Welding of medium-carbon structural steel

The optimum filler material was selected and the technological and mechanical properties and structure welded joints are investigated.     

Development of ceramic backing for friction stir welding and processing

Usually, a workpiece is deformed during friction stir welding due to high applied loads. Consequently, fully and consolidated friction stir-welded joints as well as tool life time can be affected promoting unscheduled manufacturing stops, which favour decreasing the welding productivity. Furthermore, the workforce is dislocated to not predicted maintenance steps. This work proposes the development of a special ceramic backing to joining and processing material using FSW technologies. Four ceramic deposits were tested over a steel plate, which allowed selecting those with less porosity and, thus, better strength. This backing allowed us to obtain full penetration welds for duplex stainless steels, to high forces during engagement for high-strength low-alloy steels and to obtain consolidated aluminium–steel dissimilar joints. For the last one, there was not adherence of the soft material in the workpiece. In addition, the ceramic backing allowed us to confine the heat and plasticized metal, as well as develop established welding parameters.     

Development of gap sensing system for narrow gap laser welding

Narrow gap welding with an oscillation laser beam is one of the effective processes for thick plate welding. To put this welding process into practical manufacturing, a groove-sensing system using image processing for narrow gap welding with an oscillation laser beam is used. This developed system uses still images of the weld zone taken by a coaxial CMOS camera. It can recognize the position of the groove wall by analysing the brightness distribution in the still image. It can then control the oscillation width and the laser-irradiated area by calculating the groove width and the groove centre position. Some narrow gap welding experiments were performed to evaluate the performance of the developed system. The results revealed that the developed system is effective for narrow gap welding with an oscillation laser beam. Using this system, the narrow gap groove can be welded even if the groove width has changed during the welding process.     

Effect of welding methods on the structure and mechanical properties of welded joints in creep-resisting titanium alloys with different initial structural conditions

Problems of welding rotor components made of creep-resisting titanium alloys are investigated. Comparative tests of the effects of fusion welding and rotational friction welding (FW) on the structure and properties of welded joints in titanium alloys are carried out. The experimental results show that welded joints produced by rotational FW have a structure identical to the structure of the parent metal, and the heat-affected zone does not form at all. The optimum conditions of FW of creep-resisting titanium alloys are determined. Irrespective of the initial type of structure, these conditions result in the mechanical properties of the welded joint at a level of 0.9 of the properties of the parent metal.     

Fatigue life of multilayer hard-faced specimens

Specimens and the method for experimental evaluation of the fatigue life of multilayer hard-faced metal subjected to cyclic mechanical loading are described. The tests were carried out by three-point bending with cyclic non-zero loading in the centre of the specimen, which reproduces, with certain assumptions, the force loading characteristics of rolling rolls, the rolls of continuous casting installations and other tools and equipment for deformation of metals and alloys which are subjected in service to the simultaneous effect of cyclic mechanical and thermal loads. The proposed method is then used to investigate the durability of the specimens of 40Kh steel, hard faced with PP-Np-25Kh5FMS flux-cored wire with and without a ductile sublayer. The sublayer was deposited using Sv-08A solid wire or the PP-Np-25Kh5MF flux-cored wire. The experimental results show that the deposition of the ductile sublayer with Sv-08A and PP-Np-25Kh5MF wires increases the fatigue life of the deposited specimens 1.3 and 1.6 times, respectively. PP-Np-123Kh1MF wire, which produces a deposited metal with higher mechanical properties in comparison with the Sv-08A wire, results in a higher fatigue life of multilayer hard-faced specimens.     

压力对水下焊条局部干法焊接电弧稳定性的影响

在压力舱中进行不同压力下的水下焊条局部干法焊接试验,采用统计分析和快速傅立叶变换研究了压力对水下电弧稳定性的影响.结果表明,铁粉低氢钾型焊条焊接主要进行粗熔滴短路过渡,随着压力的增加,短路时间由常压焊接的5~7 ms增加到8~10 ms,表明熔滴的平均尺寸增大.压力环境下,焊条熔化速度增大,弧压反馈调节系统的工作点上移,电弧电压增大.傅里叶变换结果表明,常压电弧电压信号的主要特征频率低于10 Hz,压力下电压信号的频谱图中出现大量高于10 Hz的谱线,说明信号突变性更强,电弧稳定性降低.     

DP600/AZ31无匙孔搅拌摩擦点焊塑性金属流动特性及断裂行为研究

在最优焊接参数下,对1 mm DP600镀锌钢板和3 mm AZ31镁板进行无匙孔搅拌摩擦点焊试验,焊后对接头分别进行横切、纵切及层切,采用扫描电镜（SEM）分析焊接接头显微组织和断口形貌.结果表明,镁钢间的混合主要发生在搅拌针作用区域,形成“机械互锁”的组织形貌,有利于增加两种材料的有效接触,形成复相强化;轴肩作用区镁钢间搅拌不明显,界面较平滑,镁钢界面形成了金属化合物以及氧化镁,降低了接头的塑性和韧性.对DP600/AZ31无匙孔搅拌摩擦点焊焊接接头进行拉伸试验,发现焊接接头从搭接界面上断裂,断口呈“脉状花样”,为延性断裂.     

V形坡口和K形坡口Q345/SUS304异种钢对接接头残余应力和变形

以ABAQUS软件为平台,开发热-弹-塑性有限元方法模拟了V形坡口和K形坡口Q345/SUS304异种钢多层焊对接接头的温度场、残余应力和焊接变形.同时采用试验的方法测量了接头的残余应力和角变形.计算结果与试验测量结果吻合良好,验证了计算方法的妥当性.数值结果表明,不同坡口Q345/SUS304异种钢接头的Q345母材与焊缝交界处的应力分布均出现不连续性,且SUS304侧的高拉伸残余应力区明显宽于Q345侧;K形坡口开口朝向Q345侧相较于开口朝向SUS304侧的接头,Q345/焊缝交界处附近的峰值应力和高拉伸残余应力区均明显较小.试验和数值结果表明,坡口形式对接头的角变形有明显的影响.     

铝合金双光束激光焊接过程稳定性分析

从成形、气孔、熔深的波动、激光匙孔、光致等离子体、飞溅等方面研究了铝合金高功率单光束激光和双光束激光焊接过程的稳定性。结果表明,在相同工艺参数下,双光束激光焊缝表面成形明显优于单光束,熔深的波动较单光束小;在相同工艺参数及相同熔深条件下,双光束焊缝气孔率较单光束小,小孔及等离子体的波动周期较单光束长,面积波动变异系数较单光束小,飞溅较单光束更加细小均匀。     

逆变焊接电源的离散建模与最少拍控制

逆变焊接电源所采用的全桥、半桥等功率变换电路可以等效为Buck变换器。在对Buck变换器离散建模的基础上,通过直接时域推导,建立了可用于逆变焊接电源闭环控制的最少拍控制律。所构建的控制算法充分考虑了模型参数与实际参数之间误差的影响。输出滤波电感的变化影响最少拍控制的稳定性和控制效果。稳定条件为模型所用最大电感值不超过实际电感值的1。67倍。结果表明,当模型电感值和实际电感值相等时,系统为最少拍控制。在模型参数和实际负载参数匹配时,系统实现了“没有稳态误差、不存在输出纹波、输出幅值受限”的最少拍控制。