In the process of metal milling, especially in the machining of low?stiffness workpieces, chatter is a key factor affecting many aspects such as surface quality, machining efficiency and tool life. In order to avoid the chatter, a milling chatter recognition method based on dynamic and Wavelet Packet Decomposition(WPD) is proposed from the signal processing. The modal parameters of the system are obtained by modal experiments. Based on the principle that the chatter frequency will peak near the natural frequency of the system, the original milling force signal is decomposed by WPD, and the sub?signals containing rich chatter information are selected for signal reconstruction. Finally, the time?frequency and Hilbert spectrum characteristics of the reconstructed signal are compared and analysed, and the chatter recognition is performed. At last, the proposed method is verified by the experiments. The results demonstrate the effectiveness and reliability of the proposed method.

Aero?engine usually contains a large number of pipes, the arrangement sequence of these pipes has a certain impact on the overall layout effect of the system. In order to reduce the degree of cross layout of multiple pipes, the evaluation method of pipe disassembly complexity was designed based on product assembly and disassembly, a Discrete Chicken Swarm Optimization (DCSO) algorithm was used to solve the pipe layout sequence planning. First, a calculation method of pipe disassembly complexity was proposed to evaluate the complexity of pipe system layout scheme. Next, the pipe was pre?planned by A* algorithm. Then, an obstacle avoidance algorithm was designed based on engineering rules to adjust the pipe. Finally, taking the pipe length and disassembly complexity as the optimization objectives, the pipe layout sequence was optimized based on DCSO, and the feasibility of the proposed method was verified by a layout example.

The pollution of water is becoming more and more serious, and photocatalytic degradation of pollutants in water by sunlight plays an important role in the future development. A simple chemical precipitation method was introduced. CNTs were compounded on the surface of Bi₁₂O₁₇Cl₂ to obtain a series of CNTs/Bi₁₂O₁₇Cl₂ composites. The structure, morphology and optical properties were measured and characterized by XRD, TEM, UV?Vis DRS and PL. The results show that compared with single?phase Bi₁₂O₁₇Cl₂, CNTs/Bi₁₂O₁₇Cl₂ composites show excellent pollutant degradation activity and good photocatalytic stability and cycling performance. It is found that superoxide radical (·O {}_{\mathrm{2}}^{-} ) and hole (h⁺) are the main active species through trapping experiments, and the possible degradation reaction mechanism is speculated. This study provides a cheap and simple modification method for improving the photocatalytic performance of the catalyst, and has a certain guiding role in the synthesis of other high efficiency photocatalysts.