Application of the hottest rapid prototyping techn

The history of the development of automobile body is the history of designers constantly developing new resources and adopting new technologies to create "things" according to the law of beauty. Automobile body is the product of the combination of industrial technology and artistic modeling, which plays an extremely important role in automobile design and production. The body shell is smoothly composed of many large covering parts (top cover, hood, fender, etc.) with spatial curved shape. The procedures and methods of body design have a great impact on the preparation cycle, manufacturing accuracy and economic benefits of body design and subsequent product production

since the advent of Daimler Benz, the first car in the world, car body design has experienced a century of development. From the early design based on experience analogy to the traditional design based on the production of body clay model, the body shape design is developing in the direction of shortening the design cycle, improving the design quality, reducing the development cost and improving the market competitiveness of automotive products

rapid prototyping (RP) technology is a prototype manufacturing technology rising in the 1990s, which integrates the latest achievements in the technical fields of cad/cam technology, laser processing technology, numerical control technology and new materials. Rapid prototyping uses three-dimensional CAD models to directly generate product prototypes, and it can easily modify the CAD models and then remanufacture product prototypes. Due to the large number of computer-based three-dimensional design in automobile body design, the application of rapid prototyping technology in body design is possible

2 traditional body design and development

the traditional body design steps are mainly based on manual design, which is divided into two stages: preliminary design and technical design, as shown in Figure 1. This vehicle body design method is to transmit information through physical objects, models, drawings and templates. The clay model can more intuitively reflect the designer's intention than the effect drawing. It can express all the details of the designed product, and convey the designer's complete and detailed idea to the customer in the most intuitive way through careful carving. In the whole design process, the production of 1:5 clay model and 1:1 clay model has a crucial impact on the whole body design. They can conduct wind tunnel tests to preliminarily understand the aerodynamic performance of the body shape, and can also be used as the basis for discussion by the sales department

the first step is to materialize the design idea, and show the things on paper in form, so that designers can have a more detailed and specific discussion. First, select and determine several renderings, and make a 1:5 body clay model according to the figure. Due to the large-scale production of modern cars, any design error will lead to huge losses and waste to facilitate the management and operation of different personnel. Therefore, the designer's research and development on the reduced scale car model is an essential part of the work

the full-size clay model refers to the same size as the real car. The contour curve and size of the model are made according to strict requirements. Designers can compare and modify the details of the body surface. The full-scale sludge model is a product of high simulation. Body accessories, headlights, small lights and water brush arms will be placed in their respective positions. Some model surfaces are also painted, similar to real cars. Usually, the sculpture of 1:1 clay model should be repeatedly revised with the 1:1 body layout tape drawing to finally determine the shape. The sculpted clay model is placed on a platform that can rotate within 360 ° for designers to observe the modeling effect of the car body

in the process of making the clay model, first take out the template of the contour line of the vehicle body outline from the vehicle body layout drawing, and scrape out the general vehicle model. This is an iterative process. You must use the measurement drawing for many times, and take points with height. The more sampling points, the more accurate the model is. Then, according to the design data of the elevation effect drawing, the side molding, the front and rear molding, the front and rear windows, the rear cover molding and the details molding are completed

the traditional design process starts with making 1:5 clay model and full-size three-dimensional model, and then designers manually draw all body drawings and mold processing drawings according to the clay model. Therefore, the traditional design process has the following problems:

1) long development cycle. The design process follows the order from outside to inside, from model to drawing. Any slight change in the sludge model will directly lead to the modification of the main model and a large number of drawings, and the resulting modification design is extremely cumbersome and arduous

2) the design cumulative error is large. The body curve needs to be determined by manpower through repeated measurement and modification of painting model drawing board, and the design accuracy is difficult to guarantee

3) high development cost. It is precisely because of the repetition in the above design that a lot of materials, funds and labor are consumed

4) low degree of generalization and serialization of products

3 application of rapid prototyping technology in body development

3.1 principle of rapid prototyping

rapid prototyping technology (RPM) is a high-tech manufacturing technology that has been commercialized since the late 1980s. It integrates advanced technologies such as computer-aided design, computer-aided manufacturing, computer digital control, laser, precision servo drive and new materials. According to the three-dimensional design model of the workpiece formed on the computer, it is sliced in layers to obtain the cross-sections of each layer. On the other hand, the two-dimensional profile of pollutants is completely solved. The forming head selectively solidifies a layer of liquid resin to form each cross-sectional profile and gradually superimposes it into a three-dimensional workpiece in sequence

rapid prototyping technology completely gets rid of the traditional "removal" processing method - partially removing the material on the rough embryo of the workpiece to get the workpiece. The new "growth" processing method is adopted, which uses a layer of small sections to gradually stack into large workpieces, and decomposes the complex three-dimensional processing into a combination of simple two-dimensional processing. Therefore, it does not need to use traditional processing machine tools and processing molds. Because rapid prototyping technology has the above outstanding advantages, it has developed rapidly in recent years to become a pillar technology in modern advanced manufacturing technology and an indispensable means to implement concurrent engineering

3.2 application of rapid prototyping technology in car body modeling

3.2.1 generation of three-dimensional digital model of car body

one of the prerequisites for rapid prototyping of car body model is to construct three-dimensional digital model on computer, so CAD software used to construct model is required to have strong three-dimensional modeling function

eds' Unigraphics software is an advanced all-round product solution for modern manufacturing enterprises. Its CAD function adopts the most advanced direct modeling technology in the world. Using it can not only produce impeccable solid models, but also have powerful functions in surface modeling. Plus the perfect integration with the industrial modeling module shape studio. Make the surface modeling methods more abundant, so that the surface modeling that reflects art and inspiration is perfectly integrated into the product design, and can fully meet the modeling requirements of the complex surface of the automobile appearance. At the same time, the software provides a large number of surface smoothing tools, and the quality of the body surface generated by it is very high. Therefore, many world-famous automobile companies use this software to design the car body and establish the three-dimensional numerical simulation of the car body

3.2.2 generation of body solid model

because there are often some irregular surfaces on the solid model, approximate them before machining. The most common approximation is to use a series of small triangular surfaces to approximate the free-form surface. Among them, each triangle is described by the coordinates of three vertices and a normal vector. The 3D model file after the above approximate processing is called STL format file. The file can be directly generated by UG software

the Β The hole file is transferred to the rapid prototyping system for data conversion and processed according to the profile of one layer. This data conversion is to use slicing software to slice the three-dimensional model at certain intervals according to the height direction of the molding, so as to extract the profile of the section. The essence of slicing is to change the geometric model into contour representation

finally, the car body model is generated on the rapid prototyping system. At present, the more mature technologies include stereo printing (SLA), layered solid manufacturing (LOM), selective laser sintering (SLS), and melt deposition forming (FDM). SLA technology is also known as light curing rapid prototyping technology. Its principle is that the computer controls the laser beam to scan the surface of photosensitive resin point by point, and the thin layer of resin (about a few tenths of a millimeter) in the scanned area produces photopolymerization reaction and solidifies, Form a thin layer of the part. Move the workbench down a layer thickness distance, so that a new layer of liquid resin can be coated on the cured resin surface, and the next layer of scanning processing can be carried out. Repeat this process until the whole prototype is manufactured. Because the photopolymerization reaction is based on the action of light rather than heat, only a low-power laser source is needed during operation. In addition, because there is no thermal diffusion and the chain reaction can be well controlled, it can ensure that the polymerization reaction does not occur outside the laser point, so the processing accuracy is high, the surface quality is good, and the utilization rate of raw materials is close to 100%. Using SLA technology, a car body model with complex surface can be manufactured, and the formed car body surface has high precision and good surface quality. The model demonstration can be carried out through simple processing

3.3 application of rapid prototyping technology in the development of body accessories

modern automobile production is characterized by multiple models and short cycle. Compared with ordinary auto parts, the exterior accessories and interior trim parts that highlight the personality and characteristics of the vehicle change faster and have a shorter life cycle. In order to meet different production needs, it needs to be constantly modified. Although modern computer simulation technology continues to improve, which can complete various dynamic, strength and stiffness analysis, it is still necessary to make a physical object in research and development to verify its appearance, tooling, installability and disassembly. For parts with complex shape and structure, rapid prototyping technology can be used to make part prototypes to verify the design ideas of designers, and use part prototypes to make functional and assembly tests

3.4 application of rapid prototyping technology in body mold manufacturing

in recent years, RPM technology has developed from the initial prototype manufacturing to rapid tooling mold manufacturing, and based on the good practices and experience of work areas 3 and 6, the rapid mold manufacturing technology of PM has become the focus of RPM application research and development at home and abroad. Based on RP's active communication with local health and epidemic prevention institutions, hospitals and other medical and health institutions, M's rapid tooling manufacturing methods generally include direct method and indirect method. The direct molding method is to directly use RPM technology to make molds. Among the methods of RPM technology, the selective laser sintering method (SLS method) can directly make metal molds. The service life of the steel copper alloy injection mold manufactured by this method can reach more than 50000 pieces. However, the material shrinks greatly in the sintering process and is difficult to control, so it is difficult to quickly obtain high-precision molds. At present, most of the methods of rapid tooling based on RPM are indirect tooling, which refers to the indirect reproduction of molds using RPM prototypes

compared with the traditional machining method, rapid tooling manufacturing based on RPM prototype is more effective