Procedural CAD Model Edge Tolerance Negotiation for Surface Meshing

Abstract

Geometrical models output from CAD software often require modification before they may be used for analysis-quality mesh generation. This is due primarily to the inconsistencies in tolerances used by the CAD operator and the tolerances required for analysis. This paper presents a method for construction of watertight surface meshes directly on imperfect non-modified CAD models. The method is based on a hierarchical grid topology structure that defines a surface mesh by a grid and a collection of curves defining the boundary. Curve boundaries on component surfaces are iteratively split and merged according to user-set tolerances, allowing adjacent surface meshes to become computationally watertight via their shared edge curves. The collection of watertight surface meshes may then be made model-independent through interactive agglomeration of the surface meshes, followed by refinement and decimation sweeps to remove artifacts of original surface edges. Interactive procedures used for difficult cases are also explained, as are ongoing efforts for further automation.

Product data quality assurance for e-manufacturing in the automotive industry

“…While analysing the tolerance between two entities, Deshpande et al (2000) used a model object tree to evaluate the topological entities of a B-Rep model. After approximating the exact B-Rep shape as a polyhedron of a faceted B-Rep, Barequet et al (1996), Barequet (1997), and Steinbrenner et al (2001) repaired the gap and overlap that occurs between polygons. A synopsis is given in table 1.…”

Repairing CAD model errors based on the design history

“…Steinbrenner et al [6] checked and corrected the gaps or overlaps between adjacent curves in a 3-D shape that consisted of curved surfaces with various degrees.…”

“…Previous studies on poor-quality CAD models have focused on the boundary representation (B-Rep) of 3-D shapes [3][4][5][6][7][8] However, although the B-Rep approach is effective for locating errors with the maximum or minimum tolerance as defined by the designer, an unstable topological structure can unintentionally distort a repaired B-Rep shape or cause the shape to collapse. As a result, only limited types of errors can be corrected, and automation of the correction process is difficult.…”

Industrial challenges for numerical simulation of crystal growth

“…Probably the most time (and expense [54]) consuming part of the problem statement is a geometry speci¯cation. Unfortunately, geometry import of a CAD model usually requires a number of user actions generically referred to as CAD data repair [7].…”

“…Thus, the topology of the model must be reconstructed and this procedure is non-trivial due to the erroneous gaps between the neighbor elements [62]. Often the primary reason for numerous geometry and topology inconsistencies in CAD data (such as, for example, an edge whose path intersects itself or a face with edges that do not form a closed loop) is a di®erence between tolerances used by a CAD designer and tolerances needed for grid generation [54]. Thus at present a manual repair of imported CAD data (probably assisted by interactive repair and defeaturing tools [57]) seems to be inevitable for complex geometry.…”