Xing Yintian, Li Chuang, Liu Yue, Yang Chao, Xue Changxi
Opt Express. 2021 Feb 1;29(3):3708-3723. doi: 10.1364/OE.417307.
The mold core fabrication of a freeform surface on die steel by ultra-precision machining can make the optical elements of freeform be mass-produced by plastic injection and glass mold pressing. However, because steel is a typical difficult-to-cut material, the technical limitations of existing machining methods hardly meet the current requirements of design. In this paper, a novel machining method, one-dimension ultrasonic-assisted slow tool servo (UASTS) turning, is proposed to manufacture the freeform surface with high-precision and large-steepness on the die steel. Aiming at the characteristics of UASTS turning, the tool trajectory is generated by analyzing the compensation of tool radius and confirming the position of ultrasonic displacement. The 2D surface model contours of residual tool marks are established for predicting the 3D surface topography based on considering the effects of kinematics, material elastic recovery and plastic side flow. In the experiments, the large-amplitude bidirectional sinusoidal wave grid (BSWG) surface is successfully fabricated by UASTS technology on the material, Polmax steel, for which the value Rt of surface roughness is less than 70nm and the value Ra of surface roughness can achieve to 3.298nm. The results show that the freeform surface with high-precision and large-steepness can be machined by UASTS turning technology on mold steel.
通过超精密加工在模具钢上制造自由曲面的型芯，可使自由曲面光学元件通过注塑成型和玻璃模压进行批量生产。然而，由于钢材是典型的难切削材料，现有加工方法的技术局限性很难满足当前的设计要求。本文提出了一种新颖的加工方法——一维超声辅助慢刀伺服（UASTS）车削，用于在模具钢上制造高精度、大斜率的自由曲面。针对UASTS车削的特点，通过分析刀具半径补偿并确定超声位移位置来生成刀具轨迹。基于考虑运动学、材料弹性恢复和塑性侧向流动的影响，建立了残留刀痕的二维表面模型轮廓，用于预测三维表面形貌。在实验中，采用UASTS技术在Polmax钢材料上成功加工出了大振幅双向正弦波网格（BSWG）表面，其表面粗糙度Rt值小于70nm，表面粗糙度Ra值可达3.298nm。结果表明，采用UASTS车削技术可在模具钢上加工出高精度、大斜率的自由曲面。
