A novel technique to join electron beam perforated metallic sheets to core structures in the design of hybrid laminar flow control suction panels

The technique of Hybrid Laminar Flow Control (HLFC) as employed to suction panels segmented into the airfoil structure has been widely investigated to serve the purpose of sustainable energy-efficient aviation. HLFC suction panels under consideration in this study are sandwich panels with a metallic perforated suction surface as face sheet and laminated structures or Triply Periodic Minimal Surfaces (TPMS) as the core. One of the biggest challenges associated with the optimal design of HLFC suction panels is the blockage of micro-holes on the perforated suction surface. This highly depends upon the perforation technique employed as well as the joining method used for bonding the perforated face sheet to the core structure. While laser drilling has been widely used to perforate the metallic face sheet, it is a slow process, generates a lot of thermal effects and most of the time, requires a protective gas to prevent the deformation and burning of the specimen. As opposed to this, electron beam drilling generates minimal to no thermal effects and is a very fast perforation method. Adhesive bonding has been widely used to join the perforated metallic sheets with the core structures. However, the bonding after perforation still leads to the blockage of the micro-holes. Hence, this paper focuses on a novel method to perforate the metallic face sheet using electron beam drilling with prior applied adhesive and bonding it to the core structure on specimen level. A highly viscous adhesive is chosen with high stiffness and strength properties for bonding. For this purpose, two different adhesives are tested for their mechanical and bonding properties. Different TPMS core structures are employed to have a look at their influence on the properties of the suction panel. Scanning Electron Microscope (SEM) is used to check for the blockage of the micro-holes as well as the hole morphology. Once the sandwich specimens are produced, compressive tests are performed on them to determine their structural integrity and load-bearing capacities of the selected adhesives. • The airfoil's leading edge requires a metallic skin and robust core for HLFC suction-panels to withstand high loads, needing a differential design with metallic skin and TPMS core adhesively bonded. • Laser drilling of metallic skins causes thermal damage and compromised hole morphology. • Electron beam drilling is faster, with minimal thermal effects and better hole morphology. • Adhesive application on suction skins before perforation reduces blockages. • Adhesive films are easier to apply and cause minimal to no blockages compared to liquid adhesives.