Numerical prediction of distortions during machining of large aluminium aeronautical parts

摘要

Aluminium alloy structural aerospace parts are usually large monolithic parts machined from rolled plates or preformed parts. Previous to machining, several manufacturing steps (forming, heat treatments and mechanical stress relief operations) are performed, resulting in the creation of residual stresses. During machining, a redistribution of the residual stresses occurs due to the material removal. This residual stress redistribution is the main reason for machining errors such as dimensional variations and post-machining distortions. In order to predict the mechanical behaviour of the workpiece during machining and the final part quality in taking into consideration both the machining parameters (fixture layout and machining sequence) and the residual stress redistribution, a specific numerical tool has been developed [1]. Using this numerical tool, an analysis of the influence of the initial residual stresses as well as of the fixture layout and the machining sequences (tool path) on the machining quality of parts machined from an AIRWARE (R) 2050-T84 alloy rolled plate is performed. The numerical results are compared with experimental ones in terms of both post-machining distortions and dimensional errors. Similar results are obtained for both, showing that the developed numerical tool allows to predict dimensional and geometrical errors due to the redistribution of the residual stresses during machining. The machining of these cases and results obtained are then analysed, demonstrating the feasibility to adapt and to optimize the machining process plan to ensure conformity of the part with the tolerance specifications.