基于LabVIEW的电火花线切割放电加工状态的研究

电火花线切割加工时放电加工状态决定着加工的质量和速度,电极丝和工件之间的放电电压是对放电加工过程进行实时检测的重要参数.以LabVIEW为开发平台,以放电电压为检测参数,构建了电火花线切割放电加工状态识别仿真系统.该系统主要包括线切割放电状态识别模块、BP神经网络放电预测模块以及加工稳定性分析模块,对提高电火花线切割加工质量、加工效率及智能化加工有良好的效果.     

慢走丝线切割放电状态在线识别新方法

在慢走丝电火花线切割加工过程中,由于其放电机理的复杂性、放电点的随机性和最优加工参数的不确定性,放电加工过程中的放电间隙电压可大致分为开路、正常放电、电弧、短路和复杂放电五种放电波形。在不同加工参数下,各类放电波形的比例不一样,不适当的加工参数将显著降低正常放电波形的比例,严重影响慢走丝加工过程中的效率、精度和稳定性。建立一种慢走丝线切割放电状态浮动电压阈值在线识别方法,在放电波形识别系统中,根据不同的加工工况,调节阈值电压的参考值。再根据识别的各种放电波形的比例,采取相应的措施,改变加工参数,已达到最优的放电波形比例。实验数据表明,该系统具有较高的识别精度、实时性和稳定性,且提高材料去除率约20%,降低表明粗糙度约27%,该放电波形识别系统可在电火花线切割加工中具有较好的实用性。     

放电位置随机分布的电火花线切割加工仿真模型

在电火花线切割单脉冲放电过程仿真的基础上,基于有限元软件ANSYS提出了一种放电位置随机分布的电火花线切割加工温度场仿真模型。在仿真过程中,放电位置随机分布,并引入"生死单元技术"去除高温蚀除的单元,得到了线切割连续脉冲放电加工过程的表面效果。然后利用温度场仿真结果计算不同放电参数下的材料去除率,并基于脉冲利用率和电极丝换向时间进行修正,发现修正后材料去除率仿真结果与实际加工结果之间误差小于10%,验证了电火花线切割加工连续脉冲随机放电的仿真模型的准确性。其中,电火花线切割加工过程的脉冲利用率、电极丝换向时间是导致仿真结果出现偏差的主要因素。为了分析实际加工过程的脉冲利用率,搭建了脉冲利用率检测装置,对不同伺服条件下的脉冲利用率进行了统计。     

线切割加工条件对模具零件表面粗糙度的影响

为改善快走丝电火花线切割加工的表面粗糙度,提高模具加工的质量和使用寿命,分析了快走丝电火花线切割加工条件中放电参数、工作液和电极丝对零件表面粗糙度的影响,并在此基础上提出了改善零件表面粗糙度的相应措施和方法。     

浅析电参数对快走丝电火花线切割表面质量和加工精度的影响

针对快走丝电火花线切割中存在的表面质量差、加工精度低的问题,分析了快走丝电火花线切割加工条件中放电参数（脉冲宽度ON、功率管数IP、脉冲间隔OFF、开路电压、脉冲频率）对零件表面粗糙度、加工精度的影响,为快走丝电火花线切割加工积累了经验。     

GH4169高温合金电火花线切割加工质量预测研究

针对镍-铬-铁基高温合金GH4169电火花线切割加工质量预测问题,通过正交实验设计并结合方差分析,分析放电电流及脉冲宽度、放电间隙、管数、加工限速对GH4169高温合金电火花线切割加工表面粗糙度和线切割速度的影响规律。在实验数据基础上训练BP神经网络,建立脉冲宽度、放电间隙、管数、加工限速对表面粗糙度和线切割速度影响的预测模型,预测结果表明,将正交实验与BP神经网络融合应用在GH4169高温合金电火花线切割加工中,不仅减少了工艺参数优化选择的盲目性,也提高了加工质量的预测精度和效率。     

电火花线切割温度场有限元分析及参数验证

建立了电火花线切割脉冲放电模型,利用有限元法分析了单脉冲放电的温度场分布。计算出该条件下工件及电极丝放电凹坑几何特征,与实际切割条件下的表面粗糙度、电极相对损耗比、切割速度等工艺指标进行了对比,并根据电火花线切割的加工特点进行了修正,研究了电火花线切割的蚀除规律。结果表明:模拟的单脉冲放电凹坑几何特征经修正后可以近似表征实际连续切割时的表面粗糙度;实际切割中放电点在电极丝上的通道转移是导致电极丝相对损耗较低的主要原因;考虑到实际切割相关因素,对理论切割速度进行修正后,其值与实际值是吻合的。     

慢走丝电火花线切割加工精度影响因素的研究

分析总结了电火花线切割加工技术的研究现状.通过在慢走丝电火花线切割机床上针对具体的参数进行了大量的实验,考察了各种因素对慢走丝电火花线切割加工精度的影响规律.基于对这些实验数据的分析研究,分析了有关电火花线切割加工精度和稳定性的各种影响因素,得出了相关结论.     

电火花线切割加工中线电极的动态特性仿真与实验研究

研究慢走丝电火花线切割加工中电极振动对加工状态的过程的影响。应用计算机仿真技术,分析连续放电力作用下线的振动模态以及对放电点转移和分布的作用。结果表明,加工工艺参数明显影响放电点的转移与分布,适当地选择工艺参数可获得最佳的放电分布率。该研究对提高慢走丝加工稳定性,防止断丝的发生提供了相应理论依据。     

基于C8051单片机的电火花线切割自适应电源研究

对电火花线切割脉冲电源的原理进行了探讨与分析,介绍了一种基于C8051单片机的新型电火花线切割自适应电源的设计方法.对放电状态进行在线检测,该系统能够通过对放电脉冲的自适应调整,使极间放电状态总是处于理想状态,能够较好地适应加工条件的剧烈变化,大大提高了线切割加工过程的稳定性和加工品质.     

Experimental investigation of the real-time micro-control of the WEDM process

The wire electrical discharge machining (WEDM) process has inherent instability due to its high complexity and stochastic characteristics. For more stable and efficient machining, the process must be actively controlled in real time while precisely determining the state of the instantaneous machining process. Feedback information when used in conjunction with an unstable discharge pulse ratio and instantaneous discharge energy can be applied to this micro-control system. This study presents the design and implementation of a system that fulfills these demands. Experimental results demonstrate that the proposed system is capable of simultaneously enhancing the machining stability, machining efficiency, and machining performance. For fine machining, the surface quality was enhanced by approximately 10 % without a loss of machining efficiency. Overall, both the feedrate and the surface roughness could be improved concurrently by more than 5 %.     

Improvement of EDM efficiency with a new adaptive control strategy

In most of the commercially available EDM systems, the control parameters such as the electrode jump height and the discharge machining time between two consecutive electrode jump actions are set manually to constant values which can ensure stable machining even under the worst machining conditions. It is beneficial to keep the machining process stable, but much time is consumed in the electrode jump process. In order to improve the EDM efficiency, a new adaptive control strategy which directly and automatically regulates the electrode jump height and discharge machining time has been developed in this paper. Experimental results show that the adaptive control system can obviously improve the machining efficiency regardless of the surface area, shape, and depth of the machined dies. Meanwhile, the accuracy and surface roughness of the fabricated dies can be well retained.     

Detecting discharge status of small-hole EDM based on wavelet transform

Discharge waveforms contain information representing the gap discharge status of an EDM process. The gap discharge status has a great influence on the machining performance including the machining efficiency, workpiece surface integrity, and tool wear rate in EDM processes. In order to identify the gap discharge status effectively, wavelet transform is used to analyze the discharge waveforms. A data acquisition and processing system based on DSP is developed for high-speed wavelet transforms and related calculations. The wavelet transform result shows that each EDM pulse can be classified by judging the approximation coefficients of the wavelet transform result. Experimental results demonstrate that the wavelet transform detection is capable of capturing the primary features of each single discharge pulse, which are usually unable to be discovered by conventional discharge detection methods such as the average gap voltage detection. By analyzing the local extreme values of approximation coefficients, the numbers of different pulses within a detection time period can be identified. The gap discharge status coefficient, which is a function of the numbers of different pulses, is then calculated and used as a feedback signal to an adaptive EDM process controller. A small-hole machining test demonstrates that, with the online adaptive controller based on the wavelet transform method, the machining efficiency and stability are improved significantly.     

基于STEP-NC加工工步的优化

研究了基于精英选择遗传算法的加工工步序列优化技术。传统的加工工艺路线是以工序为制造单元,而在基于STEP-NC的加工中,是以加工工步为制造单元,并且面向数控加工中心的一种加工过程,由加工工步变换所带来的零件转位、刀具更换等所消耗的辅助加工时间为最短作为优化目标,来进行加工工步序列的优化,并对加工工步序列的优化算法进行了验证。     

大面积钛合金电火花加工放电产物运动规律研究

在大面积钛合金电火花加工过程中,容易造成电蚀产物聚集且不易冷却从而产生集中放电、拉弧及短路现象,严重的甚至会烧伤工件的表面。因此,为了实现持续稳定的正常火花放电,在放电过程中放电点的位置分布必须均匀。电火花放电产生的气泡及加工屑是影响放电点分布均匀性的关键因素。为此,首先通过计算流体动力学软件Fluent对气泡的运动规律进行了仿真分析,然后通过高速摄像机拍摄透明电极下气泡的运动规律验证仿真的可靠性。结果表明气泡在间隙内的运动经过了膨胀、收缩及破裂的过程。通过试验对脉冲放电产生的加工屑颗粒的直径分布及数量进行了研究,并对加工屑在放电瞬间的抛撒机理做出了合理的假设,建立了电火花加工过程中放电间隙流场的气液固混合相三维模型,仿真分析了气泡运动对加工屑运动的影响规律。研究发现加工屑在气泡内部时,由于空气对加工屑的阻力小于工作液对气泡膨胀的阻力,加工屑快速向气泡的边界靠近。而当加工屑穿透气泡的边界进入工作液中后其速度迅速降低,且随着气泡的收缩逐渐靠近放电发生的位置。因此可以通过改变脉冲间隔实现控制气泡的大小及加工屑的分布,从而可以有效避免集中放电提高放电点分布的均匀性。     

Electrical discharge precision machining parameters optimization investigation on S-03 special stainless steel

S-03 is a novel special stainless steel, which is widely used in precision aerospace parts and electrical discharge machining technology has the merit of high-accuracy machining. This paper aims to combine gray relational analysis and orthogonal experimental to optimize electrical discharge high-accuracy machining parameters. The four process parameters of gap voltage, peak discharge current, pulse width, and pulse interval are required to optimize in the fewest experiment times. The material removal rate and surface roughness are the objective parameters. The experiment were carried out based on Taguchi L9 orthogonal array, then we carried out the gray relational analysis to optimize the multi-objective machining parameter, finally, we verified the results through a confirmation experiment. The sequence of machining parameters from primary to secondary are as follows: discharge current 7A, pulse interval 100 μs, pulse width 50 μs, and gap voltage 70 V. Using the above machining parameters, we can obtain good surface roughness Ra1.7 μm, and material removal rate 13.3 mm³/min. The machined work piece almost has no surface modification layer. The results show that combining orthogonal experiment and gray relational analysis can further optimize machining parameters, the material removal rate increased by 23.8 %, and the surface roughness almost has no change.     

Non-linear mechanism in electrical discharge machining process

Electrical discharge machining (EDM) is an advanced non-traditional manufacturing technology that has many advantages over other machining methods. Many papers have discussed the machining mechanism and modeling of the EDM process. However, previous mechanism models have mainly been linear, which contradicts their precondition that EDM is a stochastic process. In this paper, a non-linear mechanism model is proposed for the EDM process. A threshold condition that leads to chaos is calculated using the Melnikov theory. The theoretical results indicate that the EDM system can generate varied chaos in the evolution of electrical discharge. To verify this conclusion, validation experiments are implemented. Several sets of complete EDM processes’ real-time series are analyzed by multiple chaotic numerical criteria, including power spectrum analysis, principle component analysis (PCA), correlation dimension analysis, and Lyapunov exponent analysis. The experimental results provide further qualitative and quantitative evidence that a complete EDM process has dynamical chaotic characteristics.     

PULSE DISCRIMINATION FOR ELECTRICAL DISCHARGE MACHINING WITH ROTATING ELECTRODE

This article presents a new method for discrimination of various types of pulses generated during an electrical discharge machining process in presence of a rotating electrode. Existing pulse discrimination methods do not perform efficiently in an electrical discharge machine with rotating electrode, as arcs rarely occur during the machining process. Our method involves simultaneous comparison of the gap voltage and current signals with various thresholds. The main advantage of our proposed method is its efficient computation and significantly better accuracy in discriminating between various pulse classes for electrical discharge machining devices with rotating electrode. Experimental studies demonstrate a superior performance of our method in distinguishing normal pulses from harmful arcs, open circuit and short circuit pulses, compared with the state-of-art methods.