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Multi-Point Incremental Forming (MPIF) process is a new hybrid process that combines two common manufacturing methods. These are Multipoint Forming (MPF) and Incremental Sheet Forming (ISF) processes. In this study, an experimental set-up, based on a MP reconfigurable die, was designed and manufactured to explore the flexibility of this innovative process and its potentialities to produce complex parts using the same tools. The obtained results have indicated that this novel technique, that doesn’t require costly equipments, is an effective approach to manufacture multitude of parts with different shapes. Moreover, it has been shown that the parts geometrical accuracy as well as thickness distribution are enhanced compared to the conventional ISF process and that the geometrical defects, called ‘dimples’ and caused by the pins’ ends, are significantly reduced and almost eliminated after the insertion of a rubber piece between the reconfigurable die and the blank sheet. On the other hand, the effect of the size and geometry of the rectangular pins on the geometrical accuracy and the dimpling defect has been studied using a finite element analysis.

The present work focuses on the simulation of the heat treatment applied after printing of Ti-6Al-4V parts. The numerical tool aims at predicting the influence of heat treatment conditions (e.g. holding time, temperature) on the residual stress field and the distortions for SLM produced parts. The numerical model relies on a thermo-viscoplastic constitutive model. To determine the corresponding material parameters, different creep tests have been performed at temperatures ranging from 723 K to 1173 K. According to the results, the stationary creep strain rate is independent of the hydrostatic pressure, which indicates that the high temperature behavior is not impacted by the initial porosity. Also, the material parameters are observed to change significantly from 873 K, which is due to the progressive transformation of the initial martensitic α ′ microstructure into the α + β lamellar microstructure. To validate the proposed approach, some numerical simulations have been performed for two different parts, for which distortions have been measured. The numerical and experimental distortions have then been compared to each other. For both parts, the agreement between experimental and numerical data is correct.

Because of its excellent properties, such as good corrosion resistance, high specific strength and important ductility, the AA5383 aluminum alloy is largely employed for naval applications. In this work, the mechanical behavior of the AA5383 alloy at elevated temperatures, which is an important aspect for the control of forming operations, is investigated. For this purpose, an experimental campaign, including uniaxial tension, biaxial tension, and shear tests, is performed to cover an important range of temperatures (623∼723 K) and strain rates (10−4∼10-1 s-1). A constitutive model for the description of the high temperature behavior of the AA5383 alloy is then proposed. For the deformation behavior, this model combines a viscoplastic flow rule with the BBC2003 anisotropic yield criterion. Also, the prediction of ductile fracture, which is an important aspect for formability, relies on an extended version of the modified Mohr-Coulomb criterion. The extension allows including the impact of temperature and strain rate on ductile fracture as well as a cut-off value for stress triaxiality. Finally, numerical simulations of the experimental tests are performed to identify the flow rule, yield criterion and fracture criterion parameters by combining different optimization methods. The numerical and experimental results of the different tests are in good agreement, which indicates that the proposed constitutive model is well suited for investigating the impact of process conditions on the formability of the AA5383 alloy at high temperatures.

Incremental sheet forming is a flexible forming process based on the sheet progressive localized deformation where a forming tool follows a trajectory predetermined in advance by CAD/CAM programs. Although it is a slow process compared to conventional processes, this relatively new technique is very adequate for prototyping and small series production since it does not require complex tooling (die, punch, etc.). This paper presents a numerical and an experimental study of the Increment Sheet Forming process for a spiral toolpath. A 30 mm depth conical forming part is considered for this purpose. The experimental forming operation has been conducted on a 3-axis milling machine and the experimental data analysis was performed using a Kistler measurement system and a 3D scanner. Moreover, a Finite Element simulation has been realized in order to predict the evolution of the forming forces and the part final profile. The numerical results were in good agreement with the experimental ones. Moreover, the analysis of the scanning data has successfully restituted the part final profile and the surface details.

During the incremental sheet forming process, tool paths are generated by CAM software. The obtained files have several possible formats such as the APT or the G-code ones which can be directly transferred to CNC machines for parts forming. However, when it comes to the process simulation, the G-code format could not be used in common finite element programs. In this paper, a new method is developed to implement the G-code into the FE software Abaqus using the Python programming language. The G-code commands are translated into appropriate boundary conditions describing the exact forming tool motions without any decomposition or modification. The numerical results obtained by the proposed method and the conventional tool path decomposition method are compared in terms of the part shape, thickness distribution, forces evolution, and CPU times as well. On the other hand, a comparison of the surface roughness of two conical parts formed using these two formats has been conducted in order to investigate the potential effect of the tool path decomposition on surface quality.

The shear behavior of aluminum alloys containing increased amounts of Si or Mg compared with the 6061 alloy has been investigated by carrying out isothermal and non-isothermal tests in the mushy state during solidification. In isothermal conditions, it is shown that (i) an increase in Mg content leads to a more resistant semi-solid alloy compared with the 6061 alloy for the same solid fraction and (ii) an increase in Si content leads to a more brittle mushy alloy. In non-isothermal conditions, stress increases continuously with decreasing temperature with the formation of cracks for some compositions. This study shows that an increase in Mg content seems to be the most appropriate solution to reduce the formation of cracks in a solidifying 6061 alloy.

The aim of this work was to determine the ability to produce thin metallic foils by self-induced ion plating. Foils of pure copper and pure zinc with a thickness of 35 µm have been successfully produced and their characteristics have been compared to foils obtained by conventional techniques (i. e. electroplating and rolling). Results show the following: (i) more or less compact microstructures can be obtained by self-induced ion plating depending on gas pressure and substrate temperature; (ii) microstructures obtained by self-induced ion plating are quite different from those obtained by electroplating and rolling; (iii) Young’s modulus depends on foils roughness; (iv) hardness depends on grain size by exhibiting a Hall-Petch behavior in the case of copper foils and an “inverse” Hall-Petch behavior in the case of zinc foils. DOI: http://dx.doi.org/10.5755/j01.ms.20.2.4019

Superplasticity is a characteristic of certain materials, in particular aluminium alloys, whereby very large deformations (up to 1000 %) can be obtained before fracture under certain conditions. Superplastic forming is therefore the process of deforming a flange under these conditions by applying a variable pressure. The final geometry is obtained when the flange takes the form of a die. In order to deform a material superplastically, the temperature of the material should be approximately a half of the absolute melting point of the material and the strain rate (or flow stress) should remain within a certain range. The most important issues concerning the industrial process are the prediction of the final thickness distribution and the computation of the optimal pressure law to maintain superplastic conditions. Finite element simulations make these predictions possible for industrial components. To ensure the precision of the simulations, it is important to have good knowledge of the material behaviour in the superplastic domain: rheological parameters, grain size, damage law, etc. This paper presents an experimental analysis of the superplastic behaviour of a 7xxx aluminium alloy used for aeronautic applications. The parameters of the constitutive equations (including damage) are identified by using tensile tests, spherical bulging tests and numerical simulations [1, 2]. The performance of the proposed laws [1, 3, and 4] is tested using axisymmetrical geometries with complex shapes by the comparison of numerical simulations and bulge tests.

International audience; The mechanical behavior of alloys resulting from a mixture of a AA6061 base alloy with different alloys from the Al-Si and Al-Mg series used as filler alloys during welding has been investigated under conditions close to welding. The specimens have been subjected to constrained solidification carried out at a high cooling rate of 80 K/s. In the test developed in this study, the central part of the specimen is initially melted. During solidification, this zone suffers strains only generated by thermal contraction and solidification shrinkage, which can possibly lead to the formation of hot cracks. The hot cracking sensitivity of the various alloys has been determined thanks to X-ray microtomography observations which have allowed imaging the zone solidified under constrained conditions and measuring the volume fraction and the number of open cracks as a function of Si and Mg contents. The variation of stress induced by deformation of the solid during constrained solidification has been also measured as a function of solid fraction. The results show that: (1) stress developed within the solidifying alloy exhibits the same variation whatever the Si and Mg contents. Stress starts increasing at the coherency of the solid skeleton and increases much more sharply when coalescence occurs. (2) the alloys with Si and Mg contents exceeding 3 and 2 wt% respectively are less sensitive to hot tearing in comparison with the base alloy; (3)Al-Mg filler alloys seem to be the best solution to reduce hot cracking in 6061 welded joints.