Overview
ISO 12004-1:2020 specifies a practical, shop-floor procedure for developing forming-limit diagrams (FLDs) and forming-limit curves (FLCs) for metallic sheets and strips (thickness range 0.3 mm to 4 mm). The standard describes how to measure major and minor engineering strains on formed parts in the press shop, determine the onset of necking or fracture, and plot the material’s forming limits for use in process assessment and troubleshooting.
Key topics and technical requirements
- Scope: Measurement and application of FLDs/FLCs for sheet and strip metals in press-shop conditions (0.3–4 mm thickness).
- Principle: Apply a precise grid to the flat test piece, form until first fracture, then measure change in gauge lengths to calculate major/minor engineering strains and plot points on the FLD.
- Gauge lengths: Recommended 1.5 mm to 5.0 mm; initial lengths must be known to ±2%.
- Strain measurement: Use three adjacent gauge lengths in the major strain direction (repeat until within ±10 %) and measure orthogonal gauge length for minor strain. Calculate percent engineering strain from change in gauge length.
- Test conditions: Ensure uniform strain in the critical area prior to necking; any tooling that achieves this (presses, tensile machines, bulge rigs) is acceptable. Stop tests at the first occurrence of fracture.
- Grid patterns: Annex B shows common grid types (circular, square, center crosses) used to measure strain.
- Reporting: Clause 9 requires inclusion of reference to ISO 12004-1, part identification, thickness, plotted FLC/FLD, gauge length, and lubrication conditions. Optional items include mechanical properties, chemical composition and deviations (see Annex A for permitted FLC modifications).
Applications and users
- Who uses it: Press-shop engineers, stamping/die designers, quality/control engineers, material and process engineers in industries performing sheet metal forming (e.g., automotive, appliance, aerospace).
- Practical uses:
- Validate whether component features are in the safe-forming region or likely to neck/fail
- Compare forming behavior of production batches or tooling changes
- Support troubleshooting of stamping defects and optimize lubrication/tooling
Related standards
- ISO 12004-2 - determination of forming-limit curves under laboratory conditions (material characterization using defined strain paths).
- ISO 10275 - determination of tensile strain-hardening exponent (n-value), referenced for possible FLC adjustments (Annex A).
Keywords: ISO 12004-1:2020, forming-limit diagram, forming-limit curve, FLD, FLC, sheet metal formability, press shop measurement, strain measurement, metal forming.