Mingbo Zhao’s research while affiliated with Beijing Jiaotong University and other places

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.

The cutting force prediction of worn tool is very important for wear state identification, tool life optimization, and machining quality improvement. The wearing force is mainly produced by the tool-workpiece contact which influenced by several factors such as the flank wear and the spring back. In this paper, the prediction of cutting force for worn ball-end tool with spring back influence is investigated. Firstly, the tool is separated into differential cutting edges and the differential cutting force is divided into shearing force computed by shearing coefficients and contacting force computed by contact stress. Considering the influence of spring back, the real contact width is applied instead of the flank wear width and a variable declining coefficient is introduced into the stress distribution function. Secondly, the cutter-workpiece engagement of base cutting process and spring back cutting process is analyzed and the cutting force is computed with the accumulation of all the engaging differential cutting forces. Then, a spring back value computation method with the measured force data of single-tooth cutting is presented. Lastly, the machining experiments are designed and carried out for parameter identification and accuracy validation. As the experimental results shows, the deviation between the average force of predicting results and the measured data is small. Comparing to the prediction without spring back, the instantaneous cutting force computed in this paper also shows better fitness and accuracy.

In mould manufacture the elliptical torus cutters are used for their high cutting velocity, but the special geometry also brings issues in tool path generating and machining quality controlling. In this paper a guide curve tool path generating method for elliptical torus cutters is presented with the cutter location points computed by a minimum distance algorithm and the path spacing determined by an adaptive method. In the minimum distance algorithm, the calculation is resolved into an iterative process from point to freeform surface and an algebraic calculation process from point to elliptical torus surface considering the geometry of the cutter, which reduces the iterative process and improves the computing speed. In the adaptive path spacing method, the contacting geometry between the elliptical cutter and the workpiece surface is analysed and the relations among the scallop height, the tool tilt angle and the path spacing are deduced, based on which the guide curves are adjusted in advance to control the scallop height. Calculating examples and experiments are carried out, showing that the consuming time of cutter location (CL) points computation algorithm is reduced by 30% comparing to earlier method, and the adaptive path spacing method performs better than constant method in both scallop height controlling and tool path shortening. The results indicate that the presented tool path generating method can help to reduce both the machining and machine waiting time as well as ensuring the machining quality.