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.     

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.     

自由曲面数控刀位轨迹生成方法的实验研究

依据逆向工程中自由曲面造型理论,结合数控编程中等距面法和参数线法,给出了一种较为简便的数控铣削加工刀位轨迹生成方法.在此基础上用VC开发一个基于Microsoft Windows系统的小型CAM软件,实验验证系统运行稳定.     

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.     

Generating tool-path with smooth posture change for five-axis sculptured surface machining based on cutter’s accessibility map

In five-axis high speed milling, one of the key requirements to ensure the quality of the machined surface is that the tool-path must be smooth, i.e., the cutter posture change from one cutter contact point to the next needs to be minimized. This paper presents a new method for generating five-axis tool-paths with smooth tool motion and high efficiency based on the accessibility map (A-map) of the cutter at a point on the part surface. The cutter’s A-map at a point refers to its posture range in terms of the two rotational angles, within which the cutter does not have any interference with the part and the surrounding objects. By using the A-map at a point, the posture change rates along the possible cutting directions (called the smoothness map or S-map) at the point are estimated. Based on the A-maps and S-maps of all the sampled points of the part surface, the initial tool-path with the smoothest posture change is generated first. Subsequently, the adjacent tool-paths are generated one at a time by considering both path smoothness and machining efficiency. Compared with traditional tool-path generation methods, e.g., iso-planar, the proposed method can generate tool-paths with smaller posture change rate and yet shorter overall path length. The developed techniques can be used to automate five-axis tool-path generation, in particular for high speed machining (finish cut).     

等残留高度法加工椭球面的刀具轨迹算法

鉴于采用等间隔参数法和截面法加工椭球面零件时存在残留量不均匀、表面质量和加工效率不高等缺点,提出采用等残留高度法原理加工椭球面。推导了该方法的加工刀具轨迹算法,并采用VB编程实现了该算法,生成了NC加工程序。加工结果表明,该方法可以满足光学自由曲面的加工精度要求。     

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.     

Engagement Angle Modeling for Multiple-circle Continuous Machining and Its Application in the Pocket Machining

The progressive cutting based on auxiliary paths is an effective machining method for the material accumulating region inside the mould pocket. But the method is commonly based on the radial depth of cut as the control parameter, further more there is no more appropriate adjustment and control approach. The end-users often fail to set the parameter correctly, which leads to excessive tool load in the process of actual machining. In order to make more reasonable control of the machining load and tool-path, an engagement angle modeling method for multiple-circle continuous machining is presented. The distribution mode of multiple circles, dynamic changing process of engagement angle, extreme and average value of engagement angle are carefully considered. Based on the engagement angle model, numerous application techniques for mould pocket machining are presented, involving the calculation of the milling force in multiple-circle continuous machining, and rough and finish machining path planning and load control for the material accumulating region inside the pocket, and other aspects. Simulation and actual machining experiments show that the engagement angle modeling method for multiple-circle continuous machining is correct and reliable, and the related numerous application techniques for pocket machining are feasible and effective. The proposed research contributes to the analysis and control tool load effectively and tool-path planning reasonably for the material accumulating region inside the mould pocket.     

新型5轴混联加工单元的后置处理算法

5轴混联加工单元因其高刚性、快速响应及灵活调姿等优点,已被视为复杂铝合金结构件高效加工的一种替代方案。后置处理是改善此类装备加工能力的重要环节。以一种新型5轴混联加工单元为研究对象,提出一种可提高其加工件表面质量的后置处理算法。首先,基于B样条曲线构造一种双参数曲线插补算法,进行刀尖和刀轴轨迹的光顺处理,并采用参数同步化保证刀尖点与刀轴点的同步插补。其次,通过推导混联加工单元的速度映射模型,构造驱动轴的速度分配算法以确保刀尖进给速度的稳定性;接着,运用混联加工单元的位置逆解与速度分配策略,将其末端的进给速度、光顺处理后的刀尖插补点及刀轴插补点转换成驱动轴的位置与速度运动控制点集,实现混联加工单元刀具轨迹的后置处理;最后,基于前期开发的实验样机开展一组S形试件的切削实验,验证所提后置处理算法的有效性。     

Integrated rough machining methodology for centrifugal impeller manufacturing

In mechanical engineering, most products or components, especially those for aerospace applications, are designed to fit the requirements of free-form surface features. The impeller often required by 5-axis machine operations is a key component of the aerospace industry. When 3-axis CNC machining center is used to manufacture the impeller, great difficulties, i.e., collisions between the cutting tool and impeller, need to be overcome. Presently most commercial CAM systems for 5-axis control lack generality, and functions for the rough tool-path generation are far from sufficient. Although the rough machining is the most important procedure influencing the machining efficiency and the condition for the following finishing process, many difficulties arise in performing 5-axis rough machining. The main objective of the present study is to overcome this problem by integrating the state-of-art machining technology, and consequently effective rough tool-paths are to be generated. This study aims to implement the algorithm of the constant scallop height method to improve tool-path planning of rough machining. As a result CL data based on the geometry model of blade and hub are generated. The CL data are confirmed by comparing them with original CAD model through software simulations and later by machining experiments. The verification results show that the machining methodology and procedure adopted turn out to be a successful case.     

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。     

复杂曲面五坐标数控铣削表面粗糙度预测的关键技术研究

针对CAD/CAM复杂曲面数控加工刀位点曲率与走刀行距关系进行分析,给出了不同刀具路径下走刀行距的计算方法,并且对影响表面粗糙度的因素进行了讨论,该方法可用于对表面粗糙度的一个范围进行预测.并提出一种基于主曲率匹配的等残留高度刀具路径规划改进算法,该方法能够提高加工效率,改善加工表面粗糙度.     

复杂曲面环形刀五轴端铣加工的刀具轨迹规划方法

为了降低复杂曲面类零部件加工的刀具路径,减小刀具路径条数,提高加工效率,提出了一种新的复杂曲面环形刀五轴端铣加工刀具轨迹优化方法。在局部可铣性基础上对刀轴矢量角进行自适应优化,采用新型加工带宽计算方法——等残留高度算法,给出了等残留高度算法的刀具轨迹生成具体步骤。仿真结果表明:与传统等残留高速算法相比,刀具轨迹优化算法的刀具路径更短、条数更少,能够有效提高复杂曲面加工效率。     

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 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.     

基于最小距离法的鞋楦加工无干涉刀具轨迹生成

在刀具及鞋楦三维模型离散数据的基础上,通过曲面的空间变换,将干涉检查转化为基于投影方向的最小距离判断,实现了鞋楦加工的无干涉刀具轨迹生成。对于计算刀位点时计算量大的问题,提出了一种针对鞋楦曲面特征的最小距离点的快速搜索方法。实际加工表明,提出的算法能够较好地提高鞋楦的加工质量和效率。
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基于CQEM的海量测量点集刀位轨迹生成算法研究

提出基于约束二次误差度量(CQEM)的海量测量点集刀位轨迹生成算法。算法以大规模测量点集为待加工曲面,依据刀具大小动态生成刀具邻域的插值网格,以平面截交网格交点作为初始刀触点,对其进行CQEM优化并细分该截交网格,在此基础上生成无干涉刀位轨迹。算法不仅利用网格的动态局部构造节约了大量的空间消耗而且通过刀触点集的COEM优化减小了加工曲面逼近测量点所在曲面的误差。     

基于插铣加工的非等参数刀具轨迹生成方法

针对复杂多曲面通道的多坐标数控粗加工,提出了一种新的刀具轨迹生成算法.该算法以传统的插铣加工方法为基础,提出适合于复杂多曲面通道的新插铣方法;利用曲面参数线,使用B样务曲线正算反算方法,在流道划分的多个截面上做由初始孔到截面轮廓的渐变曲线;通过计算满足残留高度的走刀行距,在各个截面的渐变曲线上提取参数点并拟合出相应曲线,进而得到刀具接触点轨迹.     

基于数控面加工的图形自动编程系统的研究与开发

提出了一种基于面加工的图形自动编程系统，利用自行设计的三维绘图模块进行屏幕绘图，再根据工艺要求，进行刀具轨迹计算，自动生成刀位文件，然后通过后置处理，再进行动态仿真，最后生成数控代码，通过通讯接口传送给机床进行加工。     

Double spiral tool-path generation and linking method for complex pocket machining

Complex pockets with one or more islands have been widely used in industrial and manufacturing production. In this paper, a new double spiral tool-path generation and linking method are proposed for complex pockets with islands which can be used for high-speed machining (HSM) is used. Taking into account the path interval, step length and other processing parameters, precise milling can be achieved without cutter lifting and retraction motions to guarantee machining accuracy and reduce processing time. The method has been implemented in several simulations and validated successfully through the actual machining of a complicated pocket. The results indicate that this method is superior to other existing machining methods, and it can achieve HSM of complicated shaped pockets based on parametric surface.