A monitoring method for welding by UV thermal radiation

本文讨论了一种激光或电弧焊接过程的模型参考监测方法，首先进行了一项可行性研究，以确定紫外辐射测温法是否可用于激光或电弧焊接过程的监测。红外辐射测温法通常用于激光焊接或电弧焊接过程的温度场监测。然而，在激光或电弧焊接工艺的情况下，在待测工件的发射率不准确的情况下，红外测温的可靠性受到限制。为了避免上述发射率问题，讨论了一种紫外辐射测温方法。研制了一套带紫外滤光片和像增强器的CCD摄像机测量系统。将紫外线测量系统应用于焊接温度场的监测中，阐明了该系统可以在不进行发射率修正的情况下准确地测量温度场。其次，建立了焊接过程监测的数学模型，其中利用热传导方程计算焊接温度场，应用表面张力平衡方程对焊接熔池形状进行了预测。通过对电弧焊接过程的计算和实验结果的比较，表明该模型是一种有效的焊接过程监测和模拟工具，从而说明本文提出的紫外热辐射监测方法对激光焊接或电弧焊接过程的监测是有用的。

A model reference monitoring method for laser or arc welding process has been discussed in the present work.In the first, a feasibility study has been conducted to determine if an UV (ultra violet) radiation thermometry can be used for monitoring laser or arc welding processes. The IR radiation thermometry is usually applied to monitor the temperature field in laser or arc welding process. The reliability of the IR thermometry is, however, limited under the condition that the emissivity of the work to be measured is not accurately known as in the case of laser or arc welding process. To avoid the above emissivity problem, an UV (ultra-violet) radiation thermometry has been discussed. And a measuring system of CCD camera with UV-filter and image intensifier was developed in the present work. The UV measuring system was applied to monitor the temperature field in welding, and it was clarified that the developed system made it possible to detect accurately the temperature field without any emissivity correction.In the second, a mathematical model for monitoring the welding process was developed, where the equation of heat conduction was used to calculate the temperature field in welding, and a surface tensional balance equation was applied to estimate the molten pool profile in welding. As a result of the comparison between calculation and experiment on arc welding, it has been made clear that the model is a useful tool for monitoring and simulating the welding process.Accordingly, it is concluded that the monitoring method by UV thermal radiation, proposed in the present work, is useful for laser or arc welding process.