【作者】 言兰；

【导师】 周志雄；

【作者基本信息】 湖南大学 ， 机械制造及其自动化， 2010， 博士

【摘要】 淬硬模具钢由于其硬度高及耐磨性好等优点被广泛应用于模具制造业。但是淬硬模具钢磨削加工后表层／亚表层容易发生烧伤、白层软化等变质现象,磨削表面容易产生残余拉应力和微观裂纹,严重影响产品的使用性能和使用寿命,因此有必要对淬硬模具钢磨削机理进行深入研究。本论文从单颗磨粒切削过程研究入手,结合砂轮表面形貌测量和建模,将单颗磨粒切削机理与AISI D2淬硬模具钢磨削实验过程的磨削力、磨削温度以及磨削表面质量联系起来,揭示了砂轮状态、磨削工艺参数与表面完整性的联系,为磨削表面质量控制和磨削工艺参数优化提供了理论依据。所做的工作主要包括：(1)基于砂轮表面形貌测量的砂轮表面磨粒分布建模。用白光干涉仪对不同粒度氧化铝砂轮表面形貌进行了测量；根据砂轮形貌的空间频率组成,用功率谱密度分析法对测量结果进行了滤波,去掉了高频分量和测量白噪声,对砂轮表面形貌进行了重构；引入伯明翰三维粗糙度特征参数对砂轮表面磨粒密度、磨粒局部尖端形状及磨粒锋利程度进行了评价,对磨粒的出刃高度统计结果进行参数检验,建立了磨粒出刃高度符合正态分布规律的氧化铝砂轮模型。(2)单颗磨粒切削仿真有限元模型的建立及实验验证。根据单颗磨粒切削的物理模型建立了单颗磨粒切削的力学模型；建立了单颗磨粒切削的有限元模型,包括基于砂轮形貌测量的磨粒几何模型,基于霍普金森压杆实验数据的AISI D2钢材料本构关系建模,氧化铝磨粒对AISI D2钢的摩擦实验等；通过直角切削实验验证了材料模型的准确性,进一步通过球—盘摩擦实验验证了单颗磨粒切削有限元模型的可靠性。通过单颗磨粒切削有限元仿真,研究了磨粒粒度及切削参数对材料变形、耕犁—切削转变临界切深、切削力(比)、切屑厚度以及剪切角等物理量的影响规律。(3) AISI D2淬硬模具钢的正交和单因素平面磨削实验。进行了氧化铝砂轮磨削AISI D2钢的正交磨削实验,建立了氧化铝砂轮磨削AISI D2钢的磨削力经验模型,通过影响因素分析法判断了砂轮粒度和磨削参数对磨削力的影响程度；进行了单因素磨削实验,并利用单颗磨粒切削机理研究的结论解释了砂轮粒度和.磨削工艺参数对磨削力(比)的影响规律。(4)基于砂轮表面磨粒分布和单颗磨粒切削力的磨削力预测及磨削实验验证。根据砂轮表面磨粒出刃高度分布模型,针对具体磨削工艺参数,假设单位时间内磨削去除材料体积等于磨削区域参与磨削的有效磨粒去除材料总体积,计算各有效磨粒的切削深度,将相应的单颗磨粒切削仿真力的结果在磨削区域内进行集成,预测磨削力；将磨削实验获得的磨削力和预测磨削力进行比较,验证了磨削力预测方法的可靠性。(5)磨削温度估计及磨削表面质量的研究。将磨削过程与二次回火热处理过程联系起来,将不同温度下二次回火后试样的表层／亚表层硬度,与磨削实验后磨削表层／亚表层硬度进行对比,对磨削区平均温度进行了估计；利用白光干涉仪、金相显微镜、显微硬度计和X射线残余应力测试仪对AISI D2钢磨削表面的表面完整性进行了测量分析,利用单颗磨粒切削机理研究的结论解释磨削表面完整性的产生机理,揭示了砂轮粒度和磨削参数对磨削表面形状误差以及粗糙度、表层／亚表层微观组织变化、表层／亚表层加工硬化以及残余应力的影响规律。更多还原

【Abstract】 Hardened cold-work die steel is widely used in the die manufacturing industry due to its high hardness and good wear resistance. Grinding is an important process to improve the surface quality and geometrical precision. But AISI D2 is a typical hard-to-cut material. Burn and white layer usually occur in the ground surface or sub-surface during AISI D2 grinding. And micro-crack and residual tensile stress in the ground surface greatly influence the product performance and life. Therefore, it is necessary to deeply study the grinding mechanism of AISI D2 steel. Combining with the measurement and modeling of grinding surface topography, the cutting mechanism of single grain is related with the grinding forces, grinding temperature and ground surface integrity during AISI D2 grinding. It reveals the relationship between grinding conditions and surface integrity, which provides the base of surface quality control and grinding process parameters optimization. The main contents in this study include:(1) Modeling of grain distribution on the grinding wheel surface based on the measurement of grinding surface topography. Wyko NT9300 white light interferometer was employed to measure the surface topography of alumina grinding wheel with different grain size. The power spectral density (PSD) analysis and Fourier filtering was used to remove the high frequency component of the measurement results and white noise. The characterization of wheel topography, such as grain density, grain protrusion height, grain shape and sharpness, were characterized through the employment of "Birmingham set" three-dimensional (3D) surface characterization parameters. The statistical normal distribution of grain protrusion height of alumina grinding wheel topography model was built.(2) The modeling and verification of finite element models of single grain cutting processes. The mechanistic model of single grain cutting was built based on the physical model of single grain cutting. The finite element model of single grain cutting was built including the grain geometrical model based on the measurement of grinding wheel topography, material model based on Split Hopkinson Pressure Bar (SHPB), friction model of alumina grain against AISI D2 steel. The material model of AISI D2 steel was verified by the orthogonal turning experimrnts. The FEM model of ball plate friction has been built to compare with the experiments, which validated the FEM model of single grain cutting process. The influence of grain size and cutting parameters on material deformation, plowing-cutting transition critical depth of cut, cutting forces (ratio), chip thickness and shear angle were studied by the aid of single grain cutting simulation.(3) Orthogonal array and single factor experiments of hardened cold-work die steel AISI D2 grinding. The orthogonal experiments of AISI D2 grinding were performed to build the empirical model of grinding forces with grain size of 60# and 80#. The analysis method of variance was used to analyze the influence degree of grain size and grinding parameters on grinding forces. The single factor grinding experiments were performed and the influence of grain size and grinding parameters on grinding forces (ratio) were analyzed by the aid of conclusions from single grain cutting mechanism.(4) Prediction and verification of grinding forces based on simulated single grain cutting forces and grain distribution on the grinding wheel surface. It supposed that the material removal volume in the given grinding time was equal to the total volume removed by all the single grains in the contact zone. Based on the normal distribution model and grinding parameters, the depth of cut of each single grain was calculated. The related single grain cutting forces were integrated to predict grinding forces. The experimental grinding forces showed good agreement with the predicted grinding forces.(5) Prediction of grinding temperature and study on the ground surface quality. The influence of grinding process on the workpiece materials was similar to the influence of temper process. The micro-hardness of surface/sub-surface in the different temper temperatures was obtained. Comparing with the micro-hardness of surface/sub-surface on the ground surface, the average grinding temperature was predicted. The surface integrity of AISI D2 grinding was analyzed by white light interferometer, metallurgical microscope, micro-hardness tester and X-ray residual stress tester. The generation mechanism of ground surface integrity was presented based on the single grain cutting mechanism. It revealed the influence rule of grain size and grinding parameters to the surface integrity.更多还原