Modeling of Welding Process and its Application to Laser Materials Processing

本文首先讨论了焊接过程的数学模型，通过对热传导方程的数值分析，确定了焊接过程中熔池尺寸的大小，然后对焊接过程中熔池尺寸的变化规律进行了分析，最后对焊接过程中熔池尺寸的变化规律进行了讨论。数值求解表面张力平衡方程，得到焊接时熔池表面轮廓。通过对激光焊接和电弧焊接过程的模型分析与实验结果的比较，表明本文建立的数值模型是激光焊接和电弧焊接过程模拟的有效工具。本文第二部分将辐射测温技术应用于激光焊接和电弧焊接过程的温度场监测，但其可靠性有待进一步研究。在激光焊接或电弧焊接过程中，由于被测工件的发射率不能准确地确定，因此，在测量过程中，辐射温度的测量受到了限制，为了避免上述发射率问题，提出了一种紫外辐射测温法，并进行了实验研究。本文采用带紫外滤光片的CCD摄像机测量系统，在不进行发射率修正的情况下，实现了焊接过程中板材表面温度图像的实时检测，从而证明利用该模型和本文研制的紫外辐射测温系统，建立焊接过程的模型参考控制系统是可行的。

In this work, a feasibility study has been conducted to determine if a numerical model can be used for optimizing laser or arc welding processes.In the first part of this work, a mathematical model of welding process has been discussed, where the equation of heat conduction is numerically analyzed to estimate the molten pool size in welding, and a surface tensional balance equation is solved numerically to obtain the molten pool surface profile in welding. As a result of the comparison between model analysis and experiment on laser or arc welding, it is made clear that the numerical model, developed in this work, is a useful tool for the simulation of laser or arc welding process.In the second part of this work, the radiation thermometry has been applied to monitor the temperature field in laser or arc welding process.The reliability of the 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.In order to avoid the above emissivity problem, an UV (ultra-violet) radiation thermometry has been proposed and discussed experimentally. A measuring system of CCD camera with UV-filter, used in the present work, made it possible to detect the temperature image on the plate in welding without any emissivity correction.It is concluded that a model reference control system of welding is possible by using the model and the UV radiation thermometry developed in this work.