A new in-processes active control method for reducing the residual stresses induced deformation of thin-walled parts

It is usually deformed severely for thin-walled workpiece when the fixture is removed after machining, which is mainly caused by the redistribution of internal stress and machining induced residual stress (MIRS). Previous works have tried to relax the fixture in-processes to release the residual stresses (i.e. internal stress and MIRS), and perform the following machining operation after re-fasten the workpiece at its totally relaxed state. However, the totally relaxed state is only an equilibrium of residual stresses and the MIRS on the top layer of the workpiece will be changed after the following machining process. The residual stresses of the workpiece become imbalance again and thus will lead to the deformation of final component. In this paper, a novel research work of actively controlling the in-processes deformation of thin-walled part is presented, which is aimed at balancing the internal stress/MIRS and preventing the redistribution of residual stresses after last machining step. Firstly, the variations of internal stress, MIRS and clamping force during machining are analyzed through a simplified inprocess model of blade. An equilibrium equation is established by taking the residual stresses as the equivalent loads of clamping point. Next, to achieve the proposed in-processes active control method, a mathematical model of how to actively adjust the fixture between machining operations is established. And then, the finite element method (FEM) is used to calculate the MIRS induced deformation, in which the MIRS is measured through experiment. A prototype of active control fixture for blade part is developed to adjust the in-process deformation. Finally, three groups of machining experiments on a simplified blade with three different treatments on the fixture after the rough machining - no relaxing the fixture at all, totally relaxing the fixture in-process, and actively controlling the deformation in-process- are carried out. The validation demonstrates that the proposed in-process active control method could decrease machining deformation significantly. The maximum deformation reduced to 18.3 % and 42.9 % compare to the no relaxing and totally relaxing the fixture after rough milling.