## 4 Geometric Reconstruction of Topology Optimization Results
### Geometric Reconstruction Criteria  
Based on the manufacturing constraints of SLM technology [27, 28, 45, 46] and undesirable features such as isolated bodies and disconnected branches affecting the structural performance in the TO results from Section 3, the following geometric reconstruction criteria are established:  
1. _Removal of isolated body features_: Isolated body features are primarily caused by intermediate-density units generated by the variable density method of TO. These features do not contribute to structural performance improvements, but they can lead to mesh failure in the FEA and thereby an increase in ineffective branches during AM; hence, they must be eliminated.
2. _Material removal from thin branches_: Thin branches can be considered thin-walled features. Unless the structure design specifically requires thin-walled features, such a feature generally increases the need for a support material and could damage the surface quality during support material removal; thus, such features should be eliminated.
3. _Material removal and connection of disconnected branches_: The presence of disconnected branches suggests that they may become part of the optimal load transfer path. These disconnected branches should be extended and connected to ensure that the structural performance meets the loading requirements. If additional weight reduction is feasible, the elimination of this feature should be validated to see whether the loading requirements can still be met, thereby maximizing the benefits of weight reduction.
4. _Transition treatment of sharp corner features_: Metal-based AM technologies typically use lasers as energy sources, and their laser spots are approximately circular with a minimum focal diameter. For instance, EOS devices have laser spot diameters ranging from 40 to 100 \(\upmu\)m, and the SLM solution devices range from 70 to 115 \(\upmu\)m. Therefore, unless fine sharp corner features must be retained, sharp corners should undergo transition treatment to accommodate the physical characteristics of the laser spot and improve manufacturing quality.
5. _Removal of closed internal hole features_: During TO, intermediate-density units may lead to the creation of closed internal holes. Metal AM technologies using powder spreading or powder delivery methodologies are ineffective at removing powder particles inside internal holes, thus requiring secondary processing to eliminate them. This post-processing reduces structural performance and damages the surface quality. Therefore, the generation of closed internal hole features should be avoided as much as possible.  
6. _Ensuring machining allowance_: Although SLM technology offers higher manufacturing precision than other metal AM technologies, regions requiring higher precision than the SLM capability (e.g., mating surfaces or fixed connection areas) must be reserved with a machining allowance to allow for subsequent surface finishing to improve surface smoothness.
7. _Shape optimization of stress concentration regions_: TO is conducted based on the existing geometric model, and its optimization results are constrained by geometric boundary conditions. For stress concentration areas placed at geometric boundaries, shape optimization should be performed during post-processing to lessen stress concentrations and enhance mechanical performance.