A study on ray tracing method for CFD simulations of laser keyhole welding: progressive search method

In the laser keyhole welding process, one ray can have several reflections and absorptions during the process. This is called multiple-reflection and is considered to be one of the important physical phenomena in the laser keyhole welding process. To calculate the multiple-reflection in laser keyhole welding simulations, a ‘Ray tracing’ methodology is used. Through ray tracing, several ray properties, such as the current location of a ray, the location of reflection, and the reflected direction, can be calculated. This study investigated the numerical simulations of two ray tracing methods, the Direct Search Method (DSM) and Progressive Search Method (PSM). There are differences between the two ray tracing methods. PSM uses a real equation for the surface and ray direction vector while DSM uses a discriminant. A reflected ray is moved step by step in PSM, but only once by the discriminant in DSM. The reflected ray starts from the real contact point in PSM, but from the center of the contacted sub-cell in DSM. PSM can depict the multi-path of the ray by employing a set of sub-rays concept. On the other hand, DSM cannot depict the multi-path of the ray, because it uses a single ray definition. Therefore, PSM is a more physical numerical method and can depict various phenomena, such as transmission and scattering. PSM has a higher accuracy in laser keyhole welding simulations. In PSM, two new models were applied, the transmission and scattering models. All simulations were performed with the computational fluid dynamics (CFD) method including the volume of fluid (VOF) technique. Simulations using the DSM and PSM were performed to compare these two methods.