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DOI 10.1007/s00170-004-2195-3 ORIGINAL ARTICLE Int J Adv Manuf Technol (2005) 26: 405414 Jian Gao De Tao Zheng Nabil Gindy Doug Clark Extraction/conversion of geometric dimensions and tolerances for machining features Received: 28 January 2004 / Accepted: 31 March 2004 / Published online: 28 July 2004 Springer-Verlag London Limited 2004 Abstract It is important for a feature-based system to preserve feature integrity during feature operation, especially when fea- ture interaction occurs. The paper presents a feature conversion approach to convert design features used in a design model into machining features for the downstream applications. This pro- cess includes both form features (geometric information) and non-geometric features conversion. Most researchers have con- centrated on geometric information extraction and conversion without tackling the important problem of non-geometric feature information. This paper focuses on the extraction and conver- sion of feature geometric dimensions and tolerances (GD Step 5: Comparing the real value of a dimension with the dis- tance d01and d02, which represents the distance between face f0and f1and face f0and f2, respectively. If the distance d01 is equal to the Value(dim(i), then substitute the boundary iden- tifi cation id1of e0 with the identifi cation of f1, which means the representation of the edge element has been changed to the rep- resentation of the face element. If the distance d02is equal to Value(dim(i), then substitute identifi cation id1of edge e0with the one of face f2and go to step 7. Step 6: Comparing the real value of a dimension with the dis- tances d11, d12, d21, d22(dijrepresents the distance between face f1iand face f2j, and i, j = 1,2), there must exist a distance that has the value of dim(i). If d21is equal to the Value(dim(i), then substituting dimension d21 s two boundary identifi cations with those of face f12and f21, and go to step 7; Step 7: If i datum number N, then end; otherwise, seti =i+1, go back to step 2 By means of the above algorithm, the co-planar array stores the datum elements corresponding to the real feature elements. The algorithm fl owchart is shown in Fig. 8. Combining with the two-stage conversion algorithms, the positional geometric toler- ances can be fully converted. 413 Table2. Dimension boundary after feature conversion Feature idDimDimension typeDimension boundaryDimension boundary signelement1element1 #id_feat#dLINANGDIA/RADSRFAXISEDOSRFAXISEDO #1dOYes#14#18 basedlYes#16#12 featured2Yes# 7#2 #20d3Yes#37#33 slotd4Yes#16#35 asYes#33#18 asYes#16#68 #59d9Yes#71#73 blind-holedlOYes# 7#76 dl 1Yes#18#76 #81dl JYes#93#95 holed!4Yes# 7#98 dlSYes#33#98 d29Yes#207#203 #190d30Yes#16#205 blind-slotd31Yes#207# 2 d34Yes#198#33 5 A component example An example of geometric dimension conversion to a prismatic component is presented in this section. The component model used is shown in Fig. 9. Through the form feature conversion module developed and introduced in 19, the component in the viewpoint of process planning application is a compound of the base feature, slot, blind-hole, hole and blind-slot features. Fea- ture attributes (non-geometric feature), especially the geometric dimensions of the model, need to be converted so as to de- scribe correctly these machining features. Before the conversion algorithm is applied to the component model, the geometric di- mensions are extracted and listed in Table 1. It is found that some boundary elements of the dimensions are edge elements and these need to be converted. After the conversion, all dimensions with edge boundary elements are converted into the dimensions with face boundary elements (shown in Table 2). 6 Conclusions Feature technology has been an important research topic used for CAD/ACPP/CAM integration. Due to the variety of feature rep- resentations from application to application, the main unsolved problem now is to completely explain the design-feature-based component model, in particular regarding feature interactions. Based on the investigation and analysis of the design feature modelling process, it was found that the inconsistency between the fi nal component model and the information available in database is the key issue to be solved for downstream applica- tions. In order to correctly represent the component model by a number of machining features, this paper focuses on the ex- traction and conversion of the non-geometric features, that is, the geometric dimensions and tolerances (GD&T), which play a key role in the process planning modelling process. In this paper, GD&T feature conversion algorithms were de- veloped and described in detail. Due to the different represen- tations between the design features and the machining features an algorithm was developed to convert the dimension bound- ary elements to recognisable elements for process modelling. In the situation of feature interactions, since the feature informa- tion in the database does not change accordingly, the algorithm was implemented to detect whether the feature dimensions are consistent with the feature model and to convert those virtual di- mensions into the real dimensions that correctly describe the ma- chining features. For geometric tolerance conversion, the main task is to locate each tolerance of the component to the corres- ponding feature, and convert the virtual datum elements in the design model into recognisable elements for the machining ap- plication. Combined with the geometric information conversion de- scribed in 17, the machining features can be generated in terms of the process-planning system requirements. Through the inter- face of the STEP fi le, the feature-based CAD/CAPP integration can be implemented 18. The feature-based Pro/Engineer sys- tem was used to build the design model, and the feature conver- sion algorithm was implemented through the Pro/Develop tool written in C+ on a Sun Sparc 20 workstation. References 1. Shah JJ, Mantyla M (1995) Parametric and feature-based CAD/CAM: concepts, techniques, and applications. Wiley, New York 2. Liu X (2000) CFACA: component framework for feature-based design and processing planning. Comput-Aided Des 32:397408 414 3. Han J, Requicha A (1998) Feature recognition from CAD models. IEEE Comput Graphs Appl 18(2):8094 4. Gindy N, Yue Y, Zhu CF (1998) Automated feature validation for cre- ating/ editing feature-based component data models. Int J Prod Res 36(9):24792495 5. Wang H-F, Zhang Y-L (2002) CAD/CAM integrated system in collabo- rative development environment. Robot Comput Integr Manuf 18:135 145 6. Han J (1996) 3D geometric reasoning algorithms for feature recogni- tion. Dissertation, The University of Southern California, Los Angeles 7. 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