Control Methods for the Electron Beam Free Form Fabrication Process

Engineering a closed-loop control system for an electron beam welder for additive manufacturing is challenging. For earth and space based applications, components must work in a vacuum and optical components must be protected from becoming occluded with metal vapor. For extraterrestrial applications added components increase launch weight and increase complexity. Here we present three different control methods for electron beam free form fabrication. A relatively simple coarse feedback control method is introduced that couples path planning and electron beam parameter controls into the build process to increase flexibility and improve build quality. The different approaches may be applied separately or together to provide enhanced EBF3 system performance.Mechanical Engineerin

Control of Space-Based Electron Beam Free Form Fabrication

Engineering a closed-loop control system for an electron beam welder for space-based additive manufacturing is challenging. For earth and space based applications, components must work in a vacuum and optical components become occluded with metal vapor deposition. For extraterrestrial applications added components increase launch weight, increase complexity, and increase space flight certification efforts. Here we present a software tool that closely couples path planning and E-beam parameter controls into the build process to increase flexibility. In an environment where data collection hinders real-time control, another approach is considered that will still yield a high quality build

A Decision-Support Model for Selecting Additive Manufacturing Versus Subtractive Manufacturing Based on Energy Consumption

This paper presents a simple computational model for determining whether additive manufacturing or subtractive manufacturing is more energy efficient for production of a given metallic part. The key discriminating variable is the fraction of the bounding envelope that contains material i.e. the volume fraction of solid material. For both the additive process and the subtractive process, the total energy associated with the production of a part is defined in terms of the volume fraction of that part. The critical volume fraction is that for which the energy consumed by subtractive manufacturing equals the energy consumed by additive manufacturing. For volume fractions less than the critical value, additive manufacturing is more energy efficient. For volume fractions greater than the critical value, subtractive manufacturing is more efficient. The model considers the entire manufacturing lifecycle from production and transport of feedstock material through processing to return of post-production scrap for recycling. Energy consumed by processing equipment while idle is also accounted for in the model. Although the individual energy components in the model are identified and accounted for in the expressions for additive and subtractive manufacturing, values for many of these components may not be currently available. Energy values for some materials production and subtractive and additive manufacturing processes can be found in the literature. However, since many of these data are reported for a very specific application, it may be difficult, if not impossible, to reliably apply these data to new process-material manufacturing scenarios since, very often, insufficient information is provided to enable extrapolation to broader use. Consequently, this paper also highlights the need to develop improved knowledge of the energy embodied in each phase of the manufacturing process. To be most valuable, users of the model should determine the energy consumed by their manufacturing process equipment on the basis of energy-per-unit-volume of production for each material of interest considering both alloy composition and form. Energy consumed during machine idle per unit time should also be determined by the user then scaled to specific processing scenarios. Energy required to generate feedstock material (billet, plate, bar, wire, powder) must be obtained from suppliers

Tailored Wingbox Structures through Additive Manufacturing: A Summary of Ongoing Research at NASA LaRC

The use of wingbox structural design for improved performance (i.e., fuel burn reduction) of subsonic transports is driven by two trends: reduced structural weight and increased wingspan. These two trends are in direct competition, as the increased span will exacerbate the structural reaction to aerodynamic loading, and the reduced structural weight will nominally weaken the aircrafts ability to handle this response. Novel structural configurations, enabled by recent improvements in manufacturing, may be critical toward bridging this gap.This paper summarizes pertinent activities at the NASA Langley Research Center in terms of additive manufacturing of metallic wing structures and substructures. Numerical design optimization activities are summarized as well, in order to understand where on a wingbox an additively-manufactured part may be useful and the way in which that part beneficially impacts the flight physics. The paper concludes with a discussion of how these two research paths may be better married in order to fully integrate both the benefits and realistic limitations of additive manufacturing and numerical structural design

Elastically Deformable Side-Edge Link for Trailing-Edge Flap Aeroacoustic Noise Reduction

A system is provided for reducing aeroacoustic noise generated by an aircraft having wings equipped with trailing-edge flaps. The system includes a plurality of elastically deformable structures. Each structure is coupled to and along one of the side edges of one of the trailing-edge flaps, and is coupled to a portion of one of the wings that is adjacent to the one of the side edges. The structures elastically deform when the trailing-edge flaps are deployed away from the wings

Development of a Prototype Low-Voltage Electron Beam Freeform Fabrication System

NASA's Langley Research Center and Johnson Space Center are developing a solid freeform fabrication system utilizing an electron beam energy source and wire feedstock. This system will serve as a testbed for exploring the influence of gravitational acceleration on the deposition process and will be a simplified prototype for future systems that may be deployed during long-duration space missions for assembly, fabrication, and production of structural and mechanical replacement components. Critical attributes for this system are compactness, minimal mass, efficiency in use of feedstock material, energy use efficiency, and safety. The use of a low-voltage (less than 15kV) electron beam energy source will reduce radiation so that massive shielding is not required to protect adjacent personnel. Feedstock efficiency will be optimized by use of wire, and energy use efficiency will be achieved by use of the electron beam energy source. This system will be evaluated in a microgravity environment using the NASA KC-135A aircraft

A Design of Experiments Approach Defining the Relationships Between Processing and Microstructure for Ti-6Al-4V

A study was conducted to evaluate the relative significance of input parameters on Ti-6Al-4V deposits produced by an electron beam freeform fabrication process under development at the NASA Langley Research Center. Five input parameters where chosen (beam voltage, beam current, translation speed, wire feed rate, and beam focus), and a design of experiments (DOE) approach was used to develop a set of 16 experiments to evaluate the relative importance of these parameters on the resulting deposits. Both single-bead and multi-bead stacks were fabricated using 16 combinations, and the resulting heights and widths of the stack deposits were measured. The resulting microstructures were also characterized to determine the impact of these parameters on the size of the melt pool and heat affected zone. The relative importance of each input parameter on the height and width of the multi-bead stacks will be discussed