IGES vs STEP – The Definitive Guide

For most design engineers, the following scenario should look familiar: Bob, the lead designer for company X, needs to send a CAD model to Susan, the design engineer for company Y. Bob designed the part using Solidworks and Susan only works in Pro Engineer. Bob’s Solidworks file can’t be opened in Susan’s software, so the simple transfer of a part file has now become a problem.

This issue of non-interchangeable proprietary file formats for CAD data has been around for decades. Software companies want to promote the use of their own modeling packages, and one way to do this is to ensure that only their package can open a file created in their software. Unfortunately, every major 3D modeling software company has done this, so communicating between them is a problem.

Luckily, a solution exists in the form of neutral file formats. A neutral file format is one that can be passed between different modeling software packages. Bob could use a neutral file format to pass his CAD model to Susan, who could then open it and work with it as needed.

The most common variants of these neutral file formats are the IGES (pronounces eye-jess) and STEP formats. You can recognize these formats because the file name will end in .iges, .igs, .stp, or .step.

The History of Neutral file Formats

In the mid-seventies, the United States government realized that it had a problem. With all of the unique proprietary CAD programs used by its different contractors, millions of dollars and countless hours were wasted on the tedious process of sharing and converting data between all the systems. You can imagine how many times this scenario played out on a large project like an aircraft carrier or missile delivery system with hundreds of suppliers!

So, the Air Force launched a project in conjunction with Boeing and several other large industry partners to create a neutral file format. The result was IGES (Initial Graphics Exchange Specification), which is a flexible file format that codifies drawing, 3d geometry, and other critical CAD data in a format that can be shared between all major CAD systems.

Since the eighties, the US Department of Defense has required that the IGES format be used for all weapons and defense contracts, and it has been adopted in other industries as well.

STEP (Standard for the Exchange of Product data) was created in the eighties as an improvement on the IGES standard by ISO (the International Standards Organization), with the goal of creating a global standard for a range of CAD-related data types. Due to the complexity of the undertaking, it has taken years of development and is still being continuously upgraded. It is currently the largest of all of ISO’s standards.

IGES vs STEP

IGES is the most widespread standard, and is supported by nearly all major CAD systems worldwide.

An IGES file contains basic CAD information:

• 2D and 3D geometry (curves, surfaces, and wireframes)
• Presentation elements (drafting elements like lines and annotations)
• Electronic and pipe schematic elements
• Finite element modeling elements
• Language and product definition data

STEP is a newer standard, and is therefore not as widespread as IGES. However, most major CAD programs recognize STEP and its ubiquity is steadily growing as the standard improves.

STEP files contain the same product definition information as IGES, with the following additions:

• Topology
• Tolerances
• Material properties
• Other complex product data

Practical Considerations

In most cases where solid models or drawings are being shared, either file format will work fine. For compatibility it is safest to start with IGES, since it is the more common format and therefore more likely to work with the receiving party’s software.

However, a designer should also consider the information being shared. If the file being sent needs to contain more product definition (for example, geometric dimensioning and tolerancing data, material properties, etc), then STEP would be a better choice.

It is not uncommon for one supplier to have trouble working with one format, and to request its alternative. Depending on your industry and software, you will likely become familiar with one or the other and stick to it in most situations.