In common FEM fatige rating tools, the orthotropic fatigue resistance orientation at welds is defined by the mesh. Hence, a labourous manual model preparation is required. This article describes an approach to automatically detect the local weld line tangent by analysing CAD geometry, and to derive into stress result interpretation, afterwards. The notch orientation thus becomes independent from the mesh, which allows a full-automated model setup. The described simulation approach has been verified by a large heavy-duty vehicle main frame test bench run with known multi-axial load time series and precisely recorded crack occurrences. The comparison with observed physical failure in test bench has shown a remarkable precision in durability prediction. Due to its automation capabilites, a new time-saving custom method for fatigue analysis, especially on large welding structures is introduced.