Generating Tool Paths for Free-Form Pocket Machining Using z-Buffer-Based Voronoi Diagrams

Voronoi diagrams for closed shapes have many practical applications, ranging from numerical control machining to mesh generation. Curve offsetting based on Voronoi diagrams avoids the topological problems encountered in traditional offsetting algorithms. In this paper, we present a new procedure for generating tool paths using z-buffer-based Voronoi diagrams specially to deal with free-form shaped pockets. Using a z-buffer, a proposed algorithm effectively extracts the topological information on the Voronoi diagram, and generates the geometric information on the Voronoi edges approximately. These Voronoi edges are refined using a numerical algorithm. This method is independent of curve type and is applicable to any pockets with parametric curve boundaries that are twice differentiable.     

采用Voronoi图生成任意形状凹槽的刀具轨迹

为了自动生成任意形状凹槽的刀具轨迹 ,采用Voronoi图为基础的曲线置偏方法 ,避免传统的置偏算法所遇到的拓扑问题 ,提供了一种以Voronoi图为基础的简便有效的算法 ,可用来处理带“岛屿”的任意形状凹槽的刀具轨迹生成。     

Machining Tactics for Interior Corners of Pockets

The cutter–workpiece contact of an end mill fluctuates when cutting along a curvilinear tool path. It increases sharply when reaching a concave corner. Since conventional contour-parallel tool-path cutting does not take this condition into account, it will cause a momentarily rise of cutting resistance in concave corner regions, producing undesirable effects such as machine chatter, gouging and even cutter breakage. This paper proposes to use machining tactics in which a corner-looping tool path is employed to remove progressively the concentrated material at corner regions, thereby restricting the cutting resistance to an acceptable level. Different corner types are categorised and the procedures of generating the proposed machining tactics are described. Experimental results demonstrate that using the proposed machining tactics can significantly control and reduce the cutting resistance fluctuation encountered in concave corner regions. ID="A1"Correspondance and offprint requests to: Dr H. S. Choy, Department of Mechanical Engineering, The University of Hong Kong, Pokfulam Road, Hong Kong. E-mail: hangshan@hkem.com     

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     

NC Machining of Freeform Pockets with Arbitrary Wall Geometry Using a Grid-Based Navigation Approach

A tool path must be determined in an efficient manner to generate NC (numerical control) code for machining. This is particularly important when machining freeform pockets with arbitrary wall geometry on a three-axis CNC machine. In this paper, a grid-based 3D navigation algorithm for generating NC tool-path data for both linear interpolation and a combination of linear and circular interpolation is presented for three-axis CNC milling of general pockets with sculptured bottom surfaces. The pocket surface is discretised by defining a grid and the navigation algorithm plans the tool motion. The grid size and the cutter diameter are chosen so that a predefined tolerance for surface roughness is satisfied. The grid-based navigation algorithm is simulated graphically and verified experimentally.     

面向曲面NC加工刀位计算的基本单元模型

提出一个面向曲面ＮＣ加工刀位计算的曲面离散基本单元模型及其误差控制方法。该模型考虑了对基本单元的逼近精度以及偏置精度的控制。将该模型应用于曲面加工刀位计算能有效地改善现有方法在误差控制,行距计算和干涉检验等方面存在的不足。同时,模型的形式非常简单,可有效简化ＮＣ刀轨的生成计算。     

对称多型腔粗加工刀轨快速生成算法

对具有对称特性的多型腔零件的刀轨规划方法进行了研究，提出了一种新的算法：首先生成其中一个型腔的刀轨，然后通过阵列生成其余刀轨，并对刀轨的进退刀进行处理，从而快速生成完整的、连续的、有序的刀具轨迹。该算法尤其适用于高速加工的刀轨规划，实践表明，可大大提高编程效率．节省加工时间。     

Optimisation of Multiple Tool CNC Rough Machining of a Hemisphere as a Genetic Algorithm Paradigm Application

This work presents the development of a method to achieve optimal roughing of a hemisphere in terms of least machining time and maximum material removal from the original material block. This is considered as a problem formulation case study in the field of genetic algorithm applications – a preamble to more complex and generic geometry. A genetic algorithm is used off-the-shelf as an optimisation tool. Three different process parameters are used to model the problem : the number of scallops, the height of each scallop, and the tools used. Multiple tools are considered, in particular their diameters, maximum depths of cut and maximum feed allowed, as defined in a tool database, whereas the strategy of the tool path on each slice (but not the path details) is taken as known. Fitness functions that can be used independently or combined are the cutting time and the remaining material. The proposed method results in a concentrated result table containing the sequence of the tools employed and the corresponding scallop heights. ID="A1"Correspondance and offprint requests to: Dr G. Vosniakos, Department of Mechanical Engineering, Manufacturing Technology Division, National Technical University of Athens, Iron Polytexneiou, 157 80 Zografou, Athens, Greece. E-mail: vosniak@central.ntua.gr     

超精密加工机床的关键部件技术

论述了亚微米级超精密加工机床的主轴、直线导轨、,进给与微量进给,隔振与恒温等关键元部件的设计原理、实施方案,及其在ＨＣＭ－１超精密加工机床中的应用。     

圆环面刀具五坐标数控加工旋转切触刀位算法

针对圆环面刀具加工开阔自由凹曲面,提出一种新的五坐标旋转切触刀位算法。算法来自于传统多点切触加工的逆向思考,首先确定刀具在工件曲面等距面上局部坐标系中的初始位置,然后优化调整刀具的后跟角和侧偏角,使刀具表面和工件曲面在不发生局部过切的前提下在最小主曲率方向两侧实现两点切触。与传统的多点刀位算法根据两个切触点来计算刀位不同,旋转切触刀位算法通过刀具的后跟角和侧偏角来确定最优刀位,而刀具表面和工件曲面之间的两个切触点则不需要求出。实例计算和加工仿真表明,旋转切触刀位算法不仅能够有效地产生无局部过切的多点刀位,从而不需要额外的局部过切检测及修正过程,而且在相同的加工误差下其产生的加工带宽约为UG算法的两倍,加工效率得到明显提高。     

复杂光学表面的快刀伺服加工特性与路径规划

复杂面形和微结构阵列等类型的光学元件应用范围越来越广,传统的机械加工方法难以满足面形精度和加工效率要求,超精密快刀伺服(Fast tool servo,FTS)是实现这类零件优质高效加工的有效手段.但是在复杂光学表面的快刀伺服加工中,面形的高低起伏将会使刀具和工件的相对位置实时变化,导致加工状态恶化、面形精度下降,甚至...     

汽车底盘支架轴承孔加工刀具研究分析

在机械加工工艺设计中,刀具的选择对加工效果,特别是加工工艺节拍的长短有着决定性的影响作用。而在汽车零部件竞争日益激烈的今天,成本的高低又决定着企业的竞争力和生存能力。通过对刀具的调整,减低汽车底盘支架轴承孔加工工艺节拍。     

Tool Positioning Algorithm Based on Smooth Tool Paths for 5-axis Machining of Sculptured Surfaces

The current research of the 5-axis tool positioning algorithm mainly focuses on searching the local optimal tool position without gouging and interference at a cutter contact(CC) point,while not considering the smoothness and continuity of a whole tool path.When the surface curvature varies significantly,a local abrupt change of tool paths will happen.The abrupt change has a great influence on surface machining quality.In order to keep generated tool paths smooth and continuous,a five-axis tool positioning algorithm based on smooth tool paths is presented.Firstly,the inclination angle,the tilt angle and offset distance of the tool at a CC point are used as design variables,and the machining strip width is used as an objective function,an optimization model of a local tool positioning algorithm is thus established.Then,a vector equation of tool path is derived by using the above optimization model.By analyzing the equation,the main factors affecting the tool path quality are obtained.Finally,a new tool position optimization model is established,and the detailed process of tool position optimization is also given.An experiment is conducted to machine an aircraft turbine blade by using the proposed algorithm on a 5-axis blade grinding machine,and the machined blade surface is measured with a coordinate measuring machine(CMM).Experimental and measured results show that the proposed algorithm can ensure tool paths are smooth and continuous,improve the tool path quality,avoid the local abrupt change of tool paths,and enhance machining quality and machining efficiency of sculptured surfaces.     

一种支持型腔粗加工刀具序列高效优化的刀具筛选方法

型腔加工是现代数控加工中广泛面临的一类加工问题。刀具筛选是型腔粗加工刀具序列优化过程中的一个重要环节。现有的基于几何、设备和工艺等约束的刀具筛选方法并不能判别因刀具之间相互制约而产生的冗余刀具,降低了刀具序列优化的效率。通过对比刀具组合过程中因不同刀具的优势互补而产生的效益增量与因换刀带来的相关效益损失量,建立一种用于判断刀具序列是否有效的分析模型;在此基础上,从刀具序列的组合形态的角度构造并证明一种可以判别部分冗余刀具的规则,并将其与基于几何、设备和工艺等约束的刀具筛选方法相串联,得到一种可支持刀具序列高效优化的刀具筛选方法;研究新方法的实现技术,包括刀具加工能力的估算方法和刀具组合有效性的计算方法;算例结果表明所提方法在去除冗余刀具上的效果明显,能为刀具序列的高效优化提供有效支持。     

五坐标端铣刀加工复杂曲面轨迹的规划

针对复杂曲面加工干涉现象,提出一自动识别的系统,该方法通过计算曲面曲率来判别是否干涉并消除干涉。该算法明显减少了刀具路径生成时间,提高了加工效率。     

类回转体曲面数控加工刀位轨迹规划

针对类回转体曲面高速进给数控加工,提出螺旋线驱动方式下圆环刀具加工轨迹的规划方法。构造螺旋线作为类回转体曲面的导动线,根据曲面上已知接触点轨迹的切线方向估算后续导动点对应的初始接触点。计算初始接触点处圆环刀具的刀心位置,再计算初始刀心位置与后续导动点对应的目标刀位点分别在圆周方向以及轴向的距离差值,利用相邻刀位点与相邻接触点存在的准相似关系,得到接近目标接触点的搜索方向和步长,经过迭代得到目标接触点和刀位点。在分析接触点处曲面曲率和圆环刀曲率的基础上,给出圆环刀加工误差计算方法。将所提出的算法用于鞋楦的五轴数控轨迹规划中,计算结果表明,该算法搜索效率较高,具有理论和实际应用价值,并通过鞋楦的五轴数控加工试验验证了算法的有效性。     

Optimising Tool Positioning for End-Mill Machining of Free-Form Surfaces on 5-Axis Machines for both Semi-Finishing and Finishing

End-milling of free-form surfaces on 5-axis NC machine tools is a complex problem which has been studied by a large number of research scientists. When end-milling non-convex surfaces there is a risk of interference between the tool and the surface. Using a 5-axis NC machine tool enables the tool to be oriented in any spatial direction to access a given point. This means interference can be avoided and the position of the tool can be optimised so as to minimise residual material. Here, a new method is presented for tool positioning in end-milling of free-form surfaces based on evaluating the interference for a set of test points distributed around the circumference of the tip of the tool. Distinction is made between the cases of semi-finishing and finishing which can be performed using a large diameter flat-end tool and a toroidal tool, respectively. Further, all developments are implemented for interactive use in a CAD/CAM software environment.     

一种新的数控加工刀位轨迹排列算法的研究

提出一种基于密切曲率法的刀位轨迹预控优化算法 ,使相邻加工轨迹间的残留高度值都等于预定的精度 (残留高度值 ) ,从而达到最大的切削带宽 ,在保证精度的前提下 ,大大提高了数控加工的效率     

复杂形状区域行切加工刀具轨迹生成

讨论了由任意多段直线、圆弧、自由曲线及其组合构成边界轮廓，且边界内包含多个岛屿的复杂区域加工刀具轨迹计算问题。详细介绍了岛屿分解、边界轮廓刀具干涉处理、加工路线规划及刀具轨迹生成原理与算法。