Tumbling mills using balls as grinding media are used in a variety of ways to produce fine powders. Mills in this category are ball, planetary and vibratory mills. The fineness of powder produced in such mills depends on the powder strength characteristics as well as the impact energy of the tumbling balls. In order to understand the collision frequency and the collision intensity of the ball media, a numerical simulation tool using the discrete element method (DEM) has been developed. The impact energy spectra of these mills can be modified via suitable choice of operating conditions. The significance of the impact energy spectra of vibratory and planetary mills are discussed.