【作者】 吴琦；

【导师】 胡德金；

【作者基本信息】 上海交通大学 ， 机械制造及其自动化， 2007， 博士

【摘要】 耐高温(≥500℃)、耐高压(≥30MPa)、耐磨损、抗热冲击、抗热腐蚀球阀是煤液化工程中高压煤油浆输送与控制的关键部件之一,也是钢铁冶炼、石油化工、核电等重大工程项目中关键部件之一。为了适应上述苛刻的工作要求,阀门关闭件球体表面必须进行硬化处理,其表面硬度HRC≥62、形状精度要求为400mm直径形状误差≤0.008mm,大面积合金化球面高精度加工制造成为一大难题、也是煤液化球阀加工制造的核心技术。本文针对高硬度回转球面精密磨削加工的难点,设计了适用于高硬度回转球面精密磨削加工的方法和装备、研究了高硬度涂层材料的精密磨削机理、探讨了高硬度回转球面磨削工艺系统的几何误差补偿技术,最后将上述研究结论和成果应用于高硬度回转球面精密磨削加工、并进行了大量的试验研究,成功地实现了高硬度回转球面高质量和高精度的磨削加工。整个课题研究具有较强的系统性,促进了该项技术的国产化,具有极其广阔的经济效益和社会效益。设计了适用于高硬度回转球面精密磨削加工的方案。该方案综合考虑了高硬度涂层材料加工困难的特性和回转球面加工的精度保证技术等两方面,同时又降低了机床的开发成本、操作简单可靠。其实现原理主要是利用工件和杯形砂轮的旋转运动、并使它们的轴心线相交,进而利用砂轮的坐标运动来调整加工位置和进给方向;机械结构设计的独特之处在于“四心合一”思想,即通过调整主轴、尾座顶尖、回转工作台和磨头等回转轴线的位置、并在空间相交于一点,从而保证球面加工精度。对高硬度涂层材料精密磨削的磨削力从理论和试验等方面进行了系统研究。为了较为方便地研究高硬度涂层材料的磨削机理,试验采用杯形砂轮平面磨削模拟球面磨削来加工高硬度涂层材料;系统分析了杯形砂轮平面磨削过程,提出了有效磨削宽度的概念,进而分析了磨粒切削刃的磨削模型。基于单颗磨粒切削模型,从理论上分析了WC-Co涂层精密磨削的磨削力,推导了磨削力理论公式。对WC-Co涂层精密磨削力进行试验研究,分析了磨削力的特点,验证了磨削力理论公式的有效性,探讨了磨削工艺参数对磨削力、磨削分力比、磨削比能和磨削力信号的特征频谱等指标的影响规律。对高硬度涂层材料精密磨削的磨削温度从理论、数值模拟和试验等三方面进行了深入系统的研究。针对杯形砂轮磨削高硬度涂层的实际工况,分别使用梯形移动热源和三角形移动热源模型对杯形砂轮平面磨削温度场进行理论建模、并推导出相应的温度场理论公式;将有限元法热分析应用到杯形砂轮磨削WC-Co涂层的温度场仿真中,建立了有限元热分析的模型、阐述了有限元热分析的步骤、讨论了工件表面温度仿真结果的变化规律;使用热电偶测温法对杯形砂轮磨削WC-Co涂层磨削温度进行测量,得出了杯形砂轮磨削WC-Co涂层的磨削温度曲线、讨论了磨削工艺参数对磨削温度的影响规律;磨削温度抑制试验结果表明,向磨削弧区施加冷却液可以大幅降低磨削温度、有效改善磨削工况;磨削工件表面XRD物相分析试验结果表明,现行磨削用量最大条件下干磨削后工件表面物相组份基本未变、磨削温度对工件表面材料性能影响不大。对高硬度涂层材料精密磨削的砂轮磨损进行了深入细致地探讨和研究。分析了WC-Co涂层精密磨削过程中的砂轮磨损形式,试验研究发现存在的磨损形式有磨耗磨损、磨粒脱落、结合剂磨损和粘附磨损;阐述了砂轮磨损状态在线评估的基本原理,并将基于小波包分解的时域信号特征提取方法应用于砂轮磨损状态的监控和评估,试验结果为砂轮修整时机的选择、砂轮耐用度的合理确定提供依据,从而达到提高磨削加工生产率和保证磨削加工质量之目的。对数控精密球面磨削工艺系统的几何误差补偿进行研究,以求进一步提高球面磨削的精度。分析了数控精密球面磨削工艺系统移动副、转动副和正交副的运动误差,阐述了几何误差建模的方法、原理和步骤,推导了工艺系统几何误差模型;并将此误差模型应用于数控精密球面磨削工艺系统的几何误差补偿研究,试验结果表明几何误差补偿后球体加工的形状精度有所提高、从而验证了误差补偿的有效性。在研究高硬度回转球面精密磨削方法、高硬度涂层材料精密磨削机理和球面磨削工艺系统几何误差补偿的基础上,将研究成果和结论应用于高硬度回转球面精密磨削、并进行了大量的试验研究。对自行研发的数控精密球面磨床特性进行研究发现磨头组件的刚性数值存在变化、其规律随进给增大刚度也相应增大,在磨削加工进给系统间隙消除后可以满足高硬度回转球面精密加工要求;采用了定压力磨削策略,避免了砂轮钝化造成对磨削过程和加工表面质量的破坏;提出了高硬度回转球面精密磨削工艺参数的评价标准,即加工效率(材料去除率)、表面质量(SEM形貌分析)和形状精度(球度)等,并通过大量的工艺试验研究了磨削工艺参数对上述三个评价指标的影响规律;通过调整磨削工艺参数、综合平衡三个指标之间的关系,实现了一定加工效率条件下的高硬度回转球面高精度和高表面质量的磨削加工。更多还原

【Abstract】 High-performance sphere valve, which can resists high temperature of over 500 centigrade, high pressure of over 30MPa, wearing, thermal impact and heat erosion, is one of key components used in delivery and control of high temperature and high pressure coal oil liquid in coal liquification engineering, and also used in steel smelting, petroleum chemical engineering and nuclear power. In order to satisfy the bad working conditions stated above, the surface of close part of sphere valve must be harden processed, which rigidity of HRC can up to 62. So it is a large difficult problem in machining high rigidity and high precision sphere. At the same time, it is a core-technology of sphere valve manufacturing in coal liquification. In order to solve the difficulty in high-rigidity rotary sphere precision manufacturing, the grinding method and equipment which is suitable to machining high-rigidity rotary sphere was designed, the precision grinding mechanism of high-rigidity coating material was researched, and the geometric error compensation technique in machining high-rigidity rotary sphere was discussed in this paper. At last, the results and achievements obtained above were used in high-rigidity rotary sphere grinding precisely, a large number of grinding experiments were performed, and high-quality and high-accuracy sphere machining were realized successfully. The whole research possesses better systematicness, promotes the localization of this technology, and has large profits for economic and society.The grinding method which is suitable to machining high-rigidity rotary sphere precisely was designed. The machining theory is discussed in the following. Work piece and cup wheel perform rotation movement and their axial line are intersect in a point, then the machining position and feed direction can be adjusted by coordinate movement of wheel. Uniqueness of the mechanical design is that the four points, which are the rotation center of spindle, tail stock, rotary work table and grinding head, intersect in a point so as to ensure the machining accuracy.The grinding force in machining high-rigidity coating precisely was researched in theory and experiment. The reason which is using flat grinding instead of sphere grinding was explained and its feasibility was discussed too. The flat grinding course of cup wheel was analyzed, the concept of effective grinding width was put forward and cutting model of grit was analyzed too. Due to a research blank in high-rigidity grinding force theoretical model, the theoretical formula of grinding force was deduced. By performing experimental research on grinding force in machining WC-Co coating, the characteristic of it was analyzed, the relationships between grinding parameters and grinding force, grinding force ratio, grinding energy and character frequency were explored.The grinding temperature in machining high-rigidity coating precisely has been researched in theory, numerical simulation and experiment. According to working condition in grinding high-rigidity coating by cup wheel, theoretical models of grinding temperature field were built by means of trapezium moving heat source and triangle moving heat source. Heat analysis method of FEM was applied to grinding temperature field simulation of WC-Co coating grinded by cup wheel, the analysis procedure and results were discussed too. Experiments of grinding temperature were performed by using thermocouple, and the relationships between grinding parameters and grinding temperature were discussed. Experimental results of grinding temperature controlling showed that grinding temperature may be decreased rapidly by injecting coolant to grinding area. Experimental results of XRD phase analysis of work piece surface indicated that grinding temperatures have not obvious effect on property of work piece under maximum grinding parameters.The wear of grinding wheel in machining high-rigidity coating precisely was researched. The wear mechanism of wheel was analyzed. Experimental results showed that there were many wear formats including abrasion wear, grit falling off, bond wear and adhesion wear. The theory of on-line evaluation on wheel’s wear was introduced and feature extraction method based on wavelet packet decomposition was applied to inspection and evaluation of wheel’s wear. Experimental results may provide references for time selection of wheel’s dressing and exact definition of wheel’s life.In order to improve the machining precision of sphere, geometric error compensation for NC precision sphere grinding machine was researched. Firstly, motion errors of movement couple, rotation couple and orthogonal couple were analyzed. Secondly, method, theory and procedures of model building of geometric errors were given and the model was deduced. Lastly, experiments on geometric error compensation showed the effectiveness of the error model.On the basis of researches on grinding method for machining high-rigidity rotary sphere precisely, grinding mechanism of high-rigidity coating, and geometric error compensation for sphere grinding, experimental researches on high-rigidity rotary sphere precision grinding were performed. The rigidity of grinding head may change, but it can satisfy the precision grinding after eliminating clearance of feed system. The constant pressure grinding was put forward in order to avoiding damage to grinding course. And evaluation standards for grinding parameters, which are material remove rate, surface quality and shape precision, were given. A large number of experiments were performed to research the relationships between grinding parameters and evaluation standards. By adjusting grinding parameters and balancing three evaluation standards, high-precision and high-quality machining of high-rigidity rotary sphere were realized.更多还原