STEP, which stands for Standard for the Exchange of Product Data, is a widely used CAD file format that allows the digital storage and transfer of 3D model data. STEP files (which use the .stp and .step file extensions) provide a robust way to share 3D models between different computer-aided design (CAD) software platforms in a way that preserves the model’s data integrity.
In this comprehensive guide, we’ll cover everything you need to know about STEP files, including:
- What is a STEP file and how does it work?
- The history and development of the STEP standard
- Key benefits and capabilities of STEP files
- How STEP files compare to other 3D model formats
- Software that supports STEP files
- Use cases where STEP excels
- Tips for working with STEP files
Ready to become a STEP file expert? Let’s get started!
What is a STEP File and How Does it Work?
A STEP file is used to represent 3D object data in a standardized way. STEP files describe 3D models using both geometric and non-geometric data in a complete and self-contained manner.
Some of the key information contained within a STEP file includes:
- 3D coordinates defining the geometric shapes (points, curves, surfaces, solids, etc.)
- Colors, fonts, layers, and other presentation attributes
- Mass, density, and other physical properties
- Manufacturing features like fillets, holes, and chamfers
- Model topology and relationships between components
- Text strings, notes, and other annotations
All of this model information is encoded within the STEP file as text using the EXPRESS data modeling language. When the STEP file is imported into CAD software, this data can be used to faithfully reconstruct the 3D model.
A major benefit of the STEP format is its use of solid and surface modeling techniques. This allows the geometry to be defined in a complete and unambiguous way, avoiding many of the problems caused by approximations and differing interpretations of model data.
STEP files support both polygonal and NURBS-based surface representations. They can also store wireframe geometry, making STEP a highly versatile format.
History and Development of the STEP Standard
The initial development of STEP began in the 1980s under the leadership of the American National Standards Institute (ANSI) and the European Computer Manufacturers Association (ECMA). The goal was to address the difficulty of sharing CAD data between different proprietary software systems at the time.
The first version, STEP (AP203) was released in 1994. This provided basic 3D modeling capabilities. Further development by the ISO led to the release of STEP AP214 in 1998. This version improved support for mechanical CAD models.
In the 2000s, additional AP modules were introduced to expand STEP’s capabilities:
- AP209 – Composite and polymeric parts
- AP210 – Electronic printed circuit board assemblies
- AP203 & AP214 – Updated in 2005
- AP242 – Managed model-based 3D engineering released in 2014
The latest STEP releases improve support for model-based enterprise by allowing linkage of 3D models with manufacturing, simulation, and PDM/PLM information. Development continues today under ISO TC184/SC4 to expand STEP’s capabilities.
Benefits and Capabilities of STEP Files
Some of the major advantages of using STEP files include:
- Neutral Format – STEP is not controlled by a single software vendor, allowing true interchange between CAD platforms.
- Third Party Certification – Tests like the STEP File Analyzer Tool (SFA) can validate and certify STEP files as geometrically accurate representations of the source model.
- Robust Geometry Definitions – STEP uses advanced solid and NURBS surface modeling for precision and uniqueness. This avoids reliance on faceted approximations.
- Manufacturing Information – In addition to geometry, STEP files can contain manufacturing features, tolerances, metadata, and product manufacturing information (PMI).
- Long Term Archiving – STEP files can encapsulate all aspects of a design in a self-contained format suitable for archiving.
- Automated Processing – STEP files lend themselves well to automated analysis, code generation, and data exchange due to their completeness and use of EXPRESS.
- Variety of Representations – STEP allows combinations of solids, surfaces, wireframes, point clouds, polygon meshes, and other data within a single file.
These capabilities make STEP well suited for a wide range of applications across mechanical, automotive, aerospace, shipbuilding, architecture, and other manufacturing industries.
Comparison to Other CAD Formats
STEP offers some advantages over more commonly used CAD file formats like IGES, Parasolid, ACIS, and native CAD file types:
- More robust than IGES, which has geometric approximations
- Includes manufacturing data unlike Parasolid or ACIS
- Not controlled by a single vendor like native CAD file types
- Supports a wider range of engineering use cases than formats like STL (focused on 3D printing)
- Text-based definition allows easier interoperability than binary formats like OBJ
However, STEP files do have some downsides:
- Verbose data format leading to large file sizes
- Limited support for spline curves and other geometric constructs
- Handling of precise NURBS data can be computationally intensive
- Full implementation requires significant development effort for software vendors
Overall, STEP provides the best common format when detailed product information needs to be preserved, but smaller file sizes or more rendering-focused formats like OBJ may be better suited for visualization applications.
CAD Platforms and Software Supporting STEP
Many major CAD platforms and 3D modeling programs have support for importing and exporting STEP files:
- SolidWorks
- Autodesk Inventor
- PTC Creo Parametric
- CATIA
- Siemens NX
- BricsCAD
- FreeCAD
- Onshape
- IronCAD
- Solid Edge
- Vectorworks
- AutoCAD
In addition, many CAM packages, BIM software, engineering simulation tools, and other applications can leverage STEP files for interoperability.
Basic STEP support is available in Adobe Illustrator, SketchUp, and other 3D modeling tools aimed at graphic design. For rendering and animation, STEPs files can be converted to OBJ, FBX, glTF and other formats.
Applications and Use Cases for STEP Files
Some of the most common use cases that benefit from STEP files include:
- CAD Data Exchange – Transferring 3D models between different CAD systems in manufacturing for CNC programming, analysis, etc.
- Archiving & Long Term Data Retention – Archiving designs, as-built structures, factory layouts, etc. in a neutral format.
- Supplier & Contractor Model Sharing – Distributing design models to external suppliers, contractors, and partners.
- Numerical Analysis Input – Meshing, FEA, CFD, and other simulations using the precise geometry from STEP files.
- 3D Printing – Converting STEP to STL for 3D printing while preserving accuracy.
- CMM & Quality Inspection Programming – Extracting precise geometry for coordinate measuring machine (CMM) inspection.
- MATLAB, Mathcad & Programming – Extracting geometric constructions programmatically from STEP files.
- Technical Illustration – Converting engineering models to Illustrator or vector graphics for technical diagrams.
STEP is commonly mandated by industry groups like automotive and aerospace manufacturers to ensure fidelity of exchanged 3D model information throughout the supply chain.
Working with STEP Files: Top Tips
When working with STEP files, follow these best practices:
- Use the latest certified software versions to minimize geometry errors during import/export.
- Validate STEP files after export using a checker tool to verify correctness.
- Export using higher-fidelity lossless geometry options if available. Avoid faceted or tessellated conversions.
- Watch out for issues with splines, procedural features, and complex NURBS surfaces which older software may not fully support.
- Split files into smaller portions if size limits are encountered when exporting complex assemblies.
- Compress STEP files for storage using gzip or similar algorithms to reduce space.
- Use current STEP AP242 interfaces for building information modeling (BIM) and manufacturing workflows.
- Take advantage of PMI and manufacturing extensions for linking engineering data to models.
Conclusion
STEP provides a vendor-neutral and standardized format for exchanging complete 3D model data between different CAD platforms while retaining full engineering precision. With over 30 years of development and support across the CAD industry, STEP remains an essential component for streamlining today’s multisystem engineering workflows.
This guide has provided a comprehensive overview of STEP files, their capabilities, use cases, and recommended practices. With an understanding of the STEP standard and how to leverage it effectively, engineers and designers can maximize their ability to reuse CAD data and avoid the need for manual rework caused by proprietary formats.
