| SUN Xu-feng,YAO Peng,WANG Qing-wei,BAO Xiao-yu,HUANG Chuan-zhen.Mechanical Properties and Ultra-precision Turning of Cesium Iodide Crystal[J],51(10):284-292 |
| Mechanical Properties and Ultra-precision Turning of Cesium Iodide Crystal |
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| DOI：10.16490/j.cnki.issn.1001-3660.2022.10.030 |
| KeyWord:cesium iodide crystal ultra-precision turning surface roughness mechanical properties anisotropy high strain rate |
| Author | Institution |
| SUN Xu-feng |
a.School of Mechanical Engineering,Center for Advanced Jet Engineering Technologies, c.Key Laboratory of High Efficiency and Clean Mechanical Manufacture Ministry of Education, Shandong University, Jinan , China |
| YAO Peng |
a.School of Mechanical Engineering,Center for Advanced Jet Engineering Technologies, c.Key Laboratory of High Efficiency and Clean Mechanical Manufacture Ministry of Education, Shandong University, Jinan , China |
| WANG Qing-wei |
a.School of Mechanical Engineering,Center for Advanced Jet Engineering Technologies, c.Key Laboratory of High Efficiency and Clean Mechanical Manufacture Ministry of Education, Shandong University, Jinan , China |
| BAO Xiao-yu |
a.School of Mechanical Engineering,Center for Advanced Jet Engineering Technologies, c.Key Laboratory of High Efficiency and Clean Mechanical Manufacture Ministry of Education, Shandong University, Jinan , China |
| HUANG Chuan-zhen |
School of Mechanical Engineering, Yanshan University, Hebei Qinhuangdao , China |
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| Abstract: |
| This work aims to reveal the mechanical properties of CsI (cesium iodide) crystal on (110) plane and the influence of turning parameters on surface roughness in an ultra-precision turning process. Firstly, the mechanical properties under quasi-static and high strain rates were obtained and analyzed by nano-indentation and split Hopkinson pressure bar (SHPB) experiments, respectively. Then, single point diamond turning (SPDT) experiments on crystal were conducted in different cutting orientations with different turning parameters. Meanwhile, white light interferometer, dynamometer and infrared thermal imager were utilized to measure the machined surface roughness, cutting force, and cutting temperature during the ultra-precision turning process, respectively. Experimental results show that CsI crystal mainly undergoes plastic deformation during the indentation process without obvious brittle cracks and the elastic recovery coefficient is 0.03. The Vickers hardness of (110) crystal plane is about 100 MPa. These results indicate that CsI crystal is one kind of typical soft and ductile materials. In SPHB experiments, when strain rate increases from 6 000 s–1 to 8 000 s–1, the yield strength of crystal increases by 7 MPa, which proves that the hardness and strength of this material can be improved by high strain rate. In the turning experiments, overall surface roughness below 20 nm was obtained by turning along the orientation of 270°, while along the turning orientations of 0°, 90°, 180°, surface roughness Ra of some positions on the machined crystal reached 80 nm. The results of response surface experiment along this direction indicate that the best surface quality can be obtained when the tool rake angle is 10°, rotational speed is 2 000 r/min, feed rate is 4 μm/r, and the depth of cut is 2 μm. The mean surface roughness is Ra 8.53 nm, and the maximum surface roughness is Ra 11.02 nm. When utilizing a 0° rake angle tool, and the rotational speed is 3 000 r/min, feed rate is 6 μm/r, and the depth of cut is 6 μm, a finish surface can also be obtained. The mean surface roughness is Ra 9.07 nm, and the maximum surface roughness is Ra 17.36 nm. The negative rake angle tool is not suitable for turning the CsI crystal. As for the influence of turning parameters, the surface roughness is mainly affected by the rotational speed (cutting speed) in the experiments, and higher cutting speed is beneficial for better machined surface. However, the impact of feed rate and depth of cut on the surface roughness is not significant. The machining efficiency can be raised by relative high feed rate and large depth of cut in the rough machining process. Through above experiments and analysis, it can be concluded that the CsI crystal is a kind of ductile material with low hardness. The strength and the hardness increase significantly under high strain rate. Increased cutting speed and strain rate in the ultra-precision turning process improved the machinability of soft and ductile materials, and the surface roughness of the CsI crystal was reduced by 80%. A smooth surface below Ra 10 nm was obtained by combining with other optimized turning parameters, such as the turning orientation, tool rake angle, feed rate and depth of cut. |
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