Explainer
What Is Model-Based Definition (MBD)?
The Short Answer
The Model Is the Definition
For most of the twentieth century, a product was defined by its drawing, and any model was a picture made alongside it. MBD reverses that. The annotated 3D model is the controlled definition, and anything else, such as a 2D drawing or a viewable file, is derived from it.
In U.S. defense work, MBD reaches contracts through the technical data package. MIL-STD-31000 defines a Type 3D package built on native 3D models, with derived drawings, viewables, or neutral files supplied as the contract requires, and derived data must never conflict with the master model. Our guide to the technical data package explains the package itself, and the MIL-STD-31000 page covers the standard.
Contents
What Is Inside an MBD Model
- Geometry
- The 3D shape of the part or assembly, built so that its measurements can be trusted rather than approximated.
- Product manufacturing information
- The dimensions, tolerances, notes, and material and finish specifications a drawing used to carry, attached to the model's features as annotation. People call this PMI.
- Structure and organization
- How the model is arranged: which views, annotations, and related data belong together. ASME Y14.47 addresses this, so that one team's model reads like another's.
- Related documentation
- Specifications, lists, and other data the model refers to. The model is the definition only when everything essential is in it or linked from it.
Vocabulary
MBD, MBE, and the TDP
- Model-based definition (MBD)
- The practice of defining a product in an annotated 3D model. It answers one question: where does the authoritative definition live?
- Model-based enterprise (MBE)
- The wider strategy of using that model across engineering, manufacturing, quality, and support, instead of re-creating information at each step. MBD is its foundation.
- Technical data package (TDP)
- The contractual package that carries the product definition to the customer. In a model-based program it is a 3D package built on the MBD.
Authority
The Model as a Legal Document
The phrase “model as a legal document” is shorthand, and no single standard carries that title. What exists is a body of practice that lets an annotated model do the job a drawing used to do. ASME Y14.41, Digital Product Definition Data Practices, sets requirements for preparing and revising digital product definition data, and ASME Y14.47, Model Organization Practices, gives a schema for organizing the model and its related information. MIL-STD-31000A (2013) added a model organizational schema for MBD compliant with Y14.41, so the defense package standard and the ASME standards line up.
The test is completeness. A model is authoritative only when nothing essential lives somewhere else; a program that keeps a drawing set “just in case” and consults it when in doubt is running two records. ASME has published newer editions of both standards over time, so check the edition your contract cites. For the standards in more depth, and for what this means for publications, read when the source of truth is a model.
Ownership and use of the model are a separate question from authority. The data rights clauses decide what the government may do with delivered model data; see technical data rights.
Downstream
Where MBD Data Goes Next
A model-based package feeds manufacturing, inspection, and sustainment. Technical manuals are not an element of a TDP, but they are written from its engineering data, so an MBD program changes where their source comes from. Figures can start from model geometry instead of a re-drawn view, which is the practical bridge into technical illustration, and a revised model becomes a revised source for every manual that depends on it.
Which manual standard applies is still decided by the contract, not by the package; see which MIL-STD applies to a technical manual. And a package is ordered through the contract, where the TDP option selection or the data list can set its level and type; see what a CDRL is.
FAQ
Questions We Hear
What does MBD stand for?
In engineering and defense acquisition, MBD stands for model-based definition: defining a product in an annotated 3D model rather than in drawings derived from it. The abbreviation has unrelated meanings elsewhere, so spell it out the first time you use it.
What does 'model as a legal document' mean?
It is shorthand, not a standard. It means the annotated 3D model, not a drawing, is the controlled record of what the product is, so a change to the product is a change to the model. What backs the idea is a set of standards, chiefly ASME Y14.41 and ASME Y14.47, and the TDP standard MIL-STD-31000. Whether a particular model is authoritative on a particular program is set by that program's contract and configuration process, and legal questions belong with counsel.
What is the difference between MBD and MBE?
MBD is how the product is defined: the annotated model is the authority. MBE is the wider way of working in which that model is used downstream, in manufacturing, inspection, and sustainment, without being re-created. You can do MBD without MBE, but MBE depends on MBD.
Does MBD mean there are no drawings?
Not necessarily. MIL-STD-31000 allows a 3D package to carry derived 2D drawings, 3D viewables, or neutral files as the contract requires, as long as they do not conflict with the master model. Drawings become views of the model rather than the authority.
Which standards define MBD?
ASME Y14.41 covers preparing and revising digital product definition data, and ASME Y14.47 covers model organization. MIL-STD-31000 defines the 3D technical data package for Department of Defense contracts. Check which edition your contract cites, because ASME has issued newer editions of both.
How does MBD affect technical manuals?
Technical manuals are not part of a technical data package, but they are written from its data. When the definition is a model, the figures and parts information can trace back to it, and a model change reaches the manual as a source change. Our model-based technical data guide covers that handoff.
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