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.     

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.     

大型螺旋桨五轴加工中基于方向包围盒层次树的全局干涉碰撞检测

针对大型螺旋桨五轴加工中重叠区存在的全局干涉碰撞，构建了一种基于动态OBB层次树的检测算法：建立螺旋桨和特殊铣刀头的方向包围盒层次树，利用多刚体系统的运动学理论，获得螺旋桨和特殊铣刀头在每个加工位置处包围盒的动态坐标变换矩阵，根据分离轴理论，实现每个加工位置的全局干涉碰撞检测。通过包围盒分组以及运动趋势判断，提高了全局干涉碰撞检测算法的效率。     

典型五轴零件的数控加工工艺分析与编程加工

文中在典型五轴零件的结构分析和工艺分析基础上,基于传统的三轴数控加工工艺,融合前沿的五轴加工策略,使用CAXA制造工程师设计了典型五轴零件的刀路,并完成了五轴零件的数控编程和加工,获得了满足要求的加工效果。     

基于OpenGL的五轴数控铣削仿真

在UG中进行多轴加工后处理时,由于选项设置和机床数据文件配置不当,会导致生成的G代码程序存在错误.为了及时发现程序中的错误,利用OpenGL三维图形接口,在Visual C++开发环境下实现了五轴G代码程序的离线和在线仿真功能,集成到自行开发的等离子熔积铣削复合机床上位机软件中;并利用仿真功能进行了铝合金整体叶轮的铣削加工试验.     

EQUIVALENT NORMAL CURVATURE APPROACH MILLING MODEL OF MACHINING FREEFORM SURFACES

A new milling methodology with the equivalent normal curvature milling model machining freeform surfaces is proposed based on the normal curvature theorems on differential geometry. Moreover, a specialized whirlwind milling tool and a 5-axis CNC horizontal milling machine are introduced. This new milling model can efficiently enlarge the material removal volume at the tip of the whirlwind milling tool and improve the producing capacity. The machining strategy of this model is to regulate the orientation of the whirlwind milling tool relatively to the principal directions of the workpiece surface at the point of contact, so as to create a full match with collision avoidance between the workpiece surface and the symmetric rotational surface of the milling tool. The practical results show that this new milling model is an effective method in machining complex three- dimensional surfaces. This model has a good improvement on finishing machining time and scallop height in machining the freeform surfaces over other milling processes. Some actual examples for manufacturing the freeform surfaces with this new model are given.     

自由曲面五轴加工刀具轨迹规划技术的研究进展

利用五坐标设备进行自由曲面的数控加工是提高加工质量和加工效率的有效途径,自由曲面形状和五坐标机床运动的复杂性导致其刀具轨迹规划技术十分困难。针对自由曲面五坐标端铣加工、侧铣加工以及碰撞干涉分析中的关键技术,综述了近年来自由曲面五坐标数控加工领域刀具轨迹规划技术的研究进展和现状。结合自由曲面数控加工的工程实用性要求,分析了当前研究中存在的不足,指出目前的研究成果在通用性、稳定性和有效性方面尚不能完全满足工程应用,认为自由曲面五坐标数控加工刀具轨迹规划技术的研究应从三维的角度出发,在更为广域的刀具影响空间研究刀具同自由曲面之间的几何啮合关系,同时需要考虑机床的运动学和动力学特性以实现五坐标机床的高速和高效运行。     

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.     

一种带缘头避让的叶片高效螺旋加工方法

针对航空发动机叶片螺旋铣加工中前后缘处刀位点密集、刀轴矢量变化剧烈而导致的过切等问题,本文提出了一种带缘头避让的叶片高效螺旋加工方法。在叶片螺旋加工中,只有叶盆和叶背曲面参与切削,缘头曲面从螺旋加工过程剥离并对其实施单独处理。为实现螺旋加工中缘头部分的避让,本文利用三次非均匀B样条曲线给出了避让曲线的构造方法。切削实验结果表明,本文方法可有效提高航空发动机叶片的加工效率,并能有效保证缘头处的加工质量。     

A 3D curvature gouge detection and elimination method for 5-axis CNC milling of curved surfaces

Based on the concept of Eular-Meusnier Spheres (EMS) that portrays the generic curvature model of surfaces, a new three-dimensional (3D) method for curvature gouge detection and elimination in sculpture surface machining is presented. The new method is superior for presenting one-dimensional (1D) and two-dimensional (2D) approaches for curvature gouge detection and curvature gouge-free machining due to its capability to consider both normal and osculate curvatures of the cutter and machined surfaces and their interactions. The method can be applied to all three types of commonly used milling cutters (end, torus and spherical mills) and all concave curved surfaces. Test results from machining simulations are presented to demonstrate the new method and its advantages. The work forms the foundation for further research on the automated generation of highly efficient and high quality 5-axis CNC tool paths for machining curved surfaces.     

数控展成电解磨削整体叶轮叶片型面的研究

为解决整体叶轮叶片型面的精加工难题 ,进行了五轴联动数控展成电解磨削的基础研究。根据数控展成电解磨削整体叶轮叶片型面这一加工方法的特点 ,在分析了数控展成电解磨床的结构与运动的基础上 ,介绍了经济型多轴数控系统及其联动控制方法 ,建立了电解磨削非平行直纹展成曲面的数学模型 ,开发了五轴联动数控展成电解磨削自动数控编程系统 ,对航空发动机整体叶轮的叶片型面进行了电解磨削的工艺试验。结果表明 ,数控展成电解磨削工艺的加工精度和表面粗糙度可满足整体叶轮的技术要求。     

弯管内表面数控铣削加工方法研究

介绍了依据五轴联动加工原理避免弯管内表面加工干涉和改善切削不均匀的加工方法,进行了实验工艺规划、加工区域划分、数控程序编制等研究。采用球头刀具,调整刀具姿态,使刀具和工件表面的位置角近似不变,在四轴及五轴联动机床上进行了样件的试制。研究结果表明,该铣削加工方法可避免刀具与工件的局部干涉和整体干涉;切削状态稳定;最终表面质量一致性好,粗糙度满足技术要求（Ra=3.2μm）。研究结果为核电主管道以及同类弯管内表面的铣削加工提供了理论和试验依据。     

五轴数控工具磨床热变形控制策略研究

对五轴数控工具磨床进行热变形的控制是提高其加工精度的关键,在指出五轴数控工具磨床的主要热源后,分析了机床热变形对其加工精度的影响,综合误差防止与误差补偿两种方法提出了五轴数控工具磨床热变形控制的策略.     

工作台旋转式五轴加工中扫掠轮廓线的求解

国内外对五轴数控加工中的扫掠轮廓线的研究往往集中于主轴摆动式机床。本文给出了实际生产中应用广泛的工作台旋转式五轴加工中环形刀具上扫掠轮廓线的显式表达式,分析了扫掠轮廓线在刀具曲面上的几何特性。所用的计算方法高效精确,为复杂曲面加工过程的动态模拟和加工误差的控制奠定了数学基础。     

五轴数控机床转动轴误差元素的球杆仪检测方法

提出一种立式高速精密五轴加工中心转动轴C轴误差元素的球杆仪检测方法。建立了影响加工精度较大的C轴4项误差的球杆仪检测模式。通过机床多轴联动使球杆仪完成一圆弧轨迹运动,此过程中,采集球杆仪的杆长变化量,由数学建模及轨迹仿真,结合误差敏感方向分析,最终分离得到各误差元素值。通过对比球杆仪检测误差值与预设误差值,证明球杆仪检测法是一种高效准确的转动轴误差检测方法。     

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。     

螺杆转子的旋风式法曲率包络铣削技术

针对石油工业用大型螺杆钻具转子螺旋曲面的数控铣削加工,提出了一种新的旋风式法曲率包络铣削技术。该技术的核心是在每一走刀行程中,实时调整刀具的轴心线绕接触点工件理论曲面外法线向量转动的角度,使铣刀刀尖圆与理论曲面的切触线具有相同的曲率,对理论曲面形成等法曲率的逼近包络。该铣削技术的表面成形精度高,且铣刀切削刃在曲面上的扫描面积大,能显著提高切削效率。在保持加工精度不变的条件下,可大幅度地减少刀具切削     

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.     

Implementation of the principal-axis method for machining of complex surfaces

In this paper a new strategy for 5-axis machining of complex surfaces is presented. The method uses curvature alignment and matching between the design surface and the cutting tool to improve surface finish and reduce machining time. The method is implemented on two configurations of 5-axis machines, and used to machine a test surface. The results of the tests show a considerable improvement over conventional 3-axis machining.     

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.