Numerous analytical methods are available to predict the stability of milling processes. Most of these methods base on the assumption, that the dynamics of the machine tool are time invariant. This assumption seems to be valid in many cases. However, in case of huge translational or rotatory axes movements or process-induced changes in the work piece's mass and elasticity a time variant dynamic model might be needed. This paper presents a method to model the axis position dependent dynamics of a multi-axis milling machine. According to this method, the modal parameters of the machine tool are predetermined in different discrete axis positions. An interpolation strategy allows calculating the modal parameters in arbitrary resolution along arbitrary tool paths. Here, an exemplary 2.5-dimensional milling process serves as an example. The conventional step-by-step time domain simulation procedure is complemented by the modal interpolation strategy to account for changing machine dynamics. The effect of changing dynamics on the process is determined and a comparison to a cutting test is performed.