If you’re an engineer or designer, you’ve probably already heard about model-based definition (MBD), the practice of adding non-geometric engineering information to a 3D model. (Traditionally, that data is added to a 2D drawing.)
Intuitively, it makes sense to keep everything in one place. But are the benefits worth the effort of changing the way an enterprise has been doing things for a very long time? Perhaps decades?
Curtis Brown, a principal engineer at a multinational company, seems to think so. He’s helping his team create trusted product models that others can confidently reuse throughout the enterprise.
He says companies make the switch for better products (among other reasons). “Quality improvements can be achieved through the use of smart computer-readable MBD data and formats and the automation of the related processes.”
How exactly? It involves semantic tolerancing …. but we're getting ahead of ourselves. Read Madhavi Ramesh's recent conversation about quality, MBD, and the future of product design with a man who’s well on the road to creating a model-based enterprise:
Madhavi: How do you define Model Based Definition (MBD)?
Brown: I define MBD as the digital information needed to fully describe the geometry (for example, 3D model) and all associated data elements required for defining the product. This includes:
Simply put, MBD is the 3D annotated model and its associated data elements that fully define the product in a manner that can be communicated and used effectively by all downstream customers without a 2D drawing graphic sheet.
Madhavi: How do you define Model Based Enterprise (MBE)?
Brown: MBE is an organization that successfully uses MBD. Put another way, MBE is a fully integrated and collaborative environment founded on 3D MBD data that’s validated, authorized and shared across the enterprise to enable the realization of products from concept through sustainment.
Madhavi: Why do companies implement MBD?
Brown: You always hear about “faster, better, and cheaper” with MBD. This means speeding up the product realization process with fewer resources. Also, another critical driver for MBD is the improvement in product quality. Quality improvements can be achieved through the use of smart computer-readable MBD data and formats and the automation of the related processes. And, this touches on the topic—associative and semantic tolerancing.
Associative tolerancing is graphical representation of annotations that are associated to geometry/faces or whatever other feature you find in the CAD model.
Setting up tolerance values
Semantic tolerancing is more about the meaning and behavior of these graphically represented annotations. Some people think that we are already doing semantic tolerancing, but we are not. At the moment, we are doing associative tolerancing, at best. And, that means annotations are associated to a face. However, I’m confident that the next major step in re-using MBD data will move us toward improving product quality through the use of semantic tolerancing.
Madhavi: Who needs PMI (within the extended organization)? And, how do they use it?
Brown:PMI is non-geometric attributes, such as dimensions, tolerances, datums, etc. that are required to manufacture the product. In a drawing-centric organization, you find this information on the 2D drawing. However, in an MBE, PMI must be associated to 3D CAD model. Further, the 3D CAD model should include product characteristic designators, called PMII (Product Manufacturing Inspection Information), which is just another type of PMI.
PMII is critical for the quality and inspection processes. At present, PMII is created on the inspection floor. As part of the inspection planning process, all of the critical characteristics are identified and then balloons are drawn on the drawing. Imagine the use case where the PMII information could be set up early in the planning stage or at the MBD stage. This information drives downstream processes and allows for closed loop quality feedback to be provided earlier in the product development process.
Annotated 3D model
Quality lives and dies by the PMI. We all want the PMI to be smart as it can be. MBD data that includes product characteristics and designations helps uniquely identify and unambiguously verify the product.
Madhavi: What are the advantages of using semantic tolerancing?
Brown: We want the PMI to be as smart as it can be so downstream organizations can take full advantage of the MBD data.
Let’s say a certain dimension happens to be on a 2D static drawing. That dimension cannot be directly sent over to your CMM (coordinate-measuring machine) program or the inspection software. This means that critical characteristics information, such as different tolerances, metrology features, etc. need to be re-created by downstream users. This results in about 80% of the errors introduced, which are due to inaccurate or incorrect information.
The future with MBD data is to have all tolerances and annotations associated with that feature sent to the execution environment automatically. With semantic tolerancing, the verification process could be automated, ensuring tolerances are complete and un-ambiguous. This means downstream users don’t discover issues later in the process, which results in product development delays.
Madhavi: Are there any frameworks and standards related to semantic tolerancing?
Brown:One standard is the STEP AP242 format that has been around for some time. There’s also the ANSI standard, QIF (Quality Information Framework). One aspect of QIF covers semantic characteristics of PMI and the association to features of interest in the 3D Model. QIF is a suite of XML schemas consisting of a library of reusable components and various application schemas, such as quality measurement plans and quality measurement results.
MBD is quickly becoming the preferred approach to design. Engineers are discovering the benefits of MBD outweigh any challenges. Plus, hurdles to creating a single source authority model for every stage of product development are falling away as more teams implement an MBD approach.
To learn more about model-based definition, check out the free eBook from PTC. You’ll find out more about the limits of 2D drawings, how MBD simplifies complexity, and where to get started. Download your copy today.