Author details

of gravity, by the shortest distance that results in a collision of particles. This compressing is repeated until the potential energy is below a user-defined tolerance. The particles are then "shaken", or moved laterally, and the process is repeated. The build volume is then refilled with more particles and the process is repeated until the volume is full [43]. Another geometric method, displayed in Figure 6b, focuses on a tetrahedral mesh. In this method, the build volume is meshed and particles are placed on the nodes and edges based on a set of rules. This allows for an efficient filling of the space that has a packing density approximately

Each of these methods can be used to simulate the powder bed process, however, the selection can be based on a couple of main factors. If speed is required then a geometric approach should be used. This approach takes on the order of seconds for a full simulation whereas the DEM approach will take hours to days to simulation an identical setup. If physical accuracy is needed then it necessary to use the DEM approach. This is because it tracks the powder particles through time and space. They are subjected to the forces of nature that result in a realistic simulation, whereas the geometric approach is simply a packing problem where the particles are placed where they can fit. This can result in packing densities that are not

Modeling of the blown powder DED has only been done with the DEM approach previously discussed. To apply the DEM to blown powder, the nozzle must be modeled as a boundary condition and the particles should be fed through the feed system and tracked to determine

In order to mathematically model the AM process, it is necessary to couple several distinct mathematical models. The necessary models are thermal, fluids modeling and energy input

matching reality [44].

106 3D Printing

Figure 6. Powder bed modeling techniques.

6. Conclusion

representatives of natural occurrences.

when and where they strike the melt pool.

Aaron Flood\* and Frank Liou

\*Address all correspondence to: ajfrk6@mst.edu

Department of Mechanical and Aerospace Engineering, Missouri University of Science and Technology, Rolla, USA
