forming (NIF) and positive incremental forming (PIF) processes by geometrical considerations, finite element method (FEM) analyses, and experimental evaluations. Conical frusta were manufactured starting from AA5052H19 aluminum alloy sheets using both techniques. The processes were also simulated with LS-DYNA software and a close correlation between the experimental and numerical results was observed. The analysis of forming forces, forming limit diagrams (FLDs), and sheets thinning highlights that the PIF technique allows one to reach higher formability and geometrical accuracy. Finally, the differences in terms of surface quality were also discussed.

Superplastic Forming/Diffusion Bonding of a Titanium Alloy for the Realization of an Aircraft Structural Component in Multi-Sheets Configuration

Superplastic forming and diffusion bonding (SPF/DB) is a near-net-shape forming and joining process used with alloys having superplastic properties in order to make manufact which should have light weight and high stiffness. The aerospace is one of those sectors in which such technology is mainly used. This process allows to reduce the buy-to-fly ratio and consequently the production costs thanks to the possibility to produce complex shape components in a single shot. The material widely used for this application is the Ti-6Al-4V alloy for its high strength vs weight ratio, excellent mechanical proprieties, corrosion resistance and galvanic compatibility with carbon fiber reinforced composite materials. In this study, finite element analysis of the SPF/DB process has been carried out in order to investigate the thickness prediction, the optimization of the tooling’s geometry and the definition of the sheets initial thickness in the blow forming process of a multi-sheets configuration.

Innovative core material produced by infusion process using hemp fibres

This paper investigates the mechanical properties in term of compression, tensile, flexural and shear strength of a new hemp core based on woven fabric. The hemp core is manufactured by means an innovative vacuum infusion process in which the input both of epoxy resin and of air was allowed. In addition, a comparison among this and others more known materials used as core in sandwich structures was carried out. The results showed that the core under investigation has higher mechanical properties, without shear and indentation failure during the tests on the respective sandwich structures.

Numerical Optimization of Selective Superplastic Forming of Friction Stir Processed AZ31 Mg Alloy

Superplastic forming is a near net shape process used to produce various items with complex geometry. However in many cases, only some portions of the workpiece undergo superplastic deformation. In these cases, instead of choosing expensive starting sheet material with superplastic properties, a low-cost conventional material can be chosen and a grain refinement process can be performed in the selected regions to enhance superplastic properties locally [1]. This process is known as “selective superplastic forming” [R.S. Mishra, M.W. Mahoney, US Patent 6,712,916, 2002]. In some previous works the use of Friction Stir Processing (FSP) was used to obtain locally a microstructure with ultrafine grains in the AZ31 magnesium alloys [2, 3]. In this study a modeling approach was adopted thanks to a commercial FE code and different simulations were conducted in order to correlate the experimental and numerical results for the model optimization [4, 5]. Free bulge forming tests of friction stir processed AZ31 sheets, in conjunction with numerical simulations, were used to evaluate the proposed optimization approach, with the aim to reduce the time and costs in the design of components with complex geometry.

Characterization of Ti-6Al-4V Tribopairs: Effect of Thermal Oxidation Treatment

This paper deals with the study of the influence of the thermal oxidation (TO) treatment on the tribological properties of Ti-6Al-4V tribopairs. A detailed experimental campaign, including tribological tests, microgeometrical measurements, microhardness tests and phase composition analyses, was carried out on both treated and untreated components. The tribological behavior was studied through the pin-on-disk tests in four different contact conditions: treated disk coupled with untreated pin, untreated disk coupled with treated pin, both treated and both untreated. The effectiveness of the treatment in enhancing the tribological properties of the Ti-6Al-4V alloy sheets was found. In particular, the thermal oxidation treatment, promoting hardness enhancement and the formation of a superficial rutile layer, changed the wear mechanism of the titanium alloy, passing from adhesive wear type, for the untreated case, to abrasive wear, in the treated one.

Robotized Filament Winding of Full Section Parts: Comparison Between Two Winding Trajectory Planning Rules

Robotized filament winding technology involves a robot that winds a roving impregnated by resin on a die along the directions of stresses to which the work-piece is submitted in applications. The robot moves a deposition head along a winding trajectory in order to deposit roving. The trajectory planning is a very critical aspect of robotized filament winding technology, since it is responsible for both the tension constancy and the winding time. The present work shows two original rules to plan the winding trajectory of structural parts, whose shape is obtained by sweeping a full section around a 3D curve that must be closed and not crossing in order to assure a continuous winding. The first rule plans the winding trajectory by approximating the part 3D shape with straight lines; it is called the discretized rule. The second rule defines the winding trajectory simply by offsetting a 3D curve that reproduces the part 3D shape, of a defined distance; it is called the offset rule. The two rules have been compared in terms of roving tension and winding time. The present work shows how the offset rule enables achievement of both the required aims: to manufacture parts of high structural performances by keeping the tension on the roving near to the nominal value and to markedly decrease the winding time. This is the first step towards the optimization of the robotized filament winding technology.

Formability Evaluation of Grade 1 Titanium Sheets Depending on the Temperature by FE Analyses

Nowadays, the need of developing high flexible forming processes matches with the need of weight reduction. In this light, the incremental forming of titanium alloys sheets can guarantee both these aspects by combining the flexibility of the process, particularly suggested for small batches and customized parts, with the good properties of titanium alloys, in particular for aerospace applications.The aim of this work was to obtain information useful to enhance the general knowledge of the hot incremental forming processes of grade 1 titanium sheets at different temperatures.First, both tensile and straight groove tests were carried out by varying the test temperature; in this phase, information regarding both the forming forces and the wear phenomena due to the tool-sheet contact was acquired.Successively, on the basis of the mechanical characterization of the sheets previously carried out, explicit analyses, effectuated by a non-linear FE code, allowed to determine the formability curves of the sheets for the different temperatures.

Titanium Hot Stretch Forming: Experimental and Modeling Residual Stress Analysis

Titanium alloys, due to their high mechanical properties coupled with light weight and high corrosion resistance, are finding a widespread use in the aeronautic industry. The use of titanium in replacing the conventional alloys, such as aluminum alloys and steel, is reduced by both the high cost of the raw material (it costs anywhere from 3 to 10 times as much as steel or aluminium) and the machining costs (at least 10 times that to machine aluminium). For such a reason new technologies have been studied and developed. In particular many researchers are searching for technologies, such as the precision hot forming, that allows to obtain components with a low buy to fly ratio. Many of the airframe component structures are designed to fit against the inside radius of the fuselage curvature. By combining traditional stretch forming technology with hot titanium forming techniques, the HSF guarantees a saving in material and machining time, which are two serious cost issues for todays aircraft manufacturers. In addition, the process allows for consistent quality in a productively efficient manner, assuring the sustainable attainment of delivery and build schedules. In order to develop and improve the HSF process a modeling of the process itself was executed in order to study the stresses and strains undergone by the material among the deformation. The FEM model was validated through the residual stresses, and in particular the residual stresses provided by the model were compared with the ones experimentally measured using the hole drilling technique. Good agreement, in terms of stress range, was recorded both for the maximum and the minimum stress.