五轴加工奇异区域内的刀具路径优化

针对五轴加工在奇异区域内由于旋转轴运动的剧烈变化导致非线性误差过大并对工件、刀具和机床部件造成损害等问题,给出一种奇异区域内加工路径的优化方法。以AC双转台五轴联动数控机床为研究对象,在反向运动学变化中根据正弦、余弦三角函数的周期性对C轴转角进行初次优化;按照加工是否通过奇异点两种情况,采用设定奇异点处的C角值或者修改奇异点附近的刀轴方向两种方法,进一步降低C轴过大转角;以当前加工区间的非线性误差是否超过允许值为判断条件,对仍然不满足精度要求的区间进行递归插值处理。仿真试验和实际加工结果表明,与单纯采用线性插值方法相比,该方法在提高奇异区域内加工精度的同时,有效减少新插入点的数量,从而尽量降低加工速度的损失。     

五轴数控加工奇异点问题研究

研究了五轴数控加工奇异点问题,分析了奇异现象及产生的原因。在对前人工作分析的基础上,提出了在刀轨规划时避免奇异现象的方法。该方法通过监测刀轴与旋转轴的夹角,找出产生奇异的刀位点,并以上一刀位点对当前刀位点进行优化。结果显示机床各运动轴能平缓通过奇异区域,证明该方法切实可行。     

固体火箭发动机药柱整形虚拟轴机床的运动学分析

概述了机床的软件、硬件,计算了该数控机床并联机构的自由度。建立了并联结构机床的反解和正解,计算了机床的雅可比矩阵,并给出了奇异点的条件,为机床的下一步分析做好了准备。     

冗余轴解决五轴加工奇异问题的研究

为解决五轴加工在奇异点附近加工误差较大且易对工件和机床造成冲击的问题,对带有冗余ABC三转轴机床解决CA双摆头型五轴奇异问题进行了研究。建立了机床模型,依此得出了此冗余轴机床的运动关系,并根据加工刀位点特点对刀路进行初步研究。仿真结果表明,与其他解决奇异问题方法相比,该冗余轴机床可以有效克服五轴机床奇异问题,基本消除奇异区域的较大加工误差,并且各轴旋转角度得到了优化,从而使加工效率大大提高。     

平面五杆可控机构运动性能和误差的研究

应用平面五杆机构的雅可比矩阵，分析输出运动的灵巧性。计算雅可比矩阵的条件数，通过对雅可比矩阵的微分，研究机构运动的速度误差。最后基于机械制造的工艺理论，对误差综合问题提出优化目标函数和约束条件。     

零件的五轴加工

采用三维CAD系统,能够设计更为复杂的零件。要加工这类零件的五轴加工程序的编制是很困难的事。但是,随着功能完善和容量强大CAD系统的推广,从设计、制造到切削加工过程就变得容易了。因此,五轴加工中心的应用日益普遍,越来越多的零件采用五轴加工中心进行加工。智能机床方案使生产零件的五轴加工更趋实用。     

日本五轴加工机床的市场在扩大

在日本,生产销售五轴加工机床企业在不断扩大。市场销售五轴加工机床和相关设备的企业共计22个,其中,销售五轴加工机床的企业19个,销售托盘系统和CAM软件等与五轴加工机床相关企业3个。各企业产品销售市场的主要目标,针对飞机零件生产的有15个,其次是模具生产的有9个。也有企业把医疗器械、信息相关产业、光学仪器等小型精密复杂零件加工作为销售的主要目标。     

用途广泛的五轴加工机床

巨浪(Chiron)公司的FZ 12K S五轴加工机床是一种以通用、高速、精密、经济为特点的高柔性、高效能五轴加工中心.该机床还具有达到专业水准的车削功能.     

五轴加工的“舞魅”

五轴加工技术为复杂几何形状工件的加工提供了新的可能性。而采用五轴机床用尽可能短的时间加工出高质量的工件则对控制器提出了特别高的要求。海德汉iTNC530控制器在计算运动路径和控制进给轴运动时都采用了与机床机械和电气性能相适应的方法。     

五轴端铣3D刀补中运动突变的处理

五轴联动数控系统执行端铣3D刀具半径补偿功能时,当刀轴矢量与曲面法矢量非常接近时,相邻插补点处的半径补偿矢量会出现转角过大的现象,从而引起机床直线轴的速度突变。在建立切触点到刀心点再到机床轴的传递关系的基础上,分析半径补偿矢量存在奇异解并引起机床轴运动突变的原因。以平底刀为例给出相应的控制算法。通过旋转优化奇异区域内各插补点处半径补偿矢量的位置,消除相邻半径补偿矢量反向的极限现象;通过插值进一步降低速度突变程度,使各轴速度都降至最大允许值以内。与直接使用相邻插补周期的半径补偿矢量进行赋值的方法相比,该算法通用性更高,对突变的处理效果更好。仿真试验证明了该算法的正确性和有效性。     

Tool-path verification in five-axis machining of sculptured surfaces

This paper presents a systematic scheme for the verification of tool paths in five-axis machining of sculptured surfaces. The criterion of interference detection is developed for a general APT cutter. Tool interference problems which occur across multiple surfaces can be dealt with. In this work, sculptured surfaces are subdivided into discrete sample points for interference detection. The undetected interference error introduced in the surface subdivision process is ensured within a user-specified tolerance. Simulation results of test examples are included to demonstrate the feasibility of the proposed scheme.     

五轴联动叶片加工中心的应用

介绍一款五轴联动叶片加工中心的主要结构及其在叶片加工中的应用,并分析其结构特点,目的是对叶片加工和五轴联动叶片加工中心设计和应用有更好的了解,为今后相关的加工和设计提供借鉴。     

Optimal sequencing of rotation angles for five-axis machining

In this paper, we propose two new algorithms to correct the trajectories of the tool tip of a five-axis milling machine by adjusting the rotation angles in such a way that the kinematics error is reduced. The first algorithm is based on the shortest-path optimization with regards to feasible rotations of the inverse kinematics. The cost function is represented in terms of the total angle variation. We show that such an optimization increases the accuracy of machining and is the most appropriate in the case of a rough cut. The shortest-path procedure applies to either the entire set of trajectories or to only the most inappropriate undercuts inside the workpiece. In the latter case, the algorithm generates an interesting family of solutions characterized by smaller undercuts obtained at the expense of increased overcuts. The second algorithm also exploits the idea of the minimization of the angle variation. It is based on the uniform distribution of the cutter contact points with regards to the rotation angles. The method inserts additional tool positions by numerically finding a grid of points distributed uniformly in the angular space. We prove that the proposed algorithm in the neighborhood of stationary points requires 3–4 times fewer additional points than the conventional scheme. Also, if a maximum angular speed has been exceeded, the controller detects this event and reduces the angular speed. Our correction algorithms minimize the total angle variation, thus, reducing the probability of such an event. Finally, the efficiency of the two algorithms has been verified by a five-axis machine MAHO600E at the CIM Lab of the Asian Institute of Technology of Thailand and HERMLE UWF920H at the CIM Lab of the Kasetsart University of Thailand.     

Planning of tool orientation for five-axis cavity machining

This study examines the feasibility of using open regions and vector fields to determine the appropriate tool orientation in five-axis NC machining of cavity regions with undercut areas. The first step involves slicing the to-be-machined surface into thin layers and then comparing those layers to find the position of the undercut; that is, the position of open region. Two-staged checking is proposed to determine the tool orientation that prevents collision. The two stages are initial tool orientation and collision inspection. An initial tool orientation is obtained by assessing the angle of the vectors determined by data points of contours of the open region and cutter contact (CC) points. If a collision is found in the initial orientation, then the tool orientation must be revised until no obstacles are generated from the collision.     

五轴数控加工程序设计研究

五轴数控加工编程技术复杂和处理信息量大的特点决定了采用手工编程方法难以实现,通常采用UG等自动编程软件对五轴数控加工进行程序编制.从应用UG自动编程软件对造型进行前置和后置处理,得到适合五轴数控机床能够执行的代码指令来研究五轴数控加工程序编制方法,归纳出五轴数控加工编程应遵循的基本原则.     

Prediction and compensation of machining geometric errors of five-axis machining centers with kinematic errors

Kinematic errors due to geometric inaccuracies in five-axis machining centers cause deviations in tool positions and orientation from commanded values, which consequently affect geometric accuracy of the machined surface. As is well known in the machine tool industry, machining of a cone frustum as specified in NAS979 standard is a widely accepted final performance test for five-axis machining centers. A critical issue with this machining test is, however, that the influence of the machine's error sources on the geometric accuracy of the machined cone frustum is not fully understood by machine tool builders and thus it is difficult to find causes of machining errors. To address this issue, this paper presents a simulator of machining geometric errors in five-axis machining by considering the effect of kinematic errors on the three-dimensional interference of the tool and the workpiece. Kinematic errors of a five-axis machining center with tilting rotary table type are first identified by a DBB method. Using an error model of the machining center with identified kinematic errors and considering location and geometry of the workpiece, machining geometric error with respect to the nominal geometry of the workpiece is predicted and evaluated. In an aim to improve geometric accuracy of the machined surface, an error compensation for tool position and orientation is also presented. Finally, as an example, the machining of a cone frustum by using a straight end mill, as described in the standard NAS979, is considered in case studies to experimentally verify the prediction and the compensation of machining geometric errors in five-axis machining.     

Grind-free tool path generation for five-axis surface machining

This paper discusses automatic tool path generation for five-axis filleted end mill finish-surface machining. A new method of automatic five-axis tool path generation is introduced called Grind-Free (GF) tool path generation. GF surfaces result from tool paths that avoid gouging and have scallops that are within the surface profile or waviness tolerances. New algorithms are presented for determining tool forward step and tool path step-over that produce a GF surface. Gouge-free tool paths can be generated directly from CAD data based solely on local and global machining constraints. The proposed methodology for GF tool path generation has been implemented in the C language using the CODE/Robline system. Surfaces were machined on a Boston Digital 505 five-axis milling machine to confirm this method.     

面向五轴加工的等距双NURBS刀具路径同步插补方法

针对由离散刀位点数据生成的五轴加工等距非均匀有理B样条曲线刀具路径中两条非均匀有理B样条曲线参数不同步的问题,建立了一种等距双非均匀有理B样条曲线参数的同步模型,实现等距双非均匀有理B样条曲线刀具路径插补过程中两条非均匀有理B样条曲线参数的同步运动。将三轴非均匀有理B样条曲线插补算法应用于五轴加工等距双非均匀有理B样条曲线刀具路径中的刀具中心点非均匀有理B样条曲线,根据参数同步模型将插补算法同步到刀轴点非均匀有理B样条曲线中。仿真表明,采用该算法能够使刀具始终沿着等距双非均匀有理B样条曲线刀路进行同步插补,参数同步插补精度主要集中在10-6 mm级数上,适用于复杂曲面的五轴加工。     

Variable-period feed interpolation algorithm for high-speed five-axis machining

To alleviate the feed fluctuation and to maintain a smooth feed in conventional five-axis machining, an optimal feed interpolation algorithm (look-ahead) is proposed. However, the problem arises where the segment usually cannot be interpolated exactly in an integer period because of the nonzero joint feed at the junction. To overcome this problem, and to achieve faster machining speed and higher quality parts, this paper presents an optimal feed interpolation algorithm for high-speed, five-axis machining having the function of “look-ahead”, i.e., variable-period linear interpolation algorithm. In real applications, the proposed algorithm results in: (1) constant speed; (2) high machining accuracy. Moreover, in this paper, an efficient method for acceleration and deceleration control is presented to achieve the highest-quality feed profiles and to shorten machining times. The precision and speed of machining is improved greatly. Experimental results verify the effectiveness of the proposed method.     

五轴加工全局干涉检查及其避免

基于坐标系变换原理进行五轴数控加工刀具全局干涉检测,将曲面检测点变换到刀具局部坐标系中,通过判断曲面点是否落到刀具半径范围内来判断是否为干涉点,大大降低了计算量,提高了数控加工效率.对干涉点通过最小二乘法确立最小包容区域以及刀具姿态最优偏转轴及偏转角.为了防止在偏转过程中产生新的干涉,确立了刀具姿态有效区域,使得偏转角度能够避免刀具干涉且在有效区域内.通过实例验证了所提方法的可行性和有效性.