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1 Gear CAD/CAPP integrated system function design Gear CAD/CAPP integrated system mainly includes computer aided design (CAD) and computer aided process design (CAPP) 2 parts, which can be used uniformly or separately in application. The following functions are realized: gear parameterized design and optimized design; parameterized drawing of gear parts drawing; automatic generation of process specifications.
The overall structure of the system and the corresponding modules are shown in Figure 1.
2 Characteristic information of gear CAD/CAPP system 2.1 Feature-based gear type part information model The key of CAD/CAPP integration system is the definition and representation of features and their unification in CAD and CAPP modules. Part feature modeling is based on the idea that a part is a combination of a feature set that performs a certain function and is associated with a particular machining method. The basis for the design of the part is its function, the function is embodied by a certain structural shape and technical requirements, and the structural shape conforming to the process requirements corresponds to one or several sets of processing methods, so that the CAD of the part and the CAPP are organically combined. The tie is the feature.
The part information model adopts the hierarchical feature description method, that is, the feature model is oriented to the whole design and processing process, which can accurately and comprehensively describe the information required in each part of the part generation process and use the feature as the knowledge unit. The hierarchical structure of the feature-based gear-type part information model is shown. The hierarchical structure of the information model includes a part layer, a feature layer, and a geometry layer. The part layer mainly reflects the overall information of the part. The feature layer contains the composition of each feature model and their relationship. The geometric layer reflects the geometric/topological information of the point, line and surface of the part. The geometry/topology information of the part is the basis of the whole model, and it is also the object of the module of the part drawing, and the feature layer is the core of the part model. The interrelationship between the various feature sub-models reflects the semantics between the features. Relationships make features a basic unit of structural parts and have a high level of engineering meaning. This hierarchical description includes not only the geometry/topology information of the features in the part model, but also the process information necessary for the machining, which not only facilitates the geometric modeling of the CAD module, but also facilitates the extraction of the required feature information by the CAPP module.
2.2 Characteristics of Gear Parts The gear characteristics are the carriers for information transmission used by designers in communication and communication during gear design, manufacturing and machining process development. Classification of gear parts:
(1) The shape feature is the shape, size, geometric coordinates of the surface of the gear to be processed and the relationship of other surfaces.
(2) Accuracy characteristics are used to describe a collection of information such as dimensional tolerances, geometric tolerances, motion accuracy tolerances, and surface roughness of the gears.
(3) General characteristics A set of information describing the overall characteristics of the gear parts, including part number, part name, blank form, overall size, material and heat treatment.
2.3 Modeling process of gear parts The characteristics of gear parts are recorded separately. Finally, these features are organized by combination to become a complete feature including all information.
The precision feature information is described in a chain structure, and is placed as a part of the shape feature under the shape feature. The additional attribute method is used to integrate the precision information of the part with the shape feature, and the relationship between the precision feature and the shape feature is established by reference. Feature relationship. The shape features are divided into main features and sub-features, which are represented by a binary tree data structure, wherein the left pointer of the binary tree points to the auxiliary feature of the node, and the right pointer points to its same-level node, that is, the adjacent main feature, wherein the main feature is used The 2-digit code indicates, for example, 01 hub, 02 spoke, 03 rim, etc., the secondary feature is represented by a 4-digit code, the first 2 digits represent the main feature code, and the last 2 digits are their own codes, such as 0101, where the first 2 digits Indicates the main feature 01 hub, and the last 2 digits indicate the sub-feature chamfer, indicating that the chamfer is attached to the 01 hub. And the code number size relationship indicates the order of combination. The main attributes of shape features are mainly used to describe the main attributes of shape features, including feature names, code names, feature types, and so on. Accuracy features such as dimensional tolerances, geometric tolerances, surface roughness, etc., as additional attributes of shape features, point to the corresponding geometric features, precision and datum nodes, respectively, and also use pointers in the geometric features, precision, and datum data structures. Point to its corresponding reference geometry node. This kind of reference geometry is used, on the one hand, to refer to the geometric elements and features of the geometric expression precision. On the other hand, the reference geometry also uses precision as an attribute of the geometric element to express the precision acting on different geometric elements. With the input of precision information, the system dynamically establishes and maintains a reference geometry list to establish the relationship between features, geometric features and precision, and integrates geometric and non-geometric attribute information to form a complete CAD/s that meets the integration needs. CAPP integrated system information model.
3 Case Analysis 3.1 Feature Model of Gear Parts 3 is a part drawing generated by CAD module, which is gear feature information.
1 gear parts feature feature category feature name feature code parameter overall feature overall feature 00 part number, part name, blank form, overall size, material, heat treatment, batch shape feature hub 01 inner diameter, outer diameter, outer slope, length, surface roughness Degree, positioning information, machining accuracy chamfering 0101 chamfer length and angle, positioning information keyway 0102 keyway length, chain slot width, keyway depth, positioning information spoke 02 outer diameter, width, surface roughness, positioning information, machining accuracy spokes Hole 0201 bore, depth, surface roughness, positioning information, machining accuracy rim 03 teeth number, pressure angle, tooth width, modulus, helix angle, spiral direction, tooth height, tip height coefficient, radial displacement coefficient, tooth Thickness, surface roughness, positioning information, machining accuracy, tooth tip cylinder 04 diameter, length, surface roughness, positioning information, machining accuracy 3.2 Data processing feature model of the characteristic information model The entire product design and manufacturing process can fully describe the part Information required at each stage of the production process and the relationship between the information, feature modeling and geometric construction
The information processing process of the feature information model is also the process of CAD/CAPP integration implementation. The VF public database table is used to store feature information.
(1) General structure information of the main feature information database table (connection number, feature name, [radial size and deviation], [axial dimension and deviation], [roughness, geometric tolerance], [other])
(2) General structure of the auxiliary feature information database table Featureex (connection number, feature name, [shape size], [roughness], [shape tolerance], [positioning size and others]) [shape size], [positioning size And other] 2 items vary with the characteristics.
Corresponding to each feature name in the database can create a database table (.dbf), each parameter of the feature is used as a field of the data table, such as the database table structure established for the hub in the see 2.
The structure of the 2 wheel hub data table adds the feature information data of 1 to it, which is an important link to determine the integration of CAD and CAPP modules of the system. The plain text file is used as the carrier of feature information transmission, and correspondingly written in CAD and CAPP modules. The program segment realizes the transmission and reception of the feature information data, thereby achieving information sharing. For specific methods, see the literature [3].
4 Conclusion By analyzing various data of gear parts, the corresponding feature names and their parameters are obtained, and a database table (.dbf) is created for each feature name. Each parameter of the feature is used as a field of the database table. The program is written in the CAD and CAPP modules to write various characteristic information data of the gear working diagram into the database table, thereby realizing the data sharing of the part geometric information and the process information.