Trajectory optimisation in electrical discharge machining of three-dimensional curved and twisted channels

Numerical control electrical discharge machining(NC EDM) is one of the most widely used machining technologies for manufacturing a closed blisk flow path, particularly for three-dimensional(3D) curved and twisted flow channels. In this process, tool electrode design and machining trajectory planning are the key factors affecting machining accessibility and efficiency. Herein, to reduce the difficulty in designing the electrode and its motion path in the closed curved and twisted channels, a heur...     

带冠整体涡轮盘电火花加工成形电极的设计与制造

以带冠整体涡轮盘电火花加工专用CAD/CAM系统(BliskCad/Cam)为辅助工具,详细介绍了某带冠整体涡轮盘电火花加工成形电极的设计和制造工艺,通过加工实验,得到满足精度要求的成形电极。     

Four-axis trochoidal toolpath planning for rough milling of aero-engine blisks

The Blade Integrated Disk (Blisk) is one of the key components in the aero-engine, it is generally manufactured by the multi-axis milling and almost 90% raw materials are removed. To avoid the full immersion of a cutter in the rough machining of a blisk channel, the trochoidal milling is a promising strategy since it can keep a small immersion angle in the rough milling process while maintaining the high machining efficiency. However, while toolpaths are being planned for the trochoidal milling process, the conventional methods are mainly for the planar machining area with fixed tool orientations, which cannot be used for complex channels where the multi-axis machining should be employed. To this end, this paper presents a four-axis trochoidal toolpath planning method with a ball-end cutter, and thus the blisk channel can be machined efficiently. For this to happen, the trochoidal paths are planned in the parametric domain and then mapped into the physical domain, with tool orientations controlled by the quaternion interpolation method to have smooth tool movement along the toolpaths. Both geometric simulation and physical milling experiments of the proposed method have convincingly demonstrated the validation of the proposed method.     

扭叶片整体涡轮电火花成形加工技术

论述了扭叶片整体涡轮的结构特点、加工现状以及其几何造型方法。提出了基于电铸工艺来制造低损耗成形工具电极,由电火花成形加工方法加工整体涡轮弯扭叶片的高效、低成本组合工艺。根据整体涡轮叶间通道的特点以及工艺要求,研究了成形电极的运动轨迹和位姿确定。     

基于UG 二次开发的电火花加工成形电极设计系统

针对闭式整体涡轮叶盘的结构特点,在UG平台上通过二次开发设计了一套涡轮盘电火花加工成形电极设计系统,包括电极初步设计、减厚处理、电极剖分、电极基座设计和电极运动轨迹搜索等模块.通过实验对电极设计系统的正确性和实用性进行了验证,加工出满足设计要求的整体涡轮盘样件.     

闭式整体叶盘通道五坐标分行定轴加工刀轴矢量规划方法

闭式整体叶盘是新一代航空发动机实现减重增效的关键零件,其通道结构属于典型多约束复杂通道结构。针对闭式整体叶盘通道精加工,提出了一种基于五坐标分行定轴加工的刀轴矢量规划方法。从加工原理上给出了分行定轴加工方法的基本概念,并分析了闭式整体叶盘通道五坐标加工的特征;在刀具预定义和建立检查面球体包围盒层次树结构的基础上,给出了刀轴矢量无干涉区域的计算方法;基于刀位点最短刀长的计算与分析,进行了叶盘通道加工区域划分,建立了分行定轴加工刀轴矢量规划方法。实验验证表明:分行定轴相对五轴联动加工方法不仅可明显提高加工过程中的稳定性和叶片加工表面质量,还可提高叶片精加工效率。     

气体介质中深小孔电火花加工技术研究

 深小孔加工一直是机械制造领域的难题之一。在分析和研究气体介质中电火花加工技术的基础上,就其在深小孔加工中的应用进行了深入的理论与实验研究。分别用管状圆柱电极和削边电极在通用电火花成形加工机床上成功地加工出直径为2 mm、深径比大于20、锥度小于0.5%的深小孔。研究表明,相对于传统的液中电火花加工,气体介质中电火花加工深小孔具有电极损耗率低、加工过程稳定等特点。而且由于无需庞大的工作液系统,该方法适合于大型零部件上深小孔加工。     

Effect of tube-electrode inner diameter on electrochemical discharge machining of nickel-based superalloy

Nickel-based superalloys are widely employed in modern aircraft engines because of their excellent material characteristics, particularly in the fabrication of film cooling holes. How-ever, the high machining requirement of a large number of film cooling holes can be extremely chal-lenging. The hybrid machining technique of tube electrode high-speed electrochemical discharge drilling (TEHECDD) has been considered as a promising method for the production of film cooling holes. Compared with any single machining process, this hybrid technique requires the removal of more complex machining by-products, including debris produced in the electrical discharge machin-ing process and hydroxide and bubbles generated in the electrochemical machining process. These by-products significantly affect the machining efficiency and surface quality of the machined prod-ucts. In this study, tube electrodes in different inner diameters are designed and fabricated, and the effects of inner diameter on the machining efficiency and surface quality of TEHECDD are inves-tigated. The results show that larger inner diameters could effectively improve the flushing condi-tion and facilitate the removal of machining by-products. Therefore, higher material removal efficiency, surface quality, and electrode wear rate could be achieved by increasing the inner diam-eter of the tube electrode.     

Electrochemical machining on blisk channels with a variable feed rate mode

Electrochemical machining (ECM) is an economical and effective method for blisk manufacturing and includes two steps: channel machining and profile machining. The allowance distribution after the channel machining will directly affect the profile machining. Therefore, to improve the uniformity of allowance distribution in the machining of channels, a method that incorporates a variable feed rate mode is developed. During the machining process, the feed rates are dynamically changed according to the needs of the side gap at the different feed depths. As a result, the side gaps at the different feed depths vary, contributing to a decrease in the allowance difference. In this study, the dissolution processes of a blisk channel are simulated using different feed rates, and prediction profiles are obtained. Based on the prediction profiles, the relationship among the feed rate, feed depth, and side gap is established. Then, the feed rates at different feed depths are adjusted according to the relationship. In addition, contrast experiments are conducted. Compared with blisk channel ECM using a constant feed rate of 1 mm/min, using the variable feed rate decreases the allowance differences in the convex and concave parts by 62.2 % and 67.4 %, respectively. This indicates that using the variable feed rate in the ECM process for a blisk channel is feasible and efficient.     

冰层辅助对电火花-电解复合穿孔的影响

电火花-电解复合穿孔(ECDD)加工方法有望实现难加工材料涡轮叶片气膜冷却孔无重铸层高效加工,为了进一步提升小孔孔壁的加工质量,提出了在工件底部填充冰层的电火花-电解复合穿孔加工新方法。分析了冰层辅助对复合加工过程中两极之间电流电压的波形、复合穿孔的加工效率、小孔的出入口孔径、孔壁重铸层去除等的影响,进行了冰层辅助与无冰层辅助电火花-电解复合穿孔对比试验。试验表明:冰层辅助加工可以在小孔穿透之后形成充分的反向冲液,有效地解决小孔穿透之后的漏液问题。在增加底部停顿时间的基础上,即小孔穿透后管电极到达预设深度继续停留一段时间,延长管电极对孔壁的电解作用时间,可以显著提高重铸层的去除效果,有望实现小孔整个孔壁重铸层的完全去除。     

Surface-improvement mechanism of hybrid electrochemical discharge process using variable-amplitude pulses

Superalloys are commonly used in aircraft manufacturing; however, the requirements for high surface quality and machining accuracy make them difficult to machine. In this study, a hybrid electrochemical discharge process using variable-amplitude pulses is proposed to achieve this target. In this method, electrochemical machining (ECM) and electrical discharge machining (EDM) are unified into a single process using a sequence of variable-amplitude pulses such that the machining process realizes both good surface finish and high machining accuracy. Furthermore, the machining mechanism of the hybrid electrochemical discharge process using variable-amplitude pulses is studied. The mechanism is investigated by observations of machining waveforms and machined surface. It is found that, with a high-frequency transformation between high- and low-voltage waveforms within a voltage cycle, the machining mechanism is frequently transformed from EDM to pure ECM. The critical discharge voltage is 40 V. When pulse voltages greater than 40 V are applied, the machining accuracy is good; however, the surface has defects such as numerous discharge craters. High machining accuracy is maintained when high-voltage pulses are replaced by low-voltage pulses to enhance electrochemical dissolution. The results indicate that the proposed hybrid electrochemical discharge process using variable-amplitude pulses can yield high-quality surfaces with high machining accuracy.     

三元流闭式叶轮组合电加工技术研究Ⅱ——数控电解预加工

数控电解预加工是组合电加工技术中不可或缺的关键工艺,本文专题论述了三元流闭式叶轮数控电解预加工中阴极及其运动轨迹设计等关键技术。提出了采用多个阴极分区域加工流道的方法,利用先层切再叠加的方法将三维问题简化为二维问题处理而实现阴极加工型面的数值求解。在完成阴极结构优化设计专用工装夹具设计和数控加工程序编制的基础上,以某型三元流闭式叶轮为研究对象进行了加工工艺试验,并加工了符合设计要求的三元流闭式叶轮。试验研究表明,采取数控电解预加工工艺方案能够满足实际生产要求,可提高效率40%,降低电火花加工的电极损耗50%。     

金属基圆弧成形砂轮的电火花修整

根据电火花修整的需要,研制了电火花修整脉冲电源。根据圆弧成形砂轮的修整需要,研制了摆动电极式电火花修整装置。通过电火花修整试验研究了修整过程中的极性效应以及不同电参数对修整效率和整形精度的影响。     

Efficiently constructing collision-free regions of tool orientations for holder in five-axis machining of blisk

Blisks with the integral structure are key parts used in new jet engines to promote the performance of aircrafts, which also increases the complexity of tool orientation planning in the five-axis machining. It is an essential task to find the collision-free tool orientation when the tool holder is pushed deep into the channel of blisk to increase rigidity and reduce vibration. Since the radius of the holder varies with the height, the line-visibility is no longer applicable when constructing collision-free regions of tool orientation. In this paper, a method of constructing collision-free regions without interference checking is proposed. The work of finding collision-free regions resorts to solving the local contact curves on the checking surfaces of blisk. And it further transforms into searching the locally tangent points (named critical points) between the holder and surface. Then a tracking-based algorithm is proposed to search the sample critical points on these local contact curves. And the corresponding critical vectors are also calculated synchronously. Besides, the safety allowance, discrete precision and acceptable deviation are introduced in the algorithm to ensure accuracy by controlling the angle between two adjacent critical vectors properly. After that, the searched critical vectors are mapped orderly to two-dimensional space and the collision-free regions are constructed. This method is finally verified and compared with a referenced method. The results show that the proposed method can efficiently construct collision-free regions for holder under the given accuracy.     

带冠整体叶轮铣削加工工艺的探讨

为解决传统制造存在的问题,本文提出了采用五轴联动数控铣削加工技术,实现带冠整体叶轮整体铣削加工,大大缩短了工艺流程。本文阐明了带冠整体叶轮铣削加工要点,制定了加工工艺方案;同时基于UG 7.5中CAM模块,详细说明了铣削加工内弧、轮毂、外环和背弧所应用的各种加工策略。并在实际加工过程中,证明了加工工艺的合理性和可行性,提高了加工质量。     

Trajectory control strategy of cathodes in blisk electrochemical machining

A turbine blisk, which combines blades and a disk together, is one of the most important components of an aero engine. In the process of blisk electrochemical machining (ECM), the sheet cathode, which is usually used as a tool electrode, has a complicated structure. In addition to that, the channel between the adjacent blades is narrow and twisted, so interference is apt to happen when the sheet cathode feeds into the channel. Therefore, it is important to choose suitable trajectory control strategy. In this paper, a new trajectory control strategy of the sheet cathode is presented and corresponding simulation analysis is conducted on the basis of an actual blisk model. The simulation results demonstrate that the sheet cathode can feed into the channel by a spatial line trajectory without interference. Moreover, the verification experiments are carried out according to the simulation. The experimental results show that the cathode can move into the channel without interference. It is verified that the new trajectory control strategy is correct and can be used in the blisk ECM process successfully.     

基于电极切向旋转进给法的 低刚度锥杆类零件精密电火花加工

提出了基于圆盘电极切向旋转进给法的低刚度锥杆类零件的电火花精密加 工方法。首先介绍了基于等厚损耗原则的圆盘电极设计原理,进而通过电火花加工工艺 的三因素全因子实验考察了峰值电流、脉宽、占空比对工件材料去除率（MRR）、相对 电极损耗率（TWR） 和表面粗糙度（SR） 的影响, 并对电火花加工工艺参数进行优化 从而应用于锥杆类零件的加工。加工出的反馈杆性能一致性高、表面质量好,加工时间 短,试验结果表明基于圆盘电极切向旋转进给法的电火花加工工艺对提高低刚度锥杆的 加工工艺的可靠性和加工效率、提高电极利用率方面有较大优势。     

高缠绕叶轮流道4+1轴高效分段开槽方法

高缠绕叶轮流道的高效粗加工是提高整个叶轮加工效率和缩短生产周期的关键。针对高缠绕叶轮流道的粗加工,提出了一种4+1轴高效分段开槽方法。首先,给出了分段开槽加工方法的基本概念,并分析了高缠绕叶轮流道加工特点;然后,结合机床结构特征,给出了五轴机床在主轴摆角固定为常值时切削点处单点最大刀具尺寸的计算方法;基于各切削点加工特征参数的分析,采用聚类算法进行了叶轮流道加工分段区域的划分;最后,确定了各分段区域的可加工刀具尺寸和4+1形式的刀轴矢量。算例分析表明,提出的4+1轴分段开槽方法得到的开槽轨迹旋转轴变化均匀,材料去除量较传统开槽方法增加了32.5%,改善了切削过程稳定性,提高了叶轮的粗加工效率。     

电火花平动加工策略研究

研究了工具电极进给速度和电规准对加工速度和表面粗糙度的影响规律,提出一种优化工具电极进给速度和电规准的加工策略,在保证加工精度和表面粗糙度要求的前提下,可大幅度提高生产效率。     

电火花铣削加工中工具电极损耗补偿策略研究

在电火花铣削加工中,由于工具电极作旋转运动,其损耗呈轴对称分布,使工具电极的补偿成为可能。本文对工具电极的损耗形状进行了研究,提出一种在线工具损耗补偿措施,从而避免了工具损耗形状的检测,极大地提高了生产效率和加工精度