Formability of Friction Stir Welded AZ31 Magnesium Alloy Sheets
The formability of friction stir welded AZ31 magnesium alloy sheets was investigated by means of uniaxial tensile and hemispherical punch tests performed under different process conditions. The results of the tensile tests were analysed in terms of flow stress and ductility at different temperature and strain rate; the hemispherical punch tests, carried out at different temperatures, provided the limiting dome height. The formability of FSW-ed blanks was compared to the one exhibited by the base material in order to evaluate the quality of the welded joints.
The evaluation of springback in 3D stamping and coining processes
Abstract An effective predictive technique of the elastic springback in a fully 3D 90° V-punch V-die bending process is presented. This is based on a combined approach in which an explicit finite element code was used to simulate the loading phase of the process whilst an implicit procedure was used to analyse the springback phase. Two different punches with a nose radius of 4 and 8 mm were used. An increase in the springback ratio with the coining load was observed with the lower nose radius. Conversely, an increase in the springback ratio with the coining load up to a peak value (>1), corresponding to a force of about 20 kN, followed by a decrease in the springback ratio with increasing t…
In-process tool force and rotation variation to control sheet thickness change in friction stir welding of magnesium alloys
Two different in-process control strategies, developed in order to produce sound joints in AZ31 magnesium alloy by Friction Stir Welding on sheet blanks with a non-uniform thickness, are presented and compared. To this purpose, sheets with dip or hump were machined and welded by either changing the rotational speed or the tool plunging in order to keep constant the vertical force occurring during welding. The mechanical strength of the joints was measured in the zones where the sheets before welding were characterised by different thicknesses. The sheets welded by the two different strategies are characterized by very similar ultimate tensile strength values. Finally, the results showed tha…
Springback evaluation in fully 3-D sheet metal forming processes
Abstract In the modern manufacturing industries the knowledge and proper control of the sheet metal springback after forming is a fundamental aspect in the achievement of near net shape stamped parts. In this paper an effective springback prediction in some fully three-dimensional stamping processes is carried out. Such a prediction is based on a combined approach in which an explicit finite element code has been employed to simulate the forming phase while a traditional implicit procedure has been used to analyse the springback phase. The results obtained have been compared with a set of experimental tests and an excellent correlation between the predicted and experimental data has been fo…
Constant Heat Input Friction Stir Welding of Variable Thickness AZ31 Sheets Through In-Process Tool Rotation Control
Tailored blanks characterized by variable thickness were friction stir welded (FSWed) with the aim to obtain constant joint properties along the weld seam, regardless of the thickness change. To pursue this goal, the heat input was kept constant by in-process control of tool rotation. A dedicated numerical model of the process was used to determine the tool rotation values as a function of the sheet thickness. The mechanical properties and the microstructure of the FSWed joints, produced with varying process parameters, were studied. It was found that the proposed approach can produce joints with uniform properties along the weld line in terms of stress–strain curve shape, joint strength, e…
Sheet metal forming of titanium blanks using flexible media
Abstract Sheet metal forming processes using flexible media are increasingly utilized in the industrial practice due to the relatively low tooling cost. In the present investigation, a rubber forming process is applied to the manufacturing cycle of a titanium alloy component for acoustic tweeters. The proposed process allows a reduction in manufacturing costs and production time since it permits the elimination of some joining operations. The FEM analysis has permitted the definition of the optimal process parameters and tooling geometry. Accordingly, several components have been produced; the achieved quality level is comparable with the one obtained utilizing the conventional technology a…
Tool Geometry in Friction Stir Welding of Magnesium Alloy Sheets
Friction Stir Welding (FSW) has been arousing a continuously increasing interest among joining processes since its invention in 1991. Although mainly used for aluminum alloys, it can also be applied to other light alloys. In the present work, experimental and numerical campaigns have been performed with the aim to study the effect of the tool geometry on the mechanical properties of FSW-ed AZ31 magnesium alloy sheets. The results, presented in terms of tensile strength, ductility, micro-hardness values and numerical field variables distributions, allow to reach a deeper knowledge on the behaviour of such relatively new material when FSW-ed, and can be used for a full optimization of the joi…
Solid State Joining of Thin Hybrid Sandwiches Made of Steel and Polymer: a Feasibility Study
Abstract The growing demand for more environmentally friendly vehicles has led to an increased use of light materials in the transportation industry with the aim to reduce structural weight, fuel consumption, and gas emissions, thereby boosting cost-effectiveness and recyclable properties. Complex multi-material steel-based components would allow to improve mechanical properties and minimize weight even further. In particular, new sandwich materials made by steel outer skins and a polymeric internal layer seems very promising for obtaining mechanical performance and lightness at the same time. Unfortunately, traditional welding techniques, like arc welding, laser welding, and resistance spo…
Computer simulation of metal flow in the hot upsetting of a high-strength aluminium alloy
Abstract The effects of metal-working temperature on the hot axisymmetric upsetting of AA 7012 aluminium alloy were investigated in the temperature range of from 250 to 400°C, at a strain rate of 4 s −1 . The material behaviour was studied by means of simulative methods based on the analysis of torsion-test results which have shown that when the strain increases, the flow stress increases to a peak value and then decreases to a fracture value. Furthermore, the flow stress decreases with decreasing strain rate and with increasing temperature. Constitutive equations, describing accurately the hot deformation behaviour of the material, were defined and used subsequently in a numerical model th…
In-process control strategies for friction stir welding of AZ31 sheets with non-uniform thickness
Two different in-process control strategies were developed and compared with the aim to produce AZ31 magnesium alloy joints by friction stir welding on sheet blanks with a non-uniform thickness. To this purpose, sheets with dip or hump zones were welded by either changing the rotational speed or the tool plunging in order to keep constant the value of the vertical force occurring during the welding stage of the process. The influence of the main process parameters on the tool force, the micro- and macromechanical properties, and the joints microstructures in the dip and hump zones were analyzed. The results showed that using the rotational speed change-based approach, the hump zones are sub…
Experimental and numerical analysis on post welding formability of FSWed AZ31 magnesium alloy thin joints obtained using a "Pinless" tool configuration
The post welding formability of friction stir welded AZ31 magnesium alloy thin sheets (1.5 mm thick), obtained using a “pinless” tool configuration, was widely investigated by means of the hemispherical punch method at 350°C, with a constant crosshead speed of 0.1 mm/s. The results were compared with those obtained on the base material. It has shown that formability of the joints is lower than the one of the base material. The experimental work was supported by a numerical investigation based on FEM in order to highlight the material flow occurring during the welding process. Additionally, hemispherical punch tests were simulated starting from the calculated conditions, in terms of accumula…
In-process tool rotational speed variation with constant heat input in friction stir welding of AZ31 sheets with variable thickness
In the present work, friction stir welding experiments on AZ31 magnesium alloy sheets, characterized by a variable thickness along the welding line, were carried out. The approach adapted during welding consisted in maintaining constant the heat input to the joint. To this purpose, the rotational speed of the pin tool was increased with decreasing thickness and decreased with increasing thickness in order to obtain the same temperatures during welding. The amount by which the rotational speed was changed as a function of the sheet thickness was defined on the basis of the results given by FEM simulations of the FSW process. Finally, the effect of the in-process variation of the tool rotatio…
Validation of frictional studies by double-cup extrusion tests in cold-forming
Abstract Studies on frictional conditions in cold-forming have shown that, for a given lubricant, friction factor values are strongly affected by the test method. In the present paper, different cold-forging processes of an aluminium alloy, are modelled by a FEM numerical code using the m values obtained by both the double cup extrusion and ring compression tests. It appears that the m values given by the ring tests can be effectively used in the simulation of upsetting processes, while the m values derived by the double cup extrusion tests are more appropriate for predictions in extrusion and closed-die forging operations.
Experimental and Numerical Analysis on FSWed Magnesium Alloy Thin Sheets Obtained Using “Pin” and “Pinless” Tool
The present investigation aims at studying the effect of different tool geometries and process parameters on FSW of thin sheets in AZ31 magnesium alloy. In particular two properly designed tools, with shoulder diameters equal to 8 and 19 mm, were used; each of them was manufactured both in pin and pinless configurations. The effect of the different tool configurations and sizes, and welding parameters on mechanical properties of FSWed joints were analyzed in detail. The results were compared with those obtained on the base material. It was shown that FSWed joints are characterized by strength and ductility values lower than those of base material. Furthermore, the pin tool configuration, wi…
Benchmarking the sustainable manufacturing paradigm via automatic analysis and clustering of scientific literature: A perspective from Italian technologists
Abstract The number of scientific papers in the field of Sustainable Manufacturing (SM) shows a strong growth of interest in this topic in the last 20 years. Despite this huge number of publications, a clear statement of the profound meaning of Sustainable Manufacturing, or at least a strong theoretical support, is still missing. The 6R framework seems to be a first attempt to rationalize this issue, as it is an axiomatic identification of its true nature. Recognizing the pursuing of one or more of the Reduce-Recycle-Reuse-Recover-Redesign-Remanufacture principles allows users to identify if any manufacturing action is in the right direction of sustainability. In the paper, the authors spec…