复合型陡峭曲面高速加工刀路的优化

针对现有数控加工中螺旋刀轨对曲面形状适应性差、无法应用于复杂陡峭曲面的问题,提出了一种复合型内侧陡峭面螺旋刀轨。一方面,通过构建圆柱螺旋线的方法获得光顺的螺旋驱动曲线;另一方面,通过抽取实体并将顶部曲面替换为平面的方法构建检查几何体;然后将螺旋驱动曲线和检查几何体导入CAM软件,对进退刀轨迹进行光顺化处理,从而生成连续光顺的螺旋刀轨。刀轨模拟和实际加工结果表明,复合型内陡峭面螺旋刀轨有效解决了高速加工中的切削颤振,显著提高了内侧陡峭面的加工效率和加工精度。     

面向高速加工的复杂曲面螺旋刀路优化

针对现有螺旋切削轨迹对曲面形状适应性较差,无法直接应用于复杂曲面的局限,提出一种基于曲面重构的螺旋曲线切削法。对于复杂曲面根据各自的特点分别采用曲面提取、修补、延伸等方法重构目标曲面,以重构后的曲面作为圆柱螺旋线的投影对象获取驱动曲线,在CAM软件中以曲线驱动方式生成螺旋曲线轨迹并进行优化。VERICUT软件仿真和实际加工的结果表明:复杂曲面采用曲面重构螺旋切削法可以获得满足高速加工要求的光顺切削路径,扩展了先进螺旋切削方式的应用范围。     

复杂陡峭曲面分段式螺旋刀路的设计

针对现有螺旋刀轨在实际应用中限制较多、无法直接应用于复杂陡峭曲面加工的局限,提出一种分段式螺旋刀轨。通过对流线驱动刀轨、曲面驱动刀轨和螺旋复合曲线驱动刀轨的有机整合,对复杂陡峭曲面的不同部位采用不同的加工方式,工艺针对性更强。同时,对作为流线的边界曲线采用提取、光顺和替换的方式进行重构,使得流线驱动螺旋刀轨更加光顺。实际加工和VERICUT软件仿真的结果表明,分段式螺旋刀轨能够满足高速加工刀轨连续光顺的要求,在生产中可操作性强。     

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。     

非典型叶轮数控5轴技术的研究

由于非典型叶轮结构复杂,无法使用主流CAD/CAM软件提供的叶轮5轴模块,在粗加工阶段采用3轴定向加工时,残余毛坯留量体积大形状不规则,严重影响了5轴加工的效率和质量。为此,一方面对于叶轮开式区域采用双圆柱面投影法获得驱动曲面,从而实现4轴联动粗加工,切削刚性大效率高;对于非开式区域则通过构建驱动曲面获得5轴联动刀轨,刀轨连续且刀轴矢量无突变。另一方面,提出了一种基于NC程序的刀轴矢量评价方法,可快速直观地评价5轴编程质量。实际使用结果表明:基于驱动曲面的刀轴矢量优化法能够显著提高复杂工件5轴加工的效率和质量。     

面向零件陡峭面加工的刀路优化问题研究

针对目前数控加工过程中零件陡峭面螺旋切削加工方式的局限,在对高速加工（HSM）切削路径进行研究的基础上,借鉴手工编程的优点,通过整合辅助螺旋线和平面轮廓线的投影对计算机辅助制造(CAM)过程进行优化,提出一种新型复合式螺旋切削刀路,从而扩展了先进螺旋切削方式在高速加工中的应用范围。VERICUT软件模拟和实际加工的结果表明,新型刀路能够满足陡峭面和平面并存零件高速加工路径的要求。     

自由曲面行距自适应五轴数控加工刀轨生成方法

在满足残留高度的前提下,增大行距能够有效减少加工刀轨的行数,从而减少刀轨总长度。针对自由曲面平底刀五轴加工,提出了一种行距自适应的刀轨生成方法。在刀具进给方向法平面上,以椭圆等效表示平底刀切削轮廓,基于曲面局部轮廓线和等残留高度点的几何特征提出迭代计算等残留高度点的方法;再根据等残留高度点、切削轮廓和曲面之间的几何关系,通过迭代调整下一行切削轮廓位置计算出满足残留高度要求的下一行刀轨信息;最后以下一行和当前行刀触点之间最小的参数差值作为自适应行距值规划刀轨。以叶片曲面为例生成刀轨,验证了算法的可行性和有效性。     

基于改进型Butterfly细分的三角网格自由曲面环形刀具轨迹规划

针对刀具轨迹连续性差、切削刀具负荷波动大的问题,提出一种基于改进型Butterfly细分的三角网格曲面环形刀具轨迹规划方法。以三角网格曲面的几何特征为基础构建曲面定点数据表达结构,结合环形刀的几何特征对刀触点(CC点)的刀具曲面及工件曲面进行几何分析,构建三角网格曲面环形刀切削模型。根据切削刀具干涉原理计算刀具的最小前倾角以获得切削路径的最大宽度,并据此采用改进型Butterfly细分方法对三角网格曲面进行细分,使刀具轨迹的行距达到切削路径宽度的要求。以曲面轮廓曲线为初始刀具轨迹,沿着三角网格边界进行螺旋型刀具轨迹刀触点(CC点)的逐行规划,最终根据环形刀几何模型求解刀心(CL点)位置。根据选择的刀具参数和给定的残余高度要求,仿真生成的三角网格曲面螺旋刀具轨迹的连续性好,从而降低了切削刀具负载的波动,最后通过机加工实验验证了刀具轨迹的可行性。     

深型腔模具精密加工技术的研究与实现

针对淬硬工具钢切削性能差、深型腔模具加工廓形精度不易保证等问题,提出了一种深型腔模具精密高速加工工艺优化技术.该技术根据构建的加工刀轨长度以及刀具悬伸长度与型腔加工廓形误差之间的数学模型,计算随加工刀轨长度变化的廓形误差值,设计瞬时的螺旋线加工刀轨,运用曲线过渡法,生成了适合深型腔模具精密高速加工的优化刀轨.基于米克朗Duro800高速加工机床,对内星轮模具型腔进行精密加工,结果表明,加工精度可提高IT1～2级,表面粗糙度Ra≤0.8.     

细分曲面粗加工刀轨生成算法

研究了细分曲面等高粗加工刀轨生成算法。以Catmull-clark细分曲面为研究目标,首先利用基于面误差的自适应细分算法构建粗加工模型,该方法构建的模型不仅具有均匀的加工余量,且能完全包围精加工模型,;然后采用层切法生成切层轮廓,在计算切削区域边界轮廓时采用了有效边追踪算法,该算法可以有效快速正确的得到每层的加工区域;为了验证算法的可行性及有效性,最后给出了加工实例,实例表明该方法可以有效地控制加工模型的网格数量,并能快速地生成粗加工刀轨。     

Development of automatic surface reconstruction technique in reverse engineering

The computer-aided design model reconstruction process is generally very complex, as it requires substantial efforts in planning and editing data points, curves, and surfaces. A novel method is developed in this study for automatic surface reconstruction from a huge number of triangular meshes. The proposed method is mainly composed of the following five steps: mesh simplification, quadrilateral mesh generation, curve net construction, connectivity data preparation, and multiple surfaces fitting with G¹ continuity across the boundaries. The first three steps build the boundary curves of the surfaces. The fourth step prepares the data needed for surface fitting, which includes segmented points, continuity conditions on the boundaries, and topological relationship of the data. In the final step, all regions of points are fitted into appropriate surfaces, with the accuracy and smoothness of the surfaces controlled and G¹ continuity between the surfaces. A detailed discussion for each of the above algorithms is provided. Successful examples are also presented to demonstrate the feasibility of the proposed method.     

Machining of complex-shaped parts with guidance curves

Nowadays, high-speed machining is usually used for production of hardened material parts with complex shapes such as dies and molds. In such parts, tool paths generated for bottom machining feature with the conventional parallel plane strategy induced many feed rate reductions, especially when boundaries of the feature have a lot of curvatures and are not parallel. Several machining experiments on hardened material lead to the conclusion that a tool path implying stable cutting conditions might guarantee a better part surface integrity. To ensure this stability, the shape machined must be decomposed when conventional strategies are not suitable. In this paper, an experimental approach based on high-speed performance simulation is conducted on a master bottom machining feature in order to highlight the influence of the curvatures towards a suitable decomposition of machining area. The decomposition is achieved through the construction of intermediate curves between the closed boundaries of the feature. These intermediate curves are used as guidance curve for the tool paths generation with an alternative machining strategy called “guidance curve strategy”. For the construction of intermediate curves, key parameters reflecting the influence of their proximity with each closed boundary and the influence of the curvatures of this latter are introduced. Based on the results, a method for defining guidance curves in four steps is proposed.     

特种回转面刀具螺旋槽的通用几何模型

针对数控磨削螺旋槽的特点 ,提出了基于一般特种回转面刀具刀刃曲线和刀面截形的螺旋槽通用几何模型。该模型采用统一的形式表示螺旋槽 ,为特种回转面刀具的设计和数控加工提供了理论基础。该模型也适用于其它类型的回转刀具     

改进的NURBS曲面片拼接算法

研究了已网格化的曲面片之间的拼接技术并对现有的拼接算法进行了改进。首先,根据哈特利-贾德的弦长参数化算法求取非均匀有理B样条（NURBS）曲线上的节点向量,利用节点向量和曲线反求出控制顶点,并采用投影变换的方法求出权因子。其次,根据要求调整曲面片上的控制顶点,使曲面片之间达到G1连续。最后,再对已拼接好的曲面片上的控制顶点进行整体修改,重新排列整张曲面片上的控制顶点,从而实现曲面片的无缝拼接。用专业的三维造型软件对拼接后合并的曲面片进行了测试,结果表明,该方法在保证曲面片之间G1连续的情况下可使多块曲面片实现无缝拼接,无缝拼接试验中的平均误差为0.0049°。     

Reverse engineering of compound surfaces using boundary detection method

This paper proposes an efficient reverse engineering technique for compound surfaces using a boundary detection method. This approach consists in extracting geometric edge information using a vision system, which can be used in order to drastically reduce geometric errors in the vicinity of compound surface boundaries. Through the image-processing technique and the interpolation process, boundaries are reconstructed by either analytic curves (e. g. circle, ellipse, line) or parametric curves (B-spline curve). In other regions, except boundaries, geometric data are acquired on CMM as points inspected using a touch type probe, and then they are interpolated on several surfaces using a B-spline skinning method. Finally, the boundary edge and the skinned surfaces are combined to reconstruct the final compound surface. Through simulations and experimental works, the effectiveness of the proposed method is confirmed.     

Numerically Controlled Machining of Freeform Curves Using Biarc Approximation

To machine a shape incorporating freeform curves, the free-form curves must be approximated and represented in a form suitable for numerically controlled (NC) tool-path generation. Instead of the commonly used line segment approximation, a new method using biarc approximation is presented here. The purpose is to reduce sudden changes in tool movement and increase continuity and smoothness. A biarc can be described as two consecutive circular arcs with an identical tangent at the connecting point. Therefore, tangent continuity can be maintained. Furthermore, curvature continuity can be improved if the difference between the two curvatures is minimised. In this research, biarc segments are used to approximate the freeform curves by controlling the largest deviation distance between the curves and the biarcs. The test results show that the biarc approximation method generates fewer tool-path segments than the traditional line approximation. The definitions of the biarcs are used to generate NC tool paths. A new tool-path generation method is developed for processing rough cutting and finish cutting paths. Example parts modelled with B-spline curves are tested and machined.     

服役破损叶片的曲面重构及刀路生成方法

A model reconstruction and CNC tool path generation of broken blades was proposed for the conditions that damage regions locatesd on the leading/trailing edges and on the tips. Measured data points were sorted, adjusted, and then utilized to construct sectional spline curves. The section curve was smoothed based on the theory of minimized energy, a method of aligning the sectional curves according to the curvatures was proposed. A model reconstruction method based on the lofting strategy was presented for the edge broken blades and the tip broken blades. The damaged regions were extracted, based on which the algorithm for generating zigzag tool path and the spiral tool path was given for CNC machining. Preliminary simulation results reveal that the proposed method guarantees the smoothness of the reconstructed surfaces and the approximation to the blade's real size. The feasibility of the proposed tool path generation method was testifiecl.     

Double-spiral tool path in configuration space

Using a spiral tool path is a common strategy in many NC machining applications. It can be used for high-speed machining of pockets or as a space-filling curve for finish applications. When using spirals for finishing application, a double spiral is desired to avoid having a starting or end-point at the center of the workpiece. In this paper, we present an algorithm to create a double spiral from offset curves in a precomputed configuration space (c-space). CAD/CAM systems that operate on NURBS surfaces or on triangular meshes have to deal with the issues of patch-boundary oscillations or long, stretched triangles, respectively. This can be avoided when operating in c-space. The c-space is given in the form of a regular quadrilateral heightfield mesh, which may be adaptively subdivided, where the slope is large. This simple data structure is memory efficient and has proven to be beneficial in CAD/CAM frameworks. Our algorithm creates a double spiral by blending adjacent offset curves. The center of the spiral is filled by a b-spline curve. When given offset curves split into multiple components, the algorithm creates multiple smaller spirals and connects them appropriately. The resulting tool path is one large intersection-free curve with starting and end-point on the boundary of the workpiece.     

An Improved Sculptured Part Surface Design Method with Jerk Continuity Consideration for Smooth Machining

This paper presents an investigation of jerk continuity in milling operations for sculptured surfaces of mechanical parts. It has been realised that chattering in machining operations can cause detrimental effects on the quality of machined parts as well as on the life of the cutting tool. One of the major reasons of chattering is known to be the rough transition of cutter accelerations when traversing through desired part sur-faces. The problem becomes serious when machining sculptured surfaces of parts. In this work, an effective computer-aided sculptured surface design technique is proposed. The ultimate goal is to achieve smooth and near chattering-free machining for producing precision parts. The proposed surface design scheme models the part’s sculptured surfaces in such a way that it warrants a smooth "jerk" transition at the boundaries of common surface patches on the part. This results in a drastic reduction of large step changes of cutter accelerations during machining operations which will in turn eliminate a good portion of the chattering effects. Three theorems concerning the necessary jerk continuity conditions for surface patches connections are developed and their proofs are presented. Examples of an aerofoil and a concept car model are implemented, using the proposed modelling approach, to demonstrate its effectiveness.