A Solid “STEP” Towards MBE: STEP 242

The STEP neutral file formats have been widely used in the manufacturing industry to exchange CAD data. For example, as we discussed in a previous article, “How Gulfstream Ensures Data Integrity for MBD,” in order to move data in and out of proprietary CAD applications, Gulfstream exports the released models to the STEP format per the ISO 10303 Application Protocol (AP) 203 standard (STEP 203) as required by the Federal Aviation Administration in the United States. In addition, in the automotive industry, the ISO 10303 AP 214 standard (STEP 214) is well adopted.

In December 2014, an updated STEP standard was released, the ISO 10303 AP 242 (STEP 242). Its full name is “Industrial automation systems and integration—Product data representation and exchange—Part 242: Application protocol: Managed model-based 3D engineering.” The 2014 version was the first edition. The second edition is planned in the future.

By the way, just in case that you are puzzled by these seemingly random standard index numbers, 203, 214 and 242, here is a nerdy way to remember all of them. Their last two decimal places are 03, 14 and 42, respectively. Coincidentally, 3 multiplied by 14 equal 42. I said coincidentally because I highly doubt the standard committee came up with the index numbers based on this calculation. Nevertheless, it works for my memory and I hope it works for you too.

Let’s drill a bit further down to the standard content. It features a more dedicated model-based definition (MBD) support, such as 3D product and manufacturing information (PMI) integrated with models. Therefore, it has generated strong interest in the industry. Enterprises that want their suppliers to read the MBD data without 2D drawings can now export STEP 242 with PMI. This way, the clients don’t have to send out the original proprietary CAD files or force the suppliers to maintain the matching CAD software to read the files. The clients will have a larger eligible vender pool from which to choose.

On the other hand, suppliers can now just fulfill the numeric control (NC) machining orders directly using the neutral STEP 242 data from customers. From the technical standard point, a machinist can now program the NC code according to the models integrated with PMI at one place. As a comparison, a typical way today is that the machinist must look back and forth between two sets of documents to conduct the NC programming. One is the model in a CAM software application. The other is the corresponding 2D drawing, either digital or hard copy, to extract the tolerances, surface finishes or other key requirements and then enter into the CAM application. Obviously, the back-and-forth interpreting of two sets of documents is not as efficient as reviewing everything at one place.

Business-wise, machine shops may not have to maintain all the proprietary CAD products to open the various client MBD data formats any more. The vender’s potential customer base can be expanded because of this common MBD data communication protocol.

One step further, STEP 242 has the potential to enable the continuous digital threads throughout the extended model-based enterprise (MBE). As highlighted in a previous article, “Top 5 Reasons to Use MBD,” the number one benefit of MBD is to further automate manufacturing with software-readable PMI. One of the driving philosophies of STEP 242 is to communicate software-readable PMI so that manufacturing applications, such as CAM or coordinate measuring machines, can program the NC code automatically, according not only to the models, but also per the 3D PMI.

It’s important to note that there can be two levels of 3D PMI in STEP 242 or other MBD data, presentational (also called human-readable or graphical) and representational (also called software-readable or semantic). Presentational PMI means that human eyes and intelligence can interpret it, but software applications hardly can. Figure 1 shows an example. Despite the rough handwriting, we can still recognize it as a diameter of 20 with plus and minus 0.05 tolerances, but this interpretation is very hard for software, at least today.

Figure 1. A presentational PMI example.

On the other hand, representational PMI can be recognized not only by human eyes, but also by software. Figure 2 shows an example of a representational hole pattern callout. Please notice the callout is automatically highlighting both instances of the pattern in the viewport. Furthermore, the callout properties are parametrically defined on its property manager on the left, such as the reference feature, callout value, tolerance type and decimal places, all of which can be extracted and reused by other software applications automatically.

Figure 2. A representational 3D hole pattern callout in SOLIDWORKS MBD 2017.

A common misunderstanding is that if a callout can highlight the associated features, then it’s representational. As noted above, the cross-highlighting only means that the association from the PMI to the reference features exists. Representational PMI also requires the underlying parametric properties that are consumable by software to automate downstream manufacturing processes.

You can find more about the recommended practices of STEP 242 PMI at the CAx implementer forum. The latest recommended practice version of PMI presentation and representation was published in 2014. A 2016 version is still under review at the time of this article. Along with other companies, Dassault Systèmes, including the CATIA and SOLIDWORKS brands, is an active member of this forum to improve the STEP translator quality.

In summary, STEP 242 and its implementation practices are evolving rapidly in the recent years. Software developers and the industry are monitoring this new MBD communication protocol closely because of its potential benefits noted above. SOLIDWORKS MBD 2017 started publishing presentational PMI attached to models as shown in Figure 3. The published STEP 242 3D PMI in eDrawings 2017 is shown in Figure 4.

Figure 3. Publish STEP 242 with 3D PMI in SOLIDWORKS MBD 2017.

Figure 4. STEP 242 presentational 3D PMI display in eDrawings 2017.

Although Figure 4 shows only presentational PMI, the communication still can be more efficient than looking back and forth between the model and separate 2D drawings. One example is NC programming in CAM as noted above. I hope that SOLIDWORKS MBD can publish representational PMI in STEP 242 in the future releases.

Lastly, it’s important to point out that although 3D PMI is a key feature of STEP 242, this STEP standard scope is much broader than 3D PMI. Figure 5 summarizes the high-level coverage, such as process planning, data management and 3D composite design. You may find more details from the ISO standard itself and the AP242.org website.

Figure 5. The high-level scope of STEP 242. (Image courtesy of AP242.org.)

In this article, we first introduced the STEP 242 standard and its potential benefits to MBD implementations. Then we clarified the differences between presentational and representational PMI. I’m glad that SOLIDWORKS MBD 2017 can now publish this format and eDrawings 2017 can read it. 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 and smart manufacturing.

Recent Articles

Related Stories

Enews Subscribe