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Common Mistakes in the MBD Implementation Process and How to Avoid Them

CAD Concept Design

Common Mistakes in the MBD Implementation Process and How to Avoid Them

A previous article shared two lessons learned in the model-based definition (MBD) cultural shift:

  1. Don’t take 2D drawings as the master documents over 3D models anymore.
  2. Don’t treat MBD the same as you would paperless processes.

Now, let’s review two typical process shift mistakes made in MBD implementations. One is to try to take on too much at once. For example, let’s look at the experience of Paul Huang, model-based engineering program leader at the U.S. Army Research Laboratory. In 2009, the Red River Army Depot started an MBD project, but bit off more than it could chew. Its first project, the Bradley cross-drive transmission, comprised more than 2,000 parts. Huang later commented that it perhaps hadn’t been a good idea due to the lack of repetition, which would have helped team members learn the process.

The Red River Army Depot was not alone. Many other manufacturers advised against upfront complicated MBD projects too because they could easily frustrate and even deter participation. I’ve personally known several MBD enthusiasts dropping out of the implementation teams due to the initial uphill challenges.


Figure 1. Bradley cross-drive transmission. (Image courtesy of Paul Huang.)

Instead, MBD proponents such as Huang and Prashant Kulkarni of GE Power and Water advocate for a progressive rollout strategy to help with adoption. The strategy is designed to help users gain familiarity with tools and accumulate best practices through repetitive use first, followed by larger and trickier projects.



Figure 2. Three-step rollout strategy at GE Power and Water. (Image courtesy of Prashant Kulkarni.)

Another common mistake is to skip critical-to-function 3D product and manufacturing information (PMI) in the hope that data consumers can query models as needed. This is one of main reasons why MBD is resisted by downstream teams, especially the supply chain. Some suppliers even dismissed the obsession with MBD and dropping 2D drawings as pure laziness” because their clients only provided a 3D native CAD model or 3D PDF with no 3D dimensions, tolerances or 2D drawings. Clients asked them to measure the model when dimensions were needed.

However, in reality, shop floors still need readily available critical-to-function PMI to machine and inspect. Consequently, many suppliers end up having to recreate 2D drawings according to the models in PDF or CAD to fulfill contracts. Therefore, the supply chain sees no benefits while still getting burned: “Maybe our clients saved some time because they skipped 2D drawings and 3D PMI, but the workload was simply shifted to us.”

Worse still, if the self-generated 2D drawings by suppliers for various manufacturing activities mismatcha client’s design intention and compromise the quality, the finger-pointing begins: “You didn’t measure the model!” “You didn’t markup dimensions and tolerances for machining!”Going to court wouldn’t be a surprise.

To avoid all these messy issues, designers and engineers should try to call out at least the key PMI in models explicitly. Here are the major reasons:

  1. Designer and engineers know best the product use cases, design intentions, important features and technical requirements. Therefore,they should be the authority to convey such critical information in explicit PMI. If these important callouts are absent and left free to other’s interpretations, then misunderstandings and even conflicts are prone to happen. Let’s remember. It’s in the production team or suppliers’ best interests to interpret and simplify requirements in favor of manufacturing, but not necessarily the ultimate product quality.
  2. Calling out PMI at the design phase is an opportunity not only to communicate, but also to review, verify and improve the design and manufacturability. Skipping this step means missing this opportunity.
  3. The magnitude of PMI, even that which is merely critical, could be convoluted. If downstream data consumers always have to measure models manually in order to retrieve them on an ad-hoc basis, then it not only takes more time and effort, but also may easily result in oversights because the key information is hidden in models. The consequences include jeopardized quality, a prolonged cycle and increased costs. For example, suppliers may bump up their quotes to compensate the operational overhead and risks. On the other hand, explicit key callouts not only ease the reading of each and every requirement, but also present a complete check list as a visual reminder.
  4. Model geometries provide dimensions, but not necessarily tolerances. The lack of tolerances obviously is prone to misreading. Factory floors may follow undocumented conventions to machine and inspect, but what if some exceptionally tight tolerance requirements are missed? The worst case is that even the conventions are unknown, leaving the shop floor clueless. Some companies may define both dimensions and tolerances in sketches or features. If so, we might as well just expose these callouts explicitly in 3D to avoid recreations and repeated manual lookups.
  5. Downstream data consumers may not be able to measure adequately and accurately using the tools in Adobe Reader or other viewers. Table 1 compares the wrong and right usages of the Adobe Reader measuring tool.









Table 1. Wrong and right results using Adobe Reader.

By the way, to get the correct result, two buttons must be pressed in advance in

image013Figure 3. Two important settings in Adobe Reader.

Let’s remember, this is just a simple screw. Now imagine a complicated assembly with thousands of parts—such measuring errors are almost inevitable. The point of this example is not to discourage the use of measurement tools but to illustrate that both engineering and manufacturing, both clients and suppliers, have to be extremely careful and well prepared when obtaining critical information on the fly, because the stakes are high and the techniques are tricky. So to avoid the unnecessary complexities, at least at the beginning of an MBD journey, we would be better off annotating explicitly.

From the change management perspective, we all know change is hard. Therefore, we would be better off to over-communicate rather than under-communicate during an MBD transition. The ideal message to all involved should be,“MBD doesn’t take any important information away from me. Rather, it adds another dimension of clarity and functions. My job will actually be easier.”

It’s worth noting that when model-based workflows can be fully integrated and automated in the future, explicit callouts may not be so important anymore, because software and machines can seamlessly leverage implicit digital model data in machining, inspection and other procedures. However, in today’s reality, most infrastructure and manufacturers are not there yet.

We reviewed two lessons for the process of implementing MBD: Don’t take too big a bite at first and don’t skip calling out critical PMI. You’re welcome to discuss in the comment area below. To learn more about how SOLIDWORKS MBD can help you with your MBD implementations, please visit its product page.

About the Author

Oboe Wu is a SOLIDWORKS MBD product manager with 20 years of experience in engineering and software. He is an advocate of model-based enterprise (MBE) and smart manufacturing.  


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