STUDY OF IN-PROCESS MONITORING DURING HIGH POWER YAG LASER WELDING

在这项研究中，我们提出了一种检测连续4kW激光焊接深熔模式和浅熔模式焊接特性的方法。测量了低碳钢SS400、不锈钢SUS304和铝合金A5083在堆焊和对接过程中的光发射和声发射。对这些辐射进行了频率分析，最高可达40 kHz。在低碳钢堆焊过程中，当焊接特性由深熔向浅熔转变时，随着熔深的减小，声谱的主要频率成分由低频段向高频段移动。光谱的主要频率成分也发生了相似的变化，这种现象与材料无关，在对接焊接过程中也可以观察到。为了更清楚地了解光谱的变化，将两个特征频率范围内的发射强度之比与焊道的纵横比进行了关联。结果发现，光谱的低频分量与高频分量的强度比与长宽比有很好的相关性。例如，在堆焊过程中，23-25 kHz和2-4 kHz的光发射强度比与长径比有很好的相关性，32-35 kHz和2-4 kHz的声发射强度比与此有很好的相关性。因此，可以通过分析发射信号的频率成分来判断焊接是深熔还是浅熔。频谱的不同可能有助于开发用于控制焊接质量的反馈系统。

In this study, we propose a technique to detect the welding characteristics between deep penetration mode and shallow penetration mode in CW 4kW YAG laser welding. The optical and acoustic emissions during bead-on plate welding and butt welding were measured for mild steel SS400, stainless steel SUS304 and aluminum alloy A5083. A frequency analysis of these emissions was performed up to 40 kHz. When the welding characteristics changed from deep penetration mode to shallow penetration mode in mild steel during bead-on plate welding, main frequency components of the acoustic spectrum shifted from lower frequency range to higher frequency range according to the decrease in the penetration depth. The similar shift of the main frequency components was observed for the optical spectrum.This phenomenon was observed independent of kinds of material and also observed during butt welding.In order to make clearer these changes in frequency spectra, ratio of the emission intensities in two characteristics frequency ranges was correlated to aspect ratio of the welding bead. As a result, we found that the intensity ratio of low frequency components versus higher frequency components of the spectra correlated well to the aspect ratio. For example, the intensity ratio of the optical emission of 23-25 kHz to 2-4 kHz showed a good correlation with the aspect ratio during bead-on plate welding, and the intensity ratio of the acoustic emission of 32-35 kHz to 2-4 kHz correlated well to that. Thus we could evaluate whether the welding was deep penetration mode or shallow penetration mode by analyzing the frequency components of the emission signals. The deference of the frequency spectrum may be useful in the development of a feedback system for control of weld quality.