## 2 Materials and Methods
The object is sliced into layers that are oriented with the X-Y plane, which are then filled with pathing. The secondary geometry, for the purposes of this proof-of-principle experiment, was a two-dimensional (2D) geometry oriented with the Y-Z plane. This is not the only representation or orientation that is possible, however. Other formats may make sense for accomplishing different objectives. The intersections between the layer and the secondary geometry then drive the generation of trigger points, which are distances from a common edge such as the leading edge of the primary geometry, which for the test geometry in this study was the starting point for the pathing for each layer. The trigger points must be stored in some format that can be attached to the toolpath and used by the printer. For this study, the trigger points were used by the printer's control system to command step changes in melt pool size, and therefore two trigger points form a complete step (up some prescribed magnitude and back down to nominal size). \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Value** & **Units** \\ \hline Delivered laser power & 8.71 & kW \\ Deposition rate & 2.4 & kg/hr \\ Print speed & 8 & mm/s \\ Layer height & 1.6 & mm \\ Bead stepover & 9.5 & mm \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Primary process parameters. Figure 2: Closed-loop controller architecture. The primary geometry selected for this study was a double-bead wall, 175 mm in length and 150 mm in height (94 layers with a 1.6 mm layer height). The ORNL Slicer (Manufacturing Demonstration Facility, Knoxville, TN, USA), which was developed specifically for large-scale AM, was utilized. Figure 4 shows the primary geometry in the slicer environment after slicing. Note that the geometry is a simple double-bead wall with two paths per layer, known as skeletons, and no additional geometric detail. Beads were deposited with the front-feed wire orientation, with the exception of a bead termination routine that took place at the end of each bead, in which the print head reversed to deposit additional material for a prescribed distance that could evolve on a per layer basis. This routine served as an additional measure to maintain proper layer height. The reversal distance and the nominal deposition rate evolved in the termination routine according to the parameters in Table 2. In addition to helping maintain layer height, the use of the termination routine could also manifest as slight wall width increases that were evident in the wall geometry scans. Figure 4: Double-bead wall in ORNL Slicer environment. Figure 3: Concept of generating trigger points using a secondary geometry. The secondary geometry selected for this study was an oak leaf. The oak leaf is a complex geometry that afforded the opportunity to study the melt pool size response over a large variety of step durations, a function of step distance and print speed. The oak leaf design, segmented with layers, contained 139 total steps, 116 of which were of unique distances, ranging from 0.7 mm to 77.5 mm. It was anticipated that short step distances would be bandwidth limited, i.e., the rate of change of melt pool size is limited by the physics of the melt pool, even under active closed-loop control, and would provide an interesting behavioral study. Figure 5 shows the conceptual workflow for the generation of the oak leaf trigger points. The workflow starts with a 2D sketch of the geometry, which must be appropriately scaled and then segmented into layers using the known layer height. The intersection points of the secondary geometry and the layer lines become the trigger points at which the melt pool size setpoint would change. For the purposes of this study, trigger points were limited to a maximum of six per layer, yielding a maximum of three complete step changes in melt pool size per layer. This required some filtering of fine details from the oak leaf geometry, particularly at the leaf tips, but maintained the overall design and sufficient complexity.