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Cong Feng,Zhaojun Yang,Chuanhai Chen,Jinyan Guo,Hailong Tian,Fanning Meng 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.6
Accuracy retention is an important performance index of CNC machine tools. At present, research on the evaluation of machining accuracy retention of CNC machine tools mainly focuses on accuracy value of a fixed time point or different time periods, but studies on the fluctuation degree of degradation trajectory related to time change are limited. Extracting simple and effective degradation characteristics of machining accuracy and then evaluating machining accuracy retention considering fluctuation of degradation trajectory are necessary. The volume error model of CNC machine tools is established on the basis of multibody system theory in this study. Three-dimensional volume error vector is transformed into one-dimensional machining accuracy degradation by calculating offset distance between spatial error and origin points. Degradation data obtained via regular measurement and calculation are used to establish the complete degradation trajectory model of the CNC machine tools machining accuracy using radial basis function interpolation method according to the fluctuation degree of degradation trajectory, and concepts of average degradation rate and average degradation amount are defined. Lastly, examples showed that these two indicators can intuitively reflect fluctuation degree of machining accuracy degradation of CNC machine tools and effectively and quantitatively evaluate accuracy retention of CNC machine tools. The quantitative evaluation method of accuracy retention of CNC machine tools defined in this study considers the fluctuation degree of accuracy degradation trajectory. The quantitative evaluation index of accuracy retention demonstrates satisfactory engineering application because it can reflect not only the accuracy change of a single machine tool but also accurately compare the accuracy retention between different machine tools.
Reliability optimization design of hydraulic system considering oil contamination
Xinda Zhou,Zhaojun Yang,Hailong Tian,Chuanhai Chen,Liding Wang,Yongfu Zhu,Jia Liu 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.12
This paper presents a reliability optimization design method for a hydraulic system that considers oil contamination. The proposed method applies the quantitative relationship between oil contamination and system reliability to the reliability design of a hydraulic system, while considering the performance, layout, and other design factors. A global reliability model of the hydraulic system is constructed based on the oil contamination control model. Further studies aiming at an optimization design model of the hydraulic system is established where the cost is the objective function, reliability index, size and structure range, performance requirements are constraints, structure size and oil change period are design variables. For illustration, a case study on the reliability optimization design of the oil supply point branch of the static pressure bracket of a certain type of heavy CNC horizontal lathe is considered.
Study on failure warning of tool magazine and automatic tool changer based on tool-pulling force
Hailong Tian,Zhaojun Yang,Guofa Li,Chuanhai Chen 대한기계학회 2019 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.33 No.9
A tool magazine and automatic tool changer is used to store and change tools in a machining center. Its failures would increase the maintenance time and repair cost. For decreasing failures, an early warning system of failures can be used to detect characteristic signals which can reflect potential failures. The tool-pulling force is increasing to peak value instantly when the tool changing arm draws a tool holder out of a tool pocket. To predict failures, the tool-pulling force signals are analyzed and the relationship between the maximum tool-pulling force and the severity of the lock spring failure is established, then, calculation method of the tool-pulling force threshold of the lock spring failure which can lead to tool falling failures is developed and demonstrated. The verification testing results show that the failure warning method based on the tool-pulling force threshold is feasible to predict the tool falling failures.