All additive manufacturing (AM) processes have a characteristic ‘stair case’ layering effect at the boundaries, as this process family fabricates components by stacking layers upon each other. This effect is noticeable at shallow angles and where there is significant surface curvature. Some AM processes, such as material extrusion and directed energy deposition (DED), are bead-based deposition processes. For these processes, there are additional surface roughness variations caused by the side to side positioning of the beads within a layer due to the bead’s geometry (i.e., elliptical for material extrusion processes). Therefore, non-periodic regions are introduced. &nbsp;Measuring the surface roughness from virtually modeled beads of an additive manufactured product helps to have an initial estimation of the surface quality during process planning.In this paper, a technique is developed to measure the profile and areal surface roughness from an ‘as-built’ CAD model generated from theoretical bead geometries. Commercial AM process planning software (APlus) is employed to create the additive manufacturing toolpaths and bead geometries of the products. Two CAD files are needed as inputs for the developed virtual surface roughness solution: a model of the ideal part geometry and the model created based on the bead geometry, percent bead overlap, and the fill strategy.The results of four samples are verified by analytical calculations with less than 5 percent variation. The samples include flat faces, an arc, an S shape (a double arc), and curved surfaces. Sensitivity studies for measurement area/length are conducted as well. The results for the sample where only the boundary passes are exposed are independent of measurement length, whereas it varies for the samples that raster passes are exposed. The reason is that the raster patterns and internal voids affect the measurement results especially when the measurement region is small. Additionally, the results are compared to surface roughness results for an experimentally built hemispherical dome to study how manufacturing parameters such as real bead shape and material spatter affect the surface roughness. This hemisphere was fabricated using a DED process. A build strategy that did not require support structures was employed.As DED process planning software is being expanded to include radial and multi-axis tool paths, as well as adaptive slicing strategies, the surface roughness analyses will become more complex for AM built parts. This solution approach should analyse the surface roughness for these build approaches as well. Estimation of the surface roughness values before a component is being built will help designers to evaluate how much material stock is needed to be added if subsequent machining processes are required. Therefore, it is anticipated that this research will assist process planners in developing their desired build solutions for both AM and hybrid manufacturing.

Virtual Surface Roughness Measurements From an ‘As-Built’ Virtual CAD Model for Bead Based Deposition Additive Manufactured Components

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.