Model-based cutting prediction for a self-vibratory drilling head - spindle system
Résumé
The drilling of deep holes remains an unsatisfactory machining operation due its limited productivity. This manufacturing process requires the chips to be evacuated through the use of retreat cycles and high-pressure lubrication, which is problematic both for productivity and the respect of the environment. An alternative response to the chip evacuation problem is the use of a vibratory drilling head which enables the chip to be split thanks to the drill's axial vibration. The high-speed drilling operation requires specific cutting conditions to be determined in order to maintain self-excited axial vibration throughout the drilling process. The prediction of adequate cutting conditions is determined on the basis of the frequency characteristics of the spindle/self-vibratory drilling head and the dynamics of the cutting process. It can be expressed in terms of a specific stability diagram indicating the zone of stable self-excited axial vibration. The aim of this study is to develop a high-speed spindle/drilling head/tool system finite element model to evaluate the system's dynamic characteristics and the adequate cutting conditions allowing stable self-excited axial vibration. The model is elaborated on the basis of rotor dynamics prediction, and takes into account the interfaces between system components, using the receptance coupling method. Using the model, adequate cutting conditions are determined by integrating the model-based tool tip transfer function into the chatter vibration stability approach proposed by Budak and Altintas. The simulated results are validated by performing vibration and drilling tests. The proposed model can be used to accurately evaluate the dynamic performance of the spindle/self-vibratory drilling head and can also be used to design an optimised spindle/drilling head for a given drilling process.