While additive manufacturing (AM) processes have come a long way in producing a variety of shapes and sizes in printed components using an array of materials, an ideal process for producing large monolithic titanium components with user-customized control has remained a challenge. This means the aerospace industry has been lacking an optimized AM process for plate material for components such as wing spars, bulkheads, and frames.
UK-based GKN Aerospace and the U.S. Energy Department’s Oak Ridge National Laboratory (ORNL) recently signed a five-year research agreement to address the technology. The partnership will focus on improving the deposition process of additive manufacturing for aerospace to achieve volume production of large titanium components using a process called laser metal deposition with wire, or LMD-w. LMD-w involves using a robot-manipulated laser to melt the surface of a titanium substrate, creating a localized pool of molten titanium into which titanium wire is fed to form a bead. Also using robotics, the melt pool is manipulated along a 3-D path to create a net-shaped (or near-net-shaped) aerospace preform component bead by bead onto the substrate in layers.
The process is highly efficient for aerospace compared to current subtractive manufacturing methods, which waste an enormous amount of expensive raw materials. GKN’s LMD-w process is already flying on several aero and space applications and remains under ongoing development for new products at the company’s Additive Manufacturing Centre of Excellence in Trollhattan, Sweden.
According to Rob Sharman, GKN’s Global Head of Additive Manufacturing, the LMD-w process has several advantages over other metal deposition processes. For starters, it leverages widely tunable laser energy and a wire feed rate that allows users to choose the deposition rate and material properties. This way, they can optimize build strategies and tailor the mechanical performance of the parts to the application.
GKN Aerospace's AM cell located at Oak Ridge National Labs. Photo credit: GKN Aerospace
“In addition, the wire feedstock used in the LMD-w process is completely consumed in the melt pool, resulting in a higher material efficiency than powder-based deposition processes, which typically have powder that is not completely consumed in the melt pool,” Sharman told Design News. “The laser heat source provides other advantages over electron beam or plasma heat sources as it is capable of depositing finer features, does not require a vacuum chamber, and does not vaporize critical alloying elements during deposition.”
The LMD-w process is intended to be a complement to existing manufacturing processes for the production of large-scale titanium aircraft structures (rolling, forging, extruding, forming, and machining). In most cases, it won’t fully replace traditional methods.
“LMD-w is another tool in the design toolbox; it creates the opportunity to design a new manufacturing sequence using a combination of manufacturing processes that reduces cost, material usage, work in progress, and cycle time,” said Sharman. “Currently, the biggest cost savings for aerostructure components are those with high buy-to-fly ratios that require lengthy machining operations to remove material from hard-to-machine areas with high aspect ratio features (e.g., deep pockets).”
The ability to customize the build process from incoming material to