基于Hilbert填充曲线的自由曲面刀具路径规划研究

利用平面Hilbert填充曲线生成方法简单、易于控制填充疏密的优点,将其用于了自由曲面数控加工刀具路径的生成.对平面Hilbert填充曲线的生成原理进行了研究,用矩阵运算的方法生成该曲线.结合自由曲面的形成过程,提出将平面Hilbert曲线通过与曲面参数域相对应的方法映射到曲面上,进而生成加工刀具路径的思想.最后用一个具体应用实例验证了生成平面Hilbert曲线方法的正确性,和用此曲线作为数控加工刀具路径的可行性.通过与经典刀具路径生成方法比较可见该方法具有算法简单,加工余量均匀,加工效率与表面质量高的优点.     

Hilbert填充曲线用于刀具路径生成的算法及改进研究

对Hibert填充曲线的生成方法进行了研究,建立了平面Hilbert填充曲线与Bezier参数平面之间的映射关系,得到了平面Hilbert填充曲线到空间曲面的映射规则和相应算法。针对该方法用于刀具路径生成时存在转向过于频繁等缺点,为了减小加工过程中对刀具和工件的冲击,提出了用倒角或圆弧进行过渡来代替原来的直角过渡的方法生成加工刀具路径。针对改进后的生成刀具路径的方法编制了仿真程序,对改进前后的刀具路径的长度和生成时间进行对比分析。通过一具体曲面加工路径生成仿真,验证了该方法的有效性。     

自由曲面数控加工刀具轨迹映射算法

对自由曲面的数控加工,寻求最优的刀具轨迹生成方法至关重要。本文基于开源3D库Open CASCADE(OCC)和编程开发环境Microsoft Visual Studio 2010(VS2010),应用B样条表达的自由曲面,采用“投影法”思想,研究“重用已有相似刀具路径”方法,提出了处理自由曲面的NC刀具轨迹映射算法。为了验证算法的有效性和可行性,实验建立5类自由曲面,启动设计的轨迹映射算法,输出曲面的NC加工轨迹质量可以满足设计要求,实现了刀具轨迹的重用。     

基于ABF的自由曲面上三维复杂图案的雕刻方法

利用五轴数控机床在自由曲面上快速生成美观的图案在珠宝纹饰雕刻、吹塑/挤压模具图案制作、复杂产品外观图案的自动喷绘等方面具有潜在的广泛应用.针对目前图案映射对单一参数曲面参数域处理的依赖,提出一种可应用于复合裁剪曲面、网格曲面甚至点云曲面的三维复杂图案雕刻方法.利用图像边界处理技术,将二维的数字图案转化为可用于数控加工的离散点集.进而根据保角映射(Angle-based flattening,ABF)原理,将目标曲面映射到二维平面域,建立三维曲面与二维平面域之间的一一映射关系.以此映射为向导,提出基于面积坐标的线性映射方法,将离散图案逆映射到目标曲面上.根据选择的刀具参数及给定的切削深度,生成用于三维复杂图案雕刻的刀具轨迹,并进行雕刻仿真试验和实际雕刻加工试验.试验结果证明,所提方法简单实用,能够在复杂自由曲面上生成美观的雕刻图案.     

基于参数曲面映射的五轴数控螺旋加工轨迹计算方法

采用五轴数控机床进行高速加工时,加工干涉及曲面转角处的突变会造成刀轴矢量剧烈变化,而采用传统的退刀再进刀的方法又难免导致加工效率及质量的降低.针对上述问题,提出一种新颖的适用于五轴高速加工的刀具路径生成算法.该方法由偏微分方程的热传导模型,计算得到映射参数域内满足加工参数的温度等值线,制定映射规则并在标准参数域内规划出加工轨迹,从而在对应参数域内映射生成螺旋轨迹,并将该轨迹映射到参数曲面上获得曲面的螺旋加工轨迹,该轨迹可以实现无退刀加工.采用上述算法进行了仿真,仿真结果表明该方法优于现有加工方法,可实现基于参数曲面及裁剪曲面的复杂型腔的高速加工.     

球头铣刀曲面多轴加工的刀具接触区半解析建模

刀具接触区界定了切削过程刀具与工件的相互作用范围,是研究切削力学/动力学的基础,复杂曲面加工的刀具接触区往往呈现不规则几何形状且沿曲线刀具轨迹不断变化。针对球头铣刀复杂曲面多轴加工,提出一种刀具接触区半解析建模方法。基于微元离散和刚体旋转变换的思想,将一般复杂曲面加工看成是一系列微小斜平面加工的组合,并且认为球头铣刀斜平面多轴加工的刀具接触区,可由球头铣刀水平面三轴立铣加工的刀具接触区经刚体旋转变换而得。通过将切削余量材料看成是一系列微厚材料薄层的叠加,构建了球头铣刀水平面三轴立铣加工的刀具接触区解析模型,从而建立球头铣刀复杂曲面多轴加工的刀具接触区半解析模型。仿真实例分析了模型的精度和效率,结果表明该半解析模型能够精确高效地描述复杂曲面多轴加工的刀具接触区。     

基于误差补偿的高速等残留高度刀具轨迹的研究

根据微分几何中短程线的原理,在传统的基于等残留高度刀具轨迹生成方法的基础上,通过判断曲面特性,提出基于曲面特性的误差补偿步长计算法.引入NURBS曲线实现相邻刀具轨迹的平稳过渡,实现高速加工下刀具轨迹行间的平滑优化.以上算法利用Visual C+ +实现,通过仿真得到平稳光顺、载荷均匀的曲面高速加工刀具轨迹.     

自由曲面数控加工刀具轨迹曲线的一种生成算法

提出一种自由曲面数控加工轨迹曲线计算方法。根据这一方法,可由自由曲面上一定数量的任意分布型值点来 计算曲面加工时的刀具曲线。算法的基本思想是,型值点影响并决定着其控制区域内的曲面形状,这种影响的大小与到 型值点的距离及权指数相关。分别给出了沿X向进给及Y向进给时刀具轨迹曲线的生成算法。讨论了算法中参数选取 对加工曲面形状及拟合精度的影响。     

基于ACIS几何平台的复杂多曲面数控加工编程技术

针对复杂多曲面数控加工方法自动生成刀具轨迹的问题,本文提出并在ACIS几何造型平台上实现了一种采用截平面法进行复杂多曲面精加工刀轨规划的方法.该方法采用一组截平面去截取加工表面,得到一系列交线,将这些交线按一定规律排序,组成加工环,刀具沿着这些加工环运动,便完成模型的加工.通过实例证明运用该方法使生成的刀轨连续,进退刀得到优化,大大提高了加工效率.     

圆锥刀侧铣非可展直纹面刀轴轨迹规划的特征线方法

针对圆锥刀侧铣加工非可展直纹面中复杂的刀轴轨迹规划问题,提出一种直观简便的刀轴轨迹生成方法。利用圆锥面的性质,给出法向映射曲线的定义即刀具轴线上诸点在设计曲面上的法向投影点的集合,将刀具包络面向设计曲面的逼近问题转化为每个刀位下法向映射曲线与特征线的最小二乘逼近问题,并给出刀具包络面尚未形成时单刀位下理想特征线的生成方法。用两点偏置法生成初始刀位,以此为基准,利用刚体运动学方法将刀轴位姿描述为3个回转与3个平移运动参数的函数,从而建立单刀位优化条件与6个运动参数的非显性的函数关系。采用拉丁超立方的试验设计方法求解,分析并优选计算过程中的影响因素,得到最优刀位,进而获得优化后的刀轴轨迹面。实例计算可知,刀轴优化后的包络误差显著降低,并且计算结果稳定。该方法可为非可展直纹面的圆锥刀侧铣加工提供一定的理论依据。     

基于奇异避免的薄壁件镜像铣削加工路径优化

在双五轴镜像铣削加工中,由于旋转轴运动突变带来的奇异问题,导致薄壁件表面加工质量以及加工效率降低。在分析奇异问题产生原因的基础上,提出一种奇异区域加工路径优化的方法。基于C-空间的概念,在奇异区域边界约束条件下,同时满足镜像铣削加工中刀轴矢量与工件表面保持垂直,以最小刀轴矢量距离确定备选刀轴矢量,对奇异区域的刀轴矢量进行局部修正。然后对整条加工路径进行B样条曲线拟合,基于最小参数曲线应变能建立优化模型,通过对参数曲线的调整,提高路径的光顺性,保证加工效率,提高加工质量。最后,通过仿真实验和实际加工结果验证所提方法的有效性。研究结果表明,最小壁厚误差减小50%,最大壁厚误差减小75%,整体壁厚误差范围缩小了68.75%,同时完整的路径加工时间缩短了2.1%。     

基于空间填充法的刀具路径生成算法及其仿真

针对空间填充曲线法的网格只具有正则矩形,生成的刀具路径存在频繁转向、长度冗长、生成时间长等缺点,提出一种基于空间填充法的刀具路径生成算法。选用T样条曲面为造型曲面,生成具有非正则矩形的网格并进行回路的规划;用改进的Hamiltonian算法初步生成刀具路径;用改进的倒圆角算法进行拐角优化,获得最终的刀具路径。开发出了基于该算法的仿真系统,对算法进行了仿真验证和实际的加工实验,结果表明所提出算法有效可行,生成的刀具路径长度及生成时间都得到缩短。     

A study on the five-axis end milling for sculptured surfaces

The direction vector of milling cutter for CL-data of five-axis milling is obtained by the fact that the bottom part of the milling cutter rides on free-form surfaces using the z-map method. Since the direction vector is known, CL-data can be transformed to the NC-code with regard to the geometry of the five-axis machine and post-processing. For uniform surfaces, the tool path is created from the prediction of cusp heights. After generating the NC-code, a sculptured surface was machined by five-axis end milling and cusp heights on the machined surface were measured by a three-dimensional CMM with laser scanner. From this machining test, it was found that this machining method is effective.     

Geometric modeling and tool path generation of model propellers with a single setup change

A model propeller plays important roles in the design of the marine vehicles. The cavitations, the erosion, the pressure fluctuation, and the flow are measured by the model propeller. These measurements help to create the actual marine propeller. In this paper, geometry modeling and tool path generation for a model propeller are proposed, and the hub surface and lateral surface of the wing surfaces are generated by the proposed method. Considering the characteristics of the model propeller, efficient Cutter Location (CL) data are proposed: (1) the finish machining is completed with one setup posture. (2) A four-axis machining algorithm is proposed that makes it possible to the propeller with one setup and that minimizes machining error. (3) To minimize the maximum machining load, zigzag machining and an outside-to-inside tool path are introduced. A tilting guide curve is proposed to determine the tool axis vector. A smoothly changing tool axis vector is obtained through this curve, and the calculation is simple and fast. The results demonstrate that the proposed method is useful for the manufacturing of model propellers.     

基于FDM技术的Hilbert曲线路径优化算法

熔融沉积成型(fused deposition molding, FDM)的填充路径不连续,电机频繁停止极易导致翘曲变形。结合轮廓偏置法和空间填充曲线中的Hilbert曲线填充,提出了一种基于轮廓偏置与拟合Hilbert曲线的路径优化算法。该算法将Hilbert曲线进行三次B样条曲线拟合,降低了打印过程中电机变化率,减少了电机停止次数,进而减少打印件的翘曲变形,提高打印件精度。通过实验验证,模型平均最大翘曲量减少了60.70%,总平均翘曲量减少了62.26%。     

Curve interpolation with variable feedrate for surface requirement

Finish machining of a curved surface is often carried out by an NC system with curve interpolation in the field. This function, called a NURBS interpolation, adopts a feedrate optimizing strategy based on both the geometrical information of the curved path and dynamic properties such as the curvature of the curve, the allowable acceleration and the time constant. However, in the case of a finish cut using a ball-end mill, the curve interpolator needs to take the machining process into account for improved surface roughness, while reducing the polishing time. This surface roughness on high-speed machining is theoretically defined by the feed per tooth and the pickfeed at the given radius of the tool. In this study, the effect of low machinability at the bottom of a tool on surface roughness is also considered. A curve interpolation algorithm is proposed for generating particular feedrate commands that are able to control the roughness of a curved surface. The simulation of the machined surface by the proposed algorithm was carried out, and experimental results are presented. A feedrate scheme that depends on the inclination angle has important potential application in part finishes consistent with prescribed surface roughness. The results show that the proposed algorithm is potentially useful for roughness-controlled machining of curved surface products.     

Three-dimensional tool radius compensation for multi-axis peripheral milling

Few function about 3D tool radius compensation is applied to generating executable motion control commands in the existing computer numerical control (CNC) systems. Once the tool radius is changed, especially in the case of tool size changing with tool wear in machining, a new NC program has to be recreated. A generic 3D tool radius compensation method for multi-axis peripheral milling in CNC systems is presented. The offset path is calculated by offsetting the tool path along the direction of the offset vector with a given distance. The offset vector is perpendicular to both the tangent vector of the tool path and the orientation vector of the tool axis relative to the workpiece. The orientation vector equations of the tool axis relative to the workpiece are obtained through homogeneous coordinate transformation matrix and forward kinematics of generalized kinematics model of multi-axis machine tools. To avoid cutting into the corner formed by the two adjacent tool paths, the coordinates of offset path at the intersection point have been calculated according to the transition type that is determined by the angle between the two tool path tangent vectors at the corner. Through the verification by the solid cutting simulation software VERICUTwith different tool radiuses on a table-tilting type five-axis machine tool, and by the real machining experiment of machining a soup spoon on a five-axis machine tool with the developed CNC system, the effectiveness of the proposed 3D tool radius compensation method is confirmed. The proposed compensation method can be suitable for all kinds of threeto five-axis machine tools as a general form.     

机器人模具抛光自由曲面刀具轨迹的生成研究

以HNC-IR教学机器人为对象,对机器人模具抛光中自由曲面的抛光刀具轨迹的生成和干涉处理进行了研究,提出了适合于机器人抛光的面自由曲面刀具轨迹生成算法,此算法生成的抛光刀具轨迹具有形式简单、在曲面表面分布均匀等优点,适合于机器人抛光。