Getting Started with Model-Based Definition

Is your company embarking on design documentation improvements? You are far from alone.

Some 69% of respondents in Lifecycle Insights’ Engineering Executive Strategic Agenda study stated they invested in such efforts last year, with an additional 54% planning changes in the coming year. To make such improvements, many organizations are transitioning to model-based definition (MBD) initiatives.

The Function of Design Documentation

Manufacturing organizations are always looking for ways to optimize the product development process. Today, many have their eye on design documentation improvements. But, before considering alternatives to the way organizations currently create and consume design documentation, it is crucial to set a baseline for what such deliverables need to do at a functional level. Mechanical engineers create design documentation deliverables to:

• convey the complete and detailed geometric form of a component,
• define the measurements and thresholds within which a component meets quality standards, and
• provide a deliverable that can be used to create derived deliverables.

   

Engineers can meet these vital objectives with the traditional 2D drawings commonly used in design documentation or via an MBD approach. But while both methods work, an MBD approach has significant advantages. Let’s take a look.

Using a Drawing for Design Documentation

To convey the complete and detailed geometric form of a component, drawing-based design documentation relies on a combination of 2D entities, dimensions, and multiple views. The complete detailed form of any component, traditionally, is the combination of three views of a drawing and its dimensions.

The effort to define the measurements and thresholds within which a component meets quality standards, builds, at least partially, on the earlier efforts to convey its complete and detailed geometric form. The dimensions to define the component’s form already exist. However, not all processes involved with measuring conformance to quality standards require all of those dimensions. Therefore, engineers must explicitly identify the dimensions for measurement once component manufacturing is complete. They also have to add tolerances to the existing dimensions in order to define the thresholds within which those dimensions must fall.

To date, many organizations are still using this approach in design documentation efforts. Though it is the status quo, accurately annotating the drawings with all of this vital data is arduous and time-intensive. And even when these drawings are properly annotated, there is always the risk that downstream development players will misinterpret the information.

Using an MBD for Design Documentation

An MBD, on the other hand, is an annotated 3D model that replaces the multi-view 2D models of yore. MBDs define individual components and product assemblies. They also contain additional design and manufacturing data required for successful development.

An MBD conveys the complete and detailed form of a component in an entirely different manner than do traditional three-view drawings. The MBD model’s geometry inherently defines its form. No additional dimensions or information are necessary to fulfill this function of an MBD. An MBD offers time savings right off the bat.

But taken on its own, that inherent form does not satisfy the need to define the measures and thresholds within which a component meets quality standards. Additional data is required to fully outline product development needs.

So engineers add product manufacturing information (PMI) to the MBD’s 3D model. In this way, they can correctly define the required measurements to assess the model’s conformance. They also add tolerances to those dimensions or to the model’s geometry to define acceptable manufacturing thresholds.

Organizations that are moving toward becoming model-based enterprises (MBEs) also include semantic PMI, or PMI that is readable not only by employees but by a variety of manufacturing software applications. This permits the automation of key activities like development of tool paths for manufacturing and coordinate-measuring machines (CMM), saving time and reducing potential errors.

Contrasting Approaches

When comparing and contrasting these two approaches to design documentation, companies should consider the following issues.

Documentation Burden

Today, companies develop 3D models to produce practically every view you can think of for a given drawing. Extra time and effort are required to annotate those views with details and vital PMI. That effort is partially redundant, given the dimensions needed just to create that 3D model.

When organizations transition to an MBD, engineers need only add the additional PMI used to verify conformance. The result is a dramatic decrease in documentation burdens for the engineering team. Less time and less frustration—and more easily consumed deliverables.

Documentation Interpretation

Interpreting traditional design drawings requires skill, knowledge, and expertise. Individuals who consume these design deliverables must build a 3D visual of the component in their head based on the drawing’s three standard views to complete their work. That can be cumbersome work, and, too often, it leads to downstream errors.

With an MBD, functional departments that rely on design documentation for their own tasks can view, spin, pan, and interrogate the 3D model and its PMI directly. This removes ambiguity and the potential for misinterpretation from the design documentation.

Shortcuts vs. Automation

Development schedules are tight—and they are only getting more compressed as the complexity of design requirements increases. To meet aggressive deadlines, engineers will often export the drawing and edit it in a 2D computer-aided design (CAD) application instead of updating a complex 3D model. While it may save time in the short term, it can lead to divergent definitions of the design - and problems later on in the process.

With MBD use, you can include semantic PMI. Different manufacturing software applications can then read the data to automate the creation of machining and inspection tool paths in a standard fashion at a faster pace.

Embracing MBD Initiatives

More and more organizations are looking to MBD initiatives to drive their design documentation improvement efforts. And for good reason: MBDs offer notable advantages over traditional 2D drawing-based design documentation. Though stakeholders are familiar with drawing-based approaches, these take more time and increase the risk of errors and delays in production.

MBD approaches, on the other hand, can reduce annotation burden, facilitate accurate design documentation consumption, and provide a means of automating vital manufacturing and quality processes.