To successfully control the welding process and to make it appropriate for solid freeform fabrication (SFF), it is necessary to fully understand the influence of the welding parameters and the geometry of the substrate on the resulting weld bead dimensions. Extensive experiments with different welding parameters and complex geometrical features such as edges and corners have been designed and completed. The experimental data show a clear correlation between the heat input, the weld bead

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... ns, and the two dimensional (2D) geometrical features. This correlation may be used for on-line welding process control. It is found that the geometry of the molten pool is directly related to the heat transfer conditions determined by surrounding mass of material. A machine vision system based on a high-resolution CCD camera coaxially integrated with a gas tungsten arc welding (GTAW) torch is used to acquire the images of the molten pool. The results demonstrate the capability to adjust GTAW process parameters according to complex external and internal geometrical features of the substrate. The heat loss affected by the surrounding mass of material will be used to determine the optimal energy input.