STEP (Product Model Data)

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Introduction

The full name of STEP is Standard for the Exchange of Product Model Data. It is an international standard 3D CAD data exchange format. The standard number is IS10303. STEP file is an internationally used 3D model data exchange format. The extension is usually step or .stp. It can share data between different CAD software, which is very convenient.

File Structure

The structure of STEP files (standard extensions are usually ‌.step‌ or ‌.stp‌) is defined by the international standard ISO 10303 and is designed in a text format to achieve cross-platform compatibility. Its core structure is divided into two parts:

Header Section

Located at the beginning of the file, it stores the file’s ‌metadata‌, mainly including:

File identification information‌: such as file name, generation date, version number;
Generation tool information‌: the name and version of the CAD software that created the file;
Protocol specification‌: the STEP subprotocol used (such as AP203/AP214/AP242, etc.)‌.

Data Section

Contains actual product model data, using a hierarchical modular structure:

Geometry and topology data‌
- Basic geometric elements (points, lines, surfaces, bodies);
- Complex surfaces (NURBS surfaces) and solid boundary representations (B-Rep)‌.
Assembly hierarchy‌
- Position and orientation of components in the assembly;
- Parent-child component association‌.
Attribute and semantic information‌
- Material attributes (density, material type);
- Product manufacturing information (PMI), such as dimensional tolerance, surface roughness;
- Display attributes such as color and layer‌.
Product structure tree‌
- Component name, ID and hierarchy‌.

Pros

Software interoperability: STEP adopts the neutral text format (ASCII encoding) defined by the ISO 10303 international standard, breaking the barriers of CAD software private formats, and can achieve lossless transmission of geometric data and assembly relationships between mainstream design software such as SolidWorks, CATIA, Creo, etc., solving the problem of heterogeneous system collaboration. ‌
Product structure tree mapping: Through the hierarchical entity association mechanism, the parent-child component positioning relationship and constraint conditions in the assembly are accurately transmitted to ensure the logical consistency of the model tree. ‌
Guarantee of technical autonomy: Based on open standards (non-manufacturer private protocols), it supports secondary development of open source kernels such as OCCT, reduces technical dependence on commercial software, and conforms to the trend of industrial supply chain security. ‌
Reduce collaboration costs: Unified formats reduce repeated conversion time, and PMI data transmitted by AP214/AP242 protocols can directly drive downstream CAM/CAE processes, shortening the product development cycle by more than 30% (proven in the field of automotive parts). ‌

Cons

Character encoding problem: Early STEP protocols (such as AP203/AP214) did not support the UTF-8 character set, resulting in garbled Chinese paths or comments, which needed to be partially fixed by the later protocol (AP242), but cross-software compatibility was still unstable.
Slow parsing of large files: Complex assembly STEP files contain massive amounts of triangular patch data, which significantly increases the time it takes to open them in software such as SolidWorks, and the hardware configuration has limited impact.
Weak support for binary formats: Text formats (.stp/.step) are the mainstream, and the binary format (.stp) has a narrow application range, resulting in large file sizes.

Application Scenario

STEP files are widely used in cross-platform design collaboration (such as data exchange between heterogeneous CAD systems in the automotive and aviation fields) and product lifecycle management (such as long-term data archiving for military and medical equipment). They also support manufacturing process integration (CAM processing, 3D printing) and industry-specific requirements (ship AP218 protocol, medical AP239 protocol).