电火花成形加工中极性对加工表面形貌的影响

在用YT15硬质合金电极对45钢进行电火花加工时，若采用正极性加工，可得到显微硬度大大高于基体且抗腐蚀性好的白亮层，但加工效率低，电极损耗快；若采用负极性加工，则无白亮层出现，但加工效率高，电极损耗小。基于以上经验，通过改变极性，对45钢工件进行电火花成形加工与电火花表面强化，可简单高效地得到高硬度的加工表面。     

石墨电极放电加工

本文介绍了用石墨电极和铜电极进行的单脉冲放电及一般连续脉冲放电加工的对比实验。初步分析了石墨电极正、负极性加工效果不同的机理。     

添加剂在电火花低损耗加工中的应用

本文作者研制的DJT-1型中、精加工电极低损耗添加剂在煤油介质中使用,能使紫铜电极比原来降低损耗30～45％左右。电火花中、精加工电极的损耗问题一直是电火花型腔加工中最重要的理论和实际问题之一。众所周知,在电火花中、精加工时利用电极的极性效应,将工件接到脉冲电源负极,工具电极接到正极的“负极性”加工容易呈现相对电极损耗较小的低损耗加工;使用耐腐蚀的铜钨、银钨等粉冶合金材料作为     

混粉准干式电火花复合强化TC4钛合金试验研究

以石墨和紫铜为强化电极,TC4钛合金为基体材料,在混粉准干式工作介质中对TC4钛合金进行电火花表面强化,分析了不同电极材料对强化层微观组织和性能的影响。结果表明,复合强化可以获得组织致密且厚度均匀的表面强化层,显著改善基体表层质量。强化层显微硬度约为1 500 HV,相对磨损率约为基体材料的27%。TC4钛合金表面强化层的显微硬度和耐磨性能均大幅提高。     

45钢电火花成型表面组织结构的研究

在煤油介质中,以YT15硬质合金作为电极加工45钢.正极性加工时,在45钢表面得到显微硬度高于基体的白亮层,且其厚度和表面质量可通过改变放电参数进行调整.利用电子探针对白亮层进行了成分分析.本研究为利用电火花成型机完成表面强化加工提供了依据.     

混粉准干式电火花表面强化TC4钛合金强化层组织与性能

利用混粉准干式电火花表面强化技术对TC4钛合金进行表面强化。工作介质中混入B4C粉末,工具电极选用石墨电极,在其表面形成富含C、B、Ti、Al等元素的强化层来改善钛合金表面的硬度。结果表明,强化后合金表面形成一层致密的、呈菊花瓣状层叠式组织的强化层,与基体结合良好,电流增大菊花瓣状晶粒明显增大;经峰值电流为3.7和6.6A的电火花强化后,强化层硬度(HV)由强化处理前的312分别提高至899和1 039。XRD分析表明,强化层中出现了TiC、TiB、B_8C、Al_3BC、Al_3Ti和Al_5Ti_2等相,电流增大至6.6A时还出现了Al_(3.3)Ti亚稳相,且Ti-Al化合物相含量明显增多,实现了对钛合金表面的混杂强化。     

不同工作介质条件下电火花表面强化H13钢组织与性能研究

以硬质合金YG8为工具电极,分别在煤油和雾状工作介质中对H13钢进行电火花表面强化,并对强化层的微观组织、厚度、相组成及硬度进行了分析.结果表明,2种工作介质条件下获得的强化层组织均呈橘皮状,强化层断面由表及里依次由白亮层、过渡层和基体组成.雾状介质条件下强化层表面更平整,组织更致密,强化层的厚度为煤油介质条件下的2倍.对强化层进行物相分析表明,煤油介质条件下强化层主要有α-Fe,Cr,FeCr及Co3Fe7相,雾状介质条件下强化层主要以Fe3C,FeCr,α-Fe及Co3Fe7相为主.强化层显微硬度较原始H13钢均有大幅提高,煤油介质条件下强化层显微硬度为HV855.6,而雾状介质条件下高达HV1 286.3.     

H13钢模具电火花表面强化工艺参数优化分析

采用正交试验法对H13钢模具电火花表面强化工艺参数进行了研究。优选结果表明,电极材料是影响电火花强化层性能的最主要因素;石墨电极是最佳的强化电极,其强化的涂层在耐磨性、组织形貌和显微硬度方面都表现出优异特性。     

两种基体材料的脉冲放电强化层对比研究

从强化层的厚度、硬度、结构及强化层与基体之间的扩散程度方面对Ｍ２和５０ＣｒＭｏＶ两种基体脉冲放电强化层进行了对比研究。结果表明,两种基体材料强化层的特点、性能等方面明显不同;电极材料主要相在放电形成涂层中发生变化。     

电火花振动沉积TiC功能涂层的显微组织与性能

为了提高镀锌钢板点焊电极的寿命,以TiC为沉积材料,在铬锆铜球型点焊电极表面进行了电火花振动沉积功能涂层的工艺试验,研究了首次单点沉积、限时沉积、清洗前处理、扩散后处理等方法获得功能层的显微组织与性能.结果表明,首次单点沉积后功能层呈溅射状,类似树枝晶.限时沉积后材料由强化层、过渡层、热影响区、基体组成.强化层结构致密、硬度很高;过渡层有微孔及微裂纹,存在明显的元素互扩散,表明功能层与基体之间为冶金结合.通过清洗前处理可改善过渡层的显微组织,而不影响功能层硬度;而扩散后处理改善了过渡层的组织,但降低了功能层的硬度与厚度.     

TC4钛合金混粉电火花表面改性研究

目的通过混粉电火花加工方法,分别使用紫铜和石墨作为工具电极,获得综合性能较好的TC4钛合金表面。方法利用手持式TR200粗糙度仪对工件表面的粗糙度进行测量,用扫描电子显微镜(SEM)、X射线衍射仪对工件组织形貌和物相结构进行分析,用FM800型显微硬度计对工件表面进行显微硬度测量。结果在相同电参数下,紫铜电极加工的工件较石墨电极加工的工件表面粗糙度要低,硬度也相对低。当I=4.5A、tON=30?s时,紫铜电极加工的工件表面平均粗糙度值Ra=2.223?m,表面硬度约为600HV;石墨电极加工的工件表面平均粗糙度值Ra=2.796?m,表面硬度约为700HV。当I=9 A、tON=30?s时,紫铜电极加工的工件表面平均粗糙度值Ra=2.748?m,表面硬度约为650HV;石墨电极加工的工件表面平均粗糙度值Ra=3.705?m,表面硬度约为750HV。结论在不同电极条件下混粉电火花加工后,TC4钛合金工件表面都达到了强化的效果。     

混粉准干式介质下电火花表面强化TC4钛合金的显微裂纹探究

以混粉准干式为工作介质,分别用石墨电极和紫铜电极对TC4钛合金进行电火花表面强化,研究了强化层的微观形貌和显微裂纹。结果表明:工具电极和峰值电流是影响电火花强化TC4钛合金强化层表面微裂纹数量和强化时间的主要因素。正确选用工具电极和峰值电流可获得较好的强化层,且强化层表面微裂纹较少。     

点焊电极用铜合金材料强化技术的研究现状

在现代工业中广泛应用的点焊电极用铜合金材料多为铬铜、铬锆铜和Al_2O_3弥散强化铜,主要因其导电性、导热性、高温强度、硬度和可加工性。综述了多种强化技术的机理和工艺,通过对基体进行固溶时效和形变强化处理,或进行深冷处理,或通过Al_2O_3、TiB_2、石墨、碳纳米管等对基体进行弥散强化,可以有效地提高铜合金性能。展望了点焊电极用铜合金的强化技术。     

Effect of electrode material on electrical discharge machining of alumina

Technologies for machining advanced insulating ceramics are demanded in many industrial fields. Recently, several insulating ceramics, such as Si₃N₄, SiC and ZrO₂, have been successfully machined by electrical discharge machining (EDM). As unstable discharges occur during the machining of Al₂O₃ ceramics, inferior machining properties have been obtained. The formation mechanism of the electrical conductive layer on the EDMed surface is much different as compared to other ceramics. In addition to this, the electrically conductive layers are not formed sufficiently to adhere to the EDMed workpiece surface and keep a stable and continuous discharge generation on the ceramics. Graphite is widely used as electrode material in EDM. It is expected that carbon from graphite electrode implant and generate a conductive layer. Copper, graphite (Poco EDM-3) and copper-infiltrated-graphite (Poco EDM-C3) electrodes were used to compare the effects of generation of a conductive layer on alumina corresponding to EDM properties. The electrical discharge machining of 95% pure alumina shows that the EDM-C3 performs very well, giving significantly higher material removal rate (MRR) and lower electrode wear ratio than the EDM-3 and copper electrodes. The value of MRR was found to increase by 60% for EDM-3 with positive electrode polarity. As for EDM-C3, MRR was increased by 80% under the same condition. When the results were investigated with energy dispersive spectroscopy (EDS), no element of copper was observed on the conductive layer with both EDM-3 and EDM-C3. However, surface resistivity of a conductive layer created with EDM-C3 is less than with EDM-3. Surface roughness was improved to 25 μm with positive polarity of EDM-C3.     

一种实现变极性焊接电流波形的新方法

介绍了一种实现变极性焊接电流波形的新方法。正、负半波电流分别供电，在主弧负半波以冷却良好的铜喷嘴代替钨棒作阳极，既满足了对铝工件氧化膜清理的需要，又降低了钨电极的烧损，实现了稳定的变极性焊接过程。     

电火花表面强化工艺对强化层组织性能的影响

采用电火花表面强化设备 ,以硬质材料作为强化电极材料 ,白口铸铁为基体材料 ,研究了电火花表面强化工艺对强化层性能的影响。结果表明 ,选择合适的工艺参数 ,可获得好的强化层表面质量 ,且强化层硬度高 ,耐磨性显著提高。     

EDM performance of Cr/Cu-based composite electrodes

Electrode materials for electrical discharge machining (EDM) are usually graphite, copper and copper alloys because these materials have high melting temperature, and excellent electrical and thermal conductivity. The electrodes made by using powder metallurgy technology from special powders have been used to modify EDM surfaces in recent years, to improve wear and corrosion resistance. However, electrodes are normally fabricated at high temperatures and pressures, such that fabrication is expensive. This paper proposes a new method of blending the copper powders contained resin with chromium powders to form tool electrodes. Such electrodes are made at low pressure (20 MPa) and temperature (200 °C) in a hot mounting machine. The results showed that using such electrodes facilitated the formation of a modified surface layer on the work piece after EDM, with remarkable corrosion resistant properties. The optimal mixing ratio, appropriate pressure, and proper machining parameters (such as polarity, peak current, and pulse duration) were used to investigate the effect of the material removal rate (MRR), electrode wear rate (EWR), surface roughness, and thickness of the recast layer on the usability of these electrodes. According to the experimental results, a mixing ratio of Cu–0wt%Cr and a sinter pressure of 20 MPa obtained an excellent MRR. Moreover, this work also reveals that the composite electrodes obtained a higher MRR than Cu metal electrodes; the recast layer was thinner and fewer cracks were present on the machined surface. Furthermore, the Cr elements in the composite electrode migrated to the work piece, resulting in good corrosion resistance of the machined surface after EDM.     

The influence of positive polarity time on GTAW AC of aluminium

In this work, experiments were carried out to determine the welding behaviour of aluminium 1200 based on an increase in the activation time of the positive polarity for tungsten inert gas AC welding of this metal. To achieve this objective, a series of experiments was developed, in such a way that the intensity of the electrical current in the positive and negative polarities was the same; only the duration times in each polarity were modified. During the experiments, the current and voltage signals were acquired. In this way, the arc voltage and potential could be determined for each condition tested. In terms of the fusion behaviour, an increase in penetration and in welded areas was verified to the extent that longer positive polarity times were used. This behaviour is different from that commonly indicated in the literature about welding processes with non-consumable electrodes, which suggests a reduction in penetration with an increase in the positive polarity activation time. However, this trend grows constantly during the experiments from a determined point, where the positive polarity activity times are greater than 4.0 ms in a total period of 20.0 ms. The use of a minimum positive polarity time (1.3 ms) was shown to be effective for cathode cleaning, as it produced welds with satisfactory fusion characteristics and with minimum wear to the tungsten electrode. The good fusion capacity obtained in welds produced with long positive polarity times was attributed to phenomena arising from the emission of electrons due to the field effect that occurs during the positive electrode phases.     

石墨电极在彩电模具电火花加工中的应用

通过彩电前壳模具喇叭网孔镶件电火花加工,对紫铜电极和石墨电极加工结果进行分析比较,指出石墨材料在制作大电极,特别是在对电极损耗有严格要求的电火花加工时,石墨电极比紫铜电极有许多优点。指出专用石墨作电火花加工电极的优势正逐渐被大家认识,将成为企业首选的电火花加工电极材料。