Convert IGS to CAD

A supplier may send an IGES model that the receiving CAD system cannot edit reliably in its native workflow. Converting it to STEP, Parasolid, BREP, or a manufacturer-specific format can make the geometry easier to inspect, revise, and share.

What the IGS format is

IGS, usually stored with the .igs or .iges extension, is the filename form of IGES (Initial Graphics Exchange Specification), an ASCII exchange format for engineering geometry. It can contain points, curves, wireframes, trimmed surfaces, and solid-related entities, but it does not preserve the complete parametric feature history of a native part file.

Mechanical CAD systems, industrial design software, inspection applications, and legacy tooling workflows use IGES. Files may originate in CATIA, Siemens NX, PTC Creo, SolidWorks, Autodesk Inventor, Fusion, or older CAD systems. IGES is common for supplier models, surface geometry, legacy designs, CNC preparation, and inspection data.

What the CAD format is

There is no single universal .cad format. CAD refers to a group of file formats, so the correct target depends on the receiving application. Common 3D targets include STEP (.step, .stp), Parasolid (.x_t, .x_b), ACIS SAT (.sat), Open CASCADE BREP (.brep), and native formats such as SolidWorks .sldprt, Fusion .f3d, and FreeCAD .FCStd.

STEP is generally the most compatible neutral target for mechanical parts because it transfers solid and surface geometry between many CAD systems. Parasolid or SAT may be preferable when the recipient uses the corresponding geometry kernel. A native format may provide application-specific editing, but importing IGES cannot normally recreate the original sketches, constraints, feature tree, or design history.

How to convert an IGS file to CAD

FreeCAD is a free desktop option for converting IGES to STEP, BREP, and other formats supported by its import and export modules.

1. Install a current FreeCAD release and open model.igs or model.iges through File → Open.
2. Wait for the IGES import to finish, then inspect the imported solids, surfaces, and compounds in the 3D view and Model tree.
3. Select the required object and choose File → Export. Save it as model.step or model.stp for general exchange, or model.brep when the recipient specifically requires Open CASCADE BREP.
4. Reopen the exported file in FreeCAD or the destination CAD system. Check the part count, units, visible faces, solid status, and at least one known dimension.

Commercial CAD systems can usually perform the same operation. In Autodesk Fusion, import the IGES file through the data panel or File → Open, then use File → Export to create STEP or SAT. SolidWorks, Siemens NX, PTC Creo, CATIA, and Autodesk Inventor also import IGES and export neutral or native formats. Use the destination system when possible because its geometry kernel may heal imported faces more effectively.

CAD Exchanger Desktop and CAD Exchanger Web provide another option for converting IGES to supported neutral and native CAD formats. Online conversion avoids installing software but requires uploading the model; file-size limits, unsupported assemblies, conversion quotas, and server processing can affect the result. Do not upload proprietary, regulated, customer-owned, aerospace, medical, or tooling geometry without authorization.

Quality and compatibility limitations

Many IGES files contain disconnected trimmed surfaces instead of a watertight solid. After import, check for open edges, gaps, self-intersections, reversed faces, duplicate entities, and missing surfaces. A model can look correct while still failing Boolean operations, mass-property calculations, shelling, or CNC preparation.

When the original CAD system is available, export STEP directly from that system instead of converting an already exported IGES file. Use AP214 or AP242 when the receiving application supports it; these schemas can preserve colors, layers, names, and other product data more effectively than older STEP exports. STEP does not turn surface-only geometry into a solid automatically.

Verify units before and after conversion. IGES contains unit information, but importers can interpret it incorrectly, producing a scale error such as 25.4 times. Compare a known dimension in both files, then repair, stitch, or sew surfaces before saving the final model. IGES generally cannot preserve editable feature history, assembly constraints, sketches, or manufacturing metadata, so those elements must be rebuilt in the target application.