曲面数控加工刀具轨迹生成方法的研究

一、引言 曲面数控加工刀具轨迹计算是数控编程操作的基础和关键,随着CAD/CAM技术的快速发展,国内外学者对曲面的造型方法和数控加工刀具轨迹的生成方法进行了大量的研究,并且提出了许多曲面造型理论和数控加工刀具轨迹的算法。     

数控加工无干涉刀具轨迹生成的偏置算法

提出了用偏置方法来检查复杂曲面ＮＣ加工的刀具干涉及生成相应的刀具轨迹。通过对加工曲面进行上包络偏置表面操作，以及边界曲线“保护表面”的引入和导动平面与加工曲面求交时出现的非唯一性问题的处理，可获得一种生成３轴ＮＣ加工无干涉刀具轨迹的通用算法。该方法实现简单，算法稳定，具有广泛的适用范围。     

数控加工中参数线刀具轨迹生成方法的研究

一、引言 曲面的数控加工广泛应用于航空、航天、汽车、造船、模具、机械等行业复杂型面的加工中.其中曲面的三轴数控加工是应用最为广泛的加工方法之一.长期以来曲面数控加工刀具轨迹的生成,组合曲面的粗、精加工,曲面型腔的粗、精加工,刀轨优化、干涉处理、切削过程动态仿真模拟,一直是在CAD/CAM系统中实现数控编程的关键技术.     

应用构形空间理论处理自由曲面加工的干涉问题

文中简述了自由曲面数控另工编程中干涉检查的各种方法，利用构形空间概念，提出一种自由曲面加工的干涉检查算法，该算法先得到刀位面和保护面的离散三角表示，然后根据三角的上包络求刀位轨迹，从而避免干涉，算法适合于用球头刀，圆角刀和平底端刀的任意加工方式的三轴铣削，且实用，稳定，可靠。     

空间自由曲面数控加工轨迹的计算方法

现有的数控编程系统和ＣＡＤ／ＣＡＭ软件，往往只能在空间自由曲面上生成球面刀的数控加工轨迹，而实际生产中正逐渐采用非球面刀来替代球面刀完成空间自由曲面的数控加工。本文提出一个在空间自由曲面上计算非球面刀数控加工轨迹的新方法－点涉法，只要已知被加工曲面的参数表达式，就可运用点涉法在该曲面上生成非球面刀的数控加工轨迹。     

复杂曲面五轴加工局部干涉处理技术研究

针对复杂曲面环形刀五轴数控加工中的局部干涉问题,提出了一种基于曲 率匹配及网格点的干涉处理技术。首先,利用曲率匹配原则选出合理的刀具半径,以保证在 切触点处沿任何方向上刀具与被加工曲面之间不会发生干涉,然后在各个切触点处通过比较 刀具曲面最小主曲率与加工曲面最大主曲率确定出刀具的初始倾角。为了判断切触点邻近区 域是否存在干涉问题,采用了网格点来快速自动生成检测区域及初始检测点。文中对有效检 测点的筛选以及干涉的判断和处理技术分别进行了详细论述。最后,以非均匀有理B 样条 曲面为加工实例,对上述算法进行了测试和验证。     

未知曲面数控加工干涉区域求取算法研究

质量和效率是自由曲面零件数控加工所追求的一对相互矛盾的目标，曲面的分片加工可以较好地解决这这一问题，而自由曲面零件分片加工方法中一个关键问题是如何求取自由曲面的干涉区域，提出了在对自由曲面密集采样测量的基础上，利用未知曲面测点信息，通过参数曲面局部逼近和干涉区域测点问几何关系遍历求取干涉区域的算法，该方法避开了烦琐的自由曲面重建处理，仿真和实验研究的结果验证了算法的有效性。     

数控加工刀具轨迹生成方法探讨

目前,零件造型的方法主要有三种:线架造型、曲面造型和实体造型.在数控加工中,通常采用曲面造型和实体造型相结合的方法来进行.本文就在CAXA制造工程师软件中进行实体造型零件的数控加工曲面时,刀具轨迹生成的方法进行探讨.……     

数控加工刀具轨迹生成方法探讨

目前,零件造型的方法主要有三种:线架造型、曲面造型和实体造型.在数控加工中,通常采用曲面造型和实体造型相结合的方法来进行.本文就在CAXA制造工程师软件中进行实体造型零件的数控加工曲面时,刀具轨迹生成的方法进行探讨.     

技术文摘

技术文摘曲面加工的刀具轨迹计算北京航空航天大学制造工程系冉瑞江王亚平马德昌讨论了曲面加工的刀具轨迹计算方法，给出了刀具偏置的基本计算公式。行距与步长的控制方法，接触轨迹曲线的定义和干涉检查与修正算法。最后，讨论了对几种典型的曲面加工情形的处理方式，包...     

Optimal and collision free tool posture in five-axis machining through the tight integration of tool path generation and machine simulation

The generation of collision free NC-programs for multi-axis milling operations is a critical task, which leads to multi-axis milling machines being exploited below their full capacities. Today, CAM systems, generating the tool path, do not take the multi-axis machine movements into account. They generate a multi-axis tool path, described by a sequence of tool postures (tool tip+tool orientation), which is then converted by a NC-postprocessor to a machine specific NC-program. As the postprocessing is normally done in batch mode, the NC-programmer does not know how the machine will move and the chance for having collisions between (moving) machine components is often very high. The execution of a machine test run or the application of a machine simulation system (NC-simulation) is the only solution to inform the NC-programmer about possible machine collisions during operation.This paper describes a multi-axis tool path generation algorithm where the tool orientation is optimised to avoid machine collisions and at the same time to maximise the material removal rate along the tool track. To perform efficient collision avoidance, the tool path generation module (traditional CAM), the postprocessing (axes transformation) and machine simulation has been integrated into one system. Cutting tests have been carried out to define the allowable tool orientation changes for optimisation and collision avoidance without disturbing the surface quality.The developed multi-axis tool path generation algorithm is applicable for the machining of several part surfaces within one operation. This, together with tool path generation functionality to adapt the tool orientation for both, maximal material removal and avoidance of collisions between (moving) machine components, are the innovative aspects of the presented research work.     

曲面数控加工中面向NURBS刀具路径生成的刀位点分段算法

曲面数控加工中,NURBS刀具路径生成技术需要在大量有序刀位点中提取适合于NURBS刀具路径表示的刀位点段,刀位点的分段质量是决定NURBS刀具路径生成的前提.通过分析NURBS刀具路径的特点,对由刀位点表示的刀具路径之间的连接方式和边界点进行分类,提出通过层次聚类法将刀具路径进行分段的算法.在此基础上,通过判断连接点的类型来提取合适的刀位点段以进行NURBS刀具路径的生成.实例结果表明,该算法分段可靠、快捷,对不同曲线曲面轮廓刀具轨迹点进行分段的适应性强,分段结果可以满足NURBS刀具路径的生成.     

基于遗传算法的动态可变参数的测试数据自动生成工具

测试数据的生成是实现软件测试自动化的关键,这一技术的实现大大节省了软件开发的时间和费用。利用遗传算法的理论与算法特点,建立了动态可变参数的测试数据自动生成工具。通过该工具的可视化界面可以动态地输入遗传算法参数,而且能够根据不同的路径选择输入相应的适应度函数,克服了以往在源代码中修改适应度函数的缺陷。最后通过两个实验,证明了算法的优越性。     

基于复杂曲面分片建模的五坐标加工路径规划

采用曲面分片思想建立复杂参数曲面模型并进行了曲面特征分析。在曲面片域内基于环形铣刀几何特征的一般性,进行了精度误差分析,建立了等波高刀具路径规划策略,使刀具姿态随工件曲面的曲率而变化,并完成曲面片间的光顺整合。基于该分片算法,可有效改善复杂曲面的加工质量并能积极预防刀具与工件的干涉。     

三角网格表面等残留高度刀轨生成算法

针对截平面法规划的三角网格表面的刀轨长度较长、加工表面残留高度不均匀的问题,提出一种基于改进截平面法的等残留高度刀轨生成算法.首先在估算刀触点轨迹线垂直方向曲率半径的基础上,计算刀触点轨迹投影线并对其进行修正,去除其中冗余的投影点;然后由修正后的刀触点轨迹投影线构造驱动表面,利用驱动表面和网格表面迭代计算刀触点轨迹线;最后由刀触点轨迹线计算无干涉刀轨.与截平面法生成的刀轨进行比较分析的结果表明,文中算法生成的刀轨长度较小且获得的残留高度保持均匀,适合于三角网格表面表示的复杂表面的精加工.     

Sculptured surface machining using triangular mesh slicing

In this paper, an optimized procedure for tool path generation in regional milling is presented. The proposed procedure computes tool paths by slicing a CL-surface (Cutter Location surface), which is a triangular, mesh containing invalid triangles. Tool path generation consists of two steps: firstly, it obtains a set of line segments by slicing the triangular mesh with two-dimensional geometric elements (slicing elements), and, secondly, it extracts a valid tool path from the line segments by removing invalid portions. Two algorithms based on the slicing elements are presented: a ‘line projection’ algorithm based on the plane sweeping paradigm, which works efficiently by using the characteristics of a monotone chain; and a ‘curve projection’ algorithm for the projection of curves, which transforms the curve projection problem into a line projection problem by mapping the XYZ-space of the cylinder surface to the TZ-plane of the unfolded cylinder. The proposed procedure has been implemented and applied to tool path generation in regional milling. Performance tests show the efficiency of the proposed procedure.     

Smooth tool path generation for 5-axis machining of triangular mesh surface with nonzero genus

NC machining of a nonzero genus triangular mesh surface is being more widely confronted than before in the manufacturing field. At present, due to the complexity of geometry computation related to tool path generation, only one path pattern of iso-planar type is adopted in real machining of such surface. To improve significantly 5-axis machining of the nonzero genus mesh surface, it is necessary to develop a more efficient and robust tool path generation method. In this paper, a new method of generating spiral or contour-parallel tool path is proposed, which is inspired by the cylindrical helix or circle which are a set of parallel lines on the rectangular region obtained by unwrapping the cylinder. According to this idea, the effective data structure and algorithm are first designed to transform a nonzero genus surface into a genus-0 surface such that the conformal map method can be used to build the bidirectional mapping between the genus-0 surface and the rectangular region. In this rectangular region, the issues of spiral or contour-parallel tool path generation fall into the category of simple straight path planning. Accordingly, the formula for calculating the parameter increment for the guide line is derived by the difference scheme on the mesh surface and an accuracy improvement method is proposed based on the edge curve interpolation for determining the cutter contact (CC) point. These guarantee that the generated tool path can meet nicely the machining requirement. To improve further the kinematic and dynamic performance of 5-axis machine tool, a method for optimizing tool orientation is also preliminarily investigated. Finally, the experiments are performed to demonstrate the proposed method and show that it can generate nicely the spiral tool path or contour-parallel tool path on the nonzero genus mesh surface and also can guarantee the smooth change of tool orientation.     

Computing of the actual shape of removed material for five-axis flat-end milling

This paper describes an algorithm that predicts the shape of material removed by a flat-end milling tool, and this may be used to compute machining strip width and scallop height at different positions of the tool path track. The algorithm computes swept sections, profiles which are swept by a moving tool bottom by passing through given planes. The technique is applicable for finish and semi-finish multi-axis milling strategies that use flat-end tools. For these strategies, the algorithm complexity can be reduced from computation of the 3D envelope of swept volumes to computation of plane-circle intersections. A new adaptive derivative-free method to sample tool motion provides robust means to generate intermediate tool positions. The step length is constrained by and dependent on different geometrical measures. At each point of a tool path, in the plane perpendicular to the cutting direction, the bottom profile of the swept section is an estimate of the profile of material left. By calculating the distance between part geometry and the computed profile of removed material, machining strip width and a scallop profile can be derived. These results can be used by tool path generation and validation routines to accurately determine the step-over between tool path tracks and surface quality.     

密集型多轮廓裁片的刀具空行程路径寻优

服装行业中缩短刀具裁剪空行程对于高效裁剪布料具有重要意义。结合服装裁片排列具有轮廓形状复杂、分布密集的特点,将问题转化成广义旅行商问题。 基于最大最小蚁群(MMAS)算法提出了一种新的用于裁片刀具空行程路径寻优的算法--密集多轮廓蚁群算法,该算法包括4步:1)用MMAS算法确定初步裁片顺序;2)由裁片顺序寻找各裁片入刀节点;3)将各裁片的入刀节点再次用MMAS进行顺序优化重组得到初步裁剪路径;4)反复迭代第2)步和第3)步以求得最优路径。实验验证了所提算法的有效性,对比现有的扫描算法以及双信息素蚁群(NACS)算法其结果分别提升了60.15%和22.44%,该算法在刀具空行程优化上具有明显优势。     

面向路径的测试数据自动生成工具的设计

设计了一个通用的基于控制流和数据流的结构测试数据自动生成的工具。该工具根据控制流和数据流测试中所采用的覆盖标准来选取测试路径,并以改进后的迭代松弛法为核心,对所选取的路径生成测试数据。同时工具采用Fibonacci法优化选取路径,对不可达路径进行处理,并对测试数据的分支覆盖率、DCP覆盖率等进行了统计。实验结果表明该工具是可行的。