Tool Condition Characterization Based On Dynamic Sensitivity Of Tool Workpiece System Of CNC Lathe

Development of high precision machining of CNC machine tools present higher requirement for the study of cutting vibration and tool condition.The change of cutting tool condition in cutting process has obvious influence on the dynamics of tool workpiece system, workpiece surface quality, and the vibration of machine tool components. So it is very important to analyze the dynamic characteristics of the tool workpiece system and to monitor the condition of the cutting tool. There are some deficiencies in the current resrarch of characterization of the tool condition by using the vibration signal. Firstly, the existing research focused on the high frequency of the tool or the spindle rotation frequency. Secondly, the analysis of the peak of the spectrum of the vibration response signal is generally carried out, and power frequency will affect the results. Then,the most important one is that the existing characterization methods are influenced greatly by the cutting parameters.In this paper, the dynamic change of tool workpiece system is studied by using low frequency operational modes. The low frequency operational modes characteristics of the tool workpiece system will change with the change of cutting tool and workpiece, and the influence of cutting speed is small. Operational modal analysis is used to analyse cutting vibration response signal. The sensitivity of the low frequency operational modes identified to the change factor of tool workpiece system is analyzed. Tool condition characterization is carried out based on dynamic sensitivity.The research contents of this paper include the following four aspects:Firstly, the static low frequency modal characteristics of the CNC lathe were analyzed. modal parameters are identified in the static state.The sensitive direction and the sensitive components of different order modes are analyzed, and the dominant modes are identified.Secondly, dynamic sensitivity analysis of tool workpiece system is analyzed by using operational modes. The sensitivity analysis of the different operational modes of different structures of CNC machine tool in different directions to the change factor of tool workpiece system is carried out in continuous cutting process, and the sensitive mode of the tool wear characterization is identified, which is defined as dynamic sensitivity method.Then the tool condition characterization based on dynamic sensitivity method is analyzed. The tool wear condition is characterized by the change of sensitive operational modes amplitude under the condition of constant cutting parameters and changing cutting speeds. Due to the amplitude of sensitive operational modes is less affected by the cutting parameters. A reliable tool wear monitoring method is found, which is independent of the cutting parameters.At last, the paper discusses the processing application based on dynamic sensitivity. The cutting condition is optimized to delay the tool wear. Combined with the low amplitude stability stage of sensitive mode of the main cutting force direction and tool stable wear stage, the important process required high surface quality is designed in this phase. Cutting parameters can be optimized to improve the cutting efficiency in this stage. In precision cutting process which the cutting depth is very small, the small tool tip wear has a great influence on workpiece surface quality.Cutting depth should be real-time optimized according to the amount of tool wear.The results indicates that the cutting speed have a small effect on the sensitive operational modes of the cutting process. The dynamic change factors of tool workpiece system are characterized by the different operational modes, which has differences in the different directions, components and frequency band. The tool wear condition can be characterized reliably by the change of the sensitive operational mode amplitude, which is independent of the cutting speeds.