This paper presents the results of FEM (Finite Element Method), CFD (Computational Fluid Dynamics) and modal analyses of model semi-axial pump. Two sets of impeller blades were printed by metal 3D printing technology with internal honeycomb structures. The set of solid blades, manufactured by CNC machining for a comparison, was also included. 3D printed blades were designed with internal structures in order to save material, and with respect to mechanical and dynamic properties. Saved material can change the starting moment, modulate modal properties or decrease strength properties. The 3D printed blades can be produced very quickly and with accurate blade surface finish. One of the reasons of this approach can be the use of 3D printed blades as spare parts for industrial applications or for model pump research. This paper contains short introduction to blade design with internal honeycomb structures and their one-way FSI analyses (Fluid Structure Interaction). The final results of best design are presented and discussed.