TC4钛合金激光深熔焊等离子体羽流喷发过程研究

Plasma Plume Eruption During Laser Deep-Penetration Welding of TC4 Titanium Alloy

在激光深熔焊过程中,等离子体羽流的喷发过程作为等离子体振荡的关键阶段,与熔池小孔行为密切相关,而小孔的行为又决定着焊缝成形及焊接质量.由于等离子体喷发过程具有很强的随机性,通过检测该过程的热力学基础参数,可以更好地监测焊接过程.本文利用无源双探针检测装置与高速摄像组成的多源光电信号同步检测系统,对钛合金在激光焊接过程中的等离子体羽流喷发行为进行分析.结果表明:等离子体喷发过程分为初期、中期和后期3个阶段;在喷发初期,激光功率在1200~1500W时,等离子体喷发速度最高超过100 m/s,最低小于10 m/s,随功率增加喷发速度分布范围呈减小趋势,概率最大的喷发速度也随之减小;在喷发中期,根据等离子体喷发经过双探针时间差之比的k值来衡量喷发过程中温度变化程度,发现两探针检测等离子体相同温度的时间差是初始阶段等离子体流经两探针时间差的3倍及以上;在喷发后期,两探针电信号波形到达极小值点时间差值的正负可用来判断等离子体喷发的剧烈程度,差值为负时等离子体喷发剧烈,反之等离子喷发较弱.

In laser deep-penetration welding,as a key stage of plasma oscillation,the plasma plume eruption is closely related to the behavior of the keyhole,affecting the weld forming and welding quality.Owing to the strong randomness of the plasma eruption,the welding can be better monitored by detecting its basic thermodynamic parameters.Herein,a multisource photoelectric signal synchronous detection system integrating a passive dual-probe detection device and a high-speed camera was used to analyze the plasma plume eruption behavior of titanium alloy during laser welding.Results showed that the plasma eruption was divided into three stages:early stage,middle stage and later stage.In the early stage,when the laser power ranged from 1200W to 1500W,the maximum eruption velocity of the plasma was higher than 100 m/s,and the minimum was lower than 10 m/s.The distribution range of the eruption velocity tended to decrease with the increase of power,and the eruption velocity with the maximum probability also decreased.In the middle stage,the temperature change during the eruption was measured based on the k value of the ratio of the time difference between the two probes.The time difference between the two probes to detect the same temperature of the plasma was thrice or higher than the time difference between the two probes in the early stage.In the later stage,the positive and negative differences in the time difference between the electrical signal waveforms of the two probes reaching the minimum point can be used to judge the severity of the plasma eruption.When the difference was negative,the plasma eruption was severe;otherwise,the plasma eruption was weak.