Research And System Design Of CAPP-NC Technology For Parts Based On MBD

With the continuous development of computer technology,computer-aided systems CAD,CAPP(Computer Aided Process Planning),CAM,CNC,and CAE have emerged.The use and promotion of these systems have facilitated the change of traditional design and manufacturing toward digitalization and intelligence.However,the lack of direct interaction between these systems makes the data dissemination between systems cumbersome and slow,which cannot realize the integrated design and manufacturing and hinders the process of intelligence.MBD(Model Based on Definition)is a product information definition technology,which integrates all the design and manufacturing information of a product based on a 3D model.To address the above problems,this paper takes MBD model as the only data source for the whole life cycle of parts,and develops a CAPP-NC system with intelligent prospect based on it to meet the industrial change.The key technologies for system implementation are investigated,and the main contents are as follows:(1)The overall scheme of the system was designed,the boundary representation and MBD process model were introduced,and the model parameterization was realized.Firstly,the requirements of CAPP-NC system are analyzed,and the structural framework of the system is designed using the multi-layer architecture management model,followed by the detailed introduction of the main functional modules of the parts and the elaboration of the system workflow.The boundary representation is able to describe the geometric topological information of the 3D model in detail,and the specific way of its representation is explained.Facing the model design and process planning segments,the MBD design model and the MBD process model are standardized,and the contents of the data sets contained in both are described in detail.In order to make the model parts serially modifiable in terms of size,the parts are parameterized using directed acyclic hypergraphs.(2)Machining features are defined and classified,and a machining feature identification method based on the extended attribute adjacency graph is proposed,and PMI information contained in the model is extracted.Machining features were first defined and classified,followed by the extraction of part geometry topology information described by the B-rep method using the API functions provided by NX,in preparation for subsequent machining feature identification.In the identification process,the meaning of attribute adjacency map was first introduced,and then extended to form the extended attribute adjacency map,and the extracted geometric topology information was represented as EAAG and saved in the extended attribute adjacency matrix,followed by the establishment of a library of predefined machining features,and finally the isomorphic matching algorithm was used to match the features to be identified with the predefined features to complete the identification of machining features.(3)A detailed planning of the process route of the part is carried out.Firstly,a modified BP neural network based on chaotic particle swarm is proposed to make decision on the positioning reference of the part,and the same method is used to realize the decision on the machining method of common machining features,then the machining route of the part is generated by using the machining operation priority map algorithm with the machining element as the minimum unit,and finally the machining route is optimized by genetic algorithm to achieve the shortest time for the whole machining process.(4)The generation process of MBD process model is introduced,the machining module of the system is designed,and a prototype system is developed.The MBD process model of the part is generated by using the inverse generation method combined with wave technology and simultaneous modeling technology.During the machining process,NC codes were generated based on the process model using customized machining templates,and then machining simulations were performed in VERICUT software in order to verify the correctness of the codes.During the development process,the NX-based secondary development process and approach were first detailed,then the prototype system was developed,and finally the feasibility of the CAPP-NC system was verified by using the fixture mat as the experimental object.