What Is Additive Pipe in FreeCAD Part Design

The Additive Pipe tool is a modeling feature in FreeCAD's Part Design workbench used to create complex 3D geometry by sweeping a closed 2D profile along a specified path. This article explains the fundamentals of the Additive Pipe feature, its core geometric requirements, its primary configuration settings, and how to execute the operation correctly within your parametric modeling workflow.

Understanding the Additive Pipe Feature

In parametric 3D modeling, an Additive Pipe performs a "sweep" operation. It takes a cross-sectional shape and extrudes it along a trajectory, adding solid material to an active Part Design Body. Unlike a simple Pad feature, which only extrudes straight along a normal vector, an Additive Pipe allows geometry to curve, twist, and follow intricate multi-segment lines or curves in 3D space. It can be used to generate the initial base feature of a body or to fuse additional geometry onto an existing solid.

Core Requirements

To successfully generate an Additive Pipe, FreeCAD requires two distinct geometric elements within the same active Body:

  1. The Profile: A closed, non-self-intersecting 2D sketch that represents the cross-section of the final solid (such as a circle, rectangle, or custom polygon).
  2. The Spine (Path): A sketch, edge, or continuous wire that dictates the path the profile will follow. This path does not need to be planar, but it should ideally intersect or align with the plane of the profile to prevent unexpected twisting or self-intersection.

Key Orientation and Corner Modes

FreeCAD provides several parameters to control how the profile behaves as it moves along the path:

  • Orientation Mode: Controls the alignment of the profile during the sweep.
    • Standard: Keeps the profile perpendicular to the path direction.
    • Fixed: Keeps the orientation angle fixed relative to the starting orientation.
    • Frenet: Uses Frenet-Serret framing, orienting the profile based on the path's curvature and tangent vectors to reduce unwanted twisting on complex 3D curves.
    • Auxiliary: Uses a secondary curve to guide the direction and twisting of the profile.
  • Corner Transition: Defines how the pipe handles sharp angles in the path. Options include transformed sharp corners or rounded corners that blend the geometry cleanly.

How to Create an Additive Pipe

  1. Activate your target Body in the Part Design workbench.
  2. Create the Path sketch defining the route of the pipe.
  3. Create the Profile sketch defining the cross-section, ideally on a plane perpendicular to the start of the path.
  4. Select the Profile sketch in the tree view and click the Additive Pipe icon in the toolbar.
  5. In the Task panel, click the Path button and select the edge or sketch representing your path from the 3D view.
  6. Adjust the orientation mode and corner transitions as needed, then click OK to generate the solid feature.

Additive vs. Subtractive Pipe

While the Additive Pipe generates material, FreeCAD also features an identical counterpart called the Subtractive Pipe. The Subtractive Pipe uses the exact same sweep mechanics and parameters, but instead of creating volume, it carves the swept shape out of an existing solid body, functioning like a complex parametric sweep-cut.