Introduction <br> <br> in the development of new products, it is always necessary to invest a lot of money before tissue processing or assembly of the parts or the entire system design process a simple example or prototype. This is mainly due to the high cost of production and the large amount of time required for the production of the mold. Therefore, the working prototype can evaluate, modify and verify the product design before preparing to manufacture and sell a complex product system.
A typical development process for a product is to find errors from the prototypes of the previous generation, or to find more effective and better design solutions from further research. The production of a prototype is extremely time consuming, and the preparation of the mold takes several months, so a complex It is very difficult to process parts using conventional methods.
Rapid Prototyping technology is a general term for the rapid development of prototypes or parts based on CAD models. It integrates modern scientific and technological achievements such as CAD technology, numerical control technology, laser technology and material technology. It is advanced. An important part of manufacturing technology. Unlike traditional manufacturing methods, rapid prototyping starts from the CAD geometry of the part, and through software layered discrete and numerically controlled forming systems, the material is stacked by laser beams or other methods to form solid parts. Because it transforms complex 3D manufacturing into a series of 2D manufacturing overlays. As a result, almost any complicated part can be produced without using a mold and a tool, which greatly improves production efficiency and manufacturing flexibility.
A more interesting issue is the speed of a product from concept to saleable finished product. As we all know, in the market competition, products are more profitable to enter the market before competitors and can enjoy a greater market atmosphere. At the same time, there is a more interesting issue that is the high quality of the product. For these reasons, it is extremely important to strive to bring high-quality products to market quickly.
Since the advent of rapid prototyping technology, a considerable market has been realized and it has developed very rapidly. The new manufacturing method of layer-by-layer addition of materials has gradually adapted. This technology has become a powerful means of modern model, mold and parts manufacturing through the combination of numerical control processing, casting, metal cold spraying, and silicone mold manufacturing. It has been widely used in aerospace, automobile and motorcycle, home appliances and other fields.
1 Advantages of rapid prototyping technology 1) Rapid prototyping As an important means of visualizing design concepts, the physical model of computer-aided design parts can be processed in a short time, so that the processing capability and design results can be evaluated very quickly. .
2) Since rapid prototyping technology solves the problem of converting a complex three-dimensional body into a two-dimensional section, it can manufacture high-precision parts of any complex body without any tooling die.
3) Rapid prototyping As an important manufacturing technique, using appropriate materials, this prototype can be used in subsequent production operations to obtain the final product.
4) The rapid prototyping operation can be applied to mold manufacturing, and the mold can be obtained quickly and economically.
5) The manufacturing process of the product is almost independent of the complexity of the part, and it can be freely manufactured, which is unmatched by traditional manufacturing methods.
2 the basic principle of rapid prototyping <br> <br> one layer is actually based on the discrete part during the manufacturing rapid prototyping material accumulated operation principle. To visualize this operation, imagine that the entire bread structure is a piece of bread that accumulates on top of another piece of bread. There are many different processes for rapid prototyping, but all rapid prototyping processes produce parts one layer at a time, with the difference that the method and material used to make each layer is different.
2. 1 General Process Principle of Rapid Prototyping 2.1.1 Construction of 3D Model A CAD file describing the part is obtained in a 3D CAD design software (such as Pro/EUGSolidWorks Solid Edge, etc.), as shown in Figure 1 (a). . At present, the file output format supported by general rapid prototyping is a 5TL model, that is, the approximation processing of the solid surface, that is, the so-called Tessallation processing, which approximates the model surface with a planar triangular patch. The advantage of this processing is that the data format of the GAD model is greatly simplified, thereby facilitating subsequent layered processing. Because it is relatively simple in data processing and has nothing to do with the CAD system, it has quickly developed into a standard for data exchange between CAD systems and rapid prototyping machines in the field of rapid prototyping. Each triangular patch is represented by 4 data items. That is, three vertex coordinates and a normal vector, and the entire CAD model is such a set of vectors.
When the C.AD model is face-formed by the 3D CAD design software, there is an output precision control parameter in the general software system. By controlling this parameter, the surface approximation processing error can be reduced. For example, the Pro/E software selects the eh-chord height as the accuracy parameter of the approximation, as shown in Figure 1 for a sphere, given the conversion of two ch values. For a model, a range of choices is given in the software. In general, this range can meet the engineering requirements. However, if the value is chosen too small, the processing time and storage space should be sacrificed, and the medium and complex parts should have several megabytes or even tens of megabytes of storage space. And this data conversion process inevitably produces errors, such as the vertices of a triangle in the middle of another triangle edge, the triangle is not closed, etc., which is often encountered in practice, which brings trouble to subsequent data processing. Further check for repairs.
Figure 1 Effect of different ch values
(a) ch=0.05 (b) ch=0.2
2.1.2 Discrete processing of 3D models
The three-dimensional solid model (generally a 5TL model) is layered by a dedicated layering program. After the production (stacking) direction is selected, the CAD model needs to be one-dimensionally discrete to obtain each thin layer section. Profile and entity information. Through a cluster of parallel planes along the production direction and the CAD model, the resulting cross-section line is the outline information of the thin layer, and the entity information is obtained by some discriminant criteria. The distance between the parallel planes is the thickness of the layer, which is the thickness of the single layer deposited during molding. In this process, due to stratification, the continuity of the surface of the CAD model in the slice direction is destroyed, and some information of the model is inevitably lost, resulting in the size and shape error of the part. The thickness of the slice layer directly affects the surface roughness of the part and the profile accuracy of the entire part. Each layer of information obtained after layering is the upper and lower contour information and the entity information of the layer, and the contour information is because of the plane and CAD. The STL file of the model (the CAD model after the facetization) is obtained by intersection, so the contour is composed of a series of intersecting points in which the intersecting points are sequentially connected. Therefore, the contour of the model obtained after the layering is already approximated. However, the contour information between the layers has been lost, the layer thickness is large, and the lost information is excessive, resulting in a profile error during the molding process.
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