冷等离子体辅助金刚石切削黑色金属基础研究

发布时间：2018-05-24 14:47

本文选题：冷等离子体 + 超声椭圆振动　；参考：《大连理工大学》2017年博士论文

【摘要】：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。论文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。论文在分析金刚石刀具磨损及抑制磨损机理的基础上,首先研制了冷却润滑效果好、易输送至刀-工接触界面进行特性调控的大气压冷等离子射流,然后采用分子动力学、热分析、摩擦磨损等理论和试验方法研究了冷等离子体射流辅助切削的作用机理,最后进行了基础的切削试验。论文的主要研究工作如下:为从降低刀-工界面化学亲和性和改善切削区的热力作用两个方面抑制金刚石刀具的磨损,研制出温度较低、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。研究发现,氮气作为工作气体适合于裸电极放电产生冷等离子体射流,并且频率对氮气放电的伏安特性影响较明显,而气流量对氮气放电的伏安特性影响较小。采用柔性等离子体射流方案可实现等离子体的有效输送,柔性射流的长度随驱动电压和气体流量的增大而增加,且与普通冷等离子体射流具有相似的伏安特性。涡流管对工作气体预冷却可降低等离子体射流的温度,且流量越大射流温度越低;而驱动电压的升高会提高等离子体射流的总体温度。因此,借助涡流管通过调节流量和放电电压可得到温度在一定范围内可控的等离子体射流。特别的,当驱动电压为3.0 kV、流量为50 L/min时,柔性氮等离子体射流的整体温度可低至-7 ℃。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。结果表明,NAK80表面和晶界会吸附大量活性粒子,并与黑色金属反应生成与金刚石化学亲和性较低的氮化物,最终达到抑制金刚石石墨化磨损的目的。为验证冷等离子体改善切削区热力作用的效果,在空气射流、氮气射流和氮冷等离子体射流氛围中进行了 NAK80/金刚石摩擦副的摩擦磨损试验。结果表明,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。转速较低时,氮冷等离子体气氛对NAK80/金刚石摩擦副没有明显的减摩作用。转速较高时,NAK80/金刚石摩擦副在氮冷等离子体气氛中的摩擦系数低于空气气氛。冷等离子体与固体表面作用时不会破坏工件表面的微观形貌,且对润湿性的改性在切削加工后也会逐渐恢复。利用自行研制的振动特性可控的超声椭圆振动装置,进行了切削试验,分析了超声椭圆振动的切削特性。刀具在超声振动装置的驱动下沿椭圆轨迹高频振动,同时沿进给方向运动,两种运动模式的复合使得刀具对工件进行周期性的分离式切削。当刀具以超声椭圆振动切削时,在刀具耕犁作用形成的条状结构上会生成"鱼鳞"状振纹,且切削速度越低,"鱼淲"状振纹越密集,并可明显改善工件表面质量,冷等离子体和超声椭圆振动共同作用时的工件表面粗糙度最低。超声椭圆振动切削会增加工件表面的残余应力,而冷等离子体对切削区润滑冷却有助于降低工件表面的残余应力。为验证冷等离子体抑制金刚石切削黑色金属时的刀具磨损效果,开展了不同气氛中的切削试验。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%。
[Abstract]:The lack of effective method to restrain tool wear is a bottleneck to restrict the progress of ultraprecision cutting technology for black metal diamond. The paper proposes that the active particles of the cold plasma jet are more easily combined with the iron atom to form stronger chemical bonds and good cooling effects than the carbon atoms, and apply it to the cutting interface. In real time, the chemical affinity of the tool interface and the thermal effect of the cutting area are reduced, thus cutting tool wear, stabilizing the machining process and improving the machining quality of the diamond cutting black metal. On the basis of the analysis of the mechanism of diamond tool wear and the inhibition of wear and tear, the paper first developed a good cooling and lubrication effect and easy to transfer to the knife. The atmospheric pressure cold plasma jet is controlled by the contact interface, and the mechanism of the cold plasma jet assisted cutting is studied by the theory and test method of molecular dynamics, thermal analysis and friction and wear. Finally, the basic cutting tests are carried out. The main work of this paper is as follows: reducing the chemical interface chemistry from the tool tool interface. Two aspects of affinity and improving the thermal effect of the cutting area are used to suppress the wear of diamond cutting tools. The temperature is low, and it is easily transported to the tool contact interface. It is suitable for the air pressure flexible plasma jet in the auxiliary cutting. It is found that nitrogen is a working gas suitable for producing cold plasma jets from the bare electrode discharge. The effect of the gas discharge on the volt ampere characteristics of nitrogen discharge is less obvious. The effective delivery of the plasma can be achieved by the flexible plasma jet. The length of the flexible jet increases with the increase of the driving voltage and the gas flow, and it has a similar volt ampere with the ordinary cold plasma jet. Characteristics. The pre cooling of the working gas can reduce the temperature of the plasma jet, and the larger the flow rate is, the lower the jet temperature, and the increase of the driving voltage will increase the overall temperature of the plasma jet. Therefore, the plasma jet can be controlled by the flow and discharge voltage by the flow and discharge voltage. In addition, when the driving voltage is 3 kV and the flow rate is 50 L/min, the overall temperature of the flexible nitrogen plasma jet can be lower to -7 C. through molecular dynamics simulation and thermal analysis test, it is concluded that the nitrogen cold plasma can reduce the chemical affinity of the black metal to the diamond. The results of molecular dynamics simulation show that the temperature of the graphitization of the diamond is the result of molecular dynamics simulation. Between 1200 and 1700 C, the temperature of the graphitization of diamond can be reduced to about 773 C under the catalysis of the iron atom. The thermal analysis test shows that the temperature of the diamond graphitization at the NAK80/ diamond contact interface without nitrogen cold plasma is 882, and the sample treated by the nitrogen cold plasma appears at 1185. It is obvious graphitization. That is, the iron atom will reduce the graphitization temperature of the diamond, and the temperature of the diamond graphitization on the black metal / diamond interface after the nitrogen cold plasma treatment will increase. The results show that the NAK80 surface and grain boundary will adsorb a large number of active particles and react with the black metal to produce nitrogen with low chemical affinity of diamond. In order to verify the effect of the cold plasma to improve the thermal effect of the cutting zone, the friction and wear tests of the NAK80/ diamond friction pair were carried out in the air jet, nitrogen jet and nitrogen cold plasma jet atmosphere. The results showed that the nitrogen and nitrogen cold plasma jet atmosphere had been tested. The oxidation wear of the friction pair can be reduced by the anoxic action. The nitrogen cold plasma atmosphere helps to reduce the adhesion and wear of the friction pair. The friction and wear properties of the NAK80/ diamond friction pair in the nitrogen cold plasma atmosphere are the best. The nitrogen cold plasma atmosphere has no obvious antifriction effect on the NAK80/ diamond friction pair. The rotational speed is higher. The friction coefficient of the NAK80/ diamond friction pair in the atmosphere of nitrogen cold plasma is lower than that in the air. The effect of cold plasma on the surface of the solid will not destroy the microstructure of the workpiece surface, and the modification of wettability will be gradually restored after cutting. The cutting test is carried out. The cutting characteristics of ultrasonic elliptical vibration are analyzed. The cutting tool vibrate along the elliptical track under the drive of the ultrasonic vibration device and moves along the direction of the feed. The two kinds of motion modes make the tool make periodic separation cutting to the workpiece. When the tool is cutting with ultrasonic elliptical vibration, the tool plow is used. The "fish scale" pattern will be formed in the strip structure formed by the action, and the lower the cutting speed, the more dense the "fish" shape is, and the surface quality of the workpiece can be improved obviously. The surface roughness of the workpiece is the lowest when the cold plasma and ultrasonic elliptical vibration act together. The ultrasonic elliptical vibration cutting will increase the residual stress on the workpiece surface, and the cold is away from the cold. The lubricating cooling of the sub body helps to reduce the residual stress on the surface of the workpiece. In order to verify the tool wear effect of cutting the black metal by the cold plasma, the cutting experiments in different atmospheres have been carried out. The wear of the cutting tool in the ordinary cutting and ultrasonic elliptical vibration cutting is the wear of the cutting edge; the cold plasma is real-time in real time. The wear of the diamond cutting tool is slightly worn and the wear amount of the diamond cutting tool drops significantly. When the cold plasma and ultrasonic elliptical vibration are combined, it is the best to reduce the wear of the diamond cutting tool. The acoustic elliptical vibration cutting can increase the effective cutting distance of the tool by 10 times, and the surface roughness of the workpiece is the lowest. At the same time, the carbon element in the diamond can be reduced by 68.49% and 70.37%. to the workpiece and the chip respectively.
【学位授予单位】：大连理工大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TG506

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