The Reconstruction Of 3D Machining Features Based On STEP

With the development of manufacture technology, feature technology and Feature Modeling are becoming an important area in the integration process of CAD/CAPP/CAM system, especially machining feature technology is the representative of the processing, has been widely used in the actual production, But at the same time the reconstruction and the modeling of machining features are difficult points in CIMS. This thesis starts with the architecture of machining feature, through the analysis of the machining feature description content, extracts the deep manufacturing information of engineering drawing, and combines the description of the single feature and the whole feature entity, achieves the reconstruction and setting up the model of machining features.First, this thesis discusses the research in the feature technology and Feature Modeling related, elaborates situations on the research at home and abroad, analysis advantages and disadvantages in methods at current researches, and then the way and direction of this thesis is put forward based on the situations.The information of machining features being described is given after that, including geometric entities elements,size and location dimensions in geometric information, the constrains of features in the internal and external, furthermore, advanced semantics information such as accuracy and tolerances are necessary, for example surface roughness, dimensional tolerances, etc.Second, the standard for the exchange of product model data (STEP) is analyzed and the three-dimensional (3D) structure and geometrical entity description method of the STEP documents is studied. EXPRESS language based on STEP neutral file is used for describing three-dimensional feature entities and then geometric information is extracted form that, which lay the foundation for the reconstruction and modeling of the machining feature.For the deficiencies in description basing on graph and matrix, this thesis adopts Directed Graph (DG) based on semantics to describe constrain relations between features. this thesis divides the basal constrain of features into three types: geometrical constraints,locational constraints and dimensional constraints. With using feature as nodes and semantic relations containing direction arc, constrain relations between features are showed, adjacent constraint based on boundary representation in geometrical constraint is emphasized.Though an analysis of the characteristic of machining features, this thesis has a classification of machining features, proposes a method of pattern recognition based on syntax and describes basic machining features with the knowledge expression method to set up machining features template. Get basic machining features and then match them to machining features template in the library, recognizes machining features and reconstruct them, but these, machining feature model has been set up.Finally, with the development of feature technology and Feature Modeling, 3D machining feature reconstruction objects are summarized and the future research work is put forward.