Manufacturing & engineering
PMI
Product and manufacturing information
Definition
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.
Also known as: product manufacturing information, 3D annotations, semantic PMI
Updated
Graphical and semantic PMI#
Some PMI is only a visual annotation: text floating in the 3D view. Semantic PMI is linked to the faces and features it describes, so downstream CAM or inspection software can read it. Onshape's MBD page describes PMI as dimensions, tolerances, materials, and annotations carried alongside the geometry.
PMI only helps if it survives export. STEP AP242 can carry it, and the CAx Interoperability Forum tests PMI exchange between CAD systems. Check with the receiving team before assuming they can read it.
Sources
Related terms
MBD
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.
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.
Tolerance
A tolerance is the allowed variation from a nominal dimension, such as 10.00 ± 0.05 mm. Tolerances drive fit, cost, and inspection, and they have to be specified deliberately because a CAD model on its own stores only nominal sizes.