High Speed Orbital Drilling Optimization and Fatigue Life Enhancement by Orbital Roller Burnishing for Aluminum Alloy

Orbital drilling has proved to be advantageous to achieve aeronautical-level quality drilling (surface roughness, geometry control…) fully adapted for complex assemblies in a single operation. However, compared to conventional drilling method, this process leads to a drastic change in structure’s fatigue life probably due to a non-optimised level of residual stress. The control of the mechanical behaviour of parts obtained by orbital drilling is the goal of the European-CleanSky collaborative R&D project RODEO (Robotized Orbital Drilling Equipment and Optimized Residual Stresses, GA no.738219). In this work, an orbital drilling unit (ORBIBOT) allowing high speed machining conditions was developed by PRECISE France, that can be integrated on a lightweight industrial robot. Cutting parameters were determined through an original Tool-Material Couple optimization strategy dedicated to orbital drilling, developed with MITIS Engineering and carried out on 2024-T351 Aluminum alloy. In order to enhance the mechanical behaviour of the system (fatigue, surface hardening…), an innovative mechanical surface treatment has been introduced for investigations: orbital roller burnishing, performed right after orbital drilling. The burnisher follows a helical path around the hole axis. Orbital burnishing and its associated tool have been patented by PRECISE (N°FR16 60693). A comparative study between axial drilling, orbital drilling and orbital drilling+burnishing was done in terms of hole diameter, surface roughness, burr height, fatigue life…. Performances and quality levels obtained by using orbital drilling (with or without burnishing) are significantly different compared to conventional drilling. On open-hole samples, a significative fatigue life improvement was exhibited using orbital drilling, even more important with burnishing. Tests were performed also on filled-hole configurations. The innovative coupling of orbital drilling and burnishing tools suggested by PRECISE offers new high-speed machining opportunities, especially in the controlled strain hardening and residual stresses domains.