【作者】 周志民；

【导师】 孙宝元； 张元良；

【作者基本信息】 大连理工大学 ， 机械电子工程， 2010， 博士

【摘要】 奥氏体不锈钢因有优秀机械综合性能,在工业上得到广泛的应用,但其塑性强、韧性大、切屑粘附性强、导热率低以及采用传统加工工艺时,切削力大、切削温度高、刀具容易磨损、工件加工表面质量差、表面加工硬化严重等,属于典型的难加工材料。天然金刚石以其优良特性被认为理想精密切削的刀具材料,但金刚石刀具在常规条件下车削不锈钢材料时磨损极快,不锈钢材料的精密车削一直是尚未解决的技术难题。研究天然金刚石刀具精密车削不锈钢工件,有巨大的实用价值和理论意义。文中从选择刀具材料和加工工艺及改变切削冷却方式入手实现精密加工不锈钢材料。刀具材料选为天然金刚石,加工工艺为超声振动辅助车削,切削冷却方式为油气雾化冷却。研制了三套不同频率的天然金刚石超声振动车削系统：研制组装超声发生器、变幅杆、换能器及建立组装金刚石超声振动车削系统；研制油气雾化冷却系统；进行传统车削和超声振动车削对比实验,不同冷却润滑方式加工效果对比实验,改变切削参数对刀具磨损量和表面粗糙度影响实验；探索超声振动车削促进切削液冷却润滑作用机理；探索超声和油气雾化冷却联合作用下,天然金刚石车削不锈钢能减少刀具磨损机理；探索油气雾化冷却中二氧化碳气体及四氯化碳切削液有助于减少刀具化学磨损机理；经反复的加工实验得到天然金刚石刀具磨损量、切削参数以及工件表面粗糙度等各要素之间的关系及规律。由实验分析得知,天然金刚石超声振动车削不锈钢工件中,利用油气雾化冷却技术,刀具磨损量明显减少,工件表面质量得到提高。油气雾化冷却促进快速形成边界润滑膜,减少刀具与工件的摩擦,气流中所携带的细小切削液雾滴容易渗透到切削区,润滑作用得以充分发挥,达到很好的润滑作用；采用油气雾化冷却方法,气液两相流体混合形成的雾状射流喷射切削区,射流中微小液滴以较高的速度在切削区发生相变换热,油气雾化冷却中雾滴汽化的热交换效果更充分,从而实现强力降温,切削区域内的热量大幅度下降,工件变形量减小；气液两相流体喷射到切削区时,有较高的速度,动能较大,渗透能力较强,达到更好冷却目的；油气雾化装置的喷雾气流供给切削区,在二氧化碳的作用下,液体挥发迅速,把热量带走,冷却效果较好。油气雾化冷却结合超声振动车削有利于降低金刚石刀具和不锈钢工件间的石墨化,从而保护金刚石刀具。超声振动车削时的切削力很小,减少了金刚石刀具沿其晶面的微断裂；超声振动车削时的切削温度低,远低于金刚石发生石墨化的温度；油气雾化冷却中二氧化碳气体及四氯化碳切削液有助于减少刀具化学磨损,在切削区中提供富碳环境,能有效阻止金刚石刀具中的碳原子的扩散；二氧化碳气体在高温下,有效的打破金刚石中碳原子与工件碳原子的扩散平衡,根据优先反应原理,有效的阻止金刚石中的碳原子的扩散分解现象。在现有实验条件下,天然金刚石超声车削120个直径为30mm的不锈钢工件端面,工件表面粗糙度Rα小于0.06μm,后刀面磨损带宽小于9μm。增大刀具振幅可显著减小工件表面粗糙度和刀具磨损量。在一定进给量、切削速度和切削深度的情况下,采用超声振动结合油气雾化冷却方法,可实现不锈钢的天然金刚石精密车削。更多还原

【Abstract】 The austenitic stainless steel has been enjoyed wide use in industry for its excellent mechanical properties, however, it is also known as a typical hardly machinable material for the low thermal conductivity, active reactivity, and short interface between the tool and the chips, high cutting temperature, small modulus of elasticity etc. In this paper, the machining was realized by choosing the tool material and changing the cooling method. The natural diamond is regarded as the ideal tool material for precise machining, but as for turning stainless steel, it is easy to produce wear, which is a difficult problem to solve. Hence it is a significant topic to advance the stainless steel cutting technology.In this paper, the tool material was the natural diamond, the ultrasonic vibration turning was adopted, and the cooling method was the atomization of oil gas. Three types of ultrasonic vibration systems of different frequencies were developed, the ultrasonicators, horns, transducers were developed accordingly. What’s more, the atomization system was established. Meanwhile, the traditional turning was also placed to compare with the ultrasonic turning, and the turning results were compared by different cooling methods.Further more, the influence on the tool life and surface roughness could be evaluated by changing the cutting parameters. The mathematical models of the action of the ultrasonic turning and the atomization system were established to explore the mechanism of the lubrication mechanism of the cooling fluid. After reiterative experiments, we summarized the rules and relations among different factors such as the life of diamond turning, tool cutting parameters, material of piece, dimensional accuracy, surface quality, etc.Based on the analysis of the experiments, it follows that:in the ultrasonic vibration turning system, owing to the atomization scheme, the tool wear was decreased significantly, and the surface quality of the work piece was improved. In this type of cooling method, the lubricant film was formed rapidly leading to well lubrication action, which was also enhanced because of the fog drops contained in the cooling draught, reducing friction between the tool and the work piece. In addition, the heat exchange was more enough to control the deformation of the piece. The cooling effect in the cutting area was enhanced by the spraying of ill and gas with big speed and kinetic energy. In the cutting area, due to the carbon dioxide, the liquid volatilized rapidly removing the heat and improving the cooling effect.The combination of the ultrasonic vibration and the atomization system was good to reduce the affinity between the diamond and the stainless steel, protecting the tool. The small cutting force leaded to an improved micro-fracture, and a low cutting temperature which was far lower than the graphitizing temperature. The carbon dioxide and carbon tetrachloride were contributed to reduce the chemical wear of the tool in the abundant carbon cutting area. According to the prior reaction, the carbon dioxide could protect the carbon atom of diamond form diffusing and decomposing effectively under high temperature.The experimental results showed that, when turning 120 faces with diameter 30mm of the stainless steel, the surface roughness Ra was less than 0:15μm, and the wear land of the major flank was less than 5μm. Therefore, increasing amplitude of the tool could improve the surface roughness and wearing capacity obviously. With certain feed amount, cutting speed and cutting depth, by the combination of the ultrasonic vibration and the atomization system, it was feasible to turn the stainless steel precisely by the natural diamond.更多还原