This paper investigated the machining stability influenced by tool posture and position in ball-end milling with parallel kinematic machine tool (PKM). Initially, the geometric structure was identified, and the machinery stiffness was measured by impulse respond method at several positions with four tool postures. Then, the milling tests were conducted on flat work surface using a ball-end mills. Cutting force and acceleration signals of milling tests were measured by three-axis dynamometer and accelerometer. Furthermore, these signals were analyzed by using Fast-Fourier transform and Hilbert–Huang transform (HHT). The results showed that the length of arm change with tool posture, where the machinery stiffness decreased with the total length of arms for any tool position. The experimental results also demonstrated the machining stability varied with tool posture; the trend of stability corresponds with the machinery stiffness. The vibration analysis by HHT presented the increasing of power level in the time–frequency plot when the length of arm increase during milling process. Therefore, the geometric influence must be considered to support process planning on the PKM.

本文研究了平行运动机床（PKM）在球头铣削中受刀具姿态和位置影响的加工稳定性。最初，确定了几何结构，并通过脉冲响应方法在四个具有四个刀具姿态的位置上测量了机械刚度。然后，使用球形立铣刀在平坦的工作表面上进行铣削测试。用三轴测功机和加速度计测量铣削试验的切削力和加速度信号。此外，这些信号通过使用快速傅立叶变换和希尔伯特-黄变换（HHT）进行分析。结果表明，臂长随工具姿势的变化而变化，其中机械刚度随任何工具位置的臂长的增加而降低。实验结果还表明，加工稳定性随刀具姿态的变化而变化。稳定性的趋势与机械刚度相对应。通过HHT进行的振动分析表明，在铣削过程中臂长增加时，时频曲线中的功率水平会增加。因此，必须考虑几何影响以支持PKM上的过程计划。