【作者】 朱大虎；

【导师】 李蓓智；

【作者基本信息】 东华大学 ， 机械制造及其自动化， 2011， 博士

【摘要】 高速磨削是在大幅度提高加工效率的基础上,显著提高加工质量的最有效途径,同时也是解决材料磨削瓶颈的核心技术。高速磨削中,工件与砂轮上无数磨粒周而复始地相互高速撞击,力的瞬态作用使剪切局限在一个微区域,能量在此微区的耗散使材料局部高温,可能达到熔化或接近熔化的状态。工件与磨粒的正反馈效应使局部绝热剪切作用愈加增强。磨削速度越高,这种绝热剪切作用也越强,接近音速的高速磨削走向极端条件,由此产生的诸多新机理及其对表面完整性的作用机制正亟待研究和实践。高速磨削机理研究是磨削领域研究的重点与难点。相对于已被广泛研究的平面磨削,高速外圆磨削的砂轮轴和工件轴的双向旋转运动则给其相关研究提出了更高的挑战。在高速外圆磨削极端工作条件下,传统平面磨削加工成屑机理中的滑擦-耕犁-切削理论已很难适用于高速外圆磨削。且近年来随着航天、航空、汽车、军工、仪器仪表、通讯工程、电子工业及机械制造等行业的快速发展,使用到的新型材料越来越多,而且这些材料机械性能高、化学性能稳定、耐高温、高压,可以适应各种特殊工作环境,它们成为推动这些领域技术发展的一个重要因素。然而,这些新材料中有许多是难以用传统的机械加工方法进行加工的,这就制约了这些材料的应用范围,提高了产品的加工成本,通常把这类材料称为难加工材料。因此,针对典型的难加工材料的高速外圆磨削,为了探索其成屑机理、热传导机制、表面完整性特征等,本课题旨在已掌握的传统磨削机理的基础上,通过理论建模和高速外圆磨削仿真与实验相结合的方法,对难加工材料高速外圆磨削中的多场强耦合作用下的材料去除理论进行深入系统的研究,最终实现优质、高效、低耗、绿色等综合目标的磨削工艺。本文研究的主要成果及创新点包括：(1)研究和揭示了难加工材料的高速外圆磨削动态行为及其高速特性。通过单颗磨粒的外圆磨削仿真研究与工程实验研究,提出了单颗磨粒外圆磨削五个阶段三种作用形态的成屑模型(Five-phase-Three-behavior-based Chip Formation Model, FTCFM),揭示了砂轮线速度对单颗磨粒切削形态的作用机制及其高速特性,构造了三种作用形态下弧长计算模型(Three-behavior-based Grinding Length Model, TGLM),并在材料去除率计算模型中引入了砂轮线速度这个对高速磨削效率具有重要影响的因素,构建了基于等效未变形磨屑厚度的材料去除率模型(Equivalent Undeformed Chip Thickness-based Material Removal Model, EUCTMRM),并以TC4为例,进行了仿真与工程实验验证,为解释和定量考察高速磨削的高效特性提供了理论依据。(2)通过对难加工材料的高速外圆磨削力的研究与实验,探讨了磨削过程中两个重要工艺参数砂轮线速度、工件转速对磨削力的影响机制,分析了磨削力、磨削力比、比磨削能随比磨除率的变化规律及特征。实验结果表明磨削TC4时,法向力使得工件“软化”难以被去除,其材料去除方式主要由切向力来进行控制；在砂轮线速度一定的情况,发现磨削力的增幅要小于比磨除率的增幅,因此在合理的磨削力范围内,可以通过增加工件进给速度来提高比磨除率；在保证恒定的比磨除率的条件下,可以适当控制工件转速以到达稳定磨削力的效果；基于磨削力试验结果,建立了难加工材料高速外圆磨削力模型(High-Speed Cylindrical Grinding Force Model, HSCGFM),为定量考察磨削质量和效率的完美结合提供了科学依据。(3)基于外圆磨削的未变形磨屑厚度,提出了磨削弧区热源模型为二次曲线的假设,据此构造了基于二次曲线热流分布的温度计算模型(Quadratic Curve Distribution-based Temperature Prediction Model, QCDTPM),以及基于实验温度法的进入工件能量分配比模型(Experiment Temperature Method-based Energy Partition Model, ETMEPM),以考察不同工艺条件下磨削热的作用机制。研制了可适用于不同难加工材料的外圆磨削弧区温度测试传感器,为解决高速外圆磨削工件表面温度难以有效度量难题提供了有效途径。理论分析与实验结果表明,二次曲线热流分布模型的计算结果与实验结果基本一致。在高速磨削条件下,进入工件的热量分配比大约为30%-60%,与传统磨削速度情况相比,进入工件的热量分配比下降了24%-54%(与均值84%相比),其中,工件转速对温度变化影响较大,砂轮速度增加使得磨削温度呈现缓慢的升高趋势,而切深的影响适中,因此,上述三要素对磨削问题的作用大小依次为工件线速度、磨削深度和砂轮线速度。这说明在磨削难加工材料时,砂轮线速度不是最主要因素,应选择合适的磨削参数组合来实现质量与效率的统一。此外,还发现沿着工件深度方向,磨削热主要集聚在工件切入端表层及亚表层区域,上述发现为高速磨削冷却效果、优化设计与安装提供了科学设计依据。(4)探讨了磨削工艺参数对表面粗糙度和表面残余应力的影响,实验结果表明,磨削速比对工件表面粗糙度的影响较大,存在一个临界速比能实现表面质量与磨削效率的完美统一,同时砂轮线速度的提高使得工件表面残余压应力向拉应力过渡,进而加快工件磨损,影响其使用寿命,因此提出了磨削质量与效率统一的多因素综合考虑模型(Quality-Efficiency-based Comprehensive Factor Model, QFCFM),得出一味地追求砂轮线速度并不能达到理想的加工质量和磨削效率相统一的要求,必须综合考虑其它磨削工艺参数、材料的物理化学性能,并且在综合考虑磨削功率以及进入工件的热量分配比的基础上寻找合理的砂轮线速度范围,以实现对高速磨削热损伤的控制。通过上述内容探索和研究,本文作者希望此课题的研究工作能为高速磨削装备设计制造提供科学依据,为多种难加工材料的高速磨削研究的新突破奠定基础,更希望能为后续高速加工领域研究者们探索新的科学问题提供更清晰的解决问题的方向。更多还原

【Abstract】 High-speed grinding is considered as the most effective way to significantly improve the processing quality based on the substantial increase in processing efficiency, also is the core technology to resolve the grinding bottleneck for different materials. In high-speed grinding, the numerous abrasives on the workpiece and wheel are again and again high-speed impact with each other, the transient effect of the shear force is limited to a micro-region, and the energy dissipation in the micro-local temperature of the material may reach the melting or near the molten state. The effect of positive feedback between workpiece and abrasive makes the local adiabatic shear even more enhanced. The higher the grinding speed, the stronger the role of adiabatic shear, close to the speed of sound to the extreme conditions of high speed grinding, resulting in number of new mechanism and the mechanism of surface integrity are to be studied and practice.Mechanism of high speed grinding is important and difficult area of research on grinding. With respect to the surface grinding has been extensively studied, the two-way rotation of the cylindrical grinding wheel spindle and the workpiece axis presents greater challenge to its research. In the extreme operating conditions of high-speed cylindrical grinding, the sliding-plowing-cutting theory in the traditional surface grinding process has been difficult to apply in high-speed external cylindrical grinding. And in recent years with the rapid development of the aerospace, aviation, automotive, military, instrumentation, communications engineering, electronic industry and machinery manufacturing industries, new materials used become more and more, and these materials are high mechanical properties, chemical stability, resistance to high temperature and high pressure, can be adapted to a variety of special working environment, they become an important factor to promote technology development in these areas. However, many of these new materials are difficult using conventional machining methods for processing, which restrict the application of these materials, improve the product processing costs, and usually such materials are called as difficult-to-cut materials.Therefore, focusing on the typical difficult-to-cut materials for high-speed cylindrical grinding, in order to explore the chip formation mechanism, thermal conduction mechanism, surface integrity characteristics, the subject aims to be through the theoretical modeling, the combination of simulation and experiment of high-speed cylindrical grinding, to conduct the in-depth and systematic research on the theory of material removal in high-speed cylindrical grinding of difficult-to-cut materials. Based on the available conventional grdinding mechanism of materials, it aims to be ultimate realization of high quality, high efficiency, low consumption, and green grinding. The main contributions of this dissertation are as follows:(1) It studied and revealed the dynamic behavior and high-speed characteristics of high-speed cylindrical grinding of difficult-to-cut materials. By the simulation study and engineering experiments on single grain grinding of TC4 titanium alloy, it has been found the chip formation phenomenon of single of the five stages of the three forms in single grain grinding, revealed the effect of wheel speed on the mechanisms of single grain cutting and its high-speed characteristics, constructed the calculating models of arc length with different forms, and introduced the wheel speed in the material removal rate model which has important impact on the high-speed grinding efficiency, and provides a theoretical basis for the interpretation and quantitative study of the efficiency characteristics of high-speed grinding.(2) Through the research and experiments on the high-speed cylindrical grinding force of difficult-to-cut materials, this study explored the impact mechanisms of the two important process parameters, including the grinding wheel speed, workpiece speed in grinding process, on the grinding force, analyzed the variation and characteristics of the grinding force, grinding force ratio, and specific grinding energy with the specific removal rate. Experimental results showed that grinding TC4 titanium alloy, the normal force makes the workpiece "softening" difficult to be removed, its main mode of material removal is completed by the tangential force; in the case of certain wheel speed, it found the increase in grinding force is less than the increase in the specific removal rate, so in a reasonable range of grinding force, increasing the workpiece feed rate can enhance the specific removal rate; under the conditions ensuring the constant specific removal rate, workpiece speed can be properly controlled to reach stable grinding force; in addition, it also can be integrated to consider raising the wheel speed and workpiece feed rate to increase grinding efficiency and surface quality for achieving the perfect combination.(3) Based on cylindrical grinding of undeformed chip thickness, it proposed the assumption that the grinding arc area source model is for the quadratic curve, thereby constructing the calculating model of workpiece surface and sub-surface temperature to study the grinding thermal mechanism under different conditions. It developed the temperature test sensor in cylindrical grinding arc that suitable for different-to-cut materials, and solved the problem that the high-speed cylindrical grinding surface temperature is difficult to be effectively measured. Grinding temperature test results showed that the calculating results by the quadratic curve heat flux distribution model optimized with Rw model were consistent with the experimental results. In high speed grinding conditions, the energy partition entering the workpiece was approaxiately between 30%-60%. Compared with the conventional grinding, it reduced 24%-54%(compared with the average value 84%). Here, the workpiece has the largest influence on the temperature, the whlle speed makes the temperature rise slowy, and the influence by the depth of cut locates between the othere two factors. Thus the influence of the above three factors on the temperature is in order:workpiece speed, depth of cut, and wheel speed. The results showed that the wheel speed is not the main considerable factor in grinding difficult-to-cut materials, while should take into account the combination of grinding parameters to achieve the grinding quality and efficiency. In addition, it was also found that along the depth direction of workpiece, the grinding temperature also gradually moves to the cut-in side of the grinding arc, grinding heat is mainly concentrated at the workpiece surface and sub-surface near the cut-in side, the above findings provide scientific basis for cooling effect, optimization design and installation in high-speed grinding.(4) It discussed the influence of grinding process parameters on the surface roughness and residual stress. The experimental results showed that the grinding speed ratio q has greater impact on the surface roughness, there is a critical speed ratio that can achieve the combination of grinding quality and efficiency, at the same time, the increase in wheel speed will make the surface residual stress transit to tensile stress, thus accelerating the wear of ceramic materials, affecting its life. Therefore, the blind pursuit of wheel speed can not achieve the desired processing quality requirements, but should be taken into account the physical and chemical properties of these materials. In addition, it also found there exists a reasonable wheel speed range can achieve the effective control of grinding thermal damage, thus it should comprehensively take the grinding power and energy partition into account.Through the above study, the author hopes this research can provide the scientific basis for the design and manufacturing of high-speed grinding equipment, prepare the theoretical paths for processing various difficult-to-cut materials in high speed grinding, and further hopes to guide a clear direction for the follow-up researchers in the field of high-speed processing.更多还原