Pressure die casting is a powerful series production method for parts with complex shape. In this process the performance of the casting tools is a crucial factor. Dies are expensive and have vital influence on the quality of the produced parts. Therefore it is necessary to know how they are loaded and damaged in service. The main issues are on the one hand the prevention of early catastrophic failure of the tools and on the other hand the initiation and evolution of cracks due to the high number of thermomechanical cycles. As a result of the thermomechanical loading cracks are typically generated on the entire surface of the tools. In this work numerical fracture mechanics is used to analyse surface crack networks. Due to the thermo-mechanical loading cyclic plastic deformation takes place and residual stresses are induced at and near the tool surface in depths up to about 0.5mm to 2mm. The influence of these residual stress fields on the crack-tip loading and on the growth of cracks is explored. Crack interaction effects due to different crack lengths and crack spacing are considered. The results of the numerical simulations are compared with the experimental evidence.