Forming Limit Curve (FLC) to ISO 12004

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

Particular importance in sheet metal forming is attributed to determination of the forming limit curve (FLC), which is used in a two-stage experiment to generate critical deformations in tests. These are then compared with existing deformations on actual components, 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 in order to establish the most suitable material for a forming process. In addition, the forming limit analysis can be applied to production process monitoring.

Forming limit curves are usually determined using a hemispherical cupping die (Nakajima) or a flat die (Marciniak).




In the FLC test to ISO 12004, sheet metal specimens with different geometries are formed until failure.
Sheet metal plates with different geometries are formed until failure. With the variation in specimen width, different deep drawing and stretch forming conditions (from uniform biaxial deformation to a simple tensile load) are set on the sheet metal surface.

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

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

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.

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