Overview
EN ISO 12004-2:2021 (ISO 12004-2:2021) specifies laboratory procedures for determining forming-limit curves (FLCs) for flat metallic sheet and strip. The standard covers tests performed at ambient temperature using predominantly linear strain paths for materials with thickness between 0.3 mm and 4 mm. It defines test-piece preparation, grid application, measurement methods and criteria for valid tests to produce reproducible FLC data for sheet-metal forming and ductility assessment.
Key topics and requirements
- Scope and material limits: Applies to metallic sheet and strip (0.3–4 mm thickness) at ambient temperature; thickness limit tied to allowable punch-diameter/ thickness ratios.
- Test methods: Laboratory FLC construction using established punch-expansion methods such as Nakajima and Marciniak; both methods are described with validity requirements (e.g., failure location near the dome apex). Nakajima’s known non-linear strain paths are acknowledged and accepted when test validity is met.
- Test pieces and grid: Requirements for test-piece geometry, number of geometries and tests per geometry, and grid application (type, accuracy and evaluation) to enable accurate strain mapping.
- Strain measurement and analysis: Procedures for strain determination (section-line and position-dependent evaluation), extraction of the characteristic “bell-shaped” strain distribution, use of numerical fits (inverse best-fit parabola), and second-derivative filtering methods (normative annexes).
- Test equipment and parameters: Specifications for test rigs, measurement instruments and recommended operating ranges (e.g., punch velocity range clarified/expanded in the 2021 edition).
- Documentation and reporting: Required test-report content and documentation of analysis steps; normative and informative annexes provide validation datasets, flowcharts and mathematical representation of FLCs.
Applications and who uses this standard
- Materials testing laboratories and certification bodies generating FLC data for material specifications.
- Automotive, aerospace and metal-forming engineers performing die design, process simulation and failure analysis.
- R&D groups evaluating new alloys, temper conditions or sheet processing routes.
- Quality control teams using FLCs to define safe formability limits and to validate forming simulations (FEA) and process windows.
Related standards
- ISO 12004 series - Part 1 addresses alternative or complementary methods (see ISO 12004-1 for guidance on when to use Part 1 vs Part 2).
- Relevant standards for mechanical testing and strain measurement referenced in normative clauses and bibliography.
Keywords: forming-limit curve, FLC, ISO 12004-2:2021, metallic materials, sheet and strip, Nakajima test, Marciniak test, laboratory FLC determination, sheet-metal forming, strain measurement.