Diamond cutting is a popular method to fabricate microlens array (MLA) on polymethyl methacrylate (PMMA); however, it is limited by brittle fracture, which is formed easily on the surface of MLA during the cutting process. In this paper, the formation mechanism of the brittle fracture is studied via a series of experiments including the slow tool servo (STS) cutting experiment of MLA, surface scratching experiment and sudden-stop cutting experiment. The effects of undeformed chip thickness, feed rate, and machining track on brittle fracture formation are investigated in detail. In addition, based on the fracture formation mechanism, a bi-directional cutting approach is proposed to eliminate the regional brittle fracture of the microlens during diamond cutting. An experiment was then conducted to verify the method; the results demonstrated that bi-directional cutting could eliminate brittle fracture entirely. Finally, a spherical MLA with the form error (v_PV) of 60 nm and the surface roughness (R_a) of 8 nm was successfully fabricated.

中文翻译：

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聚甲基丙烯酸甲酯微透镜阵列金刚石车削中的脆性断裂机理

金刚石切割是在聚甲基丙烯酸甲酯（PMMA）上制造微透镜阵列（MLA）的一种流行方法。但是，它受到脆性断裂的限制，该脆性断裂在切割过程中很容易在MLA的表面形成。本文通过MLA的慢刀伺服切削实验，表面划伤实验和急停切削实验等一系列实验研究了脆性断裂的形成机理。详细研究了未变形切屑厚度，进给速率和加工轨迹对脆性断裂形成的影响。此外，基于断裂形成机理，提出了一种双向切割方法，以消除金刚石切割过程中微透镜的局部脆性断裂。然后进行实验以验证该方法。结果表明，双向切削可以完全消除脆性断裂。最后，球形MLA的形状误差为（v _PV）为60 nm，表面粗糙度（R _a）为8 nm。