基于极坐标投影法的五轴加工刀具路径生成法

针对五轴加工中刀具矢量变化较大且易产生干涉的问题,提出了基于极坐标投影法的五轴加工刀具路径生成法。利用微分几何理论计算得自由曲面的法矢、主曲率及其极值,利用极坐标投影法获得刀轴矢量,并求得可能的干涉区域;应用等距偏移曲面法计算出曲面数控精加工刀位数据,并通过控制切削残留高度的方法求得切削行距。结果表明,极坐标投影法可以得到无干涉的五轴加工刀位数据,并可以获得均匀变化的刀轴矢量。     

航空发动机复杂曲面零件数控加工刀具轨迹规划研究分析

整体叶盘等复杂曲面零件是航空发动机中的核心零件,其数控加工技术中的关键是刀具轨迹的规划技术.本文针对当今国内外复杂曲面的数控加工刀具轨迹规划的研究现状和发展进行了分析.主要对复杂曲面数控加工中三种主要刀具的轨迹规划进行了对比分析,并对刀具轨迹规划中的关键技术进行了分析,包括：轨迹拓扑、轨迹参数、干涉避免和刀轴控制的算法理论和适用特点,并对刀具轨迹规划中的曲线插补和刀具组合方向进行了分析和展望,为后续研究提升零件数控加工效率和质量打下了基础.     

基于UG的叶轮流道四轴联动数控加工编程分析

为了控制复杂叶轮结构的加工精度和加工质量,提出一种基于UG的叶轮流道四轴联动数控加工编程方法,以某典型叶轮为加工对象,确定其加工工艺方案,并采用"相对于驱动体"和"插补矢量"结合的刀轴控制方法,从而避免发生复杂小曲面加工的干涉和跳刀现象。通过合理设定"步距"和"切削步长"来降低加工误差,保证加工精度,从而为结构复杂曲面叶轮的精确数控加工提供参考。     

汽轮机叶片圆环形盘铣刀包络铣削方法

为提高汽轮机叶片的加工效率,缩短汽轮机生产周期,在分析汽轮机叶片曲面构成及其加工方法的基础上,提出了采用圆环形盘铣刀包络铣削汽轮机叶片曲面的新方法.利用定向最小距离原理,对圆环形盘铣刀包络加工刀触点和刀具轨迹进行计算,研究了刀触点的计算模型和计算方法.采用该加工方法后,刀具轨迹行程相对于采用球头铣刀包络加工时有明显缩短,在提高叶片加工效率方面作用明显.研究内容为汽轮机叶片专用数控机床和叶片抛光机的设计提供了理论参考.     

钛合金整体闭式叶轮五轴高速加工工艺试验研究

钛合金整体闭式叶轮是一个难于加工的复杂零件。结合工厂钛合金整体闭式叶轮的研制加工过程, 借助MIKRON HSM400U五轴高速机床, 提出一套钛合金整体闭式叶轮的五轴高速加工工艺方案, 充分利用Hyper MILL的五轴加工模块进行刀路设计, 实现了叶轮的五轴高速加工。试验结果表明, 该方案保证了产品的质量, 提高了加工效率。以上分析和实验结果对类似零件的加工工艺的制订具有一定的指导意义和参考价值。       

切触在侧铣加工叶轮直纹面上的应用

提出用侧铣方法加工叶轮曲面的切触理论,按接触条件确定刀具圆柱表面与工件的相对位置,按切触条件确定刀具的相对姿态。介绍了叶轮抛物面叶片表面的加工计算算例,其加工计算方便,加工效率高。相比于端铣加工,可大幅度减小切削余量。     

6-TPS并联机床曲面加工的刀具姿态能力分析

为了研究6-TPS并联机床曲面加工的刀具姿态能力问题,首先对刀具的切触干涉、外缘干涉以及机床支链杆长极限、支链干涉、铰链约束和奇异位形对刀具姿态的制约进行了分析,得到了相应的约束表达式;其次分析了相邻支链同侧铰链点的布位对支链干涉检验计算量的影响,并从降低运算复杂性的角度提出了确定同侧铰链点间的距离公式. 基于得到的约束表达式及距离公式,给出了确定6-TPS并联机床采用平底刀加工曲面时刀具姿态角许用取值域的有效算法. 该算法可用于曲面加工过程中的刀具姿态控制,以避免曲面的过切现象.     

闭式叶轮铣削加工干涉自修正轨迹规划算法

针对目前绝大部分商用CAD/CAM软件在刀具轨迹规划过程中只能检测干涉碰撞的发生、而无法自动生成无干涉碰撞刀具轨迹的问题,提出了一种干涉碰撞自修正算法.该算法提取避让几何体边界,利用配置空间理论把提取的避让几何体边界映射到二维配置空间中,将三维空间中的干涉碰撞问题转化到二维空间中,并利用空间分区二叉树、多边形偏置等算法,解决了自动修正干涉碰撞处刀具姿态的问题.应用该算法生成了闭式叶轮流道的刀具轨迹,从刀具轨迹规划的效果上看,提出的算法确实避免了闭式叶轮刀具轨迹规划过程中干涉碰撞的发生.     

Smoothness-oriented path optimization for robotic milling processes

Industrial robots are increasingly used for five-axis machining operations, where the rotation of the end effector along the toolaxis direction is functionally redundant. This functional redundancy should be carefully resolved when planning the robot path according to the tool path generated by a computer-aided manufacturing(CAM) system. Improper planning of the redundancy may cause drastic variations of the joint motions, which could significantly decrease the machining efficiency as well as the machining accuracy. To tackle this problem, this paper presents a new optimization-based methodology to globally resolve the functional redundancy for the robotic milling process. Firstly, a global performance index concerning the smoothness of the robot path at the joint acceleration level is proposed. By minimizing the smoothness performance index while considering the avoidance of joint limits and the singularity and the constraint of the stiffness performance, the resolution of the redundancy is formulated as a constrained optimization problem. To efficiently solve the problem, the sequential linearization programming method is employed to improve the initial solution provided by the conventional graph-based method. Then, simulations for a given tool path are presented. Compared with the graph-based method, the proposed method can generate a smoother robot path in which a significant reduction of the magnitude of the maximum joint acceleration is obtained, resulting in a smoother tool-tip feedrate profile. Finally, the experiment on the robotic milling system is also presented. The results show that the optimized robot path of the proposed method obtains better surface quality and higher machining efficiency, which verifies the effectiveness of the proposed method.     

基于多体理论的双摆头五轴数控机床RTCP误差研究

为了提高五轴数控机床的加工精度,对双摆头五轴数控机床RTCP(rotation tool center point)模块的误差进行了分析.以多体系统运动学理论为基础,结合刚体六自由度假设理论,建立了误差分析模型.对旋转运动引起的RTCP刀具中心点误差和刀具矢量误差进行了深入分析,推导出了刀具中心点误差和刀具矢量误差公式,并利用实验室开发的刀具轨迹仿真软件,对理想轨迹和实际轨迹进行了对比分析,验证了理论和方法的正确性.     

带冠整体叶轮叶间通道的数控电解加工方法

针对目前用电火花加工带冠整体叶轮叶间通道存在的加工效率问题，在分析和处理带冠整体叶轮型面数据的基础上，提出了电解粗加工与电火花加工相结合的加工方法，并依据计算机仿真对加工轨迹和工具阴极的形状进行了设计和修正，经过初步工艺试验表明，整个加工效率可提高20％。     

Tricept型并联机床曲面加工的刀轨规划

研究了Tricept型并联机床采用平底刀加工曲面时的刀轨规划问题. 首先简要地介绍了机床的结构组成,并对机床的逆运动学及其位姿作业空间进行了分析. 在此基础上,给出了刀具干涉检验及刀具位姿作业空间检验的有效算法. 借助于传统五坐标数控机床曲面加工的等残高刀轨路径生成方法,提出了适用于Tricept型并联机床的刀轨规划算法.     

汽车覆盖件模具的非球头刀宽行加工方法

汽车覆盖件模具型面一般是由大面积平坦面和一定陡立面结合的构成的自由曲面.针对汽车覆盖件模具粗加工及半精加工中球头刀效率低的问题,将非球头刀的宽行加工应用于汽车覆盖件模具粗加工与半精加工过程,在工艺上使用环形刀加工陡立面,高进给铣刀加工平坦面的组合加工方式来代替普通球头刀加工,论述了高进给铣刀在加工平坦类曲面中的优势,提出了平底类刀具铣削平坦凹曲面的最小曲率半径判定原则,并对环形刀和高进给铣刀铣削区域内的刀路轨迹进行优化.最后,在三轴数控机床上进行了实验验证,实验结果表明:宽行加工工艺与球头刀加工相比可提高加工效率44.75%.     

Jerk-limited feedrate scheduling and optimization for five-axis machining using new piecewise linear programming approach

In this paper, a new computation method and an optimization algorithm are presented for feedrate scheduling of five-axis machining in compliance with both machine drive limits and process limits. Five-axis machine tool with its ability of controlling tool orientation to follow the sculptured surface contour has been widely used in modern manufacturing industry. Feedrate scheduling serving as a kernel of CNC control system plays a critical role to ensure the required machining accuracy and reliability for five-axis machining. Due to the nonlinear coupling effects of all involved drive axes and the saturation limit of servo motors, the feedrate scheduling for multi-axis machining has long been recognized and remains as a critical challenge for achieving five-axis machine tools' full capacity and advantage. To solve the nonlinearity nature of the five-axis feedrate scheduling problems, a relaxation mathematical process is presented for relaxing both the drive motors' physical limitations and the kinematic constraints of five-axis tool motions. Based on the primary optimization variable of feedrate, the presented method analytically linearizes the machining-related constraints, in terms of the machines' axis velocities, axis accelerations and axis jerks. The nonlinear multi-constrained feedrate scheduling problem is transformed into a manageable linear programming problem. An optimization algorithm is presented to find the optimal feedrate scheduling solution for the five-axis machining problems. Both computer implementation and laboratorial experiment testing by actual machine cutting were conducted and presented in this paper. The experiment results demonstrate that the proposed method can effectively generate efficient feedrate scheduling for five-axis machining with constraints of the machine tool physical constraints and limits. Compared with other existing numerical methods, the proposed method is able to find an accurate analytical solution for the nonlinear constrained five-axis feedrate scheduling problems without compromising the efficiency of the machining processes.     

基于压缩体素模型的锥形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锥形刀空间扫描体构造新方法,将锥形刀分解为球体和圆锥体部分,分别给出球体和圆锥体空间扫描体构造公式并构造其表面模型,利用R ay Casting方法分别将球体和圆锥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锥形刀空间扫描体压缩体素模型。该模型采用沿X、Y、Z 3个坐标轴方向相互垂直的D exel模型表示,各个D exel模型之间按体素模型大小均匀分布。刀具空间扫描体模型和仿真工件模型之间的布尔运算转化为D exel模型之间的一维布尔运算,简化了布尔操作并提高了操作速度。通过M arch ing Cubes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,编程人员可从空间任意方向观察和验证仿真结果。该方法在《基于压缩体素模型的五坐标数控加工仿真系统》中得到了应用,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。     

Real-time Bezier interpolation satisfying chord error constraint for CNC tool path

G01 code generated by a computer-aided manufacture (CAM) system is the most common form of tool trajectory in computer numerical control (CNC) machining. A tool path composed of short line segments has discontinuous tangency and curvature, generating large fluctuations of feedrate and acceleration, which in turn produces vibration in a machine tool. To obtain a smooth tool path, many methods on tool-path smoothing have been developed. However, the shortcomings in these methods exist when they are employed in a CNC system. It is difficult to simultaneously to guarantee the following requirements of CNC machining: (1) chord error should be rigidly constrained; (2) G01 points should be interpolated; (3) curvature should be continuous (G²); (4) machining should be applicable to spatial cases; (5) real-time performance of computation is required. Based on these various requirements, this study proposes an interpolation scheme using cubic Bezier curves and includes an adjustment strategy to eliminate deficiencies in the tool path. The tool path generated is G², chord-error-constrained, G01-point-interpolated, loop-free, and optimized for both stretch and jerk energy. The method is applicable to 3D cases and involves only simple algebraic computations. Thus, the algorithm can be applied to real-time CNC machining. A simulation is conducted to validate the efficiency of the algorithm. In addition, an experiment reveals its advantage over Hermite interpolation in surface quality and machining efficiency.     

Optimization of cutter-location for 5-axis NC machining freeform surface with a flat-end cutter

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环形刀高度变化刀路轨迹规划方法

为提高汽车覆盖件模具加工效率,将环形刀应用于汽车模具小曲率面的半精及精加工过程.通过对三坐标铣削小曲率面的刀具切触几何分析,确定环形刀最佳进给方向应沿工件高度变化方向,此时可使有效切削带宽达到最大.基于此结论,分别对两类特殊型面进行了刀路轨迹规划.对于单一方向曲率变化面采用垂直截面法,截面方向沿最大主曲率方向,实验表明:垂直截面法与等高线法相比可提高加工效率25%,并且有较好的表面质量;对于圆鼓面采用放射精加工方法,仿真结果表明:此方法与三维偏置方法相比可提高加工效率22.64%,并且避免了周边欠切.     

Global optimization of tool path for five-axis flank milling with a cylindrical cutter

In this paper, optimum positioning of cylindrical cutter for five-axis flank milling of non-developable ruled surface is addressed from the perspective of surface approximation. Based on the developed. interchangeability principle, global optimization of the five-axis tool path is modeled as approximation of the tool envelope surface to the data points on the design surface following the minimum zone criterion recommended by ANSI and ISO standards for tolerance evaluation. By using the signed point-to-surface distance function, tool path plannings for semi-finish and finish millings are formulated as two constrained optimization problems in a unified framework. Based on the second order Taylor approximation of the distance function, a sequential approximation algorithm along with a hierarchical algorithmic structure is developed for the optimization. Numerical examples are presented to confirm the validity of the proposed approach. Supported by the National Natural Science Foundation of China (Grant Nos. 50775147 and 50835004), the National Basic Research Program of China (“973” Project) (Grant No. 2005CB724103), and the Science & Technology Commission of Shanghai Municipality (Grant No. 07JC14028)     

自由曲面砂带磨削轨迹规划与误差控制分析

砂带磨削是提高自由曲面工件型面精度和表面质量的重要手段之一,针对目前自由曲面砂带磨削加工在效率和精度方面存在不足,基于砂带磨削加工的特性,提出了一种基于加工精度控制的自由曲面砂带磨削加工的轨迹规划方法。首先,对实现无曲率干涉的接触轮半径及满足加工允差的接触轮宽度进行了公式推导,结合轮与曲面上加工点主曲率关系,通过双倍体的遗传算法优选出满足自由曲面要求的加工允差,并获取无曲率干涉加工需求的接触轮尺寸参数。然后,基于加工点的主曲率方向实现加工轨迹的自适应宽行距规划,同时采用柔顺处理算法对其点导动规划过程中当曲面存在扭曲时的磨头潜在的大幅往复摆动运动进行了柔顺处理,获得了行距稳定且满足加工时接触轮在磨削点处始终与自由曲面达到最佳贴合效果的磨削轨迹。最后,应用该方法对某航空发动机叶片型面进行轨迹规划,并在数控砂带磨床上进行了加工验证。结果表明：规划的磨削加工轨迹能够使得叶片轮廓截面精度较好地满足加工要求,提高了叶片型面的表面质量和精度,证实了该方法的有效性和实用性。本文提出的轨迹规划方法可科学合理地控制曲面预期加工允差,解决了在自由曲面砂带磨削过程中因接触轮尺寸参数选择不当而引起的局部干涉的计算难题,能够有效提高砂带磨削加工的效率和精度。