First, the significance of the model in product design

Engineering design is a kind of thinking activity, and it is "a strict pre-concept of the creativity of technical products".

The design process is the process that the design object changes from uncertainty to certainty with the designer's thinking activities.

On the one hand, this process means opportunities for technological innovation. The technical content, technical performance, manufacturing cost and marketing income of a product depend largely on the design.

On the other hand, this process means a kind of risk: the risk of detours, the risk of going the wrong way, and even the risk of failure. The higher the complexity of the product, the greater the risk. Designers have to consider this risk in the design process, and often give up innovation in order to avoid this risk. How can we make full use of the innovation opportunity, improve the design quality, reduce the design cost, minimize the risk and improve the first success rate of product development? In addition, the fierce market competition also requires that the design and development work be completed in the shortest time to improve the response speed to market demand. Therefore, it is necessary to study the characteristics and laws of engineering design itself, and design methodology was born.

According to the viewpoint of design methodology, the thinking activity of engineering design has both internal and external characteristics. The so-called "inner" means that thinking is carried out in the designer's brain, and everyone's thinking and way of thinking are different, which is invisible to outsiders. The so-called "externality" means that the designer's thinking process and thinking results should be recorded and expressed in a certain form and communicated with others (other designers, manufacturers and users). This kind of thinking process and thinking result can be expressed in the form of language, but in engineering design, it is more expressed by models. Sketches and sketches are models, drawings and calculation books are models, cardboard models, wooden models and clay models are models, calculation models, CAD models and finite element models in computers are models, and the manufactured prototype is also a model. So the "model" here is broad, including all the contents expressed by English words sketch, drawing, model and prototyping. In the process of engineering design, when the design object changes from uncertainty to certainty, these models play different but important roles in different stages, especially with the improvement of the complexity of the design object and the implementation of concurrent engineering aimed at improving design efficiency, shortening design cycle and improving one-time success rate, the requirements for models in the early stage of the design process are becoming more and more urgent.

Three-dimensional CAD model can effectively meet this demand. With the 3D CAD model, we can analyze the structure and performance, simulate the assembly, render the appearance and even operate and use it in the virtual reality environment. Virtual design and virtual manufacturing have injected brand-new research content into design methodology.

However, the appearance of virtual models in computers does not and cannot completely replace other models, especially other models with three-dimensional shapes, such as:

In the modeling design of products, we should not only examine the appearance and color effect of products, but also examine their feel.

In the design of aviation and spacecraft, the aerodynamic "wind tunnel" test has not been abandoned because of the adoption of three-dimensional CAD. Similarly, the structural safety "collision" test is inevitable in any new car development in the automobile industry.

Although there are very detailed military maps, "sand table" is still indispensable in the command of large-scale campaigns.

All this is because:

1. After all, the computer model can't provide all the information of the product (such as feel);

2. Computer models can only simulate known environmental conditions;

3. The solid model in 3D space is more real and touchable than the model on 2D screen.

4. The computer model itself also needs to be verified.

Therefore, while vigorously studying and applying virtual design and virtual manufacturing based on 3D CAD, we should also actively study and adopt rapid prototyping technology which is also produced and developed on the basis of 3D CAD.