Jiawei Mei’s research while affiliated with Beijing Jiaotong University and other places

To improve the machining quality of free-form surfaces, machining deformation and chatter should be considered in 5-axis ball-end milling. In this paper, a Pareto multi-objective optimization method for cutter orientation is presented. Firstly, the cutting force is calculated by the differential element method. To improve the computational efficiency of cutting force, the proposed cutting force model considers the influence of surface curvature on the cutter workpiece engagement (CWE) region and gives an analytical calculation method. Then, the deformation and chatter of 5-axis ball-end milling are studied. The static deflection corresponding to different cutter orientations is calculated based on the large-scale sparse matrix inversion algorithm. The chatter-free stability region is calculated based on the 3-dimensional semi-discretization method (SDM). It was found experimentally that the smaller the eigenvalue of the SDM transition matrix is, the more stable the machining is and the better the surface quality is. On this basis, the minimum eigenvalue is proposed as optimization criteria for chatter. Finally, a non-dominated sorting genetic algorithm (NSGA-II) is used to obtain the Pareto optimal region of the cutter orientations. The optimization model takes the minimum value of static deflection and stability eigenvalue as optimization objectives. For each key cutter location point, the feasible region of the cutter orientations with high precision and surface quality is obtained based on NSGA-II. Furthermore, based on the optimization results at the key cutter location points, Dijkstra algorithm and quaternion interpolation algorithm were used to optimize the cutter orientations of the whole free-form surface, which ensured the kinematics performance of the 5-axis machine. The experimental results are in good agreement with the simulation results, which shows that the theoretical model is effective. The results provide a theoretical basis for the comprehensive optimization of machining deformation and chatter of thin-walled parts with the free-form surface.

Trochoidal milling is an efficient machining technique that extends tool life and is widely used for slotting hard-to-cut materials. It offers the advantage of reducing cutting force, heat accumulation, and tool wear compared to conventional milling processes. However, due to the variable tool orientation in five-axis milling, trochoidal milling has been less commonly employed for machining 3D complex freeform slots. Existing 3D trochoidal milling methods primarily generate toolpaths by optimizing parameters based on fixed-curve paths, which do not fully leverage the efficient and stable characteristics of trochoidal milling. In this paper, a novel five-axis trochoidal milling method for machining complex 3D slots is proposed. This method generates the toolpath by determining suitable cutter location (CL) points by step, allowing flexible adjustment of the cutter-workpiece engagement (CWE) at each CL point. The CWE area must remain stable and maximized during the machining process to ensure stable cutting, reduce tool wear, and improve machining efficiency. An efficient and accurate CWE model for five-axis trochoidal milling slotting is established, and a multi-layer ruled surface fitting method to avoid interference is provided. Simulation and physical cutting experiments have been performed, and the results validate the effectiveness of the proposed method, which guarantees a stable cutting force and a 22.5% improvement in efficiency compared to the traditional method.

Tool wear is an important issue to be considered in machining analysis and improvement. The non-uniform flank wear of ball-end tool is a commonly existing phenomenon in ball-end milling but has been less concerned so far. In this paper, the non-uniform flank wear of ball-end tools in 5-axis machining based on real cutting length calculation is discussed. Firstly, the flank wear model of differential cutting edge is constructed considering the real cutting length (RCL). Secondly, the RCL is obtained with intersection point calculation according to the cutter workpiece contact analysis. Then, the distributions of accumulated RCL and flank wear are analyzed and the similarity between them is found, based on which a tool orientation optimization method is given to improve the tool wear conditions. Lastly, machining experiments are carried out to validate the efficiency and accuracy of the prediction method. The results of the calculation and experiment show that the tool orientation optimization can help to reduce the maximum flank wear.