Enhanced strength-ductility synergy in a wire and arc additively manufactured Mg alloy via tuning interlayer dwell time

Strength-ductility trade-off is a common issue in Mg alloys. This work proposed that a synergistic enhancement of strength and ductility could be achieved through tuning interlayer dwell time(IDT) in the wire and arc additive manufacturing(WAAM) process of Mg alloy.The thermal couples were used to monitor the thermal history during the WAAM process. Additionally, the effect of different IDTs on the microstructure characteristics and resultant mechanical properties of WAAM-processed Mg alloy thin-wall were investigated. The results showed that the stable temperature of the thin-wall component could reach 290 ℃ at IDT=0s, indicating that the thermal accumulation effect was remarkable. Consequently, unimodal coarse grains with an average size of 39.6 μm were generated, and the resultant room-temperature tensile property was poor. With the IDT extended to 60s, the thermal input and thermal dissipation reached a balance, and the stable temperature was only 170 ℃, closing to the initial temperature of the substrate. A refined grain structure with bimodal size distribution was obtained. The remelting zone had fine grains with the size of 15.2 μm, while the arc zone owned coarse grains with the size of 24.5 μm.The alternatively distributed coarse and fine grains lead to the elimination of strength-ductility trade-off. The ultimate tensile strength and elongation of the samples at IDT=60s are increased by 20.6 and 75.0% of those samples at IDT=0s, respectively. The findings will facilitate the development of additive manufacturing processes for advanced Mg alloys.

A spatiotemporal evolution model of a short-circuit arc to a secondary arc based on the improved charge simulation method

The initial shape of the secondary arc considerably influences its subsequent shape.To establish the model for the arcing time of the secondary arc and modify the single-phase reclosing sequence,theoretical and experimental analysis of the evolution process of the short-circuit arc to the secondary arc is critical.In this study,an improved charge simulation method was used to develop the internal-space electric-field model of the short-circuit arc.The intensity of the electric field was used as an independent variable to describe the initial shape of the secondary arc.A secondary arc evolution model was developed based on this model.Moreover,the accuracy of the model was evaluated by comparison with physical experimental results.When the secondary arc current increased,the arcing time and dispersion increased.There is an overall trend of increasing arc length with increasing arcing time.Nevertheless,there is a reduction in arc length during arc ignition due to short circuits between the arc columns.Furthermore,the arcing time decreased in the range of 0°-90°as the angle between the wind direction and the x-axis increased.This work investigated the method by which short-circuit arcs evolve into secondary arcs.The results can be used to develop the secondary arc evolution model and to provide both a technical and theoretical basis for secondary arc suppression.

Effect of interlayer cooling time on the temperature field of 5356-TIG wire arc additive manufacturing

In the paper, the finite element model(FEM) of wire arc additive manufacturing(WAAM) by TIG method was established by the ABAQUS soft, and the phase transformation latent heat was considered in the model. The evolution rules of temperature field at the interlayer with the cooling time of 10 s, 30 s and 50 s were obtained by the model. The WAAM experiment were performed by 5356 aluminum alloy welding wire with φ1.2 mm, and the simulated temperature field were varified by the thermocouple. The result shows that the highest temperature at the molten pool center increases with the increased interlayers at the same interlayer cooling time;the highest temperature drops gradually and the decline is smaller with the increased interlayer cooling time at the same layer. No remelting occurs at the top layer, and at least two remelting times occur in the other layers, resulting in complex temperature field evolution.

Critical Length Criterion and the Arc Chain Model for Calculating the Arcing Time of the Secondary Arc Related to AC Transmission Lines

The prompt extinction of the secondary arc is critical to the single-phase reclosing of AC transmission lines, including half-wavelength power transmission lines. In this paper, a low- voltage physical experimental platform was established and the motion process of the secondary arc was recorded by a high-speed camera. It was found that the arcing time of the secondary arc rendered a close relationship with its arc length. Through the input and output power energy analysis of the secondary arc, a new critical length criterion for the arcing time was proposed. The arc chain model was then adopted to calculate the arcing time with both the traditional and the proposed critical length criteria, and the simulation results were compared with the experimental data. The study showed that the arcing time calculated from the new critical length criterion gave more accurate results, which can provide a reliable criterion in term of arcing time for modeling and simulation of the secondary arc related with power transmission lines.

Numerical analysis of keyhole establishment time in keyhole plasma arc welding

Numerical analysis of keyhole shape and keyhole establishment time is of great significance for selection and optimization of the process parameters in keyhole plasma arc welding. In this paper, a three-dimensional transient model is developed to analyze the evolutions of keyhole shape and keyhole establishment time in continuous current plasma arc welding process. Firstly, a combined volumetric heat source model is used to simulate the transient variation of temperature field. And then the surface deformation equation is adopted to calculate dynamic features of the keyhole shape and keyhole establishment time inside weld pool, in which the force action on weld pool surface is considered. Experiment is cond^ted to validate the numerical simulation results. The predicted keyhole size and keyhole establishment time are in agreement with the experimental measurement. And the calculated fusion zone geometry is consistent with the measured one.

Prediction of cooling time t8/5 in twin wire submerged arc welding of intermediate thickness plate

Twin wire submerged arc welding （SAW） is widely used in oil or gas line pipe fabrication because of its high productivity. To investigate the strength and toughness of the heat-affected zone （HAZ） in twin wire SAW, the cooling time t8/5 of the coarse grained zone must be studied. The authors presented a method of predicting the cooling time in twin wire SAW of intermediate thickness plate. Based on Rosenthal analytical solutions, an energy factor was introduced to describe the energy contribution of the two wires, equations of thermal cycle and cooling time in twin wire SAW of both thick, and thin, plates were developed. Weighting factors determined by actual thickness and critical thickness were adopted to represent the thermal cycle and cooling time of intermediate thickness plate through linear interpolation with thick, and thin, plate solutions. The predicted cooling time for an intermediate thickness plate was verified experimentally, and the predicted results agreed therewith.

Real-time monitoring of weld penetration quality in robotic arc welding process

It is of great significance to develop an intelligent monitoring system for weld penetration defects such as incomplete penetration and burn-through in real-time during robotic arc welding process. In this paper, robotic gas metal arc welding experiments are carried out on the mild steel test pieces with Vee-type groove. Through-the-arc sensing method is used to capture the transient values of the welding voltage and current. The raw data of the captured welding current and voltage are processed statistically, and the feature vector SIO is extracted to correlate the welding conditions to the weld penetration information. It lays foundation for intelligent monitoring of weld quality in robotic arc welding.

Digital arc welding power supply based on real-time operating system

A digital arc welding power supply was designed with the advanced reduced instruction set computer machine （ARM） and embedded real-time multi-task operating system micro C/OS- Ⅱ. The ARM, with its powerful calculating speed and complete peripheral equipments, is very suitable to work as the controller of the digital power supply. The micro C/OS- Ⅱ transplanted in ARM, helps to improve the respondent speed against various welding signals, as well as the reliability of the controlling software. The welding process consists of nine tasks. The tasks of great significance on reliability of the welder, for example, the A/D conversion of current and voltage, enjoy top priority. To avoid simultaneous-sharing on A/D converter and LCD module, two semaphores are introduced in to ensure the smooth performance of the welding power supply. Proven by experiments ,the ARM and the micro C/OS- Ⅱ can greatly improve both the respondent speed and the reliability of the digital welder.

Time-Frequency Entropy Analysis of Arc Signal in Non-Stationary Submerged Arc Welding

The use of time-frequency entropy to quantitatively assess the stability of submerged arc welding process considering the distribution features of arc energy is reported in this paper. Time-frequency entropy is employed to calculate and analyze the stationary current signals, non-stationary current and voltage signals in the submerged arc welding process. It is obtained that time-frequency entropy of arc signal can be used as arc stability judgment criteria of submerged arc welding. Experimental results are provided to confirm the effectiveness of this approach.

架空配电线路故障电弧的电磁辐射特性及故障定位应用

针对架空配电线路电弧接地故障点定位难题,该文研究架空配电线路故障电弧的电磁辐射特性,探索基于电磁辐射信号的电弧故障定位方法的可行性。通过10 k V配网真型故障模拟试验平台,分析接地电弧电磁辐射的时域与频域特性及传播衰减规律,结果表明:电弧电流的电磁辐射特征频段为20~30 MHz,该特征频段不会受到中性点接地方式、电弧接地介质与线路结构参数的显著影响,且特征频段内辐射信号在传播过程中衰减较慢。在此基础上,设计一种小型化三角形单极子–环形组合平面天线,工作频率为20~500 MHz。利用自制天线开展小型电弧故障定位实验,为后续配网电弧故障定位的应用研究提供基础。

基于零序特征参量差异的谐振接地系统熄弧时刻判别方法

在谐振接地系统中,熄弧时刻的准确判别对于接地故障的选线、消弧效果评估以及熄弧后暂态信息提取和利用具有指导意义。该文针对谐振接地系统单相接地故障,分析了故障点工频电流熄弧前后的故障电气特征,并利用母线零序电压和消弧线圈电流,通过求取其信号的一阶导数及其平方信号的二阶导数,构造两种特征参量。研究发现该特征参量在熄弧前为常数,熄弧后发生明显变化,据此可形成相应的熄弧时刻判别的基本判据。考虑到系统实际运行中各种因素的影响,在此基础上形成熄弧时刻判别的附加判据,从而最终提出基于零序特征参量差异的谐振接地系统熄弧时刻判别方法。通过Mat Lab/Simulink仿真和现场实测,验证了该熄弧时刻判别方法的有效性和准确性。

双曲型法向圆弧齿轮传动的动力学分析

为探究啮合刚度、传动误差及侧隙对双曲型法向圆弧齿轮传动动态响应的影响,建立齿轮副的动力学方程,并在数值计算的基础上进行仿真分析。运用有限元方法,计算接触位置处的载荷及变形,并对时变啮合刚度、静态传动误差和侧隙进行量化分析。仿真结果表明:对振动位移响应影响最大的是侧隙,其次是时变啮合刚度;对动态啮合力影响最大的则是时变啮合刚度和侧隙。

基于COMSOL的7075铝合金微弧氧化时间及正向电压对氧化膜层的影响

研究了微弧氧化时间及正向电压对7075铝合金膜层厚度以及生长趋势的影响。以7075铝合金为研究对象,在多物理场仿真软件COMSOL Mutiphysics的帮助下建立铝合金成膜过程中的物理模型,基于有限元的方法求解出了微弧氧化成膜过程中的膜层厚度变化。仿真得到特定时间或者特定电压下的膜层厚度分布图,根据仿真结果绘制了电压-膜层厚度曲线、时间-膜层厚度曲线。由仿真结果可以看出:当正向电压分别为350、400、450 V时,膜层的最大厚度分别为38.804、50.150、61.496μm;当微弧氧化时间分别为15、25、35、45 min时,膜层的最大厚度分别为25.075、41.792、58.508、75.225μm,且膜层厚度均呈现由中间向两侧逐渐减小的现象。根据仿真结果可以得出以下结论:随着正向电压的升高,膜层厚度增大;随着氧化时间的增加,膜层的厚度也增加。在膜层厚度分布上,越靠近阴极的位置膜层越厚,远离阴极的位置膜层比较薄,且不同参数下膜层的最厚点与最薄点出现的位置不变。

船闸深孔反弧门实时在线监测技术应用研究

针对船闸输水系统工作反弧门长期在深孔动水条件下频繁启闭,给船闸安全运行造成安全隐患,提出一种深孔反弧门实时在线监测技术方案。为掌握深孔反弧门运行情况,将已密封好的应变及倾角等传感器布置在闸门上,再利用钢丝网架胶管将采集信号输送至在线监测系统。监测系统实时进行反弧门在线监测与数据显示,并实时分析结构应力、运行姿态及启闭力,根据分析结果,给出不同等级报警信息及相应的处置建议,提示运行操作人员对反弧门采取对应措施。对广西大藤峡水利枢纽船闸反弧门实施实时在线监测,测试数据表明实施的反弧门实时在线监测系统是可靠稳定的,证明将实时在线监测技术应用于深孔且动水频繁启闭的闸门是可行的。

工艺参数对电弧增材制造工件的影响

电弧增材制造具有高沉积速率、高质量、无尺寸限制的特点,能够满足具有高机械性能要求的中大型部件的制作需求。电弧增材制造AlMg合金过程中制备工艺参数对工件的宏观形貌、微观组织及力学性能均会产生重要影响。本文通过研究焊丝盘松紧度、焊接速度、焊接电流和层间等待时间对电弧增材制造AlMg合金成形的影响,确定了最佳制备工艺参数。研究表明,焊丝盘松紧度为2时,增材设备送丝顺畅,焊道成形效果好;焊道成形与热输入有关,焊接速度越小,增材过程产生的热输入值越大,当焊接速度为36 cm/min时,单道焊缝的成形缺陷最少,成形效果良好;焊接电流越大,增材过程产生的热输入值就越大,当焊接电流为65 A时,焊道形貌均匀;层间等待时间增加到150 s时,合金晶粒为均匀细小的等轴晶,平均晶粒尺寸降至52.9μm。

窄间隙GMAW咬边缺陷的电弧声信号特征分析与识别

针对窄间隙熔化极气体保护焊(Gas Metal Arc Welding,GMAW)焊道侧壁处局部咬边缺陷检测困难的问题,提出了一种基于电弧声信号特征提取与处理的咬边缺陷在线检测方法。通过分析正常、临界咬边和咬边这3种焊接状态的电弧形态和电弧声信号特征,证实坡口侧壁引起的电弧形态变化是影响电弧声信号变化的重要因素。在此基础上采用小波包时频分析,同时引入特征类间标准差作为评价指标,确定了能有效识别3种焊接状态的敏感特征。采用Sigmoid支持向量机和五折交叉验证建立预测模型,实验结果表明该模型能较好地实现3种焊接状态的预测分类,识别准确率达到96.0%。

高速有ARC定时恒比定时甄别器

介绍了一种高速的TTL输出恒比定时甄别器。该甄别器同时实现恒比定时(CFD)功能及幅度和上升时间补偿定时(ARC)功能。最小传输延迟仅为22 ns,最大计数率为100 MHz,可内部调节恒比延时。适用于多种幅度和前沿时间范围的输入信号,时间分辨能力好。电路设计简单,价格低廉,便于制作使用。

基于双通道时频卷积神经网络的故障电弧检测

交流故障电弧产生的高温极易点燃周围的可燃材料,是引发电线火灾的重要原因之一.准确检测不同类型的故障电弧对于预防重大火灾事故的发生具有重要意义.然而故障电弧的复杂性与隐蔽性给检测方法带来了极大挑战.基于阈值和电流特征提取的技术难以全面概括故障电弧的特征,而大多数基于深度神经网络的方法直接对电流信号进行特征学习,忽略了信号中的频率信息,从而导致泛化能力差的问题.对此,本文提出了基于时频特征学习的双通道时频卷积神经网络的故障电弧识别方法,设计了可学习的自适应离散小波变换,用于提取一维信号中的多尺度特征,同时通过短时傅里叶变换获取二维的时频图像特征,分别在这2种特征信号上进行卷积,最后将2个通道中学习的特征进行融合,用于分类预测.通过对故障电弧发生器采集到的3种工况下电弧电流信号进行性能评估,验证所提方法的有效性.实验结果表明,该方法与其他同类方法相比具有更高的电弧识别准确率,达到了97.91%.

基于电磁辐射到达时差的电弧故障定位及精度

为了实现利用电磁辐射信号进行配网电弧故障定位,提出了一种基于到达时差(time difference of arrival,TDOA)方法的Chan-LM协同定位算法。该算法采用Chan算法快速获得的初始点,再经过LM(Levenberg-Marquart)算法迭代修正定位结果。仿真分析了TDOA定位算法、电磁辐射传感器配置对定位精度的影响,结果表明Chan-LM协同算法比Chan算法的定位误差减小40%,参考主站位于中心位置的Y形布站方式,传感器所在海拔高度相同时的监测区域整体定位准确度较高。利用实测电弧电磁辐射波形验证了Chan-LM协同算法能够有效改善定位精度,为基于电磁辐射TDOA的电弧定位策略应用提供参考依据。