Novel Shape and Rule-Based Approach to Identify Standardized Threads and Screw Heads in Neutral 3D CAD Product Models

Screws are used to join parts in almost all assemblies. For automated assembly sequence planning based on neutral CAD product models, threads pose a particular challenge, because they are not explicitly modeled. The novel approach presented here extracts topological entities from STEP files using boundary representation to reliably identify internal and external threads as well as threads in surfaces. Subsequently, the heads of the components with external threads are identified and the tools required for assembly are determined. The identification is carried out based on well-defined procedures and rule sets. In the further course, bolted connections within an assembly can thus be reliably verified. Requirements for the joining technology are derived from the detection of bolted joints. Furthermore, they serve as restrictions for the assembly sequence optimization. With the approach presented here, bolts can be identified and described directly from STEP files, both individually and in assemblies, and the necessary tools can be provided.