How to Create Flat Patterns in FreeCAD SheetMetal

This guide provides a straightforward walkthrough for generating accurate 2D flat patterns (unfolds) from 3D sheet metal parts using the FreeCAD SheetMetal workbench. You will learn how to prepare your model, select the appropriate reference face, utilize the Unfold tool, adjust critical parameters like the K-factor, and export the resulting flat pattern for manufacturing processes like laser cutting or CNC punching.

Step 1: Install the SheetMetal Workbench

If the SheetMetal workbench is not already installed:

  1. Open FreeCAD and navigate to the top menu: Tools > Addon Manager.
  2. Locate SheetMetal in the list of workbenches.
  3. Click Install, then restart FreeCAD when prompted.

Step 2: Prepare Your 3D Model

The Unfold tool works best on models created directly with the SheetMetal workbench tools (such as Make Base Wall and Extend Face).

  1. Ensure all bends have an explicit, uniform internal bend radius defined.
  2. Confirm the model thickness is consistent across all walls and flanges.
  3. Ensure there are no overlapping flanges or zero-clearance self-intersections.

Step 3: Select the Fixed Reference Face

The Unfold tool requires a stationary reference plane from which to calculate the flattening of all adjacent bends.

  1. Switch to the SheetMetal workbench from the workbench dropdown.
  2. In the 3D viewport, click to select a single, flat face on your model that will serve as the base (the face that will remain stationary while the rest of the part unfolds around it).

Step 4: Run the Unfold Tool

  1. With the reference face selected, click the Unfold icon on the toolbar (represented by an unfolded sheet metal part) or select SheetMetal > Unfold from the menu.
  2. FreeCAD will calculate the bend allowances and generate a new object named Unfold in the Tree view.
  3. To view the flattened pattern clearly, hide the original 3D model by selecting it in the Tree view and pressing the Spacebar.

Step 5: Adjust Bend Parameters and K-Factor

Accurate flat patterns depend on precise material deformation values:

  1. Select the Unfold object in the Tree view.
  2. Go to the Data tab in the Property View panel below.
  3. Locate the K-Factor property (standard default is typically 0.5 or 0.42 depending on your setup) and adjust it according to your specific material type, tooling, and bend deductions.
  4. If necessary, toggle properties such as Generate Sketch or Manual K-Factor to update the bend line outputs and geometry.

Step 6: Export the Flat Pattern

Once the flat pattern is generated:

  • For DXF Export: Select the 2D sketch generated by the Unfold feature in the Tree view, go to File > Export, and select **Autodesk DXF (*.dxf)** from the file format dropdown.
  • For Technical Drawings: Switch to the TechDraw workbench, create a new drawing page, select the Unfold object, and insert a standard TechDraw View to add bend annotations, dimensions, and bend angles for shop-floor documentation.