On improving chatter stability of thin-wall milling by prestressing

Abstract

Some long strip-like thin-walled workpieces such as blades usually need to be manufactured by milling with two ends being clamped on the machine table. This paper presents a stability improvement method in this kind of thin-wall milling by applying tensile prestress to the workpiece. The methodology is described by developing theories to establish the relationship between the needed tensile prestress and the expected critical axial depth of cut. Influence of the workpiece natural frequency on the critical axial depth of cut is theoretically explained for the first time. It is found that increasing the workpiece natural frequency can locally improve the stability in milling, and based on this conclusion, quantitative equations relating the expected critical axial depth of cut to the workpiece natural frequency are theoretically derived and solved in detail. With the aid of modal analysis from finite element simulation, problem on how much tensile prestress should be used to increase the workpiece natural frequency to the expected level is explained. In short, the stability lobe of a thin-wall milling system is shifted to the expected stable zone by manipulating tensile prestress to the clamping areas of long strip-like part. Besides, a prototype device, which has the capacity of fixing and prestressing the workpiece, is originally invented to check the effectiveness of the proposed methodology. The proposed method together with the invented prestressing device is experimentally validated by carrying out a series of milling tests with and without prestress.