The ground-based system (see above photo and schematic) is a commercially-available electron beam welder that has been adapted for performing EBF3 process development. This system includes a 42 kW, 60-kV accelerating voltage electron beam gun, a vacuum system, a positioning system, and dual wire feeders capable of independent, simultaneous operation. The two wire feeders may be loaded with either a fine and a coarse wire diameter for different feature definition, or two different alloys to produce components with compositional gradients. Positioning is programmable through six axes of motion (X, Z and tilt on the moving electron beam gun, and Y, tilt and rotate on the positioning table). This electron beam system requires a vacuum on the order of 5x10-5 torr and is housed in a vacuum chamber measuring 2.5 m by 2 m by 2.7 m (100 in. by 78 in. by 108 in.). The EBF3 process offers promise for fabrication of a variety of parts.
Examples of parts fabricated at NASA Langley using the EBF3 process. (a) Ti-6-4 wind tunnel model; (b) 2219 Al square box; (c) 2219 Al airfoil; (d) 2219 Al mixer nozzle; (e) 2219 Al converging diverging nozzle; (f) Ti-6-4 guy wire fitting; (g) Ti-6-4 inlet duct; (h) Ti-6-4 truss node with flat attachment surface.
EBF³ uses a focused electron beam in a vacuum environment to create a molten pool on a metallic substrate. This layer-additive process enables fabrication of parts directly from CAD drawings. Metal can be placed only where it is needed and the material chemistry and properties can be tailored throughout a single-piece structure, leading to new design methods for integrated sensors, tailored structures, and complex, curvilinear stiffeners. The parts can be designed to support loads and perform other functions such as aeroelastic tailoring or acoustic dampening. The EBF3 process has been demonstrated on aluminum, titanium, and nickel-based alloys of interest for aerospace structural applications; ferrous-based alloys are also planned.
Researchers at NASA Langley Research Center have developed the electron beam freeform fabrication (EBF3) process to produce unitized structures from high reflectance aerospace alloys such as aluminium and titanium. Near-term applications of the EBF3 process are most likely to be implemented for cost reduction and lead time reduction thru addition of details onto simplified preforms (casting or forging). This is particularly attractive for components with protruding details that would require a significantly large volume of material to be machined away from an oversized forging. Future far-term applications promise improved structural efficiency through reduced weight and improved performance by exploiting the layer-additive nature of the EBF3 process to fabricate tailored unitized structures with functionally graded microstructures.
EBF3 is a new layer additive process with high potential for use in numerous structural metallic applications. EBF3 offers the potential for cost and lead time reductions in production of parts and performance improvements through optimized alloy chemistries and microstructures. Microstructures and mechanical properties obtained in aluminium and titanium alloys have demonstrated the potential for achieving a wide microstructural range with properties comparable to those of wrought product forms. EBF3 offers viable solutions to issues of deposition rate, process efficiency, and material compatibility for insertion into the production environment. Although further process development and understanding is required, no barriers are evident to prevent the maturation of EBF3 into a competitive commercial process.
Solid freeform fabrication (SFF) encompasses a class of processes that can be used to design and construct parts using a layer-additive approach. SFF processes are an outgrowth of rapid prototyping processes such as stereolithography for plastics and welding repair techniques employing laser, electron beam, or arc welding for repairing metal seal knife edges, turbine blade tips, or tooling dies. Current development efforts are expanding these repair techniques and applying principles from computer-aided design (CAD) and manufacturing as well as from rapid prototyping for wider applications. These development efforts are resulting in the production of a new class of SFF layer-additive processes to build structural metallic parts directly from CAD data rather than the traditional material removal approach.