| The rapid development and application of digital technology in the industrial field has promoted the extension of three-dimensional(3D)technology from the field of product design to all fields of product life cycle.The product development and manufacturing mode with 3D model as the core has gradually become the mainstream mode of the manufacturing industry,which makes the ability to rapidly construct 3D models become one of the core competitiveness of enterprises.The 3D process models,which are oriented to the machining process,can guide process planning and production activities intuitively and efficiently.They are the essential information carriers of the MBD(model-based definition)technology and the effective means to realize intelligent process design.The rapid and automatic construction of part 3D process models is a hot spot in manufacturing research.The traditional methods of manually constructing the 3D process models require a high level of modeling knowledge and process knowledge of designers,which can not guarantee accuracy and efficiency,and are not conducive to CAD/CAPP integration.The existing 3D process model automatic construction methods have problems such as complicated algorithms due to insufficient use of design model information,low efficiency due to excessive pursuit of algorithm universality,and even unsatisfactory processing effect for various parts.Meanwhile,most of the existing methods are based on standardized blank models with regular shapes,and cannot realize the process model construction of casting parts.In this dissertation,a method for constructing part 3D process models is proposed.It starts with shaft and disc sleeve parts respectively,and realizes the automatic construction of casting blank model and 3D process models by improving the traditional volume decomposition method.The knowledge graph technology is introduced into the machining process design field to generate suitable mechanical process plans for the process models.The main research results are as follows:(1)An automatic construction method of 3D process models for shaft parts based on the improved volume decomposition method is proposed,which changes the mode of"decomposition then merging" in the traditional volume decomposition methods,and improves the efficiency.The cutting surface selection algorithm,the unit volume decomposition algorithm and the machining feature generation algorithm in the traditional methods are improved to realize the automatic construction of 3D process models for shaft parts.First,the input part design model is preprocessed.The design feature information is extracted,and an extended feature relation graph is used to represent the part model structurally.On this basis,the candidate cutting surfaces and the cutoff surfaces are selected,and the machining method chains of the main machining surfaces are generated.Second,the machining volume is obtained by the Boolean operation of the blank model and the part design model.Then the mapping and decomposition method is performed to decompose the machining volume into the machining volume units containing machining semantics.Finally,the machining feature mapping method is applied to realize the association between the machining volume units and the process information.And the 3D process models are generated in reverse order through the Boolean operation.The effectiveness of the method is verified by an example.(2)An integrated automatic construction method of 3D casting blank model and process models for disc sleeve parts is proposed,which solves the problems such as the difficult integration of the independent casting blank model construction system and process model construction system.Based on the improved volume decomposition method proposed for the process model construction of shaft parts,the algorithms such as material removal volume unit decomposition,unit volume castability analysis,and casting volume unit machining allowance compensation are added to realize the integrated construction of casting blank model and process models.First,the part design model is preprocessed to obtain the candidate cutting surface sequence as well as the machining method chains of the main machining surfaces.Second,the initial blank model is generated by creating the minimum bounding box for the design model then adding machining allowance to it.And the material removal volume is obtained by Boolean operation.Then,the material removal volume is decomposed into the unit volumes by performing the mapping and decomposition operation.And the unit volumes are classified into the casting volume units and the machining volume units by castability analysis operation.Finally,the casting blank model and the process models are generated respectively by performing the machining allowance separation operation,machining feature mapping operation and Boolean operation.The effectiveness of the method is verified by an example.(3)A machining process design method based on knowledge graph is proposed,which realizes the unified representation and management of machining process knowledge with multi-layer and multi-factor,as well as the process design driven by machining process semantics.It improves the management and utilization ability of process knowledge.Based on the research of machining process design process and a large number of machining process plans,as well as combined with the proposed 3D process model construction method,a set of multi-level and multi-element ontology models are constructed to describe the machining process design process semantically from both the macroscopic and microscopic levels.Taking machining process knowledge ontology as the driving mode,process knowledge is extracted from structured,semi-structured and unstructured process instance data.Then,the data layer of machining process knowledge graph is constructed through knowledge fusion and quality evaluation.By analyzing the semantic relationship between the part manufacturing requirements and the machining unit processing capabilities,a mapping scoring mechanism for manufacturing requirements and machining capabilities is established.According to the manufacturing requirements of the process models,the machining unit instances in the knowledge graph are evaluated to obtain the optimal one.Finally,a complete machining plan is generated by the process constraint relationship between the machining units.(4)A prototype system for automatic generation of part 3D process models is developed,and the related application verification is carried out.The prototype system of 3D process model automatic generation for shaft parts and disc sleeve parts is designed and developed.The development environment,overall architecture and functional module composition of the system are introduced in detail.Atypical shaft part is taken as an example,and the 3D process models are automatically generated through the operations such as design model preprocessing,cutting surface mapping and decomposition,machining feature generation.A typical disc part is used as an example,and the integrated construction of casting blank model and process models is realized through operations such as initial blank model generation,unit volume decomposition and castability analysis,and machining allowance separation.Meanwhile,the machining plans are automatically generated for each process model based on the knowledge graph.The experimental results show the effectiveness of the part 3D process model automatically generation method. |
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