This function is commonly referred to as ‘healing’ the CAD geometry.
ASME Y14.5 1994 THREAD STANDARDS SOFTWARE
An entire market of software to validate CAD geometry has been developed to check that the underlying geometric representation is free from any defects that might affect its downstream use by analysis, manufacturing, and inspection processes. However, some of the CAD data quality issues might not result in an obvious problem with the visual appearance of the geometry. This type of defect might result in the failure of finite element meshing algorithms, the failure of computer numerically controlled (CNC) tool paths, or create an undesired visual appearance. For example, in CAD geometry, adjacent curves, line segments, or surfaces might be separated by a gap or may overlap each other when they are expected to perfectly adjoin each other. A condition is a specific type of defect for a type of geometry. Each criterion defines the “effects of condition on CAD data quality” on design or drafting, data exchange, finite element analysis, and numerically controlled manufacturing. Department of Defense standard practice for Technical Data Packages (MIL-STD-31000A), in Appendix C section C.7.1, defines 66 criteria for evaluating the following types of CAD geometry: curves, surfaces, edges, edge loops, faces, shells, and solids. This is particularly true in a model-based environment where the geometric representation is automatically used in those downstream processes. Although the visual appearance of a part might be acceptable the underlying geometric representation might be a source of problems with subsequent downstream finite element analysis, and manufacturing and inspection processes. Defect detection might take place when the part is being modeled or after a part is translated to another CAD system.
The geometry and topology of parts modeled in CAD software can be checked for defects. The testing project results can be used as a basis for future testing, methods, and standards to evaluate defects in GD&T applied to part features.
The testing methodology, test results, and data analysis demonstrate how well the CAD system GD&T implementations perform. Errors with semantic representation and graphical presentation of the GD&T were collected and analyzed. Representative part geometry with GD&T applied to features was modeled in four of the major CAD systems. To improve that situation, the National Institute of Standards and Technology (NIST) has developed a system to test implementations of GD&T in CAD software. However, there has never been any rigorous public-domain testing of CAD software GD&T implementations.
Of course, CAD software vendors do their own internal testing of those capabilities and users evaluate CAD software so that it satisfies their CAD modeling requirements. However, it is not well characterized how CAD software implements capabilities for a designer to apply GD&T to a part.
Applying geometric and dimensional tolerances (GD&T) to part features in computer-aided design (CAD) software is essential so that the part will function properly and to guide downstream manufacturing and inspection processes.