补加工技术在曲面加工中的研究

在自由曲面数控加工中，补加工是解决曲面交线、曲面内凹区域及浅平面和陡斜面等加工的有效途径。对曲面交线和曲面过渡区域的刀具轨迹进行了理论分析，探讨了曲面内凹区域补加工中边界的识别方法，并提出了浅平面和陡斜面加工应用实例。     

自由曲面等高斯曲率线的算法研究

提出了一种自由曲面等高斯曲率线的搜索算法,给出了算法的详尽描述,即极值点和搜索起点的求取、跟踪步长的确定、搜索的终止判定及避免重复搜索的措施。还说明了本算法在曲面光顺和逆工程中的意义以及算法推广后在曲面荒加工中的应用。最后给出了相应的计算实例。     

基于极值点的曲面等高线的追踪算法

提出一种基于极值点的曲面等高线的跟踪算法。可以简单、高效地 求出荒加工的边界，大大提高计算效率。     

基于Powermill刀具路径区域控制策略

结合典型案例,阐述了采用Powermill应用残留边界、浅滩边界、曲面边界和无碰撞边界进行数控编程时刀具路径区域控制策略,保证加工质量,提高加工效率.     

发动机叶片电解加工阴极设计有限元数值解法研究

以某型航空发动机转子叶片为研究对象，讨论了加工区域内的电场分布模型和阴极、阳极需要满足的边界条件，利用有限元法对复杂边界曲面具有较强的适应能力的特性，将加工区域离散后逐层求解极间间隙内的电位分布，将有限元数值解法成功地运用到加工叶片的工具阴极的设计中，从而获得满足加工精度要求的阴极。     

整体叶盘通道去余量线切割加工技术研究

整体叶盘的加工余量主要是在其通道开槽粗加工阶段去除的,合理选取整体叶盘粗加工通道余量去除方法是降低通道加工费用、实现整体叶盘加工经济性的关键。由于线切割机床加工单位成本低的原因,采用线切割加工方法对整体叶盘通道进行去余量加工。提出利用叶型与轮毂偏置面确定通道加工边界;通过比较通道边界投影后的投影面积大小确定最优矢量;然后根据最优矢量确定线切割丝与叶盘端面之间的夹角以及切割区域,实现整体叶盘粗加工阶段去除余量最大化。该方法可以有效地解决整体叶盘粗加工阶段经济性问题。试验表明,线切割加工可以应用在整体叶盘通道去余量加工中,并且与传统数控铣削相比,单个通道的加工费用仅为数控铣削加工费用的1/20。     

汽车模具凸曲面精加工极限切削深度预测

汽车覆盖件模具因硬度较高、精加工余量较小,导致模具精加工中经常出现由于余量选择不当而造成刀具与工件之间产生滑擦,使得模具精加工后出现多处区域加工不到的现象,此现象在凸曲面加工中尤为常见,严重影响汽车覆盖件模具的合模精度,增加了后期人工修磨时间。针对汽车模具凸曲面精加工中刀具与工件之间的滑擦现象,提供一种确定工件材料最小切削厚度的试验方法,确定淬硬钢Cr12Mo V材料不同切削速度下最小切削厚度值,在此基础上,通过理论分析,建立考虑刀具变形因素的模具钢凸曲面加工极限切削深度预测模型,并通过模具钢凸曲面铣削试验验证所建立模型的准确性。该模型的建立为模具精加工余量的选取提供一个最小值,精加工余量的选取应大于该最小值,以确保刀具与工件之间能够正常切削,提高模具的加工质量及合模精度,最终为汽车覆盖件模具高品质加工工艺参数的选取提供理论依据及技术指导。     

基于叶栅通道可加工性分析的整体叶盘径向电解加工阴极设计及实验

为提高叶栅通道加工质量,针对径向进给的电解加工方式,分析了通道可加工性问题,通过通道模型离散化处理,得到了加工边界曲面;讨论了进给角度与加工余量均匀性的影响,确定了合理的进给方向。在此基础上对阴极侧面轮廓和端面型面进行了设计,并制备了加工所需的工具阴极,利用自行研制的整体叶盘电解加工平台开展了工艺实验。结果表明:加工出的通道试件轮毂成形精度高,叶根部位加工质量好,叶盆、叶背余量分布均匀一致,能够满足后续叶片精加工要求。     

数控四轴旋转刀轨优化技术的研究

现有数控四轴加工编程适应性差,无法获得与曲面特征形状一致的分层连续刀轨,进刀和出刀轨迹过多,同时由于存在切削盲区,使得精加工余量很不均匀,这已经成为数控四轴加工中的瓶颈问题。本文提出了一种数控四轴旋转刀轨,通过提取曲面边界并展开为平面轮廓线;然后以平面轮廓线为边界获得相应的平面铣刀轨,平面铣刀轨可以通过相应的后处理输出为DAT数据文件,导入DAT数据文件生成平面样条曲线,最后将平面样条曲线缠绕于目标曲面上作为驱动曲线,从而生成连续光顺的分层刀轨。刀轨模拟和实际加工结果均表明,数控四轴旋转刀轨显著提高了四轴加工的效率和质量,在生产中实用性很强。     

基于MasterCAM的刀具路径区域控制研究

Master CAM软件是一款非常优秀而专业的数控加工自动编程软件,拥有如挖槽加工、等高外形、环绕等距等十几种曲面粗精加工方法,每种曲面加工方法都有各自的特点和适应范围,对复杂曲面进行加工时,特定的加工区域总是对应一种最优曲面加工方法。所以在利用Master CAM软件进行数控加工编程时,通过采用限定刀具的背吃刀量、限制刀具边界、设置干涉面、添加辅助线、修剪刀具路径等措施来限定刀具切削的范围,控制加工区域,从而提高产品的加工效率,保证加工质量。     

RESEARCH AND IMPLEMENTATION OF A HOGGING ALGORITHM

Cast blanks with large-scale free form surfaces are very difficult to manufacture because of significant casting distortions. It is concerned that the development and application of a hogging algorithm for preparing the blanks for an extended rough cutting. The procedure includes three main phases. They are the reconstruction of the free form surface with scattered points based on a special Hermite's interpolation, intersection of curved surfaces to define the hogging areas, and the tool path planning. The result shows that the algorithm is greatly valid in reducing the invalid tool paths so that the work efficiency can be improved remarkably.     

精密硬车加工轴承套圈的表面完整性试验研究

针对磨削加工中套圈精密加工存在的不足,进行精密硬车削加工轴承套圈新工艺的开发,通过加工试验分析了精密硬车加工轴承套圈的表面完整性,探究了基准面平面度、刀具磨损量等工艺参数与加工精度的对应关系。基于精密硬车削套圈试样的表面粗糙度、沟道圆度、显微硬度、热损伤、金相组织、残余应力分布、加工效率等方面的研究,得出了精密硬车削可达到磨削加工精度的结论,且金相组织稳定,不易存在热损伤,具有可控的残余应力分布和较高的加工效率,有利于产业化生产高精密轴承。利用磁性卡盘装夹套圈,分析试样基准面平面度对精密硬车削套圈沟道圆度的影响,发现提高基准面平面度可以有效提高加工套圈的沟道圆度;分析了刀具磨损对硬车削套圈加工精度的影响,得出在精密加工阶段刀具磨损量是控制套圈圆度的重要监控工艺参数的结论。     

基于机床运动学约束球头刀多轴加工刀轴矢量优化方法

针对目前航空发动机叶片进排气边加工精度和表面质量较差的问题,提出了一种基于机床运动学约束球头刀多轴加工刀轴矢量优化方法。建立刀位优化变量与刀位数据之间的关系方程,同时建立刀位数据与机床回转轴角度之间的运动变换方程,从而推导出刀位优化变量与机床回转轴角度之间的关系方程。通过求解上述方程得到球头刀多轴加工复杂曲面的刀轴矢量计算公式。在此基础上,给出球头刀多轴加工刀轴矢量优化方法和刀轨生成方法。同时,以某航空发动机叶片为例,分析了本文算法和Sturz算法对机床回转轴角度的影响。分别利用本文算法和Sturz算法生成该叶片进气边加工的刀轨,并在五轴数控机床上进行加工试验。试验结果表明,该算法能够避免加工过程中机床回转轴的大幅波动,使机床轴运动更加平稳和光滑,从而提高曲面的加工质量和加工效率,具有一定的实际应用价值。     

采用Voronoi图生成任意形状凹槽的刀具轨迹

为了自动生成任意形状凹槽的刀具轨迹 ,采用Voronoi图为基础的曲线置偏方法 ,避免传统的置偏算法所遇到的拓扑问题 ,提供了一种以Voronoi图为基础的简便有效的算法 ,可用来处理带“岛屿”的任意形状凹槽的刀具轨迹生成。     

Generating NC tool paths from random scanned data using point-based models

This paper presents a new approach for the generation of NC tool paths from random scanned data. Instead of using smooth or triangulated surfaces reconstructed from raw data, which is usually a time-consuming reverse engineering approach, the point-based surfel models computed by a GPU (graphics processing unit) are used to generate NC tool paths. The tool-path generation is highly efficient and still maintains the advantage of having accurate and smooth machining result. The word “surfel” itself is the combination of the two words “surface” and “element”. It is originally applied to the rendering of scanned data. In this paper, the point-based model is created using an elliptical Gaussian re-sampling filter that is based on a signal re-sampling algorithm. Since the input scanned data is of discrete and random nature, the warping process is utilized to transform the input data into a continuous surface and then re-sample the continuous surface by using GPU. Because the re-sampled data can accurately represent the original surface, tool paths can be generated based on the point data set. For cutting tools with various sizes, adaptive re-sampling schemes are employed to generate sufficient sampled points for the generation of accurate and smooth tool-paths.     

A topological-free method for three-axis tool path planning for generalized radiused end milled cutting of a triangular mesh surface

A tool path generation method for a sculptured surface defined by a triangular mesh is presented. Existing tool methods require extensive computer processing power mainly because surface topology for triangular meshes is not provided. The three-axis tool path planning method presented in this paper for generalized radius end mills avoids this problem (and does not need topological information) by offsetting each triangular facet individually. Offsetting a single triangle results in many more triangles, many of which are redundant, increasing the time required for data handling in subsequent steps. To avoid the large number of triangles, the proposed method creates a bounding space to which the offset surface is limited. Applying the boundary space limits the size of the offset surface resulting in a reduction in the number of triangular surfaces generated. The offset surface generation may still result in unwanted intersecting triangles. The tool path planning strategy addresses this issue by applying hidden-surface removal algorithms. Simulation and machining tests are used to validate the tool paths generated using this method.     

Generating efficient tool paths from point cloud data via machining area segmentation

This paper presents a method of generating efficient three-axis ball-end milling tool paths directly from point cloud data. The primary objective is to achieve high efficiency in the machining of free-form surface geometry having isolated complex machining area. The high machining efficiency is attained by segmenting the entire machining domain into distinct areas according to the geometric complexity of the data points and by using cutters of different sizes for the segmented machining areas. An iterative numerical procedure is derived to determine the critical complexity that separates the data points with higher complexity (the complex points) from those with lower complexity (the non-complex points). A larger and more efficient ball-end mill is used to machine the area defined by the non-complex points. The gouging condition of all the data points is then evaluated with respect to the given ball-end mill. The isolated complex machining area is established by enclosing both the complex points and the gouge points. The smaller and gouge-free ball-end mill for the isolated complex machining area is subsequently selected from the standard commercial cutter series. Implementation of the presented method clearly demonstrates the high efficiency of the generated tool paths.     

Form-truing error compensation of diamond grinding wheel in CNC envelope grinding of free-form surface

In computer numerical control (CNC) grinding of free-form surface, an ideal arc profile of trued diamond grinding wheel is generally employed to plan 3D tool paths, whereas its form-truing errors greatly influence the ground form accuracy. A form-truing error compensation approach is proposed by using an approached wheel arc profile to replace the previously designed ideal one. The objective is to directly compensate the trued wheel arc-profile errors. It may avoid the time consumption of traditional approach that compensates the measured coordinate point errors of workpiece to an iterative grinding operation. First, the 3D tool path surface was constructed to plan the 3D tool paths. Second, the CNC arc truing of grinding wheel was conducted to analyze the form-truing error distribution relative to the applied wheel arc profile. Then, the form-truing error compensation was carried out in CNC envelope grinding. Finally, the iterative closest point (ICP) algorithm was used to match the measured coordinate points of workpiece to ideal free-form surface. It is shown that the 3D tool path surface constructed is practicable to plan arbitrary 3D tool paths for the form-truing error compensation. The ICP matching may be used to investigate 3D ground form error distribution. It is confirmed that the form-truing error compensation can directly improve the 3D ground form accuracy. It may decrease the 3D ground form error by about 20% when the 2D form-truing error is reduced by about 58% using the same truing conditions for CNC grinding.     

五轴联动激光淬火路径规划

研究了基于五轴多功能激光加工机床激光淬火的工艺特点,提出了用于复杂型面五轴联动激光淬火路径规划的方法,实现了针对于五轴多功能激光加工机床激光淬火的前计算,为使五轴联动激光淬火应用于实践奠定了一定的基础。该方法主要是在考虑了以下3个约束条件的基础上提出的:(1)在淬火的过程中要保证激光光斑相对于工件表面的扫描速度恒定;(2)在激光淬火过程中要保证工件表面激光光斑的大小不变;(3)在进行激光扫描时要使插补时产生的弦误差最小。通过保证这3个约束条件,进而保证工件表面淬火质量。     

叶片等残留高度数控螺旋铣加工刀具轨迹的规划算法

根据叶片的曲面特征,提出了基于等残留高度的叶片五坐标数控螺旋铣加工方法,设计了刀具轨迹生成算法,在UG二次开发环境下编程实现.该方法满足相邻刀轨之间的等残留高度要求,无冗余刀轨.避免了刀轨间的抬刀,可实现连续的切削加工,在满足误差要求的前提下可显著提高加工的效率.