Three-dimensional modeling technology is a three-dimensional technology that uses computer systems to describe the shape of objects. The software that implements this technology is called a 3D modeling tool. How to use a set of data to represent shapes and how to control and process these data are key technologies in geometric modeling.
In the early stage of CAD technology development, CAD was limited to computer-aided drawing. With the development of 3D modeling technology, CAD technology developed from 2D plane drawing to 3D product modeling, and then 3D wireframe models, surface models and entities were produced. Modeling technology. Nowadays, parametric and variable design ideas and characteristic models represent the development direction of CAD technology. Three-dimensional modeling technology is developed with the development of CAD technology.
The 3D modeling technology is developed from the Wire Frame Mode. At the end of the 1960s, research began to construct 3D entities with wire frames and polygons. Such models are called wire frame models. A three-dimensional object is described by the collection of all its vertices and edges. The wireframe is named after it. The wireframe model is like a human skeleton.
In the early stage, with the three-dimensional data of the object, any view can be generated, and the correct projection relationship can be maintained between the views, which brings convenience to the production of engineering drawings. In addition, it can also generate perspective diagrams and axial diagrams, which is impossible in a three-dimensional system; the data structure of the construction model is simple, saving computer resources; learning is simple, which is a natural extension of manual drawing. However, because all the floor lines are displayed, the reality of the object can be interpreted as ambiguous; lack of curved edges, it is difficult to represent curved surfaces such as cylinders and spheres; due to the lack of the relationship between edges and faces, faces and faces in the data structure Therefore, it cannot form an entity, cannot identify a face and a body, cannot distinguish between inside and outside, cannot section, cannot intersect two surfaces, cannot automatically divide a finite element network, and so on.
In the later stage, a curved surface model was developed. The curved surface model is constructed based on the data structure of the wire frame model by adding various relevant data that can form a solid surface. The characteristics of the surface model Compared with the wire frame model, the surface model has an additional surface table, which records the topological relationship between edges and surfaces. The curved model is like a muscle attached to the bone.
The surface model can realize the functions of surface-to-surface intersection, coloring, surface area calculation, and blanking. In addition, it is also good at constructing complex surface objects, such as molds, cars, airplanes and other surfaces. However, the curved surface model can only represent the surface and boundary of the object, and cannot be sectioned, and the model cannot be calculated for mass, center of mass, and moment of inertia.
Later, the development of variable technology appeared. When we carried out mechanical design and process design, we always hope that the parts can be built as we want, and can be disassembled at will, allowing us to construct a three-dimensional design on a flat display. Works, and hope to keep every intermediate result, in case of repeated design and optimization design.
The guiding ideology of the variable system is:
- The designer can adopt the design method of shape first and then size, allowing the use of incomplete size constraints and only giving the necessary design conditions. In this case, the correctness and efficiency of the design can still be guaranteed.
2) The modeling process is a process similar to that of an engineer thinking about design plans. The geometric shape that meets the design requirements is the first, and the dimensional details are gradually improved.
3) The design process is relatively free and loose. The designer thinks more about the design scheme, and does not need to care too much about the internal mechanism and design rules of the software, so the application field of the variable system is also broader.
4) In addition to the design of general serialized parts, the variable system is particularly handy in conceptual design, and is more suitable for innovative designs such as new product development and old product modification design.