Definition of Cutting Conditions for Thin-to-Thin Milling of Aerospace Low Rigidity Parts

The main drawback of the high speed milling of monolithic parts for the aerospace industry is the high buy-to-fly ratio that leads to a huge material waste. This problem is caused by the need to stiffen the part during the machining in order to avoid chatter, excessive vibration and residual stresses. The present work proposes a methodology for the milling of compliant parts based on the selection of cutting conditions free of chatter. First, the modal parameters of the part in the most problematic stages of the machining are calculated by means of the finite elements method. Secondly, a three-dimensional stability model is used in each stage to calculate a three-dimensional stability lobes diagram dependent on the tool position along the whole tool path. Given the fact that the depth of cut is defined by the bulk of material, the three-dimensional stability diagram can be reduced to a two-dimensional one, which relates tool position during the machining and spindle speed, and indicates how to change the spindle speed in order to avoid the unstable areas. What is more, the proposed methodology can also be used to dimension the bulk of material, select the proper tool or improve the fixturing of the part. Finally, the methodology is validated experimentally on a test part.