Nhu-Tung Nguyen

This study was performed to investigated the mechanism and stability prediction of flat-end milling process of SKD11 hard steel. The static milling force (MF) model, dynamic milling force (DML) model, milling vibration (MV) model, stability lobe diagram (SLD) model were developed and proposed in this study. The values of milling force coefficients (MLCs) and dynamic structure parameters (DSPs) were determined based on the combination of theoretical and experimental method. In static analysis, the relationship was very close to the linear regression with high determination coefficients (R2>97 %) in all three x, y, z directions. For experimental system of this study, the natural frequency of machine-tool system was almost half of natural frequency of machine-workpiece system. For the predicted results of SLD, the width of the stability region increased when the spindle speed increased. The machining processes were almost at the stable conditions with the axial depth of cut to be smaller than 0.3 mm at all values of spindle speed. The stable and unstable conditions in milling processes were verified with high precision for almost milling tests. With the points at the border between stable and unstable zones, the verified results had some differences between the predicted results using the proposed model and the analyzed results from experimental processes. These differences can be explained that there are many other parameters that have not been included in the predictive model such as heat, tool wear, friction, etc. In the applying of this study, it is the best way to choose the machining parameters at the absolute stable machining conditions.

Cutting forces play very important in designing the tool machine, cutting tool, and in optimization of machining processes. Modeling and prediction of cutting forces by theoretical methods are quite difficult, so, this study was focused on modeling the cutting force in face milling process using combination of theoretical and experimental methods. This study was performed to model the milling forces (MFs) and determine the milling force coefficients (MFCs) in the face milling process of aluminum alloy Al7075 using square inserts. From theoretical and experimental methods, the relationship of average milling forces (AMFs) and feed per flute (ft) were determined as the linear regression. Using experimental data, the linear regressions of AMFs and feed per flute were determined with high values of determination coefficients (larger than 95 %). MFCs were determined including shear and edge MFCs (tangential shear MFC (Ktc) of 538.127 N/mm2, radial shear MFC (Krc) of 185.967 N/mm2, axial shear MFC (Kac) of -691.297 N/mm2, tangential edge MFC (Kte) of 11.253 N/mm, radial edge MFC (Kre) of 6.991 N/mm, and axial edge MFC (Kae) of –32.971 N/mm. The MF models were successfully verified by comparing the measured and predicted MFs in face milling process of Al7075. The tendency and shape of predicted MFs were quite close to the measured ones. The differences between the predicted and the measured MFs can be due to the several reasons such as the influence of vibrations, the influence of cutting heat, etc., and these are also the limitations of this study. The modeling and prediction methods of this study can be used to model and predict the cutting forces in face milling of other milling types and other pairs of cutting tool and workpiece material as well