Hole Expansion Test to ISO 16630 - Determination of the Edge Crack Sensitivity

The hole expansion test to ISO 16630 is a method used for the determination of forming properties of sheet metal edges (determination of edge crack sensitivity).

For a hole expansion test a hole with a diameter of 10 mm is shear cut and subsequently widened with a conical punch (60° angle).

The test result comes from the so called hole expansion ratio, which is defined as the ratio of the expanded hole diameter (Dh to D0) to the initial hole diameter D0. Because of its comparatively simple implementability, the standardized hole expansion test is frequently used as a quick test or for materials release testing.

Forming properties of sheet metal edges Hole expansion test in pictures Testing machines

Hole expansion test to ISO 16630—determination of the edge crack sensitivity

Shearing Changes the Forming Properties of Sheet Metal Edges

The ISO standard was first published in 2009. Originally it was used to determine the suitability of sheet metal materials for flanging of punched bolt holes in the production of wheel discs and for similar formation methods.

Targeted lightweight steel construction, as a result of economic and ecologic conditions, is constantly using stronger and thinner sheet metals. At the same time, component geometries are becoming more complex. The hole expansion test is therefore increasingly used for the determination of the ductility of edges on punched sheet metal, as well as their edge crack sensitivity, during the production of car chassis components.

Shearing, one of the most commonly used production processes in sheet metal working, presents a challenge for the mechanical properties of the primary material. Through shear cutting, the ductility of the newly created edge can be significantly reduced in comparison with the basic material. Based on this reduced ductility, there may be crack initiation from the edge during subsequent forming processes. If during the forming process, the material cracks almost exclusively from the sheet metal edge, it is considered to be edge crack sensitive.