ISO 12004: Forming Limit Curve | Forming Limit Diagram

Forming limit diagram (FLD), forming limit curve (FLC)

The forming limit curve (FLC) to ISO 12004 is an important parameter used in sheet metal forming.

The forming limit curve is used in a two-stage experiment to generate critical deformation during testing. The results are then compared with existing deformation on the real component and evaluated.

Using the forming limit diagram (FLD), the failure limit of the material can be determined and materials can be compared to each other. This means that a suitable material for the forming process can be determined early in the development cycle and development times can be reduced. In addition, the forming limit analysis can be applied to production process monitoring, helping to increase product quality.

Forming limit curves are normally determined with cupping tests on sheet metal specimens to Nakajima (hemispherical cupping die) or to Marciniak (flat die).

Forming limit diagram Tools Evaluation Testing machines

Forming limit curve: In the FLC test to ISO 12004, sheet metal specimens with different geometries are formed until failure.

Forming limit diagram (FLD)

The forming limit diagram is used to compare the results with other materials.

The attainable deformations of different specimen shapes define the forming limit curve of a material.

As a rule, three specimens are prepared for each geometry, with three sections on each specimen. For the forming limit curve a minimum of 5 specimen geometries are tested (here there are 8).

Tools for the forming limit curve (FLC) to ISO 12004

Tool for FLC tests to Marciniak and Nakajima (ISO 12004) for determination of the forming limit diagram (FLD)

Tools for the forming limit curve (FLC) to ISO 12004

Left: Die and blank holder to Marciniak, right: Die and blank holder to Nakajima

Sketch: Determination of the forming limit curve (FLC) / forming limit diagram (FLD) to ISO 12004 with hemispherical die (Nakajima)

Sketch: Forming limit curve to Nakajima

The forming limit curve to Nakajima is determined using a hemispherical cupping die.

Sketch: Determination of the forming limit curve (FLC) / forming limit diagram (FLD) to ISO 12004 with flat die (Marciniak)

Sketch: Forming limit curve to Marciniak

The forming limit curve to Marciniak is determined using a flat cupping die.

Evaluation of the Forming Limit Curve (FLC) to ISO 12004

For manual evaluations using measuring microscopes, a circle pattern is applied to the specimens before the test. Under load, the circles deform into ellipses, the main axes of which represent the strain on the component surface in major and minor direction.

For evaluations with optical 3D measuring systems, e.g. Aramis by GOM, stochastic patterns are applied with a color spray, and the shift of the patterns under load are evaluated.