基于中轴变换的型腔高速铣削刀具轨迹生成方法

框、梁、壁板、蒙皮等飞机关键零部件中包含大量型腔特征，其加工效率直接影响零件的整体加工效率。高速铣削机床的发展为此类零件的高效加工奠定了很好的硬件基础，也给型腔铣削刀具轨迹生成带来了新的问题。例如蒙皮镜像铣由于其特殊的设计，对刀具轨迹提出平滑无抬刀、步距变化严格控制在一定范围内等更严苛的要求，从而保证蒙皮高质量加工。结构件高速加工中为了保持刀具的高进给和高转速，也要求刀具轨迹平滑且步距平稳变化。然而现有的型腔铣削刀轨生成方法大多基于局部优化解决加工残余和刀轨不平滑问题，难以生成同时满足多工艺约束尤其是步距约束的刀具轨迹，无法完全发挥高速机床的性能。针对此问题，本文提出基于中轴变换的型腔高速铣削刀具轨迹生成及优化方法。该方法首先基于中轴变换提取型腔骨架线，并进一步修正从而生成刀轨偏置基准和初始刀轨。其次利用图像变形算法对初始刀轨进行迭代变形优化，使最终优化刀轨与目标型腔区域吻合，且满足高速加工的工艺约束条件。该方法在离散的图像域内从整体角度优化刀具轨迹，不仅保证轨迹平滑无抬刀，还能保证步距在容许范围内平稳变化。实验证明本文提出的方法在保证轨迹平滑和步距平稳变化等方面的有效性，能够满足高性能加工的要求。

An approach of tool path generation based on medial transformation for high-speed pocketing

The design of key aircraft components, such as frame, beam, wall and skin parts, is composed of a large number of pocket features, whose machining efficiency directly influences the overall machining efficiency of aircraft parts. The development of high speed milling machine has provided a good hardware foundation for highly efficient machining of such parts, but also poses new challenges to generation of tool path of pocket milling. For example, in mirror milling for aircraft skin parts, due to its special mechanical setup, stringent requirements of toolpath such as smoothness, no tool retraction and prescribed stepover variation are made to ensure high quality machining of skin parts. To maintain the high feed rate and spindle speed in high speed machining of structural parts, tool path should also be smooth and the stepover should vary smoothly. However, existing pocket milling tool path strategies are mostly based on local optimization to deal with defects of uncut region and unsmoothness, and are hard to satisfy multiple process constraints, especially the constraint of stepover, so it is hard to make full use of high-speed machine. To solve this problem, a tool path generation and optimization approach of pocket high speed milling based on medial transformation is proposed in this paper. In this method, the skeleton of pocket is extracted based on medial transformation, and the offset criterion of tool path and the initial tool path are generated by further modification. Then, the image deformation algorithm is used to perform iterative deformation optimization on the initial tool path, so that the final optimized tool path conforms to the target pocket machining region and the process constraints of high-speed machining are satisfied. This method optimizes the overall tool path in the discrete image domain. The experimental results show the method can ensure not only smoothness of tool path without tool retraction, but also gentle stepover variation in the allowable range, which meets the requirements of high-performance machining.