2. Parametric Design and Associative Surfaces.

This tutorial shows how to create a surface whose shape varies when parameters are modified. The surface is generated by applying the LOFT command to a group of parametric profiles. These profiles will be created by copying a profile to which the corresponding geometric and dimensional constraints have been previously associated. The surface created will be associative, this meaning that it will be modified when the parameters of each of the profiles are modified. To be certain that the surface created is associative we must verify that the value of the SURFACEASSOCIATIVITY system variable is equal to 1 (default value).

Creating the Profile.

A 2D Polyline is used as the profile that will be drawn in the frontal plane (XZ), as our objective is to model a laminar structure. To do so, it will be necessary to rotate the UCS 90 about the X axis. We will also include a vertical line which will be used as the profile's axis of symmetry. The following video shows the process in detail. Note that we do not care about the accuracy of initial drawing, which will be adjusted when the geometric constraints are applied. Once its shape has been adjusted, three dimensional constraints are added: Radius, Angle and Length.

Copying the Profile.

Once the profile is finished four evenly spaced copies will be made. When the profiles are copied the constraints are kept, and the dimensional constraint names are modified so they are not duplicated. An exception is the FIX constraint, that defines an invariable position in space and that, of course, will not be the same for the copied object. In this case that constraint must be reapplied to each of the copies. To add the new FIX constraint the UCS origin must be moved so it lies in the same plane as the profile as shown in the following video.

The Associative Surface.

Once the profiles are copied the surface is created by applying the LOFT command. This surface can undergo infinite variations by changing the parameters that control the radius of the upper arc, the lateral taper angle and the height for each of the profiles.