【作者】 杨长勇；

【导师】 徐九华；

【作者基本信息】 南京航空航天大学 ， 机械制造及其自动化， 2010， 博士

【摘要】 钛合金具有比强度高、高温力学性能好、耐腐蚀等优异性能,在航空动力装备领域的应用越来越广泛,如发动机叶轮、叶盘、叶片等。但是,钛合金属于典型的难加工材料,采用普通切削或磨削方式加工时存在质量稳定性差、工具损耗快、加工成本高等问题,已成为制约新型航空发动机研制进程的主要因素之一。借助于立方氮化硼(CBN)磨料硬度高、热稳定性好、化学惰性大、导热性好等优点,由该种磨粒制作的各型固结磨料砂轮已在钛合金加工中得到了应用,并取得了一定的效果。但是,传统烧结和电镀CBN砂轮表面磨粒出露低、容屑空间小、砂轮易粘附、堵塞,同时磨粒结合强度低,寿命短,难以满足航空发动机行业用钛合金材料日益提高的加工质量和效率要求,因此研制性能优异的新型CBN砂轮并将其用于钛合金高效磨削非常重要。本文结合钎焊超硬磨料工具与缓进深切磨削工艺优势,开展了单层钎焊立方氮化硼砂轮缓进深切磨削钛合金的基础研究。完成的主要工作包括:(1)根据钛合金缓进深切磨削及钎焊工艺要求,设计了单层钎焊CBN砂轮。优化了钎焊加热工艺和砂轮制造工艺,重点对基体的回转精度和磨粒等高性进行了控制,并通过向Ag-Cu-Ti钎料中加入稀土元素提高了钎料的力学性能、控制了钎料对CBN磨料的润湿性。(2)开展了单层钎焊CBN砂轮缓进深切磨削钛合金试验以获得基础数据,通过磨削力、磨削温度和工件表面完整性等综合评价了单层钎焊CBN砂轮的磨削性能。研究发现,钎焊CBN砂轮缓进深切磨削钛合金过程中磨削力和工件表层温度较低,并可长时间保持稳定,显著提高了钛合金磨削效率。试验中未发现磨粒过早脱落和结合剂剥落现象,表明单层钎焊砂轮牢固把持住CBN磨粒,有助于充分发挥超硬磨料优异特性和提高砂轮寿命。(3)分析了单颗磨粒最大切厚对钛合金磨削比能的影响,获得了单层钎焊CBN砂轮缓进深切磨削钛合金时不产生“尺寸效应”现象的单颗磨粒最大切厚“阈值”。在此基础上,进行了钛合金叶片榫头高效成形磨削单层钎焊CBN砂轮的设计制作,并优化了磨削工艺参数。(4)采用新型组合式断续单层钎焊CBN成形砂轮在生产现场进行了钛合金叶片榫头加工,分析了加工精度和表面完整性,实现了钛合金结构件“以磨代切”。研究表明,采用单层钎焊CBN成形砂轮加工钛合金叶片榫头的加工精度和表面完整性满足了航空发动机用钛合金叶片榫头的设计要求。与车削加工相比,显著提高了加工质量稳定性和效率。同时,单层钎焊CBN成形砂轮亦表现出比陶瓷结合剂CBN砂轮更优异的磨削性能。更多还原

【Abstract】 Titanium alloys are widely used in the aerospace engine, such as impeller, leaf disc and blade, because of their excellent mechanical strength and resistance to surface degradation. While titanium alloys are machined with traditional abrasive tools, the surface quality is difficult to be controlled and the tool worn quickly. Cubic boron nitride (CBN) wheels have been utilized and taken good effects in grinding titanium alloy for CBN abrasive grits have some distinguished properties, such as extremely high hardness, superior thermal stability, large chemical inertia and excellent thermal conductivity. However, the shortcomings of low holding strength for grains and limited storage space for chips are always accompanied with the traditional multiplayer sintered and monolayer electroplated CBN abrasive tools. Therefore, it is helpful to develop the innovative CBN wheel and scientifically to evaluate the performance of grinding wheel for promoting titanium alloy machining with good quality ad high productivity. The innovative monolayer brazed CBN grinding wheels are developed and evaluated in the creep feed grinding of titanium alloy, in order to enhance the machining efficiency of titanium alloy. While cutting titanium alloy blade tenon, there are some problems, so gringding is considered to replace cutting. According to the design and machining requirements of the lamina rabbet, an innovative monolayer brazed CBN profile grinding wheel is developed and used to machine the rabbet in the production field.The main contents in this paper are as follows:(1) The innovative monolayer brazed CBN grinding wheels is designed according to the requirements of brazing technique to realize the creep feed grinding of titanium alloys. Moreover, on the basis of determined the suitable brazing process, the machining process of the grinding wheel hub mainly controlling the rotary accuracy of the wheel and the equal height characteristics of grains is effectively controlled, this kind of CBN grinding wheel applied to creep feed grinding of titanium alloy is successfully developed.(2) The creep feed grinding experiments are conducted to investigate the grinding performance of the innovative monolayer brazed CBN wheel by the means of studying the grinding force, temperature an specific energy as well as the wear of the grains. The experiment results show that the grinding force and temperature can be controlled effectively while creep feed grinding titanium alloy TC4 with the monolayer brazed CBN wheel and the machining efficiency can be improved obviously. Rare earth La can improve the performance of brazed CBN wheels. On the other hand, the abrasion wear is the leading wear behavior for the brazed CBN grinding wheels. The disadvantageous phenomenon, such as the fallout of CBN grits, has never happened during the experiment, which indicates that strong joining to the grains has been realized in the brazed abrasive tools. Thus, the excellent abrasion resistance of CBN grains could be exhibited completely.(3) The effect of the maximum undeformed chip thickness on the grinding specific energy is evaluated and the critical threshold of the maxmum underformed chip thickness is discussed, which can be used as a direction in the design and manufacture of brazed CBN wheels as well as the selection of machining parameters while creep feed grinding titanium alloys.(4) According to the design and machining requirements of the lamina rabbet of some aerospace engine turbine, the innovative monolayer brazed CBN profile grinding wheels are designed and manufactured. The grinding experiments are carried out in the production site. The dimension accuracy of the tenon is assessed and the results indicate that it completely meets the requirement to blade tenon of aero-engine. Compared with cutting, the efficiency and quality stability are improved obviously. And the results indicate that the grinding performance of brazed CBN wheel is better than that of vitrified ones.更多还原