A corner-looping based tool path for pocket milling

In milling around corners, cutting resistance rises momentarily due to an increase of cutter contact length. NC tool path generation in dealing with sharp corners thus requires special consideration. This paper describes an improved NC tool path pattern for pocket milling. The basic pattern of the improved tool path is a conventional contour-parallel tool path. Bow-like tool path segments are appended to the basic tool path at the corner positions. When reaching a corner, the cutter loops around the appended tool path segments so that corner material is removed progressively in several passes. By using the corner-looping based tool path, cutter contact length can be controlled by adjusting the number of appended tool path loops. The procedures of creating the improved tool path for different corner shapes are explained. The proposed tool path generation was implemented as an add-on user function in a CAD/CAM system. Cutting tests were conducted to demonstrate and verify the significance of the proposed method.     

FPGA-based hardware CNC interpolator of Bezier,splines, B-splines and NURBS curves for industrial applications

Tool path interpolation is an important part of Computerized Numerical Control (CNC) systems because it is related to the machining accuracy, tool-motion smoothness and overall efficiency. The use of parametric curves to generate tool-motion trajectories on a workpiece for high accuracy machining has become a standard data format that is used for CAD/CAM (Computer Aided Design/Computer Aided Manufacturing) and CNC systems. Splines, Bezier, B-splines, and NURBS (Non-Uniform Rational B-splines) curves are the common parametric technique used for tool path design. However, the reported works bring out the high computational load required for this type of interpolation, and then at best only one interpolation algorithm is implemented. The contribution of this paper is the development of a hardware processing unit based on Field Programmable Gate Arrays (FPGA) for industrial CNC machines, which is capable of implementing the four main interpolation techniques. It allows the selection of the required interpolation technique according the application. Two CAD models are designed for test the CNC interpolations; experimental results show the efficiency of the proposed methodology.     

Automated part programming for CNC milling by artificial intelligence techniques

This paper discusses research which has led to a working program based on artificial intelligence techniques for automatically writing a part program for milling. The paper discusses the approach used and gives details of the implementation. The input to the program is the graphic representation of the part (a drawing), and user-defined items such as tool details, material type, and so on. The program has an initial state, the shape of the raw material, and a goal state, the shape of the part. The program solves the problem of achieving the goal state from the initial state by using machining moves, and hence writes the part program. The current implementation produces a part program for a 2 $\text{1}\text{2}\text{-}\text{dimensional}$ part on a 3-axis CNC milling machine.     

VERICUT在数控加工优化中的研究与应用

通过建立和分析刀具轨迹优化的数学模型,对VERICUT的优化原理进行了探索性的研究,并通过一个“瓶子加工”的典型实例展现了VERICUT 4.4版本环境下数控加工优化设计的全过程。     

A machining potential field approach to tool path generation for multi-axis sculptured surface machining

This paper presents a machining potential field (MPF) method to generate tool paths for multi-axis sculptured surface machining. A machining potential field is constructed by considering both the part geometry and the cutter geometry to represent the machining-oriented information on the part surface for machining planning. The largest feasible machining strip width and the optimal cutting direction at a surface point can be found on the constructed machining potential field. The tool paths can be generated by following the optimal cutting direction. Compared to the traditional iso-parametric and iso-planar path generation methods, the generated MPF multi-axis tool paths can achieve better surface finish with shorter machining time. Feasible cutter sizes and cutter orientations can also be determined by using the MPF method. The developed techniques can be used to automate the multi-axis tool path generation and to improve the machining efficiency of sculptured surface machining.     

An epitrochoidal pocket—A new canned cycle for CNC milling machines

A machining strategy for milling a particular set of pockets with epitrochoidal boundary is proposed. The method is suitable to be integrated into the controller of a CNC milling machine and is particularly useful for machining chambers of rotary internal combustion engines (Wankel), rotary piston pumps and generally epitrochoidal-shaped housings. Motion generation is achieved by an algorithm which utilizes real-time CNC interpolation providing the highest possible accuracy, of which the milling machine is capable. The surface quality is controlled by applying roughing and finishing passes. The whole machining task can be programmed in a single block of the part program. Finally, the effectiveness of the proposed method is verified by simulation tests of the generated tool path.     

Automated surface subdivision and tool path generation for -axis CNC machining of sculptured parts

As an innovative and cost-effective method for carrying out multiple-axis CNC machining, -axis CNC machining technique adds an automatic indexing/rotary table with two additional discrete rotations to a regular 3-axis CNC machine, to improve its ability and efficiency for machining complex sculptured parts. In this work, a new tool path generation method to automatically subdivide a complex sculptured surface into a number of easy-to-machine surface patches; identify the favorable machining set-up/orientation for each patch; and generate effective 3-axis CNC tool paths for each patch is introduced. The method and its advantages are illustrated using an example of sculptured surface machining. The work contributes to automated multiple-axis CNC tool path generation for sculptured part machining and forms a foundation for further research.     

Optimization Problems Related to Zigzag Pocket Machining

A fundamental problem of manufacturing is to produce mechanical parts from billets by clearing areas within specified boundaries from the material. Based on a graph-theoretical formulation, the algorithmic handling of one particular machining problem—``zigzag pocket machining'—is investigated. We present a linear-time algorithm that ensures that every region of the pocket is machined exactly once, while attempting to minimize the number of tool retractions required. This problem is shown to be -hard for pockets with holes. Our algorithm is provably good in the sense that the machining path generated for a pocket with h holes requires at most 5 . . . OPT + 6 . . . h retractions, where OPT is the (unknown) minimum number of retractions required by any algorithm. The algorithm has been implemented, and practical tests for pockets without holes suggest that one can expect an approximation factor of about 1.5 for practical examples, rather than the factor 5 as proved by our analysis. Received July 3, 1997; revised September 7, 1997.     

Direct 5-axis tool-path generation from point cloud input using 3D biarc fitting

In reverse engineering, geometrical information of a product is obtained directly from a physical shape by a digitizing device. To fabricate the product, manufacturing information (usually tool-path) must be generated from a CAD model. The data digitized must be processed and in most cases, a surface model is constructed from them using some of the surface fitting technologies. However, these technologies are usually complicated and the process for constructing a surface patch from a massive digitizing data is time-consuming. To simplify the process for getting tool-path information, a simple algorithm is proposed in this paper. The algorithm is used to generate a 5-axis machining tool-path. Instead of implementing any complicated surface fitting techniques, a direct method is proposed for constructing three-dimensional (3D) triangular mesh from the digitizing data with the mesh points considered as the tool contact locations. Depending on the locations of the points digitized, a decimation procedure is applied such that some of the digitizing data will be filtered out. Then, the tool axis orientations which must be determined in 5-axis tool-path are calculated and the tool center locations are determined accordingly. A 3D biarc fitting technique is applied for all the tool center locations so that a complete 5-axis tool-path is obtained.     

Intelligent Programming of CNC Turning Operations using Genetic Algorithm

CAD/CAM systems are nowadays tightly connected to ensure that CAD data can be used for optimal tool path determination and generation of CNC programs for machine tools. The aim of our research is the design of a computer-aided, intelligent and genetic algorithm(GA) based programming system for CNC cutting tools selection, tool sequences planning and optimisation of cutting conditions. The first step is geometrical feature recognition and classification. On the basis of recognised features the module for GA-based determination of technological data determine cutting tools, cutting parameters (according to work piece material and cutting tool material) and detailed tool sequence planning. Material, which will be removed, is split into several cuts, each consisting of a number of basic tool movements. In the next step, GA operations such as reproduction, crossover and mutation are applied. The process of GA-based optimisation runs in cycles in which new generations of individuals are created with increased average fitness of a population. During the evaluation of calculated results (generated NC programmes) several rules and constraints like rapid and cutting tool movement, collision, clamping and minimum machining time, which represent the fitness function, were taken into account. A case study was made for the turning operation of a rotational part. The results show that the GA-based programming has a higher efficiency. The total machining time was reduced by 16%. The demand for a high skilled worker on CAD/CAM systems and CNC machine tools was also reduced. Received: September 2004 / Accepted: September 2005     

An application-independent methodology of feature recognition with explicit representation of feature interaction

The existing feature-based design and feature recognition methods cannot fulfil the requirements of automated process planning. It is now recognized that satisfactory modelling of interactions between features is necessary for developing an automated process planning system. The selection of an optimum manufacturing process for a part needs to be considered at the conceptual design phase to incorporate the capabilities and constraints of the process in design. This paper describes a methodology of feature recognition that is independent of manufacturing process and explicitly generates geometric feature interactions in a part. The paper illustrates generation of feature sets for shape-forming processes, and describes a method to convert the process-independent features into machinable volumes and tool paths for material removal processes.     

数控刀位轨迹的新算法

CAM中的一个关键技术就是数控刀位轨迹的生成。本文在HANSEN[1]提出的干涉标志量概念及算法基础上，提出了新的理论观点及相应的新算法。新算法用在研制的美术造型图案模腔自动加工成型系统即GNC统中，几年来运行验证效果一直良好。     

加工特征识别系统ZD-AFRS及其健壮性增强方法

介绍了混合特征识别系统ZD－AFRS的设计思想、系统结构、核心功能的设计与实现,以及增强系统健壮性的方法。以先进性与实用性并重为原则,在ZD－AFRS的研制过程中,通过设计可靠的分割面处理、合并面处理和虚链生成算法,提高系统自动特征识别功能的健壮性;通过将交互特征定义与自动特征识别进行有机集成,提高系统的容错性;通过提供用户自定义特征功能使系统具有可扩展性;通过开发体特征生成、合理特征解释生成和先坯自动生成等功能使系统的功能更完善。经过较多的测试表明,ZD－AFRS具有较好的健壮性和实用性。     

A knowledge base model for complex forging die machining

Recent evolutions on forging process induce more complex shape on forging die. These evolutions, combined with High Speed Machining (HSM) process of forging die lead to important increase in time for machining preparation. In this context, an original approach for generating machining process based on machining knowledge is proposed in this paper. The core of this approach is to decompose a CAD model of complex forging die in geometrical features. Technological data and topological relations are aggregated to a geometrical feature in order to create machining features. Technological data, such as material, surface roughness and form tolerance are defined during forging process and dies design. These data are used to choose cutting tools and machining strategies. Topological relations define relative positions between the surfaces of the die CAD model. After machining features identification cutting tools and machining strategies currently used in HSM of forging die, are associated to them in order to generate machining sequences. A machining process model is proposed to formalize the links between information imbedded in the machining features and the parameters of cutting tools and machining strategies. At last machining sequences are grouped and ordered to generate the complete die machining process. In this paper the identification of geometrical features is detailed. Geometrical features identification is based on machining knowledge formalization which is translated in the generation of maps from STL models. A map based on the contact area between cutting tools and die shape gives basic geometrical features which are connected or not according to the continuity maps. The proposed approach is illustrated by an application on an industrial study case which was accomplished as part of collaboration.     

A STEP-compliant process planning system for CNC turning operations

Over the last 50 years, there have been many significant enhancements in computer aided systems which have influenced the CNC technology. One area that can be considered as a bottleneck to these CNC enhancements, and in particular to interoperability in CNC manufacturing is G&M part programming (ISO 6983). To overcome this bottleneck, the new standard ISO 14649, known as STEP-NC, is being developed to provide detailed information on component design, process planning and machining strategies to manufacture parts for the next generation of intelligent CNCs. This standard forms the basis of a new paradigm shift in the CNC domain to support digital modelling of CNC manufacturing resources. The research in this paper aims to identify major issues and develop new software tools to demonstrate the feasibility of interoperable CNC manufacturing based on STEP-NC. Besides the literature review on recent research and development on STEP-NC, this paper proposes a Process Planning System (PPS) with surface roughness chosen as the process planning objective. PPS consists of five modules: program reader, process planner, STEP-NC CAD viewer, STEP-NC CAM viewer and program writer. The reader is responsible for interpreting the geometry and the manufacturing data from a STEP-NC text file into a stored data list. The process planner uses this data list and enables users to evaluate surface roughness based on a mathematical model. Through the STEP-NC CAD viewer, the part geometry can be shown and via the STEP-NC CAM viewer the toolpath can be verified. Finally, the writer converts the stored STEP-NC data of the system into an updated STEP-NC file. An example case study component is used to demonstrate the PPS and show the interfacing of the STEP-NC data.     

Feature extraction and feature based design approaches in the development of design interface for process planning

The quest for completely automated process planning systems has exposed the lack of techniques capable of automatically understanding the stored CAD models in a manner suitable for process planning. Most current generations of process planning systems have used the ability of humans to translate the part drawing requirements into a form suitable for computer aided process planing. Recently, research advances have been made to improve the understanding of computer stored 3-D part models. The two approaches used are feature recognition and feature based design. This paper presents a state of the art review of feature recognition techniques developed and presents feature based design as an alternative. Process planning systems developed using both approaches are presented.     

快速成型机高精度CNC系统组成及关键技术

本文介绍了基于ＰＣ总线的ＨＲＰ快速成型机高精度ＣＮＣ系统组成，并重点论述组成该数系统关键技术。     

Continuity-preserving tool path generation for minimizing machining errors in five-axis CNC flank milling of ruled surfaces

Five-axis CNC flank machining has been commonly used in the industry for shaping complex geometries. Geometrical errors typically occur in five-axis flank finishing of non-developable surfaces using a cylindrical cutter. Most existing tool path planning methods adjust discrete cutter locations to reduce these errors. An excessive change in the cutter center or axis between consecutive cutter locations may deteriorate the machined surface quality. This study developed a tool path generation method for minimizing geometrical errors on finished surfaces while preserving high-order continuity in the cutter motion. A tool path is described using the moving trajectory of the cutter center and changes in two rotational angles in compact curve representations. An optimization scheme is proposed to search for optimal curve control points and the resulting tool path. A curve subdivision mechanism progressively increases the control points during the search process. Simulation results confirm that the proposed method not only enhances the computational efficiency of tool path generation but also improves the machined surface finish. This study provides a computational approach for precision tool path planning in five-axis CNC flank finishing of ruled surfaces.     

A physically-based model for global collision avoidance in 5-axis point milling

Although 5-axis free form surface machining is commonly proposed in CAD/CAM software, several issues still need to be addressed and especially collision avoidance between the tool and the part. Indeed, advanced user skills are often required to define smooth tool axis orientations along the tool path in high speed machining. In the literature, the problem of collision avoidance is mainly treated as an iterative process based on local and global collision tests with a geometrical method. In this paper, an innovative method based on physical modeling is used to generate 5-axis collision-free smooth tool paths. In the proposed approach, the ball-end tool is considered as a rigid body moving in the 3D space on which repulsive forces, deriving from a scalar potential field attached to the check surfaces, and attractive forces are acting. A study of the check surface tessellation is carried out to ensure smooth variations of the tool axis orientation. The proposed algorithm is applied to open pocket parts such as an impeller to emphasize the effectiveness of this method to avoid collision.