Investigation Of Surface Integrity Of Aluminum Lithium Alloy In Machining

Aluminum lithium alloy will likely become the material of choice over composites as thefuselages of the next generation of narrow-body aircraft due to its high strength to weightratio, excellent corrosion resistance and super cryogenic performance. Nowadays, chemicalmilling method is usually adopted during the process of manufacturing the aircraft skin in theairplane industry, which is high energy-consuming, as well as great pollution and lowefficiency. Because of the intrinsic thermo-mechanical coupled quality of mechanical millingprocess, the surface integrity characterization such as surface topography, microstructurealteration, microhardness and residual stress has a great impact on the fatigue performance ofthe component. The following is the main research content:First, this thesis completed the modeling of surface topography and residual stress. Aanalytical method is applied in quantifying the surface roughness parameters. Three differentcombinations of nose radius and feed rate are discussed here. A FEM-ANN hybrid method isused to determine the mapping of machining parameters with residual stress profile.Second, the machining induced residual stress, microhardness change, andmicrostructure alterations are all greatly influenced by the mechanical and thermal load in themachining process. the measurement of cutting force and temperature during the millingprocess is conducted with the help of dynamometer、infrared camera and thermocouple. Therelationship between machining parameters and cutting force is concluded.Finally, aluminum lithium alloy samples are milled under air coolant condition and liquidnitrogen condition by orthogonal test design. Surface integrity factors including roughnessand residual stress are measured. The results show that the angle between feed direction androlling orientation dominates in the formation of surface finish, which is often neglected inprevious study. The results also demonstrate the capacity of liquid nitrogen on improving thesurface integrity followed by an increase of material removal rate in face milling of aluminum lithium alloy. Finally, the regression models for roughness and residual stress are establishedand the effectiveness of these models are validated.