Complex structures and decreasing wall thicknesses in modern turbine blades result in increased efficiency due to better aerodynamics, weight reduction and improved cooling properties. Since it is advantageous to cast the components close to the final contour to minimise rework and resource consumption, it is necessary to understand and master the process of casting thin-walled structures using the Bridgman process. Therefore, the influence of wall thickness and withdrawal rate on the casting of thin-walled structures has been investigated using the commercial Ni-base alloy CM186LC. Initial results on the casting of such structures have already been obtained in previous work. In order to extend the results and gain a better understanding of the effects that occur, the casting process and the microstructure formation are simulated in this work. To simulate the Bridgman casting process, an FEM simulation was conducted to determine the temperature curve and the temperature gradient. The results were compared with experimentally measured temperatures during the casting process to validate the simulation results. Using the temperature-time curve and temperature gradient from the process simulation and a suitable thermodynamic database, a phase field simulation was carried out to investigate the microstructure formed during casting. The process and microstructure simulations were carried out for wall thicknesses from 0.4 mm to 2 mm and withdrawal rates from 0.1 mm/min to 10 mm/min. Several aspects are considered from the microstructure simulation results. Of particular interest are the dendrite spacing and the segregation between dendritic and interdendritic regions. These are of special interest, as the homogenisability of the material is largely dependent on these two variables.