How to establish the parts information model accurately and effectively is the core content of CAD/CAPP/CAM integration. At present, the parts information model is based on feature modeling technology. The most common practice is to first establish a feature library according to the feature classification, then perform basic feature invocation according to the actual needs of the modeling, and establish a part model by using Boolean operations between the features. This method has several shortcomings. (1) In order to easily construct a variety of complex part models, the feature library contains all the basic features as much as possible, which is currently difficult to do. (2) The current feature recognition technology is still not mature enough. There is a certain degree of difficulty in how to manage and control the feature database effectively. (3) In the actual part modeling process, it is difficult for designers to quickly and accurately select the desired features in a short time, which greatly affects the modeling speed. (4) There is not a one-to-one correspondence between existing feature classification methods and machining methods. A processing method may correspond to several basic features. According to the principle of one-to-one correspondence between features and processing methods, it should be stored as a composite feature in the features. In the library, this is obviously unrealistic, and the contradiction has yet to be resolved. In view of the above deficiencies, this article first defines the connotation of the part information model, and on the basis of the analysis of the connecting rod processing technology, carries out feature planning and design, and then uses the Destructive Modeling with Feature to directly construct the part model. The establishment of the parts information model, instead of following the conventional method of feature classification and modeling, successfully achieved the unification of feature design and machining process, ie, each feature is consistent with each linking method of the connecting rod. 2 feature-based part information model Feature is a set unit for complete expression of part information. It is a combination of certain shapes, semantics, and abstractions [1]. A complete part model is not only a collection of part data, but also reflects the expression of various types of data and the relationship between them. Only part models based on certain expressions can be effectively accepted by various application systems. The complete parts information model should include: management features, shape features, precision features, material features, and technical features as shown in Figure 1. (1) Shape characteristics. Describe functional geometrical information with certain engineering significance, divided into primary features and secondary features. The main feature is used to construct the body's shape structure of the part. The auxiliary feature is used to modify the main feature, which is attached to the main feature and can also be attached to another auxiliary feature. Shape characteristics are the focus of product design and manufacturing personnel's consideration of problems, and also the carrier of other information. (2) Accuracy characteristics. Used to describe the dimensional tolerances, geometrical tolerances, and roughness tolerances of parts. Dimensions and tolerances are important attributes in relation to design and manufacturing. In feature design, dimensional and tolerance features are analyzed and the part information model is directly Creating dimensions and tolerances can clearly represent the non-geometric properties of shape features and the interrelationships between shape features. (3) Material characteristics. It is used to describe the type code, performance, heat treatment method, and surface treatment method of the part material. (4) Technical characteristics. Used to describe the performance, functionality, and other information of the part. (5) Management characteristics. Used to describe the management characteristics of parts, such as part name, designer, design date, quantity, figure number, version and other information. The geometry/topology information of the part is the basis. The feature layer is the core, and the interrelationships among various feature sub-models in the feature layer reflect the semantic relationship between the features. The basic unit that makes the feature a structural part has a high-level engineering meaning, thereby supporting CAPP, NC programming, and machining simulation. Demand for part data. 3 The establishment of a three-dimensional part information model The key to building a part information model is to do feature planning, as shown in Figure 1. Using direct modeling techniques, the structure can be designed hierarchically, and corresponding parameterized feature modules are established at different levels. Each feature is described by a set of parameters that uniquely determine the feature. Taking the connecting rod in the diesel engine as an example, using Pro/ENGINEER software, the modeling method and design steps of the 3D part information model are explained. 3.1 Link Function and Structure Analysis The connecting rod is an important part of the engine, as shown in Figure 2. It transmits the pressure of the expanding gas acting on the top surface of the piston to the crankshaft, which drives the crankshaft to rotate, while being driven by the crankshaft to drive the piston to compress the gas in the cylinder. The connecting rod structure is complex, and it is usually divided into two parts: a connecting rod body and a connecting rod cover at the large end. The connecting rod shaft is an I-shaped cross-section, and gradually decreases from a large head to a small head. If you do not make any feature planning, use the feature modeling technology to build the three-dimensional model of the link directly, the modeling is easy to fail, and it is difficult to obtain a better result. Because the structure of the link is complex, it is not simply a feature addition and subtraction. Figure 1 The overall model of the feature-based part information model Figure 2 The characteristics of the connecting rod 3.2 analysis of connecting rod machining process Linkage feature design is closely related to machining. Each machining method corresponds to a feature. This is the basic principle of feature planning. The connecting rod blank is a forged part, and the connecting rod body and the connecting rod cover are integrally forged. The main machining process of the connecting rod is as follows: Milling connecting rod size both ends → drill small hole, expand to the size value, pull the small hole, and ensure the size and surface roughness value → Milling head positioning boss → cut from the connecting rod Lower connecting rod cover → nut boss on the connecting rod cover, drilling bolt holes, machining threads → Fix the connecting rod and connecting rod cover together with bolts, and pry the big hole. 3.3 Feature Planning and Design Through the above analysis of the linkage function, structure and processing technology characteristics, the connecting rod model is divided into the feature level shown in FIG. 2 , and the connecting rod model is composed of these independent features. 3.4 Based on the Pro / ENGINEER platform link feature modeling 3.4.1 Solid Model In this paper, the solid model of the connecting rod adopts a feature-reduction modeling method. The so-called feature reduction modeling method is to establish the blank model of the part first, and then use the method of gradually removing the characteristics to establish the part model. The following describes the specific modeling process of the connecting rod. 1. Link modeling process (1) Determine the parting surface and draft angle. Selecting a reasonable parting surface is the first step in the blank forging production. Therefore, the parting surface and draft angle should be determined first in the modeling process. (2) Use the "stretch" method to generate a tie-in model. (3) Use the "pull touch" method to generate a 7° draft angle. (4) Using the method of "curved cutting material" and using the function of "rounding", the connecting part in the middle of the connecting rod body is produced. (5) Using the "cut material" method, get the shape of the connecting rod. (6) Using a "cut material" method, a punched skin is formed at the location of the large head hole. The connecting rod blank is shown in Figure 3. 2. Link modeling according to the machining process of the connecting rod (1) Use the "cut material" method to create large and small end faces to ensure dimensional requirements. The machining of the large and small end faces of the connecting rod is usually the first procedure of the connecting rod machining process, because this is the main positioning base surface in the entire machining process, and its processing quality has an important influence on the processing quality of the entire connecting rod. Therefore, in the modeling process, special attention must be paid to the construction of both ends of the large and small heads. (2) Select the co-axial "hole" method to generate small holes and ensure the size and surface roughness. (3) Generate a large head positioning boss by "rotation cut material". (4) Cut the large end of the connecting rod in a “CUT†manner, and divide the connecting rod into a connecting rod cover and a connecting rod body. The connecting rod is divided into two parts in order to meet the needs of subsequent processing and assembly. (5) Using a "stretch cut material" method, pry the nut bosses on the connecting rod cover, drill the bolt holes using the "hole" method, and use the "helical scan cut material" method to generate the threads. (6) Assemble the connecting rod and connecting rod cover together with bolts and pry the big hole. The big head hole can be closely matched with the bearing shell and the crankshaft, the small head hole and the piston pin, so as to reduce the impact of the impact and facilitate the heat transfer. The shape and tolerance of the large head hole and the small head hole must be ensured. Therefore, a large head hole must be built in the molding. Model with a small hole. At this point, the three-dimensional geometric model of the connecting rod has been established. 3.4.2 Other Features Construction The accuracy characteristics of the connecting rod were established, and the operation was performed directly on the geometric model using Pro/ENGINEER. The material features of Pro/ENGINEER are attached to the model in text form. Using “Settings†→ “Materialâ€, you can directly define, modify, and delete the material parameters in the text file. According to the performance requirements of the connecting rod, the material of the connecting rod is 45# steel. Technical features and management features can be added through external programs. Through the above steps, a three-dimensional information model of a part has been completely established, and a parts map can be automatically generated. Figure 4 shows a three-dimensional model of the link generated by modeling. 4 NC program and machining simulation Pro/ENGINEER provides powerful Pro/NC modules for designing NC machining and manufacturing programs. Use it to establish a three-dimensional machining simulation environment, automatically programmed NC machining program, simulate the tool path, observe the cutting conditions of the workpiece, verify whether over-cut and interference and prediction errors occur, and avoid processing failure. Pro/NC uses image-based programming techniques for automatic programming and software-led programming, so programming thinking is clear. The interference of various uncertainties in the manual programming process is avoided, and human error is avoided to the greatest extent. The automatic programming method of the image method means that each machining process of a part can be regarded as processing the shape feature group that composes the part. Using CAPP to connect CAD and CAM information, CAPP can receive part information directly from CAD, generate related process documentation, and based on this, generate NC code. By using this technology, CNC programmers no longer operate on low-level geometric information (such as: points, lines, surfaces, and entities), but they can directly change the NC programming to meet the characteristics of engineers and technicians. Programming efficiency. After the NC program is verified, the CL DATA generated by the manufacturing process will be designed and the data will be converted by Pro/NCPOST to directly obtain the NC CODE required for actual machining. According to the Pro/NC design process, the process simulation of the connecting rod plane is shown in Figure 5. Figure 3 Linkage rough model 5 Concluding remarks This article makes a reasonable planning and design of the characteristics of the connecting rod parts, and based on this, constructs its information model, uses the Pro/NC module to complete the connecting rod processing simulation and the automatic programming, and verifies the method based on the characteristic subtraction modeling. Correctness, basically realize the integration of connecting rod CAD/CAM and improve design efficiency. references 1 Wei Shengmin, Zhu Xilin, Chief Editor. Mechanical CAD/CAM[M]. First Edition. Wuhan: Wuhan University of Technology Press, 2001 Aluminum Coil For Aluminum Composite Panel Aluminium Color Coil,Painted Aluminum Coil,Prepainted Aluminium Coil,Aluminum Coil For Aluminum Composite Panel GanSu Port Logistics Co.,Ltd , https://www.gskouan.com
Figure 4 Three-dimensional information model of connecting rod 
Figure 5 Simulation of connecting rod machining process
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