微型罩局部干法焊接风场结构与电弧特性研究

发布时间：2018-02-27 23:13

本文关键词： 局部干法电弧微型排水罩数值模拟　出处：《南昌航空大学》2015年硕士论文　论文类型：学位论文

【摘要】：水下焊接技术在水下工程建设和修复方面具有大量的应用需求。在众多的水下焊接方法中,局部干法焊接利用微型排水罩将焊接区域的水排开后进行焊接,接头质量容易保证,而且无需大型排水设备,易于实现水下焊接自动化,在海洋工程建设方面具有良好的应用前景。局部干法焊接时需要在微型排水罩内通入高压空气,然而高压空气在微型排水罩内的流动难免会形成横向流动的风场,影响电弧形态和焊接过程的稳定性。若能利用这一横向流动的风场,用于横向焊接中抑制重力作用下熔池下淌的问题,将会化弊为利,从力学和能量两方面抑制熔池下淌,改善焊缝成形。首先利用数值模拟的方法,研究了不同结构的微型排水罩内高压气体的风场结构。综合对比发现,在出口上侧设挡板可大大增加出口流速,而使用多孔介质隔板又可降低流速,减少环流,并在其底部形成了稳定的层流风场。最终综合其优点,确定了微型排水罩的具体结构,并加工出了微型排水罩。其次建立了MIG焊接电弧的数学模型,借助于UDF/UDS功能对商业CFD软件Fluent进行二次开发后,以磁流体动力学理论为依据,模拟出了不同侧向风速和环境压力下电弧等离子体的温度场、速度场、压力场,并得到其变化规律:随着环境压力的升高,电弧有收缩迹象,电弧等离子体的温度场、速度稍有减小,弧柱区压力场强度增大;在侧向风场的吹袭下电弧偏向一侧,温度场、压力场、速度场变化较为一致,其偏角与风速大小均呈线性增长关系,且增长斜率相当。然后进行了焊接实验,采用高速相机拍摄电弧在不同侧向风速下的形态,发现其实际变化与模拟结果基本一致。最后,做了不同参数下有侧向风场与否的两组对应焊接实验,利用线性回归的方法,得到了电弧的静态传感特性数学模型,并与实验结果相比较,偏差在合理的范围内,结果较为真实、可信。对比发现在侧向风场的影响下,电流信号波动增大,焊接参数的设置要求更为严格,干伸长随电流变化的斜率增大。
[Abstract]:Underwater welding technology has a lot of application requirements in underwater engineering construction and repair. In many underwater welding methods, the local dry welding uses micro-drain cover to weld the water in the welding area, and the quality of joint is easy to be guaranteed. Moreover, it is easy to realize the automation of underwater welding without large drainage equipment, so it has a good application prospect in marine engineering construction. However, the flow of high pressure air in the miniature drain hood will inevitably form a transverse flow wind field, which will affect the arc shape and the stability of the welding process. If the wind field of this transverse flow can be utilized, The problem of restraining the flow of molten pool under the action of gravity in transverse welding will turn the disadvantages into advantages, which can restrain the flow of molten pool in both mechanics and energy, and improve the forming of weld. First, the method of numerical simulation is used. The wind field structure of high pressure gas in the miniature drain cover with different structures is studied. It is found by comprehensive comparison that the outlet velocity can be greatly increased by installing a baffle on the top side of the outlet, while the velocity of velocity can be reduced and the circulation can be reduced by using the porous media partition. A stable layer flow wind field is formed at its bottom. Finally, the concrete structure of the micro drain cover is determined and the micro drainage cover is machined. Secondly, the mathematical model of MIG welding arc is established. Based on the theory of magnetohydrodynamics, the temperature field, velocity field and pressure field of arc plasma under different lateral wind speeds and ambient pressures are simulated after the secondary development of commercial CFD software Fluent with the help of UDF/UDS function. With the increase of ambient pressure, the arc shows signs of shrinkage, the temperature field of arc plasma decreases slightly, the pressure field of arc column region increases, and the arc deflects to one side and the temperature field increases under the impact of lateral wind field. The variation of pressure field and velocity field is consistent, and the deviation angle is linearly increased with the wind speed, and the increase slope is equal. Then welding experiment is carried out, and the shape of arc under different lateral wind speed is photographed by high speed camera. It is found that the actual variation is basically consistent with the simulation results. Finally, two corresponding welding experiments with or without lateral wind field under different parameters are done, and the mathematical model of the static sensing characteristics of the arc is obtained by using the linear regression method. Compared with the experimental results, the deviation is within a reasonable range, and the results are more real and reliable. It is found that under the influence of the lateral wind field, the fluctuation of the current signal increases and the welding parameters are set more strictly. The slope of dry elongation increases with current.
【学位授予单位】：南昌航空大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TG456.5

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