Model-Based Definition: The Next Frontier for Digital Manufacturing

The manufacturing industry’s trend toward connected machines, automation software, and data analysis—often referred to as digital manufacturing—has shortened product development cycles and made manufacturing processes more efficient, thus altering the economics of the supply chain.

With digital manufacturing, a product engineer can typically upload a design to receive a quote with manufacturability analysis, often within hours. Once an order is placed it’s sent out to a network of machines on the factory floor and the manufacturing process begins. After the run of parts is complete, a manufacturer can employ a variety of automated technologies to visually scan the part and verify that it meets quality requirements.

As a product moves from design to production to shipping, connecting each of these steps is the digital thread. In addition to a more efficient exchange of data between what are typically disparate processes, the digital thread reduces the need for human intervention and potential for miscommunication. This leads to accelerated production time, improved part quality, and a leaner, more resilient supply chain.

Getting more from a 3D CAD model

As outlined by the ASME’s Digital Product Definition Data Practices, the manufacturing industry is moving towards a standardized approach to automating and digitalizing production processes. Most professional CAD software packages now support the inclusion of product manufacturing information (PMI) within the CAD file. So even more manufacturing information and instructions like critical dimensions, surface finishes, and materials can be included directly within a 3D model. This practice, of including PMI directly in the CAD file and foregoing the traditional 2D drawing, is referred to as model-based definition (MBD).

A model-based approach that follows these industry standards improves communication between the engineer and manufacturing supplier by eliminating the risk of misalignment between the CAD file and 2D drawings—a common source of confusion. MBD also helps manage revisions since the 3D model is the one source of truth. For example, if a manufacturer needs to find a specific tolerance or a designer needs to view a past iteration, there is a digital record that can be traced and referenced.

Putting MBD to the Test

This all sounds great but what does it look like in practice? To better quantify MBD’s benefits, Rockwell Collins, Geater Manufacturing, and the National Institute of Standards and Technology (NIST) partnered to compare MBD to drawing-based methods in a recent study. The two approaches were examined during annotation, production (in this case machining), and inspection of three part designs.

On average, the study found the total time to complete one design annotation, manufacture, and inspection cycle to be four times faster with MBD (60.3 hours for the drawing-based process, compared to 15.2 hours for the model-based process)! The study also determined that the drawing-based approach took 32 weeks to deliver all three parts, while the model-based approach required only 5 weeks (more than six times faster). The difference in delivery time was attributed to 12 questions that needed to be asked about the 2D drawings to clarify manufacturing specifications.

Based on this study, it’s clear MBD can have a dramatic impact on production time, but the researchers also found evidence of improved part quality. Final parts from both drawing-based and model-based processes closely conformed to the product definitions except for one defect. A through hole was added to one of the parts with a drawing-based product definition. This was due to the depth callout for the hole being omitted from the 2D drawing. Since the MBD approach used the 3D model as the source for manufacturing information, this error was avoided.

Automated digital inspection

Even better, MBD enables the streamlining of the inspection process, a common cause of delay in NPI processes. Once production is complete, the manufacturer can reference the 3D model to automate the inspection process since it already contains tolerance information—extending the digital thread past production and through inspection. For example, a structured-light or laser-based 3D scanner can generate a 360 degree analysis of a final part within minutes. With that scan, a manufacturer can directly compare the final part to the original CAD file, and generate a report that often fulfills FAI and other quality documentation requirements.

Creating an on-demand model of production

A model-based system approach to product design combined with greater automation and digitalization of manufacturing processes enables an on-demand model of production that can reduce costs and strengthen supply chains. Any changes to design can easily be integrated into existing manufacturing workflows with minimal impact on lead times.

Additionally, for products that have relatively low annual volumes or when demand is difficult to predict, adopting digital approach to manufacturing can offer greater flexibility and supply chain agility. That capability is becoming key as product life cycles are shortening, and product customization and SKU proliferation is increasing.

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