超声振动辅助穿孔等离子弧焊工艺及其机理的研究

发布时间：2018-01-23 17:47

本文关键词： 穿孔等离子弧焊超声振动等离子弧压力小孔图像焊缝成形微观组织　出处：《山东大学》2017年硕士论文　论文类型：学位论文

【摘要】：穿孔等离子弧焊中,等离子弧不仅作为焊接热源加热熔化待焊工件形成熔池,同时还作为力源在熔池中排开液态金属形成熔透的小孔。然而,常规等离子弧焊接(PAW)还存在穿孔能力和熔池稳定成形不易兼顾的问题。超声振动作为一种辅助能量,在与TIG/MIG等自由电弧复合时有较好的工艺效果。那么是否可以将超声振动与等离子弧复合,用以解决常规等离子弧焊接存在的上述问题?本文在这一方面进行了探索。研发了 "超声振动辅助穿孔等离子弧焊接(U-PAW)实验系统",该实验系统包括:超声振动系统、等离子弧焊接系统、控制系统和信息采集系统。针对等离子弧焊枪的结构特点,通过钨极端部将超声振动施加到等离子弧中,进而使超声振动直接作用于等离子弧和熔池。利用激光多普勒测振(LDV)的方式,测量了钨极端部的振动频率、振幅等参数。采用电弧压力测量装置,对等离子弧的压力分布进行测试;通过拍摄等离子弧弧柱图像,证明超声振动能够对等离子弧形状产生影响,使等离子弧弧柱进一步收缩,同时等离子弧高温区发生下移。结果显示,超声振动能够提高等离子弧压力。随着焊接电流的增大,超声对等离子弧压力增大的效果有所降低。在不锈钢板上开展U-PAW工艺试验,在工件背面安装视觉传感器,实时拍摄小孔出口的图像,考察超声振动对等离子弧穿孔能力的影响。在工艺条件相同的情况下,超声振动辅助穿孔等离子弧焊接能够以较低的焊接电流或较高的焊接速度实现穿孔焊透。同时,超声振动能够增大工件背面小孔的尺寸,有效降低小孔的中心后向偏移量。超声振动能够增强等离子弧的挺度,提高小孔成形过程的稳定性,焊缝横断面金相试样照片表明,超声振动能够减小焊缝上部熔宽,促使焊缝中下部熔宽变大,增大深宽比。同时,超声振动利于焊缝表面的稳定成形。等离子弧焊接焊缝金属的微观组织观测结果表明,复合超声振动之后,焊缝中粗大且方向明确的柱状晶转变为细小的等轴晶。对比同一金相试样的上下两个区域,可以发现超声振动的作用自上而下逐渐减弱。这说明超声振动改变了等离子弧的物理特性,进而改善了焊缝金属的微观组织;同时,有一部分超声振动通过等离子弧传递到熔池当中,对熔池的冷却凝固过程也产生了一定影响。
[Abstract]:In perforated plasma arc welding, plasma arc is not only used as a welding heat source to heat and melt the workpiece to be welded to form a molten pool, but also as a force source to drain liquid metal into the molten pool to form a penetration hole. Conventional plasma arc welding (PAW) also has the problems of punching ability and stable forming of molten pool. Ultrasonic vibration is a kind of auxiliary energy. When combined with free arc such as TIG/MIG, the process effect is better. Can ultrasonic vibration be combined with plasma arc to solve the above problems existing in conventional plasma arc welding? The experimental system of ultrasonic vibration assisted perforation plasma arc welding (U-PAW) is developed in this paper. The experimental system includes ultrasonic vibration system and plasma arc welding system. Control system and information acquisition system. According to the structural characteristics of plasma arc welding gun, ultrasonic vibration is applied to plasma arc through tungsten extreme part. The ultrasonic vibration is applied directly to the plasma arc and the molten pool. The vibration frequency and amplitude of the tungsten extreme are measured by the laser Doppler vibration measurement method. The arc pressure measuring device is used to measure the vibration frequency and amplitude of the tungsten. The pressure distribution of plasma arc was measured. By taking the image of plasma arc column, it is proved that ultrasonic vibration can affect the plasma arc shape, make the plasma arc column shrink further, and move down the high temperature area of plasma arc. The result shows that the ultrasonic vibration can affect the plasma arc shape and make the plasma arc column shrink further. Ultrasonic vibration can increase the pressure of plasma arc. With the increase of welding current, the effect of ultrasonic on the increase of plasma arc pressure is decreased. The U-PAW process test is carried out on stainless steel plate. The visual sensor is installed on the back of the workpiece and the image of the orifice exit is taken in real time. The influence of ultrasonic vibration on the perforation ability of plasma arc is investigated. Ultrasonic vibration assisted perforation plasma arc welding can achieve penetration with lower welding current or higher welding speed. At the same time, ultrasonic vibration can increase the size of the hole on the back of the workpiece. Ultrasonic vibration can enhance the stiffness of plasma arc and improve the stability of the forming process of the small hole. Ultrasonic vibration can reduce the upper weld width, promote the weld width of the middle and lower parts of the weld, increase the ratio of depth to width. At the same time. Ultrasonic vibration is conducive to the stable forming of weld surface. The microstructure observation results of plasma arc welding weld metal show that after composite ultrasonic vibration. The coarse and clear columnar crystals in the weld are transformed into fine equiaxed crystals, and the upper and lower regions of the same metallographic specimen are compared. It can be found that the effect of ultrasonic vibration weakens gradually from top to bottom, which indicates that ultrasonic vibration changes the physical properties of plasma arc and thus improves the microstructure of weld metal. At the same time, some ultrasonic vibration is transmitted to the molten pool by plasma arc, which has a certain influence on the cooling and solidification process of the molten pool.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG456.2

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