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

与干式加工相比，铝合金的低温加工增加了强度，减少了毛刺的形成，改善了疲劳性能和表面质量。这些有利的性能是由于较高的加工引起的压残余应力在工件的边界层。然而，我们的初步工作表明，残余应力的增加也会导致薄壁铝部件的更大变形，这通常用于航空航天工业。因此，有必要研究不同低温冷却策略对薄壁铝件加工残余应力及相关零件变形的影响。此外，零件的尺寸精度必须考虑到极低的温度，这会导致工件在加工过程中收缩。加工后，加热到室温导致工件与标称轮廓的永久几何偏差。研究项目的目的是预测薄壁铝件在低温加工过程中的零件变形和尺寸精度，并在加工过程中对其进行补偿。重点是残余应力，因为这些是造成变形的原因。在该项目中，开发了合适的基于模型的补偿技术，以最大限度地减少零件畸变并确保足够的尺寸精度。除了受冷却策略影响的加工残余应力外，还必须考虑初始体残余应力。研究它们的差异性和叠加性对零件畸变的影响是很重要的。在开发补偿技术时，应研究低温加工（与干式加工相比）是否可能通过增加加工引起的残余应力来补偿由高初始体残余应力引起的变形。在研究项目成功完成后，薄壁铝部件的低温加工将实现重量减轻和节能组件，具有比干法加工的优点，如强度增加，毛刺形成减少，疲劳性能改善和表面质量提高。同时减小了零件变形和尺寸精度下降的缺点。

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.