In model-based Systems Engineering, a model must capture a product’s functional and behavioral requirements such that product design information is traceable to the requirements. Product and Manufacturing Information (PMI) specifies, in a formal and precise language, these requirements as they apply to production. PMI communicates allowable product geometry variations (tolerances) in form, size and orientation. PMI annotations include Geometric Dimensioning and Tolerancing, surface texture specifications, finish requirements, process notes, material specifications, and welding symbols.
PMI-annotated digital product models potentially enable software developers to automate manufacturing and other downstream activities. However, PMI must be “semantic” to realize this potential requires, i.e.:
1. PMI must be represented in a computer-readable data format,
2. The data format must represent not only the annotation graphics, but also associations between annotations and product geometry features, associations between annotations and other annotations, and annotation metadata (type, text, parameters).
In many industries, 3D models are replacing traditional 2D drawings. Manufacturers want to develop, communicate, and store all product definition data as digital models so that the data can be used by software applications. This means that software applications will perform all interpretation and presentation of geometry data and PMI, requiring that PMI be “semantic”. The American Society of Mechanical Engineers (ASME) and the International Organization for Standardization (ISO) define the standards for PMI, and these standards are complex. If the software applications interpreting PMI don’t conform to standards, the same PMI data is likely to be interpreted and presented differently by different engineering and manufacturing applications. Incorrect presentation and misinterpretation of PMI can cause significant delays and costly errors.
NIST has created a Test System to measure conformance of Computer-Aided Design (CAD) software to ASME standards defining the semantics of the words and symbols used to communicate PMI. We focus on “semantic” PMI because it is so critical for automating downstream engineering and manufacturing applications.
The test system has three main components:
1. Test Cases defining part geometries with PMI concepts applied to the part,
2. Test Models that implement the Test Cases in CAD software,
3. Model Verification and Validation based on comparisons between Test Models implementing the same Test Case.
We accomplish model-to-model comparisons in partnership with consortia of software developers and testers working on CAD translators based on open data exchange standards such as ISO 10303 – the Standard for the Exchange of Product model data (STEP). These groups produce translations resulting in derivative models, exported from an original “master” CAD model. Derivative models are in turn imported into other native CAD software applications.
A Test Case Browser application provides access to 2D drawings of all of the Test Cases. The browser has multiple tabs, each providing a different way to browse the Test Cases and view their corresponding images. In the future, the browser will be extended to enable viewing of Test Models, their derivatives, and test results.