Design Intent in Part Modeling Design Intent is an important concept in Parametric Solid Modeling Design. Anyone can draw some basic shapes and construct a multi part assembly however it is often at the expense of future revisions and changes. To create a robust solid model and easily editable design, some forethought must be put into the method of construction your parts.
Design intent is the act of capturing intelligence in your model by means of parametric and geometric relationships that define the fit and function of the part. Here’s a simple example:
You create a part that is 2” wide and then want to place a hole in the center of the part. There are two basic approaches. - Place the hole 1” from an edge of the part or
- Place the hole on a parametric midplane of the part
Both workflows produce the same result however they have two distinctly different design intents. The intent of the first method is to maintain 1” from the edge of the part to the hole. If the part becomes wider as a consequence of downstream design changes the hole will remain 1” from the edge. The second workflow maintains the hole in the center of the part. No matter how wide or narrow the part becomes the hole will remain in the center. Depending on your design intent either workflow is acceptable but far too often I see users following workflow A when their intent is to keep the hole centered.
Another example of design intent is the use of geometric constraints in sketches. Let’s look briefly at an equilateral triangle. As you may know an equilateral triangle is defined by having three sides of equal length. There are three basic ways to create this shape in Inventor.
In example A, we use 3 dimensions to create the shape. In example B, we use parametric relationships to create the shape, however it still requires 3 dimensions. Finally, in example C, we use only one dimension and two equal constraints.
In example A, there is no relationship between the three sides. If one dimension changes, the others do not update. The intent to keep all sides equal is lost. Examples B & C both express design intent, however example C is clearly more elegant as there is only one dimension that is editable. In example B an unsuspecting users might edit d22 or d23 and break the design intent. In general it is better to use geometric constraints than dimensions. If two lines are meant to be parallel use the parallel constraint. If a line is meant to be equal in length to another then make them equal. The use of geometric constraints makes the sketch less cluttered while still capturing the desired design intent.
Formulas are also a very powerful way of expressing design intent. Take for example the following part. Notice the use of equations in the positioning on the first hole. When designing this part I know that I always want to maintain a 5 x 3 pattern of holes, equally spaced, regardless of the size of the base feature. By referring to the width and length of the part (d16 and d17) I am able to create a first hole that will be positioned such that the 5 x 3 pattern will fill the base feature.
One of the simplest was to express design intent is through the use of shared sketches. Many users create a simple sketch, create the feature from that sketch, create a second new sketch, then a new feature etc… While there is nothing wrong with this method, it makes for a cluttered browser as well as providing a lack of design intent. A better method is to use shared sketches.
To use shared sketches, place all of the geometric information for a part into a single sketch. Once you create the base feature you simply right click on the sketch and select “Share Sketch”. Now that same sketch can be used to create additional features. In the figure below, the part was created from one single sketch.
This workflow not only helps you to illustrate your design intent but also allows you to edit a single sketch to make any design changes. You do not have to find the sketch associated with a particular feature. Simple edit the base sketch and all of the resulting features will update. A last example of design intent illustrates how you can capture important information that is not just size or position. When creating features and work geometry (planes, axes, points) do not accept the default names of the features (Extrusion1, WorkPlane3 etc..) Rename the nodes of the browser to something meaningful. Not only does this help other users understand how you created the model, it helps you to identify features quickly in the browser. (Have you ever hovered over each feature in the browser looking to see when it highlighted in the model?)
By expressing design intent in your part models you not only create more robust models that withstand downstream changes to the design, but you also give others who might use these models an insight into your thinking process. You express, through dimensions, formulas and geometric constraints, what is important and what “rules” must be followed. Encourage everyone in your design team to use these design intent guidelines and I’m certain your projects will flow a bit more smoothly. | 
