Manufacturing & engineering
MBD
Model-based definition
Definition
MBD is the practice of making the annotated 3D model, with its PMI, the authoritative definition of a part instead of a separate 2D drawing. The model carries dimensions, tolerances, and notes directly to manufacturing and inspection.
Also known as: model-based definition
Updated
Why teams adopt it#
PTC describes the shift plainly: engineers long used 2D drawings to deliver manufacturing information even while designing in 3D, and MBD embeds that data in the model as a single source of truth. In the US, ASME Y14.41 covers digital product definition data practices.
MBD depends on the whole supply chain being able to read the model. Many shops still expect a drawing, so teams often publish both during the transition.
Sources
Related terms
PMI
PMI is the dimensions, tolerances, GD&T, materials, surface finishes, and notes attached to a 3D CAD model instead of, or in addition to, a 2D drawing. It is the core content of model-based definition.
Drawing
An engineering drawing is a 2D document generated from a 3D model, with views, dimensions, tolerances, and notes. Many shops still quote and inspect from drawings even when they also receive a STEP file.
GD&T
GD&T is a symbolic language for specifying the allowed variation in a part's form, orientation, location, and runout relative to datum features. In the US it is defined by ASME Y14.5, and it tells the manufacturer and inspector which geometry actually matters for fit and function.
STEP
STEP is the ISO 10303 family of standards for exchanging 3D product data between CAD systems, usually saved as .step or .stp files. A STEP file carries exact B-Rep solid geometry that another CAD program can measure and edit, but it normally does not carry the original feature history.