高速CO_2焊接中的熔池稳定性及焊缝成形

Stability of Molten Pool and Bead Formation in High speed CO 2 Welding

应用具有自由表面的流体稳定性理论，解释了高速焊接时驼峰焊道的产生机理，并通过对熔池形成过程的实时图像采集对该理论进行了验证。理论分析和试 验结果均表明，采用自由过渡 的熔滴过渡形式进行焊接，工件始终处于焊接电弧的加热下， 在高速焊接时，熔池不能及时冷 却，熔 池明显拉长，由扰动引起的振动波长大，当熔池的拉长达到一定程度时，会发 生液体金属的失稳和颈缩 的现象，造成驼峰焊道。在此基础上提出，可以采用短路过渡代替高电压下的自由过渡，利用短路过渡时电弧周期性的熄灭可以减小对熔池的加热量，防止熔池过长而失稳。试验结果表明，采用短路过渡焊接可以有效地防止驼峰焊道的产生，提高焊接速度。

The theory of stability of a liquid with free surface is applied to understand the ‘humping’ phenomenon in bead formation during high speed welding. A real time image sampling system is established to verify the theoretical analysis. The result shows that, when a free droplet transfer mode is applied in high speed welding, the workpiece is heated by the arc throughout the process and thus the molten pool can not solidify in time.As a result, the molten pool is very long, which gives way to the instability of bead formareron and pinch effect of the liquid metal,so that it finally leads to the humping phenomenon. Based on the analysis and experimental result, the short circuiting transfer mode is suggested to improve the bead formation in high speed welding. During short circuiting mode, the arc extinguishes periodically, so the heat transferred into the molten pool is decreased, this helps to avoid the molten pool to be extra long and in turn avoid the instability of the liquid metal.The results of experiments indicate that with short circuiting transfer mode, sound weld can be achieved in high speed welding.