窄间隙双丝GMAW三元保护气成分优化

发布时间：2018-03-28 03:08

本文选题：窄间隙焊接　切入点：三元保护气　出处：《哈尔滨工业大学》2017年硕士论文

【摘要】：针对管道焊接过程中厚板焊接效率较低的问题,本文提出采用双丝窄间隙GMAW方法对厚板进行焊接,但窄间隙焊接过程中容易出现侧壁熔合不良的问题,因此进一步提出能否通过改变保护气成分(将传统的二元保护气变为三元保护气)进而改变电弧行为,使侧壁熔深增加,避免出现侧壁熔合不良的问题。由于He导热率较高,能使电弧温度分布均匀,考虑选用Ar+CO_2+He作为焊接保护气。首先我们选择了在平焊位置下进行窄间隙单丝焊接,选定保护气流量为40L/min,通过固定He(CO_2)含量,变动CO_2(He)含量,用Ar补齐其余部分进行焊接。通过高速摄像观察变动保护气后电弧形态的变化,并拍摄电弧照片,观察总结保护气含量对电弧弧根角及弧长的影响,并分析电弧行为的变化规律,得到合适的保护气工艺窗口,发现He含量处于5%~15%,CO_2含量处于5%~15%时,可以得到比较稳定的焊接过程。此外,对焊接过程中电压电流值进行统计,观察保护气含量变动对焊接电压及电流值的影响。通过观察高速摄像拍摄的熔滴过渡情况,结合与高速摄像同步采集的焊接电压信号及电流信号,对焊接过程中熔滴过渡形式进行分析,并以此分析焊缝表面成形与熔滴过渡之间的联系。实验发现,随着CO_2含量增加,熔滴过渡形式由射流过渡变为射滴过渡,最后变为短路过渡。随着He含量的增加,熔滴过渡形式由射滴过渡变为射流过渡,再变为射滴过渡。在焊缝中部切取金相件,打磨腐蚀后测量焊缝侧壁熔深,并总结保护气含量对焊缝侧壁熔深的影响。实验发现当He含量处于10%时焊缝侧壁熔深最大,CO_2含量为10%时,也可以得到成形良好的焊缝。最后依据选定保护气工艺窗口设计响应曲面法的实验,以CO_2含量及He含量为因素,以主从丝侧壁熔深及厚度为响应值,建立响应值与因素之间的关系方程,并研究单一因素的变量对焊接主从丝侧壁熔深及厚度的影响及两因素之间相互作用对响应值的影响。依据所得响应曲面找寻最优化的保护气工艺,试验中选定最优保护气工艺为10%He及11%CO_2,实验验证后发现实际值与预测值相差不大,拟合方程较为准确。
[Abstract]:In view of the low welding efficiency of thick plate in pipeline welding process, this paper puts forward the method of two-wire narrow gap GMAW to weld thick plate, but the side wall fusion is easy to occur in narrow gap welding process. Therefore, whether the arc behavior can be changed by changing the composition of the protective gas (changing the traditional binary protective gas into the ternary protective gas) can increase the penetration of the side wall and avoid the problem of bad fusion of the side wall. Because of the high thermal conductivity of he, The arc temperature can be evenly distributed, so we consider using ar CO_2 he as welding shielding gas. First, we choose narrow gap single wire welding in the position of flat welding, and select the flux of protective gas is 40 L / min, and change the CO 2 he content by fixing the content of Hex CO2). The changes of arc shape after changing protective gas were observed by high speed camera, and the effect of protective gas content on arc root angle and arc length was observed and summarized. The variation law of arc behavior is analyzed, and a suitable protective gas process window is obtained. It is found that the relatively stable welding process can be obtained when he content is in the range of 5 ~ 15 and the content of CO2 is 5 ~ 15. In addition, the voltage and current values in the welding process are counted. The effect of the change of protective gas content on the welding voltage and current value was observed. By observing the droplet transfer in the high speed video camera, the welding voltage and current signals collected simultaneously with the high speed video camera were combined with the welding voltage and current signals. The droplet transfer form in welding process is analyzed and the relationship between weld surface forming and droplet transfer is analyzed. It is found that with the increase of CO_2 content, the droplet transfer form changes from jet transfer to droplet transfer. With the increase of he content, the droplet transfer form changes from droplet transfer to jet transfer and then to droplet transfer. A metallographic part is cut in the middle of the weld, and the weld wall penetration depth is measured after grinding and corrosion. The effect of shielding gas content on the weld side wall penetration is also summarized. The experimental results show that when he content is 10, the maximum penetration depth of the weld side wall is 10 and the COSP 2 content is 10. Finally, according to the selected protective gas process window to design the experiment of response surface method, with CO_2 content and he content as the factors, the depth and thickness of the side wall of the master and slave wire are taken as the response values. The relation equation between response value and factor is established, The influence of single factor variables on the penetration depth and thickness of the side wall of the welding master and slave wire and the effect of the interaction between the two factors on the response value are studied. In the experiment, 10%He and 11 CO2s are selected as the optimal protective gas technology. The experimental results show that the actual value is not different from the predicted value, and the fitting equation is more accurate.
【学位授予单位】：哈尔滨工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG457.6

【相似文献】