Reuse Oriented NC Process Planning Fusion And Optimization For Multi-source Similar Subparts

With the wide application of digital design and manufacturing technology in enterprises,a large amount of 3D CAD models which carry digital machining process design achievements are continuously produced and stored in the repositories.If these achievements can be reused efficiently,the product development cost can be lowed and the efficiency can be improved dramatically.In recent years,3D CAD model retrieval technology is becoming an effective tool to discover and reuse the NC process of similar features and subparts.On this basis,effectively fusing and optimizing the reusable NC process of existing multi-source similar subparts,and obtaining the optimal NC process scheme for the query part has become an effective means to improve the level of intelligence in NC process planning.In this context,the reuse oriented NC process planning fusion and optimization for multi-source similar subparts is studied in this dissertation.The main research contents of this paper are as following:(1)A novel framework for reuse oriented NC process fusion and optimization is proposed.The framework contains NC process information analysis,subpart retrieval of 3D CAD model,NC process reuse implementation for similar features/subparts and NC process planning optimization.In this way,the flexibility and effeciency in NC process planning can be inproved significantly.(2)A Medial axis transform based NC process information analysis method for pocket features is presented.First,the medial axis transform(MAT)of a pocket feature is introduced and adopted as the reference tool paths,which associates the geometry and NC machining procedure effectively.Then,the association mechanism between MAT and NC machining is established,including two modes: MAT-Feasible tools set relevance and MAT-Tool retractions relevance.Based on the association mechanism,valuable NC process inforamtion,such as feasible tools set and tool retractions number is calculated.Finally,the tool paths lengths calculation method is proposed.(3)A NC process reuse oriented subpart retrieval approach of 3D CAD models is presented.First,the rapid filtering is introduced to quickly eliminate impracticable subpart cases under the requirements of NC process reuse,which helps to speed up the retrieval effenciency.Then,taking various levels of NC process information for reuse into account,a multi-layered feature descriptor is elaborated to implement the feature similarity calculation.Finally,the matched feature pairs and space layout similarity are presented to assess the similarity between subparts.(4)A fusion and regrouping method for multi-source similar subparts is presented.First,based on the retrieved multi-source similar subparts,the composition features and associated NC process are described as multi-dimension vectors consisting of feature attibutes and NC process.Secondly,the attributes similarities of query feature and similar feature cases are calculated to establish the similarity matrix.Then,based on the multi-source similar features,the grey relational analysis is utilized to reveal the association between feature attributes and NC process,and the relation matrix is constructed.Based on the multiplication of similarity matrix and relation matrix,the adaption matrix is calculated to represent the importance degree of the NC process of similar feature cases for query feature.Through the weighted sum of adaption values and adjustments,the NC process is obtained for the query subpart.Finally,based on the feature interactions in the query subpart,the NC process of the query subpart is regrouped to meet the requirements of NC machining.(5)A multi-source similar subparts based flexible NC process planning optimization approach for prismatic parts is proposed.First,the NC process candidates for query subparts are generated automatically and effectively through the inheritance mechanisms.Secondly,the NC process for each query subpart is selected using the roulette wheel approach in terms of the reusability.Then,a parametrized precedence constraint model(PPCM)is constructed to formlize the linkes between features and operations precedence,and the NC process precedence constraint characteristic of query part is revealed from several aspects.Moreover,the operation precedence graph(OPG)of the query part is established.Finally,the global optimal NC process scheme for the query part is obtained using an OPG based hybrid ant colony algorithm(ACA)and simulated annealing(SA)approach.Based on the above approaches proposed,a prototype system is developed,which is named 3D CAD Model Retrieval System for NC Machining Process Reuse V1.1(MRS-NCMPR V1.1).Experiments are implemented and the results show that the theories and methods are effective and feasible.