FreeCAD - The FOSS Parametric CAD That Runs Headless on a Server

Most CAD software either costs thousands per seat or forces you into a cloud subscription that owns your files. FreeCAD takes the opposite approach: a fully open-source parametric CAD modeller built on the same professional geometry kernel (OpenCASCADE) used by commercial tools, licensed under LGPL, and capable of running completely without a display server for batch automation and CNC pipelines.

What is FreeCAD?

FreeCAD is a general-purpose parametric 3D CAD modeller aimed at mechanical engineers, product designers, architects, and makers. Parametric means that every dimension in your model is a parameter — change the diameter of a bolt hole and every pocket, fillet, and drawing that references it updates automatically.

“FreeCAD is a free and open-source general-purpose parametric 3D computer-aided design modeler and a building information modeling software with finite element method support.”

FreeCAD Source Code on GitHub FreeCAD Website FreeCAD Wiki

Why engineers and makers choose FreeCAD

• 📐 Parametric modelling — history-based design where changing one dimension cascades through the entire model
• 🔩 Professional geometry kernel — OpenCASCADE (OCCT), the same technology underlying many commercial CAD tools
• 🏗️ Workbench system — domain-specific toolsets for FEM, CNC, BIM, technical drawings, and more, all in one app
• 🐍 Python scripting — every object, feature, and operation is accessible from Python for automation and custom tools
• 📄 STEP, IFC, STL, DXF — comprehensive import/export for industry-standard CAD interchange formats
• 🖥️ Headless CLI — run FreeCAD on a server without a display, batch-process designs, integrate into CI/CD pipelines
• ⚖️ LGPL v2.1+ — free for commercial use, modifications must be shared, linking in proprietary software permitted

How Parametric CAD Works in FreeCAD

The PartDesign workflow is the recommended approach for solid part modelling:

1. Sketch — draw a 2D shape in the Sketcher workbench and fully constrain it with geometric and dimensional constraints
2. Feature — apply a 3D operation: Pad (extrude), Pocket (cut), Revolution, Loft, or Sweep
3. Refine — add Fillets, Chamfers, Shell operations
4. Repeat — build up a feature tree; every step is editable by double-clicking it

Change the sketch dimension or any feature parameter — FreeCAD re-evaluates the entire tree and the model updates. This is the parametric promise, and FreeCAD delivers it without a subscription.

The Workbench System

FreeCAD organises tools into workbenches — domain-specific toolsets that load on demand. You switch between them as your workflow moves from sketching to machining to analysis:

Modelling

Engineering

Architecture

Data & Automation

File Format Support

FreeCAD’s geometry kernel (OpenCASCADE) handles the heavy lifting for CAD exchange formats:

STEP import/export is particularly solid — colours, product hierarchy, and metadata survive the round-trip, which is essential for collaborating with teams using commercial CAD tools.

Installing FreeCAD

Desktop (interactive use)

# Download from GitHub Releases
wget https://github.com/FreeCAD/FreeCAD/releases/download/1.0.0/FreeCAD_1.0.0-conda-Linux-x86_64-py311.AppImage
chmod +x FreeCAD_*.AppImage
./FreeCAD_*.AppImage

flatpak install flathub org.freecadweb.FreeCAD
flatpak run org.freecadweb.FreeCAD

snap install freecad

sudo apt install freecad          # Ubuntu / Debian
sudo pacman -S freecad            # Arch Linux
sudo dnf install freecad          # Fedora

Headless server (no display required)

This is where FreeCAD becomes a pipeline tool. The freecadcmd binary is FreeCAD’s console entry point — no Qt, no Coin3D, no OpenGL:

# On Ubuntu/Debian
sudo apt install freecad-python3

# Run a Python automation script
freecadcmd my_script.py

# Interactive headless session
freecadcmd
>>> import FreeCAD, Part
>>> doc = FreeCAD.open("bracket.FCStd")
>>> Part.export(doc.Objects, "bracket.step")

No DISPLAY variable, no virtual framebuffer, no desktop session. A plain Ubuntu Server 24.04 VM is sufficient.

Automating FreeCAD with Python

The Python API is first-class — every document object, every workbench operation, every property is accessible programmatically. This is what enables batch processing, automated design variants, and integration with external data sources.

Create and export a parametric model

import FreeCAD as App
import Part

doc = App.newDocument("BracketBatch")

# Create a box
box = doc.addObject("Part::Box", "Bracket")
box.Length = 80.0   # mm
box.Width  = 40.0
box.Height = 5.0

# Cut a hole
cyl = doc.addObject("Part::Cylinder", "Hole")
cyl.Radius = 6.0
cyl.Height = 10.0
cyl.Placement.Base = App.Vector(40, 20, -2)

cut = doc.addObject("Part::Cut", "BracketHole")
cut.Base = box
cut.Tool = cyl
doc.recompute()

# Export
Part.export([cut], "/output/bracket.step")
cut.Shape.exportStl("/output/bracket.stl")
print("Volume:", cut.Shape.Volume, "mm³")

Run it headlessly:

freecadcmd bracket_gen.py

Drive a model from a spreadsheet

The Spreadsheet workbench lets you link cell values directly to model parameters. In a headless script you can update those cell values before recomputing — effectively using FreeCAD as a parametric design engine driven by external data:

import FreeCAD as App

doc = App.open("parametric_bracket.FCStd")
sheet = doc.getObject("Spreadsheet")

# Update parameters from external source
sheet.set("B2", "120")   # Length
sheet.set("B3", "60")    # Width
doc.recompute()

import Part
bracket = doc.getObject("Bracket")
Part.export([bracket], "/output/bracket_120x60.step")

Running FreeCAD in Docker

No official image exists, but the headless build runs cleanly in a container:

FROM ubuntu:24.04

RUN apt-get update && apt-get install -y --no-install-recommends \
    freecad-python3 && \
    rm -rf /var/lib/apt/lists/*

ENTRYPOINT ["freecadcmd"]

docker build -t freecad-headless .

docker run --rm \
  -v /path/to/models:/models \
  -v /path/to/output:/output \
  freecad-headless \
  /models/process_all.py

For a more current FreeCAD version, mount the AppImage into the container instead of using the distro package.

The CNC / CAM Pipeline

The CAM workbench (formerly Path) turns FreeCAD into a complete CNC pre-processor:

1. Import or model the part — STEP import or native PartDesign
2. Define a Job — set the stock material, machine coordinate system, and post-processor
3. Add operations — Profile, Pocket, Drilling, Adaptive clearing, Engraving
4. Simulate — visualise material removal before cutting
5. Post-process — export G-code for your specific controller (LinuxCNC, Mach3, Grbl, etc.)

FreeCAD ships post-processor scripts for the most common controllers. Custom post-processors are Python scripts — drop one in the appropriate directory and it appears in the Job dialog.

FEM: Finite Element Analysis

The FEM workbench is a full structural and thermal simulation environment built into FreeCAD. It uses open-source solvers — primarily CalculiX — with no additional licence cost and no seat limit.

Supported analysis types

FreeCAD also supports exporting to Z88 and Mystran solvers for specialised analyses.

Typical FEM workflow

1. Assign a material — the Material workbench ships cards for common metals, plastics, and composites (density, Young’s modulus, Poisson’s ratio, thermal conductivity). Custom .FCMat cards go in your user material directory.

2. Apply constraints — right-click faces, edges, or vertices:

• Fixed support (all DOF locked)
• Force (distributed or concentrated)
• Pressure (normal to face)
• Displacement (partial constraint)
• Fixed temperature / heat flux (thermal)
• Contact (bonded or sliding between bodies)

3. Mesh the geometry — FreeCAD bundles Salome SMESH and can call Gmsh (install separately). Choose mesh density per region with mesh refinements on fillets and stress concentrations. Tetrahedral elements for complex organic shapes; hexahedral (Gmsh) for structured grids.

4. Run the solver — CalculiX is launched as a subprocess. A typical bracket analysis on a modern laptop completes in seconds. The .inp input file is written to a temp directory and can be inspected or submitted to a remote HPC cluster.

5. Visualise results — the FEM workbench renders colour maps directly in the FreeCAD viewport:

• von Mises stress (identify yield risk)
• Displacement magnitude (deformation scale factor adjustable)
• Principal stress vectors
• Temperature and heat flux for thermal runs

Results can also be exported to VTK format for post-processing in ParaView.

Scripting FEM headlessly

import FreeCAD as App
import ObjectsFem
import femmesh.gmshtools as gmsh

doc = App.open("bracket.FCStd")
analysis = doc.addObject("Fem::FemAnalysis", "Analysis")

# Add material
mat = ObjectsFem.makeMaterialSolid(doc, "Steel")
mat.Material = {"YoungsModulus": "210000 MPa", "PoissonRatio": "0.30"}
analysis.addObject(mat)

# Mesh, solve, export results
# (full scripting documented on wiki.freecad.org/FEM_Scripting)
doc.recompute()

CFD: Computational Fluid Dynamics with CfdOF + OpenFOAM

For actual fluid dynamics — external aerodynamics, internal pipe flow, heat exchangers, fan performance — FreeCAD pairs with CfdOF and OpenFOAM to form a complete open-source CFD pipeline.

CfdOF is a FreeCAD community add-on that provides a GUI front-end for OpenFOAM. OpenFOAM is the industry-standard open-source CFD solver used by automotive OEMs, aerospace companies, and research institutions worldwide.

What you can simulate

Installing CfdOF

Step 1 — Install OpenFOAM on the host (not inside FreeCAD):

# Ubuntu 22.04 / 24.04 — OpenFOAM Foundation build
sudo sh -c "wget -O - https://dl.openfoam.org/gpg.key > /etc/apt/trusted.gpg.d/openfoam.asc"
sudo add-apt-repository http://dl.openfoam.org/ubuntu
sudo apt-get update
sudo apt-get install openfoam11

# Source the environment
echo "source /opt/openfoam11/etc/bashrc" >> ~/.bashrc
source ~/.bashrc

Step 2 — Install CfdOF via FreeCAD AddonManager:

Tools → AddonManager → search “CfdOF” → Install

Or manually:

cd ~/.local/share/FreeCAD/Mod
git clone https://github.com/jaheyns/CfdOF

Step 3 — Install cfMesh (the mesher CfdOF uses by default):

In FreeCAD: CfdOF → CfdOF Preferences → Install cfMesh

CFD workflow in FreeCAD + CfdOF

1. Create or import your geometry — model the fluid domain in PartDesign, or import a STEP file. For external aero, create a wind-tunnel box around the object using Part boolean operations and subtract the body (difference()) to get the fluid volume.

2. Set up the analysis — switch to the CfdOF workbench, create a CFD Analysis object, and choose the solver type (simpleFoam for steady incompressible, etc.).

3. Mesh with cfMesh or snappyHexMesh — CfdOF calls cfMesh automatically. Configure:

• Base mesh cell size
• Surface refinement on walls and edges
• Boundary layer (prism layers) for accurate near-wall treatment

CfdOF → Mesh → Create → Set cell size → Run cfMesh

4. Set boundary conditions — click each face of the fluid domain and assign:

• Inlet: velocity or pressure (U = [30 m/s, 0, 0])
• Outlet: zero-gradient pressure
• Walls: no-slip (solid surfaces)
• Symmetry planes: for half-domain simulations

5. Set physics — turbulence model (k-omega SST is the standard for external aero), fluid properties (density, viscosity), solver iterations and convergence tolerance.

6. Run OpenFOAM — CfdOF writes the OpenFOAM case directory (constant/, system/, 0/), then launches the solver as a subprocess. Residual plots update live in FreeCAD.

7. Post-process in ParaView — CfdOF opens ParaView automatically on completion. Visualise:

• Pressure coefficient distribution
• Velocity streamlines
• Wall shear stress
• Force and moment coefficients (drag, lift)

The OpenFOAM case directory

CfdOF writes a standard OpenFOAM case structure you can inspect, tweak, and rerun from the terminal:

MyAnalysis/
├── constant/
│   ├── polyMesh/          # Mesh from cfMesh
│   └── transportProperties
├── system/
│   ├── controlDict        # Time steps, output frequency
│   ├── fvSchemes          # Discretisation schemes
│   └── fvSolution         # Linear solver settings
└── 0/
    ├── U                  # Initial/boundary velocity
    ├── p                  # Initial/boundary pressure
    ├── k                  # Turbulence kinetic energy
    └── omega              # Specific dissipation rate

This means advanced users can bypass CfdOF entirely and run OpenFOAM from the command line — CfdOF is a convenience layer, not a lock-in.

Running CFD on a remote server

OpenFOAM scales to HPC clusters via MPI. Run the mesh generation locally in FreeCAD+CfdOF, then copy the case directory to a server and run:

# On the HPC node
source /opt/openfoam11/etc/bashrc
cd MyAnalysis
decomposePar                         # split domain across cores
mpirun -np 32 simpleFoam -parallel   # run on 32 cores
reconstructPar                       # reassemble for post-processing

The FreeCAD model and the OpenFOAM case are separate — the simulation runs on whatever hardware you have, while the geometry stays in FreeCAD.

LGPL Licence — What It Means

FreeCAD is licensed under LGPL v2.1+, which is significantly more permissive than GPL:

• ✓ Use FreeCAD for commercial projects — no restrictions
• ✓ Distribute FreeCAD with your product — fine with attribution
• ✓ Link against FreeCAD libraries in proprietary software — permitted (unlike GPL)
• ✗ Modify FreeCAD and distribute the modified binary — you must share the modifications

This makes FreeCAD genuinely usable as the backend for commercial design tools, SaaS services that process CAD files, and in-house engineering automation.

Conclusion

FreeCAD has crossed from “promising open-source CAD” to “genuinely useful for real engineering work” with its 1.0 release. The combination of OpenCASCADE’s professional geometry kernel, the modular workbench system, and a fully scriptable Python API puts it in a category of its own in the FOSS world.

For self-hosters and DevOps engineers: the headless freecadcmd CLI and the Docker-friendly architecture make FreeCAD a first-class automation engine for parametric design pipelines, automated STEP/STL exports, and CNC job preparation.

Related tools worth knowing:

• CadQuery — Python-first parametric CAD also using OpenCASCADE; code-only, no GUI, great for programmatic part generation
• OpenSCAD — CSG modelling via a scripting language; simpler, less capable, beloved by the maker community; FreeCAD can import .scad files
• KiCad — FOSS PCB design; FreeCAD is the standard companion for the 3D mechanical enclosure
• Blender — complements FreeCAD for rendering and organic shapes; STEP export from FreeCAD → Blender is a common workflow