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     

Determination of Cutter Orientation for Five-Axis Sculptured Surface Machining with a Filleted-End Cutter

In this paper, an accurate and efficient method is proposed for determining filleted-end cutter orientation based on surface analysis. With this method, the surface geometry is first analysed and classified according to its shape. Different kinds of surface shape require different treatments with regard to cutter orientation, so that the local geometry of the filleted-end cutter is matched with that of the surface as closely as possible without gouging the surface in the local region of the cutter contact points. The proposed method has been successfully implemented using the visual C ++ language and the ACIS geometric modeller. Finally, some illustrative examples are given. ID="A1"Correspondance and offprint requests to: Dr T. Chen, CAD Centre, School of Mechanical Science and Engineering, Huazhong University of Science and Technology, Wuhan, Hubei 430074, PR China. E-mail: tc29@chinese.com     

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.     

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。     

An Enhanced Force Model for Sculptured Surface Machining

Abstract

The ball-end milling process is used extensively in machining of sculpture surfaces in automotive, die/mold, and aerospace industries. In planning machining operations, the process planner has to be conservative when selecting machining conditions with respect to metal removal rate in order to avoid cutter chipping and breakage, or over-cut due to excessive cutter deflection. These problems are particularly important for machining of sculptured surfaces where axial and radial depths of cut are abruptly changing. This article presents a mathematical model that is developed to predict the cutting forces during ball-end milling of sculpture surfaces. The model has the ability to calculate the workpiece/cutter intersection domain automatically for a given cutter path, cutter, and workpiece geometries. In addition to predicting the cutting forces, the model determines the surface topography that can be visualized in solid form. Extensive experiments are performed to validate the theoretical model with measured forces. For complex part geometries, the mathematical model predictions were compared with experimental measurements.     

An Enhanced Force Model for Sculptured Surface Machining

The ball-end milling process is used extensively in machining of sculpture surfaces in automotive, die/mold, and aerospace industries. In planning machining operations, the process planner has to be conservative when selecting machining conditions with respect to metal removal rate in order to avoid cutter chipping and breakage, or over-cut due to excessive cutter deflection. These problems are particularly important for machining of sculptured surfaces where axial and radial depths of cut are abruptly changing. This article presents a mathematical model that is developed to predict the cutting forces during ball-end milling of sculpture surfaces. The model has the ability to calculate the workpiece/cutter intersection domain automatically for a given cutter path, cutter, and workpiece geometries. In addition to predicting the cutting forces, the model determines the surface topography that can be visualized in solid form. Extensive experiments are performed to validate the theoretical model with measured forces. For complex part geometries, the mathematical model predictions were compared with experimental measurements.     

Implementation of a Robot System for Sculptured Surface Cutting. Part 2. Finish Machining

Rapid prototyping plays an important role in product development. There are two ways to realise rapid prototyping: one is to develop new prototyping equipment such as stereolithography apparatus (SLA), selective laser sintering (SLS), etc., and the other is to improve existing CNC techniques. In this work, a robot system for rapid prototyping, which is an enhancement of the CNC based method, is presented. A robot arm holding a milling tool is used to machine the prototype of a solid model drawn using a commercial CAD system. In a previous paper, Part 1, a strategy using the robot for rough machining was discussed and then an automatic tool-path generation method using a grid height array was presented. As a verification of the proposed algorithm, a number of prototypes were produced, which demonstrated the feasibility and advantages of the algorithm. In this paper, Part 2, an approach to represent C-space by incorporating possible variations in tooling orientations is proposed. In order to reduce the error on complex surfaces resulting from undercut or overcut operations, a curvature-matching algorithm is also developed. Finally, experimental work using collsion-free planning for manipulator movement and stimulation for the curvature matching algorithm is carried out.     

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.     

Implementation of a Robot System for Sculptured Surface Cutting. Part 1. Rough Machining

Rapid prototyping plays an important role in product development. There are two ways to realise rapid rototyping: one is to develop new prototyping equipment such as stereolithography apparatus (SLA), selective laser sintering (SLS), etc., and the other is to improve existing CNC techniques. In this work, a robot system for rapid prototyping, which is an enhancement of the CNC based method, is presented. A robot arm holding a milling tool is used to machine the prototype of a solid model drawn using a commercial CAD system. In this paper, Part 1, a strategy using the robot for rough machining is discussed and then an automatic tool-path generation method using a grid height array is presented. This method can generate tool paths for rough machining with different tolerances. As a verification of the proposed algorithm, a number of prototypes have been produced, which have demonstrated the feasibility and advantages of the algorithm. In a companion paper, Part 2, an approach to represent C-space by incorporating possible variations in tooling orientations is proposed. In order to reduce error on complex surfaces resulting from undercut or overcut operations, a curvature-matching algorithm is developed. Finally, experimental work using the collision-free planning strategy and simulation for the curvature matching algorithm is carried out.     

一种改进的开卷机加工工艺方法

阐述机械加工工艺在机械加工中的重要性,结合生产设备的实际情况,以开卷机为实例．对其进行工艺改进．改进后的加工工艺方法使其在生产成本、生产周期上都有了很大的提高,是一种值得推广的加工工艺方法。     

环形刀五轴数控自由曲面分片光顺轨迹规划研究

采用曲面分片思想将具有相同或相似曲面信息与工艺特征的复杂曲面分成曲面片族,利用环形刀在各曲片域内建立等残留高度刀具路径规划策略,使刀具姿态随工件曲面的曲率而变化,并完成曲面片间的光顺接合.该方法可从整体上提高复杂曲面的加工精度,改善曲面加工质量.     

大型套筒类零件加工中壁厚均匀的优化算法

讨论了一种内表面为非加工表面 ,外表面为精加工表面的大型套筒类零件壁厚均匀的优化算法 ,以套筒外表面为基准测量套筒的壁厚值 ,间接确定套筒内表面的几何中心轴线 ,建立了确定套筒内表面几何中心轴线位置的最小二乘数学模型 ,根据优化计算得到的规划坐标调整并加工工件 ,不但可以保证套筒壁厚均匀 ,而且可以在加工前准确的判别毛坯件的合格与否 ,计算实例表明该方法简单、可靠 ,能够满足工程需要     

面向数控加工的三角网格法矢量及曲率估算

在面向三角网格曲面的数控加工中,网格曲面的曲率估算精度对数控加工刀具路径设计和加工质量具有重要的影响。针对数控加工需求,提出了一种三角网格曲面中网格节点曲率的精确估算方法。该方法引入网格形状因子,综合考虑三角形的形状和面积两个因素对网格节点法矢量的影响,得到了更为精确的法矢量,从而获得网格节点处更为精确的曲率估算值。此方法能够有效提高三角网格节点曲率估算的精确度,提高了三角网格曲面刀具路径设计中的刀位点计算精度和数控加工精度。     

结构可靠性分析中含交叉项的改进响应面法

针对非线性隐式功能函数的可靠性分析问题,提出一种基于试验设计技术含交叉项的改进响应面法。该方法首先采用基于试验设计的矩估计得到试验点并拟合响应面函数,然后通过计算拟合重要度得出最大贡献试验点并进行补充抽样,选择最佳交叉项,获得了隐式功能函数的更好近似,从而提高了失效概率的计算精度。算例表明该方法应用的广泛性和优越性。     

[刀具及切削工艺]一种基于几何调控的辊轧叶片前后缘加工曲面自适应重建方法

针对航空发动机压气机辊轧叶片前后缘溢料端数控加工问题,提出了一种基于设计曲面几何调控的前后缘加工曲面自适应重建方法。根据自由变形理论以及曲面能量控制原理,建立了具有变形约束能力的自由曲面几何调控模型;利用该模型建立了基于遗传算法求解的辊轧叶片前后缘加工曲面自适应重建策略。该策略通过微量调整叶片设计曲面几何形状,使其在逼近叶身型面测量数据的同时尽可能维持初始几何形状,最终实现了辊轧叶片前后缘加工曲面的自适应重建。实例验证结果表明：利用该方法获得的辊轧叶片前后缘加工曲面可以在保证叶片形状精度的同时实现其与实际叶身的圆滑转接。     

截面包络法加工椭球面的刀具轨迹算法研究

提出加工椭球面的截面包络法,采用VB编程实现了该算法并在此基础上生成NC程序。经实践验证,用截面包络法加工椭球面克服了等间隔参数法加工残留量不均匀、表面质量和加工效率不高等不足之处,能够满足光学自由曲面的加工精度要求。     

智能接口功能模块设计与实现方法研究

在自动化仪表工程施工过程中经常会遇到信号不匹配的问题，常常造成误工或停工，为解决这些问题，作者设计了一种多功能智能接口，使用它能有效地解决许多困难，本文重点介绍了该智能接口电路的工作原理和软件设计方法。     

GB 151中带膨胀节固定式换热器管板计算方法的改进

介绍了修订现行国家标准GB 151—1999《管壳式换热器》时,对带膨胀节的固定式换热器管板设计中应力计算方法的改进意见。文中指出现有计算忽略了膨胀节圆环内部压力引起轴向位移影响,会对某些高参数换热器固定管板的应力分析带来较大误差,并基于板壳理论得到膨胀节圆环内部压力与其两端受轴拉力引起轴向位移之间的相互关系,并结合现行GB 151管板计算模型,提出修订原则和方法。通过有限元计算,证明该方法是可靠的。     

Principle and Simulation of Fixture Configuration Design for Sheet Metal Assembly with Laser Welding, Part 1: Finite-Element Modelling and a Prediction and Correction Method

The quality of the stamping process has a direct effect on laser welded sheet metal assembly. The fixture plays an important role in the satisfactory metal fit-up that laser welding requires. The traditional "3-2-1" locating scheme will no longer suffice for the deformable laser sheet metal assembly process. Because of the often poor stamping quality, a complex die fixture has to be employed to meet the metal fit-up requirements. The die fixture corresponds to an "infinite-2-1" locating scheme where the tooling cost is very high and yet lacks flexibility. This limits the application of laser welding. In this paper, a new locating scheme with both total locating and direct locating for welds is proposed. A total locating scheme is used to locate the overall assembly, and a direct locating scheme is used to locate the weld location, which is critical for ensuring correct metal fit-up. A finite-element model and a prediction and correction method for the direct locator configuration are developed in this paper. A case study is used to show that the proposed method is effective for sheet metal assembly for laser welding.