Three-dimensional Stability Of Thin-walled Part In High Speed End Milling

With characteristics of light mass, high intensity and perfect dynamic performance,thin-walled parts are widely used in the high-end equipment manufacturing fields of aerospace,power and traffic. However, as there are properties of low rigidity, difficult-to-cut material,high material removal rates and complex surface, form in thin-wall parts, chatter is an unavoidable phenomenon in all milling processes,causing a reduction in processing quality and production efficiency. Thus,stability prediction of thin-wall milling is significance in suppression of chatter in milling effectively and optimization of process parameters. Hence, in this paper,the technical means of the digital modeling, dynamic simulation and experiment verification are combined together to conduct the research on stability prediction of alloy aluminum thin-wall parts in milling. The main contents are as follows:A cutting force prediction model is established for flat end mill. First, model of immersion angle considering the helix angle effect, cutter run-out and variable pitch angle cutter is developed, then the calculation of undeformed chip thickness is described the cutting force prediction model for thin-wall milling is presented. Meanwhile, the cutting force coefficients identification method considering the tool/part combination and run-out is proposed. Then, the comparison between measured and predicted cutting forces verifies the feasibility of the proposed cutting force model.Taking the variation of dynamic behavior of thin-wall milling depending on the tool position into account,the model of dynamic milling system with respect to the mode shape of thin-wall part is developed. The model can be classified into two kinds: dynamics models of the rigid tool/flexible part milling system and the flexible tool/flexible part milling system. The model analysis combined with finite element analysis and hammer experiment is presented to obtain the modal parameters of thin-wall milling system and variation law of dynamic behavior.The high order time-domain method for prediction of milling stability is presented. The method is applicable to the small radial depth of cut and has a higher converse rate. The stability prediction of typical thin-walled aluminum alloy is given and the 3D stability lobes with the coordinate axis of the axial depth of cut, spindle speed and tool path is built. The effects of the cutter geometry parameters, radial immersion and down/up milling on the stability in thin-wall milling are analyzed based on stability lobe, which can provide the reference for optimization of process parameters.Finally, with 3D stability lobe, different processing parameter combinations are selected by fixing the axial depth of cut and the thin-wall milling experiments are carried out. The comparison results illustrate that the predicted values are in good agreement with the measured one, which validates the feasibility of the proposed prediction method.