Drilling of rivet holes in stacked materials consisting of CFRP and Ti-6Al-4V still represents unique challenges. It is common practice to drill the material layers using one single tool. When exiting the final metallic layer, formation of a drill cap usually leads to undesirable burrs and debris, requiring manual post-processing. In this work, a drilling process to avoid drill caps is presented. This is realized using low frequency high amplitude vibration assisted drilling with defined coupling of the rotational speed and the axial oscillations. Drilling parameters and their impact on the quality of the drilled hole in the metallic layer are also investigated. It is found that drill tip geometries and process parameters need to be tuned together to achieve a stable and repeatable process for drill cap avoidance. A highly sensorized experimental setup with multi-sensor systems including high-speed and thermal imaging was used for process evaluation.
The objective of this research is to investigate observable process changes during multi-layer friction surfacing of EN AW 6060 aluminum, whether for repair, remanufacturing, or new part manufacturing. In this study, friction surfacing was performed with a 10-mm-diameter rod of EN AW 6060 aluminum at spindle speeds ranging from 1000 to 7000 rpm to create up to three layers of 40-mm-long deposits on a substrate of the same alloy. The process forces and layer temperatures were observed. Post-process measurement of flash geometry, layer geometry and microhardness were conducted with the motivation to understand the impact of multi-layer depositions on performance and identifying acceptable conditions required to achieve acceptable build quality. The thickness, deposition and joining efficiency of layers in the multilayer configuration remained consistent. Friction surfacing of EN AW 6060 aluminum allowed for high deposition rates of 9 kg/hr, when compared to other metal additive technologies.
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