Investigation Of Indirect Tool Tip Vibration Measurement Method For Turning Process

Cutting vibration has bad influences on shape accuracy and surface finish quality, and can reduce tool life and machining efficiency. Moreover, at certain condition, stable cutting vibration will develop into chatter, which can lead to collapse of the whole cutting system. Cutting vibration, which has become one of the main obstacles to improve machining quality and efficiency, restricts development of high-end CNC machine tool as well as high speed and high precision machining technology.Tool tip vibration, which is the most direct and important representation of cutting vibration, is the main research object in the field of cutting vibration. Tool tip vibration measurement has a great significance for surface topography prediction, cutting force control as well as active vibration control. For tool tip vibration measurement, following three problems should be considered:(1) whether installation of the vibration sensor is convenient;(2) damage to the sensor caused by chips and cutting fluid;(3) effects of clamp vibration on the sensor’s measurement results.In view of above three problems, this paper proposes an indirect tool tip vibration measurement method based on vibration acceleration sensor. Namely, vibration of the tool tip is calculated from that of the measurement point on turret or spindle. The relationship between vibration of the tool tip and that of the measurement point is called vibration transfer function, which can be obtained through impact test. In addition, criterion for the best measurement point selection is proposed, namely coherence function between the measurement point vibration and tool tip vibration.On different experimental objects, including horizontal lathe and double side synchronous lathe, a series of cutting experiments is conducted, and the accuracy of the proposed indirect tool tip vibration measurement method is verified through comparing the measured and calculated tool tip vibration in terms of overall trends of the amplitude spectrums, as well as amplitudes and phases of the frequency spectrums at each frequency. The measured tool tip vibration is directly measured by vibration sensor which is installed near to tool tip, while calculated result is obtained from vibration of the measurement point on turret or spindle using indirect measurement method. Furthermore, multiple measurement points are arranged on turret, and criterion for the best measurement point selection is validated through comparing accuracy of the calculated tool tip vibration obtained from different measurement points and corresponding coherence function amplitudes.Finally, surface topography prediction based on tool tip vibration is investigated to further demonstrate effectiveness of indirect measurement method. Tool tip vibration displacement can be calculated from its vibration acceleration through frequency-domain integration, and low-frequency cutoff algorithm is used to control integration error. Specific cutting mode is adopted to ensure that tool tip vibration generates surface topography directly. At the same time, the relationship between tool tip vibration and surface topography is established. A series of cutting experiments is conducted, and results show that tool tip vibration has significant effects on surface topography, and accuracy of surface topography prediction results based on tool tip vibration is good. Therefore, effectiveness of indirect measurement method is demonstrated further.