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Reduce Cost, Increase Speed with Model-Based Definition

Bruce Morey
By Bruce Morey Senior Technical Editor, SME Media

Moving to all-digital descriptions of parts is opening opportunities for small and medium sized business—not just the big guys

In keeping with its mission in standards, the National Institute of Standards and Technology offers test models for software vendors and manufacturers to test their ability to import STEP models.

Manufacturers need to create more production setups as batch sizes get smaller. Skilled labor continues to be hard to hire and keep. Higher levels of automation are needed, not just in material handling but also in fabricating, machining, assembly, and inspection. These tasks start with a data package describing the part, usually containing a 3D CAD model. In many cases these models are accompanied with only a sheaf of paper that describes all of the product manufacturing information (PMI). It is difficult to automate a process from this traditional way of specifying a product, with a mix of CAD and paper. It is time consuming, requires (scarce) skilled technical expertise, and is error prone.

Enter model-based definition (MBD), the use of which is growing.

“Adopting a model-based enterprise will, in the long run, make your company much more competitive,” said Allison Barnard Feeney, systems engineering group leader at the National Institute of Standards and Technology (NIST), Gaithersburg, Md. For 30 years, her mission has been helping the nation’s manufacturing base create and adopt MBD, the digital twin, and the digital thread.

MBD is a 21st century improvement on the 20th century invention of CAD models. In a single digital file, MBD adds to the CAD geometry description other product details, such as GD&T, material descriptions, finish requirements, and even paint specifications, all of which are PMI.

Why is MBD important? It contains all the information needed to manufacture and inspect a product without resorting to ancillary paper records that can be wrong and are open to human interpretation. With an MBD model comes the promise of automating inspection programs on CMMs or toolpaths on CNC machines. It should also reduce the workload on skilled labor and speed production setups. It is also easy to transport, easy to store in a database and easy to find later.

The time savings and confidence in the results can be substantial, according to Oboe Wu, SOLIDWORKS product manager for Dassault Systèmes, Velizy, France. He pointed to a case study that Dassault has on its website when Veco B.V. in the Netherlands implemented SOLIDWORKS MBD, the provider’s own application for associating MBD information with CAD models. According to the case study, the time to produce components was cut in half while interpretation errors decreased. This improvement was attributed to eliminating 2D drawings and the time required to detail, check, update, and manage them. Time needed to publish the 3D models and annotations for future use, as 3D PDFs created with SOLIDWORKS MBD, dropped from one day to 10 minutes. “The main advantages are the three I’s: Intuitive, Integrated and Intelligent,” said Wu.

3D PDF is the frequently used PDF format embedded with 3D content such as 3D models, attached annotations, views and interactive tables. It’s viewable in the widely adopted Adobe PDF Reader.

While there are opportunities for smaller businesses, he noted that since most part designs start with OEMs, “the big guys are driving the behaviors of Tier One, Tier Two and Tier Three suppliers that are smaller businesses,” said Wu. Especially in the aerospace and automotive supply chains, it may become necessary for companies to use MBD.

Standard Formats, Competitive Companies

MBD is also a cornerstone of creating a functioning digital thread. However, most CAD suppliers provide MBD in a proprietary format. That is a problem. The goal is to have a single source of truth for downstream operations in making a part, but there is no guarantee such formats can be read in another program.

There are workarounds. Many programs, like Verisurf metrology software from Verisurf Software Inc., Anaheim, Calif., have the ability to read in multiple CAD formats and attached MBD information as well. According to David Olson, director of sales and marketing, Verisurf can import files created in Dassault Systèmes CATIA, Siemens NX, or PTC Creo—what might be called the Big Three of CAD. “Our product allows people to either import it completely or take the parts of it that are in the drawing and apply it to the 3D model,” he said.

Additionally, the variety of CAD providers, and formats, is large—well beyond the Big Three. A universal format would be ideal. Fortunately, one exists. The ISO STEP format for CAD, with its accompanying AP 242 extension, includes this vital MBD. Also, fortunately, most CAD providers also export this format. Verisurf, like others, imports STEP with AP 242. “If there is just one thing I would like to say to your readers, all manufacturers from the biggest OEM to the smallest tier, it would be push your CAD vendor to output STEP AP 242 as best as possible for downstream manufacturing,” said Olson.

The opportunity for efficiencies is open to medium and small enterprises as well. “MBD doesn’t just automate the big guys; it can help automate the small shop as well,” he stated. “While MBD helps OEMs eliminate issues with parts through tolerance analysis and simulation of assemblies, the benefit to the smaller, downstream shops is in selecting CNC machine tooling and a programming strategy.”

Verisurf supports STEP AP 242 model-based definition with associative GD&T, as shown in this NIST test model, which automates inspection planning and reporting while reducing transcription errors.

It can help decide in using a VMC versus an HMC, what kind of finishing pass is used to meet surface specifications, and help choose the inspection method needed, say, a CMM versus 3D scanning. “The CAM providers are [also] working on this stuff. They’re staying up all night trying to figure out what logic they can extract from the CAD model with PMI and GD&T and automate the toolpath process. [That includes] machine choice, tool selection, machining strategy, and generating the program,” said Olson. Industry players are also working on fabricating methods as well, such as bending, punching, and welding, as well as composite parts and assemblies.

Development on a universal model continues. “My group at NIST has been working for years to build a standard digital thread,” said Feeney. “The STEP product models are now being [even more] enriched with PMI.” She agreed that this is vital to the health of all industry, not just the big companies. “This makes [smaller companies] more competitive. The larger companies can afford to buy multiple CAD systems, but standards like STEP and AP 242 level the playing field,” she said. It gives smaller companies access to all the advantages of MBD.

Adoption Strategies

For any new technology, there is a path to acceptance, and distinct stages. The first stage is understanding there is an advantage and seeing the benefits. Subsequent stages build on one another as a company matures in the use of a technology. “What we see is that customers generally fall into one of four different maturity levels towards adopting model-based enterprise,” said Dave Wingrave, model-based definition product manager for Siemens Digital Industries Software, Plano, Texas.

The first stage, as he described it, is drawing-centric, where a company is focused on the drawing only and that 2D representation is the master, the source of truth. The second stage is a transition to model-centric—people are still using the drawing as a source of truth but leveraging the 3D CAD model with some associativity of features. “The third stage is [full] model-based definition, and the fourth stage is model-based enterprise,” he said. What’s the difference between the last two stages? “Model-based definition enables the complete digital definition of a product within a 3D model and focuses on making the model the single source of truth. Model-based enterprise is the process of reusing model-based definition by downstream consumers across an enterprise.”

NX PMI Advisor is a fully integrated PMI validation solution that provides notification verifying whether PMI is compliant with industry and company standards. NX PMI Advisor removes the dependency on GD&T experts and produces higher quality parts in less time, according to the developer.

Wingrave also noted that the third stage, MBD, has been adopted more broadly with big companies in aerospace leading the way (think Boeing.) Many smaller companies are just starting to get on board with MBD, with many still following more traditional ways. But the real goal should be enterprise-wide adoption, which leads to even shorter design cycles and efficiencies. It can do other things as well, such as more easily incorporate CAE simulations for design and validation.

What are some of the challenges to companies adopting MBE? “I think culture is a big one. Just getting people to not rely on drawings and to be able to think in different ways about how you model your product in CAD,” said Feeney from NIST. She noted that since the MBD model now makes the CAD model semantically rich with information, it is no longer just an objective picture. “It requires a totally different mindset,” she said.

Existing company policies is another issue. “A manufacturer could say that our policy is to take a drawing and re-enter all of that information into our manufacturing system because we don’t want to risk ingesting somebody else’s file and having it crash our system,” she explained. Changing policies is a bureaucratic problem, not a technical one.

Siemens conducted a study and found that many companies that were adopting MBD did indeed tend to replicate drawing-based workflows in the context of 3D. “That was impacting their implementation and success,” said Wingrave. The Siemens study also found there is a desire for more tools that can capture and validate business intelligence used to drive manufacturing processes. This can impact MBE adoption. “There are a significant number of processes that could benefit from the consumption of PMI,” he said.

New Tools for Validating Correctness

New tools may be needed. MBE is continuing to evolve technically. In December, Siemens will release a new set of tools called NX Model Based Definition for its high-end NX CAD system. The tool set is dedicated to solving new problems in integrating manufacturing processes. “The new tools in the release include rapid definition and authoring of PMI with an emphasis on capturing company-specific business logic,” said Wingrave. “There’s also what we’re calling a PMI advisor, which is a solution that validates PMI as it is being created and provides immediate feedback to the user as well as guidance on corrective solutions.”

The NIST Test model #2 in STEP AP 242 format imported into Geomagic Control X, showing deviations against tolerances in a color map.

Validating an MBD model is crucial to its widespread acceptance, an issue discussed with all interviewed for this article. If attached GD&T is inconsistent, for example, how could consistent metrology programs be created? If material is not specified, how to choose the right cutting tool?

“Our solution also allows users to access pre-loaded rules and define their own, especially to meet business requirements,” said Wingrave. “Manufacturing can contribute rules to ensure effective consumption of PMI downstream.” While the coding may be complex, Siemens is providing what it calls an easy interface for engineers to provide rules and logic that operate on the PMI data. Simple pull-down menus and block diagrams make it accessible. Over-constrained models or inconsistent datums are checked and weeded out, ensuring an MBD model all can trust, according to Siemens.

Future Manufacturing, 3D Printing

As manufacturing evolves, so must the standards that control the flow of information. For example, additive manufacturing has been evolving while MBD has been adopted.

“Today, you can get a high quality STEP AP 242 import off the shelf,” said Scott Green, director of product management for 3D Systems Inc., Rock Hill, S.C. It supplies not only software for inspection and metrology, but also for 3D printing. “CAD systems continue to evolve and there are a number of interoperability software companies that sell their wares to import files like STEP AP 242. In the past three years, things have changed and it’s possible for a software company to read that format and not require users to do a ton of work to fix it or make it usable, unlike in the past.”
It used to be more true that neutral files like STEP or IGES needed some work once imported—they were never quite perfect. “If it’s hard to decode PMI or other parts of MBD on an imported part in your software environment, it’s hard to make MBD work in your manufacturing process, as you intended,” said Green.

He also noted that as the CAD systems used to author both the designs and the MBD change, more context is being added in more comprehensive formats like the Quality Information Framework (QIF). “The consortiums around, for example, QIF can contain even more metadata and more information than the standard STEP file.” It appears to Green that the world is speeding past the neutral formats and MBD definition and moving towards containing even more context.

“Additive manufacturing is helping that because you need to encode a lot of information,” he said. “Additive manufacturing is not just a push-button process. There is much context that can be added around the model, both on the functional side and the manufacturing side. You could have several layers of MBD that are actually pretty critical when someone is designing a part and especially if they have no idea what exact machine it’s going to be printed on or with what other parts, and it’s well known that even several similar production additive machines could potentially behave somewhat differently.”

This emerging standard for additive-specific MBD is occurring as additive manufacturing, especially metal AM, is also growing. Subtractive machining is a well-established industry, and developing a coherent MBD flow around it is a question of matching information needs to processes. In additive, the processes themselves are changing, getting faster, more flexible in their build-style definitions, adding more materials, and increasing build envelopes. “There are a lot more 3D printing suppliers these days than there were three years ago, especially of production metal machines,” said Green. Downstream manufacturers receiving a part description with all of its context will potentially still need to do a number of tuning loops or complex build simulation. Supports will need to be designed and redesigned. Post-process machining needs to be specified. Inspection routines that account for the complexity of, say, a lattice structure or a completely non-prismatic part need to be developed and standardized so meaningful information can be derived from them. “That’s what we really need to push for in additive,” he said.

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