During the process of ultra-precision diamond fly-cutting machine tool, due to internal heat sources, the thermal deformation of various parts of the machine tool has severely restricted the accuracy of the machine tool. Therefore, in order to improve the accuracy of the machine, it is necessary to study the mechanism of ultra-precision diamond flycutting machine tool. First, an intelligent monitoring system is arranged for the fly-cutting machine tool to collect temperature signals. Then the heat generations at the spindle motor and linear motor are calculated, and the thermal boundary conditions of the machine tool are analyzed. Finally, the finite element model of the flying-cutting machine tool was established, and the thermal-structural coupling analysis and calculation were carried out.The results show that: under the action of the internal heat source, the maximum deformation of the machine tool in the cutting direction is 6.8μm, which occurs at the spindle motor. The maximum deformation of the tool tip is 1.02μm in the cutting direction. Eventually, the machine thermal error under the tool tip and the work bench is 1.42μm. This research provides a basis for the research of machine tool thermal compensation and the improvement of the accuracy of machine tool.
The ultra-precision single point diamond flycutting is an effective way for finishing potassium dihydrogen phosphate (KDP) crystals. However, the dynamic performance and motion precision of the machine tool would introduce the errors and have an adverse effect on the surface quality of elements. In this study, a significant method is presented to trace error sources by combining monitoring the rotary errors and analyzing the machined surface. On the one hand, forward recursion method is adopted. Based on the online measuring platform, the radial error, axial error and inclination error of spindle rotation can be obtained. Through the Fourier transform algorithm, the frequency information in each direction is known. Furthermore, the waviness along the feed direction is identified, which is determined by the rotation fluctuation. On the other hand, a novel method for errors tracing is presented by a reverse thinking mode based on the surface topography. The wavelet analysis is carried out along the cutting direction, and the obvious waviness appears in the 4th layer, of which the dominant frequency is 594Hz. Through the knocking test for the spindle system, the waviness error along the cutting direction is determined as the modal vibration of the spindle system.
To improve the surface quality and laser damage resistance of Potassium Dihydrogen Phosphate (KDP) crystal processed by single point diamond fly-cutting (SPDF) technique, formation and suppression of KDP surface defects are investigated. Firstly, multiple measuring methods have been utilized to characterize KDP surface defects. According to their structure and chemical characters, KDP surface defects were classified into four categories and forming reason of each was analyzed. Based on these analysis results, theoretical model for describing the formation process of KDP surface defects was established and conditions for achieving defects-free KDP surfaces were proposed. Finally, flycutting experiments were carried out to verify the effect of the defects suppression measures. Experiment results indicate that smooth KDP surface with roughness less than 2 nm can be obtained and KDP surface defects can be suppressed effectively by applying the proposed methods.
Micro-machining has been regarded as the most promising method to mitigate the laser damage growth on KDP/DKDP crystal surfaces. In this work, the near-field and far-field light modulations caused by three kinds of typical mitigation contours (spherical, Gaussian and conical) were theoretically investigated and compared to determine the optimal contours for achieving the minimum light intensification. Then, based on Computer Aided Manufacturing (CAM), a specific machining flow combining layer milling (rough repairing) and spiral milling (fine repairing) was developed to repair the surface damage with high efficiency and surface quality. Finally, the morphology, transmittance and laser damage resistance of the repaired KDP surfaces were tested. The theoretical and experimental results indicate that the conical mitigation contours mostly possess the best repaired surface quality and optical performance. The developed combined rough and fine machining flow could be applied as a practical repairing flow to mitigate the laser-induced surface damage growth of KDP crystal optics.
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