Overview
ISO 18785-2:2018 specifies design requirements and provides practical design guidelines for friction stir spot welding (FSSW) of aluminium and its alloys. The standard focuses on the information and documentation needed to ensure manufacturable, testable and serviceable spot-welded assemblies. It complements related parts of the ISO 18785 series and aligns weld symbols with ISO 2553.
Friction stir spot welding is a solid-state joining process where a rotating tool produces frictional heat to soften and forge aluminium at discrete spot locations. ISO 18785-2 addresses how joints should be documented and detailed so that production and quality control can demonstrate conformance to the intended design and service requirements.
Key Topics
-
Documentation and drawings
- Assemblies must be designed and documented according to the intended final use.
- Technical drawings should clearly specify essential information, critical service or safety requirements, and the process control requirements necessary to demonstrate conformance.
- Weld symbols used on drawings should follow ISO 2553.
-
Design of overlap (lap) assemblies
- The standard provides examples of lap geometries and typical joint configurations (single-layer, multi-layer, stiffened details, edge folds, etc.).
- Designers must consider material properties and assembly geometry when selecting weld locations and patterns.
-
Essential information to specify
- Base metal specifications, thicknesses and metallurgical condition.
- Assembly geometry and surface condition (including coatings, adhesives or sealants present at interfaces).
- Tool penetration side, distance to edges, orientation of asymmetric spot welds relative to load, required finish and any post-weld heat treatment.
-
Weld point variables
- Size: round or oblong weld point dimensions (minimum final sizes) must be specified on drawings and verified by surface marks or equivalent measurement methods.
- Location and orientation: precise control of weld placement and, where applicable, oblong orientation must be shown on drawings.
- Strength and quality: when specified, resistance requirements and quality levels must be included in the welding procedure specification (DMOS) and demonstrated via designated test methods.
-
Control and verification
- The documentation must define control methods, acceptance criteria and inspection requirements; testing and inspection are referenced to ISO 18785-5.
Applications
ISO 18785-2:2018 is applicable where robust, repeatable spot welds in aluminium are required, including:
- Rail and mass transit structures
- Automotive and aerospace components
- Consumer goods and food-processing equipment
- Shipbuilding and marine structures
Specifying clear joint geometry, DMOS parameters and inspection criteria reduces production issues, improves structural reliability and facilitates regulatory or customer acceptance.
Related Standards
- ISO 18785-1 - Vocabulary for friction stir spot welding (aluminium)
- ISO 18785-4 - Qualification of welding procedures (DMOS-P)
- ISO 18785-5 - Quality and control requirements (inspection and test methods)
- ISO 2553 - Welding symbols on drawings
For implementation, refer to the full ISO 18785-2:2018 document and coordinate design details with process qualification and control documentation (DMOS) to ensure compliance and product performance.
