Observations of the phenomenon of abnormal arc voltage occurring in pulsed metal inert gas welding of aluminium alloy

Abstract

At the time of arc reignition after short circuiting during electrode positive polarity, cathode spots are newly formed in the centre of the weld pool surface, where oxides scarcely exist. The work function of the cathode surface increases and the cathode spots concentrate because of the lack of sufficient oxides, leading to an increase in the potential gradient across the cathode fall space and the adjoining contraction space. Consequently, the arc voltage becomes abnormally high in spite of the short arc length. Moreover, when electrode polarity is switched from positive to negative immediately after a droplet has detached from the wire tip, cathode spots are newly formed on the surface of the molten metal remaining at the wire tip, where little oxide exists, leading to an abnormal increase in arc voltage as well. Therefore, the change in arc voltage does not necessarily indicate a fluctuation in the arc length.     

Measuring the process efficiency of controlled gas metal arc welding processes

Abstract

The thermal or process efficiency in gas metal arc welding (GMAW) is a crucial input to numerical models of the process and requires the use of an accurate welding calorimeter. In this paper, the authors compare a liquid nitrogen calorimeter with an insulated box calorimeter for measuring the process efficiency of Fronius cold metal transfer, Lincoln surface tension transfer and RapidArc, Kemppi FastRoot and standard pulsed GMAW. All of the controlled dip transfer processes had a process efficiency of ～85% when measured with the liquid nitrogen calorimeter. This value was slightly higher when welding in a groove and slightly lower for the RapidArc and pulsed GMAW. The efficiency measured with the insulated box calorimeter was slightly lower, but it had the advantage of a much smaller random error.     

在自动MIG焊层中加入WC颗粒的堆焊设备及工艺

介绍一种新型的WC堆焊设备和工艺，即在自动MIG堆焊层中加入WC颗粒，以解决大部分WC下沉到底部、分解等问题。该设备结构简单，操作方便，工艺简单可行，可获得理想的加有及覆盖有WC颗粒的耐磨堆焊层。     

轨道交通用6082-T6铝合金MIG焊接接头组织与疲劳性能

对轨道交通用6082-T6铝合金进行MIG焊接,使用光学显微镜、X射线衍射仪、显微硬度计分别对焊接接头的显微组织、相结构与显微硬度进行观察与分析。结果表明,熔合区为柱状晶组织,焊缝主要由树枝晶和胞状晶组成,焊缝中心为等轴晶,焊缝体现出联生结晶的特点。母材相组成为基体α-Al固溶体、β-Mg2Si以及单质Si,焊缝金属相组成主要为α-Al固溶体。热影响区的宽度达31mm,且存在一个软化区。设定应力比R=0,测试了铝合金的疲劳寿命,通过拟合试验数据得到S-N曲线,得到MIG焊接6082-T6铝合金焊接接头的条件疲劳极限为99MPa,为母材的72.26%。用扫描电镜对疲劳断口进行观察和分析,结果表明,疲劳断口分布的二次裂纹促进了疲劳裂纹萌生和扩展,第二相粒子对疲劳裂纹的萌生起着重要的作用,焊缝中的气孔则容易成为疲劳源。稳态扩展区出现大量呈平行趋势且具有规则间距的疲劳条带,瞬断区存在大量韧窝和撕裂棱,体现出韧性断裂的特征。     

影响高效MIG/MAG焊中焊接材料熔化效率的因素

针对高效MIG／MAG焊的熔化效率、熔化速率等概念进行了分析，提出了影响MIG／MAG焊接材料熔化效率的因素和提高焊接材料熔化效率的有效方法。     

铝合金MIG焊正面熔池图像视觉传感与处理

建立了铝合金脉冲MIG焊熔池图像检测CCD视觉传感系统。应用窄带滤光的方法成功地解决了强弧光干扰，通过大量试验，在获取清晰焊接熔池区图像的基础上，分析了铝合金焊接熔池图像的特征，研究了适合铝合金MIG焊熔池图像处理方法和熔池几何尺寸的边缘检出方法，获得了满意的熔池边缘特征图像，为进一步实现铝合金MIG焊接熔透智能控制奠定了基础。     

铝镁合金料仓主体脉冲MIG自动焊工艺研究

针对铝镁合金焊接技术和焊接工艺的难点，研究确定了铝镁合金仓主体脉冲MIG自动焊工艺及其实施方法，该工艺方法克服了传统施焊方法的某些不足，能保证产品的焊接质量，降低劳动强度，提高有色金属结构件的焊接技术水平和焊接质量。     

基于FPGA的DDR3 SDRAM控制器的设计与优化

为解决超高速采集系统中的数据缓存问题,文中基于Xilinx Kintex-7 FPGA MIG_v1.9 IP核进行了DDR3 SDRAM控制器的编写,分析并提出了提高带宽利用率的方法。最终将其进行类FIFO接口的封装,屏蔽掉了DDR3 IP核复杂的用户接口,为DDR3数据流缓存的实现提供便利。系统测试表明,该设计满足大容量数据缓存要求,并具有较强的可移植性。     

AZ31B镁合金FSW接头与MIG接头性能对比研究

采用FSW和MIG焊接方法对AZ31B变形镁合金进行焊接试验。结果表明:FSW接头的焊核区受摩擦热、机械搅拌和热塑流动的综合作用,形成粒度细小、晶界明显的等轴再结晶晶粒,平均直径约为5μm;MIG接头的焊缝区在电弧的高温热作用和急速冷却作用下,形成晶界明显的等轴晶,平均尺寸约为20μm;FSW焊接接头力学特性优于MIG,平均抗拉强度达到249.8 MPa,为母材抗拉强度的96.1%,平均伸长率为11.6%;两种接头的断裂面与拉伸方向的夹角约为45°,FSW接头断裂位置在热影响区,断面上有尺寸相差很大的韧窝,而MIG多出现在焊缝区,断面上有韧窝和撕裂棱。