Full-band error control and crack-free surface fabrication techniques for ultra-precision fly cutting of large-aperture KDP crystals

doi:10.1007/s11465-017-0448-8

Front. Mech. Eng.

2017, Vol. 12

Issue (2) : 193-202 https://doi.org/10.1007/s11465-017-0448-8

RESEARCH ARTICLE

Full-band error control and crack-free surface fabrication techniques for ultra-precision fly cutting of large-aperture KDP crystals

F. H. ZHANG¹(

), S. F. WANG^1,², C. H. AN², J. WANG², Q. XU²

¹. Department of Mechanical Engineering, Harbin Institute of Technology, Harbin 150001, China
². Chengdu Fine Optical Engineering Research Center, Chengdu 610041, China

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Abstract

Large-aperture potassium dihydrogen phosphate (KDP) crystals are widely used in the laser path of inertial confinement fusion (ICF) systems. The most common method of manufacturing half-meter KDP crystals is ultra-precision fly cutting. When processing KDP crystals by ultra-precision fly cutting, the dynamic characteristics of the fly cutting machine and fluctuations in the fly cutting environment are translated into surface errors at different spatial frequency bands. These machining errors should be suppressed effectively to guarantee that KDP crystals meet the full-band machining accuracy specified in the evaluation index. In this study, the anisotropic machinability of KDP crystals and the causes of typical surface errors in ultra-precision fly cutting of the material are investigated. The structures of the fly cutting machine and existing processing parameters are optimized to improve the machined surface quality. The findings are theoretically and practically important in the development of high-energy laser systems in China.

Keywords ultra-precision fly cutting large-aperture KDP crystals spatial frequency processing error

Corresponding Author(s): F. H. ZHANG

Just Accepted Date: 14 April 2017 Online First Date: 10 May 2017 Issue Date: 19 June 2017

Cite this article:

F. H. ZHANG,S. F. WANG,C. H. AN, et al. Full-band error control and crack-free surface fabrication techniques for ultra-precision fly cutting of large-aperture KDP crystals[J]. Front. Mech. Eng., 2017, 12(2): 193-202.

URL:

https://academic.hep.com.cn/fme/EN/10.1007/s11465-017-0448-8
https://academic.hep.com.cn/fme/EN/Y2017/V12/I2/193

Fig.1 Application of large-aperture KDP crystals in a high-energy laser system [1]

Tab.1 Evaluation index for large-aperture KDP crystals [3]

Fig.2 Processing a large-aperture KDP crystal by fly cutting: (a) Schematic of the process; (b) fly cutting machine for KDP crystals

Fig.3 Fluid-structure coupled analysis of the vacuum absorption process: (a) Surface shape of the vacuum chuck; (b) pressure distribution inside the gas; (c) deformation of the KDP crystal; (d) displacement of the top KDP surface

Fig.4 Surface micro waviness distributed along the cutting direction

Fig.5 Dynamic behavior of the spindle system and surface micro waviness obtained by simulation: (a) Deformation contour and displacement curve of the spindle system; (b) simulated micro waviness

Fig.6 Surface micro waviness distributed along the feeding direction

Fig.7 Influence of D on the magnitude of micro waviness

Fig.8 Crystal surface processed by the new fly cutting machine

Fig.9 Influence of rotating speed fluctuation on surface roughness: (a) Micro waviness induced by the fluctuation in rotating speed; (b) surface profile after optimization of the spindle motor

Fig.10 Measuring the BDT depth on the doubler plane of a KDP crystal: (a) Principle for measuring BDT depth; (b) definition of cutting directions

Fig.11 BDT depth on the doubler plane of the KDP crystal

Fig.12 Surface and subsurface of the transition shoulder

Fig.13 Profiles of the processed surface of the doubler plane

Fig.14 Surface roughness of the KDP crystal produced with the optimized cutting parameters

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