A method for milling process simulation performed on a free-formed body is disclosed. In the method a three-dimensional multi-dexel representation of a free- formed body to be processed is generated by using a three-dimensional depth peeling algorithm at a first virtual camera position and a predetermined grid spacing (S110), wherein each of the dexels are stored independently of each other regarding their neighborhood relations, and each of the dexels is associated with at least the following pieces of information: information relating to the spatial position and direction of the dexel, preferably the display coordinates of the dexel and the depth coordinate of the end points of the dexels, geometric information relating to the workpiece surface intersected by the dexel at the starting point and the end point of the dexel. Then a volume representation of the tool or a volume representation the swept volume of the tool is generated by using a three- dimensional depth peeling algorithm (S120) at a second virtual camera position, wherein said second virtual camera position is identical to said first virtual camera position, and wherein the surface segments of the tool thus obtained are described by display coordinates and depth coordinates associated with said respective display coordinates. In predetermined positions of the tool along the tool path, the depth coordinates of each dexel are compared to the depth coordinates of the surface segments of the tool or the swept volume of the tool that have the same display coordinates as those ones of the dexel, and accordingly, for each of the dexels, the intersection points of the particular dexel and the surface segments of the tool (S130) are determined. A dexel is kept unchanged if the dexel has no intersection point with the tool surface (S131), or the respective parameters of the dexel are modified if the dexel has an intersection point with one surface segment of the tool (S132), or the dexel is converted into two or more shorter dexels if the dexel has multiple intersection points with more than one of said surface segments (S133). Thereby a modified three-dimensional dexel-volume representation of the workpiece is generated at a particular position of the tool.