Advanced Modeling and Simulation of Thermal Kinetics in Additive Manufacturing
Abstract
This proposal describes basic research in the modeling and simulation of thermal kinetics in additive manufacturing (AM) processes. AM is inherently a thermal process where layered building is achieved through directed energy input with melting and solidification, energy input for sintering without melting, or binding through a separate agent (e.g., a chemical reaction). In current AM processes, the heat input and its time-dependent propagation through the part plays a critical role. Therefore, basic research is warranted to better understand AM thermal kinetics and the associated impact on final part quality. Fundamental studies for two new, innovative AM applications are proposed: 1) crystal growth modeling in a new powder bed silicon carbide AM process; and 2) residual stress modeling in wire arc AM for magnesium alloys. Powder bed silicon carbide AM The innovation is the production of silicon carbide (SiC) parts in a powder bed, binder-jetting AM process using a sodium hydroxide (NaOH)-based binder that produces secondary silicon oxide (SiO2) crystal growth during sintering at moderate temperature levels. The research objective is to gain new knowledge about the role of the post-printing sintering profile on the secondary crystal growth through a synergistic combination of modeling and experiments. Example application areas for this basic research are lightweight/honeycomb space-based optics and ballistic protection, including personalized body armor for soldiers. In the proposed research, SiC powder with varying diameters will be bonded layer-by-layer using a NaOH-water solution to produce solidified gel-SiC pre-sintered parts. After the green part is removed from the power bed machine, a pressure-less sintering step will promote secondary crystal growth, which will reduce the porosity and increase the strength by bridging and sealing the gaps between the grain boundaries. In this way, these crystals will yield a Òsmart materialÓ that self-seals. Initial results are provided and modeling and experimental tasks are described. Wire arc AM for magnesium alloys In wire arc AM, arc welding principles are applied to build metal parts. The benefits are high deposition rates and dense structures that are achieved through local melting in the weld pool and solidification to produce the part geometry. Prior research has focused on the titanium alloy Ti- 6Al-4V, although other material systems have also been studied, including aluminum alloys, tool steels, nickel super alloys, stainless steels, and refractory materials. To this point, however, wire arc AM processes have not included magnesium alloys. The introduction of these alloys into AM processing capabilities is attractive due to their high strength-to-weight ratio. Magnesium alloy AM will offer new design flexibility and high strength-to-weight performance for DoD automotive and aerospace applications, as well as personal equipment and weapons for the modern soldier. Additionally, there is no practical limit on part size. Large scale, complex, monolithic components can be produced that would be difficult to produce by casting or forging. A detailed modeling and experimental task list is included that will explore the relationships between the process inputs: wire feed rate, power supply voltage/current characteristics, torch velocity and path, weld pool cooling rate, wire composition and diameter, and digital part geometry; and outputs: deposition rate, resolution, printed part geometry (including residual stress/distortion), microstructure, and material properties (including homogeneity).
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Feb 14, 2019
- Source ID
- W911NF1810482
Entities
People
- Tony L. Schmitz
Organizations
- Army Contracting Command
- Office of the Secretary of Defense
- University of North Carolina at Chapel Hill