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。     

A New Tool-Path Generation Method Using a Cylindrical End Mill for 5-Axis Machining of a Spatial Cam with a Conical Meshing Element

The geometry of a spatial cam is normally generated using a form-milling cutter and a special multi-axis machine and software. The general purpose CAD/CAM software can generate the cutter location file of this class of product only by the sculpturing method. Because of the limited choice of cutting tool when using the generating method, this paper presents a new toolpath generating method which combines the advantages of the generating and sculpturing methods for machining a spatial cam. In the machining process, the cutter location is derived for rough and finish machining using a cylindrical end mill. The guidelines for choosing cutter diameter for the machining process are discussed. To avoid interference, the principal curvatures and the principal induced normal curvatures are analysed. The mathematical errors including chordal deviation and scallop height are used as the basis for generating appropriate tool-paths. Cutting simulation of a solid model was performed to verify the proposed tool-path generation method.       

CNC Tool-Path Planning for High-Speed High-Resolution Machining Using a New Tool-Path Calculation Algorithm

Reduced machining time and increased accuracy for a sculptured surface are both very important when producing complicated parts, so, the step-size and tool-path interval are essential components in high-speed and high-resolution machining. If they are small, the machining time will increase, whereas if they are large, rough surfaces will result. In particular, the machining time, which is a key factor in high-speed machining, is affected by the tool-path interval more than the step size. The conventional method for calculating the tool-path interval is to select a small parametric increment or small increment based on the curvature of the surface. However, this approach has limitations. The first is that the tool-path interval cannot be calculated precisely. The second is that a separate tool-path interval must be calculated in three separate cases. The third is the requirement of a conversion from the Cartesian domain to the parametric domain or vice versa. Accordingly, for high-speed and high-resolution machining, the current study proposes a new tool-path interval algorithm, that does not involve a curvature or any conversion, plus a variable step-size algorithm for NURBS.     

An Effective Global Gouge Detection in Tool-Path Planning for Freeform Surface Machining

This paper examines a usually neglected gouge phenomenon in tool-path planning for machining parts having freeform surfaces with 3-axis ball-end mills. That is, when a freeform surface is being milled with a ball-end cutter, a gouge may exist anywhere around the cutter circumference, in addition to the tool driving plane. A global gouge detection concept is developed to solve this problem. An effective method is proposed to identify the potential gouge areas on the sculptured surface during machining, before generating tool paths. Thus, it greatly simplifies the tool-path planning procedure and improves the accuracy and reliability of machining. It also facilitates geometric design processes of products and cutter radius selection which are crucial to machining efficiency. The designed part surfaces tested by the proposed methodology are constructed based on bicubic B2-splines and are assumed to be at least C 2 and may possess C 1 or C 0 continuity for generality. The tested examples demonstrate the effectiveness of the developed global gouge detection approach. This revised version with a corrected online cover date was published online in April 2004.     

A Path Interval Generation Algorithm in Sculptured Object Machining

The features of a sculptured object are represented by a set of section curves. A fast algorithm is presented to calculate cutting depths based on the scallop height using these curves. The calculated cutting depth can be used for tool-path generation. This tool-path generation approach is particularly useful for constant z level contouring and high-speed machining.     

Manufacturability Analysis for a Sculptured Surface Using Visibility Cone Computation

This paper presents a general algorithm to obtain a feasible tool-approach direction for sculptured surface machining based on convex analysis. The visibility cone which represents the aggregate of all visible directions is constructed to describe geometric constraints. Combined with the convex hull computation algorithm, a detailed procedure for computing the visibility cone has been developed. The visibility cone can be used as an effective tool for manufacturability analysis of the sculptured surface when applied to CNC machining tool-path planning. After the visibility cone is acquired, tool orientation can be adjusted to adapt itself to the local geometry of the sculptured surface at each cut contact position. The proposed methodology can be applied to computer-aided planning and programming of cutter-path generation for 5-axis sculptured-surface machining.     

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.     

基于正向杜邦指标线的五坐标侧铣加工

为实现叶轮类零件的多坐标侧铣加工,通过引入正向杜邦指标线,利用鼓锥形刀对自由曲面的五坐标侧铣加工进行研究。针对具有严格凸切削刃的侧铣加工刀具,提出不发生局部干涉的充要条件是切触点处刀具曲面的正向杜邦指标线位于被加工曲面的正向杜邦指标线之内。给出利用鼓锥形刀侧铣加工自由曲面时实施干涉检查的判断准则以及消除干涉的修正方法,推导出具有严格凸切削刃的刀具在给定的残留高度下侧铣加工带宽的计算方法。在此基础上,利用等残留高度法实现鼓锥形刀侧铣加工自由曲面无干涉刀具轨迹的生成。算例表明,在相同残留高度下,鼓锥形刀侧铣较之球头刀加工效率提高37.44%,说明侧铣加工是提高切削效率和加工质量的一种有效途径。     

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。     

Optimal selection of machining direction for three-axis milling of sculptured parts

In the field of free form surface machining, CAM software allows management of various modes of tool-path generation (zig-zag, spiral, z-level, parallel plan, iso-planar, etc.) leaning on the geometry of the surface to be machined. Various machining strategies can be used for the same shape. Nevertheless the choice of a machining strategy remains an expert field. Indeed there are no precise rules to facilitate the necessary parameter choice for tool-path computation from analysis of the numerical model of a part and the quality requirements. The objective of this paper is to provide a method to assist in the choice of the machining direction for parallel plane milling of sculptured parts. The influence of the tool-path on final quality according to the intrinsic geometrical characteristics of the latter (curves, orientation) was studied. Directional beams are introduced and defined from the local surface parameter. Finally, a methodology to optimize machining time while guaranteeing a high level of quality was developed and applied to examples.     

大型水轮机叶片的多轴联动数控加工编程技术

转轮叶片是水轮机能量转换的关键部件，也是最难加工的零件，目前多轴联动数控加工是解决该类大型雕塑曲面零件最有效的加工方法。多轴联动数控加工编程则是实现其高精度和高效率加工的最重要环节。介绍了大型水轮机叶片五轴联动数控加工大型雕塑曲面编程中涉及到的转轮叶片三维造型、刀位轨迹计算、切削仿真、机床运动碰撞仿真、后置变换等关键技术。通过对这些技术的链接和研究，开发实现了大型叶片的多轴联动加工。     

基于多层次细节模型的动态切削力仿真

为了缓解雕刻曲面数控加工过程物理仿真的仿真速度与仿真精度的矛盾,减少仿真的计算量和缩短仿真时间,介绍了雕刻曲面数控加工过程仿真的多层次细节模型和基于该模型的动态切削力的仿真方法。基于雕刻曲面的多层次细节模型的动态切削力的仿真,可以根据工件毛坯不同的几何形状、仿真要求、工艺参数等在曲面上不同的区域和不同的细节层次上进行,为校验和优化数控加工程序提供依据。     

Optimal selection of machining direction for three-axis milling of sculptured parts

In the field of free form surface machining, CAM software allows one to manage various modes of tool-path generation (zig-zag, spiral, z-level, parallel plan, iso-planar, etc.) leaning on the geometry of the surface to be machined. Various machining strategies can be used for the same shape. Nevertheless the choice of a machining strategy remains an expert field. Indeed there are no precise rules to facilitate the necessary parameter choice for tool-path computation from the analysis of the numerical model of a part and the quality requirements. The objective of this paper is to provide a method to assist in the choice of the machining direction for parallel plane milling of sculptured parts. The influence of the tool-path on the final quality according to the intrinsic geometrical characteristics of the latter (curves, orientation) was studied. The directional beams are introduced and defined from the local surface parameter. Finally a methodology to optimize machining time while guaranteeing a high level of quality was developed and applied to examples .     

等残留轨迹规划方法在高速加工中的应用研究

在数控加工中,加工轨迹规划方法直接影响到加工的效率及质量,尤其在高速加工中轨迹规划方法合理的选择关系到加工的成败.本文对等残留轨迹方法与等参数线轨迹规划方法的在高速加工中加工效率和加工后表面残留高度进行了分析比较,探讨了两种方法加工效率和表面质量与自由曲面曲率的关系.结果表明等残留高度法能根据自由曲面状况,不同程度的提高加工效率及表面质量,并与曲面曲率具有较大的相关性.     

基于线锯高效切割的复杂直纹面模型建立及仿真

针对天然石材、人工晶体等材料复杂曲面加工中，初始毛坯与最终产品形状差别较大，粗加工材料去除量大，导致加工效率低、刀具磨耗严重的问题，提出了一种基于线锯加工和点加工协同去除的高效粗坯加工的解决思路。根据线锯加工特点，提出了对最终产品的数字化模型进行分层处理，利用多边形对各层二维外轮廓曲线进行包络，将层与层之间的多边形进行顺序拟合得到相应直纹面模型的建模思路。分析了不同包络多边形边数、连接方式所构建的不同直纹面模型对粗坯加工时间的影响。仿真结果表明，虽然增加多边形的边数或者通过层间旋转可以减小剩余未加工材料体积，但整体粗坯加工时间反而有所增加，从而不利于提高效率。粗坯加工时间可作为综合评价指标来优化构建直纹面模型。     

虚拟制造中基于刀具变形的复杂曲面加工误差预报

复杂曲面加工过程中刀具的弹性变形是产生曲面加工误差的重要原始误差。着重研究了虚拟制造环境下基于球面铣刀弹性变形的曲面加工误差预报模型。研究并建立了球面铣刀加工复杂曲面的切削力模型和刀具弹性变形模型,在此基础上,分析了曲面生成机理,提出了利用曲面变形敏感系数建立刀具弹性变形对法向加工误差的影响关系。利用该模型可以在实际切削加工前对曲面加工误差进行预报,用以进行误差补偿或切削参数优化。最后,以二维半圆形拉伸曲面为例通过切削实验对本文提出的模型进行了验证。     

A unified localization approach for machining allowance optimization of complex curved surfaces

The goal of workpiece localization is of interest to find the optimal Euclidean transformation that aligns the sampled points to the nominal CAD model to ensure sufficient stock allowance during the machining process. In this paper, a unified localization technique is developed for sculptured surface machining. This technique concerns an alignment process to satisfy a user-defined set of constraints for some specific surfaces where the machining allowance is preferentially guaranteed. The mathematical model of the constrained optimization alignment is firstly established, and is efficiently solved by a combination of the multipliers method and the BFGS algorithm to handle the large number of constraints in allowance optimization. To efficiently calculate the Euclidean oriented distance, a novel approach, which combines the robust arithmetic for multivariate Bernstein-form polynomials and Bezier surface segmentation algorithm, is presented based on recursive quadtree decomposition. Two typical sculptured surfaces are used to test the developed algorithm and comparisons between the proposed algorithm and the existing algorithms are given. Experiment results show that the proposed method is appropriate and feasible to distribute the stock allowance for proper sculptured surface machining.     

A five-axis rough machining approach for a centrifugal impeller

A clear trend shows that most products or mechanical components, especially those regarding aerospace applications, are designed to fit the requirements of free form surface features. When a 3-axis computer numerical controlled (CNC) machining centre is used to produce a typical centrifugal impeller, great difficulties, i.e., collisions between the cutting tool and impeller, need to be overcome. In this case, sophisticated five-axis machines have to be utilised. Presently, most commercial computer-aided manufacturing (CAM) systems for five-axis control are lacking generality, and functions for the rough tool-path generation are far less than required. The rough machining is recognised as the most important procedure influencing the machining efficiency and is critical for the success of the following finishing process. However, great difficulties are expected to arise in performing five-axis rough machining. The main objective of the present study is to overcome this problem by combining related machining technology. As a result, CL data based on the geometry model of blade and hub of the impeller are generated. Finally, the CL data is confirmed through software simulation. The results of verification prove the machining methodology and procedure to be successful.     

基于UG的大型水轮机叶片多轴数控加工研究

以UG自动编程软件体系架构为依据,研究大型混流式水轮机叶片多轴数控加工方法。探讨提高叶片加工质量和效率的途径。介绍大型水轮机叶片五轴联动数控加工雕塑曲面编程中涉及到的转轮叶片三维造型、切削仿真、刀具轨迹生成等关键技术。该方案切削力小、加工精度高、成本低,具有一定的参考价值。     

An Operation Planning System for Multi-Axis Milling of Sculptured Surfaces

Multi-axis milling of sculptured surfaces with cylindrical or toroidal cutters has many advantages compared to the use of three-axis milling with ball nose cutters. Surfaces to be machined are often of complex shape and characterised by convex, concave and saddle areas. Today, CAM-systems do not support the user in the selection of the different operations in order to finish the workpiece. This paper describes an operation planning system, which facilitates process planning for the multi-axis machining of sculptured surfaces. The core of the system is surface analysis, which divides the surfaces into regions, each characterised by a preferred milling direction and tool diameter. Further, for each region or set of regions, a drive surface is constructed that is used as the basis for the tool-path calculation. The drive surface approximates to the original workpiece as closely as possible, and the isoparametric lines which will be the tool-path feed direction lie in the preferred milling direction.