What is feature-based modeling?

Features save users from having to create every little detail.

A through hole defined as a feature. Image by Shankar NVS on ResearchGate.

A through hole defined as a feature. Image by Shankar NVS on ResearchGate.

Feature-based modeling is the part of computer modeling that recognizes a combination of geometry, such as lines and arcs, as features, such as a physical feature like a hole or chamfer. Feature-based modeling is found in solid modelers for CAD, CAM and CAE.

Features can include nongeometric information as well, such as process information, like modeling operations (mirroring, for example), manufacturing operations (sheet metal bend or fold) and material operations.

Here is a list of features recognized by Inventor, a popular feature-based modeler by Autodesk:

  • Chamfer
  • Coil
  • Round
  • Decal
  • Emboss
  • Fillet
  • Flange
  • Hole
  • Rib
  • Shell
  • Thread

Feature-based modeling comes in quite handy when you are defining or modifying a part. For example, if two circles on opposite faces of a part are recognized as a through hole, the hole will stay a through hole if the thickness of the part increases and not become a blind hole. Likewise, a slot feature will elongate properly if the centers are moved apart, rather than appear disjointed if it was a collection of geometry, forcing the user to reconnect lines to arcs.

Hole feature definition. Image: Project Lead the Way.

Hole feature definition. Image: Project Lead the Way.

Creating features in a feature-based modeler allows users to quickly define parts. Much of the geometry that composes a feature will be automatically created. For example, a drilled blind hole created as a feature will ask for various parameters that define the hole (blind, through, diameter, chamfer, thread, etc.) and create all the CAD geometry needed to fully represent it. The user will not have to make the conical bottom of the drilled hole. However, threaded holes, due to their minute detail, would require so much computing resources to model and display that they are usually left to the imagination, showing only a little representative geometry.

Features can be defined with numbers, formulae or parameters. CAD programs can be feature based and parametric modelers.

Although it was introduced for mechanical design programs, feature modeling can also be used in architectural design programs. For example, a wall could be a feature, with internal detail showing structural members, drywall, and more.

Feature selection box in SOLIDWORKS.

Feature selection box in SOLIDWORKS.

Features can be user defined. Users can store features in a library for use elsewhere in the model or other models.

When a feature is added to a part, such as a fillet feature to an edge, its location and orientation are taken care of by the program and appear as though they are automatic to the user. Contrast this to the rounding of an edge by constructing a profile with an arc, extruding it to the right length, aligning it with an edge and subtracting it from the solid part.

In the modeling hierarchy, parts are at the second level of sophistication:

  • Geometry (lines, arcs, etc.)
  • Features
  • Parts (brackets, tubes, gears, etc.)
  • Assemblies (gear trains, four-bar linkages, etc.)
  • Components (cylinders, actuators, motor)
  • Systems (electrical system, cooling system)
  • Products (computer, car, etc.)
  • Environment (that the products function in)

Mathematician Samuel Geisberg, founder of PTC, was the architect behind the 1987 release of the first successful parametric-based modeling solution, Pro/ENGINEER. Dassault Systèmes was next with CATIA Version 4 Release 1.2, which added “about 100 predefined geometric features such as pads, bosses, shafts, pockets, filets, and grooves” in 1992, as mentioned in the History of CAD by David Weisberg.