基于临界约束的四轴数控加工刀轴优化方法

针对自由曲面四轴加工中复杂刀具运动导致的干涉和刀具运动不连续等现象,提出一种基于临界约束的刀轴优化方法。基于刀具与工件约束曲面之间的相对位置关系,利用曲线上的点搜索算法确定切触点处的临界刀轴矢量,并计算当前切触点刀轴摆动的可行域;以切削行内所有切触点的刀轴可行域为基础,建立当前切削行内无干涉且相邻刀轴变化最小的刀轴矢量优化模型,实现了自由曲面四轴加工无干涉刀轴矢量的光顺控制。整体叶盘四轴加工试验表明,利用此方法获得的刀轴矢量可以显著改善机床运动的连续性,并避免刀具干涉的产生,提高了加工质量。     

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.     

叶轮数控加工中的干涉检查

针对自由曲面离心叶轮多坐标数控加工中可能出现刀具与叶片干涉的问题,提出了一种干涉检查方法。首先计算出叶片曲面的等距面,等距面的偏移距离为刀具半径,再根据所给定的刀位数据得出刀轴的表达式,然后计算该等距面与刀轴是否有交点,如果有交点则存在干涉,否则计算叶片边界线到刀轴的最小距离,若此距离大于刀具半径则无干涉,否则存在干涉。该方法计算量小,对于叶轮数控加工编程中大量刀位数据的干涉检查,可以显著地节省计算机运算时间。     

Automatic selection of cutter orientation for preventing the collision problem on a five-axis machining

The rotation joints of a five-axis machine tool can offer freedom and appropriate rotation to prevent interference problem between workpiece and the cutter. However, to a five-axis machine tool, it is quite difficult to determine the collision-free cutter orientation. Over this problem, a two-stage cutting tool collision check method is proposed to prevent the collision problem during the cutting process on a five-axis machine tool. The proposed method is capable of determining the collision free ball-end cutter orientation automatically. The first stage is to obtain the tilting and collision-free angle range in the plane that is normal to the tool path obtained. Next, a checking cone generated from this collision-free tool axis range is used for the second collision check. The collision region is formed by the intersection of the neighboring surfaces. This implies a collision-free yaw angle range. The final cutting tool orientation is determined automatically by referring the original spindle axis and the least angular variation from the spindle axis. Finally, the implementation issue is discussed with example.     

并联机床数控加工碰撞干涉检验算法研究

由于并联机床与通用数控机床在结构上差别较大 ,因此在开发与其配套的CAD/CAM系统时 ,考虑到并联机床的结构特点 ,针对哈尔滨工业大学研制的并联机床BJ -30的结构形式 ,提出了并联机床的数控加工碰撞干涉检验算法。该算法较好地解决了刀具过切、少切 ,以及动平台与工件、刀具夹具与工件的碰撞等数控加工中较难解决的问题。仿真结果证明了该算法具有运算速度快、检验效率高等优点     

<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.     

A manufacturing model of helical groove on rotary burr and a universal post processing method

A systematic machining theory and precision method to determine cutter location in a grinding system is presented for rotary burr. First, the helical cutting edge on various kinds of revolving surfaces is built. Then, based on the geometry model of the helical cutting edge, the smooth spiral rake surface with constant normal rake angle and flank surface can been formed during the one-pass grinding process by this method. No interference between the grinding wheel and workpiece happens by the wheel special rotation. The method has the characteristic of detaching the grinding wheel path solution from specified machining conditions. The grinding wheel path is suitable for different NC machine tools through post processing. Meanwhile, a mechanism kinematic model of the NC machine tool is built, and a generalized algorithm for post-processing of multi-axis NC machine tools is presented. This model is applied to arbitrary configuration of NC machine tool, and the motion value for each axis will be generated by the inputting structure and motion parameters of the machine tool. The model, together with the machining method mentioned in this paper, make the calculation and generation of the grinding wheel path simpler and universal. At last, the validity of the method given in the paper is identified by an example of grinding.     

五轴数控加工中旋转轴运动引起的非线性误差分析及控制

五轴数控(Computer numerical control,CNC)加工中,刀具路径规划阶段与实际加工阶段对旋转轴运动采用的插补方式存在差异,其中刀具路径规划阶段是根据零件的几何信息进行插补,而实际加工中则根据机床信息进行插补,这种差异将引起原理性加工误差。针对五轴数控加工中旋转轴的运动,分析采用线性插补方式控制两个旋转轴进行加工时刀具姿态变化引起的原理性误差,进一步研究不同加工情况下由此产生的在垂直于走刀方向的平面内的非线性误差。通过分析旋转轴运动过程中线性插补引起的刀轴偏差角,证明刀具在相邻两刀位点运动过程的中间时刻处刀轴偏差角取得最大值,并得到由该最大值的显式表达式,在此基础上分析最大偏差角的影响因素。提出通过限制相邻两刀位点间刀轴夹角来控制此非线性误差的方法,并给出实例验证。     

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。     

A comprehensive approach to determining minimum cutter lengths for five-axis milling

Interference detection and avoidance by the shortest cutter for the five-axis milling machining is a critical task. Short tool length increases the rigidity and chatter stability of the cutter. In this research, a new and efficient method of interference detection and avoidance by the shortest cutter is developed. For the specific five-axis machine configuration, first possible candidate parts for the collision are found, which are complete cutting system (spindle, tool holder, and cutter), the work in process model, and the fixture. Spindle, tool holder, and tool are represented by the solid geometry identity of the cylinder, truncated cone, and cylinder, respectively, with the length and diameter as parameters. The surfaces of the work in process model and the fixture model are represented as the point cloud data of the suitable density. The Kd-tree data structure is employed on point cloud data which gives an efficient searching of the potential candidate points for the interference detection with the complete cutting system. All existing methods are able to detect the collision, but they are not capable to remove it with the optimum cutter length. The proposed algorithm has not only the capability of collision detection; it can also remove the collision with the optimum tool length. Other scope of the proposed algorithm is the selection of the tool holder to minimize the overhang tool length.     

用加工中心进行多面体加工时零点的设置及计算

卧式加工中心是具有X、Y、Z和工作台旋转功能的四轴联动数控机床,具有自动换刀功能,一次装夹可进行4个工作面的多道工序的加工,非常适合进行各种箱体的加工。在进行箱体加工程序的编制时,工件各个侧面可以设置不同的编程原点,但在加工时,这些编程原点必须通过对刀校零来转化为机床可以识别的位置数据。本文给出了一种工件各个侧面编程原点在对刀校零时的计算方法,采用这种方法,可以避免对刀时的重复误差,提高工件的加工精度。     

Effect of the cutter parameters and machining parameters on the interference in gear slicing

Current researches have not yet found the effect law of the cutter parameters and machining parameters on the interference in gear slicing, the interference between the cutter and machined gear often happens because the appropriate cutter parameters and machining parameters cannot be set, which reduces the gear machining accuracy. The relative position between the major flank face and edge-sweeping surface, distribution law of the interference area in forming process of edge-sweeping surface, and effect law of relative positions among edge-sweeping surfaces on the interference are studied by graphical analysis. The effect law of the cutter parameters and machining parameters on the interference is found. The effect law shows that the interference in gear slicing can be controlled when the relief angle measured on the top edge and feed of every rotation are chosen respectively larger than 9~ and smaller than 0.15 mrn/r. An internal helical gear is sliced with the spur slice cutter and the cutter parameters and machining parameters are set based on above the effect law. The machined gear is measured in Gear Measuring Center and the detection result shows that the comprehensive accuracy reaches GB/T Class 7, where some reach GB/T Class 6. The result can meet the gear machining accuracy requirement and shows that the effect law found is valid. The problem of the interference in gear slicing is solved and the gear machining accuracy can be improved.     

基于空间分层索引模型的数控加工碰撞检测法

文章提出了一种基于微机的用于实现数控加工碰撞检测的新方法。该方法的基本思路是：建立机床最大加工范围的分层空间索引模型；在各层内，将刀具截面收缩为刀轴上一点，同时相应放大碰撞检测另一方的截面，使两物体之间的三维碰撞问题转化成判断二维平面内一点与一封闭轮廓曲线相对位置的问题。文中举例说明了该方法在ＮＣ验证系统中的应用。     

A postprocessor for table-tilting type five-axis machine tool based on generalized kinematics with variable feedrate implementation

Improvements in the machine tool and the machining process technologies increased the need for generic postprocessors in order to exploit the capabilities of the machine tools. Contrary to conventional machining approach, next-generation machining technologies such as force-based feedrate scheduling and toolpath optimization requires the implementation of the variable feedrate during toolpath which constitutes the aim of this article. Therefore, this paper introduces a postprocessor for table-tilting type five-axis machine tool based on generalized kinematics with variable feedrate implementation. Furthermore, a practical yet effective method for avoiding kinematic singularities by spherical interpolation and NC data correction is presented as well. Proposed approach is validated for various five-axis machine tools with different kinematic configurations via virtual machine simulation module. Results of the verification tests show that presented postprocessing approach can accurately convert the cutter location information into NC codes and it is demonstrated that integrated virtual simulation module can simulate toolpaths with large number of blocks.     

整体式叶轮的三维造型及数控加工

整体式叶轮的加工应在多轴数控加工中心上进行,并借助CAD/CAM软件和数控加工仿真软件,进行三维造型、自动编程和数控仿真加工.应用CAXA制造工程师和VERICUT软件,对整体式叶轮进行三维造型、自动编程和仿真校验,可在实际数控加工该零件之前,及时检查出多轴数控加工程序中出现的刀具干涉与碰撞等问题;对多轴数控加工程序的不足进行调整和修改,可提高多轴数控加工中NC程序的准确性和可靠性;协助工艺员编制出准确和合理的数控加工工艺,可保证整体式叶轮数控加工的高效率、高质量和高精度.     

Geometric equation and machining method for the sidewall of a piston

Engine pistons are generally cut with a copy machine or a CNC machine. In recent years, CNC machining has become more popular due to the necessity for increased productivity and accuracy in piston machining. CL data are essential for CNC machining, and such data are usually generated from a 3D CAD model. When using a 3D CAD model, the intersection curves between the surfaces and the cross-sectional plane must be calculated, which is both time-consuming and imprecise. In this paper, a geometric equation for the sidewall of a piston is proposed as a solution to this problem. The geometry consists of an ellipse, recesses, eccentricities, and an offset. The equation for the sidewall of a piston is expressed in terms of the distance from the center. This equation makes it possible to calculate CL data very quickly, and facilitates the compensation of tracking error. A specialized four-axis CNC lathe, suitable for machining the sidewall of a piston, is also introduced. The proposed method has been tested by actual turning using this four-axis lathe. The results demonstrate the practicality of the method in the manufacturing of pistons.     

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。     

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。     

基于敏感度分析的机床关键性几何误差源识别方法

零部件几何误差耦合而成的机床空间误差是影响其加工精度的主要原因,如何确定各零部件几何误差对加工精度的影响程度从而经济合理地分配机床零部件的几何精度是目前机床设计所面临的一个难题。基于多体系统理论,在敏感度分析的基础上提出一种识别关键性几何误差源参数的新方法。以一台四轴精密卧式加工中心为例,基于多体系统理论构建加工中心的精度模型,并利用矩阵微分法建立四轴数控机床误差敏感度分析的数学模型,通过计算与分析误差敏感度系数,最终识别出影响机床加工精度的关键性几何误差。计算和试验分析表明,该方法可以有效地识别出对机床综合空间误差影响较大的主要零部件几何误差因素,从而为合理经济地提高机床的精度提供重要的理论依据。     

复杂曲面加工过程中铣刀在线监测方法

在验证了铣削力与刀柄摆动电涡流位移信号之间存在线性关系的基础上,以机床主轴端部x,y方向的加速度信号二次频域积分结果作为刀柄摆动位移信号,提取积分位移信号的基频及其谐波信号作为监测信号,解决了电涡流位移传感器安装不便的问题,同时有效去除了干扰信号的影响。利用时域同步平均(time synchronous averaging,简称TSA)计算监测信号的一阶和二阶累积量,结合时域指标方差、偏斜度、峭度、绝对均值及有效值定量刻画累积量波形,通过设定阈值实现状态预警,较好地解决了复杂曲面加工过程中铣刀状态在线监测与预警的难题。