光学脆性材料冷等离子体射流辅助切削的机理与方法

Increasing the critical depth of ductile regime cutting and supressing the diamond tool wear is a quite difficult problem to be solved in efficient ultra-precision cutting of brittle materials. Based on the phenomenon founded in the experiments that cold plasma jet can cool and lubricate the cutting area together with reduce the surface hardness and plastic deformation resistance, an innovative method of machining optical brittle materials in the atmosphere of cold plasma jet by single crystal diamond is proposed. This project researches the generation and characteristics control of cold plasma jet together with the method of ejecting it to cutting area and the effect of tribologyical properties between tool-workpiece interfaces. Through single point scratch test and diamond cutting tests with slight elliptical ultrasonic vibration of the tool, the mechanism of action of cold plasma jet to optical brittle material (SiC, Soda-lime glass, BK7 glass, etc.) surface and brittle-ductile transition process and impact trend will be studied. The cold plasma jet assisted cutting process of brittle materials will also be analyzed and modeled using the test data, with the assistance of molecular dynamics and finite element analysis, etc. Further more, a parameters prediction model of tool life and surface quality will be built. The research will provide great important results in enriching relational theory and technology of non-tradiitional and ultra-precision cutting especially in the efficient ultra-precision cutting of optical brittle materials.

抑制金刚石刀具磨损的同时提高塑性域切削的临界切削深度，是光学脆性材料高效超精密切削亟待解决的瓶颈问题。本项目基于试验中发现的冷等离子体射流可在切削区起润滑冷却作用并能降低材料的表面硬度和塑性变形抗力的现象，提出在冷等离子体射流中进行光学脆性材料单晶金刚石切削的新思路。研究冷等离子体射流的产生、特性控制、导入切削区域的方法；分析冷等离子体射流对刀-工摩擦副摩擦磨损性能的影响；结合刀具的微幅椭圆超声振动，通过单点划痕试验和金刚石切削试验，探明冷等离子体射流对SiC、Soda-lime玻璃、BK7玻璃等典型光学脆性材料表面性质的作用机理及脆塑转变过程的影响规律；结合试验数据，借助分子动力学和有限元分析等方法对脆性材料冷等离子体射流辅助切削过程进行建模和分析，建立各参数对刀具寿命和表面质量的预测模型。研究结果对丰富非传统与超精密加工相关理论与技术，特别是光学脆性材料的高效超精密切削方法具有重要意义。

抑制金刚石刀具磨损的同时提高塑性域切削的临界切削深度，是光学脆性材料高效超精密切削亟待解决的瓶颈问题。项目提出利用大气压冷等离子体射流调控刀-工界面及光学脆性材料的力学性能，以抑制刀具磨损，稳定加工过程，提高加工质量。从气体放电和超声椭圆振动切削原理入手，研制出了温度可低至-7℃、易输送至切削区域、长度可在7cm-200cm调节的大气压柔性冷等离子射流，探究了等离子体射流的放电特性，对其活性成分进行了诊断。搭建了超声椭圆振动装置，其变幅杆的输出端振幅可在25 nm~1500 nm间线性调节，并可通过所得经验公式对振幅进行精确预测。为研究冷等离子体射流抑制金刚石刀具磨损的机理，用磨损试验机，在空气、冷等离子体射流气氛中进行了K9玻璃/金刚石摩擦副摩擦磨损试验，发现转速较高时（n=200-400 r/min），冷等离子体射流对于K9玻璃/金刚石摩擦副具有明显减磨作用。借助EDS对摩擦表面的元素成分进行分析，探究了等离子体对加工界面的作用机理，发现冷等离子体射流在刀-工接触界面发生了化学反应，形成了有助于减磨的氮化物。为分析冷等离子体射流对光学脆性材料临界切深的作用机理和影响规律，对未处理及等离子体处理后的光学脆性材料进行了弯曲试验及压痕划痕试验，研究了等离子体射流对晶体表面塑性变形抗力及断裂抗力的影响机制。研究发现，当冷等离子体射流处理光学脆性材料时，冷等离子体射流中的活性粒子吸附于材料表面引发Rehbinder效应，可延缓脆性材料受力产生塑脆转变断裂，降低材料的弹塑转变临界载荷，并可较明显增加材料的塑性去除区域，且作用效果可保持20h以上。在加工过程中预先对材料处理后再进行加工，可增加脆塑转变的临界切深，延缓材料发生脆性断裂，从而降低切削力，提高加工质量，减缓刀具磨损。