五轴数控仿真全局干涉检测算法研究

针对五轴数控加工复杂曲面的全局干涉问题,提出了一种实时干涉初步检测算法.该算法基于分层方向包围盒以及八叉树空间简化法,采用改进的分离轴理论,通过比较空间多面体在特定轴上投影的距离关系来判别多面体之间是否相交.应用简化的方向包围盒及八叉树结构,当某一节点发生干涉时,才对其子节点进行进一步处理.该改进算法有效降低了空间复杂度,提高了效率.该算法已在某型号五轴数控加工中心仿真系统的全局干涉检测模块中得到应用,通过实验比较,证明了该算法的可行性.     

加工过程的可视化仿真

讨论了虚拟加工环境建模、工件建模、NC代码解析以及加工过程仿真算法等加工仿真中的关键技术，应用这些技术建立了一个通用虚拟加工原型系统（VMS），为虚拟制造的实现提供了有效的支持基础。     

Investigations on model-based simulation of tool wear with carbide tools in milling operation

This paper deals with tool wear in milling operation using carbide tools. The main purpose of this work is to define a model-based procedure for forecasting tool-wear progression during cutting operation by using machining simulation. Firstly, a multi-axis machining simulation algorithm is proposed based on DEXEL model and local area update method. NC milling machining process simulation software NCToolWearSim is realized by using Visual C++ and OpenGL. The developed process simulation software is used to simulate the cutting process. Secondly, tool-wear simulation algorithm in the machining process is presented with tool-wear model and machining simulation algorithm and is implemented into the machining simulation software NCToolWearSim in order to evaluate the tool wear and to update the tool geometry. The tool-wear value is estimated according to the established tool-wear model from experienced tool-wear data. Thus, tool-wear progression can be visualized in milling operation by using NCToolWearSim. Finally, experimental tests, performed milling integral wheel with carbide tools, were used to calibrate and validate the correctness of tool-wear simulation process based on the tool-wear model.     

Octree-based NC simulation system for optimization of feed rate in milling using instantaneous force model

An octree-based (numerical control) NC simulation (Oct-OAC) system developed for end milling has two major applications: (1) NC verification and (2) optimization of the cutting parameters, viz., spindle speed, N (s^?1), and feed rate, f (ms^?1). Oct-OAC has a geometric modeling module to simulate the geometry of material removal process. Every object in the machining environment such as cutter, instantaneous workpiece, swept volume, etc. is stored as octree, an inexact representation of solid. Using this module, one can predict the geometry of the material removed at any instant of time and update the geometry of the blank subsequently. Optimization of cutting parameters using Oct-OAC is achieved through optimization module using a mechanistic model for computation and prediction of the cutting forces at any instant. The basic input for this module is the geometry of the contact surface between the cutter and workpiece which comes from the geometric modeling module using an octree-based solid modeler. It is through this contact surface that the cutting forces are passed from the workpiece onto the cutter and vice versa. The mechanistic modeling module can predict the instantaneous cutting forces from the instantaneous contact geometry and other process parameters like material combination of cutter–workpiece, parameters defining cutter geometry, and current cutting parameters such as N and f. Using this prediction, it will modify the cutting parameters for maximizing the material removal rate. This way, the mechanistic modeling module does what an adaptive controller will do with the help of force sensing. Therefore, the NC program optimization done using the Oct-OAC system is actually off-line adaptive control.     

截面包络法加工复杂螺旋面的几何仿真算法

以截面包络法数控加工螺旋面为例,给出了一种基于啮合基本定理的点接触包络加工表面的几何仿真算法。通过分析数控加工中刀具与工件的相对进给运动,得到刀触点的啮合方程式,由此可求得加工表面上的刀触点—几何仿真点。几何仿真的计算结果,用于螺杆加工的编程误差分析取得了良好的效果,对于提高数控编程精度具有重要意义     

虚拟加工过程中快速模拟与分析技术研究

虚拟加工的主要任务是预测和改进被加工件的加工精度。提出了一种新的技术方法以实现虚拟加工的工件受力变形快速模拟。这种方法基于可扩充的典型薄壁元素与变形解析算法库，并辅以预置区域和最小壁厚等方法，把加工中工件可能产生较大受力变形而影响尺寸精度的加工位置作为分析的重点，将变形量简化估算与少量的有限元精确分析相结合，可以提高虚拟加工模拟速度，推进虚拟加工技术的实用化。     

A novel machining of multi irregular surface using improved noncircular turning method

The backplane processing is an important part of the manufacture of electronic communication equipment; the current processing of backplane surface, especially the rough machining, is still using milling; and the production efficiency is quite low. This paper presents a new method to turn with a cylinder for the rough machining of multi backplane surfaces, which is based on a conventional horizontal lathe and uses the improved method of noncircular machining. The performance requirements of fast tool servo (FTS) device and control model for the machining of noncircular surface are analyzed firstly; the position following control strategy is used instead of traditional position interpolation, according to the multi backplane surfaces machining technology and control strategy; and a novel algorithm, which is combined UG (Unigraphics NX) software surface fitting with cubic spline curve fitting of multi backplanes’ space, is proposed for computer-aided manufacturing (CAM) software design. Finally, the proposed processing method and CAM model algorithm are proved to be effective through the simulation and actual verifications, the products meet the processing requirements and the processing time of each piece is reduced from 8 to 2 min, and they also greatly improve the production automation and achieve energy saving and emission reduction.     

Research on selection strategy of machining equipment in cloud manufacturing

Cloud manufacturing (CM) is a new type of networked manufacturing model, which is proposed in 2010. Optimization technology is one of the key techniques for CM operation, which are used for the efficient integration of manufacturing resources. In all kinds of manufacturing resources, the machining equipment is one of the most important resources. Using optimization techniques to achieve optimal selection of machining equipment is rarely studied in the CM. In order to handle the optimization selection of machining equipment in CM, comparing with the existing resources optimal configuration, an optimal selection strategy is introduced for the machining equipment in CM. In the selection strategy, first, a multiple objective and binary integer programming model is proposed to describe the optimal selection of machining equipment in CM. Second, after analyzing the mathematical model and the real-world problem of the machining equipment selection in CM, the priority method is adopted to convert the multiple-objective problem into a single-objective problem. Third, an improved particle swarm optimization (IPSO) algorithm based on a novel encoding scheme and fitness function is presented to solve the single-objective mathematical model. Finally, the simulation experiments verify the effectiveness of the IPSO algorithm and show that the selection strategy is more objective and effective to help the client select the machining equipment in the CM than current resources optimization model. This research provides a theoretical support for the development of CM.     

数控车床虚拟制造环境技术研究

提出数控车削特征参数化造型方法，实现含整个数控车削加工环境的全景仿真。基于切屑形成的几何形状及位置建立屑型判别式。基于屑型单体造型特征，利用特征体参数化方法实现加工过程切屑仿真。提出“三瞬心”成形法及“误差集聚法”，可提供车削加工实际成形过程，预测加工误差趋势，为加工质量仿真提供图形可视化支持。     

基于压缩体素模型的球头刀空间扫描体构造新方法及其应用

提出了一种基于压缩体素模型的球头刀空间扫描体构造新方法,将球头刀分解为相应球体部分和圆柱体部分,分别给出了球体和圆柱体空间扫描体构造公式并构造出其表面模型,利用RayCasting方法分别将球体和圆柱体空间扫描体表面模型进行离散,将其分别转化为压缩体素模型,通过布尔并操作生成球头刀空间扫描体压缩体素模型。该方法由于采用三个方向的Dexel模型表示体素模型,其计算机内部存贮空间得到了很大地压缩,并简化了布尔操作和提高了布尔操作速度;通过MarchingCubes方法提取数控加工仿真工件表面模型并进行图形显示,提高了显示质量和显示速度。该方法在《基于压缩Voxel模型的五坐标数控加工仿真系统》中得到了应用并完成了某叶轮的五坐标数控加工仿真,仿真结果三维信息完备,NC编程人员可从任意方向观察、验证仿真结果,克服了现有五坐标数控加工仿真方法和商品化软件系统的不足,该方法是虚拟数控加工的关键技术。     

基于体素有向连通性的深度图像拉伸特征提取

针对深度图像中的拉伸特征,提出一种基于体素连通性和区域生长的提取方法。通过线性八叉树结构建立深度图像数据的体素模型,并改进了体素邻域的搜索算法;利用种子体素特定方向上的连通性进行区域生长;然后对生长点进行判断并提取出拉伸特征数据。文中将该方法应用在液舱深度数据上,并对提取结果进行了讨论。     

Incomplete mesh-based tool path generation for optimum zigzag milling

The majority of mechanical parts are manufactured by milling machines. Hence, geometrically efficient algorithms for tool path generation and physical considerations for better machining productivity with guarantee of machining safety are the most important issues in milling tasks. In this paper, we present an optimized path-generation algorithm for zigzag milling, which is commonly used in the roughing stage as well as in the finishing stage, based on an incomplete two-manifold mesh model, namely, an inexact polyhedron that is widely used in recent commercialized CAM software systems. First of all, a geometrically efficient tool path generation algorithm using an intersection points-graph is introduced. Although the tool path obtained from geometric information has been successful to make a desirable shape, it seldom considers physical process concerns like cutting forces and chatter. In order to cope with these problems, an optimized tool path that maintains constant MRR in order to achieve constant cutting forces and to avoid chatter vibrations at all times is introduced and the result is verified. Additional tool path segments are appended to the basic tool path by using a pixel-based simulation technique. The algorithm was implemented for two-dimensional contiguous end-milling operations with flat end mills and cutting tests were conducted by measuring the spindle current, (which reflect machining situations) to verify the significance of the proposed method.     

神经网络共轭梯度优化算法在激光加工定位中的应用

在应用激光技术加工复杂曲面时,通常以采样点集为插值点来建立曲面函数,然后实现曲面上任意坐标点的精确定位。人工神经网络的BP算法能实现函数插值,但计算精度偏低,往往达不到插值精确要求,造成较大的加工误差。提出人工神经网络的共轭梯度最优化插值新算法,并通过实例仿真,证明了这种曲面精确定位方法的可行性,从而为激光加工的三维精确定位提供了一种良好解决方案。这种方法己经应用在实际中。     

Optimal curvature-smooth transition and efficient feedrate optimization method with axis kinematic limitations for linear toolpath

In industrial areas, the machining performance with linear G01 code is a crucial indicator to evaluate the computer numerical control (CNC) systems and many researchers have presented various methods to deal with the corner tracking issue. However, the axis jerk limitations are not satisfied well and the different axis kinematic limitations are not considered in most researches, which will reduce the machining efficiency and machining quality simultaneously. In this paper, a novel method including trajectory planning, feedrate scheduling, and interpolating is proposed to obtain better machining quality and higher machining efficiency. In trajectory planning, a B-spline curve is utilized to smooth the linear toolpath and obtain a curvature-smooth trajectory, which is third-order geometry continuous. Thereby, a time-optimal method for the geometric continuous trajectory is proposed based on linear programming algorithm in the feedrate scheduling and the bounded multi-constraints, including axis velocity, axis acceleration, axis jerk, and feedrate. Moreover, it can be seen that the proposed method is near Bang-bang control. To reduce the computation time of the optimal numerical method, an efficient method with a look-ahead window around the transition B-spline curve is applied. In the interpolation stage, a novel interpolation method about arc-length is proposed to improve computation efficiency. Finally, simulation and experiment are conducted to show superiorities of the proposed method to the already existing approaches. The results show that the cycling time of the proposed method is reduced by more than 7% than G² method and 20% than G³ method with better contour performance.     

基于OpenInventor的六自由度钻铣机加工仿真研究

针对面向航空装配的六自由度钻铣机,利用0penInventor结合VS2008软件构建其加工仿真系统。以虚拟现实语言VRML为数据接口,从UG和CATIA中分别导入机床本体和加工零件,完成机床的三维运动学仿真。在研究0penInventor现有的挤压函数基础上,结合实际加工过程,给出改进算法,得到多轴加工过程中理想的刀具扫描体。最后利用生成的刀具扫描体完成加工仿真以及加工过程中的碰撞检测。通过验证,系统可以实现六自由度钻铣机的加工仿真,仿真效果真实,沉浸感强。此方法同样适用于任何形式多轴机床的加工仿真。     

球头铣刀铣削球面的表面形貌建模与仿真研究

基于齐次坐标矩阵变换原理和矢量运算法则,建立了工件坐标系下球头铣刀扫掠面的数学模型,基于Z-MAP法设计了球形表面形貌的生成算法,利用该算法对球头铣刀分别采用3D环绕法和放射加工法这两种典型走刀路线加工凸球面,并对加工后的表面形貌进行了仿真,通过分析对比仿真结果,发现3D环绕法更有利于减小表面粗糙度。同时,仿真结果和试验结果具有较高的吻合度,表明该仿真方法是可靠的,可以用于实际生产中球头铣刀铣削球面表面形貌的预测。     

Octree-to-BRep conversion for volumetric NC simulation

User-friendliness such as ease of creation and modification and system-friendliness such as space and time complexities, accuracy etc. are two important criteria for the selection of a solid representation scheme. No single solid representation scheme fully meets all the requirements of user-friendliness and system-friendliness. Hence, any practical CAD/CAM system maintains the geometry of the objects in more than one solid representation scheme simultaneously. Therefore, it is often required to convert one solid representation scheme to the other. The authors have developed a volumetric NC simulation system in which the instantaneous blank is represented as an octree as its space and time complexities are independent of the number of NC blocks. However, since octree does not lend itself readily for operations such as arbitrary transformations, rendered display etc., it is not directly usable for downstream applications such as animated display, verification and optimization. Boundary representation is suitable for these downstream applications. Therefore, it is required to convert octree of the instantaneous blank into BRep. An efficient algorithm for this conversion is presented in this paper. This algorithm essentially splits the octree into three quadtrees that store the geometry along the three principal directions. This algorithm is fast as it involves only tree-traversals.     

Optimum tool path generation for 2.5D direction-parallel milling with incomplete mesh model

Many mechanical parts are manufactured by milling machines. Hence, geometrically efficient algorithms for tool path generation, along with physical considerations for better machining productivity with guaranteed machining safety, are the most important issues in milling. In this paper, an optimized path generation algorithm for direction-parallel milling, a process commonly used in the roughing stage as well as the finishing stage and based on an incomplete 2-manifold mesh model, namely, an inexact polyhedron widely used in recent commercialized CAM software systems, is presented. First of all, a geometrically efficient tool path generation algorithm using an intersection points-graph is introduced. Although the tool paths obtained from geometric information have been successful in forming desired shapes, physical process concerns such as cutting forces and chatters have seldom been considered. In order to cope with these problems, an optimized tool path that maintains a constant MRR for constant cutting forces and avoidance of chatter vibrations, is introduced, and verified experimental results are presented. Additional tool path segments are appended to the basic tool path by means of a pixel-based simulation technique. The algorithm was implemented for two-dimensional contiguous end milling operations with flat end mills, and cutting tests measured the spindle current, which reflects machining characteristics, to verify the proposed method.     

环形刀宽行加工圆弧过渡区域算法的研究

基于广域曲率吻合原则,研究了利用环形刀侧铣加工组合曲面圆弧过渡区域的新方法。首先建立环形刀的几何模型,通过调整刀具姿态角,使刀具表面和工件表面在不发生干涉的条件下实现密切接触。通过迭代判断使下行刀轨的驱动线和当前刀轨在精度范围内搭接,实现刀轨的合理编排。最后,以某航空发动机叶片为例计算了刀轨。结果表明,该算法能够精确地加工出圆弧过渡曲面,刀轨之间的没有明显的残高,加工效率较球头刀提高了5倍。     

Redesigned Surface Based Machining Strategy and Method in Peripheral Milling of Thin-walled Parts

Currently, simultaneously ensuring the machining accuracy and efficiency of thin-walled structures especially high performance parts still remains a challenge. Existing compensating methods are mainly focusing on 3-aixs machining, which sometimes only take one given point as the compensative point at each given cutter location. This paper presents a redesigned surface based machining strategy for peripheral milling of thin-walled parts. Based on an improved cutting force/heat model and finite element method(FEM) simulation environment, a deflection error prediction model, which takes sequence of cutter contact lines as compensation targets, is established. And an iterative algorithm is presented to determine feasible cutter axis positions. The final redesigned surface is subsequently generated by skinning all discrete cutter axis vectors after compensating by using the proposed algorithm. The proposed machining strategy incorporates the thermo-mechanical coupled effect in deflection prediction, and is also validated with flank milling experiment by using five-axis machine tool. At the same time, the deformation error is detected by using three-coordinate measuring machine. Error prediction values and experimental results indicate that they have a good consistency and the proposed approach is able to significantly reduce the dimension error under the same machining conditions compared with conventional methods. The proposed machining strategy has potential in high-efficiency precision machining of thin-walled parts.