Mesh-based tool path generation for constant scallop-height machining

This paper presents a new approach to mesh-based tool path generation for obtaining constant scallop heights. The mesh surface has recently become the focus of considerable interest, because its geometric computation is simpler and more robust than that of the parametric surface. These advantages make it easy to check and remove interference in the process of tool path generation. The previous tool path generation method based on the mesh surface, however, can generate only one topology of iso-planar type where tool paths have evenly spaced tool path intervals. As constant scallop heights cannot be obtained from evenly spaced tool path intervals, unevenly spaced tool paths based on offset meshes are necessary for reducing the machining time and for easy interference removal. This paper proposes and compares four methods to estimate curvatures from the mesh surface; the curvature is essential for calculating unevenly spaced tool path intervals. This paper also proposes an improved drive surface method to propagate CL-paths unevenly and to generate tool paths with various topologies.     

Iso-scallop tool path generation in 5-axis milling

This paper presents a new method of computing constant scallop height tool paths in 5-axis milling on sculptured surfaces. Usually, iso-scallop tool path computation methods are based on approximations. The attempted scallop height is modelled in a given plane to ensure a fast computation of the tool path. We propose a different approach, based on the concept of the machining surface, which ensures a more accurate computation. The machining surface defines the tool path as a surface, which applies in 3- or 5-axis milling with the cutting tools usually used. The machining surface defines a bi-parametric modelling of the locus of a particular point of the tool, and the iso-scallop surface allows to easily find iso-scallop tool centre locations. An implementation of the algorithms is done on a free-form surface with a filleted end mill in 5-axis milling.     

复杂曲面五坐标数控加工刀具轨迹的规划算法

提出了复杂曲面五坐标数控加工刀具轨迹的规划算法。该算法在保证刀具不与被加工曲面发生干涉的基础上 ,使得刀具扫描面与被加工曲面在刀触点处切平面上每个方向的曲率相匹配 ,由此规划的等残留高度刀具轨迹能改善曲面加工精度和加工效率     

液压连续升降系统研究

为适应大型构件连续升降的施工要求，消除因频繁启停产生的附加惯性载荷和冲击，用运动学观点对连续式液压提升器连续升降的运动机理进行了研究，对影响提升效率的重要参数——速度差和负载转换行程进行最优求解。建立了连续升降控制系统的数学模型，通过MATLAB仿真和连续升降台架试验，证实了连续式液压提升器能实现连续和同步升降。     

Constant scallop-height tool path generation for three-axis discrete data points machining

This paper presents a new approach for the determination of constant scallop-height tool paths in the machining of discrete data points using three-axis ball-end milling. Compared with the existing approaches for surfaces, this approach avoids offsetting data points, which is complex and time consuming. This paper firstly creates the local coordinate system centered at each CL point of the current path to calculate the corresponding scallop point and then the similar local coordinate system is created at each scallop point to calculate the wanted CL point of the next tool path. The tool paths generated by the approach keep the scallop-height constant and meet the step error requirement. The experiment result indicates that the approach is feasible and efficient and the overall tool path length can be reduced significantly compared with the iso-planar method.     

三角形网格模型上刀触点的加权补偿法矢量计算方法

研究面向三角形网格曲面数控加工刀位点的计算方法,提出了一种用于精确计算网格曲面上刀触点法矢量的方法。该方法引入了包含网格模型上刀触点所在区域附近的网格顶点的法矢量信息的加权补偿矢量及渐变影响函数,通过非线性插值三角形顶点处的法矢量得到位于网格模型上各刀触点的法矢量,使之更加接近理论参数曲面相应位置的法矢量。实例计算和误差分析表明,该方法可以有效地提高网格曲面上刀触点处法矢量的计算精度,对提高刀具轨迹上相应刀位点的位置精度和基于三角形网格曲面的数控加工精度有积极意义。      

Non-redundant tool trajectory generation for surface finish machining based on geodesic curvature matching

The increasing complexity of surface has put forward higher demands for CNC machining trajectory generation. The constant scallop height method has the disadvantage of point redundancy during trajectory discretization. Therefore, a non-redundant tool trajectory generation method for surface finish machining is put forward. The cutting row spacing is determined by the geodesic curvature according to scallop height and the convexity or concavity of the local surfaces. The adjacent cutter contact (CC) points with constant scallop height are expressed point by point from the present CC point. The redundant points are removed by maximizing each cutting step length through making the chord error equal to the machining allowable error. The dual NURBS ruled surface is constructed to realize smooth transition of the tool trajectories and tool axis vector. The prototype system taking ACIS R13 and HOOPS V11.0 as modeling kernel has been developed to verify the proposed method. The experiment results proved that the proposed method can realize non-redundant tool trajectory considering tool interference during surface finish machining.     

A Surface Based Approach for Constant Scallop HeightTool-Path Generation

The machining of sculptured surfaces such as moulds and dies in 3-axis milling relies on the chordal deviation, the scallop height parameter and the planning strategy. The choice of these parameters must ensure that manufacturing surfaces respect the geometrical specifications. The current strategies for machining, consist primarily in driving the tool in parallel planes which generates a tightening of the tool paths. A constant scallop height planning strategy has been developed to avoid this tightening. In this paper, we present a new method of constant scallop height tool-path generation based on the concept of the machining surface. The concept of the machining surface is developed and its use to generate constant scallop height tool paths is described. The approach is compared with existing methods in terms of precision and in particular its aptitude to treat curvature discontinuities.     

从测量的散乱数据点云直接生成数控刀具路径的研究

提出了一种直接从测量的散乱数据点云用球头刀对自由曲面进行三轴数控加工时生成刀具路径的方法。不同于现有散乱点云基于逆向工程的刀具路径生成方法,本法考虑并估计了曲面加工误差和粗糙度。将散乱数据点云向XY平面投影,以获得的投影边界为刀具路径的主方向,然后根据曲面所需的加工误差和残留高度要求划分该投影数据点云,得到一系列刀位网格单元。通过最小化每个刀位网格单元的加工误差以确定每个刀位网格的节点位置,加权平均相关联刀位网格节点来对齐相邻刀位网格单元的边缘。为了缩短加工时间,裁去刀位路径上多余的线段,最终生成高效合理的数控加工刀具路径。已用实测的数据点云验证了本法直接生成刀具路径的有效性。     

基于MMR的三角网格曲面五轴加工刀轨生成算法

为了提高三角网格曲面五轴加工的加工效率,提出了基于最大材料去除率(maximal materialremoval rate,MMR)的平底刀五轴加工刀轨生成算法。首先计算无曲率干涉且具有最大材料去除率的网格曲面五轴加工的刀具方位角;然后在确定网格曲面可能干涉区域的基础上,提出刀触点处干涉性假设,并以最大材料去除率、刀具无曲率干涉和全局干涉为约束条件,采用二分法确定具有最大材料去除率的无干涉刀具方位角;最后采用截面线法生成三角网格曲面MMR平底刀五轴加工刀轨。通过实验验证了采用文中算法生成的刀轨进行加工能够获得较高的加工效率和表面质量。     

Optimal five-axis tool path generation algorithm based on double scalar fields for freeform surfaces

In order to generate efficient tool path with given precision requirements, scallop height should be kept under a given limit, while the tool path should be as short as possible to reduce machining time. Traditional methods generate CC curves one by one, which makes the final tool path far from being globally optimal. This paper presents an optimal tool path generation model for a ball-end tool which strives to globally optimize a tool path with various objectives and constraints. Two scalar functions are constructed over the part surface to represent the path intervals and the feedrate (with directions). Using the finite element method (FEM), the tool path length minimization model and the machining time minimization model are solved numerically. The proposed method is also suitable for tool path generation on mesh surfaces. Simulation results show that the generated tool path can be direction parallel or contour parallel with different boundary conditions. Compared to most of the conventional tool path generation methods, the proposed method is able to generate more effective tool paths due to the global optimization strategy.     

三角网格曲面等参数线刀轨生成算法

提出一种三角网格曲面等参数线刀轨生成算法。采用调和映射的方法对三角网格曲面进行参数化,给出了四种等参数线刀轨规划方式;根据网格模型、投影网格和参数网格之间的对应关系,由残留高度确定参数网格中的x或r参数线;在此基础上,采用“区域划分”的方法快速生成了无干涉、无冗余数据的网格曲面等参数线行切和环切刀轨。实验结果表明该算法是可行和有效的。     

自由曲面三坐标加工等间距刀具路径规划

为提高自由曲面数控加工的切削效率,改善刀具的受力状态,提出了一种自由曲面三坐标加工等间距刀具路径规划方法.分析了在实际加工过程中可采用的几种刀具路径规划方法及其实现等距加工的约束条件.研究了等间距刀具路径的计算方法,并针对计算过程中出现的逼近误差校验和刀具路径延伸与裁剪问题给出了解决方法.对等参数线法和等距截面法进行了比较,表明应用该方法规划自由曲面刀具路径,可提高走刀路径对曲面形状变化的适应性和切削行间距分布的均匀性.     

一种用于多面体加工的圆弧刀轨生成算法

为提高多面体模型的加工效率,提出了一种用于多面体加工的圆弧刀轨生成算法。采用截平面和多面体模型的等距模型求交来计算初始直线刀轨;由等距模型的顶点曲率估算刀位点处沿刀轨方向和刀轨间隔方向的曲率半径,并根据残留高度确定刀轨行距。提出了基于刀位点曲率半径调节的圆弧拟合算法,算法引入拟合约束条件和曲率半径调节系数;在拟合精度范围内,迭代确定曲率半径调节系数,从而确定拟合圆弧。实验结果表明文中方法生成的刀轨保持G1连续且包含的圆弧段数量较少,有利于提高加工效率。     

Experimental investigation on various tool path strategies influencing surface quality and form accuracy of CNC milled complex freeform surface

Four tool path strategies such as equal-interval tool paths, parallel tool paths, parallel–tangency tool paths, and freeform tool paths are proposed in computer numerical control milling of a complex freeform surface. The objective is to understand how 3D tool paths influence their machining efficiency, surface quality, and form accuracy. In this study, their scallop heights were less than or equal to 15 μm. First, their scallop heights distributions and 3D tool path distances were theoretically analyzed; then, four tool path strategies were investigated with reference to machining efficiency, surface texture height, surface roughness, and form errors. It is shown that scallop heights distribution can be used to display the surface texture state and predict tool path distance. Experimental results indicate that the surface texture height, the surface roughness, and the form errors were nearly identical on the machined flat location and surface for various tool path strategies, whereas their surface quality and form accuracy are easily destroyed on the abrupt ones except for the parallel tool paths. Although the freeform tool paths produce the shortest tool path distance through 3-axes driving mode, the parallel tool paths offer the best surface quality and form accuracy through 2-axes driving mode. This is because the 3-axes driving and its vector changes on abrupt location easily lead to large machine vibration and movement errors. It is confirmed that the parallel tool path strategy with 2-axes driving mode can improve the surface quality and form accuracy in actual milling of a complex freeform surface.     

基于等残留高度的自由曲面加工刀具轨迹规划

对于曲面加工来说,效率和精度是相互矛盾的2个方面。加工时,用等残留高度法生成刀具轨迹,选择待加工曲面最长的1条边界线作为第1条加工的轨迹线,通过控制相邻刀具接触点的距离,使刀具轨迹间的残留高度均匀一致,依据刀具半径和允许的残留高度,迭代生成另一条刀具轨迹线。等残留高度法生成的刀具路径间的残留高度均为设定值,所生成的刀位点数最少,刀具路径长度最短。采用牛顿法作为等残留高度法的刀位点搜索方法,得到等残留高度刀具轨迹的生成过程。     

基于定向距离理论的五轴加工刀具轨迹规划算法

针对环形刀五轴加工自由曲面的残留误差问题,在传统等残留高度算法的基础上,提出了一种基于定向距离理论的等最大残留高度刀具轨迹规划算法。首先根据微分几何理论计算已知刀触点的初始侧向行距,并在侧向行距方向进行偏置得到相邻刀触点;然后以基于定向距离理论的残高误差计算模型对相邻刀触点间的实际残高值进行计算;最后通过迭代计算规划出等最大残留高度的相邻刀具轨迹。如此循环,从而获得整个曲面的刀具轨迹。实验结果表明,相对于商用软件MasterCAM9.0,该算法在充分保证曲面加工质量的同时最大限度地减小了刀具轨迹的总长度,从而提高了加工效率。     

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.     

A real-time surface interpolator methodology for precision CNC machining of swept surfaces

A real-time surface interpolator is developed to machine a family of swept surfaces directly from their high-level procedural definitions. All the computations required for machining are performed in real time based on the exact surface geometry, including tool path planning, tool path interpolation, tool offsetting, and tool path step-over to achieve a prescribed scallop height. A G-code command (G05) is introduced to concisely communicate the precise surface geometry and all necessary process parameters to the controller. The swept surface interpolator offers profound accuracy and efficiency advantages over the traditional approach of generating voluminous piecewise–linear/circular tool path approximations as a preprocessing step. For example, in one instance, a 36,000-line piecewise-linear (G01) approximate part program file is replaced by a 3-line exact swept surface (G05) part program file. The methodology is verified by machining a variety of swept surface forms in aluminum and wax, using a 3-axis milling machine with the surface interpolator incorporated into an open-architecture CNC controller.     

细分曲面数控加工关键技术

对三角域和四边域细分曲面数控加工的关键技术做了讨论,包括细分曲面数控加工模型的建立,粗加工模型的包围网格生成算法,NC刀轨生成常用的两种方法,精加工模型的等距网格求解算法及等距误差控制方法,给出了应用实例;指出了解决细分曲面数控加工技术实用化问题需要进一步研究的内容。