Keyhole stability during laser welding-part I: modeling and evaluation

The keyhole is a requirement in order to establish the energy efficient process of laser deep penetration welding. However, the process is highly unstable which results in unwanted pore and spatter formation. In order to avoid process defects, the physical effects in the keyhole have to be better understood to find ways for compensation. This work aims to describe the keyhole properties at different welding parameters for welding of aluminum (EN AW 1050) with the help of a semi-analytical model based on energy and pressure equations and differential equations. The resulting dynamic characteristics of different keyholes are evaluated with frequency analysis of optical observations during the welding process. The spring coefficient, that describes the radial pressure change at radius deviation, is a good indicator for the resulting keyhole dynamics. Dynamic behavior is influenced by the spatial laser intensity distribution, while higher frequencies at lower amplitudes are found at a Top Hat distribution compared to a Gaussian intensity profile.