【作者】 万小金；

【导师】 熊蔡华；

【作者基本信息】 华中科技大学 ， 机械电子工程， 2010， 博士

【摘要】 零件的加工质量取决于机床、夹具、工件和刀具组成的工艺系统及加工工艺参数等因素。对特定的机床,当工艺参数选定之后,工件-夹具-刀具系统直接影响零件的加工质量。本论文以“工件-夹具-刀具”系统为研究对象,研究误差建模方法,在物理约束、几何约束与产品性能约束的相容性条件下,建立误差源与产品性能约束的映射关系、零件加工误差与工艺参数之间的反演模型,提出制造误差补偿与控制策略,为复杂零件高精度创成提供理论基础,主要研究工作及创新点包括：第一、定位方案分析与评估针对加工期望特征所必须确保的尺寸方向上的精度,从加工几何学的角度,建立特征约束度模型,确定工件在定位系统中约束自由度的数目,构建加工特征运动旋量系和加工特征约束度数表。利用运动学分析并结合虚位移原理,构造定位系统非齐次线性方程组的线性空间齐次解,判断与尺寸精度无关的自由度所约束的数目,推导判断定位方案正确性的准则,据此,提出基于加工特征的定位方案设计方法。第二、定位误差分析评估与调整针对工件在定位系统中的位移和刀具的位姿偏差共同诱导的刀具相对工件的位姿偏差,建立工件的位移、刀具的姿态偏差与刀具相对工件的位姿偏差的映射模型,此模型能够适用于任何形状工件的不完全定位、完全定位和完全过定位。在此基础之上,构建偏差反演模型,调整刀具相对工件的位姿,减小刀具相对工件之间的偏差,实现利用一种偏差补偿多种偏差的误差补偿技术,达到减小加工特征尺寸偏差的目的。第三、装夹误差分析与刀具路径调整针对多源多工序加工过程,建立几何偏差源与物理偏差源共同作用的尺寸偏差模型,该模型能够直接用于度量加工特征尺寸偏差。基于此模型,建立加工特征点的偏差模型,用于评估加工特征平行度和轮廓度。同时针对工件-夹具系统在夹紧力及切削力作用下的超静定系统,根据变形协调原理,建立变形协调模型,利用功能转换原理,将接触变形量的求解问题转化非线性规划问题,在几何与物理约束条件下,通过求解非线性规划问题获得定位元件与工件之间的接触变形量,并对加工过程中接触变形量的动态变化以予定量评估。此外,基于预测的偏差,建立刀具路径调整模型,用于修改CAM系统的刀位源文件,调整刀具的位姿,减小加工特征尺寸偏差。第四、工件加工表面微观形貌预测针对切削力诱导的工件和刀具的振动、工件在定位系统中的位移和工艺参数对表面形貌生成的影响,建立刀刃点在加工特征活动标架下的数学模型,该模型适用于平面和一般的直纹面。根据局部活动标架特征,将加工表面残高求解问题转化为非线性规划问题,通过求解非线性规划问题获得加工特征采样点的残高,利用采样点的残高值构造加工表面形貌,并计算粗糙度。此外,结合刀具齿数对刀具偏移的影响,利用lobe图选取薄壁型腔件的铣削工艺参数,提高铣削效率。更多还原

【Abstract】 The quality of the machined part mainly depends on the complicated process system which consists of machine tools, fixture, workpiece, cutter and process parameters etc. At specific machine tools, once process parameters are selected, the machining quality of part depends on the performance of workpiece-fixture-cutter system. Therefore, in this paper, workpeice-fixture-cutter is taken as the investigated subject so that the rules of error propogration and prediction methods can be found out. Specific work includes following four aspects:(1). Location scheme design based on the machining featureA machining feature requirement driven workpiece holding scheme is proposed to constrain the degrees of freedom (DOFs) of the workpiece. In the locating scheme, the machining feature on workpiece is used to determine those DOFs which have to be constrained in machining. And then a kinematic model is used to determine the number of the constrained DOFs in a real locating scheme. By means of kinematics and the virtual displacement principle, Homogeneous solution of the linear space of non-homogeneous linear equations of location system is constructed to determine the number of the constrained DOFs of the workpiece which are unrelated to dimensional accuracy. Finally, an evaluation criterion is given to judge the correctness of the locating scheme.(2). Dimension devation evaluation and adjustment of the machining featureA model is built to integrate position and orientation errors of cutter and workpiece displacement into the relative displacement of the cutter with respect to the workpiece by means of the differential motion theory. Based on the model, a deviation adjustment model is constructed to adjust the position and orientation of the workpiece with respect to the cutter in order that the machining accuracy of workpiece can be improved. Therefore, a compensation technique which can utilize one error source to cancel out multiple error sources is proposed. Three examples are used to validate the feasibility of the proposed models.(3). Dimensional deviation propagation model and adjustment modelIn multi-source multi-processing machining operations, a machining feature from a previous machining operation is taken as the machining datum at the current machining operation. The devation from upstream will be accumulated on the current machining feature. Therefore, a comprehensive dimensional deviation evaluation framework is developed which it can be utilized to predict process deviation. At the same time, in order to obtain the displacement of workpiece due to the geometric defects of workpiece-fixture sytem, cutting forces and fixturing forces, the solution problem of contact deformation between the fixture elements and workpiece is transformed into a nonlinear programming, and solve the nonlinear programming under geometric and physical constraints and obtain the deformation magnigudes. In addition, the dynamic changing process of the deformation is evaluated in machining processs. Based on the predicted deviation, a model is built to adjust the tool path by means of the cutter source file from CAM in order that the machining accuracy of the machining feature can be improved.(4). Surface topography prediction.A general kinematic model which integrates the deflection of the cutting tools with respect to workpiece caused by cutting force and process parameters into one model is presented to build kinematic relationship between the arbitrary point of the cutter edge and the arbitrary point of the machining feature. According to the properties of moving frame, the solution problem of the machining surface scallop is transformed into a nonlinear programming problem. By means of solving the nonlinear programming problem, these scallops along the normals of nominal surface can be obtained, and then construct the surface topography and calculate the roughness values. At the same time, the stability lobe figure is constructed to select the process parameters for machining thin-walled cavity parts. Finally, the planar surface and circular arc surface texture are simulated by means of calculating a scallop value along a normal direction of an arbitrary point on nominal part surface in terms of the proposed model, three dimension profile can also be simulated. The feasibility of the proposed models is verified.更多还原