Model-Based Definition (MBD)

What is Model-Based Definition?

Model-Based Definition (MBD) is the practice of using a digital 3D product model as a primary carrier of product-definition information, rather than treating the model as geometry only and leaving every requirement to a separate 2D drawing. ISO 16792 formalises this: it specifies requirements for preparing and presenting digital product-definition data, and explicitly supports two methods of application, a 3D-model-only workflow and a 3D-model-with-2D-drawing workflow.¹

In addition to geometry, an MBD dataset can carry dimensions, tolerances, GD&T, datums, surface requirements, material information and other product or manufacturing requirements, attached directly to the model rather than described separately.

MBD does not automatically mean a 2D drawing disappears. Depending on the workflow and what a customer or supplier actually needs, the 3D model can serve as the primary product definition on its own, or it can be used together with a drawing that still carries some or all of the same requirements.

Geometry is not the same as product definition

A 3D model can describe the shape of a part with complete geometric accuracy while still leaving out most of what is needed to manufacture or inspect it. A cylindrical hole, for example, is visible directly in the geometry: its diameter and location can be measured straight from the model. Geometry alone does not say what tolerance class applies to it, what datum it is positioned from, whether a positional tolerance governs it, what surface finish is required, whether the dimension is functionally critical, or what material or process requirement applies.

NIST research into model-based product definition describes this gap directly: information that a traditional drawing carried implicitly, such as manufacturing constraints, process information and material requirements, is often not captured in the digital model that is meant to replace that drawing.² That is the practical reason MBD is a distinct concept from simply "having a 3D model": the model is necessary but not sufficient, and what counts as sufficient depends on the workflow it needs to support.

MBD, PMI and STEP AP242

These three terms describe related but different things, and are not interchangeable.

PMI (Product and Manufacturing Information) is the specific data attached to or associated with a model: dimensions, tolerances, GD&T, datums, annotations, finish requirements and material-related information where applicable. PMI is an important component of many MBD workflows, but MBD is the broader product-definition practice and PMI is one kind of content it can carry, not a synonym for it.

STEP AP242 is different again: it is an ISO application protocol for exchanging model-based 3D engineering data between systems, most recently published as ISO 10303-242:2025.³ AP242 is the mechanism many organisations use to move an MBD dataset between CAD systems, suppliers and downstream software, but it is a data-exchange protocol, not the practice itself. A model can originate as an MBD in a native CAD environment and be exchanged using STEP AP242, but how much of that definition survives the exchange depends on the source dataset and how it was exported, not on the protocol name alone.

Why this matters downstream

A model that actually carries its product-definition information can reduce how much of that context has to be reconstructed by hand at each downstream step. Manufacturing planning, CAM programming, inspection and CMM programming, quality documentation, supplier communication and other digital-thread workflows can all benefit when the information they need travels with the model instead of sitting only in a separate document.

That benefit is conditional, not automatic. Not every downstream system can consume every MBD dataset the same way, and how well a specific tool reads a specific dataset depends on both systems involved and on what was actually included at export. Machine-readable product definition lowers the amount of manual reconstruction required; it does not remove the need to check what a given model and its accompanying data actually contain.

The real-world mix

Manufacturing has not moved uniformly to drawingless MBD, and assuming otherwise is a mistake software can make quietly. A shop can receive a native CAD file, a STEP file, a 2D drawing, a PDF, a written specification and informal customer notes, in any combination, for the same part. Some of those datasets carry rich PMI; in current industrial practice, a large share still do not.²

Because of that mix, "a 3D file is present" cannot safely be treated as equivalent to "a complete manufacturing definition is present." What a specific model actually contains, and what still has to come from a drawing or a specification, has to be established per part rather than assumed from the file type.

The Subduxion interpretation

For Subduxion, MBD matters because understanding a part for manufacturing takes more than recognising its shape. It means connecting geometry, requirements and manufacturing context into one picture, whichever combination of model, PMI and drawing a specific part actually arrives with.

Where an incoming dataset already carries structured PMI, that is additional, valuable signal. Where it does not, the same requirements still have to come from somewhere else in the file set. This is an active research and development direction for Subduxion, not a claim that every incoming dataset is already read and reconciled automatically today.

Is MBD the same as PMI?

No. PMI (Product and Manufacturing Information) is the specific data — dimensions, tolerances, GD&T and similar — that a model can carry. MBD is the broader practice of using the model as the primary product-definition carrier; PMI is one kind of content it can include, not a synonym for it.

Is MBD the same as STEP AP242?

No. STEP AP242 is an ISO application protocol for exchanging model-based 3D engineering data between systems. MBD is the underlying product-definition practice; AP242 is one mechanism used to exchange an MBD dataset, not the practice itself.

Does MBD mean a 2D drawing is no longer used?

Not necessarily. Depending on the workflow, a 3D model can serve as the primary product definition on its own, or it can be used together with a 2D drawing that still carries some or all of the same requirements.