Downloaded from https://www.everyspec.com APPENDIX C MIL-STD-31000A C.5 GENERAL REQUIREMENTS. Criteria for acceptable 3D model quality depend on the types of applications that will employ the models. For example, a model that is used primarily as a visual aid may look acceptable. However, if that same model is translated to another CAD system or employed to generate tool paths for numerically controlled (NC) manufacturing machines or to produce finite element models for analysis, it may contain hidden errors that cause applications that use the data to fail. Such defects may include gaps or long and narrow faces too small for human eyes to see.
They may also include self-intersecting curves and surfaces. Designers of parts that contain invisible defects may not be aware that they have created them. Because design is an iterative process, designers may apply multiple features in the same local area to produce a desired shape. In attempting to resolve the geometry and topology of the features, the CAD software itself may introduce defects that cause problems for other applications using the model geometry. Defects also may be introduced by data translation software used to convert proprietary CAD formats to standard formats, such as IGES or STEP, or to the proprietary formats of other software vendors.
Such defects may be caused by software programming errors or because various systems employ slightly different algorithms for generating model geometry. Problems may also be caused when the resolution or precision to which the CAD system computes complex geometric intersections differs in the originating and receiving systems. Because defects may be caused without the knowledge of the people using the data, automated data- checking software is required to identify errors. So-called healing software may be required to correct the errors. The data acceptance criteria of the government will depend upon the use to which 3D models will be applied.
Models used simply for design reviews may contain unseen errors without doing any harm. However, models that are intended for use as manufacturing masters, as geometry for analysis, or for long-term archival storage (whose future uses can’t be determined) should be subjected to more rigorous acceptance criteria. This guide provides suggested values and recommendations for different classes of data use. The use classes employed in this document are defined as follows: C.5.1. Native or original 3D model data.
Native or original 3D models are those that have been created in a commercial CAD or modeling application such as Parametric Technology’s Pro/Engineer or Creo, Siemens PLM software’s NX or Solid Edge, Dassault Systиmes CATIA or SolidWorks, or Autodesk’s AutoCAD or Inventor. Native data has not been translated to any other format following its release in the native format. There are two distinct use cases for native data. 65