单层CBN砂轮高速磨削钛基复合材料试验研究

发布时间：2018-08-03 15:34

【摘要】：TiCp/Ti-6Al-4V钛基复合材料具有比强度高、耐高温与耐磨损等优异的物理力学性能,在航空航天领域具有广阔应用前景。然而,该材料中高强韧Ti-6Al-4V基体材料与高硬度TiC增强颗粒的共同存在使其普通磨削加工过程容易出现因增强颗粒脱落(或破碎)形成表面缺陷、以及磨削高温导致工件材料烧伤的问题,严重制约了加工效率与质量水平的提升。有鉴于此,本课题提出采用单层CBN砂轮与高速磨削相结合的技术方案解决TiCp/Ti-6Al-4V钛基复合材料磨削加工过程的上述难题,以期实现高效精密加工。作为总课题的一部分,本文通过开展单层电镀CBN砂轮与单层钎焊CBN砂轮高速磨削TiCp/Ti-6Al-4V钛基复合材料的对比试验,对其中涉及的钛基复合材料高速磨削加工性评价、高速磨削烧伤现象表征、加工表面缺陷表征与定量评价等关键问题进行研究。完成的主要工作和取得的成果如下:(1)揭示了单层CBN砂轮高速磨削TiCp/Ti-6Al-4V钛基复合材料的磨削力与温度变化规律,评价了磨削加工性。由于增强颗粒的添加增加了钛基复合材料的磨削难度,导致其高速磨削过程的力与温度均高于Ti-6Al-4V钛合金。磨削力随工件进给速度和切深增大而上升、随磨削速度增大而下降;磨削温度随磨削速度、工件进给速度和切深的增大均呈上升趋势,且工件进给速度、切深、磨削速度对磨削温度的影响程度依次增大。单层钎焊CBN砂轮高速磨削钛基复合材料的磨削力与温度均低于单层电镀CBN砂轮,采用前者高速磨削可提高不发生材料烧伤的最大去除率。(2)探明了单层CBN砂轮高速磨削TiCp/Ti-6Al-4V钛基复合材料的表面烧伤宏观与微观特征。钛基复合材料表面烧伤颜色与磨削温度呈现比较明确的对应关系;随着磨削烧伤程度加重,显微组织变形更剧烈,且表层材料出现软化。TiCp/Ti-6Al-4V钛基复合材料高速磨削亚表面变质层厚度与显微组织变形程度显著高于Ti-6Al-4V钛合金。基于磨削比能建立了钛基复合材料高速磨削烧伤预测模型。(3)阐明了单层CBN砂轮高速磨削TiCp/Ti-6Al-4V钛基复合材料加工表面的微观形貌特征。钛基复合材料高速磨削表面主要由磨痕、孔洞、光滑区域和不规律区域组成。磨削速度较小、工件进给速度与切深较大时,TiC颗粒容易产生破碎或者被从Ti-6Al-4V基体中拔出,在表面形成孔洞。对比分析显示,单层钎焊CBN砂轮在降低钛基复合材料磨削表面缺陷方面比单层电镀CBN砂轮更具优势。本文研究成果加深了对单层CBN砂轮高速磨削TiCp/Ti-6Al-4V钛基复合材料的认识,为后续通过工艺优化进一步控制表面缺陷与磨削烧伤提供了科学依据。
[Abstract]:TiCp/Ti-6Al-4V titanium matrix composites have excellent physical and mechanical properties such as high specific strength, high temperature resistance and wear resistance. However, the co-existence of high strength and toughness Ti-6Al-4V matrix material and high hardness TiC reinforced particles makes it easy to produce surface defects due to the shedding (or breaking) of the reinforced particles in the grinding process. And grinding high temperature leads to the problem of workpiece material burn, which seriously restricts the improvement of processing efficiency and quality level. In view of this, this paper puts forward a technical scheme which combines monolayer CBN grinding wheel with high speed grinding to solve the above problems in the grinding process of TiCp/Ti-6Al-4V titanium matrix composites, in order to realize high efficiency precision machining. As a part of the whole project, this paper evaluates the high speed grinding processability of titanium matrix composites by comparing the high speed grinding of TiCp/Ti-6Al-4V titanium matrix composites with single layer electroplated CBN grinding wheel and single brazed CBN wheel. The characteristics of high-speed grinding burn phenomenon, surface defect characterization and quantitative evaluation were studied. The main work and results obtained are as follows: (1) the grinding force and temperature of TiCp/Ti-6Al-4V titanium matrix composites grinding with single-layer CBN grinding wheel at high speed are revealed and the grinding machinability is evaluated. The grinding difficulty of titanium matrix composites is increased by adding reinforced particles, which leads to the higher grinding force and temperature than that of Ti-6Al-4V titanium alloy. The grinding force increases with the increase of the feed speed and depth of the workpiece, and decreases with the increase of the grinding speed, and the grinding temperature increases with the grinding speed, the feed speed and the cutting depth of the workpiece, and the feed speed and depth of the workpiece are increased. The influence of grinding speed on grinding temperature increases in turn. The grinding force and temperature of single layer brazed CBN wheel for high speed grinding of titanium matrix composites are lower than that of single layer electroplated CBN wheel. Using the former high speed grinding can improve the maximum removal rate of no material burn. (2) the macroscopic and microscopic characteristics of surface burn of TiCp/Ti-6Al-4V titanium matrix composites after high speed grinding with single layer CBN grinding wheel are investigated. The surface burn color of titanium matrix composites has a clear relationship with grinding temperature, and the microstructure deformation becomes more severe with the increase of grinding burn degree. In addition, the thickness and microstructure deformation of the subsurface metamorphic layer in high speed grinding of the surface material with softened. TiCp / Ti-6Al-4V titanium matrix composite is significantly higher than that of the Ti-6Al-4V titanium alloy. Based on the specific grinding energy, a prediction model for high speed grinding burn of titanium matrix composites was established. (3) the microtopography of TiCp/Ti-6Al-4V titanium matrix composites machined by monolayer CBN grinding wheel at high speed was described. The high-speed grinding surface of titanium matrix composites is mainly composed of wear marks, holes, smooth regions and irregular regions. When the grinding speed is small and the feed speed and cutting depth of the workpiece is high, the tic particles are easily broken or pulled out from the Ti-6Al-4V matrix, and the pores are formed on the surface. The comparative analysis shows that the single-layer brazed CBN grinding wheel is superior to the single-layer electroplated CBN wheel in reducing the grinding surface defects of titanium matrix composites. The research results of this paper have deepened the understanding of high speed grinding of TiCp/Ti-6Al-4V titanium matrix composites with single-layer CBN grinding wheel and provided scientific basis for further control of surface defects and grinding burns through technological optimization.
【学位授予单位】：南京航空航天大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TG580.6

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