电火花微孔加工技术的应用

介绍了电火花加工电路控制系统,脉冲电源参数对电火花加工工艺的影响,有关公式计算,加工技术应用和应注意的问题。

微纳加工中探针与工件碳元素作用机理

以加工件中碳原子为基本模型,构成与电极间相互作用系统。通过理论计算和模拟研究了碳元素在外加电极情况下,整个系统的电子传输过程与电子态密度的分布,结果显示费密能级附近态密度不为零,有能带存在,且能带较宽,离域性较强。同时对电极和工件间距不断变化时系统的电子传输和态密度的变化进行了研究,结果表明,随着距离的增加,本征能量不断减少,电子态密度降低,电子隧穿减弱,从而导致传输概率也逐渐降低。当距离大于0.4 nm时,电子不能完全通过,电火花加工处于截止状态。

140 GHz空腔滤波器设计及加工工艺研究

设计并实现了一种采用进口电火花技术加工的D波段电感膜片耦合的矩形波导空腔滤波器。采用等效电路法设计了一个140 GHz矩形空腔带通滤波器。采用有限元仿真软件HFSS分析了腔体个数对滤波器主要性能的影响,最终成功设计了一个性能优良的四阶空腔滤波器,中心频率(140±3)GHz,带内插入损耗S21在-3 d B以内,回波损耗S11在-20 d B以下。采用电火花微加工技术成功加工出了四阶滤波器的主体部分,相应完成了结构键合等关键工艺,首次制作了基于电火花技术的D波段矩形波导空腔滤波器。测试结果为中心频率(138.5±3)GHz,带内插入损耗最好达到了-4.4 d B。结果表明滤波器在140GHz具有带通特性和滤波功能,尽管与理论上的-3 d B有差异,但考虑到加工误差、夹具损耗等情况下,样品主要技术指标与设计值较为一致。

DISCHARGE CHANNEL GROWTH IN MICRO EDM OF HIGH FREQUENCY PULSE

The influences of intense magnetic pinch effect caused by electromagnetic field with high frequency on discharge channel expansion and plasma configuration change are discussed. The change of Lorentz force exerting on charged particles in discharge channel is calculated under the electromagnetic field with high frequency. Through the theoretical analysis and experimental study, the forming process of discharge channel is conjectured. And it is considered that the changes of discharge channel, such as the decrease of diameter and increase of energy density, coming from the intense magnetic pinch effect in high frequency electromagnetic field, are the main reasons for a series of special phenomena on the machined surface in micro EDM.

Characteristic evaluation of Al_2O_3/CNTs hybrid materials for micro-electrical discharge machining

The characteristic evaluation of aluminum oxide （A1203）/carbon nanotubes （CNTs） hybrid composites for micro-electrical discharge machining （EDM） was described. Alumina matrix composites reinforced with CNTs were fabricated by a catalytic chemical vapor deposition method. A1203 composites with different CNT concentrations were synthesized. The electrical characteristic of A1203/CNTs composites was examined. These composites were machined by the EDM process according to the various EDM parameters, and the characteristics of machining were analyzed using field emission scanning electron microscope （FESEM）. The electrical conductivity has a increasing tendency as the CNTs content is increased and has a critical point at 5% A1203 （volume fraction）. In the machining accuracy, many tangles of CNT in A1203/CNTs composites cause violent spark. Thus, it causes the poor dimensional accuracy and circularity. The results show that conductivity of the materials and homogeneous distribution of CNTs in the matrix are important factors for micro-EDM of A1203/CNTs hybrid composites.

Self-adaptive fuzzy controller with formulary rule for servo control of discharge gap in Micro EDM

In micro electrical discharge machining （micro EDM）, it is difficult for servo controlling the narrow discharge gap with the characters of non-linear and quick change. In this paper, aiming at solving the problems above, a self-adaptive fuzzy controller with formulary rule （SAFCFR） is presented based on the dual feedbacks composed by gap electric signal and discharge-ratio statistics. To ensure the properties of self-optimizing and fast stabilization, the formulary rule was designed with a tuning factor. In addition, the fast-convergence algorithms were introduced to adjust control target center and output scale factor. In this way, the normal discharge ratio can tend to the highest value during micro-EDM process. Experimental results show that the proposed algorithms are effective in improving the servo-control performance. According to the drilling-micro-EDM experiments, the machining efficiency is improved by 20% through applying SAFCFR. Moreover, SAFCFR is a prompt way to optimize parameters of discharge-gap servo control.

Study on manufacturing freeform surface parts in micro EDM based on skin effect theory

Micro fabrication of freeform surface parts made of hard and brittle materials is always a tough job in micro machining field. This paper tries to fabricate freeform surface feature by using smooth surface of tool electrode after tool wear in micro EDM. According to the skin effect theory, the tool end shape in the stage of uniform wear can be changed by adjusting the frequency of discharge pulse. The electrical energy distributing rule of tool electrode section in RC circuit has been investigated under the influence of skin effect, and the law of spark location change has been summarized. The experimental studies demonstrate that different shapes of tool ends can be achieved by varying the pulse frequencies of discharge power supply. Additionally, a micro part of freeform surface feature with high precision and good surface quality has been successfully obtained by micro EDM through adopting the smooth surface after tool wear.

Discussion of skill improvement in marine ecosystem dynamic models based on parameter optimization and skill assessment

Marine ecosystem dynamic models(MEDMs) are important tools for the simulation and prediction of marine ecosystems. This article summarizes the methods and strategies used for the improvement and assessment of MEDM skill, and it attempts to establish a technical framework to inspire further ideas concerning MEDM skill improvement. The skill of MEDMs can be improved by parameter optimization(PO), which is an important step in model calibration. An effi cient approach to solve the problem of PO constrained by MEDMs is the global treatment of both sensitivity analysis and PO. Model validation is an essential step following PO, which validates the effi ciency of model calibration by analyzing and estimating the goodness-of-fi t of the optimized model. Additionally, by focusing on the degree of impact of various factors on model skill, model uncertainty analysis can supply model users with a quantitative assessment of model confi dence. Research on MEDMs is ongoing; however, improvement in model skill still lacks global treatments and its assessment is not integrated. Thus, the predictive performance of MEDMs is not strong and model uncertainties lack quantitative descriptions, limiting their application. Therefore, a large number of case studies concerning model skill should be performed to promote the development of a scientifi c and normative technical framework for the improvement of MEDM skill.