Local interference detection and avoidance in five-axis NC machining of sculptured surfaces

The tool interference problem is the most critical problem faced in sculptured surface machining. This paper presents a methodology for interference detection and avoidance in five-axis NC machining of sculptured surfaces with a filleted-end cutter. The surfaces to be machined are divided into convex and non-convex regions. There is no local interference inside the convex regions. For the non-convex regions, based on the analysis of the different local interference, local gouging is first detected and avoided by determining optimal cutter orientations. Rear gouging detection and avoidance algorithms are then proposed for simple smooth surfaces and complex shaped surfaces, respectively. The techniques presented in this paper can be used to generate interference-free tool paths. The realistic results indicate that the proposed method is feasible and reliable .     

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.     

带角圆柱铣刀对自由曲面3轴NC加工的刀具干涉检测

对自由曲面用带角圆柱铣刀3轴NC加工提出了系统的刀具干涉检测方法。加工自由曲面时,刀具干涉可以出现在包括刀具驱动面的刀具周围的任何地方。本文提出先检测自由曲面上可能产生刀具干涉的区域,然后再生成刀具路径,这样不但可极大地简化安排刀具路径的过程,改善加工的精度和可靠性,而且有利于产品的几何设计和影响加工效率的刀具选择。研究表明所提方法和算法是合理有效的。     

自由曲面3轴NC加工的全干涉检查研究

对自由曲面用球头刀进行3轴NC加工的干涉检查方法进行了研究,提出了一种新的干涉检查方法,该方法不仅可检查曲面加工时的局部干涉,而且还可对曲面加工时的全局干涉进行检查。通过与传统干涉检查方法的比较,并对不同刀具半径下干涉结果的比较,验证了本文提出的干涉检查方法的完整性、精确性和实时性,可指导曲面加工时刀具的选择。最后的实例证实了该方法及算法是合理可行的。     

Incomplete two-manifold mesh-based tool path generation

This paper presents a new paradigm for three-axis tool path generation based on an incomplete two-manifold mesh model; namely, an inexact polyhedron. When geometric data is transferred from one system to another system and tessellated for tool path generation, the model does not have any topological data between meshes and facets. In contrast to the existing polyhedral machining approach, the proposed method generates tool paths from an incomplete two-manifold mesh model. In order to generate gouge-free tool paths, cutter-location meshes (CL-meshes) are generated by offsetting boundary edges, boundary vertices, and facets. The CL-meshes are sliced by machining planes and the calculated intersections are sorted, trimmed, and linked. The grid method is used to reduce the computing time when range searching problems arise. The method is fully implemented and verified by machining an incomplete two-manifold mesh model.     

曲面数控加工中刀具干涉的检验

文章讨论了雕塑曲面数控加工中单张曲面产生刀具干涉的现象；相邻两曲面在凹向交线处的无干涉加工以及曲面拼接处刀具干涉的截面验证法，给出了具体算法和加工实例，取得了较好的干涉处理效果。     

Grind-free tool path generation for five-axis surface machining

This paper discusses automatic tool path generation for five-axis filleted end mill finish-surface machining. A new method of automatic five-axis tool path generation is introduced called Grind-Free (GF) tool path generation. GF surfaces result from tool paths that avoid gouging and have scallops that are within the surface profile or waviness tolerances. New algorithms are presented for determining tool forward step and tool path step-over that produce a GF surface. Gouge-free tool paths can be generated directly from CAD data based solely on local and global machining constraints. The proposed methodology for GF tool path generation has been implemented in the C language using the CODE/Robline system. Surfaces were machined on a Boston Digital 505 five-axis milling machine to confirm this method.     

空间自由曲面非球面刀加工轨迹自动生成的新原理和计算方法

针对现有的空间自由曲面数控编程系统和CAD/CAM软件,往往只能生成球面刀加工轨迹,以及实际切削加工中极少采用球面刀,多用小直径的立铣刀等非球面刀来替代球面刀完成空间自由曲面的切削加工这一现状,提出了一个在空间自由曲面上生成非球面刀加工轨迹的新方法——点涉法。只要给定空间自由曲面的参数表达式,就可选用点涉法生成该曲面的非球面刀加工轨迹。     

并联机床加工船用螺旋桨及CAM技术研究

主要研究用并联机床加工整体式船用螺旋桨的技术以及用CAD／CAM系统进行螺旋桨辅助加工的方法。研究了并联机床加工螺旋桨的工艺方案，提出了加工螺旋桨的并串联多轴数控加工系统，分析了螺旋桨数控加工的工艺过程；介绍了在UG／CAM环境下进行螺旋桨加工的刀具轨迹编程和用Vericut加工仿真系统进行加工仿真的方法和过程；并进行加工实验。用于加工螺旋桨的并联机床具有结构简单，造价低和占地面积小等优点，具有广泛的应用价值和发展前景。     

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。     

The error analysis of the NC machined free form surfaces in reverse engineering

In this paper a feasible methodology that deals with the issues in reverse engineering is reported. It starts by introducing the cubic polynomial to construct the CAD model in accordance with the points measured from the original object by using the optical non-contact scanning system. The needed control points for reconstruction are sifted from the tight squeezed scanned point cloud. Next, based on the control point, the interference-free algorithm connected with the developed CAM system is used to generate the fine-cutting tool paths for NC machining to avoid over-cut. When carrying out the error analysis, points scanned from the machined replica are compared to the reconstructed CAD model to investigate the error distribution. The test-point is sampled statistically from the scanned points due to analyzing the large number of points. The suitable sample size can stand for the entire population with sufficient confidence and accuracy. Meanwhile, a datum is needed to unify both the coordinate systems of the test-point and the reconstructed CAD model to make sense of the aftermath of error detection. For fulfilling the tasks of coordinate alignment and error detection, the test-point is transformed iteratively by means of the rigid-body transformation matrix, so as to minimize the sum of squares distance. The Nelder–Meade simplex method is used in resolving the parameters of the rigid-body transformation matrix in an optimal fashion, where the trouble that arises from resolving the derivates of non-linear equation can be prevented. Once the sum of squares distance in the normal direction converges to a preset value, the coordinate system of the reconstructed CAD model and that of the test-point are treated as consistent. As a result, the margin of error and the error distribution are evaluated. An example for system implementation was also demonstrated to show the validity of the proposed methodology .     

INTERFERENCE-FREE TOOL POSTURE GENERATION FOR 5-AXIS NC MILLING FREE-FORM SURFACES WITH CYLINDRICAL MILL

The 5-axis NC machining offers the potential of efficient and accurate machining. However, the present CAM system for 5-axis control is still an unsolved problem due to interference between tool and surrounding objects. A new method is presented. There are two steps in this procedure. First, it detects the interference by calculating the shortest distance between the tool-axis and the surrounding surfaces. Then upon the maximum gouging, the interference-free tool posture for 5-axis NC cylindrical milling free-form surfaces is obtained by adjusting tool. The validity of the proposed method has been confirmed by machining an impeller.     

GENERATE ROUGH TOOL-PATHS FROM UNORGANIZED POINT-CLOUD DIRECTLY

An approach is presented to generate rough interference-free tool-paths directly from massive unorganized data in rough machining that is performed by machining volumes of material in a slice-by-slice manner. Unorganized point-cloud is firstly converted to cross-section data. Then a robust data-structure named tool-path net is constructed to save tool-path data. Optimal algorithms for partitioning sub-cut-areas and computing interference-free cutter-locations are put forward. Finally the tool-paths are linked in a zigzag milling mode, which can be transformed into a traveling sales man problem. The experiment indicates optimal tool paths can be acquired, and high computation efficiency can be obtained and interference can be avoided successfully.     

Theoretical model for CNC whirling of screw shafts using standard cutters

Widely increased use of screw components with complex helical surfaces in contemporary machinery makes a huge demand for high-efficiency fabrication of these components. In this paper, a typical whirling process is introduced and the helical surface of a screw shaft is mathematically modeled based on its axial section profile, which is depicted usually by a number of sampled points. Following this, a theoretical approach is proposed to whirling the screw by using standard cutters, aligned with a detailed investigation into related issues including calculations of the cross section profile and the cutting tool location points. In this approach, the helical surface can be generated according to the shaft cross section which is used as the envelope of the cutting-tool motions in the machining process. The machining error is also analyzed with focuses on the axial- and cross section scallop height. Finally a case study is presented, which demonstrates the whole process including CAD models and cutting tool in-process positioning geometry data. The error distribution of the machined component along the profiles is also simulated.     

TOOL PATH SELECTION STRATEGIES FOR COMPLEX SCULPTURED SURFACE MACHINING

High performance machining of complex free form surfaces is very critical in many different industries. In this research, an advanced mathematical model of cutting forces that is based on the kinematics and mechanics of the 3D sculptured surface machining is integrated with CAM packages in order to predict the complex tool-workpiece engagements and machining forces for any tool path. Machined 3D free form topographies and distributions of errors between the desired CAD and machined surfaces are also predicted in advance. Now, an evaluation of different tool path strategies for 3D complex sculptured surfaces can be made. Theoretical simulations of forces and surface topographies for different tool paths are presented and compared with experimental measurements.     

CAXA制造工程师在数控加工中的应用

CAXA制造工程师是一款优秀的数控加工编程软件,全中文的操作界面,集CAD、CAM于一体化,可以对零件进行二维造型、三维造型、曲面实体复合造型,数控仿真加工可在造型基础上生成刀具轨迹,生成G代码,进行数控仿真加工,解决了复杂零件数控加工程序的编制难题.     

TOOL PATH SELECTION STRATEGIES FOR COMPLEX SCULPTURED SURFACE MACHINING

High performance machining of complex free form surfaces is very critical in many different industries. In this research, an advanced mathematical model of cutting forces that is based on the kinematics and mechanics of the 3D sculptured surface machining is integrated with CAM packages in order to predict the complex tool-workpiece engagements and machining forces for any tool path. Machined 3D free form topographies and distributions of errors between the desired CAD and machined surfaces are also predicted in advance. Now, an evaluation of different tool path strategies for 3D complex sculptured surfaces can be made. Theoretical simulations of forces and surface topographies for different tool paths are presented and compared with experimental measurements.     

A new accurate curvature matching and optimal tool based five-axis machining algorithm

Free-form surfaces are widely used in CAD systems to describe the part surface. Today, the most advanced machining of free from surfaces is done in five-axis machining using a flat end mill cutter. However, five-axis machining requires complex algorithms for gouging avoidance, collision detection and powerful computer-aided manufacturing (CAM) systems to support various operations. An accurate and efficient method is proposed for five-axis CNC machining of free-form surfaces. The proposed algorithm selects the best tool and plans the toolpath autonomously using curvature matching and integrated inverse kinematics of the machine tool. The new algorithm uses the real cutter contact toolpath generated by the inverse kinematics and not the linearized piecewise real cutter location toolpath.     

高速铣削刀轨优化技术的研究

针对高速铣削的特点和编程要求 ,提出了适合高速铣削的粗精加工刀轨优化算法。这些算法主要解决了型腔和轮廓加工刀轨的合理规划和进刀方式的选取 ,运用这些算法可以自动生成光滑C1连续的高速加工无干涉刀轨。仿真结果表明 ,加工表面无过切。经测试 ,算法运算速度快、可靠性好     

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.