High speed process damping in milling

High performance milling processes are limited by two dominating factors: the available spindle power and the dynamic stability of the process. When the cutting depth exceeds the stability limit, chatter vibrations arise. These vibrations lead to wavy surfaces, increase of the tool wear, acoustic noise and can even damage the spindle. Cutting edge chamfers are a possible means to avoid such vibrations. In this paper it is shown experimentally and theoretically how such chamfers affect the process damping effect and hence the stability limit. A cutting force model is presented, that takes into account the process damping effect and the geometry of the hamfered cutting edge. Theoretically predicted stability charts are compared to experimental data. The process damping coefficients are identified by a very simple wave-on-wave planing method. It is shown that due to cutting edge chamfers process damping is not restricted to the low speed cutting range anymore but also occurs at higher spindle speeds. It is demonstrated, that the key reason for the high speed process damping effect is a kind of mode interaction of the low frequency modes with the high frequency ones. Due to this effect stable as well as unstable islands can arise in the stability charts.