The performance requirements for the processing of large thin-walled parts are getting higher in aerospace industry, which includes indicators of surface integrity, and thin-walled parts processing quality persistence in addition to the traditional processing accuracy and surface roughness [1]-[2]. The processing of aerospace thin-walled parts with complex curved surfaces can hardly realize both high precision and high efficiency. Aerospace large thin-walled components, recognized as typical large, weak rigid irregular parts, are mostly composed of irregular thin-walled profiles and ring structure with the ratio of diameter to thickness of mostly 800 or above, and both internal and external profiles need to be processed. The thin-walled parts are easily deformed by cutting force, machining path and other factors when being machined, and it is difficult to improve the machining accuracy, especially the long-term retention of the machining accuracy [3]. Therefore, the control of distortion of thin-walled part is being considered tough issues.

Aluminum alloy is widely used in the field of aeronautics and astronautics for its high strength and cutting performance, especially for large thin-walled parts, such as the skin, which is one of the most important parts of the wing and fuselage. Thin-walled aluminum alloy parts are easy to chatter and deform, which greatly affects the processing quality and long-term retention of thin-walled parts[4]-[5]. Mohamed et al.[6] researched the influence of milling process on cutting heat by Taguchi method and all-factor design technique, and the results show that the significance or non-significance of temperature changes between different cutting zones and processing operations. Dejan, Luo et al. [7] researched the multi-criteria selection of the optimal parameters for Al7075 thin-walled parts in high-speed machining.

Researches on thin-walled parts processing technology, including the influence of cutting force, thermal, deformation and residual stress, have been increasing in recent years[8]-[12]. The machining deformation and vibration caused by the weak rigidity of thin-walled parts greatly affect the machining quality of the products. Reasonable clamping can control the machining deformation and vibration, and effectively improve the machining stability of thin-walled parts. Wu Baohai et al. [13] carried out research on the development of intelligent clamping technology for thin-walled parts machining deformation and vibration control, including the optimal design of clamping scheme, thin-walled Parts Processing Auxiliary Support Technology and intelligent fixture system and its application. Zhuo et al. [14] developed a surface topography prediction model considering cutting vibration and material removal effect for the peripheral milling of thin-walled parts with curved surfaces, and results indicate that the proposed model can predict the surface topography and roughness parameters accurately under the machining condition of large axial cutting depth. Hao et al. [15] researched the actual geometric state of the deformed workpiece by using a time-varying geometry modeling method, combining cutting simulation and in-process measurement. Li et al. [16] researched the machining deformation change regulations of two typical thin-walled parts and proposed a machining deformation control method based on enhancing the equivalent bending stiffness. Jia et al. [17] established a deflection prediction model of micro-milling thin-walled parts.

The distortion of thin-walled part is significantly affected by the residual stress generated after the material removal process, in which the relations between the redistributed residual stress and the distortion are complex [18]-[19]. Investigation data have proved that residual stress has significant influence of the deformation of workpiece[20]-[24]. Luke Berry et al. [25]researched the residual stress and fatigue life caused by machining of aluminum 7075, and proposed that the increase of residual compressive stress can contribute to the improvement of fatigue life. Many researches are carried out to study the residual stress mechanism in simulation and experiment methods. Li et al. [26] established a prediction model for machining deformation considering machining-induced residual stress and initial residual stress. Y Rahul et al. [27] established the Finite Element model to research the state of residual stress at surface and sub-surface level and the effect of processing parameter on cutting force. Zhou et al. [28] predicted the temperature field of workpiece induced by complex surface milling by the analytical model for the generation of residual stresses. Most researches focus on the force, heat and residual stress induced by single machining, while the superposition of multi-process machining is also important because the actual machining is composed of multiple processes. Jiang et al. [29]-[30] constructed an empirical model of milling residual stress superposition and quantified the superposition relationship between the residual stress induced by force and heat, and researched the effects of sequential cuts on residual stress. Guo et al. [31] carried out the simulation models of the machining process and heat treatment, and researched the redistribution mechanism of residual stress during multi-process milling. Irfan Ullah et al.[32] presented a numerical and experimental method to study the effect of white layer of high-speed milling on the relationship between nano-hardness and residual stress and residual stress distribution. Therefore, the superposition of force, temperature and residual stress of thin-walled parts in multi-process machining is an urgent research topic.

This paper takes the aerospace 7075-T7451 aluminum alloy thin-walled rotational parts of "L" type as the research object through Finite element simulation. The material removal model of single cutting edge and multi-process model for semi-precision milling and fine milling were constructed and the simulation parameters were designed. The milling force, temperature and residual stress superposition mechanism of parameter combinations of semi-precision milling and fine milling were analyzed in this paper. The milling experiment of thin-walled part was carried out to verify the parameter combination, and the flatness deviation of the bottom plane and circularity deviation of the top, middle 1/3 height, middle 1/2 height, and bottom of the wall were measured. The optimization design method of process parameters considering the deformation of thin-walled parts were given.