The changing face of part inspection

Inspection software helps 3D CAD, 3D GD&T, and measuring devices work together to ensure design intent.

A necessary component of the model-based definition (MBD) approach to product design is 3D geometric dimensioning and tolerancing (GD&T), a universal symbolic and tolerancing language. In the MBD approach, the 3D CAD model is the authority, providing all the detailed product information for the entire product life cycle. The method moves the 3D CAD model from design to a manufacturing orientation, and lets software automate and validate steps in simulation, manufacturing, and inspection, thereby reducing human error.

Last updated in 2009, GD&T has been rigorously studied and applied by thousands of manufacturers around the world. It is often considered essential for communicating design intent — that is, that parts from technical drawings have the needed form, fit, function, and interchangeability. The recent update includes changes in feature design, datum references and degrees of freedom, surface boundaries and axis methods of interpretation, profile tolerances, and symbology and modifiers tools.

In manufacturing, the direction of CAD is to 3D, however not all CAD programs provide intelligent 3D GD&T data. Here, “intelligent” means computer readable, thereby capable of feeding downstream applications. There are two 3D GD&T definition-data formats. Potentially confusing, both are labeled “3D annotation,” but one format is purely for display, while the other provides intelligence back to the CAD model.

The distinction is that in the display format, tolerancing associated to the model is in the form of text. In other words, humans must interpret the GD&T information, opening the door to potential errors. The display or presentation format is similar to typing a math equation in Microsoft Word. It conveys information, but the computer cannot use it in calculations. In conversation, this approach is commonly referred to as “decorating the model.”

What makes the effort of applying GD&T to 3D models worthwhile? As part of the MBD approach, it helps users leverage data throughout product development, cutting time from processes and improving them. It can even be said that 3D GD&T data provides a form of “artificial intelligence” for manufacturing and inspection.