Research On Construction Of 3D Process Model Based On Features And Machining Elements

Digital design and manufacturing based on 3D model has become the mainstream model of discrete manufacturing,and 3D process model is one of the key technologies to realize 3D process design.However,the 3D model has strict topology and constraint relation,the 3D process model is difficult to copy/modify the 3D design model,often need to construct process model interactive and the workload is heavy.Because of the complexity of technology design and technology changes frequently,causing further change or reconstruct the 3D process model,resulting in process design efficiency is low.So how to achieve rapid construction of the 3D process model is urgent problem to achieve the design and manufacuture of single source data driven.In this thesis,a method of 3D process model construction based on manufacturing feature and machining element is proposed,which aims at exploring effective theory,method and approach for rapid 3D model construction.The design model is structural represented by the manufacturing feature and the machining element,the technology is structural represented by the process and the step,the machining element is associated with the step to realize the association between the manufacturing feature structure tree and the technology structure tree.The machining element is taken as the basic unit and the machining element volume is generated dynamically,then the process model is generated by the Boolean difference operation between the machining volume and the precursor process model.The research work and achievements of this thesis are as follows:A framework of 3D process model construction based on manufacturing feature and machining element is proposed.Firstly,the expression of 3D process model is completed theoretically,the simplified machining element as the basic unit is proposed.The 3D process model is constructed by expressing the manufacting feature?extracting the manufacturing feature and generating the maching volume.On this basis,the process model,the manufacturing tree and the technology tree is expressed and the database is managemented,the construction and the revision of 3D process model is proposed,then the modification and regeneration of 3D process model is achieved.A manufacturing feature representation method for constructing process model is proposed.Based on the manufacture feature modeling technology and its geometric characteristics,a unified representation of the manufacturing features is proposed.Then the manufacturing feature library is builded to lay the foundation for the extraction of the manufacturing feature and the generation of the machining element volume.Firstly,according to the different modeling methods,manufacturing feature is divided into template manufacturing feature,rule manufacturing feature and auxiliary manufacturing feature.Then,based on the study of the modeling techniques and their geometric characteristics,the corresponding representation methods are given,a scalable template manufacturing feature library is builded by using a relational database,the rule manufacturing feature library and the auxiliary manufacturing feature library is builded by using the object-oriented technology.Finally,the representation of manufacturing features is represented by the synthesis of the template manufacturing feature,the rule manufacturing feature and the auxiliary manufacturing featur.A method of generating machining element volume based on template model is proposed.The parametric design modeling method is learned and the base face matching of manufacturing feature extraction technology is used,the manufacturing features is extracted by matching with the template manufacturing feature library,setting parameters and locating parameters are calculated to drive the machining element model.First of all,the design model will be divided into a series of connected subgraphs by using convex decomposition algorithm;after determining the base face of the connected subgraph,the manufacturing feature will be extracted and the lost face will be completed by matching with the manufacturing feature base face.Then,the parameters are exported,the parameter value is calculated according to the feature geometry and the parameter type and is corrected according to the mapping property of the feature geometry.Finally,the machining element model is driven by parameters and allowance to position and set the machining element in the precursor process mode.A method of generating machining element volume based on extrude forming is proposed.The modeling method of extrude forming is learned and the feature extraction technology based on rule matching are used to realize the feature extraction of the rule manufacturing feature and the forming of the machining element.First of all,the part will be divided into a series of connected subgraphs by using convex decomposition algorithm,the type of manufacturing feature will be identified by using rule matching algorithm;on this basis,the base face?the extruding start face and the extruding end face of the rule manufacturing feature is extracted.Then the manufacturing feature contour is acquired by referring to the base face and the machining element reference contour is genenration by referring to the precursor process model,and an improved curve offset algorithm is proposed to generate the the machining element contours.Finally,the machining element volume is generated by extruding the machining element contour.A prototype system of 3D process model based on manufacturing feature is proposed.The system supports the key technologies of manufacturing feature representation,manufacturing feature extraction and machining element generation.The edit and management of the manufacturing feature structure tree and the process structure tree?the construction and browsing of the template manufacturing feature database,the browsing of the 3D process model are realized.Take the typical parts as an example to verify the correctness of the research ideas and theory,and the feasibility of the research methods and key technologies.It is a very complex research topic to construct 3D process model,which is related to many fields such as computer graphics,image processing,computer vision,machining design and manufacturing.The proposed manufacturing feature representation,feature extraction technology,machining element generation technology not only realizes the construction of 3D process model,but also can be applied to 3D model retrieval,3D process similarity assessment and 3D process plan reuse.