What are the existing methods of automobile sheet metal parts modeling?

2020-07-28 15:42:16

At present, there are some geometric modeling methods for Sheet Metal Parts, such as 2D geometry modeling for sheet metal parts and 3D geometry modeling for auto parts. The former includes coding method, face blending method and interactive dimension input method, and the latter includes bending transformation blending method and voxel blending method. The common disadvantage of all of these styling methods is that when the definition is wrong, it can be very cumbersome to modify and may even require re-entry. The information of the part model is also incomplete, especially the information about the engineering semantics is missing. When the parts are complex, the modeling process is also very complicated. Through the above analysis of the features of the auto parts and the requirements of the parts model, as well as the introduction of several existing geometric modeling methods of sheet metal parts, we can see that, it is an effective method to establish a sheet metal part model which can reflect the features of sheet metal parts and satisfy the requirements of CAD system. It can not only provide a complete information model of sheet metal parts, but also solve the problems of some existing geometric modeling methods. At present, some commercial modeling systems, such as P R O / E N G I N E R I N G, E U-C L I D, etc. . Feature is a set of product description information, which not only has a specific shape according to a certain topological relationship, but also reflects a specific engineering semantics, and is suitable for use in design, analysis and manufacturing. Features are the key to the integration of C A D / C A P / c a m. The features can be divided into shape feature, precision feature and material feature, in which shape feature is the key, the carrier or Matrix of other features, and the core of parametric feature modeling, it can be defined as a geometric body or entity with certain engineering significance. The structure and shape of a part is one of the main contents of the product definition. How to describe the structure and shape of a product with shape features and their relationships is the first problem of feature modeling, each sheet metal part can be decomposed into one or more shape features. Obviously, from the point of view of feature configuration, sheet metal parts are composed of a series of features. According to the features of sheet metal parts, the following features can be summarized: (1) the plane features, which constitute the plane shape of the parts, are the basic parts of the parts, are the parts connected with the bending parts, and are also the parent parts of the local forming and punching. The geometry of a plane feature is represented by a chain of graphic elements (lines, ARCS, etc.) called loops. (2) the bending feature, which is the shape produced by the bending process, in this case the simple bending feature, that is, the bending area represented by the cylindrical surface. A curved feature is represented by the geometric elements and the curved attributes that make up the feature. (3) a hole feature that is attached to other features as a general sub-feature, such as punching on a flat surface or a curved feature. The data structure of the hole is basically the same as the plane feature. (4) a local forming feature, the shape produced on a stamping part by a local forming process. Usually it has a fixed shape and a different size, so it can be expressed as a parameter. (5) user-defined features, because of the variety of sheet metal parts, some new features are often used, so it is necessary to provide user-defined means for feature modeling system. Status quo feature is not only the abstraction of low-level design information, but also the carrier of other non-geometric feature information, so it is an important part of product information model. 

At present, there is no widely accepted definition and description of features. The manual aided feature recognition is a low automatization task, and the Algorithm of automatic feature recognition is complex, so far it is only effective for simple shape recognition. It makes more sense for the designer to be able to build the model and store its information based on the shape, rather than identifying the shape features afterwards. The description of shape features is divided into three layers. The top level is the feature relation tree, which describes how the overall shape of the product is made up of feature elements, and the relationship between features is expressed in terms of connections, such as adjacency, which reflects the connections between features, the father-son relationship reflects the subordinate relationship of characteristics. The feature relation tree decomposes the object into low-level elements and displays the relationships and interactions between the expressed features. This decomposition adds a certain degree of intelligence to the product model, to provide users with a high-level environment in line with people's thinking form. The second floor is the definition of each shape feature, including engineering keywords and relevant parameters. The parameter table of each basic feature describes the attribute parameters of each feature element, such as the characteristic parameters of the bending angle are the bending angle and the radius, this is an implicit representation of a data entity that parameterizes rather than geometrically organizes shape information into a data structure. Implicit representation is more easily controlled and utilized by application operations. The three-layer is a simplified symmetric boundary graph, which describes the faces, edges and points of the objects and their relationships. The presence of the faces provides a basis for the description of the accuracy features, product topology and geometry data are also required. The modeling of shape feature has not only high-level shape feature information, but also low-level geometric feature information. Therefore, the shape information on which the precision feature and the material feature are expressed is complete, which can be divided into the description frame of precision feature and material feature, and then connected into the network by the pointer and the shape feature.