Effects of cryogenic cooling strategies on residual stresses and the resulting part distortion and dimensional accuracy for milling of thin-walled aluminum components

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Cryogenic machining of aluminum alloys increased strength, reduced burr formation, and improved fatigue behavior and surface quality compared to dry machining. These beneficial properties are due to higher machining-induced compressive residual stresses in the boundary layer of the workpieces. However, our preliminary work showed that the increased residual stresses also lead to greater part distortion of thin-walled aluminum components, which are typically used in the aerospace industry. Thus, there is a need for research on the effects of different cryogenic cooling strategies on the machining-induced residual stresses and the associated part distortion of thin-walled aluminum components. In addition, the dimensional accuracy of the components must be considered as extremely low temperatures occur, which result in a contraction of the workpiece during machining. After machining, the heating to room temperature causes a permanent geometric deviation of the workpiece compared to the nominal contour. The objective of the research project is to predict the part distortion and dimensional accuracy of thin-walled aluminum components during cryogenic machining and to compensate for them in the process. The focus is on the residual stresses, since these are the cause of the distortion. In the project, suitable model-based compensation techniques are developed in order to minimize the part distortion and to ensure sufficient dimensional accuracy. In addition to the machining-induced residual stresses, which are influenced by the selected cooling strategy, the initial bulk residual stresses must also be considered. It is important to investigate both their differentiated influence and their superposition on the part distortion. When developing compensation techniques, it shall be investigated if there is a compensation of the distortion due to high initial bulk residual stress by the increased machining-induced residual stresses of the cryogenic machining (compared to dry machining) possible. Upon successful completion of the research project, cryogenic machining of thin-walled aluminum components will enable weight-saving and energy-efficient components, with advantages over dry-machined ones such as an increase in strength, reduction in burr formation, improvement in fatigue behavior and increased surface quality. At the same time, the disadvantages part distortion and deterioration of dimensional accuracy are minimized.