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.     

<Emphasis Type="Bold">An Integrated Machining Approach for a Centrifugal Impeller</Emphasis>

When a 3-axis CNC machining centre is used for producing an impeller, great difficulties, i.e. collisions between the cutting tool and the impeller, can occur. The blade of an impeller is usually designed with a ruled surface. As the surface is normally twisted in design to achieve the required performance, it can cause overcut and collision problems during machining. The hub of the impeller is usually designed with an irregular surface, and is machined within a narrow and deep groove. The issues – how to satisfy the quality requirements of the part, reduce the machining time, and avoid the occurrence of collision – become an integral problem. This work develops an integrated 5-axis machining module for a centrifugal impeller by combining related machining technologies. As a result, cutter location (CL) data based on the geometric model of blade and hub are generated. Finally, the CL data are confirmed through software simulation. The results of verification show that the machining methodology and procedure adopted are successful.     

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.     

Comparison of 5-Axis and 3-Axis Finish Machining of Hydroforming Die Inserts

The recent growth in hydroforming technology has sparked interest in alternative methods to the current conventional die manufacturing techniques. Hydroforming dies typically have shallow forming channels and open, low curvature surfaces, making them ideally suited for 5-axis machining. To fully appreciate the benefits and to properly demonstrate the capabilities of 5-axis machining for hydroforming dies, a comparison of 5-axis and 3-axis finish machining was done. Two hydroforming die insert sets were machined on a 5-axis machine with a tilt/rotary table. The tool paths for 5-axis machining were generated using custom software based on a modified form of a tool positioning strategy called the principal axis method. The quality of generated 3-axis toolpaths was verified against the machining times of a third set of die inserts, similar to those machined in 5-axis, by an independent industrial mould and die manufacturer using a 3-axis high-speed machine. A comparison of the generated 3-axis paths versus the 5-axis paths for one of the die inserts was made using total finish machining tool path lengths to eliminate differences in machines. The results show that the generated 3-axis tool paths are longer than the 5-axis paths by at least 247%. The paper discusses the different tool-path generation methods along with the geometry of cusp formation and the effect of tool selection. Methods to improve the 3-axis results are also presented.     

基于Z-Buffer理论的三坐标无干涉刀位轨迹的生成

针对当前无干涉刀位轨迹生成算法存在的问题，提出一种基于Z-Buffer理论的用于三坐标加工的无干涉刀位轨迹生成算法。该算法已成功地应用于洗衣机波轮、水轮机叶片等复杂曲面零件的NC加工。实践证明该算法具有可行性，计算方法简单，并且能很好地解决干涉问题，对于在三坐标加工中的刀位轨迹生成具有很高的实用价值。     

整体叶轮五轴数控插铣加工刀位轨迹生成算法研究

为了提高整体叶轮粗加工效率和质量,提出了一种整体叶轮五轴插铣加工刀位轨迹的计算方法。根据整体叶轮的几何特征和插铣特点,定义与叶轮轴线垂直的截平面族,构造截平面与叶片型面交线的单侧包络直线族,作为边界面加工刀位,在边界面刀位之间插值,得到整个流道的插铣加工刀位轨迹。运用UG/Open API开发了整体叶轮插铣加工软件模块,最后通过实例验证了所提出的方法是有效的。     

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.     

Five-axis rough machining for impellers

The most important components used in aerospace, ships, and automobiles are designed with free form surfaces. An impeller is one of the most important components that is difficult to machine because of its twisted blades. Rough machining is recognized as the most crucial procedure influencing machining efficiency and is critical for the finishing process. An integrated rough machining course with detailed algorithms is presented in this paper. An algorithm for determining the minimum distance between two surfaces is applied to estimate the tool size. The space between two blades that will be cleared from the roughcast is divided to generate CC points. The tool axis vector is confirmed based on flank milling using a simple method that could eliminate global interference between the tool and the blades. The result proves that the machining methodology presented in this paper is useful and successful.     

血泵叶轮四轴数控加工方法

采用四轴数控加工的方法,解决了血泵叶轮在钳工加工、数控三轴加工中存在的问题.阐述了UG软件四轴粗、精加工的方法,提供了叶轮类回转零部件的制造方法.对医疗机械回转类零件编程和制造具有一定的参考价值.     

仿人研抛NURBS曲面的五坐标加工轨迹优化

从五坐标铣床的特点和人工分片研抛机理出发，提出了内圆和外圆变焦法，分别用于工件的边界子片和内部子片，可产生类似人工研抛的螺旋线工具轨迹，并模仿人工研抛的肘、腕关节姿态以产生工具轴方向矢量。该方法从减少工具轨迹的陡峭转折入手，产生了较光滑的准螺旋线工具轨迹，可降低被研抛工件的表面粗糙度，适用于五坐标研抛轨迹规划。用MATLAB验证了算法的正确性，给出了仿真的工具接触点轨迹和工具轴方向规划图。实验结果表明，该方法可行。     

整体叶轮鼓形刀五坐标数控加工刀位轨迹生成

研究了用鼓形刀具进行整体叶轮五坐标数控加工的编程技术.根据鼓形刀具的几何特点,设计了一种无干涉的鼓形刀刀位轨迹生成算法,开发出整体叶轮五坐标数控加工程序生成功能模块.通过算例,证明设计的鼓形刀无干涉刀位轨迹算法是切实可行的,与球头刀相比,对于同样的残留高度,可以增大加工行距,使刀轨长度变短,可提高整体叶轮数控加工的效率.     

面向特征的整体叶轮五轴数控加工技术

基于特征制定整体叶轮数控加工工艺,同时兼顾叶轮的工作要求和加工刚度,利用UGNX3.0提供的Interpolate方式规划流道特征的开粗加工和精加工轨迹,Swarf方式规划叶片特征的侧铣加工轨迹.经过仿真验证加工轨迹的合理性,最后使用配有HNC-22M数控系统的五轴加工中心VMC-1100成功加工了整体叶轮.     

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.     

直纹面叶轮插铣加工关键技术

为提高整体叶轮的粗加工效率,弥补目前商用计算机辅助制造软件在五坐标插铣加工能力方面的不足,研究了直纹面叶轮五坐标插铣加工的关键技术。根据直纹面叶片的偏移边界矢量,利用四元数插值方法计算插铣加工的刀轴矢量,提出并推导了五坐标插铣加工的行距和步距计算公式,保证了插铣加工的材料去除率和加工效率。依据上述算法自主开发了整体叶轮五坐标插铣加工专用计算机辅助制造软件,并对该软件生成的刀具轨迹进行了仿真和实际加工验证。结果证明,该方法在一定程度上提高了叶轮零件的粗加工效率。     

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.     

Optimal CNC plunge cutter selection and tool path generation for multi-axis roughing free-form surface impeller channel

Plunge milling is the most effective way for rough machining of impeller parts, but previous research had not considered the optimization of plunge cutter selection and tool path. In this paper, a new method for optimizing the plunge cutter selection and tool path generation in multi-axis plunge milling of free-form surface impeller channel is proposed in order to improve the efficiency in rough machining. Firstly, in the case of fixing a rotation axis at a certain angle in five-axis machine, a mathematical representation is formulated for the geometric model of the cutter interfering the impeller, and an optimization model of the cutter size is established at a cutter contact point on the impeller channel surface, so the largest tool could be determined. Secondly, by analyzing the machine tool movement characteristics, the geometric constraint model of the plunge tool path which relative to the largest tool, step distance, and row space is established, and a tool orientation calculation method of impeller channel machining is given, and then, the plunge tool path and tool orientation could be obtained. Finally, the generated tool path and tool orientation are simulated and verified in practical processing. Simulation and experimental result shows that the rough machining efficiency of the impeller part is improved up to 40 % with this method.     

Tool-path planning for rough machining of a cavity by layer-shape analysis

In the manufacture of parts with sculptured cavities from prismatic stock, rough machining usually constitutes most of the machining time owing to the significant difference between the stock and the part shape. When using 2 1/2-D milling or a contour-map approach to do the rough machining, the appropriate selection of tool-path pattern for each cutting layer can significantly reduce rough machining time and hence increase productivity. In this paper, the commonly used toolpath patterns are summarised. A knowledge-based parametric approach for optimising the toolpath pattern of a given cutting layer is proposed. Then, a novel methodology is developed to calculate an arbitrary polygon area and locate the concave cavities in the polygon. Procedures for cutting-layer-shape analysis and the optimal comprehensive tool-path pattern generation are also built and proposed in this paper. These procedures can not only be applied to sculptured cavity parts with simple islands, but also to parts with arbitrarily-shaped islands. Finally, an example is given to illustrate the reasoning process.     

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.     

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VB BV100五轴联动加工中心后置处理的研究

针对于Pro/E、UG等通用后置处理器生成的NC代码一般与用户使用的数控机床和系统的要求不符。为了提高自动编程效率,充分发挥加工设备优势,以某机电院研发的BV100双转台五轴联动加工中心为例,对于AC回转工作台式五轴联动数控机床结构,系统地推导了其后置处理的相关算法,包括旋转角度的计算、坐标转换以及新刀位点坐标的计算等;通过VB语言,开发了该机床的专用后置处理器,并通过某叶轮的切削加工实验验证了该后置处理器的正确性和实用性。