From 3D Models to 3D Prints: an Overview of the Processing Pipeline <s> Texture <s> Builds on previous research by the authors to establish a mathematical representation of the surface roughness of stereolithography (SL) parts. It is the intention of the research to use this modelling technique as a design tool for defining optimum build orientation and planning post‐process finishing operations. During the development of this model, a number of in‐process attributes inherent in SL were seen to affect surface deviation. Most notably the phenomenon known as “print‐through” on down‐facing planes produces a build orientation envelope of very smooth surfaces. Although capable of providing low roughness over some 50°, print‐through smoothing cannot easily be extended to other angles, hence complementary processes for surface smoothing must be developed. Discusses a number of possible solutions, showing how the generation of a meniscus between layers can prove beneficial in reducing SL surface roughness, hence reducing the need for lengthy manual finishing operations. <s> BIB001 </s> From 3D Models to 3D Prints: an Overview of the Processing Pipeline <s> Texture <s> Abstract The layered structure of Additive Manufacturing processes results in a stair- stepping effect of the surface topographies. In general, the impact of this effect strongly depends on the build angle of a surface, whereas the overall surface roughness is additionally caused by the resolution of the specific AM process. The aim of this work is the prediction of the surface quality in dependence of the building orientation of a part. These results can finally be used to optimize the orientation to get a desired surface quality. As not all parts of the component surface are equally important, a preselection of areas can be used to improve the overall surface quality of relevant areas. The model uses the digital AMF format of a part. Each triangle is assigned with a roughness value and by testing different orientations the best one can be found. This approach needs a database for the surface qualities. This must be done separately for each Additive Manufacturing process and is shown exemplarily with a surface topography simulation for the laser sintering process. A validation of the model is done with a monitor bracket of EOS GmbH. Measurements of five different orientations of the part, optimized according selected surface areas, show a good accordance between the real surface roughness and the predicted roughness of the simulation. <s> BIB002
Also known as surface roughness, or surface finish, texture aims at measuring tiny local variations on the surface, which determine visual (e.g. the way the object reflects the light), haptic (e.g. the porosity of the surface) and mechanical (e.g. friction) properties of the shape. Unlike form, texture cannot be estimated prior printing, as it mostly depends on parameters like the printer resolution and the printing material. Usually it is measured directly on the printed object, by using sampling techniques [TSB * 16]. In industrial environments the design specifies both the desired surface roughness and the metric that should be used to estimate it. The arithmetic mean surface roughness (Ra) is by far the most widely adopted metric, as stated in [TSB * 16]. Delfs and colleagues BIB002 observe that the surface roughness depth (Rz) is a better proxy to measure surface finish, as it is well representative of how a human eye assesses surface quality. Both Ra and Rz are roughness metrics defined in the ISO 4287 standard [ISO97]. They are computed on profile curves obtained by cutting the surface with an orthogonal plane. We point the reader to [Mit09] for a nice explanation of how these metrics are defined and can be estimated in practice; much other information can be found online. Different strategies have been proposed in the literature to achieve the best surface quality possible. In BIB001 Reeves and Cobb evaluate the meniscus smoothing to alleviate the impact of the staircase effect in stereolithography and produce smoother surfaces. It consists of an edited build cycle in which each layer, after solidification, is lift above the upper surface of the resin tank to stretch a meniscus of liquid between each polymerized layer. The resin meniscus is then solidified by using scan data from the previous layer, producing a smoother transition between adjacent layers. Other authors have recently observed that additional artifacts that affect surface finish may be introduced while detaching support structures from the object. In fact, tiny features may be too weak and break during this process, leaving residual support material attached to the surface. Zhang and colleagues [ZLP propose a perceptual method that optimizes for the location of the touching points between surface and supports. Their system tries to hide support removal artifacts by placing them at the least salient parts of the shape, as far as possible from its perceptually relevant features. In general, the extent to which support removal may affect surface quality depends on the printer and the material used. In metal printing supports removal is extremely challenging due to the properties of the material involved. Some recent methods to alleviate this problem are discussed in Section 3.3.1.