Dynamics Prediction And Stability Analysis Of Milling Processes

The accurate prediction of cutting forces is important in controlling the tool deflection and the machining accuracy. In this paper, the authors present an improved theoretical dynamic cutting-force model for peripheral milling with helical endmills. The theoretical model is based on the oblique cutting principle and includes the size effect of undeformed chip thickness and the influence of the effective rake angle. A set of closed-form analytical expressions is presented. Using the cutting forces measured by Yucesan [1] in tests on a titanium alloy, the cutting-force coefficients are estimated and the cutting-force model verified by simulation. The simulation results indicate that the improved dynamic cutting-force model does predict the cutting forces in peripheral milling accurately. Simulation results for a number of particular examples are presented.Using high-speed machining, increased material removal rates are achieved through a combination of large axial depths of cut and high spindle speeds. A limitation on the allowable axial depth of cut is regenerative chatter, which is avoided through the use of stability lobe diagrams which identify stable and unstable cutting zones. The machining models used to produce these diagrams require knowledge of the tool-point dynamics and application-specific cutting coefficients. Tool-point dynamics are typically obtained using impact testing; however, testing time is extensive due to the large amount of holder-tool combinations. A technique to predict tool-point dynamics and therefore limit experimental testing time is desirable. This dissertation describes a three component spindle-holder-tool model to predict tool-point response based on receptance coupling substructure analysis techniques. Experimental validation is provided.Based on the models of dynamics and cutting force above, a set of delay differential equations (DDEs) are setup to describe the dynamics of milling process. An improve semi-discretization method based on Magnus-Guassian truncation is presented for analyzing the stability of periodic orbit of the DDEs. By comparing the stability charts obtained by zero-order semi-discretization method with the stability charts obtained by the improved semi-discretization method, one can say the computational efficiency, convergence, and accuracy are improved by the semi-discretization method based on Magnus-Guassian truncation.