3 Strategies for Robust Modeling in Creo

ParametricEvan Winter

IntroductionEven with 3D modeling as popular as it is in professional circles as well as private users and hobbyists, there still seems to be a tendency to take shortcuts at the beginning of a design at the expense of time spent during rework. I see this regularly when working with customers, where deadlines or lack of training cause reduction in model quality. The unfortunate downside is that the time saved upfront is eventually spent later anyway in one of two primary ways;

A general inability for others to interrogate and rework models due to unclear design intent.

Getting trapped in a “modification loop” - The design changes, failures occur, failures are fixed by making other changes, more failures then occur.

Creo Parametric includes lots of functionalities that help make models more robust and better respondent to modifications.

Strategy #1: Build Smart Features

Use Intent References and Smart Chains/surfaces

Features that are built directly on other geometry such as Rounds, Chamfers and Draft are specifically relevant here. Since these features rely on more than one direct reference, the chances that failures occur are significantly higher because only one or more of those edges/surfaces needs to change (e.g. When a cylindrical feature becomes a hexagon). Intent Surface and Intent Edge selections change the rules of the selection by removing the dependency to individual edges or surfaces. Other selection methods include Surface Loops, Tangent chains, and boundary loops for edges. Surface selections include Seed and Boundary as well as Loop Surfaces. Any of these should be explored as alternatives to explicit selection of multiple edges/surfaces in order to ensure features that won’t fail.

Publish Geometry before Using Copy Geometry

Copy Geometry features are a great way to share information between components, but a lesser known supplement to Copy Geom and External Copy Geom features is Published Geometry. Publishing geometry is done at the “source” part or assembly level and creates a feature that collects the surfaces, edges and datums that are to be shared later using CG and ECG features in the “destination” component. PG features allow one user to decide what geometry is shared to other components and simplify the selection process during downstream CG/ECG feature creation. (This is why Creo limits CG reference selection to PG features by default). Another major benefit of publishing geometry is that the feature becomes a “container” that can have references added to it later in the source component, and any downstream CG features update automatically with the new selections. This is particularly beneficial when the same geometry is to be shared to multiple downstream components, and in concurrent engineering environments where the source geometry is controlled by someone other than the component designers.

Strategy #1: Build Smart Features (Cont.) Create Component Interfaces

Assembling library components can (and likely should) involve using the same references and constraint types each and every time. So why not build these components with instructions on how they should be assembled? Interfaces do require modification of the library component, but they also save valuable time during assembly and they can provide consistent results even with less experienced users handling the mouse.

Use Geometry Patterns

Users of pre-Creo releases of Pro/Engineer may be familiar with the “Turbo Pattern” method, in which complex geometry was captured in a local Copy Geometry feature, which was then patterned and solidified. Creo Parametric incorporated this method into a feature called Geometry Pattern, which is exponentially faster to regenerate than a standard feature pattern. This is because the geometry is much less “heavy” than the parameters and rules that created it. The benefits are most significant with complex source geometry such as bosses with secondary features like ribs and rounds attached, so a Geometry Pattern of a Hole feature won’t seem much different than a standard Pattern. So far the only limitation I have found with this feature is the inability to Reference Pattern to it, but again it won’t provide much benefit for simple holes anyway, so stick with a standard Pattern for fastener holes.

Strategy #2: Identify features Name Features

Whenever you create features, you are adding a generic title to a long list of other generic titles. Eventually your model tree becomes a mess of Extrude, Revolve and datum features, and it becomes a game of “memory” to make modifications. This can apply to models you made yourself just weeks or months ago. Instead, be sure to incorporate a simple RMB > Rename after each feature you create and give them names like “Base_Feature”, “Main_Shaft” and “Mounting_Hole”. You will thank yourself later.

Use Annotations

Another way to identify features is to use Annotations. This doesn’t involve adding a note with a leader to each feature you create, just simply adding an empty annotation feature to the Model Tree. Clicking the Annotation feature then selecting OK will add the annotation to the tree, which can be dragged to a position and renamed to identify the function of a feature or group of features.

Use Groups

Creating groups is a great way to build better models for several reasons. They clean up the model tree, they can organize features by function or references used, and they promote placing features such as rounds together in a section of the model tree that makes sense (Grouped features must be sequential in the tree).

Strategy #3: ModularizeMany believe that it’s best to create models with the fewest number of features possible, and I have even heard this touted as a best-practice at a few companies. The downside with this approach is that each of these features tend to get overly complex, as they attempt to describe too many of the design aspects of the models. The result is a feature that is difficult to modify, causes unpredictable model behavior, and with unclear design intent. A better approach is to separate features by their function and allow the Model Tree to describe the progression of the design. This results in more features that are individually easer to interrogate and modify.

Keep sketches simple

It’s best to keep sketch features as simple as possible, shoot for 10-15 entities at most to keep your sketches from becoming unruly and difficult to modify. Also, use the same frugality with your sketch references. The more features you reference in a sketch, the more likely you will experience model failures down the line when something changes.

Externalize Rounds and Chamfers

Although there are Chamfer and Fillet features in Sketcher mode, it’s worth evaluating if that geometry would be better defined as a Chamfer or Round feature outside the sketch. In addition to adding unnecessary complexity to sketches, this geometry cannot be easily Suppressed or Excluded when performing FEA preparation or other simplification actions. Unless the radius is critical to the design of the part, it’s best to create them as separate features.