IGES vs STEP – The Definitive Guide

  • Both are "neutral file formats". They were developed to be compatible with different 3D packages
  • The oldest is IGES (Initial Graphics Exchange Specification). It was developed in the mid '70s by the defense industry to solve compatibility issues between different software packages
  • STEP (Standard for the Exchange of Product data) was created in the '80s by ISO as an improvement on IGES
  • The most widespread format is IGES but it can only contain basic 2D or 3D data
  • STEP is more versatile and contains additional information such as material information and tolerances

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.

IGES vs 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.

About: Matt Coughlin

Matt is an engineer and entrepreneur from California. He has worked for several large companies and as a consultant in manufacturing and design engineering.

4 Responses to IGES vs STEP – The Definitive Guide

  1. K.I.S.S. says:

    Nice article, thank you.  Wouldn't it be even nicer if certain proprietary CAD formats allowed for the regeneration of such models in their own native format? It's all very well to view data but sometimes it's necessary to modify it… Yes, Imported 1, you know who I'm talking about… 🙂

  2. lucsimonsip says:

    Hi everybody,I am CAD design Engineer in plastic parts for a very large range of manufacturers.I am 16 years old experienced in data transfer, using Solidworks since 2000.At the beginning I used to transfer datum in IGES format.But for 10 years, I switched to STEP format that is more practical for tool makers.Moreover the STEP format is becoming the reference for free translators packages available on the Web.CAD users are dreaming for a long time that a native interface could be used by all CAD software providers, but that probably will never be a reality.It is particularly regrettable that in the world several million of  Engineers are loosing a  valuable time to recover and repair of defective transfers.Some new developments in the CAD systems are developing solutions to recover STEP files and give the possibility to modify very easily the geometry.For example, I speak of free software "DesignSpark Mechanical," the 3D design software from RS Components and Allied Electronics.Unfortunately, there are very few free software to investigate the translated files.Some discount softwares aret available and high performance.But I find it a shame that solutions such as CATIA, PTC Creo or Solidworks not offent of "light version" of its software that could be widely distributed in an enterprise or among contractors

  3. Mike Marcoux says:

    How do STP files contain tolerances and material properties? Traditionally, imported 3D models (in my experience) are usually pretty dumb, outside of the imported model geometry itself. How does one include tolerancing and material property data? Unless this refers to an imported 2D drawing which contains that data, or the new 242 Application Protocol. To my knowledge, I thought 242 was just a merging a203 and 214.

    • John Bijnens says:

      Keep in mind there are several versions of STEP AP203 (standard, edition 1, edition 2) and STEP AP214 (standard, edition 1). Check whether what version your CAD system supports and if it does support e.g. STEP AP203e2 make sure it will use this for the export. All the dimensional tolerances and GD&T that is specified within the features of the CAD model will then be exported to the STEP file and can be used in the importing CAD system if that system supports this specific AP203.John Bijnens

  4. Bjohnston says:

    The reason you don’t always see the additional features out of a step file like GD&T or material properties lies with the CAD systems. In order to be compatible with STEP they do not have to support all aspects of the standard. As mentioned in the article the standard os huge. So in order for you to get material properties or GD&T the source CAD system has to support the export of that portion AND the target has to support the reading of that portion of the standard. If either CAD does not support it you will not get it no matter how much you want it to be translated. CAD software companies would rather you believe that they can open the other CAD file directly without STEP or IGES. This is equally flawed. People are dreaming if they think all CAD companies will support all aspects of STEP equally or that “MY” CAD can open any foreign CAD file accurately. STEP and IGES are only part of the CAD interoperability solution. Some portions of your CAD file will never be able to be translated with STEP or IGES. There are other automated CAD interoperability solutions such as Acc-u-Trans that will get you more of the data in your file in a more reliable fassion but they are not free. Remember you often get what you pay for.

  5. Sergey says:

    Matt, good day,

    It’s a good article indeed.
    Although from technology point of view – there are no need for SW users to use either STEP or IGES when they send data to Pro/E (CREO). CREO opens SW files without need to convert them in STEP format now (3.0 M100).

    Any kind of changes from SW – 2 STEP&IGEST – Other CAD is prone to manual errors. It’s too much rely on your manuals skills when you convert 1000 files at ones. STEP was great in 80-s when people used to be in spare parts while using CAD. Today situation will not allow the engineer to make a mistake with file converstion. It’s enough to mill one tolerance in 100+ parts assembly to make all manufacturing floor work out of quality.

    Sergey

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