The present disclosure relates to methods and apparatuses for assembling absorbent articles, and more particularly, methods and apparatuses for imparting a line of weakness into one or more layers of an advancing substrate and separating the substrate along the line of weakness to form a separation edge. The advancing substrate may be a belt assembly including an outer layer, an inner layer, and one or more elastic strands disposed between the outer layer and the inner layer. The belt assembly may be rotated on a process member about a longitudinal axis of rotation. The process member may advance the belt assembly to one or more ultra short pulse laser sources. The ultra short pulse laser source imparts a line of weakness into the belt assembly. A trim removal member may be used to separate the line of weakness forming a trim portion and a separation edge.