交直流混合VPPA特性及铝合金立焊工艺

厚板铝合金变极性等离子弧(VPPA)穿孔立焊工艺中,由于焊接电流大,长时间焊接时钨极的烧损量大,严重影响厚板大结构自动焊接质量.为此提出了通过交直流混合输出减少钨极烧损,同时提高焊接质量的新型铝合金变极性等离子弧穿孔焊接方法.该方法在保证氧化膜清理的前提下,减小了因反极性时间过短电弧在极短时间内两次过零造成的等离子弧力下降和过大的感应电动势对开关器件的损害.其次交直流混合输出电弧具有低频调制效果,起到熔池振荡、细化晶粒的作用.在实现交直流混合VPPA软硬件功能基础上研究了交直流混合VPPA等离子弧力学特性、焊接过程稳定性及焊缝成形机理.通过对焊缝显微组织及焊缝成形检验发现,交直流混合输出时焊缝晶粒细化,焊缝成形美观,实现了减少钨极烧损和提高焊缝质量双重目标.     

Shunting of the arc current in plasma-arc consumable electrode welding (plasma-MIG welding)

ABSTRACT

Special features of the process of shunting plasma arc current with a consumable electrode are investigated. The effect of the diameter of the consumable electrode, its visible extension and plasma arc current on the shunting current is determined. The effect of shunting current on the electrode metal transfer and the rate of electrode melting is determined.     

放电通道振荡特性分析及其蚀除机理的研究

从理论上对单脉冲放电通道的等离子体振荡特性进行了分析,发现其振荡频谱包含了金属晶格振动的本征频率.由此提出了受激原子共振的观点:在放电电流上升阶段,因放电通道中等离子体振荡频率可覆盖金属晶格振动频率,会使电极材料表面晶格原子产生共振或接近共振,加剧放电的热作用,使电极表面材料以"共振"形式去除;而在放电电流趋于平稳后,等离子体振荡频率则远远小于晶格振动频率,电极材料表面晶格原子不具备共振的必要条件,此时材料主要是以"碰撞"形式去除.从这个观点出发,说明了放电电流初始阶段和短脉冲加工是对电极消耗影响较大的原因.     

Development of empirical model for different process parameters during rotary electrical discharge machining of copper–steel (EN-8) system

The present work investigates the machining characteristics of EN-8 steel with copper as a tool electrode during rotary electrical discharge machining process. The empirical models for prediction of output parameters have been developed using linear regression analysis by applying logarithmic data transformation of non-linear equation. Three independent input parameters of the model viz. peak current, pulse on time and rotational speed of tool electrode are chosen as variables for evaluating the output parameters such as metal removal rate (MRR), electrode wear ratio (EWR) and surface roughness (SR). Analysis of the results, by using Taguchi's recommended signal–noise ratio formulae and ANOVA, has been conducted to identify the significant parameters and their degree of contribution in the process output. Analyzed results shows that peak current and pulse on time are the most significant and significant parameters for MRR and EWR, respectively. But peak current and electrode rotation become the most significant and significant parameters for SR, respectively. Experimental results further revealed that maximizing the MRR while minimizing EWR and improving the surface roughness, cannot be achieved simultaneously at a particular combination of control parameters setting. In addition, the predictions based on the above developed models have been verified with another set of experiments and are found to be in good agreement with the experimental results.     

铝合金变极性TIG焊接电弧行为

分别采用正弦波变极性和方波变极性氩弧焊对铝合金试板进行了焊接试验,利用高速摄像机和汉诺威分析仪分别对焊接过程中变极性电弧形态及电信号进行采集分析. 结果表明,电弧电压概率密度分布和高速摄像图证实了较小焊接参数条件下正弦波变极性比方波变极性电弧稳定性差的现象. 正弦波变极性TIG电弧随EP(反极性)的增加清理宽度增加,但熔宽未增加,证明此条件下正弦波变极性TIG电弧过于发散;焊接参数较大时,随EP的增加,正弦波变极性熔宽变宽,证实正弦波变极性TIG电弧稳定性随之提高,证明了铝合金变极性TIG焊接过程中EP极性电弧产热大于EN极性电弧能量的本质特征.     

变极性TIG焊接电源功率因数校正控制策略

对变极性TIG焊电源的输出功率进行研究,发现其输出功率随变极性周期和占空比变化而变化,EP（钨极接正）时的功率远大于EN（钨极接负）时的功率.这种周期性变化输出功率会导致弧焊电源周期性地从电网抽取能量.当采用常规的PFC（功率因数校正）电路和控制策略也会给输入电流带来奇次谐波、偶次谐波、间谐波、直流分量、三相不平衡等＂...     

Advanced methods of improving the quality and increasing the efficiency of welded structures

The process of hardfacing by plasma transferred arc (PTA) has been increasingly accepted in recent years. It has attractive features from the metallurgical point of view, as well as offering low distortion, little dilution, a homogenous structure, and refined coatings. Major innovations and optimized engineering component processing could be achieved if companies had access to a study of different processing parameters. However, owing to the scarcity of literature about the process, comparing it with other welding processes, which contains divergent information in some areas, demands a wider and more systematic study of the effect of the welding variables. This work is intended to contribute to this, and the main objective is to verify the effect of the process variables on the characteristics of a weld bead deposited by the PTA. Using a constant direct current, the influence of the sharpening angle was studied on a tungsten electrode, plasma gas flow, and torch nozzle constriction, using a cobalt-based alloy commercially known as Stellite 6 as the support material. The characteristics of the coating were evaluated in terms of their surface finish, dilution, wettability, and hardness. The results showed that the characteristics of the deposits were determined by the intensity of the current, followed by the nozzle constriction, and that the electrode sharpening angle did not influence the results.     

铝合金VPPA-MIG复合焊接电弧形态及伏安特性

试验使用VPPA-MIG复合焊方法对铝合金进行对接试验. 通过高速摄像和数据采集系统获取复合电弧形态和伏安特性. 结果表明,由于磁场间的耦合作用,在VPPA正极性阶段电弧相互排斥,反极性阶段相互吸引,采取外加横向交变磁场,电弧摆动幅度明显减小. 由于MIG焊电弧的存在,等离子电弧伏安特性发生了改变. 弧柱气氛更容易电离,使得等离子电弧电压下降. 等离子电流较小时,电弧电压随MIG焊电流的增加而降低;等离子电流较大时,随着MIG焊电流进一步增加,电弧电压降低程度有所减少. 试验结果为实现厚板铝合金高效焊接及其电弧耦合机理研究提供理论依据.     

2.45 GHz强流脉冲质子源

介绍了一台用于强流质子直线加速器注入的2.45GHz电子回旋共振强流脉冲质子源。采用2.45GHz的微波馈入实现以氢气为载气的氢等离子体,在三电极引出系统下获得能量50keV,50mA的强流脉冲离子束。其中三电极分别为等离子体电极、抑制电极及地电极。用CST仿真软件和PBGUNS分别模拟计算了匹配波导能量的传输效率与引出束流传输轨迹,得出信号输入端口反射系数S11约为0.119,整个匹配波导内正向传输系数S21为0.993,引出束流在Z=26cm处,束流包络约为2cm。研究了离子源轴向磁场变化对引出束流强度的影响,结果得出,当螺线管电流从0A增加至50A时,引出混合束流强度从20mA上升至50mA。     

Thermal characteristics of the arc discharge used for vacuum welding processes

The results of investigation of the formation of a spot welded joint in welding aluminium alloys with a constricted arc with a tungsten electrode and alternating current in argon are presented. The technology of spot plasma welding of aluminium alloys has been developed. The results of metallographic analysis and mechanical tests on welded specimens show high-strength properties in the absence of defects in spot welded joints.     

铝合金变极性等离子焊接电弧产热机理

从铝合金变极性等离子焊接电弧物理特性出发,研究了铝合金变极性等离子焊接电弧产热机理,分析了焊接参数对电弧热的影响规律。通过理论分析和试验研究,发现铝合金变极性等离子弧焊接时不对称电极特性对正、反极性期间电弧的产热具有很大的影响。反极性期间由于铝合金作为阴极,阴极压降大电弧产热量也增大。在变极性等离子弧焊接时正、反极性期间的焊接电流和持续时间等参数不同也是造成正、反极性等离子电弧产热不同的重要原因。     

高效能超音速等离子喷涂系统的研制

研制的HEPJet高效能超音速等离子喷涂系统，最大功率80kW，最大工作气体流量6m^3／h，可以喷涂金属粉末、碳化物陶瓷粉末和氧化物陶瓷粉末。单阳极内送粉结构的高效能超音速等离子喷枪，为国内外研究超音速等离子喷涂技术开创了一条新路。80kW级20kH脉宽调制IGBT逆变电源解决了输出电压高、输出电流大、高频干扰强等一系列难题，工作可靠。在保证涂层的结合强度、孔隙率等性能指标的前提下，喷涂成本比国外产品降低一半以上。     

新型大气长层流等离子体喷涂方法和研究进展

介绍了一种新型大气等离子喷涂方法,该方法采用特殊内通道结构的直流非转移电弧等离子发生器,可以直接在大气条件下获得长度100～1000 mm之间变化的等离子射流。在大气条件下,等离子射流的流动特性具有"长、直、准"的层流或类层流状态,工作时噪音小于80 dB。在工作参数范围内,等离子射流的长度在固定总气流量条件下可以随输出功率的增加而增长;射流的长度在固定输出功率的条件下随总气流量的增加而减小。当使用在大气等离子喷涂技术中时,会为飞行粉末颗粒带来超长的加热和加速过程。文中详细介绍了大气层流等离子喷涂技术的研究历史和研究现状,以及研究团队利用该新型技术制备的6种涂层的显微结构、颗粒的飞行和加热特点,并对比了目前其他大气等离子喷涂技术的结果。结果表明,文中介绍的方法在最低的输出功率和气流量条件下,为金属和陶瓷颗粒提供了超长的飞行和加热条件,表现为较低的颗粒飞行速度和超高的颗粒表面温度。可以在不同的射流长度或喷涂距离下,获得不同的颗粒熔化状态或涂层结构,并发现可以直接在大气条件下获得大规模气液共沉积的涂层。     

Modeling and analysis of resistance spot welding based on neural network

A numerical study on the multi-parameter control method based on nonlinear auto-regressive with exogenous input neural network (NARX) is presented here. Welding current was set as the input parameter; electrode displacement and dynamic resistance were set as the output parameters. The NARX model using these parameters was set up to simulate the multi-parameter resistance spot welding process. By comparing actual experimental data and NARX model output data, it was validated that the results from the model reflect the relationship between input parameter and output parameters correctly under the influence of many affecting factors.     

焊接与切割设备的使用和维修(六十八)——空气等离子弧切割机的使用与维修

讲述了250D空气等离子弧切割机的工作原理、故障现象、过程分析以及解决方法;介绍了影响等离子切割机使用效果的几个主要因素如工件材质、切割电流、空气压力和流量、喷嘴孔径、操作手法等,以及电极制造材料和消耗特性.最大限度地帮助焊工理解等离子切割常识,提高切割效果.     

Development of a kilowatt class PEMFC stack using Au-coated LF11 Al alloy bipolar plates

Investigations on alternative material for bipolar plates of PEMFC (polymer electrolyte membrane fuel cell) are becoming a research hotspot for many fuel cell researchers. In this paper, LF11 Al alloy bipolar plates via a surface plasma Au plating preparation were applied as bipolar plates. Performances and duration times of PEMFC single cells using graphite; Au-coated LF11 Al bipolar (ALABP) and Au-coated 316L stainless steel plates were compared. It was shown that ALABP exhibited preferable properties. Based on the preparations illustrated above, a kilowatt class proton exchange membrane fuel cell stack consisting of 30 cells was successfully assembled. Pure hydrogen and air were used as the fuel and oxidant, respectively, in the stack. External humidification was employed and cycle cooling water was used to remove the heat from the reaction in order to maintain a constant temperature. A Nafion 1135 membrane and Johnson-Matthy platinum on carbon with a Pt loading of 0.4 mg/cm² were adopted as the electrolyte and catalyst, respectively. The working temperature of the stack ranged from 25 to 100°C. The stack typically worked well under conditions in which the pressure ratio of H₂/air was 0.2/0.22 MPa. The output power, current and voltage were 1–1.3 kW, 40–80 A, and 26–20 V, respectively. The normal current density of the electrode was 200–800 mA/cm², and the energy efficiency of the stack was 51%.     

基于支持向量机的高速电火花小孔加工穿透检测技术

为解决高速电火花小孔加工穿透检测技术的难题,分析并提出采用支持向量机分类算法对穿透检测特征量进行处理,将小孔穿透检测看作数据分类问题,利用支持向量机构建穿透检测的SVC模型。通过实验分析和数据处理,选择脉冲宽度、脉冲间隔、加工电流、有效放电频率和电极进给速度作为SVC模型的五个输入量,输出为是否发生穿透。穿透检测的SVC模型采用径向基核函数,通过对样本的训练学习,实现了对小孔穿透瞬间的可靠辨识。实验结果表明:在正常加工情况下,支持向量机辨识模型对不同的工件厚度均能在电极穿透工件瞬间进行有效辨别。     

Linear polarisation resistance measurements using a potentiostatically controlled guard ring

The use of a sensor controlled guard ring has been developed in recent years to enhance the accuracy of linear polarisation corrosion rate measurements on reinforced concrete structures. The established method of measurement uses a galvanostatically controlled guard ring device. In the method reported in this article the reinforcing steel is polarised potentiostatically by an inner auxiliary electrode and the real time plot of the current response is displayed on a laptop computer which controls the guard ring device. The area of steel polarised is confined by a current applied from an outer guard ring electrode which is controlled by two sensor electrodes positioned between the inner auxiliary and outer guard ring electrode. The potential between the two sensor electrodes is continually monitored, and the current output from the guard ring electrode varied to maintain a constant potential difference between the two sensor electrodes. The method has been validated on an electrical test circuit simulating active and passive reinforcement corrosion. Further testing has been conducted on a reinforced concrete specimen and the results compared with those of commercially available galvanostatically controlled equipment and those of standard unconfined linear polarisation resistance measurements.     

Efficient multilayer organic light emitting diode

Some organic light emitting diodes with Alq₃ as emission layer, multilayer composed of m-MTDATA, NPB, TPD or SA as hole transport layer and lithium doped Alq₃ as electron injection assistant layer have been investigated. The current voltage characteristics and the electroluminescent (EL) output voltage characteristics have been investigated. It is found that the m-MTDATA is suitable as a hole injection layer close to the hole injection electrode ITO, NPB is suitable in contact with the emission layer, SA and TPD can be inserted between them to form an energy ladder structure, with which the efficiency of device has been increased. When thin lithium doped Alq₃ layer is inserted between Alq₃ and the aluminium electrode, the driving voltage of the devices has been clearly decreased while the current density and the EL output increased.     

Gas analogue of the Ganna effect under conditions of two-electrode discharge of continuous current

The existence of a mode of periodic movement of a volumetric charge of negative sign from an electrode with a negative potential (600–4500 V) in the direction of the other earthed electrode was discovered. The experiments were carried out with the discharge of a constant current in the presence of the pressure of air (10^?3–10 Torr) in tubes with various internal diameters (3.8, 6.6, 15.5, 20.1, and 25.8 mm) but with the same (510 mm) distance between the electrodes. The opportunity for the appearance of the mode of periodic discharge was provided by the connection to the potential output of a source of several condensers of large capacity (300 μF). It is supposed that the discovered periodic mode of the gas discharge is similar to the Gann effect—the movement of a volumetric charge of negative sign in the volume of a semiconductor.