Free online IGES to BREP converter

Source format: IGES

IGES (Initial Graphics Exchange Specification) is a long-established CAD interchange format used to move 2D and 3D engineering data between different design systems. It is common in mechanical design, tooling, aerospace, and manufacturing workflows where models must be shared across software from different vendors. IGES files often contain wireframes, surfaces, curves, annotations, and sometimes solid-related data, but support for exact feature history is not part of the format.

Target format: BREP

BREP (Boundary Representation) describes a 3D shape by its faces, edges, and vertices. It is widely used in CAD and solid modeling because it represents the actual boundaries of a model in a precise geometric way. BREP data is commonly stored inside formats such as STEP, IGES-derived CAD files, or native CAD formats, and it is useful for downstream modeling, analysis, CAM, and interoperability with solid-modeling systems.

How to perform the conversion

In practice, converting IGES to BREP usually means importing the IGES model into CAD software and then exporting or saving it as a file that contains BREP geometry. The exact filename extension depends on the target application, but the underlying result is a boundary-representation solid or surface model.

1. Open your CAD application that supports both IGES import and BREP export. Good desktop options include FreeCAD, Open CASCADE-based tools, Autodesk Fusion, SolidWorks, CATIA, or Siemens NX, depending on what you have available.
2. Import the IGES file using File → Open or File → Import. Select the .igs or .iges file.
3. Inspect the imported geometry for missing faces, gaps, or broken surfaces. IGES files often contain surface-only data, so healing may be needed before export.
4. If the software requires it, convert the imported surfaces into a solid or sew the surfaces into a closed shell. In FreeCAD, for example, you may use the Part workbench tools to create or refine a solid from imported geometry.
5. Export or save the model in a format that preserves BREP geometry. In many CAD tools this is done through File → Export or File → Save As, then choosing a BREP-capable format such as .brep, .step, or a native CAD format that stores boundary representation.
6. If your goal is specifically a standalone BREP file, choose the export option that writes .brep directly. In FreeCAD, for example, select the object and use File → Export, then choose BREP if available in the export list.

For command-line workflows, Open CASCADE-based utilities or scripts can read IGES and write BREP, but the exact commands depend on the toolchain. This is useful for batch conversion or automation when you need to process many files.

Notes on quality and limitations

IGES to BREP conversion is not always one-to-one. IGES may contain loose surfaces, trimmed surfaces, or incomplete topology, so the resulting BREP can differ from the original intent if the model is not watertight. If the IGES file has gaps, self-intersections, or inconsistent surface normals, the export may fail or produce a non-manifold result.

Another important limitation is that IGES does not preserve modern CAD feature history, so the converted BREP will usually be a geometric body without editable design features such as sketches, constraints, or parametric operations. Also, some applications use the term BREP to refer to the internal solid model rather than a specific file extension, so the available export options may vary by software.

For best results, use a CAD tool with strong geometry healing and surface sewing capabilities, and verify the output by reopening the exported file to confirm that the body is closed and dimensionally accurate.