Downloaded from https://www.everyspec.com APPENDIX C MIL-STD-31000A C.1 FORWARD. The use of three-dimensional model-based definition (3D MBD) for design of military equipment has become common practice. Prime contractors on every major weapons program use 3D computer-aided design (CAD) software to design, analyze, manufacture, and inspect the mechanical components and structures of their products. Yet because 3D model data is not currently approved within the Department of Defense for use as master product data, contractors must submit 2D drawings of their designs to serve as permanent records throughout each system’s life.
Drawings are less useful than 3D models for activities taking place later in the equipment’s life such as manufacturing spare parts, improving existing designs, and analyzing systems when unexpected failures occur. It is therefore desirable that the Department of Defense be capable of accepting 3D models in lieu of or in addition to drawings. In order to accept 3D mathematical models, the DoD requires approved processes for validating that 3D models are suitable for master reference data.
This document provides technical guidance to the Government and its contractors about validating digital 3D models prior to their distribution to Government agencies and subcontractors during the design, manufacturing, and logistical-support phases of the life of a weapons system. The reason that formal, algorithmic validation processes are necessary for 3D models is because models may contain subtle defects that can prevent them from being used by ancillary applications such as numerically controlled manufacturing, finite element analysis, and inspection with coordinate-measuring devices.
This guide identifies and classifies the causes of defects in 3D digital models, indicates which defects are likely to cause difficulties for various types of computer applications that use the models, and provides recommended tolerances and acceptance criteria for models. Validation may be divided into 3 classes: geometry, annotation, and attributes. Geometry validation identifies defects in geometric entities such as lines, curves, and surfaces, and errors in relationships among entities, such as gaps or overlaps. Geometry validation also encompasses model topology including faces, edges and vertices.
Annotations consist of symbols, dimensions, geometric tolerances, notes, and other symbols attached to the model. Validation examines the locations, orientations, values, layers, context, and syntax of annotations. notes, material descriptions, or combinations of the above that are required to complete the product definition but are not visible when viewing the model. Attributes must be evaluated for their existence, type (integer, floating point, text), and values.
Model attributes consist of views (model orientation and zoom state), layers, numerical values, The recommended practices in this guide are based on currently available, commercial technology for inspecting and validating 3D models produced by commercial CAD software. The validation 52