The MATLAB code uses this value to select the location of the next slice to fabricate. Controlled via Instrument Control Toolbox ™, this system directs a laser beam onto the part being fabricated to determine its current height. Our solution is a laser measuring system called Sequential Horizontal Automated Z-Axis Measurement, or SHAZAM. The operator cannot manually adjust the height of the welder to correct for this error. Although layer thickness typically varies from what was expected by less than 0.002 inches, when several hundred layers are required to form a part, repeating even a small error on each layer can cause a noticeable discrepancy between the part’s height as designed and its height as fabricated. Because it is impossible to precisely control the height of the metal bead produced by the welder, the thickness of each deposited layer may vary. Having automated the process of producing G-code to create an arbitrary 3D shape, we turned our attention to the welding process. The G-code for such structures was difficult to write by hand, particularly the code needed to prevent excessive amounts of material from being deposited at the intersections. Our first priority in automating this process was to simplify the creation of G-code for more complex shapes, such as the orthogrid geometries used to reinforce cryogenic tanks (Figure 2). Even with specialized skills and knowledge, it was a challenge to write the G-code and shepherd the process to completion for any part more complicated than a basic 3D shape. If the estimate was off, the engineer had to manually readjust the height of the welding platform during deposition. Because the precise thickness of the bead cannot be predetermined, the engineer had to estimate where the next layer should begin. These instructions would, for example, turn on the electron beam and set its intensity, start feeding the wire to initiate a molten pool of metal, and move the robotic welder to create a bead of metal. In the manual EBF 3 process, an engineer wrote instructions in G-code, a computer numerical control programming language.
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