Análisis de las condiciones de mecanizado, geometría de pieza y secuencia de fresado en la fabricación de piezas aeronáuticas de bajo espesor con sujeción local

Abstract

Aluminum alloy parts are widely used in the aeronautical sector, among others, for covering components and fuselage skins. These parts are extremely thin, and therefore their rigidity is reduced. They were manufactured by assembly or chemical milling, but due to the disadvantages of these techniques, mechanical milling is becoming increasingly popular. However, the reduced stiffness of fine parts poses a number of challenges for mechanical milling, such as dealing with the vibrations that occur, minimizing the distortions produced by the redistribution of residual stresses, as well as achieving an appropriate surface quality. There are several techniques to cope with these challenges, such as the use of flexible and reconfigurable holding fixtures, and the selection of optimal milling conditions by means of stability lobe calculations. However, in the case of aeronautical skins, in flexible fixtures, a large part of the skin is left unsupported and without adequate stiffening. For this reason, mechanical milling is difficult, resorting to expensive ad hoc tooling, or opting for assembly or chemical milling instead, which are inefficient, polluting and have poorer mechanical properties. The main purpose of this thesis is to promote the use of flexible fixtures for aeronautical skins. Therefore, mechanical milling tests have been carried out on thin plates with different cutting conditions and different part geometries, using an experimental configuration that emulates the one of aeronautical skins in flexible tooling. Stability lobes have been calculated and the vibration, roughness, final thickness and forces produced in this milling process have been analyzed. Likewise, an empirical, integral and predictive force model focused on aeronautical skins has been elaborated, which allows to optimize milling conditions, tool trajectory, part geometry and fixture distribution in the tooling. In addition, the analysis is complemented by a study of the machining of an aeronautical part, which seeks the optimal sequence of machining operations that causes the least distortion in the final part as a result of the redistribution of the inherent residual stresses.

Date of Award	2023
Original language	English
Awarding Institution	Universidad del País Vasco (UPV/EHU)
Supervisor	Aitzol Lamikiz Mentxaka (Supervisor) & Veiga Suárez (Supervisor)