球头铣刀数控加工表面形貌几何仿真的研究

几何仿真是建立铣削力预测模型的基础,而传统的几何仿真只考虑刀具的平动而忽略其转动。本文在同时考虑刀具平动和转动的基础上,利用工件Z-Map表示模型和刀刃离散表示法,提出了一种球头铣刀三轴数控铣削的微观几何仿真算法。该算法鲁棒性好、适用范围广,不仅能高效而准确地仿真铣削表面形貌,而且能准确提供切屑的轮廓,为建立精确的切削力预测模型提供了重要的几何参数。     

提高仿真效率的四叉树阵列的几何建模方法研究

为了提高三轴铣削图形仿真的效率,提出了四叉树阵列结构,研究了适用于三轴铣削实时仿真的动态建模方法。该方法集成了单元离散法和四叉树表示工件模型的优点,在整体上工件模型采用单元离散法表示,细节上采用四叉树表示,即每个单元就是一棵四叉树结构体。该建模方法对于给定的精度,根据不同区域几何特征的差异,可自动地调节四叉树表示的层次,既增强了工件模型关键细节特征的表达,又降低了数据量和计算量。通过对比分析,该方法可在保证仿真精度的前提下显著提高仿真效率。     

复杂曲面环形刀五轴端铣加工的刀具轨迹规划方法

为了降低复杂曲面类零部件加工的刀具路径,减小刀具路径条数,提高加工效率,提出了一种新的复杂曲面环形刀五轴端铣加工刀具轨迹优化方法。在局部可铣性基础上对刀轴矢量角进行自适应优化,采用新型加工带宽计算方法——等残留高度算法,给出了等残留高度算法的刀具轨迹生成具体步骤。仿真结果表明:与传统等残留高速算法相比,刀具轨迹优化算法的刀具路径更短、条数更少,能够有效提高复杂曲面加工效率。     

三轴数控侧铣空间刀具半径补偿算法

通过深入分析三轴数控侧铣加工的特点,利用几何平面投影原理,采用平面轮廓刀具半径补偿算法推导的类似方法,建立三轴数控侧铣加工的空间刀具半径补偿算法.将三轴数控侧铣加工的空间刀具半径补偿归纳为三种转接过渡类型处理,通过加工平面的投影相交求出空间两相邻程序段的过渡转接点坐标分量x、y,然后通过逆投影计算转接点的第三分量z,从而推导出各类型转接点的坐标计算公式.基于UG平台编写了三轴数控侧铣刀具补偿仿真软件,模拟和铣削加工实例结果表明所建立的三轴数控侧铣加工空间刀具半径补偿算法正确有效.基于该算法的空间刀具半径补偿G指令将可避免由于刀具磨损和刀具更换导致的三轴侧铣数控代码重生成.     

薄壁件铣削过程仿真与分析

针对薄壁件加工过程中易产生变形等问题，提出了利用有限元法对铣削过程进行三维仿真的方法，重点研究了LS-DYNA的动态接触算法，建立了薄壁件铣削加工的有限元模型，对工件变形及切削力的变化规律进行了分析。最后，利用分析结果对铣削参数进行调整与优化，可以减小工件变形，保证加工精度。     

基于Z-Map留量模型的补加工研究

补加工是CAM软件编程的关键技术之一,补加工就是适时确定毛坯的残留状态及残留量并据此生成相应刀具的精简高效、科学合理的刀轨.Z-Map留量模型是一种描述留量的几何模型,毛坯加工过程中不断变化的数字模型由大量的Z-Map点构成,Z-Map留量模型能如实反映毛坯适时的残留状态、可自动识别补加工区域且计算简单,对传统Z-Map留量模型的改进处理可提高加工精度及运算处理速度.基于Z-Map留量模型CAM软件易于实现补加工编程智能化.     

A cutting sequence optimization algorithm to reduce the workpiece deformation in thin-wall machining

A thin-wall part of lower stiffness can be subject to significant deformation during its cutting process. This study proposes a cutting process optimization algorithm to reduce the workpiece deformation. First, the volume to be removed is divided into a set of blocks. The proposed algorithm starts from the finished workpiece shape, with all the blocks removed. The objective of the proposed algorithm is to find a sequence of adding the blocks, such that the workpiece deformation is always smaller than the given threshold value when the cutting forces is imposed at each step. The workpiece deformation at each step is simulated by using the FEM (finite element method) simulation. By inverting the sequence of adding the blocks, the optimized sequence to remove the blocks can be obtained. Additionally, the block size can be modified to reduce the axial depth of cut to further reduce the workpiece deformation, or to increase the radial depth of cut to enhance the efficiency. Experiments are conducted to confirm the effectiveness of the algorithm to reduce the maximum workpiece deformation during the entire cutting process.     

INFLUENCE OF MATERIAL REMOVAL ON THE DYNAMIC BEHAVIOR OF THIN-WALLED STRUCTURES IN PERIPHERAL MILLING

Machining is a material removal process that alters the dynamic properties during machining operations. The peripheral milling of a thin-walled structure generates vibration of the workpiece and this influences the quality of the machined surface. A reduction of tool life and spindle life can also be experienced when machining is subjected to vibration. In this paper, the linearized stability lobes theory allows us to determine critical and optimal cutting conditions for which vibration is not apparent in the milling of thin-walled workpieces. The evolution of the mechanical parameters of the cutting tool, machine tool and workpiece during the milling operation are not taken into account. The critical and optimal cutting conditions depend on dynamic properties of the workpiece. It is illustrated how the stability lobes theory is used to evaluate the variation of the dynamic properties of the thin-walled workpiece. We use both modal measurement and finite element method to establish a 3D representation of stability lobes. The 3D representation allows us to identify spindle speed values at which the variation of spindle speed is initiated to improve the surface finish of the workpiece.     

INFLUENCE OF MATERIAL REMOVAL ON THE DYNAMIC BEHAVIOR OF THIN-WALLED STRUCTURES IN PERIPHERAL MILLING

Machining is a material removal process that alters the dynamic properties during machining operations. The peripheral milling of a thin-walled structure generates vibration of the workpiece and this influences the quality of the machined surface. A reduction of tool life and spindle life can also be experienced when machining is subjected to vibration. In this paper, the linearized stability lobes theory allows us to determine critical and optimal cutting conditions for which vibration is not apparent in the milling of thin-walled workpieces. The evolution of the mechanical parameters of the cutting tool, machine tool and workpiece during the milling operation are not taken into account. The critical and optimal cutting conditions depend on dynamic properties of the workpiece. It is illustrated how the stability lobes theory is used to evaluate the variation of the dynamic properties of the thin-walled workpiece. We use both modal measurement and finite element method to establish a 3D representation of stability lobes. The 3D representation allows us to identify spindle speed values at which the variation of spindle speed is initiated to improve the surface finish of the workpiece.     

Chatter prediction utilizing stability lobes with process damping in finish milling of titanium alloy thin-walled workpiece

Machining chatter often becomes a big hindrance to high productivity and surface quality in actual milling process, especially for the thin-walled workpiece made of titanium alloy due to poor structural stiffness. Aiming at this issue, the stability lobes are usually employed to predict if chatter may occur in advance. For obtaining the stability lobes in milling to avoid chatter, this article introduces an extended dynamic model of milling system considering regeneration, helix angle, and process damping into the high-order time domain algorithm which can guarantee both high computational efficiency and accuracy. Via stability lobes, the reasonability and accuracy of the proposed method are verified globally utilizing specific examples in literature. More convincingly, the time-domain numerical simulation is also implemented to predict vibration displacement for partial stability verification. In this extended model, process damping is well-known as an effective approach to improve the stability at low spindle speeds, and particularly, titanium alloy as typical difficult-to-machine material is generally machined at low spindle speeds as well due to its poor machinability. Therefore, the proposed method can be employed to obtain the 3D stability lobes in finish milling of the thin-walled workpiece made of titanium alloy, Ti-6Al-4V. Verification experiments are also conducted and the results show a close agreement between the stability lobes and experiments.     

一种新的螺旋刃球头铣刀铣削力模型

为提高铣削加工的安全性和生产效率，有必要在加工实际进行之前准确地预测切削过程的物理信息，如铣削力、刀具振动等。给出了球头铣刀丸线几何模型，采用理论削力分析与实验--系数识别相结合的方法建立了新的螺旋刃球头铣刀的铣削力模型。对不同切削条件下的铣削力进行了仿真，与实验测量数据吻合良好，证明离线仿真可以对铣削力做出较准确的预测。     

Error Compensation of Thin Plate-shape Part with Prebending Method in Face Milling

Low weight and good toughness thin plate parts are widely used in modern industry, but its flexibility seriously impacts the machinability. Plenty of studies focus on the influence of machine tool and cutting tool on the machining errors. However, few researches focus on compensating machining errors through the fixture. In order to improve the machining accuracy of thin plate-shape part in face milling, this paper presents a novel method for compensating the surface errors by prebending the workpiece during the milling process. First, a machining error prediction model using finite element method is formulated, which simplifies the contacts between the workpiece and fixture with spring constraints. Milling forces calculated by the micro-unit cutting force model are loaded on the error prediction model to predict the machining error. The error prediction results are substituted into the given formulas to obtain the prebending clamping forces and clamping positions. Consequently, the workpiece is prebent in terms of the calculated clamping forces and positions during the face milling operation to reduce the machining error. Finally, simulation and experimental tests are carried out to validate the correctness and efficiency of the proposed error compensation method. The experimental measured flatness results show that the flatness improves by approximately 30 percent through this error compensation method. The proposed method not only predicts the machining errors in face milling thin plate-shape parts but also reduces the machining errors by taking full advantage of the workpiece prebending caused by fixture, meanwhile, it provides a novel idea and theoretical basis for reducing milling errors and improving the milling accuracy.     

SIMULATION CONCEPT FOR PREDICTING WORKPIECE VIBRATIONS IN FIVE-AXIS MILLING

The characteristic discontinuous cut of the milling process influences the whole machining process by an increased susceptibility to vibrations of the machine-tool-workpiece system. This can result in undesirable effects on the workpiece surface or in a shorter lifetime of the tool and the spindle. Especially with regard to the machining of thin-walled components, such as turbine blades and thin profiles, the dynamic behavior of the workpiece is of particular interest. In this paper a simulation concept for predicting regenerative workpiece vibrations during the five-axis milling process is presented. This concept combines an accurate and fast simulation of the five-axis machining process including material removal and force calculation with an implemented finite element model for computing workpiece displacements. The simulation results are compared with data from experiments, which were conducted using a milling tool with high stiffness in order to minimize the influence of the milling tool dynamics.     

数控铣削仿真系统的研究

根据数控铣削加工特点,提出一个基于Z-MAP结构的工件分解表达模型,利用该模型与刀具实体模型做布尔减运算,实时模拟工件材料的去除加工过程,并对仿真结果进行检验。仿真实例证明,该系统运行可靠,可提高数控加工效率。     

Extracting cutter/workpiece engagements in five-axis milling using solid modeler

Predicting cutting forces in milling process simulation requires finding cutter/workpiece engagements (CWEs). The calculation of these engagements is challenging due to the complicated and changing intersection geometry between the cutter and the in-process workpiece. In this paper, a solid modeling based methodology for finding CWEs generated in five-axis milling of free form surfaces is presented. The proposed methodology is an extension of the solid modeler based three-axis CWE extraction method given in [21]. At any given instant of the five-axis tool motion, the velocity vectors along the cutter axis may move in directions that do not lie in the same plane, and therefore the cutter envelopes need to be approximated by spline surfaces. Considering the spline surface approximations, the CWE methodology described in [21] does not work properly for the five-axis milling. Therefore in the proposed method, the in-process workpiece is used instead of the removal volume for extracting the CWEs. A terminology the feasible contact surfaces (FCS), defined by the envelope boundaries, is introduced. To extract the CWEs at a given cutter location, first the BODY entity, obtained by offsetting the FCS with an infinitesimal amount, is intersected with the in-process workpiece. Then, the resultant removal volume is decomposed into faces. Finally, the surface/surface intersections are performed between those faces and the FCS to obtain the CWE boundaries. To be used in the force model, the CWE boundaries are mapped from Euclidean 3D space to a parametric space defined by the engagement angle and the depth-of-cut for a given tool geometry.     

Optimal fixture design in peripheral milling of thin-walled workpiece

In order to optimize the positions of the locators in peripheral milling of a thin-walled workpiece, a finite element model along with an accurate cutting forces model is proposed in this paper. The finite element model takes into account the thickness variations of the workpiece in peripheral milling. The locators on the secondary locating surface directly influence the surface errors in peripheral milling of thin-walled workpiece, so this paper deals with the optimization of the positions of the locators on the secondary locating surface. A method including two steps is presented. In the first step, the initial positions of the locators are determined by adding the locators at the position with the maximum deformation. In the second step, a heuristic algorithm is proposed to optimize the positions of the locators. Finally, a simulation example is used to illustrate the method.     

自由曲面零件余量加工算法

从提高产品加工效率出发,提出并实现了三维自由曲面零件余量加工方法。该方法大大地缩短了粗加工时间,而且留给半精加工和精加工的余量较少,从而使得零件加工整个过程的总效率提高。实践表明,算法稳定、可靠,具有很好的工程应用价值。     

球头铣刀铣削球面的表面形貌建模与仿真研究

基于齐次坐标矩阵变换原理和矢量运算法则,建立了工件坐标系下球头铣刀扫掠面的数学模型,基于Z-MAP法设计了球形表面形貌的生成算法,利用该算法对球头铣刀分别采用3D环绕法和放射加工法这两种典型走刀路线加工凸球面,并对加工后的表面形貌进行了仿真,通过分析对比仿真结果,发现3D环绕法更有利于减小表面粗糙度。同时,仿真结果和试验结果具有较高的吻合度,表明该仿真方法是可靠的,可以用于实际生产中球头铣刀铣削球面表面形貌的预测。     

三维有限元分析在高速铣削温度研究中应用

高速切削过程中切削温度对刀具磨损、工件加工表面完整性及加工精度有极大的影响。应用有限元法对高速铣削铝合金薄壁件过程中工件与刀具接触面温度、工件内部的温度分布进行了仿真研究,仿真过程中考虑了切削速度、进给量对切削温度的影响。通过红外热像仪对不同主轴转速下工件表面温度的测量,验证了仿真结果与试验结果比较接近。得出在高速切削铝合金过程中,随着切削速度的增加,刀具与工件接触区的温度变化存在二次效应。该结论对铝合金薄壁件加工具有重要的实用价值。     

铣削加工表面几何特征的仿真研究

基于坐标矩阵的齐次变换和矢量运算法则,建立了铣削加工过程中刀具的运动轨迹方程,并在工件离散、刀具离散和加工过程离散的基础上,设计了铣削表面形貌仿真算法,并基于MATLAB的GUI功能开发了铣削加工表面形貌仿真系统。验证结果表明,仿真结果与实验结果一致性程度高,可应用于实际铣削加工表面几何形貌的预测和分析之中。