Design for Manufacturing: How to Define Features Directly

In a Code Conference 2016 interview, Elon Musk stressed that for Tesla to hit its ambitious Model 3 delivery deadline in late 2017, “the biggest thing is to design for manufacturing.” Unlike the Model S or Model X, which are “great cars, but super hard to build,” the Model 3 was designed with manufacturability in mind.

Design for manufacturing has been a longstanding challenge, not just for Tesla, but in the engineering community overall. From a design standpoint, many manufacturing software applications have been developed to optimize products and address manufacturability issues before mass production. From the definition and communication perspective, one best practice is to go beyond basic CAD geometries to define manufacturing features directly.

CAD geometries are easy to understand. Vertices, lines, curves and faces are typical examples. Manufacturing features are generally CAD geometries or features grouped by manufacturing operations. For example, a counterbored hole may be considered as one manufacturing feature because the large hole, its flat bottom and the small coaxial hole are typically produced together to hold socket cap screws.

In other words, manufacturing features are a close depiction and therefore a direct guidance of manufacturing operations, while CAD geometries are often individual resulting elements of these operations. This is why defining manufacturing features directly is more comprehensive and accurate. It conveys the full picture and allows us to see the forest beyond the trees in order to prevent manufacturability issues.

Figure 1 lists 14 manufacturing features predefined in the SOLIDWORKS MBD library. When we select one surface, MBD will try to recognize the possible manufacturing feature sets and ask us what to define besides this surface itself. The most comprehensive one will be set as the default callout. Then, the appropriate constructing product and manufacturing information (PMI) will be provided for the selected manufacturing feature.

Figure 1. Predefined manufacturing features in the SOLIDWORKS MBD library.

Let’s walk through several models to explain better. We will use the datasets in the NIST MBE PMI Validation and Conformance Testing project, so that you can download them and try out too. For instance, in Figure 2, we can simply pick a hole edge on one of the mounting counterbore holes. Then, MBD will make three inferences behind the scene:

  1. “This edge belongs to an individual hole, so the user may want to define this hole.”
  2. “Wait a second. This hole is part of a counterbore manufacturing feature, so defining this combination may help the user get closer to the goal.”
  3. “Oh, I see. This counterbore hole is actually one of the six instances in a pattern, so this pattern is the most comprehensive representation of the manufacturing goal to mount this part to another component. Let me present this option as a default selection and ask the user to choose.”

Figure 2. A pattern of six counterbore holes is automatically called out by default.

This chain of intelligent inferences greatly saves mouse clicks and time because we don’t have to manually pick all the faces one by one to define a pattern. The combined callout will also save the screen space and alleviate crowded PMI displays. If we have to, we can still break these combined dimensions as explained in the previous article “Top SOLIDWORKS MBD Tips and Tricks: Hole Callouts.”

Of course, if we decide to call out one counterbore hole only or just a simple hole, Figure 3 shows more options on the context command bar. The cylinder and hole callouts are identical in this case, but a cylinder can represent a partial cylindrical face to specify a radius, such as the one in Figure 4.

Figure 3. Additional options of a cylinder, a hole and an individual counterbore.

Figure 4 shows a slot being recognized as one manufacturing feature. Its key callouts are provided automatically: length, width and radius. Again, we only need to pick a cylinder edge and leave the rest to the software.

Figure 4. A slot is called out as a manufacturing feature.

Similarly, if we were to cut this slot into a notch, it would be recognized by the MBD library and provide the notch width and length automatically as shown in Figure 5.

Figure 5. A notch is called out as a manufacturing feature.

While we are working on this slot, a useful setting is the Arc Condition. Sometimes, we need to tell quickly how wide a slot is between the tops of two cylindrical faces or how thin a surrounding wall is. In Figure 6, we are using the Max Arc Condition on the Leaders tab on the Dimension properties manager to call out the slot overall width, which in this case is 120 mm. We can also determine the wall thickness on the left, 55 mm, using the Min Arc Condition.

Figure 6. Arc conditions to call out the overall slot width and the wall thickness.

In addition to the above library manufacturing features, it’s often necessary to group some seemingly unrelated features together to define surface profile tolerances, surface qualities or painting instructions. Figure 7 illustrates one such example in the NIST dataset.

Figure 7. A surface profile tolerance defined to a collection of 17 features.

The entire group may not be automatically recognized as a frequent manufacturing feature, so some users assign colors to these surfaces to identify them visually. However, a more semantic (or software-readable) way is to create a collection of manually picked surfaces and define them together as shown in Figure 8. Of course, in this selection list, constructing manufacturing features such as fillets or hole patterns in the MBD library can be still recognized as one combination to reduce mouse clicks. Once this collection is built, it can be used for PMI definitions such as the profile tolerance in Figure 7. Detailed benefits on the software-readable PMI can be found in a previous article “Top 5 Reasons to Use MBD.”

Figure 8. Select features to create a collection.

To avoid the situation where we can’t see the forest for the trees, we have the ability to define manufacturing features to guide downstream more directly. We covered counterbore holes, patterns, slots, notches and manual collections in this article. To learn more about how the software 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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