Challenges for Finishing Operations for AM Parts
Typical Operational Challenges for Metal AM Components Due to Surface Morphologies and Topographies
Challenges of Surface Topography
For applications, such as medical implants, and functions, such as fluid flow, fatigue resistance and more, there are a variety of features on the surface that need to be removed or altered to ensure suitable functionality (Section 5.3.1). Large asperities, such as particles, particle clusters and spatter across top, side and overhanging surfaces, may need to be removed in order to improve mating surfaces, reduce wear with other components and reduce risk of contamination or damage, especially when used in medical applications. The size and shape of these asperities can differ across different orientations of the surface with respect to the build (Grimm et al. 2015, Triantaphyllou et al. 2015, Sidambe 2017), which will have an influence on the surface texture parameters for the surface, surface function and type of finishing required.
Porosity on the surface, or sub-surface porosity that can emerge through removal of the upper surface, also needs to be considered as it is known to influence fatigue life and act as crack-propagation zones (Alrbaey et al. 2016, Bagehorn et al. 2017, Brandao et al. 2017). By altering the surface to relieve it of any porosity, by re-melting or by finishing mechanisms, the fatigue life can be improved (Bagehorn et al. 2017, Brandao et al. 2017).
Supporting Material and Witness Marks
For aesthetic, bearing surface and medical applications, a high level of surface finish and surface uniformity may be required. After supports have been removed, there may remain some remnants of the support structure. As a part of the surface topography, these remnants are seen as large plateau regions that sit higher than the bulk surface and as a result may require more aggressive surface finishing to remove. Support removal techniques may also leave process-specific features on the AM surface that do not match with the surrounding surface topography, and these may require removal to ensure that a consistent surface topography can be achieved.
Distortion of the part may have a significant impact on assembly and functional operations. Although distortion does not directly impact or change the final part surface finish, it does impact the choice of the technique that can perform the material removal, as the part in some areas is different to the geometry expected and planned. If the technique selected cannot account for a change in shape caused by distortion (through either quick process re-planning or high process conformability, such as adaptive programming or flexible tooling), this can lead to high scrap or re-work rates.