GlossaryKind of term: Manufacturing termPMI and MBD
What are PMI and MBD?
PMI covers the dimensions, tolerances and notes in the 3D model itself; MBD is the practice in which that annotated model is the source of the requirements.
In full PMI is product and manufacturing information: dimensions, geometric tolerances, datums and roughness, usually attached to faces and edges, plus material and notes. Under MBD, model-based definition, a reduced 2D drawing may still sit beside the model, but it is no longer the source. PMI can be visual, meant for a person to read on screen, or semantic, machine-readable data attached to the intended feature.
What does the standard say about PMI and MBD?
How a model is annotated and presented is described in ISO 16792 and, in American documentation, ASME Y14.41. What a tolerance means follows from the tolerancing standard the model refers to: ISO 1101 with ISO 8015 on the ISO side, ASME Y14.5 on the American side. For exchange between systems, STEP AP242 is a common neutral format for semantic PMI. None of these standards decides whether the model is authoritative: that is an agreement between customer and supplier, to be recorded in the order or the purchasing terms.
How do PMI and MBD work in practice?
Under MBD with no drawing, every requirement has to be in the model; if one is missing, an operation or inspection step may be missing from your price. When a PDF comes with a PMI model, a revision that updates only one of them leaves a difference that surfaces only during machining or inspection. Semantic PMI can feed a measuring program or a ballooned drawing if your software supports it; visual PMI has to be transcribed. If material, roughness, finishing or the general tolerance are missing from the model, ask for them before quoting.
What are PMI and MBD often confused with?
PMI is not the same as a STEP AP242 file: AP242 is a format that can carry PMI, PMI is the content. MBD is not a file format either, but a practice. And PMI in a model does not make the model authoritative: only the agreement with the customer does.
Where do the requirements in Blake come from?
In Blake, material, tolerances, roughness, finishing and threads sit with the part as proposals from the PDF drawing. You confirm or correct them; who did so and when stays visible, with a note if you add one. More on requests.
Frequently asked questions
What is the difference between PMI and MBD?
PMI is the content: dimensions, tolerances and notes in the model. MBD is the practice in which that model replaces the drawing as the source of requirements. You can have PMI without MBD, as long as the drawing remains authoritative.
How do I know whether a model contains PMI?
Open it in a viewer or CAD system that displays PMI and check whether dimensions and tolerances are attached to the faces. If nothing shows, price from the PDF drawing.
Can I price without a drawing if the model has PMI?
Only if the customer has agreed that the model is authoritative and the PMI is complete: material, roughness, finishing and the general tolerance all belong in it. If anything is missing, ask first.