Wire Plus Arc Additive Layer Manufacture: Developments for Large Scale Aircraft Metal Components

Over the last few decades metal additive layer technologies have gained a widespread interest in the high tech aerospace industry for low batch manufacture applications or repair of functional components. In addition, the growing emphasis on the use of exotic and high specific strength raw materials, such as Ti, Al and their alloys, as well as constrained budgets, and restricted carbon emission quotas urged for greener and more cost effective manufacturing solutions. Nowadays various powder based additive layered techniques are commercially available providing high resolution and high complexity to size ratio components, but often limited to small scale components with a low rate of production. For this reason the need for faster processing speed systems and techniques capable of fabricating structural components with no theoretical size limit and increased Material Utilization Factors (MUF´s) has become clear. Recently, various low cost Wire + Arc Additive Layered Manufacture (WAALM) techniques have gained research interest in order to allow the freeform fabrication of large-scale components made of highly reactive metallic alloys in an out-of-chamber condition. The main attributes of such manufacturing techniques include: high deposition rate (over 3.5 kg/h) and a process material efficiency factor of close to 100% of the wire feedstock. In the present study a Gas Metal Arc Welding (GMAW) variant designated by Cold Metal Transfer (CMT) and a cold wire feed Gas Tungsten Arc Welding (GTAW) processes are utilised for the manufacture of large titanium (Ti-6Al-4V) and aluminium alloy components. The advantages and drawbacks of both processes are compared in terms of their process parameters and deposition rate limits. The mechanical and microstructural properties of the resultant component are compared and examined. Tensile strength properties are investigated both in parallel and transverse to the deposition directions, and the fracture surfaces are analysed by Scanning Electron Microscopy (SEM). Finally, the microstructural features such as grain size distribution and morphology are investigated by optical microscopy.

Keywords: Wire + Arc Additive Layered Manufacture (WAALM), Cold Metal Transfer (CMT), Material Utilization Factors (MUF), aerospace, repair, functional components, titanium, aluminium, freeform fabrication, deposition rate, efficiency, large components.