SIMP-Aero

This project, which concerns the production of aircraft structural parts, aims at developing simulation software to predict the deformation of laminated, forged or pre-formed parts during milling operations, in order to optimise the machining process and to validate or modify the geometrical definition. The project follows on from a FUI project carried out by Aubert&Duval, Constellium, the Cemef and Pascal Institute / IFMA, which ended in February 2015 and addressed the post-machining deformation of a new class of aluminium-lithium alloy. The project resulted in the identification of more fundamental scientific issues. The design of aircraft structural parts must satisfy the requirement of mechanical strength associated with a reduction in weight and a minimisation of the manufacturing cost. Starting from a pre-formed part, between 80 and 90% of the material is removed by milling, which induces a significant re-distribution of the internal stresses generated by the initial forming process. This deforms the workpiece and increases the cost and manufacturing time. Managing this deformation is thus an important factor in reducing costs and optimising the process, by simplifying operations and controlling the volume of metal involved. During machining, the deformation of the part depends on the milling process and milling parameters, and in particular the type of clamping used and the design of the milling tool path, which produces a continuous re-distribution of internal constraints. The problem of identifying which tool path will give rise to the minimum distortion of the workpiece has not yet been resolved. The project comprises five parts: - Characterisation of residual stresses in large pre-formed parts, to identify the stress fields required for the simulation for various different materials and processes. Residual stress measurement and the evaluation of the associated accuracy are complex problems in the case of massive industrial parts. - Numerical development, using Forge© software to model material removal and estimate machining distortion, with the aim of reducing computation time and improving the accuracy of the estimation. - Measurement of distortion, and correlation between measurement and simulation, in order to propose a non-intrusive method to measure parts during machining, taking into account the visual interference engendered by the industrial production environment. - Optimisation of milling process planning in order to check the influence of deformations on the conformance to geometrical specifications and to adapt the design of parts. - Validation of the simulation by comparison with experimental results on industrial parts. This project will contribute to a better understanding of the mechanical behaviour of parts during machining, as is already the case for other processes such as casting or forging. Indeed, there are currently no software tools to assess the mechanical behaviour of a workpiece during milling. At the industrial level, the control of workpiece deformation and the enhancement of the expertise of Aubert & Duval and Constellium is a major competitive advantage in a rapidly changing aeronautical market which must adapt to a significant reduction in production times and the emergence of low-cost competitors in the highly technical pre-formed parts market. Customers now expect their suppliers to be able to advise on the downstream processes with a cost-cutting approach.