Lamb waves have shown great potential for structural health monitoring. The technique is based on guided ultrasonic waves introduced into a structure at one point and sensed at a different location. Damage in a structure is identified by a change in the output signal. However, previous studies show that even simple structural configurations can lead to complex response signals. Therefore a knowledge and understanding of wave propagation can ease the interpretation of damage detection results. This paper reports an application of the local interaction simulation approach for Lamb wave propagation modelling in metallic structures. The focus of the analysis is on two-dimensional wave interactions with slot-type defects. The method shows the potential for complex modelling of acousto-ultrasonic waves in damage detection applications.