Abstract
The damaging of ZnSe crystal has a significant impact on its service performance and life. Based on the specific cutting energies for brittle and ductile mode machining, a model is proposed to evaluate the damage depth in the shoulder region of ZnSe crystal during single point diamond machining. The model considers the brittle-ductile transition and spring back of ZnSe crystal. To verify the model, the elastic modulus, hardness, spring back, and friction coefficient of ZnSe crystal are measured by nanoindentation and nanoscratch tests, and its critical undeformed chip thickness is obtained by spiral scratching. Meanwhile, orthogonal cutting experiments are conducted to obtain the different shoulder regions and cutting surfaces. The shoulder damage depth is analyzed, indicating that the effect of the feed on the damage depth at a high cutting depth is stronger than that at a low one. The model is verified to be effective with an average relative error of less than 7%. Then, the model is used to calculate the critical processing parameters and achieve a smooth ZnSe surface with a roughness Sa = 1.0 nm. The model is also extended to efficiently predict the bound of the subsurface damage depth of a cutting surface. The research would be useful for the evaluation of surface and subsurface damages during the ultra-precision machining of ZnSe crystal.
Highlights
Single point diamond turning (SPDT) has high efficiency, precision, and repeatability and is broadly used to fabricate high-precision parts in the fields of optics, clean energy, information communication, etc. [1]
The maximum subsurface damages (SSDs) depth generally increases with feed or cutting depth
Based on the specific cutting energies for brittle and ductile mode machining, the model of the shoulder damage is proposed for ultra-precision diamond cutting of ZnSe crystal
Summary
Single point diamond turning (SPDT) has high efficiency, precision, and repeatability and is broadly used to fabricate high-precision parts in the fields of optics, clean energy, information communication, etc. [1]. Many researchers have studied the generation process of micro-cracks or pits for SPDT-processed brittle crystal materials, which are closely related to the damages in the shoulder region. Tie et al [11] used the deliquescent magnetorheological finishing spot method to measure the depth of a subsurface defect in KDP crystal These methods are direct and reliable, and can precisely provide the damage information, but they are time-consuming and may modify the physical properties of the tested sample. Our previous research has proposed a theoretical model to calculate the SSD depth of ZnSe crystal in diamond cutting [18]. In this paper, based on the specific cutting energies for brittle and ductile mode machining, a model of the shoulder damage is developed for diamond-processed brittle material. This study will provide an important reference for the nanodefect-free machining of ZnSe optical elements
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