Enhanced virtual machining for sculptured surfaces by integrating machine tool error models into NC machining simulation

Sculptured surface machining is a time-consuming and costly process. It requires simultaneously controlled motion of the machine axes. However, positioning inaccuracies or errors exist in machine tools. The combination of error motions of the machine axes will result in a complicated pattern of part geometry errors. In order to quantitatively predict these part geometry errors, a new application framework ‘enhanced virtual machining’ is developed. It integrates machine tool error models into NC machining simulation. The ideal cutter path in the NC program for surface machining is discretized into sub-paths. For each interpolated cutter location, the machine geometric errors are predicted from the machine tool error model. Both the solid modeling approach and the surface modeling approach are used to translate machine geometric errors into part geometry errors for sculptured surface machining. The solid modeling approach obtains the final part geometry by subtracting the tool swept volume from the stock geometric model. The surface modeling approach approximates the actual cutter contact points by calculating the cutting tool motion and geometry. The simulation results show that the machine tool error model can be effectively integrated into sculptured surface machining to predict part geometry errors before the real cutting begins.     

Optimized tool path generation based on dynamic programming for five-axis flank milling of rule surface

This paper presents a computation scheme that generates optimized tool path for five-axis flank milling of ruled surface. Tool path planning is transformed into a matching problem between two point sets in 3D space, sampled from the boundary curves of the machined surface. Each connection in the matching corresponds to a possible tool position. Dynamic programming techniques are applied to obtain the optimal combination of tool positions with the objective function as machining error. The error estimation considers both the deviation induced by the cutter at discrete positions and the one between them. The path planning problem is thus solved in a systematic manner by formulizing it as a mathematical programming task. In addition, the scheme incorporates several optimization parameters that allow generating new patterns of tool motion. Implementation results obtained from simulation and experiment indicate that our method produces better machining quality. This work provides a concise but effective approach for machining error control in five-axis flank milling.     

一种立方体监测网络的声发射源和微震源解析定位方法(英文)

通过选取合理的坐标原点及传感器位置简化声发射源定位方程, 得到声发射源或微震源三维定位方法的解析解。算例研究表明,对于传感器阵列内、外的声发射源事件, 解析方法定位结果完全与实际坐标一致;对于传感器阵列内的声发射源事件,传统方法略有误差,一般为 0.010.03m, 而对于传感器阵列外的微震源, 传统时差定位方法的定位误差很大,最大的达到 1080986 m;采用横截面为 100mm×98mm、长度为350mm 的花岗岩试样, 进行 5 次断铅定位实验,分别用传统方法和解析方法进行定位,结果发现在监测网络外的4个声发射事件, 解析定位的误差亦小于传统方法的定位误差。可见解析定位精度较传统方法有明显提高,最高可提高 17.61mm;利用解析解定位, 无需确定拟合初值和拟合迭代算法, 仅通过简单的四则运算即可定位,用常规的计算器或Microsoft Excel 即可求解。     

厚壁压力容器声发射技术声源定位误差分析

声发射技术（AE）已经被广泛应用到压力容器、压力管道等检验中。声源定位在整个声发射检验与评定结果过程中起重要作用,目前这方面的研究热点是如何提高定位精度。声发射技术通常采用时差定位法来检测压力容器和压力管道的缺陷,通过检测声波到达不同传感器的时间来确定声源位置。对于厚壁压力容器来说,若声源位于容器的内表面或内部,显然容器壁厚会对声源的精确定位产生一定的影响。针对此问题,详细推导并得出厚壁压力容器中声发射检测的定位误差的解析解,分析和讨论了声源定位误差的变化规律。分析结果表明,定位误差的试验值和理论分析符合良好,计算数据与试验值之间的最大误差为7．12％。当容器壁厚小于600mm的情况下,建议实际声发射检测中对声源位置200nm以内区域采用其他常规无损检测方法进行复验以确定实际声源位置。     

Runout effects in milling: Surface finish, surface location error, and stability

This paper investigates the effect of milling cutter teeth runout on surface topography, surface location error, and stability in end milling. Runout remains an important issue in machining because commercially-available cutter bodies often exhibit significant variation in the teeth/insert radial locations; therefore, the chip load on the individual cutting teeth varies periodically. This varying chip load influences the machining process and can lead to premature failure of the cutting edges. The effect of runout on cutting force and surface finish for proportional and non-proportional tooth spacing is isolated here by completing experiments on a precision milling machine with 0.1 μm positioning repeatability and 0.02 μm spindle error motion. Experimental tests are completed with different amounts of radial runout and the results are compared with a comprehensive time-domain simulation. After verification, the simulation is used to explore the relationships between runout, surface finish, stability, and surface location error. A new instability that occurs when harmonics of the runout frequency coincide with the dominant system natural frequency is identified.     

Tool deflection and geometrical error compensation by tool path modification

Accuracy of CNC machined components is affected by a combination of error sources such as tool deflection, geometrical deviations of moving axis and thermal distortions of machine tool structures. Some of these errors can be decreased by controlling the machining process and environmental parameters. However other errors like tool deflection and geometrical errors that have a big portion of total error need more sophisticated solutions. Conventional error reduction methods are considered as low efficiency and human dependent methods. Most of recently developed solutions cannot fulfill workshop needs and are limited to research papers. In the present study, machining code modification strategy has been considered as an applicable and effective solution to enhance precise machined components. Appropriate tool deflection estimation model as well as geometrical error analyzing methods have been selected and complementary algorithms for compensation of these errors have been developed. Metal cutting process has been modeled in a 3D simulation environment and implemented in force/deflection calculations. A software has been developed to generate compensated tool path NC program by tracing the initial tool path and compensating deflection/geometry deviations. The new procedure developed in the present work has been validated by machining Spline contours. The results show that using the new method, accuracy of machined features can be improved by about 8-10 times in a single pass.     

Approximating circular arcs by Bézier curves and its application to modelling tooling for FE forming simulations

When constructing a rigid tool surface with fillets using triangular Bézier surface patches for an FE forming simulation, it is difficult to determine the number of segments required to accurately model a blend arc. This paper presents a combined numerical and analytical method to investigate the error of approximating circular arcs using cubic Bézier curve segments. It is established that there is a linear variation of the error with respect to the Tangent Magnitude Parameter (TMP) in certain regions, and an approximate linear variation of the error against the number of curve segments in log–log scales. In addition, the location of the maximum error and its variation with respect to the TMP are illustrated and analysed. The results obtained are applied to the creation of rigid tool surfaces for FE forming simulations. Two FE analyses are carried out: one to simulate the process of superplastically forming a 3D rectangular box with fillet surfaces, and the other to wrap a decorative pattern onto an axisymmetric ceramic pot.     

Two efficient iterative algorithms for error prediction in peripheral milling of thin-walled workpieces considering the in-cutting chip

Due to the deflection of tool and workpiece induced by cutting force, there is a high complexity associated with the prediction of surface form errors in peripheral milling of thin-walled workpieces. Based on the systematic study of in-cutting chip, this paper proposes a new efficient iterative algorithm named flexible iterative algorithm (FIAL)， which is suitable for surface form errors prediction in peripheral milling of low rigid thin-walled workpiece. In FIAL, an iterative scheme for calculations of tool/workpiece (TW) deflections are developed by considering the former convergence cutting position, and in the scheme a new important variable Δ is proposed for the calculation of radial cutting depth which never been considered before. Based on FIAL and the analytical study of in-cutting chip, a double iterative algorithm (DIAL) is brought forwarded to calculate the positions and magnitude of the maximum surface form errors, which always take the peak point include in each iterative step. Comparisons of the form errors and cutting forces obtained numerically and experimentally confirm the validity of the proposed algorithms and simulation procedure. The experimental and analytical results have shown that FIAL is faster in the iteration convergent speed and more accurate than the rigid iterative algorithm in surface form errors prediction, and DIAL is proved to be valid in the maximum errors prediction.     

Relocation method of microseismic source in deep mines

A new method, named relocation, was proposed to reduce the impact of sensor errors systematically, especially when available data of sensors are abundant. The procedure includes evaluating the reliability of every sensors datum, processing the initial location by the credible data, and selecting a set of equations with optimal noise tolerance according to the relative relationship between the initial location and sensors location, then calculating the final location by k-mean voting. The results obtained in this research include comparing traditional location method with the presented method in both simulation and field experiment. In the field experiment, the location error of relocation method reduced 41.8% compared with traditional location method. The results suggested that relocation method can improve the fault-tolerant performance significantly.     

Acoustic emission source location considering refraction in layered media with cylindrical surface

To solve the problem that the existing acoustic emission (AE) source location algorithms cannot always obtain accurate results for multilayer cylindrical media, a new acoustic emission source location method considering refraction was proposed. AE source coordinates were solved by the complex method. Pencil-lead-break experiments were used to verify this method. The absolute distance errors of location results are less than 3 mm, much less than those by the traditional method. The numerical experiments were used to further analyze factors that affect location accuracy. The results of numerical experiments show that the location accuracy of the proposed method is not affected by the ratio of wave velocities but affected by the measurement accuracy of wave velocity. These results show that new method can obtain accurate AE source location in the two-layered cylindrical surface media such as the triaxial compression test.     

基于数控车削加工的刀尖圆弧半径补偿误差研究

针对数控车削复杂圆弧面零件时产生的形状误差问题,从单一象限圆弧面的刀尖圆弧半径补偿原理出发,分析出假想刀尖方位代码不一致是导致复杂圆弧车削时出现形状误差的原因,并在此基础上提出3种解决方法。     

Time domain simulation of torsional–axial vibrations in drilling

A time domain model of the torsional–axial chatter vibrations in drilling is presented. The model considers the exact kinematics of rigid body, and coupled torsional and axial vibrations of the drill. The tool is modeled as a pretwisted beam that exhibits axial and torsional deflections due to torque and thrust loading. A mechanistic cutting force model is used to accurately predict the cutting torque and thrust as a function of feedrate, radial depth of cut, and drill geometry. The drill rotates and feeds axially into the workpiece while the structural vibrations are excited by the cutting torque and thrust. The location of the drill edge is predicted using the kinematics model, and the generated surface is digitized at discrete time intervals. The distribution of chip thickness, which is affected by both rigid body motion and structural vibrations, is evaluated by subtracting the presently generated surface from the previous one. The model considers nonlinearities in cutting coefficients, tool jumping out of cut and overlapping of multiple regeneration waves. Force, torque, power and dimensional form errors left on the surface are predicted using the dynamic chip thickness obtained from the exact kinematics model. The stability of the drilling process is also evaluated using the time domain simulation model, and compared with extensive experiments. This paper provides details of the mathematical model, experimental verification and simulation capabilities. Although the surface finish from unstable cutting can be predicted realistically, the actual drilling stability cannot be determined without including process damping.     

Modelling of the stability of variable helix end mills

Chatter in milling is still the main obstacle in achieving high-performance machining operations in industry. In this paper, an analytical model is presented to predict the chatter stability of the variable helix end mills. Owing to the lack of accurate and rapid modelling, variable helix tools are used simply on a trial and error basis, in the hope that they will improve the stability of the process. This work provides a comparative study of the performance of variable helix and variable pitch end mills. Time domain chatter recognition techniques and analytical models are explored and tested against experimental results. For the experimental validation, aluminium test pieces were used to enable a broad range of spindle speeds to be covered. The linearity of the machine tool dynamics is explored through validation of standard stability lobes. A comparison of the predicted and observed performance of variable helix against constant helix, variable pitch end mills are presented.The stability lobes are validated for each of the variable helix, variable pitch and standard tools. The analytical model assumes the variable helix tools to behave as variable pitch tools, calculating the average pitch angle for each flute. This approximation is proven to be accurate for some of the cases. For certain combinations of pitch and helix angle greatly enhanced stability is demonstrated empirically with up to a 20-fold increase in depth of cut for the variable helix over the equivalent variable pitch tool. This enhanced stability is neither predicted by the analytical nor time domain solutions. The time domain chatter recognition criterion is investigated and found to have little influence on the predicted stability plots. It is concluded that the enhanced stability is a result of some mechanism not represented in the well-established time domain model. It is possible that this is a result of the disturbance of regeneration in the manner of an alternating spindle speed or due to a non-linear process damping effect.     

Effects of the hob cutter regrinding and setting on ZE-type worm gear manufacture

A mathematical model for a ZE-type worm gear set is proposed. The characteristics of a ZE-type worm gear cut with an oversize hob cutter are investigated. Bearing contacts and kinematic errors in the ZE-type worm gear set due to regrinding of oversize hob cutters are also studied. Bearing contacts in the worm gear set were obtained using surface separation topology techniques and tooth contact analysis. It was found that bearing contact locations are sensitive to the hob cutter setting angle and setting distance. Kinematic error minimization was achieved modifying worm normal tooth angle. By applying the optimization theorem and computer simulation programs, optimum hob cutter settings and worm normal tooth angle were determined to improve bearing contact location and minimize the worm gear set kinematic errors. A numerical example is given to demonstrate the results of the investigation. The developed computer-aided manufacture program has successfully been applied to the worm gear manufacture and hob cutter design.     

Investigation of accuracy of aerostatic guideways

Aerostatic guideways are often used in machines requiring very high motion accuracy such as coordinate measuring machines. Currently, positioning error analysis for such machines focuses on the relationship between volumetric errors on one hand and axes’ motion errors and axes’ relative location errors on the other. The internal mechanisms causing motion errors are rarely considered. In order to gain a deeper understanding of aerostatic guideways, this paper investigates the relationship between the motion errors of the axis’ carriage and the guideways’ geometric errors both mathematically and experimentally. The analytical model uses bearings location and stiffness, guideway geometry and static equilibrium to produce a model in matrix form. Validation experiments are conducted on a machine axis moving on aerostatic guideways with and without preload.     

工程机械用开关磁阻电机绕组电感计算与分析

在工程机械用开关磁阻电机设计中,电感作为衡量电机性能的基本参数,起到了尤为重要的作用。开关磁阻电机电感呈非线性,直接解析较为困难,故在线性假设条件下,采用磁路分析方法首先对磁导分量进行解析,推导出最小电感位置与最大电感位置处的磁导分量计算式,由此得到最小电感和最大电感计算公式;然后,推导出12/8极平行齿结构开关磁阻电机关于电感的6个转子特殊位置角的计算公式,得到电感解析曲线;最后,将电机计算结果与仿真结果进行比较。结果表明：电感计算结果与仿真结果误差在4%以内,磁链相对误差在10%以内,验证了该解析的准确性,为后续电机优化提供了理论基础。     

钢-混凝土栓接结合面法向参数辨识方法研究

钢-混凝土栓接结合面接触特性严重影响着结构的静动特性。为了避免辨识过程中求逆过程带来的数值误差,以及大型试件引入的边界条件误差,设计一种可将混凝土及钢结构考虑成杆的实验试件,通过杆理论的解析方法获得纵向振动的特征值,采用锤击振动实验直接得到试件的固有频率与阻尼比,从而完成结合面参数的辨识。通过对比考虑结合面影响的仿真结果与实验结果,验证了辨识方法的正确性及精度,为进一步分析异性材料结合面特性提供了参考。     

新能源汽车齿轮箱齿轮修形设计及效率分析

齿轮箱作为新能源汽车驱动系统的关键部件之一,如何提高其均载特性、改善NVH性能,成为新能源汽车关注的焦点问题之一。综合考虑齿轮、轴系的弹性变形以及齿轮制造、安装误差等因素,计算齿轮修形参数。建立齿轮箱仿真模型,分析修形前后齿轮接触应力、传递误差以及传动效率的变化规律;制作齿轮箱样机,进行传动效率测试,并与仿真结果进行对比,验证齿轮修形的可靠性。结果表明：修形后的齿轮齿面接触应力显著减小,齿面载荷分布均匀,传递误差峰峰值大幅降低;效率测试结果与仿真结果基本吻合。     

一面两孔定位方案的计算机数据处理

通过分析工件"一面两孔"定位时的定位误差,得到当被加工孔与定位孔位置关系不同时产生的定位误差的计算公式,用VB6.0语言编制计算机程序,对定位误差进行数据处理;从结果分析中,找出减小定位误差的方法.并简要地讨论了VB编程语言在AutoCAD中的应用.     

Investigation of a 2-D planar motor based machine tool motion system

A new 2-D planar motion system for precision machining operations is investigated. Characteristics of the 2-D planar motor system are studied to gain better understanding of its capabilities, limitations and interactions with machining processes. The planar motor system is applied to an end milling process, where experimental data on cutting force and surface finish are in agreement with simulation results. Of further interest is that the motor's fast response and ability to perform simultaneous motion in two directions potentially provides a simpler means to compensate for errors such as runouts. Issues associated with such compensation motions to improve surface finish are discussed.