【作者】 宋新玉；

【导师】 赵军；

【作者基本信息】 山东大学 ， 机械制造及其自动化， 2010， 博士

【摘要】 高速、高效切削加工技术近年来以其独特的优势成功应用于钢铁、铝合金以及高温合金的切削加工。论文主要针对镍基高温合金Inconel718高速切削加工过程中刀具摩擦磨损过程、前、后刀面的热-力耦合场以及热-力耦合场作用下刀具寿命的预测模型展开研究,为镍基合金加工刀具材料选择、刀具结构设计及切削参数优化提供理论依据和技术支撑。依据热力学熵产生计算方法,结合涂层硬质合金刀具高速切削Inconel718磨损特点,计算了粘滞性流动、扩散和氧化反应三个磨损子过程的熵产生,从而得到系统总熵产生与切削速度和后刀面平均磨损量VB之间的变化规律。根据系统总熵产生变化趋势深入研究了刀具自组织特性和形成过程机理,探究了积屑瘤、切屑流动带、氧化层和粘结层4种自组织表现形式和各种表现形式所对应的减摩机理。利用总熵产生变化规律,映射了刀具磨损的层次特性,此特性根据具体切削参数选择不同,会出现一个或三个磨损阶段的情况。建立了考虑刀尖圆弧半径和刀具磨损的刀具前、后刀面的热-力耦合场的三维解析模型。分析了不同切削参数和不同刀具几何参数下,各切削微元的剪切角、剪应变、刀屑接触长度的变化。通过计算高速切削摩擦、磨损系统的热分配系数计算每个切削微元由剪切热源和摩擦热源引起的刀-屑接触面的温升。通过假设切屑流动速度为匀速,从而得到每个切屑微元受力矢量和为零,进而求得刀具所受三向分力以及合力数值。模型的计算结果表明：刀具磨损时,刀具前刀面切削力增加不显著,切削温度略有降低,而刀具后刀面所受力和温度都随着刀具的磨损明显增大。依据热-力耦合场影响机制,分析了涂层硬质合金刀具车削Inconel718在不同的切削参数下切屑形态特征和切屑形成机理,同时分析了切削速度、进给量和刀具磨损对工件表面质量的影响。在不同的磨损阶段中各种磨损机理所占的比重有较大差异。由于初始磨损阶段粘结层的频繁剥落与生成,导致广义扩散力增大,所以扩散磨损对刀具寿命的影响最大,但是此阶段由于扩散浓度小、切削温度低氧化磨损所占的比重最小甚至不能发生。然而在稳定磨损阶段,粘结层相对稳定,剥落的频率降低,元素的浓度梯度减低,扩散速度减慢氧化磨损提供了适合的条件,氧化磨损速率持续升高,其所占比重也越来越大,进而分析发现在磨损末期氧化磨损对刀具寿命的影响占绝对优势。综合考虑上述三阶段磨损的特点,依据扩散磨损、粘结磨损和氧化磨损机理,结合热-力耦合作用机制建立了刀具寿命预测模型,并实验验证了理论模型具有一定的可行性和精确性。结合实验加工的具体要求,重点分析了涂层硬质合金刀具和Sialon陶瓷刀具高速车削以及涂层硬质合金刀具高速铣削镍基合金Inconel718时刀具每个磨损阶段刀具磨损形态和磨损机理的变化。本课题得到国家自然基金(50575126)和国家重点基础研究发展计划(2009CB724402)的支持。更多还原

【Abstract】 High speed cutting (HSC) and high performance machining technology has been applied in steel, aluminum and high-temperature alloys cutting successfully because its particular advantages. Our research focused on the tool friction and tool wear process, the thermal-mechanical coupling in the rake face and flank of cutting tool and tool life prediction model under thermal-mechanical coupling action. The analysis of HSC process of Nickel-based superalloys Inconel 718 provided theoretical foundation and technical support for cutting tool material selection on Nickel-based superalloys machining, cutting tool structure design and cutting parameters optimization.During HSC Inconel718 process with coated carbide tools, by the calculation of thermodynamic entropy production on three wear sub-processes (viscosity flow, diffusion and oxidation), the entropy production of system was investigated with the changes of cutting speed and flank wear VB. The self-organization process of cutting tool was analyzed according to the changing of the entropy got from the system, the cutting process was divided into three (one) wear stages. When the values of the cutting parameters on HSC friction and wear system were with in a certain range, the friction films of self-organization kept friction and wear system in a stable stage. When these values exceeded a certain rage, the friction film of self-organization was difficult to be generated, which led cutting tool only has one wear stage and a short tool life. Mechanisms of 4 self-organization friction films (BUE, chip flow zone, oxide layer and the bonding layer) were considered in the high speed cutting process.The thermal-mechanical coupling 3D analytical model in the rake face and flank of cutting tool was created consedering nose radius and tool wear. The changes of shear angle, shear strain and tool-chip contact length for each differential cutting element were analyzed under different cutting parameters and different tool geometries. The temperature rised on each cutting element on the tool-chip contact surface was caused by shear and friction heat which was calculated by the heat distribution coefficient of HSC friction and wear system. By assuming that flow velocity of chip as uniform motion, the force vector sum was zero, and then three direction components and composition of forces on the tool could be calculated. The calculation of model show that the increased of cutting force on the rake face of cutting tool was not significant and cutting temperature decreased a little when the cutting tool is worn. The cutting force and temperature on the flank of cutting tool increased significantly with the tool wear. The influence of chip shapes, chip formation mechanism, cutting speed, feed rate and cutting tool wear on workpiece surface quality were analyzed based on the thermal-mechanical coupling on Incone1718.The proportion of each wear mechanisms on different wear stage was very different. In a beginning wear stage, general diffusion wear increased caused by frequent spalling and generation of bonding layer, so the most important influence factor in this stage for tool life was diffusion wear. And small diffusion concentration and low cutting temperature result the proportion of oxidized wear was so small to happen. In the stable wear stage, relatively stable bonding layer reduced spalling frequency, decreased concentration gradient of element and decreased diffusion speed, which provided suitable conditions for oxidation wear. Oxidation wear rate continued to rise, in the end of wear stage, it became the biggest influence factor on tool life at the failure stage. Considering the characteristics of the three wear stage and the thermal-mechanical coupling, tool life prediction model was established with diffusion wear, adhesive wear and oxidation wear were considered as the main wear mechanism.The tool wear and wear mechanisms in different cutting tool wear stages and a variety of cutting tools changed when the nickel-based superalloys Inconel 718 was cutting with coated carbide tools and Sialon ceramic tools.This research is supported by the National Natural Science Foundation of China (50575126) and the National Basic Research Program of China (2009CB724402).更多还原