Tips for Successful Design Reuse




Everybody wants to get to market faster and keep costs down. That’s why it makes sense to reuse as much of your existing design data as possible. When you can update CAD files from a current product, previous product, or just common components, your work gets out the door faster, and that can lead to significant savings.

Unfortunately, engineers, designers, and managers often make decisions that prevent data from being leveraged. So it’s not easy to simply make a few changes to last year’s model, even when the part or assembly design seems to be exactly what you need.

Nobody wants to build the model again from scratch. And you don’t have to if you follow these best practices today. You’ll be glad you did:

Follow Design Intent

If people create models with the wrong goals, such as fastest time, or fewest number of features, they will create models that aren’t robust, flexible, or take advantage of parametric CAD modeling. When models lack those qualities, they will be sloppy and difficult, if not impossible, to reuse.

Design Intent guides us to make our modeling choices based on potential changes to our products. Since the initial design phase is only a small portion of the lifecycle of a product, we want to make choices based on how we expect our requirements and models to change in the future. Choices based on Design Intent should be extrapolated to the next generations of our products, not just the current one.

 

How we build Design Intent into Sketches, Parts, and Assemblies

As an end user, I completely understand the impulse to cut corners in order to meet a schedule; I’m sad to admit I’ve done it myself. I’ve made direct External References between components, when I really should have created a Skeleton and driven the parts from it. I have driven dimensions with manually entered values, when I should have figured out the correct Relations so they would update properly with changes to parent features. I’ve buried features and built features on top of features when I should have edited the definition of the original feature.

Every time I cut a corner, I was making a decision to take on technical debt. I would suffer through regeneration failures even with simple changes to the models. I would see Circular References appear and wait through longer regeneration cycles. I knew at some point the messy references would become too unwieldy and I’d have to fix the model.

Here’s what you have to remember about technical debt: it accrues interest and at some point you have to pay it off. The longer you wait, the harder it becomes. One of the most expensive long-term penalties of this technical debt is not being able to reuse your models for new products.

It always feels like there’s never enough time to do it right, but somehow there’s always enough time to do it over. Save yourself time and effort in the long run, both in your current product and future ones, and build your Design Intent into the model correctly the first time.

Minimize External References

Top Down Design is an extremely powerful assembly design methodology. As a matter of fact, it’s the most effective method of building Design Intent into products, compared with other techniques such as Bottom-Up, Middle-Out, and Outside-In. However, Top Down Design depends heavily on establishing interrelationships from Skeletons and Notebooks to target components. External References to Skeleton geometry results in significant challenges to design reuse, because we can’t reuse data if we can’t change it.

The weight that External References bring to CAD data management can be even more problematic. In order to regenerate and update the model properly, the source models for its External References must be in session as well. Sometimes this means having an entire other assembly in session when you want to work on one part.

You can prevent this by following the Golden Rule of External References: Design with External References only when they are absolutely necessary.

  • Make sure that your Design Intent requires the External Reference, and that you’re creating it properly.
  • Use Update Control with Data Sharing features to break dependencies to other objects when they should no longer change when the parent changes.

Designing with External References provides a high level of control in assembly modeling, but if you choose to design with them, you’re limiting the capability of those models to be reused later.

Complement Parametric Modeling with Direct Modeling Techniques

There are generally two situations in which a model cannot be modified in order to be reused:

  • The model does not contain native parametric geometry. It could have been imported from some vendor-neutral file format such as STEP or IGES, or it could have been created in another CAD package.
  • The model was created natively, but contains too many features or is too complicated to modify. It has the wrong dimensions, or simple changes result in a cascade of regeneration failures.

In the past, you might have needed to recreate the model from scratch, or add and subtract geometry on top of the original model.

However, in tools like Creo, you can blend parametric modeling with direct modeling. In this approach, you make changes directly to model geometry, without having to consider the model’s history or Design Intent. This paradigm is especially useful in these situations:

  • At the beginning of the design phase, you often want to generate concepts quickly, not caring about exact dimensions, exact shapes, or parent-child relationships.
  • Late in the design phase, when you want to modify the geometry, either without knowing the history of the part, or in ways that conflict with the original Design Intent.

Early in the design phase, you can use direct modeling to create and iterate concepts. Late in the design phase, direct modeling allows you to select shapes (like bosses, cuts, rounds, chamfers, and surfaces) and then move, offset, modify, or remove them. Direct modeling can save you hours of effort when traditional modifications would be too cumbersome or impossible.

 

Using Pattern Recognition in a direct modeling tool, like Creo Flexible Modeling, to change the number of blades in an imported part.

By using a hybrid of parametric and direct modeling techniques, you get the best of both worlds.

 [Update: Now there are MORE Tips for Successful Design Reuse! Check out part 2 in this series here.]

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