Proceedings of the
9th International Conference of Asian Society for Precision Engineering and Nanotechnology (ASPEN2022)
15 – 18 November 2022, Singapore

Study on the Ultra-Precision Machining of Polycrystalline Tin

Min Lai1,a, Zhifu Xue1,Peng Lyn1 and Fengzhou Fang1,2,b

1State Key Laboratory of Precision Measuring Technology and Instruments, Laboratory of Micro--Nano Manufacturing Technology, Tianjin University, Tianjin 300072, China

2Centre of Micro/Nano Manufacturing Technology (MNMT-Dublin), School of Mechanical & Materials Engineering, University College Dublin, Dublin 4, Ireland


Metallic tin finds wide applications in the high-tech fields of atomic power industry, extreme ultraviolet light source, etc. Thus, high surface finishing and form accuracy of the tin components are in great demand. However, the low melting point and low stiffness of the metallic tin induce strong plastic deformation easily in micro- and nano-scale machining process, resulting in side-flow, burr formation and stick-slip phenomenon of materials on machined surface, which cause the deterioration of surface roughness. In this study, the polycrystalline tin is processed by single point diamond turning, and the factors contributing to the machined surface roughness are analyzed. It is found that the grain boundary steps are the major influence factors for the surface roughness with optimized processing parameters. Based on this knowledge, the surface modification methods to improve the machined surface roughness of polycrystalline tin are proposed. The first approach is using the thermal effect generated by the continuous wave laser, to achieve the grain refinement and case hardening of polycrystalline tin. Then single point diamond turning experiments are carried out on the modified workpiece and the machined surface roughness (Sa) reaches 2 nm, while the unmodified polycrystalline tin has a machined surface roughness of around 10 nm. Another way is to use the large thermal gradient treatment by induction discharge plasma, to achieve the grain expanding and fusion. Thus the amount of grain boundaries on the surface is decreased. After single point diamond turning, the surface roughness (Sa) of tin can achieve less than 1 nm.

Keywords: Ultra-precision machining; Polycrystalline soft metals; Grain boundary; Surface roughness

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