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

在本研究中，我们提出了一种检测连续4kW YAG激光焊接中深熔透模式和浅熔透模式焊接特性的技术。对低碳钢SS400、不锈钢SUS304和铝合金A5083进行了焊接和对焊时的光声发射测量。对这些发射进行频率分析，直至40千赫。低碳钢串焊板焊接过程中，当焊接特性由深熔接模式转变为浅熔接模式时，声谱的主要频率分量随熔接深度的减小而从低频范围向高频范围偏移。在光谱中观察到类似的主要频率分量偏移。这种现象与材料种类无关，也可以在对焊过程中观察到。为了更清楚地了解这些频谱变化，将两个特征频率范围内的发射强度之比与焊头的长径比相关联。结果，我们发现光谱的低频分量与高频分量的强度比与长宽比具有良好的相关性。例如，23-25 kHz至2-4 kHz的光发射强度比与串焊长宽比具有良好的相关性，32-35 kHz至2-4 kHz的声发射强度比与串焊长宽比具有良好的相关性。通过分析发射信号的频率成分，可以判断焊接是深熔还是浅熔。频谱的差异可用于开发用于焊接质量控制的反馈系统。

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.