The laser-based Directed Energy Deposition (DED-LB) process involves a complex thermal history which strongly de-pends on the geometry of the deposited structure and substrate. The thermal mechanisms of the process are highly influenced by key process parameters like laser power, powder mass flow and scanning speed. Additionally, the size of the substrate influences the cooling behavior. The cooling behavior can be externally influenced and controlled by tempering the substrate, for example using a laser preheating method. The control of the cooling rate is crucial to ensure consistent properties and maintain constant conditions for subsequent finishing processes, irrespective of the size and geometry of the deposited structure and substrate. In this work, the influence of the substrate size on the cooling behav-ior and the properties of DED-LB manufactured structures is determined. The deposition of a cube with an edge length of 30 mm on different sized substrates and different cooling rates was simulated and executed. The impact of the dif-ferent cooling behavior is evident in the hardness and the residual stresses of the deposited structures. Furthermore, the effect can be observed during a subsequent milling process. This work enables the creation of a model for the determi-nation of the cooling rate and part properties depending on the substrate size.