A study on machining dynamics in flat-end mill process of SKD11 hard steel

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Abstract
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.

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