Feature Recognition And Process-model Reverse Generation For Sheet Metal Parts

Sheet metal part models in standard format can be input and output in various CAD systems across multi-platform and multi-version,but it is inconvenient for model processing and digital manufacturing due to its lack of design features.In this thesis,by analyzing the geometric and topological information of the sheet metal model in STEP format,the method of feature recognition and process-model reverse generation is studied for sheet metal parts.According to the process types applied in sheet metal processing,sheet metal feature is divided into basic feature,deformation feature and trimming feature.The topological information including faces,loops and edges is extracted and stored in several kinds of appropriate data structure designed specially.Based on the geometric continuity and adjacency condition between faces,the faces are classified and transformed.The joggle face-sets,web face-sets and flange face-sets are created after grouping faces.Then,through the depth first search,the loops are classified according to the characteristics of the edges and the faces surrounded by the loops.Based on the types of faces sharing edge and the geometric type of edge,the edge type is divided.In the feature recognition of sheet metal boundary represention model,the corresponding feature information classes are designed to store the geometry structure,parent-child relationships and parameters of the feature.By using joggle face-sets,web face-sets and flange face-sets formed in preprocessing,web feature,joggle feature,flange feature and deformed flange feature are recognized,with feature relationships gained and the possible twin joggle can be recognized.On the outer boundary of faces,the pairs of flange face-sets meeting the specific conditions are found,and the stringer cutout,bend relief and corner are recognized by using the geometric continuity between adjacent edges.According to the type of loops on the faces and the characteristics of the faces surrounded by the loops,features including the hole,cutout,drawn hole and drawn cutout are recognized.During recognizing sheet metal features,the parameters between features are extracted and the relationship between features is gained.The reverse generation method of sheet metal process-model is studied.Starting from the final model of sheet metal parts,along following the process route,Boolean operation is performed to process the features in the current process-model,and the previous process-model is generated step by step until the blank model is gained.The feature processing methods include the removal of local features,the unfolding of bending,the removal of drawn holes and cutout,and the completion of stringer cutout.In NX software environment,C++ language by programming with NX API are used to realize feature recognition and reverse generation of process-model.Through Menu Script technology,the dynamic link library files generated is combined with the dialog box designed by NX Block UI Styler to realize human-computer interaction in NX platform.Experiments proved that the method could effectively recognize feature of sheet metal model in standard format and quickly generate the intermediate process-model.