机械制造业数控机床几何误差自动控制

为了降低数控机床几何误差,提升加工精度,提出机械制造业数控机床几何误差自动控制方法。通过激光跟踪仪辨识机械制造业数控机床的几何误差,采用快速定位补偿算法与圆弧插补补偿算法相结合的方法补偿数控机床几何误差。利用计算机辅助制造软件生成刀位文件,依据刀位文件生成数控机床加工程序,通过补偿控制器生成数控机床各轴运动的控制指令,数控机床伺服系统接收控制指令后,自动控制数控机床各轴运动,以达到数控机床几何误差自动控制的目的。实验结果表明,采用该方法自动控制数控机床几何误差后,方向与角度的几何误差分别低于0.03 mm与0.1°,实际应用效果较好。     

Developing a postprocessor for three types of five-axis machine tools

This paper presents a postprocessor capable of converting cutter location (CL) data to machine control data for three typical five-axis machine tools to establish an interface between computer-aided manufacturing (CAM) systems and numerically controlled (NC) machines. The analytical equations for NC data are obtained using the homogeneous coordinate transformation matrix and inverse kinematics. In addition, the developed postprocessor method is implemented through a trial-cut on a five-axis machine and verified on the coordinate measurement machine. Experimental results confirmed the effectiveness of the proposed postprocessor method which can be used to integrate the various five-axis machine tools employed in manufacturing systems.     

Modeling an envelope generated by 3D volumetric NC tool motion

Simulation and verification of numerically controlled (NC) manufacturing processes require efficient visualization and analysis of the swept volume generated by the motion of freeform NC tools along complex 3D paths. State-of-the-art methods are either based on approximation techniques (thus lacking the level of accuracy required in NC manufacturing) or are based on analytical solutions with high computational complexity, which are not suitable for real-time applications. In addition, until recently, modeling the self-intersection of a generated volume was thought to be obstructed by seemingly complex mathematics. This paper proposes solving the sweeping problem by using the sweep-envelope differential equation (SEDE). This method has advantages over other methods in terms of low computational complexity and high accuracy. Moreover, this method includes efficient tools for self-intersection detection and modeling. In this paper, we present an enhanced self-intersection algorithm and apply the SEDE algorithm on a ball-end cutter that is swept along non-intersecting and self-intersecting cutter paths.     

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.     

NC METHOD FOR GENERATION OF CONJUGATINGHYPOID GEARS BASED ON NC‘S FLEXIBILITY

It is known that manufacture of hypoid gears is difficult and complicated, the reason lies on the limitation of traditional mechanical machine tools. With the development of NC machine tools, there should be new ways of cutting this kind of gear. Therefore, an idea to generate gears with conjugating tooth surfaces is proposed, based on the "flexibility" characteristic of NC that means various motions, in a sense, can be performed arbitrarily on NC machine tools. Using this method, the direction of the contact path on tooth surfaces can be controlled, and also, theoretically, the generated tooth surfaces can transmit motion at specific transmission ratio curve.     

Tool path optimization in postprocessor of five-axis machine tools

Generally, tool path is generated in a computer-aided manufacturing software considering only the geometry of machining parts. It is converted into numerical control (NC) codes in the postprocessor based on the particular machine kinematics. For some special types of five-axis machine tools, e.g., non-orthogonal five-axis machine tools, the generated NC codes may produce unqualified parts because of the existence of the non-linear error. Conventional commercialized postprocessors usually do not have the function of non-linear error checking. Observing that the tool path is a non-smooth trajectory full of corners and a series of connected line segments, cubic spline interpolation is applied to smooth the tool path at regular points in this study. The cutter tip center points are computed by the cubic spine interpolation, while the cutter posture vectors are obtained via linear interpolation. At the splines (for regular points) and the line segments (feature points), more points are chosen to be converted into NC codes to reduce the non-linear error, which is called data densification. Using the cubic spline to smooth the tool path and the data densification to reduce the non-linear error, a novel tool path optimization algorithm in postprocessor is proposed. Experiments were carried out on an inclined rotary spindle axis non-orthogonal five-axis machine tool. It shows that the proposed tool path optimization provides improved accuracy and surface quality.     

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     

面向并联机床的后置处理方法

为了解决并联机床的后置处理问题,克服现有方法开发的难度和工作量大的缺点,提出了直接转化传统数控机床数控代码,得到并联机床数控代码的方法。对5-虎克铰-移动副-球铰／移动副-转动副-移动副-虎克铰并联机床和刀具双摆动5轴数控机床进行运动学分析,得出并联机床动平台的两个可变化的姿态角具有与刀具双摆动5轴数控机床中两个摆动转角相同的性质;然后直接利用智能制造后置处理软件进行后置处理得到刀具双摆动5轴数控机床的数控程序;再经过适当的变换,得到并联机床的数控程序。曲面加工的计算机模拟结果表明,该方法正确、有效。     

Post-Processor Development for a Six Degree-of-Freedom Parallel-Link Machine Tool

A coordinate system with multiple non-orthogonal axes, defined for a parallel-link machine tool is very different from that for a conventional serial-type machine. Therefore, a special post-processor that can automatically transfer the cutter location data (CL-data) into machine specific NC commands is essential for real machining applications of a parallel-link machine tool. Parallel-link machine tools have been investigated by many previous workers. However, work on the theory of post-processors for this machine tool is very sparse, and most is focused on the orthogonal serial motion. The potential benefits of the parallel-link machine tools make work necessary and urgent on the transformation of the CL-data from a CAD/CAM system into NC commands for special parallel-link machine tools. A six degrees-of-freedom (DOF) parallel-link machine tool constructed as a 6-3-3 mechanism was selected in this work to investigate the theory of post-processing, and the effects of the cutter shapes and the machine construction on it. The parametric representations of different cutter shapes defined by the DIN standard were adopted in the work, increasing the usefulness of the post-processor theory developed. Specific parameters must be modified in the post-processor for different tools applied for real cutting. The tilt angle and yaw angle of the cutter, relative to the normal direction of the cutting surface, is also included in the theory. Finally, the NC code is generated using LabVIEW software, and simulations were performed to investigate the correctness based on several designed tool paths.     

A Precision Tool Model for Concave Cone-End Milling Cutters

The paper presents a comprehensive manufacturing model that can be used to produce a concave cone-end milling (CCEM) cutter on a two-axis NC machine. A CCEM cutter possesses many distinct features that are superior in many cases to the traditional flat-end milling cutter for producing parts with multiple sculptured surfaces. Based upon the given design parameters and criteria, the equation of the helical flute groove and the curve of the cutting edge at the end of the helical flute are derived and presented. By using an inverse problem-solving technique, the sectional profile of the grinding wheel, the tool compensation for machining, and the feedrate of both NC axes are consequently obtained. The design results are compared with the measured data obtained from the NC produced CCEM cutter. The satisfactory comparative verification indicates that the tool design and manufacturing model presented in this paper is theoretically sound and it can be automated easily. The proposed method is widely applicable for the mass production of various high-efficiency milling cutters.     

混联数控机床虚拟加工系统的研究与开发

针对混联机床加工过程中干涉检查、空间刀具半径补偿及编程难等问题,分析了混联机床运动学逆解,提出了一种空间任意面内的刀具半径补偿方法,给出了干涉检查的判断条件。以V is-ual C++为开发环境,应用AutoCAD二次开发工具ObjectARX,建立了由NC代码驱动的混联数控机床加工仿真系统,实现了以真实加工条件为依据的加工过程实时动态模拟,预估加工的过程和结果,为检查NC代码的正确性提供了可靠的依据。     

插齿刀CNC成形磨齿制造技术的研究

提出用CNC成形磨齿技术制造插齿刀的新方法 ,在铲磨插齿刀后刀面时用砂轮的附加螺旋运动和横向补偿运动减少插齿刀的重磨误差。介绍了运动补偿参数的计算软件与计算流程 ,计算实例表明 ,运动补偿技术可将成形磨齿制造的插齿刀的重磨误差降低约 80 %。在实验室进行的渐开线插齿刀磨齿实验的测量结果证实了上述计算结果的正确性。研究结果表明 ,用CNC成形磨齿技术制造插齿刀是可行的 ,这为降低插齿刀制造成本找到了一条新途径     

新型并联机床曲面加工的运动控制与后置处理算法

以6自由度6PM2混联数控机床为研究对象,阐述了其独特结构及特性,指出了混联机床数控加工后置处理中的两个关键问题——刀位数据转换和运动控制算法。给出了后置处理中刀位数据的转换方法和过程,提出了一种基于并联结构和串联结构的新型并联机床即混联机床的运动控制算法。     

Machining and dimensional inspection of spatial cams on 5-axis machine tools

An analytical methodology is developed for NC data generation to produce and measure spatial cams on 5-axis machine tools. The Denavit-Hartenberg notation is used for expressing the ability function of the employed machine tool and in the generation of the desired cutter/measuring-probe location. NC data equations are determined by equating the corresponding elements of the machine tool's ability function to the desired tool location matrices. To validate this methodology, a designed cam was machined and its surfaces were measured by an online measurement system equipped with a touch-trigger probe on a 5-axis machine tool. The resultant cutting speed and material-removal rate during machining are also investigated. This methodology is a general one and is applicable to various spatial cams. It also combines the activities of design, manufacturing, and measurement, thus making the production process more flexible, automatic, and controllable.     

基于计算机数字控制弧齿锥齿轮加工机床的准双曲面齿轮的制造

基于五轴联动数控铣齿机的概念模型,提出一种新的加工准双曲面齿轮主动设计齿面的切齿原理.推导出相应的切齿啮合方程、工件齿面二阶参数展成控制方程和工件齿深控制方程,并给出机床运动函数、刀盘中心速度以及刀尖半径的具体求解方法.在求解过程中,不涉及刀盘中心加速度以及更高阶运动参数的计算,可简化求解过程.使用该切齿原理进行切齿时,可在有效保证齿深的前提下,在切齿加工过程中实现对沿工件齿面设计接触迹线切矢和切齿接触线切矢两个方向上齿面二阶参数的精确控制.同时,该切齿加工理论还可以推广到其他多种复杂点啮合齿面的加工过程中.     

基于五坐标数控圆柱形刀具线接触加工自由曲面的几何学原理

从微分几何学的角度,探讨了在五坐标数控机床上采用圆柱形刀具线接触加工自由曲面的几何学原理,分析了刀具面与被加工曲面二阶密切的条件。通过对二次型半正定的判别,求得了刀具轴线的位置,给出了点邻域内三阶离差的计算公式,证明了圆柱形刀具与被加工曲面的密切条件等价于刀具轴线与被加工曲面的等距面的密切条件,通过实例验证了所提方法的正确性。     

Space cutter radius compensation method for free form surface end milling

The numerical control (NC) program for multi-axis end milling depends on the parameters of the tool, in particular, the radius of the tool. When there is any tool dimensional change due to various reasons, the user needs to re-generate the NC program, which is a time-consuming procedure. In this article, a cutter radius compensation method for multi-axis end milling is proposed. It takes a general NC program as the input, recovers the normal vectors of the machined surface from the NC program via surface reconstruction, and uses these vectors as compensation vectors to realize space cutter radius compensation. The proposed algorithm of shape reconstruction and normal vector computation has a linear complexity in terms of the number of cutter center location points in the NC program. Thus, real-time computation and compensation is possible. Our method also provides a way to restore the machined surface if the CAD model of the machines surface is not accessible. This has other applications, such as interference detection and manufacturing simulation. The compensation algorithm is shown to be very effective in reducing the number of undercut points through simulation with the software VERICUT and with real milling for real-world NC programs.     

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.     

Machining of plate cam profiles on CNC machine tools using a highly integrated part programming system

The concept of NC (Numerical Control) and CNC (Computerised Numerical Control) in machine tools has contributed a great deal to automation and flexibility in manufacturing. In small/medium batch manufacturing, machining of complex contours with conventional machining is neither economical nor accurate. These can be achieved on a CNC machining centre more economically. The can machining system is designed to provide the necessary CNC program blocks for machining the plate cam profiles. The cam profiles can be defined by geometric curves, by follower motion or through a set of points. A promising new concept for approximating the tool path close to the defined cam profile, within the specified tolerance, has been proposed. The CLIP algorithm, presented in this paper, automatically chooses the best of the available interpolations (e.g. linear and circular interpolations) for selecting the intermediate points on the profile to guide the cutter for machining the profile. It provides the minimum number of intermediate points. This module can also be used for machining the elliptical profiles and pockets. The cam module, with little modification, is also used for machining the scroll threads of any pitch.     

基于CAXA数控车间解决方案的DNC通讯系统的应用

数控机床作为数控加工车间的核心和网络化制造系统中最基础和最底层的设备,其联网方案已经成为网络化制造中的重要环节。本文在介绍了CAXA数控车间解决方案的内涵和为企业提供不同层次解决方案的基础上,采用了基于CAXA数控车间的分布式数控（DNC）通讯系统,该系统可用1台计算机同时与多台具有RS232串口的数控机床进行实时数据通信,并实现数控代码的远程传输与接收,为企业网络化制造、高自动化生产奠定良好底层技术基础。系统已在企业成功应用并取得良好效果。