New Vibration System for Advanced Drilling Composite-Metallic Stacks

To reduce the weight of aero structures, composite materials are combined with metallic parts. These multilayer materials are one-shot drilled during the assembly process. During drilling, interactions appear between the different layers creating new quality issues. To improve machining efficiency, the portable semi-automated drilling units commonly used for such operations need to be upgraded. For this purpose, vibration systems have been recently introduced into drilling units. This article first considers the effect of the reciprocating axial movement on the quality of the machined surface, then focuses on the effect of the oscillation parameters (frequency, magnitude) on the cutting process (cutting forces, thermal load, etc.). Experimental and numerical results are used to find the method that produces the optimal vibration setting. This method is then applied to the case of drilling composite-metallic stack. We conclude that specific vibration parameters need to be set up according to the type of material drilled (composite, metallic). A new vibration system concept has therefore been specifically developed to adapt the oscillation magnitudes to each kind of material. The entire mechanism of the system is shown and analytically modeled. In conclusion, the article describes briefly the auto-adaptive drilling technique for an understanding of the benefit of the new vibration system when associated with this technique.