Investigating surface topography effects on directional emissivity of metallic additively manufactured parts

Researchers are focusing on qualification methods and simulations to gain a better understanding of metal powder bed additive manufacturing (AM) processes. Because of the direct relationship between thermal history and mechanical behavior, in-situ thermal monitoring is key in gauging the quality of both the process and produced parts. To accurately monitor the temperatures of an AM process, key environment and object parameters need to be known, most importantly, object emissivity. The emissivity of an object is dependent on several variables, including: wavelength of light, material composition, temperature, and surface topography. Most have been concerned with the thermal emissivity dependence on temperature since large temperature ranges are seen in metal powder bed processes, but there is also an extensive range of surfaces produced by AM. This work will focus on discovering what surface characteristics control directional thermal emissivity. In addition to defining the surface characteristics, in build conditions will be simulated while conducting thermal measurements of AM parts to quantify errors that result from incorrect emissivity assumptions. Lastly, a method for determining the surface topography in-situ to allow for layerwise correction of emissivity will be implemented in an additive machine