Improvement of stiffness during milling thin-walled workpiece based on mechanical/magnetorheological composite clamping

Abstract

Because of the weak rigidity and complex structure, aerospace thin-walled parts are prone to deformation under the influence of machine tool vibration, cutting force and heat during milling. Based on the previous magnetorheological fluid (MRF) flexible fixture, this paper proposes a mechanical/magnetorheological composite clamping method to suppress vibration and improve machining accuracy. Firstly, the relationship between shear stress, workpiece position and MRF height is experimentally analyzed, and a mathematical model of composite clamping is established. Through the single-factor test, it is found that the experimental and predicted milling force curves tend to be consistent, and the maximum milling force errors in X, Y and Z directions are 19.9%, 13.4% and 16.2% respectively. When the spindle speed, depth of cut and feeding speed change, the errors between experimental and predicted milling force in three directions are controlled within 10%, which can verify the reliability of the prediction model. Then, the frequency response impact experiments are carried out on single mechanical clamping and composite clamping respectively, which proves that the stability of composite clamping is better than single mechanical clamping. Finally, by comparing the test results of milling thin-walled part, it is found that the surface roughness values Ra, Rq and Rz of composite clamping parts decrease by 49.0%, 56.7% and 43.3% respectively. Therefore, the mechanical/magnetorheological composite clamping method proposed in this paper has remarkable effect on suppressing chatter, which can effectively improve the milling surface quality of parts.