In 3D printing, the 3D digital model is the premise and foundation, and 3D printing is the result, which makes the 3D model "flower on the ground". However, in many cases, the 3D model cannot be directly output to a 3D printer or the printed objects do not meet the needs of users. At this time, it is necessary to go through some geometric modeling and processing methods to correct, adjust, process and optimize the input 3D model, so that it can better meet the needs of 3D printing and prevent the printed object from not functioning normally. .
In computer graphics or computer-aided geometric design, the main purpose of 3D modeling is modeling, rendering or animation, considering the mathematical properties of the model, such as the shape, continuity, smoothness, material, deformation and other properties of the surface; In 3D printing, the output of the 3D model is a physical model, and the physical properties (mechanical properties and functional properties) of the physical model need to be considered more. Therefore, the traditional 3D modeling and processing methods need to be further revised and strengthened, and the mechanical and functional properties of the output physical model need to be considered during the modeling process. On the one hand, the mathematical properties of the model affect its physical properties; on the other hand, the requirements for physical properties affect the modification of the mathematical properties. These two properties affect each other and often require iteration in the process of processing and optimization. We call it Fabrication oriented geometric design and optimization. There are a lot of geometric processing and optimization calculation problems, we briefly summarize as follows:
1. Geometric calculation problem: Given a 3D digital model, it needs to be discretized into a triangular grid (STL file), then fill structure and support structure are added, then slice calculation and path planning, and finally sent to 3D printer through G code Output a physical model. This process is the main work of the slicing engine software of the 3D printer, involving a lot of geometric calculations;
2. Printing constraints: In many cases, the input 3D model has some problems and cannot be directly output to the 3D printer. For example, the topology of the 3D model itself is not standardized and cannot be sliced; the printing fails due to the floating part; The size of the model is too large, exceeding the size limit that the printer can print; without considering the stability, the printed object cannot be placed normally, etc.;
3. Structural optimization problem: As the designer lacks some design experience and mechanical knowledge, the design result will not be printed normally due to structural problems or there will be some structural strength problems after 3D printing. Insufficient strength may damage the 3D model during printing, transportation or daily use. We call this kind of problem a structural analysis and optimization problem; at this time, it is necessary to optimize the structure of the model through mechanical and physical simulation calculations (Finite Element Method-FEM) to meet the requirements.
4. Functional customization issues: Customization is one of the biggest advantages of 3D printing, and a large number of research questions and research methods have been spawned here. For example, (1) apply various models and methods developed in drawing theory to 3D printing, involving the appearance simulation, measurement and synthesis optimization of printed materials; (2) for medical, education, entertainment and fashion needs The model customization problem and the reverse design problem for light, shadow and sound effects; (3) Objects with specific functions assembled by sub-block design and printing and through hinges, pulleys, gears, motors and other mechanical devices, including many mechanisms Design and optimization issues.
In recent years, research on geometric design and optimization for manufacturing has received extensive attention and has gradually become a research hotspot.