Overview
ISO 16630:2017 - "Metallic materials - Sheet and strip - Hole expanding test" defines a standardized method to determine the limiting hole expansion ratio (λ) of metallic sheets and strips. The test applies to sheet thicknesses from 1.2 mm to 6.0 mm (inclusive) and specimens with a width of at least 90 mm. It reproduces flange-forming (plunging) conditions by punching a hole and forcing a conical expanding tool into that hole until a through‑thickness crack appears, allowing assessment of material ductility and suitability for forming flanges.
Key topics and technical requirements
- Test principle: Punch a circular hole (standard punch diameter 10 mm), then expand the hole with a conical tool until a through‑thickness crack forms.
- Limiting hole expansion ratio (λ): Calculated as λ = (D_h − D_o) / D_o × 100, where D_o is the original hole diameter (10 mm) and D_h is the average ruptured hole diameter. The average λ from the set of tests is rounded to an integer following ISO 80000-1.
- Specimens and sampling: At least three test pieces from the same sample; hole centers must be ≥45 mm from edges and ≥90 mm apart.
- Punching and clearance: Punching clearance is specified as a percentage of sheet thickness (nominally around 12% with defined tolerances depending on thickness). Example die inside diameters for various thickness ranges are given in the standard.
- Tooling: Conical expanding tool with a tip angle of 60° ±1° and minimum hardness of 55 HRC. Clamping die corner radius between 2 mm and 20 mm (recommended 5 mm).
- Test conditions and execution:
- Temperature: generally 10 °C to 35 °C; controlled tests at (23 ± 5) °C when required.
- Punch speed: driving speed not more than 1 mm/s.
- Observe for microcracks; stop when a through‑thickness crack with max opening 0.1 mm appears.
- Measure ruptured hole diameter to 0.05 mm accuracy in two perpendicular directions, avoiding the crack.
- Reporting: Include reference to ISO 16630, specimen ID and thickness, average λ, number of tests, and any deviations.
Applications and users
- Primary users: automotive manufacturers, sheet‑metal fabricators, material and quality laboratories, and R&D teams evaluating formability and ductility for flange/plunge forming.
- Practical uses: qualifying sheet steels and other metallic sheets for rim/flange forming, comparing batches or processes, and supporting material selection and process parameter setting in forming operations.
Related standards
- ISO 80000-1 (quantities and units) - used for rounding rules in the calculation/reporting of λ.
- ISO/TC 164 guidance (mechanical testing of metals) - ISO 16630 is produced by the subcommittee on ductility testing.
Keywords: ISO 16630, hole expanding test, limiting hole expansion ratio, sheet metal testing, flange forming, metallic materials, punch clearance, conical expanding tool.
