冷等离子体射流调控黑色金属金刚石切削中加工界面特性的机理与方法

The lack of an effective way to restrain tool wear has been a bottleneck to restrict progress of the ultraprecision diamond turning technology of ferrous metals. Based on the characteristic that the energetic particles in nitrogen cold plasma jet (NCPJ) combine with iron atoms more easily and rapidly than carbon atoms do to form stronger chemical bonds, the method real-time regulates the ferrous metals properties in the processing interface including tool-workpiece interface and tool-chip interface to prevent interactions between iron in workpiece and carbon in tool, restrains the tool graphite wear, stabilizes the machining process and improves the processing quality. Some key issues will be studied, including the rule of the mass transfer and the heat transfer between NCPJ and the processing interface, and then the properties of reactants and the evolution law of friction characteristics in processing interface. The reaction dynamic model to describe the processing interface reaction rate constants and interface movement rules and the prediction model to describe the relations among factors such as the NCPJ properties, mode of delivery etc., the tool wear and the processing quality will be established. How the NCPJ full service the processing interface also will be studied. A new technical foundation for tool wear restraint will be formed by revealing the NCPJ real-time regulation mechanism of the processing interface properties and mastering the inherent relationship between machining effects and processing conditions. The new subject will have important scientific significance in enriching non-traditional processing and ultraprecision machining theory and technology, and in widening the application area of diamond cutting technology.

鉴于缺乏抑制刀具磨损的有效方法是制约黑色金属金刚石超精密切削技术进步的瓶颈，提出利用氮冷等离子体射流（NCPJ）中的载能粒子比碳原子更易与铁原子快速结合形成更强化学键的特点，实时调控加工界面（包括刀-工界面和刀-屑界面）处的黑色金属特性，阻止工件铁原子与刀具碳原子相互作用，抑制刀具石墨化等磨损，稳定加工过程和提高加工质量。将研究NCPJ与加工界面之间传质及传热规律，进而研究加工界面反应物特性及摩擦特性演变规律；建立描述加工界面反应速度常数和界面移动规律的反应动力学模型，以及描述NCPJ特性、送达方式等因素与刀具磨损、加工质量之间关系的预测模型；研究如何把NCPJ充分送达加工界面等关键技术。揭示加工界面特性的NCPJ实时调控机理，掌握加工效果与加工条件的内在联系，形成新的抑制刀具磨损的技术基础。对丰富非传统加工及超精密加工理论与技术，拓宽金刚石切削技术应用范围具有重要的科学意义。

缺乏抑制刀具磨损的有效方法是制约黑色金属金刚石超精密切削技术进步的瓶颈问题。项目提出利用冷等离子体射流的载能活性粒子比碳原子更易与铁原子快速结合形成更强化学键和冷却润滑效果好的特点，将其施加于切削界面，实时降低刀-工界面的化学亲和性和改善切削区的热力作用，从而抑制金刚石切削黑色金属时的刀具磨损，稳定加工过程和提高加工质量。项目研制出了温度较低、易输送至刀-工接触界面、适用于辅助切削的大气压柔性冷等离子射流。通过分子动力学模拟和热分析试验，得出氮冷等离子体可降低黑色金属对金刚石的化学亲和性。分子动力学模拟的结果显示，金刚石石墨化的温度在1200 ℃~1700 ℃之间，但在铁原子的催化作用下，金刚石石墨化的温度可降低至约773 ℃。热分析试验则证明，未经氮冷等离子体处理的NAK80/金刚石接触界面上金刚石石墨化温度为882 ℃，而经氮冷等离子体处理的试样在1185 ℃时才出现明显的石墨化。即铁原子会降低金刚石的石墨化温度，而氮冷等离子体处理后黑色金属/金刚石界面上的金刚石石墨化温度又会提高。氮气射流和氮冷等离子体射流气氛的绝氧作用可减轻摩擦副的氧化磨损，氮冷等离子体气氛有利于减轻摩擦副的粘着磨损，氮冷等离子体气氛中NAK80/金刚石摩擦副的摩擦磨损性能最佳。普通切削和超声椭圆振动切削时刀具的磨损表现为切削刃磨损；冷等离子体实时调控时表现为轻微的前刀面磨损，且金刚石刀具的磨损量显著下降。冷等离子体和超声椭圆振动共同作用时，以切削刃轻微的粘附磨损为主，此时抑制金刚石刀具磨损的效果最佳。相比普通金刚石切削黑色金属加工，冷等离子体辅助超声椭圆振动切削可将刀具的有效切削距离提高10倍，并且工件的表面粗糙度最低，同时可将金刚石中的碳元素向工件和切屑中的扩散磨损分别降低68.49%和70.37%。