Mathematical formulation and simulation of specular reflection based measurement system for gas tungsten arc weld pool surface

Weld pool surface can change dynamically during welding and is indicative of information critical to controlling the process. Research has picked up in the field of observing the weld pool surface to understand the dynamics of the welding process. This paper will help visualize and understand the physics involved in observing the weld pool surface. A study of laser properties, weld pool and camera optics was incorporated in developing a model to describe the mechanism of observing the weld pool surface from specular reflection. This observation method projects a laser beam on the pool surface through an optical grid with a frosted glass attached. The corresponding specular reflection is calculated, which is derived based on the reflection law. The reflected laser beams are then captured by the camera to form the image. The model can be used to predict the outcome of experiments with grids placed in front of the laser and to determine the position where the camera should be placed to acquire the best image. Preliminary results showed that the camera should be placed with the weld pool along the optical axis, and the aperture should be as large as possible to allow as many rays into the camera as possible. The model can be used to find the optimal location of the laser and camera for materials of different thickness, by moving the electrode higher in the simulation, and adjusting the laser and camera location accordingly. The paper will give some insight into problems that might be encountered in observing the weld pool, and suggest the set-up of the laser and camera for obtaining the best image.