The operational modal analysis (OMA) can be employed in the field of machine tools to measure the dynamic behaviour under operation conditions to observe and assess effects that only occurring during process. However, OMA requires an broadband excitation with preferably white noise characteristic. When assuming that the machining process is the main excitation source in machine tools, this requirement could not be fulfilled because of the great number of harmonic components that resultfrom spindle speed and number of teeth. In this paper an approach is presented to generate a broadband excitation during a milling process by variating the cutting parameters, for e.g. spindle speed and immersion. Investigations are performed simulative as well as experimental and restrictions of the machine tool and the process are considered. It is shown that an broadband excitation by milling is possible only by varying cutting parameters without using a special designed work-piece.